The Digestive SystemHonors Anatomy & Physiology

Gastrointestinal (GI) tract AKA alimentary

canal or gut Continuous

muscular digestive tube Mouth Pharynx Esophagus Stomach Small intestine Large intestine Anus

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

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

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

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

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

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

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)

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

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

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

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

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

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

Development of Digestive System

Endoderm forms lining GI tract

Rest develops from mesoderm

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