Digestive PhysiologyDigestive Physiology

Physiological functions of

pancrease & large intestine

By: M.H.Dashti

Lecture 4

Digestion & Absorption of Fat products in Small IntestineDigestion & Absorption of Fat products in Small Intestine

Final Digestion & Absorption in Of Carbohydrates in Small Intestine

Final Digestion & Absorption in Of Carbohydrates in Small Intestine

Monosaccharides leave the basolateral Membrane via GLUT-2

Final Digestion & Absorption of Protein products in Small IntestineFinal Digestion & Absorption of Protein products in Small Intestine

Chemical Digestion in Small Intestine: Nucleic Acids

Chemical Digestion in Small Intestine: Nucleic Acids

Pancreatic juice convert RNA & DNA to Nucleotides by Ribonuclease & Deoxyribonuclease

brush border enzymes (nucleosidease and phosphatase) converts Nucleotides to pentose, phosphate & nitrogenous bases

Absorption of

vitamin B12

Absorption of

vitamin B12

absorption of Fe2+ in small intestine

absorption of Fe2+ in small intestine

iron transporter DMT1, heme transporter (HT), heme oxidase (HO) , ferroportin (FP) ,hephaestin (Hp), transferrin (TF)

absorption of Ca2+ in small intestine is controlled by vitamin D3

absorption of Ca2+ in small intestine is controlled by vitamin D3

Sodium absorption in jejunum is coupled to glucose , amino acid & bicarbonate absorption

Sodium absorption in jejunum is coupled to glucose , amino acid & bicarbonate absorption

Sodium absorption in ileum is coupled

to choloride absorption

Sodium absorption in ileum is coupled

to choloride absorption

Absorption of Water Absorption of Water 9 liters of fluid dumped

into GI tract each day Small intestine reabsorbs

8 liters Large intestine

reabsorbs 90% of that last liter

Absorption is by osmosis through cell walls into vascular capillaries inside villi

Where will the absorbed nutrients go?Where will the absorbed nutrients go?

Ileocecal sphincter Ileocecal sphincter Controlled by

pressure differences

Neural events– Ileo -colic &

colono-ileal reflexes

– Ileo- gastricic & gastro-ileal reflexes

Ileal break– Oxyntomodulin &

neurotensin

Anatomy of Large IntestineAnatomy of Large Intestine

5 feet long by 2½ inches in diameter Ascending & descending colon are retroperitoneal Cecum & appendix Rectum = last 8 inches of GI tract anterior to the sacrum & coccyx Anal canal = last 1 inch of GI tract

– internal sphincter----smooth muscle & involuntary – external sphincter----skeletal muscle & voluntary control

Digestion in Large IntestineDigestion in Large Intestine

No enzymes are secreted only mucous Bacteria ferment

– undigested carbohydrates into carbon dioxide & methane gas

– undigested proteins into simpler substances (indoles)----odor

– turn bilirubin into simpler substances that produce color

Bacteria produce vitamin K and B in colon

Absorption & Feces absorption in the Large Intestine

Absorption & Feces absorption in the Large Intestine

Some electrolytes---Na+ and Cl- After 3 to 10 hours, 90% of H2O has been

removed from chyme Feces = dead epithelial cells, undigested

food such as cellulose, bacteria (live & dead)

Large intestine motilityLarge intestine motility Haustral churning

– BER (3 to 18/min) haustral shuttling

– Multihustral contraction in ascending colon

Mass movement– Mainly starts in the

pacemaker site at the beginning of transverse colon

– Affected by gastrocolic reflex

Defecation reflex – Local & central

Gostric stimulation (activates gastrocolic reflexes)

Feces

Stimulation of local

defecation

reflexes

Stimulation parasympathetic controlled defecation reflexes

Rectum

Moss movements

Colon

Presence of chyme in

the duodenum

Duodenocolic

stimulation (activates Duodenoc

olic reflexes)

Presence of food in the stomach

Stomach

Defecation Defecation Gastrocolic reflex moves

feces into rectum Stretch receptors signal

sacral spinal cord Parasympathetic nerves

contract muscles of rectum & relax internal anal sphincter

External sphincter is voluntarily controlled

Pressures in the RectumPressures in the Rectum

Neural pathways of defecation reflexNeural pathways of defecation reflex