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Large Intestine: Absorption, Fermentation, and Bacterial Action, Summaries of Physiology

An in-depth exploration of the large intestine, focusing on its structure, functions, and applied aspects. Topics include the composition of the large intestine, mucus secretion, formation of feces, fermentation, and bacterial action. The document also covers calcium and iron absorption, as well as various intestinal disorders such as constipation, celiac disease, Hirschsprung/Megacolon disease, and Irritable Bowel Syndrome.

What you will learn

  • What are the functions of the large intestine?
  • How is feces formed in the large intestine?
  • What is the composition of the large intestine?
  • How is mucus secreted in the large intestine?
  • What role do bacteria play in the large intestine?

Typology: Summaries

2021/2022

Uploaded on 09/12/2022

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Lecture series

Gastrointestinal tract

Professor Shraddha Singh,

Department of Physiology,

KGMU, Lucknow

STRUCTURE OF LARGE INTESTINE

CROSS SECTION OF LARGE INTESTINE

CHARACTERSTICS OF LARGE INTESTINE

  • Haustra - Ring like contractions of the circular muscle divide the colon into pockets called haustra
  • Teniae coli- Three seperate longitudinal ribbons of smooth muscle on otside of ascending,transverse,descending & sigmoid colons.they are visible below the serosa
  • Epiploic appendages - small pouches of peritonium filled with fat ,situated along the colon

RATE OF SECRETION OF MUCUS

  • Direct tactile stimuli
  • Local nervous reflex
  • Stimulation of pelvic nerves from spinal cord which carry parasympathetic innervation Increased mucus production Increased bowel movements

2.Formation of feces

  • Around 1500ml of chyme/day from ileum is moved to caecum,of which maximum amount is absorbed in proximal colon.only 100ml of fluid & 1-5meq of sodium,chloride is excreted in feces
  • Distal colon act as storage of feces called as storage colon
  • LI has tight junction between epithelium cells prevents back diffusion of ions back .LI secretes HCO3,chloride ions.Bicarbonates neutralises acidic products of bacterial action .Absorption of sodium & chloride ions creates an osmotic gradient which in turn causes the absorption of water

3.FERMENTATION

  • Bacteria mainly anaerobic & yeast break down substrates mainly starch,fibers,protein to give energy COMPOSITION OF FECES 3/4 water,1/4 solid Solid - 30% dead bacteria
    • 10 - 20% fat
    • 10 - 20% inorganic matter
    • 2 - 3% Protein
    • 30%undigested roughoge
  • Stercobilin,urobilin to give colour to feces & urine
  • Others-indole,skatole,mercaptans,hydrogen sulphide etc

3.BACTERIAL ACTION IN Large Intestine

  • Coliform bacilli is present which causes digestion of small amount of cellulose
  • Substances formed by bacterias are vit-k,vit B12,thiamine,riboflavin gases(co2,H2S,CH4)
  • Vit b12 helps in iron absorption
  • Vit k is used in blood coagulation

SUBSTRATES Bacterial +yeast enzymes breakdown Breakdown products Acetic acid,propionic acid,butyric acid,carboxylic acid,phenolic acid,amines,ammonia Fate of substrates Absorbed/Eliminated in feces/Rectal gases/ Utilized by microflora

CALCIUM ABSORPTION IN INTESTINE

  • Calcium entering in GIT is about 1 gm/day of which 40% is absorbed
  • Absorbed mainly in duodenum and jejunum Absorption takes place by 3 steps: a)Passive diffusion at enterocyte through ca channel b)Inside the cell binds with ca-binding protein calbindin D(CaBP ) & seqestrated in ER ,Golgi apparatus c) At basolateral membrane ca transported to blood via ca-atpase pump d)Active form of vit D stimulates uptake,increase CaBP &Ca-ATPase pump