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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
PowerPoint Lectures for Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Chapter 41Chapter 41
Animal Nutrition
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Overview: The Need to Feed
• Every mealtime is a reminder that we are heterotrophs
– Dependent on a regular supply of food
Figure 41.1
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• In general, animals fall into one of three dietary categories
– Herbivores eat mainly autotrophs (plants and algae)
– Carnivores eat other animals
– Omnivores regularly consume animals as well as plants or algal matter
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Regardless of what an animal eats, an adequate diet must satisfy three nutritional needs
– Fuel for all cellular work
– The organic raw materials for biosynthesis
– Essential nutrients, substances such as vitamins that the animal cannot make for itself
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• Animals feed by four main mechanisms
Figure 41.2
Baleen
SUSPENSION FEEDERS
Feces
SUBSTRATE FEEDERS
BULK FEEDERS
FLUID FEEDERS
Caterpillar
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• Concept 41.1: Homeostatic mechanisms manage an animal’s energy budget
• Nearly all of an animal’s ATP generation
– Is based on the oxidation of energy-rich molecules: carbohydrates, proteins, and fats
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Glucose Regulation as an Example of Homeostasis
• Animals store excess calories
– As glycogen in the liver and muscles and as fat
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• Glucose is a major fuel for cells
• Its metabolism, regulated by hormone action, is an important example of homeostasis
Figure 41.3
1 When blood glucose level rises, a gland called the pancreas secretes insulin,a hormone, into the blood.
Insulin enhances the transport of glucose into body cells and stimulates the liver and muscle cells to store glucose as glycogen. As a result, blood glucose level drops.
2
STIMULUS:Blood glucose
level risesafter eating.
Homeostasis:90 mg glucose/100 mL blood
STIMULUS:Blood glucose
level dropsbelow set point.
Glucagon promotesthe breakdown of
glycogen in theliver and the
release of glucoseinto the blood,
increasing bloodglucose level.
4
When blood glucose level drops, the pancreas secretes the hormone glucagon, which opposes the effect of insulin.
3
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• When fewer calories are taken in than are expended
– Fuel is taken out of storage and oxidized
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Caloric Imbalance
• Undernourishment
– Occurs in animals when their diets are chronically deficient in calories
– Can have detrimental effects on an animal
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• Overnourishment
– Results from excessive food intake
– Leads to the storage of excess calories as fat
Figure 41.4
100 µm
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Obesity as a Human Health Problem
• The World Health Organization
– Now recognizes obesity as a major global health problem
• Obesity contributes to a number of health problems, including
– Diabetes, cardiovascular disease, and colon and breast cancer
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• Researchers have discovered
– Several of the mechanisms that help regulate body weight
• Over the long term, homeostatic mechanisms
– Are feedback circuits that control the body’s storage and metabolism of fat
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• Several chemical signals called hormones
– Regulate both long-term and short-term appetite by affecting a “satiety center” in the brain
Figure 41.5
Produced by adipose (fat) tissue, leptin suppresses
appetite as its level increases. When body fat decreases,
leptin levels fall, and appetite increases.
LeptinPYY
Insulin
Ghrelin
Secreted by the stomach wall, ghrelin is one of the signals that triggers feelings of hunger as mealtimes approach. In dieters who lose weight, ghrelin levels increase, which may be one reason it’s so hard to stay on a diet.
The hormone PYY, secreted by the small intestine after meals,
acts as an appetite suppressant that
counters the appetite stimulant ghrelin.
A rise in blood sugar level after a meal stimulates the pancreas to secrete insulin (see Figure 41.3). In addition to its other functions, insulin suppresses appetite by acting on the brain.
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• The complexity of weight control in humans
– Is evident from studies of the hormone leptin
• Mice that inherit a defect in the gene for leptin
– Become very obese
Figure 41.6
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Obesity and Evolution
• The problem of maintaining weight partly stems from our evolutionary past
– When fat hoarding was a means of survival
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• A species of birds called petrels
– Become obese as chicks due to the need to consume more calories than they burn
Figure 41.7
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• Concept 41.2: An animal’s diet must supply carbon skeletons and essential nutrients
• To build the complex molecules it needs to grow, maintain itself, and reproduce
– An animal must obtain organic precursors (carbon skeletons) from its food
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• Besides fuel and carbon skeletons
– An animal’s diet must also supply essential nutrients in preassembled form
• An animal that is malnourished
– Is missing one or more essential nutrients in its diet
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• Herbivorous animals
– May suffer mineral deficiencies if they graze on plants in soil lacking key minerals
Figure 41.8
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• Malnutrition
– Is much more common than undernutrition in human populations
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Essential Amino Acids
• Animals require 20 amino acids
– And can synthesize about half of them from the other molecules they obtain from their diet
• The remaining amino acids, the essential amino acids
– Must be obtained from food in preassembled form
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• A diet that provides insufficient amounts of one or more essential amino acids
– Causes a form of malnutrition called protein deficiency
Figure 41.9
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• Most plant proteins are incomplete in amino acid makeup
– So individuals who must eat only plant proteins need to eat a variety to ensure that they get all the essential amino acids
Corn (maize)and other grains
Beansand other legumes
Essential amino acids for adults
Methionine
Valine
Threonine
Phenylalanine
Leucine
Isoleucine
Lysine
Tryptophan
Figure 41.10
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• Some animals have adaptations
– That help them through periods when their bodies demand extraordinary amounts of protein
Figure 41.11
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Essential Fatty Acids
• Animals can synthesize most of the fatty acids they need
• The essential fatty acids
– Are certain unsaturated fatty acids
• Deficiencies in fatty acids are rare
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Vitamins
• Vitamins are organic molecules
– Required in the diet in small amounts
• To date, 13 vitamins essential to humans
– Have been identified
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• Vitamins are grouped into two categories
– Fat-soluble and water-soluble
Table 41.1
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Minerals
• Minerals are simple inorganic nutrients
– Usually required in small amounts
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• Mineral requirements of humans
Table 41.2
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• Concept 41.3: The main stages of food processing are ingestion, digestion, absorption, and elimination
• Ingestion, the act of eating
– Is the first stage of food processing
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• Digestion, the second stage of food processing
– Is the process of breaking food down into molecules small enough to absorb
– Involves enzymatic hydrolysis of polymers into their monomers
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• Absorption, the third stage of food processing
– Is the uptake of nutrients by body cells
• Elimination, the fourth stage of food processing
– Occurs as undigested material passes out of the digestive compartment
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• The four stages of food processing
Figure 41.12
Piecesof food
Smallmolecules
Mechanicaldigestion
Food
Chemical digestion(enzymatic hydrolysis)
Nutrient moleculesenter body cells
Undigested material
INGESTION1 DIGESTION2 ELIMINATION4ABSORPTION3
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Digestive Compartments
• Most animals process food
– In specialized compartments
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Intracellular Digestion
• In intracellular digestion
– Food particles are engulfed by endocytosis and digested within food vacuoles
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Extracellular Digestion
• Extracellular digestion
– Is the breakdown of food particles outside cells
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• Animals with simple body plans
– Have a gastrovascular cavity that functions in both digestion and distribution of nutrients
Figure 41.13
Gastrovascularcavity
Food
Epidermis
Mesenchyme
Gastrodermis
Mouth
Tentacles
Mesenchyme
Food vacuoles
Gland cells
Flagella
Nutritivemuscularcells
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• Animals with a more complex body plan
– Have a digestive tube with two openings, a mouth and an anus
• This digestive tube
– Is called a complete digestive tract or an alimentary canal
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• The digestive tube can be organized into specialized regions
– That carry out digestion and nutrient absorption in a stepwise fashion
Esophagus
Mouth
Pharynx
Crop GizzardIntestine
Anus
Typhlosole
Lumen of intestine
Esophagus
Anus
Rectum
Mouth
CropGastric ceca
Anus
Intestine
Gizzard
Crop
Stomach
Mouth
Esophagus
Foregut Midgut Hindgut
(a) Earthworm. The digestive tract ofan earthworm includes a muscular pharynx that sucks food in through themouth. Food passes through the esophagus and is stored and moistened in the crop. The muscular gizzard, whichcontains small bits of sand and gravel, pulverizes the food. Digestion and absorption occur in the intestine, which has a dorsal fold, the typhlosole, that increases the surface area for nutrient absorption.
(b) Grasshopper. A grasshopper has several digestive chambers grouped into three main regions: a foregut, with an esophagus and crop; a midgut; and a hindgut. Food is moistened and stored in the crop, but most digestion occurs in the midgut. Gastric ceca, pouches extending from the midgut, absorb nutrients.
(c) Bird. Many birds have three separate chambers—the crop, stomach, and gizzard—where food is pulverized and churned before passing into the intestine. A bird’s crop and gizzard function very much like those of an earthworm. In most birds, chemical digestion and absorption of nutrients occur in the intestine.Figure 41.14a–c
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• Concept 41.4: Each organ of the mammalian digestive system has specialized food-processing functions
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• The mammalian digestive system consists of the alimentary canal
– And various accessory glands that secrete digestive juices through ducts
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IIeumof small intestine Duodenum of
small intestine
Appendix
Cecum
Ascendingportion of large intestine
Anus
Small intestine
Large intestine
Rectum
Liver
Gall-bladder
Tongue
Oral cavity
Pharynx
Esophagus
Stomach
Pyloricsphincter
Cardiacorifice
Mouth
Esophagus
Salivaryglands
Stomach
Liver
Pancreas
Gall-bladder
Large intestines
Small intestines
Rectum
Anus
Parotid glandSublingual gland
Submandibular gland
Salivaryglands
A schematic diagram of the human digestive system
Pancreas
Figure 41.15
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• Food is pushed along the digestive tract by peristalsis
– Rhythmic waves of contraction of smooth muscles in the wall of the canal
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The Oral Cavity, Pharynx, and Esophagus
• In the oral cavity, food is lubricated and digestion begins
– And teeth chew food into smaller particles that are exposed to salivary amylase, initiating the breakdown of glucose polymers
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• The region we call our throat is the pharynx
– A junction that opens to both the esophagus and the windpipe (trachea)
• The esophagus
– Conducts food from the pharynx down to the stomach by peristalsis
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• From mouth to stomach
Esophagus
Epiglottis down
Tongue
Pharynx
GlottisLarynx
Trachea
Bolus of food
Epiglottisup
To lungs To stomach
Esophageal sphinctercontracted
Glottis upand closed
Esophageal sphincterrelaxed
Glottisdown and open
Esophageal sphinctercontracted
Epiglottisup
Relaxedmuscles
Contractedmuscles
Relaxedmuscles
Stomach
Figure 41.16
1 When a person is not swallowing, the esophageal sphincter muscle is contracted, the epiglottis is up, and the glottis is open, allowing air to flow through the trachea to the lungs.
The swallowingreflex is triggeredwhen a bolus offood reaches thepharynx.
2
The larynx, theupper part of therespiratory tract,moves upward andtips the epiglottisover the glottis,preventing foodfrom entering thetrachea.
3
The esophagealsphincter relaxes,allowing thebolus to enter theesophagus.
4
After the foodhas entered theesophagus, the
larynx movesdownward and
opens thebreathingpassage.
5
Waves of muscularcontraction (peristalsis)
move the bolus down the esophagus
to the stomach.
6
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The Stomach
• The stomach stores food
– And secretes gastric juice, which converts a meal to acid chyme
• Gastric juice
– Is made up of hydrochloric acid and the enzyme pepsin
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• The lining of the stomach
– Is coated with mucus, which prevents the gastric juice from destroying the cells
Figure 41.17
Pepsin (active enzyme)
HCl
Parietal cellChief cell
Stomach
Folds of epithelial tissue
Esophagus
Pyloric sphincter
Epithelium
Pepsinogen
3
2
1
Interior surface of stomach.The interior surface of the
stomach wall is highly folded and dotted with pits leading
into tubular gastric glands.
Gastric gland. The gastric glands have three types of cells
that secrete different components of the gastric juice: mucus cells,
chief cells, and parietal cells.
Mucus cells secrete mucus,which lubricates and protects
the cells lining the stomach.
Chief cells secrete pepsino-gen, an inactive form of the
digestive enzyme pepsin.
Parietal cells secretehydrochloric acid (HCl).
1 Pepsinogen and HCIare secreted into thelumen of the stomach.
2 HCl convertspepsinogen to pepsin.
3 Pepsin then activatesmore pepsinogen,starting a chainreaction. Pepsinbegins the chemicaldigestion of proteins.
5 µ
m
Small intestine
Cardiac orifice
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• Gastric ulcers, lesions in the lining
– Are caused mainly by the bacterium Helicobacter pylori
Figure 41.18
1 µ
m
Bacteria
Mucuslayer of stomach
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The Small Intestine
• The small intestine
– Is the longest section of the alimentary canal
– Is the major organ of digestion and absorption
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Enzymatic Action in the Small Intestine
• The first portion of the small intestine is the duodenum
– Where acid chyme from the stomach mixes with digestive juices from the pancreas, liver, gallbladder, and intestine itself
Figure 41.19
Liver Bile
Acid chyme
Stomach
Pancreatic juice
Pancreas
Intestinaljuice
Duodenum of small intestine
Gall-bladder
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• The pancreas produces proteases, protein-digesting enzymes
– That are activated once they enter the duodenum
PancreasMembrane-boundenteropeptidase
Trypsin
Active proteases
Lumen of duodenum
Inactivetrypsinogen
Other inactiveproteases
Figure 41.20
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• Enzymatic digestion is completed
– As peristalsis moves the mixture of chyme and digestive juices along the small intestine
Figure 41.21
Oral cavity,pharynx,esophagus
Carbohydrate digestion
Polysaccharides(starch, glycogen)
Disaccharides(sucrose, lactose)
Salivary amylase
Smaller polysaccharides,maltose
Stomach
Protein digestion Nucleic acid digestion Fat digestion
Proteins
Pepsin
Small polypeptides
Lumen of small intes-tine
Polysaccharides
Pancreatic amylases
Maltose and otherdisaccharides
Epitheliumof smallintestine(brushborder)
Disaccharidases
Monosaccharides
Polypeptides
Pancreatic trypsin andchymotrypsin (These proteasescleave bonds adjacent to certainamino acids.)
Smallerpolypeptides
Pancreatic carboxypeptidase
Amino acids
Small peptides
Dipeptidases, carboxypeptidase, and aminopeptidase (These proteases split off one amino acid at a time, working from opposite ends of a polypeptide.)
Amino acids
DNA, RNA
Pancreaticnucleases
Nucleotides
Nucleotidases
Nucleosides
Nucleosidasesandphosphatases
Nitrogenous bases,sugars, phosphates
Fat globules (Insoluble inwater, fats aggregate asglobules.)
Bile salts
Fat droplets (A coating ofbile salts prevents small drop-lets from coalescing intolarger globules, increasingexposure to lipase.)
Pancreatic lipase
Glycerol, fattyacids, glycerides
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• Hormones help coordinate the secretion of digestive juices into the alimentary canal
Figure 41.22
Amino acids or fatty acids in the duodenum trigger the release of cholecystokinin (CCK), which
stimulates the release of digestive enzymes from the pancreas and bile
from the gallbladder.
Liver
Gall-bladder
CCK
Entero-gastrone
Gastrin
Stomach
Pancreas
Secretin
CCK
Duodenum
Key
Stimulation
Inhibition
Enterogastrone secreted by the duodenum inhibits peristalsis and acid secretion by the stomach, thereby slowing digestion when acid chyme rich in fats enters the duodenum.
Secreted by the duodenum, secretin stimulates the pancreas to release sodium bicarbonate, which neutralizes acid chyme from the stomach.
Gastrin from the stomach recirculates via the bloodstream back to the stomach, where it stimulates the production of gastric juices.
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Absorption of Nutrients
• The small intestine has a huge surface area
– Due to the presence of villi and microvilli that are exposed to the intestinal lumen
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• The enormous microvillar surface
– Is an adaptation that greatly increases the rate of nutrient absorption
Epithelialcells
Key
Nutrientabsorption
Vein carrying blood to hepatic portal vessel
Villi
Largecircularfolds
Intestinal wallVilli
Epithelial cells
Lymph vessel
Bloodcapillaries
Lacteal
Microvilli(brush border)
Muscle layers
Figure 41.23
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• The core of each villus
– Contains a network of blood vessels and a small vessel of the lymphatic system called a lacteal
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• Amino acids and sugars
– Pass through the epithelium of the small intestine and enter the bloodstream
• After glycerol and fatty acids are absorbed by epithelial cells
– They are recombined into fats within these cells
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• These fats are then mixed with cholesterol and coated with proteins
– Forming small molecules called chylomicrons, which are transported into lacteals
Figure 41.24
Large fat globules are emulsified by bile salts in the duodenum.
1
Digestion of fat by the pancreatic enzyme lipase yields free fatty acids and monoglycerides, which then form micelles.
2
Fatty acids and mono-glycerides leave micelles and enter epithelial cells by diffusion.
3
Fat globule
Lacteal
Epithelialcells ofsmallintestine
Micelles madeup of fatty acids,monoglycerides,and bile salts
Fat dropletscoated withbile salts
Bile salts
Chylomicrons containing fattysubstances are transported out of the epithelial cells and into lacteals, where they are carried away from the intestine by lymph.
4
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The Large Intestine
• The large intestine, or colon
– Is connected to the small intestine
Figure 41.25
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• A major function of the colon
– Is to recover water that has entered the alimentary canal
• The wastes of the digestive tract, the feces
– Become more solid as they move through the colon
– Pass through the rectum and exit via the anus
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• The colon houses various strains of the bacterium Escherichia coli
– Some of which produce various vitamins
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• Concept 41.5: Evolutionary adaptations of vertebrate digestive systems are often associated with diet
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Some Dental Adaptations
• Dentition, an animal’s assortment of teeth
– Is one example of structural variation reflecting diet
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• Mammals have specialized dentition
– That best enables them to ingest their usual diet
Figure 41.26a–c
(a) Carnivore
(b) Herbivore
(c) Omnivore
Incisors
Canines
Premolars
Molars
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Stomach and Intestinal Adaptations
• Herbivores generally have longer alimentary canals than carnivores
– Reflecting the longer time needed to digest vegetation
Figure 41.27 Carnivore Herbivore
Colon(largeintestine)
Cecum
StomachSmall intestine
Small intestine
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Symbiotic Adaptations
• Many herbivorous animals have fermentation chambers
– Where symbiotic microorganisms digest cellulose
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• The most elaborate adaptations for an herbivorous diet
– Have evolved in the animals called ruminants
Figure 41.28
Reticulum. Some boluses also enter the reticulum. In both the rumen and the reticulum, symbiotic prokaryotes and protists (mainly ciliates) go to work on the cellulose-rich meal. As by-products of theirmetabolism, the microorganisms secrete fatty acids. The cow periodically regurgitates and rechews the cud (red arrows), which further breaks down thefibers, making them more accessible to further microbial action.
Rumen. When the cow first chews andswallows a mouthful of grass, boluses(green arrows) enter the rumen.
1
Intestine
2
Omasum. The cow then reswallowsthe cud (blue arrows), which moves tothe omasum, where water is removed.
3 Abomasum. The cud, containing great numbers of microorganisms, finally passes to the abomasum for digestion by the cow‘s own enzymes (black arrows).
4
Esophagus
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PowerPoint Lectures for Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Chapter 42Chapter 42
Circulation and Gas Exchange
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• Overview: Trading with the Environment
• Every organism must exchange materials with its environment
– And this exchange ultimately occurs at the cellular level
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• In unicellular organisms
– These exchanges occur directly with the environment
• For most of the cells making up multicellular organisms
– Direct exchange with the environment is not possible
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• The feathery gills projecting from a salmon
– Are an example of a specialized exchange system found in animals
Figure 42.1
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• Concept 42.1: Circulatory systems reflect phylogeny
• Transport systems
– Functionally connect the organs of exchange with the body cells
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• Most complex animals have internal transport systems
– That circulate fluid, providing a lifeline between the aqueous environment of living cells and the exchange organs, such as lungs, that exchange chemicals with the outside environment
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Invertebrate Circulation
• The wide range of invertebrate body size and form
– Is paralleled by a great diversity in circulatory systems
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Gastrovascular Cavities
• Simple animals, such as cnidarians
– Have a body wall only two cells thick that encloses a gastrovascular cavity
• The gastrovascular cavity
– Functions in both digestion and distribution of substances throughout the body
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• Some cnidarians, such as jellies
– Have elaborate gastrovascular cavities
Figure 42.2
Circularcanal
Radial canal
5 cmMouth
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Open and Closed Circulatory Systems
• More complex animals
– Have one of two types of circulatory systems: open or closed
• Both of these types of systems have three basic components
– A circulatory fluid (blood)
– A set of tubes (blood vessels)
– A muscular pump (the heart)
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• In insects, other arthropods, and most molluscs
– Blood bathes the organs directly in an open circulatory system
Heart
Hemolymph in sinusessurrounding ograns
Anterior vessel
Tubular heart
Lateral vessels
Ostia
(a) An open circulatory systemFigure 42.3a
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• In a closed circulatory system
– Blood is confined to vessels and is distinct from the interstitial fluid
Figure 42.3b
Interstitialfluid
Heart
Small branch vessels in each organ
Dorsal vessel(main heart)
Ventral vesselsAuxiliary hearts
(b) A closed circulatory system
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• Closed systems
– Are more efficient at transporting circulatory fluids to tissues and cells
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Survey of Vertebrate Circulation
• Humans and other vertebrates have a closed circulatory system
– Often called the cardiovascular system
• Blood flows in a closed cardiovascular system
– Consisting of blood vessels and a two- to four-chambered heart
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• Arteries carry blood to capillaries
– The sites of chemical exchange between the blood and interstitial fluid
• Veins
– Return blood from capillaries to the heart
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Fishes
• A fish heart has two main chambers
– One ventricle and one atrium
• Blood pumped from the ventricle
– Travels to the gills, where it picks up O2 and disposes of CO2
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Amphibians
• Frogs and other amphibians
– Have a three-chambered heart, with two atria and one ventricle
• The ventricle pumps blood into a forked artery
– That splits the ventricle’s output into the pulmocutaneous circuit and the systemic circuit
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Reptiles (Except Birds)
• Reptiles have double circulation
– With a pulmonary circuit (lungs) and a systemic circuit
• Turtles, snakes, and lizards
– Have a three-chambered heart
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Mammals and Birds
• In all mammals and birds
– The ventricle is completely divided into separate right and left chambers
• The left side of the heart pumps and receives only oxygen-rich blood
– While the right side receives and pumps only oxygen-poor blood
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• A powerful four-chambered heart
– Was an essential adaptation of the endothermic way of life characteristic of mammals and birds
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FISHES AMPHIBIANS REPTILES (EXCEPT BIRDS) MAMMALS AND BIRDS
Systemic capillaries Systemic capillaries Systemic capillaries Systemic capillaries
Lung capillaries Lung capillariesLung and skin capillariesGill capillaries
Right Left Right Left Right Left Systemic
circuitSystemic
circuit
Pulmocutaneouscircuit
Pulmonarycircuit
Pulmonarycircuit
SystemiccirculationVein
Atrium (A)
Heart:ventricle (V)
Artery Gillcirculation
A
V VV VV
A A A AALeft Systemicaorta
Right systemicaorta
Figure 42.4
• Vertebrate circulatory systems
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• Concept 42.2: Double circulation in mammals depends on the anatomy and pumping cycle of the heart
• The structure and function of the human circulatory system
– Can serve as a model for exploring mammalian circulation in general
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Mammalian Circulation: The Pathway
• Heart valves
– Dictate a one-way flow of blood through the heart
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• Blood begins its flow
– With the right ventricle pumping blood to the lungs
• In the lungs
– The blood loads O2 and unloads CO2
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• Oxygen-rich blood from the lungs
– Enters the heart at the left atrium and is pumped to the body tissues by the left ventricle
• Blood returns to the heart
– Through the right atrium
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• The mammalian cardiovascular system
Pulmonary vein
Right atrium
Right ventricle
Posteriorvena cava Capillaries of
abdominal organsand hind limbs
Aorta
Left ventricle
Left atriumPulmonary vein
Pulmonaryartery
Capillariesof left lung
Capillaries ofhead and forelimbs
Anteriorvena cava
Pulmonaryartery
Capillariesof right lung
Aorta
Figure 42.5
1
10
11
5
4
6
2
9
33
7
8
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The Mammalian Heart: A Closer Look
• A closer look at the mammalian heart
– Provides a better understanding of how double circulation works
Figure 42.6
Aorta
Pulmonaryveins
Semilunarvalve
Atrioventricularvalve
Left ventricleRight ventricle
Anterior vena cava
Pulmonary artery
Semilunarvalve
Atrioventricularvalve
Posterior vena cava
Pulmonaryveins
Right atrium
Pulmonaryartery
Leftatrium
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• The heart contracts and relaxes
– In a rhythmic cycle called the cardiac cycle
• The contraction, or pumping, phase of the cycle
– Is called systole
• The relaxation, or filling, phase of the cycle
– Is called diastole
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• The cardiac cycle
Figure 42.7
Semilunarvalvesclosed
AV valvesopen
AV valvesclosed
Semilunarvalvesopen
Atrial and ventricular diastole
1
Atrial systole; ventricular diastole
2
Ventricular systole; atrial diastole
3
0.1 sec
0.3 sec0.4 sec
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• The heart rate, also called the pulse
– Is the number of beats per minute
• The cardiac output
– Is the volume of blood pumped into the systemic circulation per minute
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Maintaining the Heart’s Rhythmic Beat
• Some cardiac muscle cells are self-excitable
– Meaning they contract without any signal from the nervous system
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• A region of the heart called the sinoatrial (SA) node, or pacemaker
– Sets the rate and timing at which all cardiac muscle cells contract
• Impulses from the SA node
– Travel to the atrioventricular (AV) node
• At the AV node, the impulses are delayed
– And then travel to the Purkinje fibers that make the ventricles contract
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• The impulses that travel during the cardiac cycle
– Can be recorded as an electrocardiogram (ECG or EKG)
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• The control of heart rhythm
Figure 42.8
SA node(pacemaker)
AV node Bundlebranches
Heartapex
Purkinjefibers
2 Signals are delayedat AV node.
1 Pacemaker generates wave of signals to contract.
3 Signals passto heart apex.
4 Signals spreadThroughoutventricles.
ECG
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• The pacemaker is influenced by
– Nerves, hormones, body temperature, and exercise
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• Concept 42.3: Physical principles govern blood circulation
• The same physical principles that govern the movement of water in plumbing systems
– Also influence the functioning of animal circulatory systems
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Blood Vessel Structure and Function
• The “infrastructure” of the circulatory system
– Is its network of blood vessels
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• All blood vessels
– Are built of similar tissues
– Have three similar layers
Figure 42.9
Artery Vein
100 µm
Artery Vein
ArterioleVenule
Connectivetissue
Smoothmuscle
Endothelium
Connectivetissue
Smoothmuscle
EndotheliumValve
Endothelium
Basementmembrane
Capillary
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• Structural differences in arteries, veins, and capillaries
– Correlate with their different functions
• Arteries have thicker walls
– To accommodate the high pressure of blood pumped from the heart
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• In the thinner-walled veins
– Blood flows back to the heart mainly as a result of muscle action
Figure 42.10
Direction of blood flowin vein (toward heart)
Valve (open)
Skeletal muscle
Valve (closed)
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Blood Flow Velocity
• Physical laws governing the movement of fluids through pipes
– Influence blood flow and blood pressure
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• The velocity of blood flow varies in the circulatory system
– And is slowest in the capillary beds as a result of the high resistance and large total cross-sectional area
Figure 42.11
5,0004,0003,0002,0001,000
0
Aor
ta
Art
erie
s
Art
erio
les
Cap
illar
ies
Ven
ules
Vei
ns
Ven
ae c
avae
Pre
ssur
e (m
m H
g)V
eloc
ity (
cm/s
ec)
Are
a (c
m2)
Systolicpressure
Diastolicpressure
50403020100
120100806040200
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Blood Pressure
• Blood pressure
– Is the hydrostatic pressure that blood exerts against the wall of a vessel
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• Systolic pressure
– Is the pressure in the arteries during ventricular systole
– Is the highest pressure in the arteries
• Diastolic pressure
– Is the pressure in the arteries during diastole
– Is lower than systolic pressure
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• Blood pressure
– Can be easily measured in humans
Figure 42.12
Artery
Rubber cuffinflatedwith air
Arteryclosed
120 120
Pressurein cuff above 120
Pressurein cuff below 120
Pressurein cuff below 70
Sounds audible instethoscope
Sounds stop
Blood pressurereading: 120/70
A typical blood pressure reading for a 20-year-oldis 120/70. The units for these numbers are mm of mercury (Hg); a blood pressure of 120 is a force that can support a column of mercury 120 mm high.
1
A sphygmomanometer, an inflatable cuff attached to apressure gauge, measures blood pressure in an artery.The cuff is wrapped around the upper arm and inflated until the pressure closes the artery, so that no blood flows past the cuff. When this occurs, the pressure exerted by the cuff exceeds the pressure in the artery.
2 A stethoscope is used to listen for sounds of blood flow below the cuff. If the artery is closed, there is no pulse below the cuff. The cuff is gradually deflated until blood begins to flow into the forearm, and sounds from blood pulsing into the artery below the cuff can be heard with the stethoscope. This occurs when the blood pressure is greater than the pressure exerted by the cuff. The pressure at this point is the systolic pressure.
3
The cuff is loosened further until the blood flows freely through the artery and the sounds below the cuff disappear. The pressure at this point is the diastolic pressure remaining in the artery when the heart is relaxed.
4
70
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• Blood pressure is determined partly by cardiac output
– And partly by peripheral resistance due to variable constriction of the arterioles
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Capillary Function
• Capillaries in major organs are usually filled to capacity
– But in many other sites, the blood supply varies
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• Two mechanisms
– Regulate the distribution of blood in capillary beds
• In one mechanism
– Contraction of the smooth muscle layer in the wall of an arteriole constricts the vessel
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• In a second mechanism
– Precapillary sphincters control the flow of blood between arterioles and venules
Figure 42.13 a–c
Precapillary sphincters Thoroughfarechannel
ArterioleCapillaries
Venule(a) Sphincters relaxed
(b) Sphincters contractedVenuleArteriole
(c) Capillaries and larger vessels (SEM)
20 m
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• The critical exchange of substances between the blood and interstitial fluid
– Takes place across the thin endothelial walls of the capillaries
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• The difference between blood pressure and osmotic pressure
– Drives fluids out of capillaries at the arteriole end and into capillaries at the venule end
At the arterial end of acapillary, blood pressure is
greater than osmotic pressure,and fluid flows out of the
capillary into the interstitial fluid.
Capillary Redbloodcell
15 m
Tissue cell INTERSTITIAL FLUID
CapillaryNet fluidmovement out
Net fluidmovement in
Direction of blood flow
Blood pressureOsmotic pressure
Inward flow
Outward flow
Pre
ssur
e
Arterial end of capillary Venule end
At the venule end of a capillary, blood pressure is less than osmotic pressure, and fluid flows from the interstitial fluid into the capillary.
Figure 42.14
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Fluid Return by the Lymphatic System
• The lymphatic system
– Returns fluid to the body from the capillary beds
– Aids in body defense
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• Fluid reenters the circulation
– Directly at the venous end of the capillary bed and indirectly through the lymphatic system
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• Concept 42.4: Blood is a connective tissue with cells suspended in plasma
• Blood in the circulatory systems of vertebrates
– Is a specialized connective tissue
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Blood Composition and Function
• Blood consists of several kinds of cells
– Suspended in a liquid matrix called plasma
• The cellular elements
– Occupy about 45% of the volume of blood
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Plasma
• Blood plasma is about 90% water
• Among its many solutes are
– Inorganic salts in the form of dissolved ions, sometimes referred to as electrolytes
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• The composition of mammalian plasmaPlasma 55%
Constituent Major functions
Water Solvent forcarrying othersubstances
SodiumPotassiumCalciumMagnesiumChlorideBicarbonate
Osmotic balancepH buffering, andregulation of membranepermeability
Albumin
Fibringen
Immunoglobulins(antibodies)
Plasma proteins
Icons (blood electrolytes
Osmotic balance,pH buffering
Substances transported by bloodNutrients (such as glucose, fatty acids, vitamins)Waste products of metabolismRespiratory gases (O2 and CO2)Hormones
Defense
Figure 42.15
Separatedbloodelements
Clotting
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• Another important class of solutes is the plasma proteins
– Which influence blood pH, osmotic pressure, and viscosity
• Various types of plasma proteins
– Function in lipid transport, immunity, and blood clotting
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Cellular Elements
• Suspended in blood plasma are two classes of cells
– Red blood cells, which transport oxygen
– White blood cells, which function in defense
• A third cellular element, platelets
– Are fragments of cells that are involved in clotting
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Figure 42.15
Cellular elements 45%
Cell type Numberper L (mm3) of blood
Functions
Erythrocytes(red blood cells) 5–6 million Transport oxygen
and help transportcarbon dioxide
Leukocytes(white blood cells)
5,000–10,000 Defense andimmunity
Eosinophil
Basophil
Platelets
NeutrophilMonocyte
Lymphocyte
250,000400,000
Blood clotting
• The cellular elements of mammalian blood
Separatedbloodelements
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Erythrocytes
• Red blood cells, or erythrocytes
– Are by far the most numerous blood cells
– Transport oxygen throughout the body
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Leukocytes
• The blood contains five major types of white blood cells, or leukocytes
– Monocytes, neutrophils, basophils, eosinophils, and lymphocytes, which function in defense by phagocytizing bacteria and debris or by producing antibodies
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Platelets
• Platelets function in blood clotting
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Stem Cells and the Replacement of Cellular Elements
• The cellular elements of blood wear out
– And are replaced constantly throughout a person’s life
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• Erythrocytes, leukocytes, and platelets all develop from a common source
– A single population of cells called pluripotent stem cells in the red marrow of bones
B cells T cells
Lymphoidstem cells
Pluripotent stem cells(in bone marrow)
Myeloidstem cells
Erythrocytes
Platelets Monocytes
Neutrophils
Eosinophils
Basophils
Lymphocytes
Figure 42.16
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Blood Clotting
• When the endothelium of a blood vessel is damaged
– The clotting mechanism begins
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• A cascade of complex reactions
– Converts fibrinogen to fibrin, forming a clot
Plateletplug
Collagen fibers
Platelet releases chemicalsthat make nearby platelets sticky
Clotting factors from:PlateletsDamaged cellsPlasma (factors include calcium, vitamin K)
Prothrombin Thrombin
Fibrinogen Fibrin5 µm
Fibrin clotRed blood cell
The clotting process begins when the endothelium of a vessel is damaged, exposing connective tissue in the vessel wall to blood. Plateletsadhere to collagen fibers in the connective tissue and release a substance thatmakes nearby platelets sticky.
1 The platelets form a plug that providesemergency protectionagainst blood loss.
2 This seal is reinforced by a clot of fibrin when vessel damage is severe. Fibrin is formed via amultistep process: Clotting factors released fromthe clumped platelets or damaged cells mix withclotting factors in the plasma, forming an activation cascade that converts a plasma proteincalled prothrombin to its active form, thrombin.Thrombin itself is an enzyme that catalyzes the final step of the clotting process, the conversion of fibrinogen to fibrin. The threads of fibrin become interwoven into a patch (see colorized SEM).
3
Figure 42.17
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Cardiovascular Disease
• Cardiovascular diseases
– Are disorders of the heart and the blood vessels
– Account for more than half the deaths in the United States
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• One type of cardiovascular disease, atherosclerosis
– Is caused by the buildup of cholesterol within arteries
Figure 42.18a, b
(a) Normal artery (b) Partly clogged artery50 µm 250 µm
Smooth muscleConnective tissue Endothelium Plaque
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• Hypertension, or high blood pressure
– Promotes atherosclerosis and increases the risk of heart attack and stroke
• A heart attack
– Is the death of cardiac muscle tissue resulting from blockage of one or more coronary arteries
• A stroke
– Is the death of nervous tissue in the brain, usually resulting from rupture or blockage of arteries in the head
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• Concept 42.5: Gas exchange occurs across specialized respiratory surfaces
• Gas exchange
– Supplies oxygen for cellular respiration and disposes of carbon dioxide
Figure 42.19
Organismal level
Cellular level
Circulatory system
Cellular respiration ATPEnergy-richmoleculesfrom food
Respiratorysurface
Respiratorymedium(air of water)
O2 CO2
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• Animals require large, moist respiratory surfaces for the adequate diffusion of respiratory gases
– Between their cells and the respiratory medium, either air or water
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Gills in Aquatic Animals
• Gills are outfoldings of the body surface
– Specialized for gas exchange
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• In some invertebrates
– The gills have a simple shape and are distributed over much of the body
(a) Sea star. The gills of a sea star are simple tubular projections of the skin. The hollow core of each gillis an extension of the coelom(body cavity). Gas exchangeoccurs by diffusion across thegill surfaces, and fluid in thecoelom circulates in and out ofthe gills, aiding gas transport. The surfaces of a sea star’s tube feet also function in gas exchange.
Gills
Tube foot
Coelom
Figure 42.20a
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• Many segmented worms have flaplike gills
– That extend from each segment of their body
Figure 42.20b
(b) Marine worm. Many polychaetes (marine worms of the phylum Annelida) have a pair of flattened appendages called parapodia on each body segment. The parapodia serve as gillsand also function incrawling and swimming.
Gill
Parapodia
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• The gills of clams, crayfish, and many other animals
– Are restricted to a local body region
Figure 42.20c, d
(d) Crayfish. Crayfish and other crustaceanshave long, feathery gills covered by the exoskeleton. Specialized body appendagesdrive water over the gill surfaces.
(c) Scallop. The gills of a scallop are long, flattened plates that project from themain body mass inside the hard shell.Cilia on the gills circulate water around the gill surfaces.
Gills
Gills
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• The effectiveness of gas exchange in some gills, including those of fishes
– Is increased by ventilation and countercurrent flow of blood and water
Countercurrent exchange
Figure 42.21
Gill arch
Water flow Operculum
Gill arch
Blood vessel
Gillfilaments
Oxygen-poorblood
Oxygen-richblood
Water flowover lamellaeshowing % O2
Blood flowthrough capillariesin lamellaeshowing % O2
Lamella
100%
40%
70%
15%
90%
60%
30% 5%
O2
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Figure 42.22a
Tracheae
Air sacs
Spiracle
(a) The respiratory system of an insect consists of branched internaltubes that deliver air directly to body cells. Rings of chitin reinforcethe largest tubes, called tracheae, keeping them from collapsing. Enlarged portions of tracheae form air sacs near organs that require a large supply of oxygen. Air enters the tracheae through openings called spiracles on the insect’s body surface and passes into smaller tubes called tracheoles. The tracheoles are closed and contain fluid(blue-gray). When the animal is active and is using more O2, most ofthe fluid is withdrawn into the body. This increases the surface area of air in contact with cells.
Tracheal Systems in Insects
• The tracheal system of insects
– Consists of tiny branching tubes that penetrate the body
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• The tracheal tubes
– Supply O2 directly to body cells
Airsac
Body cell
Trachea
Tracheole
TracheolesMitochondria
Myofibrils
Body wall
(b) This micrograph shows crosssections of tracheoles in a tinypiece of insect flight muscle (TEM).Each of the numerous mitochondriain the muscle cells lies within about5 µm of a tracheole.
Figure 42.22b 2.5 µm
Air
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Lungs
• Spiders, land snails, and most terrestrial vertebrates
– Have internal lungs
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Mammalian Respiratory Systems: A Closer Look
• A system of branching ducts
– Conveys air to the lungsBranch from the pulmonary vein (oxygen-rich blood) Terminal bronchiole
Branch from thepulmonaryartery(oxygen-poor blood)
Alveoli
Colorized SEMSEM
50 µ
m
50 µ
m
Heart
Left lung
Nasalcavity
Pharynx
Larynx
Diaphragm
Bronchiole
Bronchus
Right lung
Trachea
Esophagus
Figure 42.23
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• In mammals, air inhaled through the nostrils
– Passes through the pharynx into the trachea, bronchi, bronchioles, and dead-end alveoli, where gas exchange occurs
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• Concept 42.6: Breathing ventilates the lungs
• The process that ventilates the lungs is breathing
– The alternate inhalation and exhalation of air
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How an Amphibian Breathes
• An amphibian such as a frog
– Ventilates its lungs by positive pressure breathing, which forces air down the trachea
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How a Mammal Breathes
• Mammals ventilate their lungs
– By negative pressure breathing, which pulls air into the lungs
Air inhaled Air exhaled
INHALATIONDiaphragm contracts
(moves down)
EXHALATIONDiaphragm relaxes
(moves up)
Diaphragm
Lung
Rib cage expands asrib muscles contract
Rib cage gets smaller asrib muscles relax
Figure 42.24
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• Lung volume increases
– As the rib muscles and diaphragm contract
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How a Bird Breathes
• Besides lungs, bird have eight or nine air sacs
– That function as bellows that keep air flowing through the lungs
INHALATIONAir sacs fill
EXHALATIONAir sacs empty; lungs fill
Anteriorair sacs
Trachea
Lungs LungsPosteriorair sacs
Air Air
1 mm
Air tubes(parabronchi)in lung
Figure 42.25
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• Air passes through the lungs
– In one direction only
• Every exhalation
– Completely renews the air in the lungs
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Control of Breathing in Humans
• The main breathing control centers
– Are located in two regions of the brain, the medulla oblongata and the pons
Figure 42.26
PonsBreathing control centers Medulla
oblongata
Diaphragm
Carotidarteries
Aorta
Cerebrospinalfluid
Rib muscles
In a person at rest, these nerve impulses result in
about 10 to 14 inhalationsper minute. Between
inhalations, the musclesrelax and the person exhales.
The medulla’s control center also helps regulate blood CO2 level. Sensors in the medulla detect changes in the pH (reflecting CO2
concentration) of the blood and cerebrospinal fluid bathing the surface of the brain.
Nerve impulses relay changes in
CO2 and O2 concentrations. Other sensors in the walls of the aortaand carotid arteries in the neck detect changes in blood pH andsend nerve impulses to the medulla. In response, the medulla’s breathingcontrol center alters the rate anddepth of breathing, increasing bothto dispose of excess CO2 or decreasingboth if CO2 levels are depressed.
The control center in themedulla sets the basic
rhythm, and a control centerin the pons moderates it,
smoothing out thetransitions between
inhalations and exhalations.
1
Nerve impulses trigger muscle contraction. Nerves
from a breathing control centerin the medulla oblongata of the
brain send impulses to thediaphragm and rib muscles, stimulating them to contract
and causing inhalation.
2
The sensors in the aorta andcarotid arteries also detect changesin O2 levels in the blood and signal the medulla to increase the breathing rate when levels become very low.
6
5
3
4
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• The centers in the medulla
– Regulate the rate and depth of breathing in response to pH changes in the cerebrospinal fluid
• The medulla adjusts breathing rate and depth
– To match metabolic demands
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• Sensors in the aorta and carotid arteries
– Monitor O2 and CO2 concentrations in the blood
– Exert secondary control over breathing
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• Concept 42.7: Respiratory pigments bind and transport gases
• The metabolic demands of many organisms
– Require that the blood transport large quantities of O2 and CO2
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The Role of Partial Pressure Gradients
• Gases diffuse down pressure gradients
– In the lungs and other organs
• Diffusion of a gas
– Depends on differences in a quantity called partial pressure
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• A gas always diffuses from a region of higher partial pressure
– To a region of lower partial pressure
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• In the lungs and in the tissues
– O2 and CO2 diffuse from where their partial pressures are higher to where they are lower
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Inhaled air Exhaled air
160 0.2O2 CO2
O2 CO2
O2 CO2
O2 CO2 O2 CO2
O2 CO2 O2 CO2
O2 CO2
40 45
40 45
100 40
104 40
104 40
120 27
CO2O2
Alveolarepithelialcells
Pulmonaryarteries
Blood enteringalveolar
capillaries
Blood leavingtissue
capillaries
Blood enteringtissue
capillaries
Blood leaving
alveolar capillaries
CO2O2
Tissue capillaries
Heart
Alveolar capillaries
of lung
<40 >45
Tissue cells
Pulmonaryveins
Systemic arteriesSystemic
veinsO2
CO2
O2
CO 2
Alveolar spaces
12
43
Figure 42.27
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Respiratory Pigments
• Respiratory pigments
– Are proteins that transport oxygen
– Greatly increase the amount of oxygen that blood can carry
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Oxygen Transport
• The respiratory pigment of almost all vertebrates
– Is the protein hemoglobin, contained in the erythrocytes
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• Like all respiratory pigments
– Hemoglobin must reversibly bind O2, loading O2 in the lungs and unloading it in other parts of the body
Heme group Iron atom
O2 loadedin lungs
O2 unloadedIn tissues
Polypeptide chain
O2
O2
Figure 42.28
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• Loading and unloading of O2
– Depend on cooperation between the subunits of the hemoglobin molecule
• The binding of O2 to one subunit induces the other subunits to bind O2 with more affinity
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• Cooperative O2 binding and release
– Is evident in the dissociation curve for hemoglobin
• A drop in pH
– Lowers the affinity of hemoglobin for O2
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O2 unloaded fromhemoglobinduring normalmetabolism
O2 reserve that canbe unloaded fromhemoglobin totissues with highmetabolism
Tissues duringexercise
Tissuesat rest
100
80
60
40
20
0
100
80
60
40
20
0
100806040200
100806040200
Lungs
PO2 (mm Hg)
PO2 (mm Hg)
O2 s
atur
atio
n of
hem
oglo
bin
(%)
O2 s
atur
atio
n of
hem
oglo
bin
(%)
Bohr shift:Additional O2
released from hemoglobin at lower pH(higher CO2
concentration)
pH 7.4
pH 7.2
(a) PO2 and Hemoglobin Dissociation at 37°C and pH 7.4
(b) pH and Hemoglobin Dissociation
Figure 42.29a, b
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Carbon Dioxide Transport
• Hemoglobin also helps transport CO2
– And assists in buffering
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• Carbon from respiring cells
– Diffuses into the blood plasma and then into erythrocytes and is ultimately released in the lungs
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Figure 42.30
Tissue cell
CO2Interstitialfluid
CO2 producedCO2 transportfrom tissues
CO2
CO2
Blood plasmawithin capillary Capillary
wall
H2O
Redbloodcell
HbCarbonic acidH2CO3
HCO3–
H++Bicarbonate
HCO3–
Hemoglobinpicks up
CO2 and H+
HCO3–
HCO3– H++
H2CO3Hb
Hemoglobinreleases
CO2 and H+
CO2 transportto lungs
H2O
CO2
CO2
CO2
CO2
Alveolar space in lung
2
1
34
5 6
7
8
9
10
11
To lungs
Carbon dioxide produced bybody tissues diffuses into the interstitial fluid and the plasma.
Over 90% of the CO2 diffuses into red blood cells, leaving only 7%in the plasma as dissolved CO2.
Some CO2 is picked up and transported by hemoglobin.
However, most CO2 reacts with water in red blood cells, forming carbonic acid (H2CO3), a reaction catalyzed bycarbonic anhydrase contained. Withinred blood cells.
Carbonic acid dissociates into a biocarbonate ion (HCO3
–) and a hydrogen ion (H+).
Hemoglobin binds most of the H+ from H2CO3 preventing the H+ from acidifying the blood and thuspreventing the Bohr shift.
CO2 diffuses into the alveolarspace, from which it is expelledduring exhalation. The reductionof CO2 concentration in the plasmadrives the breakdown of H2CO3 Into CO2 and water in the red bloodcells (see step 9), a reversal of the reaction that occurs in the tissues (see step 4).
Most of the HCO3– diffuse
into the plasma where it is carried in the bloodstream to the lungs.
In the HCO3– diffuse
from the plasma red blood cells, combining with H+ released from hemoglobin and forming H2CO3.
Carbonic acid is converted back into CO2 and water.
CO2 formed from H2CO3 is unloadedfrom hemoglobin and diffuses into the interstitial fluid.
1
2
3
4
5
6
7
8
9
10
11
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Elite Animal Athletes
• Migratory and diving mammals
– Have evolutionary adaptations that allow them to perform extraordinary feats
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The Ultimate Endurance Runner
• The extreme O2 consumption of the antelope-like pronghorn
– Underlies its ability to run at high speed over long distances
Figure 42.31
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Diving Mammals
• Deep-diving air breathers
– Stockpile O2 and deplete it slowly
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PowerPoint Lectures for Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Chapter 43Chapter 43
The Immune System
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• Overview: Reconnaissance, Recognition, and Response
• An animal must defend itself
– From the many dangerous pathogens it may encounter in the environment
• Two major kinds of defense have evolved that counter these threats
– Innate immunity and acquired immunity
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• Innate immunity
– Is present before any exposure to pathogens and is effective from the time of birth
– Involves nonspecific responses to pathogens
Figure 43.1 3m
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• Acquired immunity, also called adaptive immunity
– Develops only after exposure to inducing agents such as microbes, toxins, or other foreign substances
– Involves a very specific response to pathogens
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• A summary of innate and acquired immunity
INNATE IMMUNITY Rapid responses to a
broad range of microbes
ACQUIRED IMMUNITYSlower responses to
specific microbes
External defenses Internal defenses
Skin
Mucous membranes
Secretions
Phagocytic cells
Antimicrobial proteins
Inflammatory response
Natural killer cells
Humoral response(antibodies)
Cell-mediated response(cytotoxic lymphocytes)
Invadingmicrobes
(pathogens)
Figure 43.2
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• Concept 43.1: Innate immunity provides broad defenses against infection
• A pathogen that successfully breaks through an animal’s external defenses
– Soon encounters several innate cellular and chemical mechanisms that impede its attack on the body
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External Defenses
• Intact skin and mucous membranes
– Form physical barriers that bar the entry of microorganisms and viruses
• Certain cells of the mucous membranes produce mucus
– A viscous fluid that traps microbes and other particles
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• In the trachea, ciliated epithelial cells
– Sweep mucus and any entrapped microbes upward, preventing the microbes from entering the lungs
Figure 43.3
10m
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• Secretions of the skin and mucous membranes
– Provide an environment that is often hostile to microbes
• Secretions from the skin
– Give the skin a pH between 3 and 5, which is acidic enough to prevent colonization of many microbes
– Also include proteins such as lysozyme, an enzyme that digests the cell walls of many bacteria
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Internal Cellular and Chemical Defenses
• Internal cellular defenses
– Depend mainly on phagocytosis
• Phagocytes, types of white blood cells
– Ingest invading microorganisms
– Initiate the inflammatory response
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Phagocytic Cells
• Phagocytes attach to their prey via surface receptors
– And engulf them, forming a vacuole that fuses with a lysosome
Figure 43.4
Pseudopodiasurroundmicrobes.
1
Microbesare engulfedinto cell.
2
Vacuolecontainingmicrobesforms.
3
Vacuoleand lysosomefuse.
4
Toxiccompoundsand lysosomalenzymesdestroy microbes.
5
Microbialdebris isreleased byexocytosis.
6
Microbes
MACROPHAGE
Vacuole Lysosomecontainingenzymes
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• Macrophages, a specific type of phagocyte
– Can be found migrating through the body
– Can be found in various organs of the lymphatic system
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Adenoid
Tonsil
Lymphnodes
Spleen
Peyer’s patches(small intestine)
Appendix
Lymphaticvessels
Masses oflymphocytes andmacrophages
Tissuecells
Lymphaticvessel
Bloodcapillary
LymphaticcapillaryInterstitial
fluid
Lymphnode
• The lymphatic system
– Plays an active role in defending the body from pathogens Interstitial fluid bathing the
tissues, along with the white blood cells in it, continually enters lymphatic capillaries.
1
Figure 43.5
Fluid inside thelymphatic capillaries,called lymph, flowsthrough lymphaticvessels throughoutthe body.
2
Within lymph nodes,microbes and foreignparticles present in the circulating lymphencounter macro-phages, dendritic cells, and lymphocytes, which carry out various defensive actions.
3
Lymphatic vesselsreturn lymph to theblood via two large
ducts that drain intoveins near the
shoulders.
4
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Antimicrobial Proteins
• Numerous proteins function in innate defense
– By attacking microbes directly of by impeding their reproduction
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• About 30 proteins make up the complement system
– Which can cause lysis of invading cells and help trigger inflammation
• Interferons
– Provide innate defense against viruses and help activate macrophages
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Inflammatory Response
• In local inflammation, histamine and other chemicals released from injured cells
– Promote changes in blood vessels that allow more fluid, more phagocytes, and antimicrobial proteins to enter the tissues
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• Major events in the local inflammatory response
Figure 43.6
Pathogen Pin
Macrophage
Chemical signals
CapillaryPhagocytic cells
Red blood cell
Bloodclottingelements
Blood clot
Phagocytosis
Fluid, antimicrobial proteins, and clotting elements move from the blood to the site.Clotting begins.
2Chemical signals released by activated macrophages and mast cells at the injury site cause nearby capillaries to widen and become more permeable.
1 Chemokines released by various kinds of cells attract more phagocytic cells from the bloodto the injury site.
3 Neutrophils and macrophagesphagocytose pathogens and cell debris at the site, and the tissue heals.
4
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Natural Killer Cells
• Natural killer (NK) cells
– Patrol the body and attack virus-infected body cells and cancer cells
– Trigger apoptosis in the cells they attack
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Invertebrate Immune Mechanisms
• Many invertebrates defend themselves from infection
– By many of the same mechanisms in the vertebrate innate response
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• Concept 43.2: In acquired immunity, lymphocytes provide specific defenses against infection
• Acquired immunity
– Is the body’s second major kind of defense
– Involves the activity of lymphocytes
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Antigen-binding sitesAntibody A
Antigen
Antibody BAntibody C
Epitopes(antigenicdeterminants)
• An antigen is any foreign molecule
– That is specifically recognized by lymphocytes and elicits a response from them
• A lymphocyte actually recognizes and binds
– To just a small, accessible portion of the antigen called an epitope
Figure 43.7
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Antigen Recognition by Lymphocytes
• The vertebrate body is populated by two main types of lymphocytes
– B lymphocytes (B cells) and T lymphocytes (T cells)
– Which circulate through the blood
• The plasma membranes of both B cells and T cells
– Have about 100,000 antigen receptor that all recognize the same epitope
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B Cell Receptors for Antigens
• B cell receptors
– Bind to specific, intact antigens
– Are often called membrane antibodies or membrane immunoglobulins
Figure 43.8a
Antigen-bindingsite
Antigen-binding site
Disulfidebridge
Lightchain
Heavy chains
Cytoplasm of B cell
VA B cell receptor consists of two identical heavy chains and two identical light chains linked by several disulfide bridges.
(a)
Variableregions
Constantregions
Transmembraneregion
Plasmamembrane
B cell
V
V
CC C
C
V
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Antigen-Binding site
chain
Disulfide bridge
chain
T cell
A T cell receptor consists of one chain and one chain linked by a disulfide bridge.
(b)
Variableregions
Constantregions
Transmembraneregion
Plasmamembrane
Cytoplasm of T cell
T Cell Receptors for Antigens and the Role of the MHC
• Each T cell receptor
– Consists of two different polypeptide chains
Figure 43.8b
V V
C C
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• T cells bind to small fragments of antigens
– That are bound to normal cell-surface proteins called MHC molecules
• MHC molecules
– Are encoded by a family of genes called the major histocompatibility complex
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• Infected cells produce MHC molecules
– Which bind to antigen fragments and then are transported to the cell surface in a process called antigen presentation
• A nearby T cell
– Can then detect the antigen fragment displayed on the cell’s surface
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• Depending on their source
– Peptide antigens are handled by different classes of MHC molecules
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Figure 43.9a
Infected cell
Antigenfragment
Class I MHCmolecule
T cellreceptor
(a) Cytotoxic T cell
A fragment offoreign protein(antigen) inside thecell associates withan MHC moleculeand is transportedto the cell surface.
1
The combination ofMHC molecule andantigen is recognizedby a T cell, alerting itto the infection.
2
1
2
• Class I MHC molecules, found on almost all nucleated cells of the body
– Display peptide antigens to cytotoxic T cells
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• Class II MHC molecules, located mainly on dendritic cells, macrophages, and B cells
– Display antigens to helper T cells
1
2
Figure 43.9b
Microbe Antigen-presentingcell
Antigenfragment
Class II MHCmolecule
T cellreceptor
Helper T cell
A fragment offoreign protein(antigen) inside thecell associates withan MHC moleculeand is transportedto the cell surface.
1
The combination ofMHC molecule andantigen is recognizedby a T cell, alerting itto the infection.
2
(b)
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Lymphocyte Development
• Lymphocytes
– Arise from stem cells in the bone marrow
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• Newly formed lymphocytes are all alike
– But they later develop into B cells or T cells, depending on where they continue their maturation
Figure 43.10
Bone marrow
Lymphoidstem cell
B cell
Blood, lymph, and lymphoid tissues(lymph nodes, spleen, and others)
T cell
Thymus
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Generation of Lymphocyte Diversity by Gene Rearrangement
• Early in development, random, permanent gene rearrangement
– Forms functional genes encoding the B or T cell antigen receptor chains
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DNA ofundifferentiatedB cell
DNA of differentiatedB cell
pre-mRNA
mRNA Cap
B cell
B cell receptorLight-chain polypeptide
Intron
Intron
Intron
Variableregion
Constantregion
V1V2 V3
V4–V39
V40 J1 J2 J3 J4 J5
V1 V2V3 J5
V3 J5
V3 J5
V C
C
C
C
C
Poly (A)
Figure 43.11
Deletion of DNA between a V segmentand J segment and joining of the segments1
• Immunoglobulin gene rearrangement
Transcription of resulting permanently rearranged,functional gene2
RNA processing (removal of intron; addition of capand poly (A) tail)3
4 Translation
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Testing and Removal of Self-Reactive Lymphocytes
• As B and T cells are maturing in the bone and thymus
– Their antigen receptors are tested for possible self-reactivity
• Lymphocytes bearing receptors for antigens already present in the body
– Are destroyed by apoptosis or rendered nonfunctional
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Clonal Selection of Lymphocytes
• In a primary immune response
– Binding of antigen to a mature lymphocyte induces the lymphocyte’s proliferation and differentiation, a process called clonal selection
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• Clonal selection of B cells
– Generates a clone of short-lived activated effector cells and a clone of long-lived memory cells
Figure 43.12
Antigen molecules
Antigenreceptor
B cells thatdiffer inantigenspecificity
Antibodymolecules
Clone of memory cells Clone of plasma cells
Antigen moleculesbind to the antigenreceptors of only oneof the three B cellsshown.
The selected B cellproliferates, forminga clone of identicalcells bearingreceptors for theselecting antigen.
Some proliferatingcells develop intoshort-lived plasmacells that secreteantibodies specificfor the antigen.
Some proliferating cellsdevelop into long-livedmemory cells that canrespond rapidly uponsubsequent exposureto the same antigen.
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• In the secondary immune response
– Memory cells facilitate a faster, more efficient response
An
tibo
dy
con
cen
tra
tion
(arb
itra
ry u
nits
)
104
103
102
101
100
0 7 14 21 28 35 42 49 56
Time (days)Figure 43.13
Antibodiesto A
Antibodiesto B
Primaryresponse toantigen Aproduces anti-bodies to A
2Day 1: First exposure toantigen A
1 Day 28: Second exposureto antigen A; firstexposure to antigen B
3 Secondary response to anti-gen A produces antibodiesto A; primary response to anti-gen B produces antibodies to B
4
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• Concept 43.3: Humoral and cell-mediated immunity defend against different types of threats
• Acquired immunity includes two branches
– The humoral immune response involves the activation and clonal selection of B cells, resulting in the production of secreted antibodies
– The cell-mediated immune response involves the activation and clonal selection of cytotoxic T cells
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• The roles of the major participants in the acquired immune response
Figure 43.14
Humoral immune response Cell-mediated immune response
First exposure to antigen
Intact antigensAntigens engulfed and
displayed by dendritic cellsAntigens displayed
by infected cells
Activate Activate Activate
Gives rise to Gives rise to Gives rise to
B cellHelperT cell
CytotoxicT cell
Plasmacells
MemoryB cells
Active and memory helperT cells
Memory cytotoxic
T cells
Active cytotoxic
T cells
Secrete antibodies that defend againstpathogens and toxins in extracellular fluid
Defend against infected cells, cancer cells, and transplanted tissues
Secretedcytokinesactivate
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Helper T Cells: A Response to Nearly All Antigens
• Helper T cells produce CD4, a surface protein
– That enhances their binding to class II MHC molecule–antigen complexes on antigen-presenting cells
• Activation of the helper T cell then occurs
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• Activated helper T cells
– Secrete several different cytokines that stimulate other lymphocytes
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• The role of helper T cells in acquired immunity
Figure 43.15
After a dendritic cell engulfs and degrades a bacterium, it displays bacterial antigen fragments (peptides) complexed with a class II MHC molecule on the cell surface. A specific helper T cell binds to the displayed complex via its TCR with the aid of CD4. This interaction promotes secretion of cytokines by the dendritic cell.
Proliferation of the T cell, stimulatedby cytokines from both the dendritic cell and the T cell itself, gives rise toa clone of activated helper T cells(not shown), all with receptors for thesame MHC–antigen complex.
The cells in this clonesecrete other cytokines that help activate B cellsand cytotoxic T cells.
Cell-mediatedimmunity(attack on
infected cells)
Humoralimmunity
(secretion ofantibodies byplasma cells)
Dendriticcell
Dendriticcell
Bacterium
Peptide antigen
Class II MHCmolecule
TCR
CD4
Helper T cell
Cytokines
Cytotoxic T cell
B cell
1
2 3
1
2 3
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Cytotoxic T Cells: A Response to Infected Cells and Cancer Cells
• Cytotoxic T cells make CD8
– A surface protein that greatly enhances the interaction between a target cell and a cytotoxic T cell
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• Cytotoxic T cells
– Bind to infected cells, cancer cells, and transplanted tissues
• Binding to a class I MHC complex on an infected body cell
– Activates a cytotoxic T cell and differentiates it into an active killer
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Cytotoxic T cell
Perforin
Granzymes
CD8TCR
Class I MHCmolecule
Targetcell Peptide
antigen
Pore
ReleasedcytotoxicT cell
Apoptotictarget cell
Cancercell
CytotoxicT cell
A specific cytotoxic T cell binds to a class I MHC–antigen complex on a target cell via its TCR with the aid of CD8. This interaction, along with cytokines from helper T cells, leads to the activation of the cytotoxic cell.
1 The activated T cell releases perforin molecules, which form pores in the target cell membrane, and proteolytic enzymes (granzymes), which enter the target cell by endocytosis.
2 The granzymes initiate apoptosis within the target cells, leading to fragmentation of thenucleus, release of small apoptotic bodies, and eventual cell death. The released cytotoxic T cell can attack other target cells.
3
1
2
3
Figure 43.16
• The activated cytotoxic T cell
– Secretes proteins that destroy the infected target cell
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B Cells: A Response to Extracellular Pathogens
• Activation of B cells
– Is aided by cytokines and antigen binding to helper T cells
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• The clonal selection of B cells
– Generates antibody-secreting plasma cells, the effector cells of humoral immunity
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21
3
B cell
Bacterium
Peptide antigen
Class II MHCmolecule
TCR
Helper T cell
CD4
Activated helper T cell Clone of memory
B cells
Cytokines
Clone of plasma cellsSecreted antibodymolecules
Endoplasmicreticulum of plasma cell
Macrophage
After a macrophage engulfs and degradesa bacterium, it displays a peptide antigencomplexed with a class II MHC molecule.A helper T cell that recognizes the displayed complex is activated with the aid of cytokines secreted from the macrophage, forming a clone of activated helper T cells (not shown).
1 A B cell that has taken up and degraded the same bacterium displays class II MHC–peptide antigen complexes. An activated helper T cellbearing receptors specific for the displayedantigen binds to the B cell. This interaction,with the aid of cytokines from the T cell,activates the B cell.
2 The activated B cell proliferatesand differentiates into memoryB cells and antibody-secreting plasma cells. The secreted antibodies are specific for the same bacterial antigen that initiated the response.
3
Figure 43.17
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Antibody Classes
• The five major classes of antibodies, or immunoglobulins
– Differ in their distributions and functions within the body
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• The five classes of immunoglobulins
Figure 43.18
First Ig class produced after initial exposure to antigen; then its concentration in the blood declines
Most abundant Ig class in blood; also present in tissue fluids
Only Ig class that crosses placenta, thus conferring passive immunity on fetus
Promotes opsonization, neutralization, and agglutination of antigens; less effective in complement activation than IgM (see Figure 43.19)
Present in secretions such as tears, saliva, mucus, and breast milk
Triggers release from mast cells and basophils of histamine and other chemicals that cause allergic reactions (see Figure 43.20)
Present primarily on surface of naive B cells that havenot been exposed to antigens
IgM(pentamer)
IgG(monomer)
IgA(dimer)
IgE(monomer)
J chain
Secretorycomponent
J chain
Transmembraneregion
IgD(monomer)
Promotes neutralization and agglutination of antigens; very effective in complement activation (see Figure 43.19)
Provides localized defense of mucous membranes byagglutination and neutralization of antigens (seeFigure 43.19)
Presence in breast milk confers passive immunity onnursing infant
Acts as antigen receptor in antigen-stimulated proliferation and differentiation of B cells (clonal selection)
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Antibody-Mediated Disposal of Antigens
• The binding of antibodies to antigens
– Is also the basis of several antigen disposal mechanisms
– Leads to elimination of microbes by phagocytosis and complement-mediated lysis
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• Antibody-mediated mechanisms of antigen disposalBinding of antibodies to antigens
inactivates antigens by
Viral neutralization(blocks binding to host)
and opsonization (increasesphagocytosis)
Agglutination ofantigen-bearing particles,
such as microbes
Precipitation ofsoluble antigens
Activation of complement systemand pore formation
Bacterium
Virus Bacteria
Solubleantigens Foreign cell
Complementproteins
MAC
Pore
Enhances
Phagocytosis
Leads to
Cell lysis
MacrophageFigure 43.19
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Active and Passive Immunization
• Active immunity
– Develops naturally in response to an infection
– Can also develop following immunization, also called vaccination
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• In immunization
– A nonpathogenic form of a microbe or part of a microbe elicits an immune response to an immunological memory for that microbe
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• Passive immunity, which provides immediate, short-term protection
– Is conferred naturally when IgG crosses the placenta from mother to fetus or when IgA passes from mother to infant in breast milk
– Can be conferred artificially by injecting antibodies into a nonimmune person
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• Concept 43.4: The immune system’s ability to distinguish self from nonself limits tissue transplantation
• The immune system
– Can wage war against cells from other individuals
• Transplanted tissues
– Are usually destroyed by the recipient’s immune system
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Blood Groups and Transfusions
• Certain antigens on red blood cells
– Determine whether a person has type A, B, AB, or O blood
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• Antibodies to nonself blood types
– Already exist in the body
• Transfusion with incompatible blood
– Leads to destruction of the transfused cells
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• Recipient-donor combinations
– Can be fatal or safe
Table 43.1
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• Another red blood cell antigen, the Rh factor
– Creates difficulties when an Rh-negative mother carries successive Rh-positive fetuses
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Tissue and Organ Transplants
• MHC molecules
– Are responsible for stimulating the rejection of tissue grafts and organ transplants
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• The chances of successful transplantation are increased
– If the donor and recipient MHC tissue types are well matched
– If the recipient is given immunosuppressive drugs
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• Lymphocytes in bone marrow transplants
– May cause a graft versus host reaction in recipients
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• Concept 43.5: Exaggerated, self-directed, or diminished immune responses can cause disease
• If the delicate balance of the immune system is disrupted
– The effects on the individual can range from minor to often fatal consequences
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Allergies
• Allergies are exaggerated (hypersensitive) responses
– To certain antigens called allergens
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• In localized allergies such as hay fever
– IgE antibodies produced after first exposure to an allergen attach to receptors on mast cells
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• The next time the allergen enters the body
– It binds to mast cell–associated IgE molecules
• The mast cells then release histamine and other mediators
– That cause vascular changes and typical symptoms
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• The allergic response
Figure 43.20
IgE antibodies produced in response to initial exposure to an allergen bind to receptors or mast cells.
1 On subsequent exposure to the same allergen, IgE molecules attached to a mast cell recog-nize and bind the allergen.
2 Degranulation of the cell,triggered by cross-linking of adjacent IgE molecules, releases histamine and other chemicals, leading to allergysymptoms.
3
1
2
3
Allergen
IgE
Histamine
GranuleMast cell
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• An acute allergic response sometimes leads to anaphylactic shock
– A whole-body, life-threatening reaction that can occur within seconds of exposure to an allergen
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Autoimmune Diseases
• In individuals with autoimmune diseases
– The immune system loses tolerance for self and turns against certain molecules of the body
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• Rheumatoid arthritis
– Is an autoimmune disease that leads to damage and painful inflammation of the cartilage and bone of joints
Figure 43.21
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• Other examples of autoimmune diseases include
– Systemic lupus erythematosus
– Multiple sclerosis
– Insulin-dependent diabetes
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Immunodeficiency Diseases
• An inborn or primary immunodeficiency
– Results from hereditary or congenital defects that prevent proper functioning of innate, humoral, and/or cell-mediated defenses
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• An acquired or secondary immunodeficiency
– Results from exposure to various chemical and biological agents
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Inborn (Primary) Immunodeficiencies
• In severe combined immunodeficiency (SCID)
– Both the humoral and cell-mediated branches of acquired immunity fail to function
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Acquired (Secondary) Immunodeficiencies
• Acquired immunodeficiencies
– Range from temporary states to chronic diseases
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Stress and the Immune System
• Growing evidence shows
– That physical and emotional stress can harm immunity
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• Acquired Immunodeficiency Syndrome (AIDS)
• People with AIDS
– Are highly susceptible to opportunistic infections and cancers that take advantage of an immune system in collapse
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• Because AIDS arises from the loss of helper T cells
– Both humoral and cell-mediated immune responses are impaired
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• The loss of helper T cells
– Results from infection by the human immunodeficiency virus (HIV)
1µmFigure 43.22
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• The spread of HIV
– Has become a worldwide problem
• The best approach for slowing the spread of HIV
– Is educating people about the practices that transmit the virus