Digestive System

1. Digestive System Chapter 22 – Day 4

2. Large Intestine – Digestion Digestion of Macromolecules • Lipids (Fats): • Fats are broken up into smaller globules • Emulsification requires bile • Fats → Fatty Acids (monoglycerides): needs lipase • Nucleic Acids • DNA (or RNA) → pentose sugars + nitrogen compounds: needs nuclease (then they are absorbed) • Small compounds are then ready for absorption • 90% of absorption in S.I. via villi • HOW ARE THEY ABSORBED??

3. Large Intestine – Digestion • Emulsified fats = Micelles • Micelles are absorbed into epithelial cells via simple diffusion • Inside epithelial cells • Recombining & repackaging takes place • Fatty acids + monoglycerides = triglycerides • All lipids combine together • Triglycerides + cholesterol + phospholipids = coated with a special protein • Protein package of lipids in the epithelial cells = chylomicron • Enters lacteal (or Peyer’s patches) → lymph → veins → heart → liver • Inside liver – chylomicrons are broken down → lipids are released → next step = solubilization of lipids • Lipids are attached to Lipoproteins which are then distributed to the body via the blood stream (HDL) • These compounds travel through lymph via chylomicron because of solubility issues

4. Large Intestine – Digestion • Remaining materials move to large intestine • Structural Features • Ileum opens into L.I via the ileocecal pshincter → contents enter L.I. • First structure in L.I. = cecum (blind pouch) • Appendix is attached to the surface of the cecum • Contents of the intestine can enter the appendix • contains lymphoid tissue • Takes care of cellulose digestion in animals

5. Large Intestine – Digestion • From cecum L.I. extends up = ascending colon • Extends horizontally = transverse colon • Extends down = descending colon • Turns in = sigmoidal colon • Tube goes towards anus = rectum • Anus = opening to release wastes • Guarded by a sphincter Fig. 22.22

6. Large Intestine – Digestion • Folds of L.I. = haustra (pouches) • Histology: • Inside = no villi • Columnar cells with goblet cells • Peristalsis churns food, moves it through the L.I. • Thick bands of longitudinal muscle • Taeniae coli • Eventually, food moves into rectum Fig. 22.23

7. Large Intestine – Digestion • Chyme remains in L.I. for 3-10 hours • Digestion is completed • Amino acids are broken down by bacteria • Carbohydrates are fermented • Gases are formed: • N2, CO2, methane, & H2 = flatus • Absorption is completed • Large amount of H2O is absorbed • Vitamin K & B vitamins are absorbed • Gas accumulation • = Flatulence • Smell is due to methane gas

8. Large Intestine – Digestion • Material not absorbed = semi-solid at the end • =FECES • Contains materials that were not absorbed and waste products • Accumulates in rectum • Activates pressure-sensitive receptors in rectum • Leads to contraction of rectum walls (muscles) • Shortens rectum, increases pressure • Exit through anus – via sphincter • Voluntary control = relaxation of sphincter • Aided by abdominal muscles Fig. 22.24

9. Large Intestine – Digestion Fig. 22.24

10. Large Intestine – Common Problems • Diarrhea & Constipation • Diarrhea: not enough water is absorbed in L.I. • Constipation: too much water absorbed in L.I. • Diarrhea: • Usually caused by bacteria that irritate mucosa • Chyme moves too quickly for adequate H2O absorption • Constipation: • Less H2O or fiber in diet • Water is limited so larger % absorbed compared to remaining in feces • Need more fluid and fiber in diet

11. Large Intestine – Common Problems • Diarrhea & Constipation • Diarrhea: not enough water is absorbed in L.I. • Constipation: too much water absorbed in L.I. • Diarrhea: • Usually caused by bacteria that irritate mucosa • Chyme moves too quickly for adequate H2O absorption • Constipation: • Less H2O or fiber in diet • Water is limited so larger % absorbed compared to remaining in feces • Need more fluid and fiber in diet

12. Problems in Digestive System • Hemorrhoids, Appendicitis, Colon cancer, Ulcers, Liver problems (hepatitis & cirrhosis) • Hemorrhoids: • Affects rectum & anus • Varicose veins in rectal walls • Damaged valves in veins • Accumulation of blood – causes blood vessel to protrude • Damage to valves is caused by pressure against veins: • Pushing during delivery or during pregnancy (or constipation) • Can be surgically removed Fig. 22.22

13. Problems in Digestive System • Appendicitis: • Inflammation of the appendix • Usually caused by obstruction: • Foreign body, feces, tumor • If not removed it can burst & cause other problems • Symptoms: • Waves of abdominal pain on right, then becomes steady • May experience: • Vomiting • low-grade fever • Increase in WBC count Fig. 22.22

14. Problems in Digestive System Ulcers • Erosion of epithelial lining in the GI tract • Forms a lesion → eats through tissue layers • Causes • Excess acid production • i.e. hypersecretion of gastric juices • Reduced mucus secretion • i.e. hyposecretion of alkaline mucus • Bacteria or stress • Which enhance hyper- or hyposecretion • Commonly occur in the duodenum or stomach (=gastric ulcer) Fig. 22.22

15. Problems in Digestive System Ulcers • Symptoms • Severe pain, usually 1-4 hours after eating • Weight loss • Bleeding • Treatment • Antacids • Zantac (aluminum coat) • Surgery • Lifestyle changes Fig. 22.22

16. Problems in Digestive System Liver Problems • Cirrhosis • Liver cells become inflamed or sever damage, then destroyed • Cells cannot regenerate to full extent • Hepatocyte tissue gets replaced by fibrous tissue • Causes: • Damage by: • Toxins, Inflammation, Metabolic problems • Hepatitis can lead to cirrhosis • Most common cause = alcoholism • Bile duct problems • Treatment • Depends on cause • Prevent further damage Fig. 22.22

17. Problems in Digestive System Liver Problems • Hepatitis • Caused by a virus – Hepatitis A or Hepatitis B, C & D, E • Contaminated water with Feces • Sexual transmission • Food • Symptoms • Fever • Tiredness • Sore muscles • Yellowing of the skin = accumulation of bilirubin Fig. 22.22

18. Metabolism Colon Cancer • Common cancer of the G.I. tract • Tumor formation in the large intestine = polyps • Polyps may be benign or malignant • Usually in the rectum or sigmoidal colon • Polyps must be removed and analyzed for cancer cells – biopsy • Symptoms of polyps: • Pain, cramps, blood in stool • Detected by colonoscopy • http://www.mayoclinic.com/health/colonoscopy/MM00010 Fig. 22.22

19. Metabolism • After digestion & absorption: glucose, lipids etc. • Chemical reactions take place in cells • Process of cellular metabolism • Nutrients in the cell • Can either be broken down further by the process of catabolism • Or they can be joined together to form new larger molecules by the process of anabolism • Catabolic processes – release energy • Mitochondria = location for numerous catabolic activities • Energy • 40% ATP, 60% heat (released back into environment) • ATP: helps to maintain cellular activities & governs anabolism (anabolic processes require energy) • Big picture: process of metabolism is essential for homeostasis Fig. 22.22

20. Metabolism Fig. 23.1

21. Metabolism Fig. 23.2