THE DIGESTIVE SYSTEM

THE DIGESTIVE SYSTEM

CHAPTER 25

http://www.youtube.com/watch?v=9FEACJ-cXsY

System Overview•Digestive Organs•Alimentary Canal – mouth, esophagus, stomach, small intestine, large intestine, rectum

http://www.youtube.com/watch?v=9FEACJ-cXsY

•Accessory Organs – salivary glands, teeth, pancreas, liver, gall bladder

•Digestive Processes•Ingestion – taking in food •Propulsion – moving food along

•Deglutition – breaking food into smaller pieces

•Peristalsis – involuntary smooth muscle wavelike contractions

•Mechanical digestion – stomach churning

• Mastication - chewing

•Chemical digestion – begins in the mouth and continues through small intestine•carbohydrates into simple sugars

•proteins into amino acids

•lipids into fatty acids and glycerol

•Absorption – through lining of small intestine

•Defecation – eliminating undigestible solid material

Anatomy

•Peritoneum•visceral peritoneum – membrane that covers outside of organs

•parietal peritoneum – membrane that lines abdominopelvic cavity; forms ligaments to suspend organs.

Abdominal Serous Membranes

•falciform ligament – binds liver

•lesser omentum – binds stomach

•greater omentum – binds small and some of large intestine

•Mesocolon – binds large intestine

•Mesentery - suspends small intestine

•peritoneal cavity– abdominal cavity

Histology

•4 basic layers•mucosa – innermost layer, lines lumen; secretes enzymes and hormones

•Submucosa – contains nerve endings, blood vessels, lymphatic vessels (lacteals); absorption

•muscularis – smooth muscle layer; motility

•serosa – outermost layer; secretes serous fluid to lubricate

•

Alimentary Canal (GI Tract) Anatomy

•Mouth – contains teeth, tongue and salivary glands. Mechanical digestion; chemical digestion of starches begins here

•Stomach – •Chyme – consistency of toothpaste

•goblet cells – secrete mucus (protection)

•parietal cells – secretes HCl and intrinsic factor (absorbs vitamin B12)

•chief cells – secrete pepsinogen which is activated by HCl when stomach pH rises (from ingestion of proteins)

•G cells – secrete gastrin

•Rugae – folds in stomach lining

•Modifications – 3 muscle layers

•Digestion – mechanical; chemical digestion of proteins begins here

•Absorption – water and alcohol

•Pathology – ulcers (bacterial in origin), cancer, hiatal hernia, gastro-esophageal reflux disease

•Small intestine – •Regions: duodenum, jejunum, ileum

•Enzymes: peptidases (proteins) dextrinases (sugars)

•Modifications•Villi – increases surface area •microvilli – secretes enzymes•plicae circularis – keeps food “rotating”

•Absorption: sugars and amino acids; fats absorbed through “lacteals”

• Colon (with appendix)– E. coli colonies here help manufacture vitamin K

•Propulsion•Absorption of

water•Pathology:

diarrhea, constipation, colon cancer, diverticulitis

Progression from polyp to cancer

•Liver & Gall Bladder •Responsible for producing bile, process nutrients, store glycogen, store fat soluble vitamins, detoxification.

•Kupffer cells- phagocytic cells

•Hepatocytes- liver cells

•Bile – made in liver, stored in gall bladder; emulsifies fats

•Pathology – gall stones, cirrhosis, hepatitis, liver cancer

•Pancreas • Proteases – proteins• lipases – fats• amylases - starches • nucleases – nucleic acids• Insulin (hormone)– sugar metabolism• Pathology – diabetes mellitis, pancreatitis

Hormonal Control

•Gastrin – secretion stimulated by proteins and caffeine; stimulates secretion of HCl; feedback mechanism

•Enterogastrone – secreted by duodenum in response to high fat content of diet; slows stomach activity

• Secretin – •produced by duodenum in response to fatty and acidic chyme

•stimulates pancreas to secrete bicarbonate ions and increase bile output

• CCK – •produced by duodenum in response to fatty chyme;

•stimulates pancreas to secrete digestive enzymes

General Pathology•dysentery• food poisoning•periodontal disease•mumps•hepatomas•enteritis•colitis• ileitis•Crohn’s Disease

Periodontal disease

mumps

hepatoma

Any Questions?