DIGESTIVE SYSTEM

GENERAL 1st System to Develop “Tube” Within a Tube Contents Remain External Until Absorbed Through Walls Humans are (Anatomical) Omnivores Consists of Alimentary Canal/Digestive Tract and Accessory Organs

DIGESTIVE SYSTEM FUNCTIONS Ingestion – Food Enters Through Mouth Digestion – Breaking Large Molecules into Smaller, Absorbable Molecules Mechanical (Physical) Chemical (Enzymatic) Absorption – Passage of Molecules Through GI Tract Wall into Blood or Lymph Egestion – Elimination of Non-digestible Substances Through Anal End

DIGESTIVE SYSTEM ORGANIZATION Alimentary Canal (Gastrointestinal or Digestive Tract) Mouth, Pharynx, Esophagus, Stomach, Small Intestine, Large Intestine Lumen is part of External Environment Accessory Organs Salivary Glands Liver Gall Bladder Pancreas

ALIMENTARY CANAL HISTOLOGY Mucosa Innermost, Surrounds Lumen Mucous Membrane Secretes, Absorbs, Protects Submucosa Below Mucosa C.T., Blood Vessels, Lymphatics, Nervous Tissue

ALIMENTARY CANAL HISTOLOGY continued Muscularis (Externa) Smooth Muscle Inner, Circular,  Diameter of Lumen Outer, Longitudinal,  Diameter of Lumen Propels Substances Serosa (Visceral Peritoneum) Outermost Serous Membrane, Lubricates Adventitia outside of Ventral Body Cavity

MOVEMENT OF FOOD Peristalsis - Wave-like Contraction of Circular & Longitudinal Smooth Muscle for Propulsion ANS Stimulated by Parasympathetic Inhibited by Sympathetic

ALIMENTARY CANAL ORGANIZATION MOUTH Oral (Buccal) Cavity Functions in Ingestion Digestion: Mechanical (Teeth, Tongue) Chemical (Saliva Begins Carbohydrate Digestion) Cheeks Hard Palate (Bony)

MOUTH continued Soft Palate (Muscular) Blocks Nasopharynx During Swallowing Uvula - Dangling end Tongue Frenulum Anchors to Floor of Mouth Skeletal Muscle Tissue covered with Mucosa Papillae with Taste Buds Lingual Tonsil & Sublingual Gland

MOUTH continued Teeth Vestibule – Space between Teeth & Lips Two Sets: Deciduous (20) & Permanent (32) Four Types: Incisors – Biting Canines – Tearing & Grasping Bicuspids & Molars - Grinding

ALIMENTARY CANAL ORGANIZATION continued PHARYNX Connects Oral Cavity, Nasal Cavity, Larynx & Esophagus Passageway for Food, Water, Air Muscular Walls (Swallowing) 3 Regions: Nasopharynx, Oropharynx, Laryngopharynx

ALIMENTARY CANAL ORGANIZATION continued ESOPHAGUS Collapsible, 10” Tube Connects Pharynx & Stomach Lies Posterior to Trachea Lower Esophageal Sphincter Prevents Stomach Contents from Entering Esophagus Passes Through Neck  Thoracic Cavity  Esophageal Hiatus  Abdominal Cavity

ALIMENTARY CANAL ORGANIZATION continued STOMACH J-Shaped Organ, Inferior to Diaphragm Functions: Storage Digestion (Mechanical & Chemical) Protein Digestion Begins here Absorption of Water, Alcohol, Drugs

STOMACH continued Enters as Bolus – Mixture of Food & Saliva Leaves as Chyme – Milky Mixture of Partially Digested Food & Gastric Juices

STOMACH continued 4 Regions: Cardia – Connects with Esophagus Body – Principal, Main Part Fundus – Superior, Bulge, Food Storage Pylorus – Terminal Part, Pyloric Sphincter 2 Curves: Greater Curvature Lesser Curvature

STOMACH continued Wall Modifications: Rugae –Expandable Folds, Accommodate More Food Oblique Muscle in Muscularis Gastric Glands in Mucosa Mucus Cells (Protective Coating) Parietal Cells (HCl, pH = 2) Chief Cells (Pepsinogen + HCl  Pepsin (Proteolytic)

ALIMENTARY CANAL ORGANIZATION continued SMALL INTESTINE Site of Most Chemical Digestion Site of 90% of Absorption Monosaccharides  Blood Amino Acids  Blood Fatty Acids & Glycerol  Lymph

SMALL INTESTINE continued 3 Subdivisions: Duodenum First 10-12” Ampulla of Vater Receives Secretions from Liver & Pancreas Bile through Common Bile Duct Pancreatic Juice through Pancreatic Duct Jejunum –Middle Length Ileum – Last, Joins with Large Intestine at Ileocecal Valve

SMALL INTESTINE continued Wall Modifications: All Increase Surface Area for Maximum Absorption Plicae Circulares – Transverse Folds of Mucosa & Submucosa Villi – Finger-like Projections of Mucosa, contain Capillaries & Lacteal Microvilli – Microscopic Folds of Cell Membrane

ALIMENTARY CANAL ORGANIZATION continued LARGE INTESTINE Functions: Secretes Mucus Absorbs Water, Ions, Vitamins (From Bacterial Metabolism) Forms & Compacts Feces (Undigested Food, Bacteria, Water)

LARGE INTESTINE continued 3 Divisions: Cecum Blind Pouch Appendix Attached Colon - Divided into Ascending, Transverse, Descending, Sigmoid Rectum – Anal Canal Internal Anal Sphincter (Smooth) External Anal Sphincter (Skeletal)

Radiograph of large intestine following barium enema.

LARGE INTESTINE continued Wall Modifications: Taenia Coli – 3 Bands of Longitudinal Muscle from Muscularis of Colon Haustra – Pouches in Wall of Colon No Villi

ALIMENTARY CANAL MOVEMENTS Peristalsis - Wave-like Contraction of Circular & Longitudinal Smooth Muscle for Propulsion Segmentation – Mixes & Pushes Chyme Against Wall of Small Intestine Haustral Churning – Pouch-to-Pouch Movement in Large Intestine Reverse Peristalsis

Image is radiograph following barium enema

ACCESSORY ORGANS SALIVARY GLANDS Exocrine Glands Ducts Carry Secretions (Saliva) into Mouth Saliva: Amylase, Mucous, Water, Antibodies, Lysozyme 3 Pairs: Parotid (Most Salivary Amylase) Submandibular Sublingual

ACCESSORY ORGANS continued LIVER Largest Gland in Body (Exocrine) Produces & Secretes Bile (Fat Emulsifier) Nutrient Storage & Conversion Synthesizes Blood Proteins Detoxification

ACCESSORY ORGANS continued GALL BLADDER Muscular Sac Stores & Concentrates Bile Receives Bile from Liver via Common Hepatic Duct  Cystic Duct Releases into Duodenum via Cystic Duct  Common Bile Duct  Ampulla of Vater (Sphincter of Oddi)

ACCESSORY ORGANS continued Bile Release: Chyme Enters Duodenum Cholecystokinin (CCK) & Secretin Secreted by Duodenum, Enters Blood Secretin stimulates liver to produce bile CCK Stimulates Contractions in Gall Bladder & Relaxation of Sphincter

Parasympathetic stimulation via Vagus Nerve also stimulated gallbladder to contract

ACCESSORY ORGANS continued PANCREAS Exocrine (& Endocrine) Gland Secretes Pancreatic Juice (Digestive Enzymes & Buffers) Leaves Pancreas Through Pancreatic Duct(s), Enters Duodenum Through Ampulla of Vater Raises pH of Duodenum (pH 8, “Natural Antacid”) via bicarbonate ions Secretin stimulates release by Pancreas of watery solution with high HCO3- CCK stimulates release by Pancreas of enzymatic solution