3/31/08 Digestive System Chapter 22 – Day 4

3/31/08 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??

3/31/08 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

3/31/08 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

3/31/08 Large Intestine – Digestion  From cecum L.I. extends up = ascending colon  Extends horizontally = transverse colon  Extends down = descending colon Fig  Turns in = sigmoidal colon  Tube goes towards anus = rectum  Anus = opening to release wastes ♦Guarded by a sphincter

3/31/08 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

3/31/08 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: ◦N 2, CO 2, methane, & H 2 = flatus  Absorption is completed ♦Large amount of H 2 O is absorbed ♦Vitamin K & B vitamins are absorbed  Gas accumulation ♦= Flatulence ♦Smell is due to methane gas

3/31/08 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

3/31/08 Large Intestine – Digestion Fig

3/31/08 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 H 2 O absorption  Constipation: ♦Less H 2 O or fiber in diet ♦Water is limited so larger % absorbed compared to remaining in feces ♦Need more fluid and fiber in diet

3/31/08 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 H 2 O absorption  Constipation: ♦Less H 2 O or fiber in diet ♦Water is limited so larger % absorbed compared to remaining in feces ♦Need more fluid and fiber in diet

3/31/08 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

3/31/08 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

3/31/08 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

3/31/08 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

3/31/08 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

3/31/08 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

3/31/08 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 ♦ Fig

3/31/08 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

3/31/08 Metabolism Fig. 23.1

3/31/08 Metabolism Fig. 23.2