NME 2.23 Flashcards
describe the functional microanatomy of large intestine?
- mostly absorptive epithelial
- in the crypts are mostly secretory
- stem cells for regeneration
- more goblet cells in the colon than small intestine
what is the mucus for?
- lubrication
describe fluid secretion in the colon?
- secrete very little fluid
- secrete bicarbonate in faeces
- enhanced secretion will cause loss of potassium and bicarbonate
- cause acidosis
- lack of potassium
describe the fluid secretion in the small intestine?
- bicarbonate is secreted
- sodium, chloride, potassium and water is absorbed
describe absorption and secretion of sodium in the duodenum and jejunum?
- sodium will be absorbed
- water will be absorbed
- the sodium gradient will draw amino acids into the cells
how is the sodium gradient attained in duodenum and jejunum?
- sodium potassium pump
describe absorption and secretion of sodium in the ileum and proximal colon?
- sodium is absorbed through sodium hydrogen exchanger
- bicarbonate is pumped out
- chloride will follow bicarbonate cause bicarbonate secretion
- sodium absorption and water will follow
describe the absorption and secretion of sodium in distal colon?
- sodium concentration is kept low inside cell
- sodium concentration is controlled by sodium potassium pump
- sodium will be absorbed
describe absorption and secretion of chloride?
- paracellular will draw chloride
- chloride will follow sodium movements
- bicarbonate is secreted at the ileum, proximal and distal colon
- build up of chloride concentration inside the cell
- then when concentration is high enough leave using channel as chloride flow into lumen
- as chloride move will draw sodium to move togther
- sodium will draw water movement into the lumen
what is the secretory pathway follow?
chloride movement
what is the absorptive pathway driven by?
sodium movement
describe the absorption and secretion of potassium at proximal and distal colon?
- secreted at paracellular
- chloride is absorbed at basolateral therefore sodium and potassium will follow
- sodium and potassium are recycled
describe the absorption and secretion of potassium at distal colon?
- potassium is absorbed as hydrogen ions is secreted into lumen
describe control of intestinla fluid through enteric nervous system?
- secretagogues increase calcium concentration or cAMP to increase chloride transport cause increase in secretion and decrease in absorption
- enkephalins and norepinephrine will cause decrease in calcium concentration and increase NaCl absorption and water will follow which cause drying out of faeces
how does angiotensin II help with control of intestinal fluid?
- increase absorption of sodium through apical sodium hydrogen exchange
how does aldosterone help with control of intestinal fluid?
- increase in sodium absorption through ENaC and sodium/potassium ATPase
how does somatostatin help with control of intestinal fluid?
- increase in sodium absorption through increase calcium concentration
- increase NaCl absorption
how does guanylin help with control of intestinal fluid?
- secreted by cells
- stimulate chloride secretion
- binds to receptors that bacteria or pathogens bind to
how does inflammatory mediators help with control of intestinal fluid?
- NF-KB make the paracellular route across epithelia more permeable allowing fluid to pass into the lumen of the intestine
how does prostaglandin secretion help with control of intestinal fluid?
- stimulate chloride secretion by increasing cAMP
how does antigens help with control of intestinal fluid?
- act on immune cells
- histamine released will cause increase chloride secretion through enteric nervous system
how does bacterial toxins affect intestinal fluid?
- cause secretory diarrhoea
- activation of adenylate cyclase
- activation of guanylate cyclase
- opening tight junctions
how does cholera affect intestinal fluid
- endocytosis of toxin receptor complex
- activates adenylate cyclase
- increase cyclic AMP
- activation of protein kinase A
- PKA phosphorylate proteins and opens CFTR
- increase chloride secretion
what does neurotransmitters do to affect control of intestinal fluid?
- activate adenylate cyclse and cause chloride to be secreted
what does histamine do to affect control of intestinal fluid?
- activate adenylate cyclase and increase chloride secretion
what does pathological alterations do to affect control of intestinal fluid?
- nutrient malabsorption which cause osmotic diarrhoea
- intestinal hypermotility
- congenital chloride diarrhoea through chloride malabsorption
- pancreatic cholera will cause decrease in absorption and cause secretory diarrhoea
what three pharmalogical control of diarrhoea by reducing motility?
- morphine
- opiate
- atropine
what does kaolin do to control diarrhoea?
- absorbents
what three pharmalogical control of diarrhoea by inhibiting secretion?
- opiates
- non-steriodal anti inflammatory agents
- antibiotic and pro-biotic therapy
