The Digestive System

Body Cavities Cranial Thoracic pleural pericardial Spinal Abdominal Pelvic

Digestion Digestion (cont.) Digestion the breaking down of food molecules Digestive System organs that collectively perform the breaking down of food

Digestive Processes Ingestion taking food into the mouth Mixing and movement of food muscular contractions mix food and secretions and move food along the gastrointestinal tract Digestion breakdown of food by chemical and mechanical processes

Digestive Processes Absorption passage of digested food from the GI tract into the cardiovascular and lymphatic for distribution to cells Defecation elimination of indigestible substances from GI tract

Digestive Processes Mechanical Digestion chewing/churning Peristalsis waves of muscular contraction, (peri=around; stalsis=contraction) Takes place  esophagus  stomach  small intestine  large intestine

Digestive Processes Chemical Digestion series of reactions that break down the large, complex carbohydrate, lipid, and protein molecules into small molecules we can absorb through the gastrointestinal wall

Organs of Digestion Gastrointestinal Tract /Alimentary Canal begins with mouth – ends at anus mouth, pharynx, esophagus, stomach, small intestine, large intestine Accessory Structures teeth, tongue, salivary glands, liver, gall bladder, pancreas

Mouth (Oral or Buccal) Cavity Hard palate Soft palate Tongue floor, food maneuvering Lingual Frenulum mucous membrane connects underside of tongue to floor over buccal cavity Papillae line tongue on top and sides some contain taste buds

Salivary Glands Parotid under and in front of ears Submandibular lies beneath base of tongue Sublingual lies in the tissues beneath and on each side of the tongue

Salivary Glands Saliva 99.5% water and 0.5% solutes water helps to moisten food mucous (mucin) lubricates food, binds it into a bolus amylase bicarbonate lysozyme destroys bacteria to protect mucous membrane from infection and the teeth from decay

Wall of GI Tract – 4 Layers Mucosa – inner lining mucous membrane epithelium areolar connective tissue, smooth muscle (muscularis mucosae) Submucosa consists of areolar connective tissue that binds with mucosa to the muscle layer

Wall of GI Tract 4 - Layers Muscularis thick layer of muscle smooth muscle inner sheet of circular fibers and outer sheet of longitudinal fibers & nerves Serosa and Peritoneum outermost layer serosa composed of simple squamous epidermis and connective tissue

Wall of GI Tract 4 - Layers Secretes serous (wet) fluid to allow the organs to glide Peritoneum largest serous membrane  Parietal  lines wall of abdominal cavity  Visceral  covers some of the organs

Gastrointestinal Tract Begins with esophagus Esophagus joins with stomach at esophageal sphincter Stomach joins duodenum at the pyloric sphincter Stomach can absorb water, electrolytes, certain drugs and alcohol

Pancreas pan=all kreas=flesh lies behind the stomach Made up of pancreatic islets (islets of Langerhans) produce glucagon and insulin Made up of acini exocrine glands that secrete digestive enzymes called pancreatic juice

Pancreatic juice includes protease lipase amylase nuclease alkaline salts

Functions of Liver Carbohydrate Metabolism convert glucose to glycogen when sugar level is high insulin breakdown glycogen to glucose when sugar is low glucagon Lipid (Fats) Metabolism stores and breaks down

Functions of Liver Protein Metabolism synthesize and convert Removal of Drugs Synthesis of Bile Weighs about 3 pounds Located under the diaphragm Divided into right and left lobes by the falciform ligament Lobes divided into lobules

Gall Bladder Located under liver Functions in storage of bile until needed in small intestine Muscularis in gall bladder contracts following hormonal stimulation

Bile Excretory product and digestive secretion salts aid in emulsification conversion of triglyceride globules into droplets and absorption of triglycerides following their digestion

Small Intestine Area of digestion and absorption Duodenum beginning of small intestine Jejunum middle section of intestine Ileum (2 meters) joins colon at Ileoceal junction Composed of same 4 layers as GI tract

Small Intestine Mucosa forms fingerlike villi 0.5 to 1 mm in length increases surface area for absorption Microvilli found in the absorptive cells of the epithelium microscopic cytoplasmic projections increase surface area (1 sq millimeter contains 200 million microvilli)

Absorption each day 9.3 liters enters the SI nearly all is absorbed 0.1 passes into LI also absorbed by osmosis electrolytes are absorbed in small intestine vitamins are absorbed in small intestine

Large Intestine Last stage of digestion is largely bacterial 40% of fecal mass is bacteria converts remaining carbohydrates into H, carbon dioxide and methane gas break down remainder of amino acids ascending colon is a double coil /clockwise spiral transverse colon continues after ascending on right side descending is final portion that leads to the rectum

Absorption By the time chyme has remained in the LI 3 to 10 hours, it has become semisolid as a result of water absorption now known as feces consists of inorganic salts, cells from mucosa of GI tract, bacteria, undigested parts of food, products of bacterial digestion