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