Bio 182- Ecology Unit Outline 1 - Glendale Community Collegeweb.gccaz.edu/~robtt84601/WORKSHEETS/Bio202Worksheets/Bio202DIGESTION2014.pdfBio 182- Ecology Unit Outline 2 10/29/14 7)

Bio 182- Ecology Unit Outline 10/29/14 1

Digestive System

Introduction1. Basic activities: a. Ingestion-process of taking food into the oral cavity via the mouth

b. Peristalsis-process of alternate muscle contractions, between longitudinal and circular smooth muscles, that pushes food along GI tract (applies to other systems as well) c. Digestion-the breakdown of food into small and absorbable units

1) Mechanical-breaking of a large food into smaller pieces; no breaking of molecular bonds 2) Chemical-breaking of molecular bonds (e.g. polysaccharides into monosaccharides)

d. Absorption-transport of monomers from lumen of alimentary canal (=GI tract) to the blood e. Defecation-elimination of nondigestible wastes from the body via the anus

2. Major organ groups: a. Gastrointestinal (GI tract or alimentary canal)-tube from mouth to anus b. Accessary organs-these empty various secretions into GI tract 3. General histology: Peritoneum a. All body cavities are lined by serous membranes

b. Serous membranes lining walls of abdominal cavity are called parietal peritoneum c. The parietal peritoneum is continuous with the visceral peritoneum that covers individual organs d. The space between the parietal and visceral peritoneal membranes is called the peritoneal cavity e. Where these membranes run between the body wall and organs, they are generally referred to as mesenteries f. Mesenteries

1) Serous membranes secreting ~ 7 L of serous fluid, a pale yellow liquid that lubricates organs 2) Extensions of peritoneal membranes are generally called mesenteries, but each gets a more specific name depending on the organ anchored 3) The mesentery that anchors the Small Intestine (SI) is called the mesentery proper 4) The mesentery that anchors the colon is called the mesocolon 5) A mesenteric cord that suspends the liver from the diaphragm and anterior abdominal wall is called the falciform ligament 6) A mesentery that runs from the greater curvature of the stomach, covers the SI, and meets the mesocolon is the greater omentum


7) A mesentery that runs from the liver to the lesser curvature of the stomach is the lesser omentum 8) Mesenteries are double-layerd 9) Functions: a) Anchor organs b) Store fat c) Support blood vessels & nerves going to & from organs d) Secrete lubricating serous fluid

g. Peritoneal cavity houses most abdominal organs h. Lying posterior to peritoneal cavity against the vertebrae is the retroperitoneal cavity where kidneys, ovaries, pancreas, duodenum, abdominal aorta, IVC, and part of colon are found i. Inflammation of peritoneal membranes is called peritonitis 1) Caused by: punctures, ulcers, appendicitis

4. General Histology: Tunics a. Listed from lumen to outer edge 1) Lumen 2) Tunic mucosa a) Epithelium b) Lamina propria c) Muscularis mucosae 3) T. submucosa 4) T. muscularis externa a) Circular smooth muscle layer b) Longitudinal smooth muscle layer 5) T. Serosa (or adventitia) 6) Body cavity b. T. Mucosa 1) Functions: a) Secretes mucus, EZ’s, H’s b) Absorption of nutrients/water c) Protection 2) 3 subdivisions: epithelium, lamina propria, muscularis mucosa 3) Epithelium

a) Most common epithelium lining GI tract is simple columnar epithelium b) Exceptions: oral cavity, esophagus, anal canal are stratified squamous epithelium c) Cell types: goblet, brush border, parietal, chief, etc.

4) Lamina propria-Loose areolar CT rich in capillaries 5) Muscularis mucosa-a thin layer of smooth muscle causing local movements & foldings along GI tract

c. T. Submucosa 1) Composed of mostly dense irregular CT


2) Filled with capillaries, lymph vessels, nerves, and fibers (collagen/elastic) 3) Houses submucosal plexus (= Meissner’s plexus)-an ANS nerve supply to gut

d. T. Muscularis Externa 1) Usually 2 sublayers of smooth muscle: inner circular & outer longitudinal 2) Thickened areas of circular layer act as valves; these are often called sphincters 3) Myenteric (=Auerbach) plexus-ANS controls peristalsis and GI motility

e. T. Serosa 1) This is also visceral peritoneum a) Areolar CT cover with mesothelium

2) In certain areas like esophagus, fibrous CT is thicker and here it is called the adventitia

f. As survey of gut is done, each modification of tunic and sublayers will be described

Mouth-Oral Cavity 1. Functions: a. Ingestion b. Mechanical and some chemical digestion c. Mastication d. Deglutition e. Speech 2. Opening to oral cavity is the oral orifice 3. Boundaries: a. Anteriorly by the lips b. Laterally by the cheeks c. Superiorly by the palate d. Inferiorly by the tongue 4. Posterior region of oral cavity is the oropharynx 5. Epithelium: mostly nonkeratinized, stratified, squamous; gums are weakly keratinized 6. Lips (labia)-anterior fleshy folds above and below oral orifice a. Help keep food in mouth b. Speech c. Controlled by orbicularis oris muscle 7. Cheeks-lateral fleshy areas on each side of oral orifice a. Helps keep food in mouth


b. Speech c. Recess between teeth & cheeks & lips & gums is called the vestibule d. Controlled by buccinators muscles 8. Palate a. Separates oral from nasal cavities b. Hard-supported by palatine bones & palatine processes of maxilla bones

1) Keeps food passage separate from air flow & provides rigid surface for manipulating food

c. Soft-posterior extension of hard palate supported by smooth muscle & mucosa 1) Uvula-finger-like projection of soft palate 2) Closes off nasopharynx during deglutition 3) Palatine tonsils found here 9. Tongue

a. Fleshy, mobile, mass of interlacing skeletal muscle fibers covered with sensory epithelium for taste and tongue b. Functions: 1) Manipulation of food under appropriate teeth 2) Mixes food with saliva & rolls into slimy round mass called the bolus 3) Lingual lipase added by glands associated with tongue c. Muscles: 2 sets 1) Intrinsic-3 planes that change shape, but not anchor to bone 2) Extrinsic-anchors to skull & alters position d. Papillae-peg-like projections of mucosa on superior surface

1) Filiform-spike-like projections without taste buds, responsible for rough feel and the most abundant papillae 2) Fungiform-mushroom-like projections, each with 3 taste buds; concentrated on sides and at tips 3) Circumvallate (Vallate)-large & arranged in ‘V’ at rear of tongue; house ~ 250 taste buds each 4) Foliate-bulbous projections on posterior sides of tongue; taste buds degenerate by 2-3 yrs of age

e. Taste receptors 1) Papillae house a variety of taste receptors 2) Help decide if food should continue to stomach or be spit back out

3) Besides sweet, salty, sour, bitter, a new taste sensation called umani has been identified a) Umani receptors react to glutamate, small peptides, & nucleotides

10. Teeth


a. Also called dentes b. Functions: 1) Mastication 2) Mechanical digestion c. Set in alveoiar sockets of alveolar processes of maxilla & mandible bones d. Anchored by periodontal ligament in a gomphosis joint e. Gingivae, or gums, surround base of crown & neck f. Tooth structure: 1) Regions: a) Crown-enamel covered region above gingivae

b) Root-portion below gingivae & embedded in socket; bone-like cementum & fibers from periodontal ligament anchor

2) Layers: a) Enamel-outermost, acellular material mineralized with Ca++ salts; hardest substance in body; ectoderm derivative b) Dentin-Bulk of tooth; similar to bone, but harder & acellular c) Pulp cavity-central region filled with blood vessels & nerves; root canal continuous with cavity leading out through apical foramen in bone; cellular

g. Kinds of teeth 1) Incisors-4 prs of single root; chisel/blade shaped; anteriormost teeth in upper & lower jaws for cutting & shearing food 2) Canines-2 prs of single root, cone-shaped teeth next to incisors for holding, tearing, and killing food 3) Premolars or bicuspids-2 cusp, 2-3 roots, flattened crown, 2 pr per jaw for crushing & grinding 4) Molar-bulky, large, 3 roots, with cusps less pronounced than premolars for crushing & grinding

h. Sets of teeth 1) Humans have 2 sets: diphyodont

2) There are usually 20 deciduous, or milk, teeth emerging between 6 mo and 2 ½ yrs 3) Usually 32 permanent teeth emerging between 6 & 17 yrs

i. Diseases 1) Dental caries or cavities-enamel dissolved by bacterial EZ’s

2) Periodontal or gum disease-results when plaque builds up at gum line; bacteria invade & destroy bone 3) Pyorrhea-discharge of pus at base of tooth (inflammatory response)


10. Salivary glands a. Secrete 1-2 L of saliva per day b. Functions: 1) Solvent that cleanses teeth 2) Dissolves food chemicals for taste 3) Contains EZ for digesting starch (& lipids) 4) Lubricates food for deglutition 5) Contains antibacterial agents

c. Several small intrinsic glands with continuous secretions, but 3 major extrinsic glands: 1) Parotid a) Largest & located anterior & inferior to ear b) Duct enters oral cavity opposite 2nd upper molar c) Virus infection inflames & causes mumps d) Lg amts of thick saliva rich in amylase e) Contributes 25-30% of saliva 2) Submandibular a) Located midway along mandible shaft b) Duct empties into floor by tongue’s base c) 65-70% volume rich in mucins, buffers, & amylase 3) Sublingual a) Sides of tongue at base b) Secretions more watery, but also has mucins & buffers c) Smallest contribution of 3-5% d. Composition 1) 99.5% water 2) Solutes: a) Electrolytes b) Mucin for lubrication c) Wastes such as urea, lactic acid, etc. d) Lysozyme-EZ that kills bacteria e) IGA-antibody that inhibits bacterial growth f) Salivary amylase for starting carbohydrate breakdown

g) Lingual lipase-EZ that breaks down lipids after activated in stomach

e. Control of secretion: 1) ANS-mostly PS via salivary nuclei in medulla 2) S-promotes secretion of thicker saliva


3) Sight, smell, sound, touch of food, but no hormonal controls 11. Deglutition or Swallowing Phases: a. Buccal- voluntary, tongue pushes bolus against palate & into pharynx

b. Pharyngeal-larynx is elevated forcing epiglottis over glottis )opening to larynx) & forced into esophagus c. Esophageal-esophageal sphincters relaxes, peristaltic waves catch bolus and move down esophagus d. Last two phase involuntary

Pharynx 1. Region where oral, nasal, and laryngeal cavities meet 2. Three regions: a. Oropharynx-between soft palate & base of tongue b. Nasopharynx-inferior & posterior part of nasal cavity c. Laryngopharynx-inferior region between hyoid bone & entrance to larynx

Esophagus 1. Description: a 30 cm (1 ft) X 2cm (3/4 in) tube that connects pharynx with stomach 2. Bordered superiorly by esophageal sphincter and inferiorly by cardiac sphincter 3. Histological modifications of tunics: a. T. mucosa-lined by stratified squamous epithelium b. T. submucosa-similar to general description, but possess esophageal glands t hat release mucus to help move food easily towards stomach

1) First two tunics folded into rugae, or folds, when esophagus is not transporting food.

c. T. muscularis externa-skeletal muscle in upper 3rd, smooth muscle in lower 3rd, and mixed muscles in middle 3rd d. T. adventitia-CT thick above diaphragm, but changes to serosa below

4. Esophageal peristalsis a. Waves of alternate smooth (skeletal in upper 3rd) muscle contractions that propel bolus along GI tract b. Circular muscles contract first & narrow diameter of tube behind bolus c. Longitudinal muscles contract & shorten tube which repositions bolus further along

5. Disorders a. Heartburn-acid reflux from stomach into lower esophagus creating sensation of chest pressure & pain


b. Hiatal hernia-lower region of esophagus expanded and continuous with stomach causing reflux of stomach acids that create heartburn and muscle spasms c. GERD-Gastroesophageal Reflux Disease

Stomach 1. Description: Expanded J-shaped region of GI tract positioned between esophagus & small intestine 2. Functions: a. Food storage b. Mixes food (mechanical digestion) c. Chemical digestion of mainly proteins d. Kills bacteria & parasites with acids e. Releases intrinsic factor for Vitamin B12 absorption f. Minimal amt of nutrient absorption 3. Macrostructure a. Greater curvature-convex lateral surface of stomach b. Lesser curvature-concave medial surface of stomach c. Greater & lesser omenta-extend from these curvatures (see earlier) d. Rugae-internal longitudinal folds of stomach mucosa & submucosa e. Regions: 1) Cardiac-small area immediately inferior to cardiac sphincter/orifice 2) Fundus-expanded, dome-shaped, superiolateral part of stomach 3) Body-midportion & largest region inferior to cardiac & fundic regions 4) Antrum-funnel-shaped medial region 5) Pylorus-small, narrow passage to the duodenum 6) Pyloric sphincter-thickened smooth muscle that controls emptying 4. Microstructure-Tunics a. Mucosa 1) Simple Columnar epithelium 2) Shallow depressions along surface are gastric pits 3) Gastric pits lead into a narrow neck & then deeper gastric glands 4) Gastric glands secrete ~ 1500 ml of gastric juice/day a) Mostly water, but composition varies by region b) Cardiac-mostly mucus c) Fundus/body-mostly HCl, EZ’s, & Intrinsic factor d) Pylorus-mucus and H gastrin 5) Cell types:


a) Mucus neck cells-goblet cells found lining neck and secrete mucus that coats stomach mucosa b) Parietal cells i. Found in neck & proximal (superficial) part of gland ii. Appear smooth under microscope iii. Secrete HCl & intrinsic factor

iv. HCl formed from H2CO3 (carbonic acid) when H2CO3 dissociates into H+ and HCO3- (bicarbonate ion); H+ pumped into lumen while HCO3- exchanged for Cl- in blood; Cl- moved into lumen where it combines with H+ to form HCl

c) Chief cells (Zymogenic cells) i. Found near base (deep) of gastric gland ii. Appear grainy under microscope

iii. Secrete pepsin, a protease that breaks down proteins into small polypeptides

d) Enteroendocrine cells i. 7 different H’s released that control various aspects of digestive process ii. Specifically, G cells release gastrin that stimulates parietal & chief cells when food enters stomach; also increases peristalsis of stomach

b. T. submucosa-this & mucosa are folded into rugae when stomach is empty c. T. Muscular externa

1) 3 layers of smooth muscle in different plants that allows peristaltic churning a. Outer longitudinal b. Middle circular c. Inner Oblique 2) Peristaltic waves:

a.Slow-gentle, rippling 3-4/min helping form chime (a pea-soup liquid); does not affect fundus region b. Strong-stronger & more frequent waves that push chime out of pyloric sphincter c. High-directional wave that involves fundus region bringing unchurned food into active body region

d. T. serosa-visceral peritoneum continuous with omenta 5. Chemical digestion a. Mechanical digestion accomplished by peristaltic waves


b. Pepsin 1) Formed from pepsinogen-an inactive EZ activated by HCl 2) Best action at 1-2 pH c. Gastric lipase-fats in milk, but limited roll in adults d. Rennin 1) Breaks down & coagulates protein casein found in milk

2) Coagulation thickens fluid for longer retention & increased nutrient extraction in infant stomach & GI tract

6. Protection of stomach mucosa a. Pepsin is stored in active form pepsinogen b. HCl is stored as separate ions c. Neck cells secrete thick mucus layer d. Epithelium is replaced completely every 2-3 days e. HCl & EZ are mixed with food & therefore diluted next to mucosa 7. Regulation of gastric secretions a. Both nervous & hormonal controls b. PS controls via vagus nerve stimulating gastric glands c. Phases: Cephalic, gastric, & intestinal

1) Named depends on which part of body (brain, stomach, SI) controls stomach actions 2) Cephalic-starts even before food enters mouth a) Sight, smell, sound, or thought of food

b) Important to start early for all aspects of digestion because EZ’s take time to synthesize in rER c) CerebrumàHypothalamusàMedullaà Vagus nerve

3) Gastric-stretch of stomach wall as food enters & increase in pH a) 2/3 of gastric secretions

b) Reflex arc: stretch receptors-à sensory neuron-à medullaà motor neurons-àgastric glands & muscularis externa c) Proteins/polypeptides stimulate G cells to release gastrin-àblood--à receptors on target cells (parietal/chief) -à release of gastric juice & increased peristalsis i. Negative feedback loop

ii. As stomach empties, pH drops below 2 where parietal cells are then inhibited

4) Intestinal-food with high protein content enters duodenum a) At first, stimulates stomach action by release of enteric gastrin (stimulates gastric glands) & neural controls


b) As greater distention occurs, enterogastric reflex inhibits or slows emptying c) Food in SI causes distention (stretch)àsensory neuron-àmedulla-àinhibits gastric glands

8. Regulation of Gastric Emptying a. Two main factors: stretch & stomach gastrin b. During gastric phase these 2 factors cause: 1) Cardiac sphincter to contrict 2) Increased stomach peristalsis 3) Relaxes pyloric sphincter c. Empties all contents between 2 & 6 hrs after ingestion 1) Carbohydrates-fastest (2-4 hrs) 2) Proteins-(3-5 hrs) 3) Lipids (4-6 hrs) d. Emptying is inhibited by EG reflex & GIP (Gastric Inhibitory Peptide) e. Rate is limited by amt of chime entering SI 9. Absorption in Stomach a. Very little nutrient absorption b. Does some water, electrolytes, and certain drugs c. Certain foods & drugs can inflame stomach mucosa, a condition called gastritis

d. Crater-like lesion in mucosal tunic is called an ulcer; in stomach is called peptic or gastric ulcer

1) Helicobacter pyloric-cause of most ulcers; invades mucosa and leads to chemical damage of tissue 2) Acid resistant 3) Antibiotics can treat, but many strains resistant

Pancreas 1. Lies along greater curvature of stomach & 1st region of SI (duodenum) 2. Divided into 3 regions: a. Head-contacts duodenum b. Body-along curvature c. Tail-tapered region 3. Histology: a. 98-99% Acinar cells that secrete pancreatic juice b. 1-2% Islets of Langerhans 4. Duct system of Pancreas, Gall Bladder, & Liver a. R & L lobes of liver give rise to R & L Hepatic Ducts


b. These ducts merge to form Common Hepatic Duct c. Gall Bladder gives rise to Cystic Duct

1) Cytstic Duct merges with Common Hepatic Duct to form Common Bile Duct

d. Pancreas gives rise to Pancreatic & Accessory Ducts 1) Pancreatic Duct merges with Common Bile Duct to form Hepatopancreatic Ampulla 2) Ampulla empties into duodenum 3) Accessory Duct branches inside pancreas & enters duodenum ~ 2.5 cm before (nearer stomach) ampulla

5. Acinar glands (pancreatic acini) secrete 1.2 to 1.5 L of pancreatic juice a. Pancreatic ducts secrete: 1) Water 2) Salts 3) Sodium bicarbonate-neutralizes acidic chyme from stomach b. Acini secrete ~ 15 different EZ’s in 4 major groups: 1) Amylases (Carbohydrases) 2) Lipases 3) Proteases 4) Nucleases c. Pancreatic EZ’s:

1) Generally, digestive EZ’s break down polymers into monomers, units that are small enough to be absorbed a) Amylases breakdown polysaccharides into monosaccharides

b) Lipases break down triglycerides into a monoglyceride & 2 fatty acids c) Proteases break down polypeptides into amino acids d) Nucleases break down nucleic acids into nucleotides

2) However, many EZ’s work on specific areas of a larger molecule 3) Amylases (Carbohydrases) a) Pancreatic amylase degrades starches into disaccharides 4) Lipases

a) Pancreatic lipase breaks down triglycerides into a monoclyceride and 2 fatty acids b) Cholesterol esterase breaks down:

5) Proteases a) Classified as endo & exopeptidases


b) Trypsin & chymnotrypsin are endo’s because they split a polypeptide near the middle of polymer c) Carboxypolypeptidae is an exo cleaving off terminal aa’s

6) Nucleases a) Ribonuclease breaks down RNA into nucleotides b) Deoxyribonuclease breaks down DNA into nucleotides c) However, nucleotides are degraded further by other intestinal EZ’s 6. Pancreatic Secretion/controls a. Hormonal

1) Secretion-stimulates pancreas to release pancreatic juice rich in sodium bicarbonate 2) Cholecystokinin (CCK)-pancreatic juice becomes richer in EZ’s; initiated during cephalic phase because it takes time to crank out EZ’s

a) Transcription of geneàModification of mRNA-à export mRNAàto rER where translation occurs-àforms protein (EZ)à EZ exported

b. Neural 1) PS via cephalic & gastric phases 2) Uses Vagus nerve that stimulates release of EZ’s 7. Pancreatitis-blocked ducts, bacterial or viral, alcohol or drug reactions cause proezymes to become active before they should and EZ’s start digesting organ tissue

Liver 1. Located under diaphragm; most of mass is to right of midline 2. 4 lobes: a. Major: Right is about 6X size of left b. Minor: Quadrate & caudate associated with R lobe c. Major lobes separated by falciform ligament 3. Round ligament runs from liver to umbilicus-former path of umbilical vein fetus 4. Duct system: see earlier Pancreas 5. Liver lobules

a. Liver is divided into histological units called lobules; these have hexagonal arrangement of cell cords around a central vein b. ~ 100,000/lobe c. Cells, hepatocytes, arranged in stacks called cords d. Capillaries with expanded sinusoids lined by Kuppfer cells (macrophages)

6. Functions: a. Over 200, but only one that affects digestion directly-synthesis of bile b. Kuppfer cells destroy old RBC’s, WBC’s, and bacteria


c. Also stores Fe++, lipids, vitamins (also heavy metals such as Hg++) d. Removes aa, glucose (insulin induced), and fat-soluble vitamins after meals e. Detoxifies drugs & poisons f. Deaminates aa g. Forms urea h. Degrades H’s i. Synthesis of clotting factors, plasma proteins, & transport proteins 7. Liver Blood Supply a. Receives two sources of blood: 1) Hepatic artery brings oxygen-rich Hb

2) Hepatic portal vein brings nutrient-laden blood, but oxygen-poor Hb from mostly SI

b. Nutrient-depleted and oxygen-poor blood exits liver via hepatic veins & joins IVC c. Portal system allows high viscosity, nutrient rich blood to have aa & glucose removed (insulin-influenced) and then small amts of these substances released (glucagon-influenced) between meals

8. Bile a. Yellowish-brown to olive-green liquid b. Synthesized by hepatocytes ~ 800-1000 ml/day c. Delivered to duodenum by duct system (see earlier pancreas)

1) Sphincter of Oddi-a muscular valve at end of hepatopancreatic ampulla controls entry (CCK opens)

d. Excess bile backs up into gall bladder for storage & concentration

Gall Bladder 1. Pear-shaped sac 7-10 cm long holdinh 40-70 ml of concentrated bile 2. Embedded in visceral surface of liver 3. Smooth muscle in walls eject into cystic duct 4. Bile 10X more concentrated here; water removed 5. Bile composition a. Water b. Bile salts for emulsification of fat globules

1) Large fat globules are broken into small fat globules so that lipases have more surface area to break down fats with EZ’s 2) Cholesterol derivative 3) Mostly reabsorbed in ileum

c. Cholesterol d. Lecithin (a PPL)


e. Bile pigments (mostly bilirubin from RBC’s) f. Sodium bicarbonate 6. GB/Liver diseases

a. Jaundice-skin/membranes turn yellow due to bile build up; a symptom of gallstones, hepatitis, cirrhosis, etc b. Gallstones-(biliary calculi)-rock-like composed of cholesterol, CaCO3, and bilirubin

1) Cholelithiasis (formation of gallstones) is most common in obese women over 40 2) Problems occur when duct system obstructed 3) Treated by lithotripsy-ultrasonic vibrations break up lg stone into sm stones that can be passed out in feces

c. Hepatitis-inflammation of liver usually caused by viral or bacterial infections d. Cirrhosis-liver tissue replaced by scar/adipose tissues can result from hepatitis or long-term alcoholism

Small Intestine 1. Tube connecting stomach to LI; averages 21 ft long X 2.5 cm (1 in) diameter in a cadaver 2. Boundaries/regions: a. Pyloric sphincter-valve between stomach and duodenum b. Duodenum (10-12 in) c. Jejunum (~ 8ft) d. Ileum (~ 12 ft) e. Ileocecal valve-valve between ileum and cecum 3. Functions: chemical digestion & absorption 4. Histology a. T. mucosa 1) Epithelium has many cell types: brush border (absorptive), goblet, etc

2) Intestinal crypts (Crypts of Lieberkuhn)-openings between villi that lead to intestinal glands 3) Intestinal glands secrete intestinal juice 4) Epithelium renewed every 3-6 days; cells in gland are pushed to tips of villi where they fall off 5) Many structural modifications for increasing digestive & absorptive SA a) SA with these foldings = 2200 ft2; w/o foldings = 3.6 ft2 6) Large SA created by: a) Plicae circularis or circular folds up to 10 mm tall


i. Involve only mucosa & submucosa tunics ii. Chyme flows in spiral path causing more contact b) Villi-fingerlike projections 1 mm tall

i. contain blood vessels & lymphatics (lacteals) for nutrient absorption

c) Microvilli are 1 um tall on luminal surface of brush border cells; brush border EZ’s for final stages of digestion

b. T. submucosa 1) Duodenum is distinguished by Brunner’s glands that secrete an alkaline mucus for coating & protecting duodenum from acidic chyme 2) Ileum is distinguished by Peyer’s patches, nodules of lymphatic tissue 3) Plicae involve first two tunics and force chyme to spiral, instead of going straight, through SI

c. T. muscularis externa 1) Two layers of smooth muscle, an inner circular & outer longitudinal 2) Create peristaltic waves d. T. serosa = visceral peritoneum 5. Generalizations of histology

a. Plicae become less numerous from the duodenum towards ileum; mostly constant in duodenum & jejunum, but #’s drop off in ileum b. Goblet cells increase from duodenum towards ileum c. Intestinal crypts decrease in ileum d. Brunner’s glands present in duodenum, but almost absent in jejunum e. Peyer’s patches absent in duodenum and most of jejunum, but present in ileum

6. Secretions: a. Goblet cells & Brunner glands secrete mucus to protect mucosal lining

b. Intestinal juice (2-3 L/day) of clear yellow fluid with pH of 7.6; there are 4 generic EZ groups: 1) Amylases (Carbohydrases)

a) Salivary amylase does not work well in acidic conditions, but initiates starch breakdown in mouth, then continues in SI b) Maltase breaks down maltose --à glucose + glucose c) Sucrase: sucrose --à glucose + fructose d) Lactase: lactose --à glucose + galactose e) Lactose intolerance-failure of SI to form lactase resulting in diarrhea, cramps, & gas i) Found in 6-8% Caucasians, 70-75% Blacks, 90-95% Asians

2) Lipases


a) Most lipid breakdown occurs in SI b) Prepared by bile salt emulsification c) Pancreatic lipase 3) Proteases

a) Pepsin has initiated significant protein breakdown in stomach, but stops working at alkaline pH’s b) Aminopeptidae-breaks peptide bonds at amine end of aa c) Dipeptidae-splits dipeptides into 2 aa’s

4) Nucleases a) SI EZ’s break down nucleotides into pentoses & N bases c. Secretion regulation:

1) Secretions regulated by myenteric reflexes in response to chyme from stomach 2) Secretin & CCK stimulate production of intestinal juice

7. Absorption a. 90% of all absorption along SI is in duodenum & jejunum b. Carbohydrates absorbed as monosaccharides 1) Glucose & galactose are actively cotransported with Na+ 2) Fructose is by facilitated diffusion 3) Enters villi capillaries & transported to liver by hepatic portal vein c. Proteins mostly as aa in duodenum & jejunum 1) Active cotrasnport with Na+ 2) Move out of epithelial cells by diffusion & taken to liver d. Triglycerides reduced to a monoglyceride and 2 fatty acids by pancreatic lipases 1) Short-chained (< 12C) diffuse into epithelium

2) Long-chained (>12C) are surrounded by 20-50 molecule of bile salts forming a unit called the micelle 3) Micelles diffuse into epithelial cells leaving bile salts behind; bile salts reabsorbed in ileum, returned to liver, and resecreted in bile 4) MonoG’s and FA’s brought to golgi body; then to sER where they are recombined into chylomicrons

a) Chlyomicrons composed of Triglycerides, PPL, cholesterol, & protein coat; can also have fat-soluble vitamins

5) These enters lactealsàlymphatic vesselsà L subclavian veinàhepatic common artery-àliver 6) Some chylomicrons are combined with additional proteins in liver to form lipoproteins a) HDL’s = High Density lipoproteins


i. 50% protein, 37% triglycerides, 13% cholesterol ii. Come from peripheral tissues to liver for disposal iii. Know as good cholesterol b) LDL’s = Low Density Lipoproteins i. 25% protein, 20% triglycerides, 55% cholesterol ii. Comes from liver out to body tissues for use

iii. Known as bad cholesterol because if receptor sites full, macrophages pick up and eventually dump forming arterial plaques

c) Counts: i. Total cholesterol should be less than 200 ii. LDL’s under 130 iii. HDL’s above 40 iv. Ratio of LDL/HDL less than 4 e. Nucleic acids absorbed as pentoses and bases f. Water soluble vitamins absorbed by diffusion

Large Intestine 1. Part of GI tract ~ 1.5 m long X 6.5 cm in diameter; runs from ileocecal jct to anus 2. Anchored to abdominal wall by mesocolon 3. 4 principle regions: cecum, colon (ascending, transverse, descending, sigmoid), rectum, & anal canal 4. Functions: a. Waste compaction, formation, & elimination of feces b. Water reabsorption, vitamin K synthesis c. Minimal nutrient (<10%) absorption 5. Ileocecal valve-regulates flow from ileum to cecum 6. Cecum

a. Blind pouch ~ 6 cm long with twisted, coiled tube attached to base called the vermiform appendix b. Processes fiber-rich plant material; very large in herbivores

7. Colon a. Main region of LI and ALMOST synonymous with LI

b. Divided into ascending (up R side of abdomen), transver (under, but in front of liver), descending (down L side), & sigmoid (L iliac crest to rectum)

8. Tunics: a. T. mucosa 1) No plicae or villi


2) Goblet cells numerous; lubricates and coats feces 3) Simple columnar cells mostly for water reabsorption 4) Becomes stratified squamous in anal canal b. T. submucosa-same as SI c. T. muscularis externa

1) 2 smooth muscle layers, but longitudinal layer thickened into 3 bands called tenia coli 2) Contraction of these bands forms pouches called haustra

d. T. serosa 1) Visceral peritoneum contains fat-filled pouches attached to tenia coli called epiploic appendages

9. Rectum a. Last 20 cm (minus anal canal) of LI b. Waste compaction, holding, & expulsion (defecation) 10. Anal canal a. Last 3 cm of LI b. Membranes thrown into longitudinal folds called anal columns

c. Feces exit controlled by 2 sphincters: internal (smooth muscle & involuntary) & external (skeletal muscle & voluntary)

11. Mechanical actions a. Haustral churning

1) Relaxed--à fills-àstretches--à contracts--à squeezes contents into next haustrum

b. Peristalsis-slower than in SI (3-12/min) c. Mass peristalsis-strong peristaltic waves that begin in middle of transverse colon and drive feces into rectum

12. Digestion, secretion, absorption a. Goblet cells secrete mucus for coating lining & feces b. Bacteria, called Escherischia coli (E. coli), reside in colon 1) Decompose bilirubin to urobilinogen giving feces brown color 2) Synthesize vitamin K and some B vitamins

3) Under right conditions, form H2S, H2, N2, CO2, CH4, and 2 amines (indole & skatole) gas called flatus 4) Indoles & skatoles give odor

c. Absorption is mostly water & electrolytes d. Substance that remains is called feces 13. Defecation reflex a. During mass peristalsis, rectal wall is stretched


b. AP’s sent to thalamus and if high enough frequency reach cerebral cortex-I GOTTA GO! c. Actions: 1) Walls of sigmoid colon & rectum contract 2) Anal sphincters relax

3) Forced exhalation against a closed glottis that increases abdominal pressure; muscles in rectum wall squeeze contents out of rectum

Documents

Bio 182- Ecology Unit Outline 1 - Glendale Community Collegeweb.gccaz.edu/~robtt84601/WORKSHEETS/Bio202Worksheets/Bio202DIGESTION2014.pdfBio 182- Ecology Unit Outline 2 10/29/14 7)