Lecture 7: Salt and Water Transport

Question 1

what is electrolyte and water secretion/absorption regulated by

Answer 1

• gut luminal content and osmolarity
• enteric and autonomic signals
• endocrine hormones
• immunogenic signals

Question 2

adaptations of the small intestine

Answer 2

• high SA due to folds and microvilli
• villi lymphatic and blood vessels
• enterocyte actin microfilaments
• rapid response to chyme acidity and water levels
• epithelium more permeable than in large intestine

Question 3

adaptations of the large intestine

Answer 3

• no villi, but surface covered in crypts / intestinal glands
• contains bacterial microbiome with role in protein digestion / vitamin synthesis
• has additional absorptive capacity for NaCl and water in exchange for K+ ions

Question 4

which parts of the GI tract absorb / secrete electrolytes and water

Answer 4

• jejunum absorbs Na+, K+, Cl- and H2O

- ileum secretes HCO3-

Question 5

what are the mechanisms for Na+ absorption in the small intestine

Answer 5

• passive diffusion
• Na / glucose cotransporter
• Na / amino acid cotransporter
• Na / H antiport
• Na / Cl symport

Question 6

what regulates absorption of water and electrolytes

Answer 6

• aldosterone upregulates sodium absorption
• glucocorticoids and somatostatins increase water and salt absorption
• the enteric nervous system is also involved

Question 7

what happens with the cholera toxin

Answer 7

• stimulates Cl- secretion
• leads to massive Na+, Cl- and water efflux
• causes profuse watery secretory diarrhoea
• treated via oral rehydration therapy