honors anatomy & physiology. aka alimentary canal or gut continuous muscular digestive tube ...
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The Digestive SystemHonors Anatomy & Physiology
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Gastrointestinal (GI) tract AKA alimentary
canal or gut Continuous
muscular digestive tube Mouth Pharynx Esophagus Stomach Small intestine Large intestine Anus
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Digestive Processes Ingestion
Taking food in Propulsion
Swallowing -voluntary Peristalsis – waves of involuntary
contractions (see fig a) Mechanical Digestion
Chewing, mixing w/saliva by tongue, churning food in stomach
Segmentation – constriction of intestines mixes food w/juices (see fig b)
Chemical Digestion Catabolic break down by enzymes
Absorption Chemical building blocks, vitamins,
minerals, and water from lumen of GI into blood & lymph
Defecation Eliminates indigestibles
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The Mouth AKA Buccal or Oral cavity
Lines w/stratified squamous epithelium
Labia (lips) – orbicularis oris (poorly keratinized)
Cheeks – buccinators for chewing Hard Palate – rigid surface for
tongue to mash food Soft palate – skeletal muscle w/
uvula Tongue- skeletal muscle fibers in
various directions, repositions food and mixes w/saliva to form bolus lingual frenulum attaches to floor
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Salivary Glands
1,000 – 1,500 mL per day! Regulated by parasympathetic division of
ANS Functions:
Cleanses mouth Dissolves food chemicals for taste Moistens food to compact into bolus Amylase breaks down starch
Composition 97% water, electrolytes pH 6.75 Amylase, mucin (forms mucus), lingual lipase Antimicrobials: lysozyme, IgA, defensins
Multiple Locations: Extrinsic salivary glands Intrinsic salivary glands – continuous
secretion Buccal galnds Paratid gland Submandibular gland Sublingual gland
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Teeth Function: Masticate (Chew) voluntary
& reflexive 20 Primary (deciduous) or milk teeth by
24 months Roots reabsorbed as adult teeth develop
causing them to fall out between 6-12 yrs 32 Permanent teeth (including wisdom
teeth) Types:
Incisors - cutting Canines – tear/pierce Premolars (bicuspids) – grinding & crushing Molars (4-5 cusps)
Structure: Enamel – acellular hardest substance in
body (Ca and hydroxyapatite), cannot be replaced
Gingiva recedes w/age Dentin – bonelike but avascular Cementum – Ca connective tissue covers
root Peridontal liagment anchors to alveolus
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Pharynx
Oropharynx & laryngopharynx
Stratified squamous epithelium w/mucus producing glands
2 skeletal muscle layers: inner layer longitudinal Constrictor muscles
encircle Peristalsis propels
food into esophagus
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Esophagus
Collapsed 10” muscular tube Pierces diaphragm to join to
cardiac sphincter of stomach Takes 2 (liquids) -8 (solids)
seconds 4 layers:
Nonkeratinized stratified squamous epithelium
Longitudinal folds when empty, flatten when food is in transit
Esophageal glands – secrete mucus as bolus moves thru
Skeletal & smooth muscle
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Stomach
Storage tank where bolus + enzymes = chyme
6-10” long, ‘J’ shaped Mechanical digestion
Vigorous peristalsis Chemical digestion
HCl denatures proteins Chief cells secrete pepsin & lipase rennin (milk proteins)
Absorption Alcohol & aspirin (lipid soluble)
pass through stomach mucosa into blood (can cause gastric bleeding)
Secretes intrinsic factor to absorb vitamin B12 in small intestine
Mucus barrier
Rugae – fold when emptyOmentum –mesenteries that tether digestive organs to body wall (fat & lymph)
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Small Intestine 20 ft long, 1.5” diameter, complete trip about 2
hours Simple columnar epithelium w/goblet cells and T
cells Intestinal crypts w/defensins & lysozyme & stem
cells 2 layers of muscle for segmentation Peyer’s patches Huge SA for absorption
Villi – 1mm fingerlike projections w/capillary bed & lacteal (lymph)
Microvilli – brush border projections of plasma membrane w/ bound enzymes to complete carb & protein digestion
3 subdivisions: Duodenum - 10” curves around pancreas
▪ Bile duct▪ Pancreatic duct▪ Duodenal glands produce bicarbonate mucus
to neutralize acidic chyme Jejunum – 8’ long Ileum – 12’ long
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Liver & Gallbladder
Liver Largest gland in body (3lbs),
4 primary lobes Produces 500-1,000 mL
bile/day – fat emulsifier Gallbladder
4” long, inferior surface of right lobe
Store bile (yellow-green alkaline solution)
Salts, pigments (bilirubin), cholesterol, triglycerides, phospholipids & electrolytes
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Pancreas Pancreatic juice (1200-
1500mL/day) released via pancreatic duct which fuses w/bile duct as enters duodenum
Acini – clusters of secretory cells Pancreatic proteases: trypsin,
carboxypeptidase, chymotrypsin Amylase, lipases, nucleases
Islets of Langerhans β cells secrete – insulin (↓ blood glucose) α cells secrete – glucagon ( blood glucose)
Bicarbonate ions – pH 8
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Large Intestine
7cm diameter, 1.5 meters Function: reabsorb remaining water from
indigestible food residue & eliminate as feces 12-24 hours to reclaim water & electrolytes Simple columnar epithelium Deep crypts w/goblet cells to ease passage of
feces Mass movements: slow powerful contractive
waves, fiber increases strength contractions Subdivisions:
Cecum - pouch Appendix – lymph tissue Colon – ascending, transverse, descending and
sigmoid Rectum – has valves to separate feces from
flatus! Anal Canal – 2 sphincters (1 involuntary & 1
voluntary), stratified squamous epithelium
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Bacteria Flora
Over 700 species! Survivors from small intestine or
enter via anus Ferment indigestible carbs
(cellulose, xylan) Metabolize proteins (mucin,
heparin, hyaluronic acid) Release 500mL gasses/day (H2,
N2, CH4, CO2, and smelly dimethyl sulfide)
Synthesize vitamin B & K Lymph cells moniter to ensure they
do not stray
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Physiology of Chemical Digestion
Catabolic process: polymers hydrolyzed monomers
Complete Enzyme Chart: Carbs: Amylase, dextrinase, glucoamylase,
maltase, sucrase, lactase Proteins:Pepsin, trypsin, chymotrypsin,
carboxypeptidase, aminopeptidase, dipeptidase
Lipids: bile, lipase Nucleic Acids: ribonuclease,
deoxyribonuclease, phosphatases
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Development of Digestive System
Endoderm forms lining GI tract
Rest develops from mesoderm
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Nutrition Nutrients – promote growth, maintenance & repair Carbohydrates
Glucose oxidized to ATP (mitochondria) Energy measured in kilocalories or Calories (heat energy required to raise 1kg of water 1OC) RDA: 130g digestible, 25-30g of fiber
Lipids Utilized for phospholipids, myelin, insulation, cushion, stored energy, steroid hormones,
absorb fat-soluble vitamins RDA: 80-100g plant/animal fats; <250mg cholesterol
Proteins Structural uses: keratin, collagen, elastin, muscle proteins, etc Functional uses: enzymes, hormones, pigments, and transport Can be oxidized for energy in liver RDA: 0.8%g/kg of body weight
Vitamins Organic compounds function as coenzymes Classified as fat or water soluble
Minerals Inorganic Ionized or bound to organic compounds
Water