Digestive System

Functions Ingestion Secretion Mixing and propulsion Digestion Absorption Defecation

Digestive Organs GI tract: Accessory organs: Mouth, Pharynx, Esophagus, Stomach, Small Intestine, Large Intestine, Anus Accessory organs: Teeth, Tongue, Salivary glands, Liver, Gallbladder, Pancreas

GI Tract Layers Mucosa Submucosa - areolar Epithelium - Strat. Squamous to Simple Columnar Lamina propria Some smooth muscle Submucosa - areolar Muscularis - skeletal higher, smooth lower Serosa - visceral peritoneum

Peritoneum Largest serous membrane Parietal and visceral Five major folds: Contain adipose tissue Anchor major organs Contain blood vessels and lymph nodes Greater Omentum and Mesentary as examples

Macromolecule Review Carbohydrates - Mono- and Polysaccharides Proteins - Amino acids form polypeptides Lipids - Simple, complex, steroids Nucleic Acids What kinds of enzymes break down each group?

Mouth Ingestion Mastication and moistening Beginning of chemical digestion Movement of bolus to oropharynx

Accessory Organs in Mouth Salivary glands - parotid, submandibular, sublingual Tongue - papillae and lingual frenulum Teeth 20 deciduous teeth, 32 permanent Incisors (4), canines (2), bicuspid (4), molars (4-6?) per jaw

Mouth Mechanical Digestion Chemical Digestion Saliva also used to: Mastication - Tongue, teeth, saliva  Bolus Chemical Digestion Salivary Amylase - starch  maltose, -dextrins Lingual Lipase - Activated in stomach - Triglycerides  F.A.s and Diglycerides Saliva also used to: Destroy bacteria (Lysozyme, IgA) Lubricate food (mucus) Remove waste Aid gustation (water)

Esophagus Laryngopharynx to stomach Upper esophageal sphincter (skeletal muscle) Lower esophageal sphincter (cardiac) Passes through diaphragm at esophageal hiatus

Esophagus Deglutition (Swallowing) Peristalsis Wavelike contractions Alternating bands of muscle

Stomach

Stomach Mechanical digestion Chemical digestion Mixing waves - produce chyme and promote gastric emptying Chemical digestion Pepsin - proteins into smaller peptides HCl - partial denaturation Absorbs some water, ions, Fas, some drugs and alcohol

Gastric Glands Gastric Juice HCl Pepsin - protein digestion kills microbes converts pepsinogen to pepsin Pepsin - protein digestion Gastric lipase - Triglycerides  Fas and monoglycerides Mucous - protects lining

Gastric glands

Pancreas Endocrine and exocrine gland Pancreatic islets: insulin and glucagon (and others) Acini: Pancreatic juice Sodium bicabonate Enzymes to digest all four macromolecule groups

Liver Secretion of Bile Bile stored in gall bladder Used for: Excretion of Bilirubin Emulsification of lipids by bile salts Easier absorption of lipids Excretion of drugs and hormones

Other Liver Functions Glycogen storage and glucose release/production Lipid Metabolism Protein metabolism - ease conversion of a.a., synthesize plasma proteins Detoxification Storage of vitamins/minerals Phagocytosis of old blood cells and some bacteria Activation of vitamin D

Small Intestine 90% of all absorption Aided by: Length (10 ft avg) Villi (1 mm) Microvilli (1 um) - “Brush Border” Monomers absorbed into capillaries or Lacteals

Small Intestine Duodenum, jejunum, ileum Intestinal glands Duodenal glands - alkaline mucus - why? Digestive enzymes along w/ pancreas Circular folds - better absorption Villi Absorptive cells Capillaries and lacteals Microvilli

Small Intestine Chemical Digestion Brush Border enzymes – all major groups Intestinal Juices - water and mucus Pancreatic Juice, Bile and Intestinal juice work in combination

Large Intestine Mechanical digestion Chemical digestion by bacteria Haustral churning - contraction following distension Peristalsis Mass peristalsis - pushes contents into rectum Chemical digestion by bacteria Absorption of water, ions, and some vitamins

Defecation Feces formed in large intestine Defecation Reflex Water, Inorganic salts, Bacteria and their products, Unabsorbed/Indigestible material, Epithelial cells Defecation Reflex Rectum distended Stretch receptors  spinal cord Parasymp  contraction of colon and rectum Internal anal sphincter opens External is voluntarily relaxed

pH Enzymes operate at optimal pH Saliva = 6.5 Gastric juice = 2 Pancreatic Juice = 7.1-8.2 Intestinal Juice = 7.6 pH adjusted by negative feedback (Buffers, Hormone release)

Hormones Gastrin - gastric glands - gastric juice , gastric emptying , Sphincter control Cholecystokinen (CCK) - s. Int - Pancreatic juice , Bile release , gastric emptying , satiation Secretin - S. Int - Pancreatic Juice , Gastric Juice 