digestion absorption gi tract anatomy of gi tract

DIGESTION

ABSORPTION

GI TRACT

ANATOMY OF GI TRACT

MOUTH

Chewing surface area of foodMixes fluid (saliva) in with foodTasteEase of swallowingCHO digestion (amylase) NO digestion of fibers and sugarsEpiglottis 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 foodPERISTALSIS –

powerful rhythmic waves propels food along circular and longitudinal muscles speed varies

PERISTALISIS

ESOPHAGUS TO STOMACHEsophagus diaphragmCardiac sphincter – 1 way valve between esophagus and stomachStomachCHO digestion stops in the stomachSaliva – is a protein and is digestedProblems:

Hiatal hernia GERD Heartburn – acidic stomach contents into

esophagus

HERNIA

GERD

STOMACH

Muscular, elastic, saclike, thickest walls, strongest muscles in GI tractParietal cells on wall release GastrinGastrin stimulates release of HCl (1.5-1.7 pH)HCl denatures proteinHCl activates pepsinogen (enzyme) pepsinPepsin large proteins smaller amino acidsDigestion of protein – little else

STOMACHChurning

circular longitudinal diagonal

Food mixed with water ~ 2 liters per dayChyme (“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/minuteWaits to re-open until chyme neutralizedChyme released in small squirtsNeutralized by bicarbonate from pancreas

SMALL INTESTINE

Three segments Duodenum Jejunum Ileum

Digestion completed for CHO, PRO, FatPancreatic enzymes-specific to need

proteases, lipases, carbohydrasesIntestinal enzymesBile (emulsifier)-livergallbladder

SMALL INTESTINE - ABSORPTION

Microvilli- fingerlike projectionsCrypts – secrete digestive enzymesSpecific areas for absorption of specific nutrients- absorption of most nutrientsAbsorbed into lymph or bloodBLOOD – liver via portal veinLYMPH – bloodstream via thoracic duct and subclavian vein

SMALL INTESTINAL VILLI

ABSORPTION OF NUTRIENTS

Diffusion – freely crosses cell membraneFacilitated diffusion – specific carriers required but no energyActive transport – requires carriers and energy

ILEOCECAL VALVE

One way valve between small and large intestine

ABSORPTION SITES

LARGE INTESTINEColon – three segmentsAscending colonTransverse colonDescending colonNormal bacterial action

Fiber kcals Vitamin K + others?

Absorption water and some minerals

LARGE INTESTINE FUNCTION

Food in large intestine 20-36 hoursWater reabsorbed – if not diarrheaHome for bacteriaFeces formed hereFew 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