![REGULATION OF NA ABSORPTION
1. feedback regulation
•Occurs on ENaCs
•Na has a negative impact on the activity of
the channels
•Increase in [Na] in the colon cells
downregulates and eventually endocytosis of
ENaC
2 Steroid-Dependent Regulation of Ion
Transport
•upregulated by glucocorticoid and
mineralocorticoid hormones.
•This leads to enhanced Na1 absorption
and K1 secretion](https://image.slidesharecdn.com/largeintestinephysiology-241101221724-6205024c/85/GIT-Physiology-Large-intestine-physiology-ppt-10-320.jpg)
GIT Physiology - Large intestine physiology. .ppt
- 1. THE LARGE INTESTINE PHYSIOLOGY DR. NYANGARESI
- 2. OUTLNE. • Outline anatomy and segments. • Outline motility in the large intestines. • Mechanisms, localization and regulation of colonic Na, HCO3 and K absorption. • Describe the role of dietary fiber in promoting colonic motility. • Describe the factors contributing to intestinal and colonic gas composition and the consequences of an altered colonic microflora. • Describe the role of short chain fatty acids in colonic sodium absorption and in both colonic and body energy metabolism.
- 4. LARGE INTESTINE - ANATOMY • Cecum • Blind sac, vermiform appendix attached • Colon • Ascending, transverse, descending, sigmoid • Rectum • Straight muscular tube • Anal canal • Internal anal sphincter (smooth muscle) • External anal sphincter (skeletal muscle)
- 5. LARGE INTESTINE – HISTOLOGY 4 layers: 1.Mucosa: • No villi • Presence of goblet cells • Deep intestinal glands i.e. crypts 2. Submucosa: not well developed. 3. Muscle layer: • Circular: • Longitudinal: form Taeni coli. 4. Serosa.
- 6. FUNCTIONS OF THE LARGE INTESTINE • Reabsorb water and compact material into feces • ELECTROLYTE ABSORPTION • Absorb vitamins produced by bacteria • Store fecal matter prior to defecation • Absorptive part: proximal colon. • Storage part: distal colon. • Immunity
- 8. NA+ ABSORPTION • Gradient created by Na – K atpase. • Chloride follows sodium. • Water follows via osmotic gradient. • Enhanced by Aldosterone • Na absoption is accompanied by Cl as well via the CFTR
- 9. SODIUM ABSORPTION VIA ENAC
- 10. REGULATION OF NA ABSORPTION 1. feedback regulation •Occurs on ENaCs •Na has a negative impact on the activity of the channels •Increase in [Na] in the colon cells downregulates and eventually endocytosis of ENaC 2 Steroid-Dependent Regulation of Ion Transport •upregulated by glucocorticoid and mineralocorticoid hormones. •This leads to enhanced Na1 absorption and K1 secretion
- 11. DIGESTION AND ABSORPTION OF SHORT CHAIN FATTY ACIDS Production: fermentation of dietary fibers by colonic bacteria. anaerobic fermentation of indigestible polysaccharides such as dietary fiber Examples of SCFA: acetate, propionate, and butyrate Absorption: mainly via H+-dependent or sodium-dependent monocarboxylate transporters (MCTs and SMCTs, respectively Functions: Neutrients to enterocytes thus trophic. Reduce inflammation. Brain gut axis interaction. Indirectly: gut homornes. Directly: via Vagus nerve.
- 12. ROLE OF DIETARY FIBRE 1. Soluble Fibre: Dissolves in water to form a gel-like substance. Sources: Oats, peas, beans, apples, citrus fruits, carrots, barley, psyllium. 2. Insoluble Fibre: does not dissolve in water and adds bulk to the stool Sources: Whole-wheat flour, wheat bran, nuts, beans, and vegetables, such as cauliflower, green beans, and potatoes.
- 13. ROLE OF DIETARY FIBRE • Regulation of Bowel Movements: • Insoluble fibre adds bulk to the stool reducing transit time and thus reducing the risk of constipation. • Soluble fibre absorbs water, making stool softer and easier to pass. • The above two reduce risk of hemorrhoids and diverticular diseases • Control of Blood Sugar Levels • Soluble fibre slows the absorption of sugar, helping to improve blood sugar levels esp those with DM • Lowering Blood Cholesterol Levels • Soluble fibre binds with bile acids in the intestines and promotes their excretion. • Prevention of Colorectal Cancer • Fibre increases the bulk and frequency of bowel movements, which reduces the time stool spends in the colon. • This decreases the exposure of the colon lining to potential carcinogens. • Improvement of Overall Gut Health • Fibre, particularly prebiotics that are progut flora.
- 14. MOTILITY OF THE COLON 1. segmental contraction increase exposure to mucosa for absorption 2. peristaltic waves Movement to rectum for defecation.
- 15. MOVEMENT IN LARGE INTESTINE
- 16. MOVEMENT IN LARGE INTESTINE Gastrocolic reflex: Trigger: food distending stomach after eating Afferent limb: stimulation of Enteric nervous system and ANS Efferent: GIT hormones and increase in motility of GIRelease of Gastrointestinal Effect: stimulate the colon's smooth muscles. This results in increased peristaltic activity in the colon. This increased motility can lead to the urge to defecate soon after eating.
- 17. MOVEMENT IN LARGE INTESTINE Duodenocolic reflex: Trigger: food distending duodenum after eating and acidic chyme. Afferent limb: stimulation of Enteric nervous system and ANS Efferent: GIT hormones and increase in motility of GIRelease of Gastrointestinal Effect: stimulate the colon's smooth muscles. This results in increased peristaltic activity in the colon. This increased motility can lead to the urge to defecate soon after eating.
- 18. MOVEMENT IN LARGE INTESTINE- DEFECATION REFLEX
- 19. MOVEMENT IN LARGE INTESTINE- DEFECATION REFLEX 1. Filling of the Rectum: from the rectum causing rectal distension. 2. Activation of Stretch Receptors: The distension of the rectal walls stimulates stretch receptors located in the rectal mucosa. 3. Afferent Signal Transmission: stretch receptors send signals to the sacral spinal cord (S2-S4) via the pelvic nerves. 4. Spinal Cord Processing: The sensory information is processed in the sacral spinal cord, initiating a reflexive response. 5. Efferent Signal Transmission: Efferent signals are sent from the spinal cord back to the rectum and anus via the pelvic nerves and the pudendal nerve.
- 20. MOVEMENT IN LARGE INTESTINE- DEFECATION REFLEX 1. Involuntary Component: 1. The internal anal sphincter relaxes in response to the efferent signals. 2. Simultaneously, the rectal muscles contract to increase intra-rectal pressure. 2. Voluntary Component: 1. The external anal sphincter (composed of skeletal muscle) is under voluntary control. 2. The cerebral cortex receives sensory input regarding rectal distension, creating the conscious urge to defecate. 3. Defecation Process: 1. Voluntary relaxation of the external anal sphincter allows feces to be expelled. 2. Additional assistance is provided by the Valsalva maneuver, which involves voluntary contraction of the abdominal muscles to increase intra-abdominal pressure.
- 21. IMMUNE FUNCTIONS OF COLON. 1. Gut-Associated Lymphoid Tissue (GALT): Includes Peyer's patches, isolated lymphoid follicles, and lamina propria lymphocytes. This generate immune responses to pathogens while maintaining tolerance to commensal bacteria. 2. Mucosal Barrier (with mucus and tight junctions: The physical barrier and the mucus layer traps pathogens and prevent entry. 3. Microbiota: Competes with pathogens for nutrients and attachment sites, produces antimicrobial substances, and stimulates immune responses. 4. Paneth Cells: Located in the crypts of the colon, they secrete antimicrobial peptides such as defensins and lysozyme that destroy pathogens. 5. M Cells: Specialized epithelial cells that transport antigens from the lumen to underlying immune cells in the GALT. 6. Dendritic Cells: Capture and present antigens to T cells in the GALT, promoting adaptive immune responses.
- 22. COMPOSITION OF FAECES Water: approximately 75% Solid waster: 25%. • Undigested fiber and solidified components of digestive juices (30%) • Bacteria (30%) • Fat (10% to 20%) • Inorganic matter (10% to 20%) • Protein (2% to 3%) Colour: •Determine by bilirubin: •acholic: in bile duct obstruction.
- 23. ODOUR Largely influenced by the foods eaten Spices increase the bad odour. Also due to bacterial action releasing odoriferous products: Examples of Odoriferous products •Indole •Skatole •Mercaptans •hydrogen sulfide
- 24. CONSTIPATION
- 25. CONSTIPATION • Pathological decrease in bowel movements • Normal frequency of defecation: Every 2 – 3 days. • Daily but less than 3X. • Breastfeeding children can take to one week. • Symptoms: bloating sensation, anorexia, abdominal distension. Causes: •Medication: opiods •Decrease in fibre and water intake. •Colon tumours or masses •Neuropathies.
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