The great Serengeti migration: A quest for minerals

Digestive system

• Functions

• Organs

Figure 23.2

Organs of alimentary canal

Figure 23.1

MonthEsophagusStomachSmall intestineLarge intestineAccessory organsSalivary glands, liver, pancreas, gall bladder

Digestive tracts of various vertebrates

Digestive tracts of invertebrates and vertebrates

Figure 4.1 The composition of the adult human body

Nutrition

• Proteins

• Lipids

• Carbohydrates

• Vitamins and minerals

Figure 4.2 Amino acid chemistry (Part 1)

Figure 4.2 Amino acid chemistry (Part 2)

Figure 4.3 Fatty acids and triacylglycerols (Part 1)

Figure 4.3 Fatty acids and triacylglycerols (Part 2)

Figure 4.4 Carbohydrate chemistry

Figure 4.5 Vitamin structures

Feeding

Examples of feeding adaptations

Food chains

Figure 4.6 Some species feed by targeting and subduing individual food items (Part 1)

Figure 4.7 Specialization of a vertebrate feeding apparatus

Dentition

Figure 4.8 Specialization of an invertebrate feeding apparatus (Part 1)

Figure 4.8 Specialization of an invertebrate feeding apparatus (Part 2)

Figure 4.10 The feeding apparatus of a baleen whale

Figure 4.12 Reef-building corals of warm waters need light because they are symbiotic with algae (2)

Figure 4.9 Short food chains deplete energy less than long food chains do

Digestive systems of insects and crustaceans

• Crustaceans’ digestive system is separate from the excretory system

• Insects– the Malpighian tubules – excretory system is connected at the junction of the midgut and hindgut

Figure 4.16 The digestive systems of two types of arthropods: insects and crustaceans

Figure 23.1

Stomach (continued)

• Contractions of the stomach churn chyme.– Mix chyme

with gastric secretions.

– Push food into intestine.

Insert fig. 18.5

Small Intestine

• Each villus is a fold in the mucosa.

• Covered with columnar epithelial cells interspersed with goblet cells.

• Epithelial cells at the tips of villi are exfoliated and replaced by mitosis in crypt of Lieberkuhn.

• Lamina propria contain lymphocytes, capillaries, and central lacteal.

Insert fig. 18.12

Histology of the Alimentary Canal

Figure 23.6

Sensors of the GI tract– regulatory mechanisms

• Mechanoreceptors and chemoreceptors involved

• Located in the walls of the tract organs

• Sensors respond to– Stretching– Osmolarity– pH– Presence of substrates and end-products

Regulatory mechanisms (2)

• Receptors initiate reflexes

• Activate of inhibit glands that secrete digestive juices

• Stimulate smooth muscle of GI tract– Move food along the tract– Mix lumen content

Peristalsis and Segmentation

Figure 23.3

Adaptation associated with animal’s diet

• Microbe-assisted digestion –animals in hydrothermal vents-trophosomes

• Dentition/mouth parts• Length of digestive tract

– Herbivores– Carnivores– Omnivores– Sharks– Birds

Microbe-dependent digestion

• Digestion assisted by microbes

Animals maintain symbiosis with three categories of microbes

• Heterotrophic microbes– Organic compounds of external origin

• Autotrophic microbes– Synthesize organic molecules from inorganic

precursors• Chemosynthetic• Photosynthetic

Figure 4.13 Hydrothermal-vent worms are symbiotic with chemoautotrophic bacteria (Part 1)

Hydrothermal-vent worms

• Symbiotic with chemoautotrophic bacteria- trophosomes

• Worms have not mouth, gut, or anus

• Food comes from sulfur-oxidizing chemoautotrophic bacteria

• Organic molecules from bacteria meets nutritional needs

• Vents- source of H2S

Hydrothermal-vent worms

• Symbiotic with chemoautotrophic bacteria- trophosomes

• Worms have not mouth, gut, or anus

• Food comes from sulfur-oxidizing chemoautotrophic bacteria

• Organic molecules from bacteria meets nutritional needs

• Vents- source of H2S

Figure 4.13 Hydrothermal-vent worms are symbiotic with chemoautotrophic bacteria (Part 2)

Comparison of the digestive tracts of carnivores and herbivores

• Carnivores- foregut digestion

• Herbivores– Hindgut– Foregut

Figure 4.14 The digestive tract of ruminants (Part 1)

Stomach of ruminants

• Several chambers

• Rumen – first chamber/fermentation occurs

• Regurgitate fermenting materials from the rumen into mouth

• Further grinding and reswallow

• From rumen reticulum omasum abomasum (true stomach)

Functions of microbes in ruminants

• Synthesize B vitamins, essential amino acids

• Fermentative breakdown of compounds that animals cannot digest– cellulose

• Recycle waste nitrogen from animal metabolism

• Make ammonia so other microbes can use it as nitrogen source

Figure 4.14 The digestive tract of ruminants (Part 2)

Figure 4.15 The digestive tracts of two hindgut fermenters

Hind and midgut fermenters

• Enlarged cecum/colon– Rabbits, horses, zebras, rhinos, apes,

elephants

• Break down of cellulose and carbohydrates

• Forms short-chain fatty acid

• B vitamins- not utilized, lost in feces

• Coprophagy– rabbits eat special soft feces

A comparison of the digestive tracts of a carnivore (coyote) and a herbivore (koala)

Digestion and absorption

• Digestive enzymes in 3 spatial contexts

• Intraluminal enzymes

• Membrane-associated enzymes

• Intracellular enzymes

Intracellular and extracellular digestion

• Intraluminal and membrane-associated enzymes are responsible for extracellular digestion

• Intracellular enzymes are responsible for intracellular digestion

• Advantages and disadvantages of intra- and extracellular digestions?

Figure 4.17 The stomach of a clam (Part 2)

Carbohydrate digestion 

Organ Substrate Enzyme End product(s) 

Oral cavity Starch Sal1vary amylase Maltose 

Stomach 

  Amylase denatured

 

Lumen of intestine

Undigested polysaccharides

Pancreatic amylase

Maltose

Brush border of small intestine

Disaacharides: maltoseSucroseLactose

MaltaseSucraseLactase

Monosaccharides

Figure 4.19 Absorption of monosaccharides in the vertebrate midgut (Part 2)

Protein digestion 

Organ Substrate Enzyme End product(s) 

Stomach 

Polypeptides Pepsinogen +HCl = pepsin

Smaller peptides

Lumen of intestine  

Polypeptides Trypsinogen, chymotrypsinogen (inactive enzymes released from the pancreas, transported to duodenum via pancreatic duct. These enzymes are activated by enterokinase from small intestine to trypsin and chymotrypsin

Smaller peptides

  Smaller polypeptides

Aminopeptidase, carboxypeptidase 

Amino acids  

Brush border of small intestine

Dipeptides 

Dipeptidase Amino acids

Figure 4.18 The digestion of a short protein by three pancreatic peptidases

 

Fat digestion

Organ Substrate Enzyme End product(s) 

Oral cavity   No enzyme to digest fat

 

Stomach 

  No enzyme to digest fat

 

Lumen of intestine Fat globules  Fat globules

Bile salt from gallbladder lipase

Emulsified fat  Glycerol, fatty acids

Brush border of small intestine

     

Chemical Digestion: Fats

Figure 23.35

Figure 4.19 Absorption of monosaccharides in the vertebrate midgut (Part 1)

Chemical Digestion: Carbohydrates

• Carbohydrates absorption: via cotransport with Na+, and facilitated diffusion– Enter the capillary bed in the villi– Transported to the liver via the hepatic portal

vein

Chemical Digestion: Proteins

• Absorption: similar to carbohydrates

• Enzymes used: pepsin in the stomach

• Enzymes acting in the small intestine

Chemical Digestion: Fats

• Absorption: Diffusion into intestinal cells where they:– Combine with proteins and extrude

chylomicrons– Enter lacteals and are transported to systemic

circulation via lymph

Coordination of digestion– neural and endocrine control

• Controls of digestive activity• Extrinsic

– Central nervous system and autonomic nervous system

• Intrinsic– Hormone-producing cells in stomach and

small intestine– Distributed via blood and interstitial fluid to

target cells

Endocrine control

• Endocrine control• Gastrin• Secretin• CCK• GIP

– Where?– When?– Why?– How?

Figure 4.20 GI function after a meal is coordinated in part by hormones secreted by cells in the gut