DIGESTION ABSORPTION

GI TRACT

ANATOMY OF GI TRACT

MOUTH Chewing  surface area of food Mixes fluid (saliva) in with food Taste Ease of swallowing CHO digestion (amylase) NO digestion of fibers and sugars Epiglottis prevents choking cartilage in throat to close off windpipe

NORMAL SWALLOW STAGES ORAL PHASE- food bolus moves to back of mouth (voluntary) PHARYNGEAL PHASE – triggering of the swallow (reflexive stage) ESOPHAGEAL PHASE – actual swallow (reflexive)

DYSPHAGIA - SYMPTOMS ORAL PHASE drooling pocketing facial droop inadequately chewed foods food falling out of the mouth excessive tongue movement

DYSPHAGIA CONT’D PHARYNGEAL PHASE “Gurgling” voice food getting stuck nasal regurgitation delayed swallowing reflex coughing while eating or drinking

TEST OF SALIVARY SECRETIONS

GI TRACT BOLUS – mouthful of swallowed food PERISTALSIS – powerful rhythmic waves propels food along circular and longitudinal muscles speed varies

PERISTALISIS

ESOPHAGUS TO STOMACH Esophagus  diaphragm Cardiac sphincter – 1 way valve between esophagus and stomach Stomach CHO digestion stops in the stomach Saliva – is a protein and is digested Problems: Hiatal hernia GERD Heartburn – acidic stomach contents into esophagus

HERNIA

GERD

STOMACH Muscular, elastic, saclike, thickest walls, strongest muscles in GI tract Parietal cells on wall release Gastrin Gastrin stimulates release of HCl (1.5-1.7 pH) HCl denatures protein HCl activates pepsinogen (enzyme)  pepsin Pepsin  large proteins smaller amino acids Digestion of protein – little else

STOMACH Churning circular longitudinal diagonal Food mixed with water ~ 2 liters per day Chyme (“kime”) – very acidic semiliquid mass of partly digested food and fluid Stomach protected by mucus membrane-from goblet cells

STOMACH

pH VALUES

STOMACH SURGERY

PYLORIC SPHINCTER Circular muscle-1 way valve Opens 3 times/minute Waits to re-open until chyme neutralized Chyme released in small squirts Neutralized by bicarbonate from pancreas

SMALL INTESTINE Three segments Duodenum Jejunum Ileum Digestion completed for CHO, PRO, Fat Pancreatic enzymes-specific to need proteases, lipases, carbohydrases Intestinal enzymes Bile (emulsifier)-livergallbladder

SMALL INTESTINE - ABSORPTION Microvilli- fingerlike projections Crypts – secrete digestive enzymes Specific areas for absorption of specific nutrients- absorption of most nutrients Absorbed into lymph or blood BLOOD – liver via portal vein LYMPH – bloodstream via thoracic duct and subclavian vein

SMALL INTESTINAL VILLI

ABSORPTION OF NUTRIENTS Diffusion – freely crosses cell membrane Facilitated diffusion – specific carriers required but no energy Active transport – requires carriers and energy

ILEOCECAL VALVE One way valve between small and large intestine

ABSORPTION SITES

LARGE INTESTINE Colon – three segments Ascending colon Transverse colon Descending colon Normal bacterial action Fiber  kcals Vitamin K + others? Absorption water and some minerals

LARGE INTESTINE FUNCTION Food in large intestine 20-36 hours Water reabsorbed – if not diarrhea Home for bacteria Feces formed here Few minerals absorbed

STOMAS

CROSS-SECTION

THE END Rectum – semisolid waste (feces) Defecation – elimination of waste from body – “moving of bowels” Anus – terminal sphincter, opens to outside of body – YOU control this valve