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Physiology

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GIT

Question
2 out of 19
 

Max potassium ions present in : (AIIMS MAY 2009)



A Colon
B Jejunal secretions

C Stomach
D Saliva

Ans. D Saliva

Daily Secretion of GIT

Daily Volume

(ml)

pH

Saliva

1000Q

6.0–7.0

Gastric secretion

1500

1.0–3.5

Pancreatic secretion

1000

8.0–8.3Q

Bile

1000

7.8

Small intestine secretion

1800Q

7.5–8.0

Brunner’s gland secretion

200

8.0–8.3

Large intestinal secretion

200

7.5–8.0

Total

6700

a. The concentration of K+ in pancreatic juice is same as plasma i.e. around 4.5 mEq/L Q

b. Liver bile contains 5-6 mEq/L whereas Gall Bladder bile has 12 mEq/L Q

c. In ileum the concentration rises due to exchange of potassium with Na+ (K+ absorption also occurs). It normally is around 10-12 mEq/L.

d. As it reaches rectum the conc. of K+ rises to 75 mEq/L Qdue to colonic secretion of K+.

e. Normal stool K+ excretion is 5-10 mEq a day Qand volume is 100-200 grams.

f. Saliva contains 25-30 mEq/L at low flow rate Q& 15-20 mEq/L at high flow rate

g. So max conc. is seen in stool Q or in colon Q but maximum levels or secretion is seen in saliva Q (since volume secreted is 1.5 L/day Q as compared to 100-200 ml of stool)

SALIVA:

a. Saliva secreted in the acini is probably isotonic, with concentrations of Na+, K+, Cl, and HCO3 that are close to those in plasma.

b. The excretory ducts and probably the intercalated ducts that drain into them modify the composition of the saliva by extracting Na+ and Cl and adding K+ and HCO3.Q

c. The ducts are relatively impermeable to water. Therefore, at low salivary flows, the saliva that reaches the mouth is hypotonic, Q slightly acidicQ, and rich in K+ but relatively depleted of Na+ and Cl.Q When salivary flow is rapid, there is less time for ionic composition to change in the ducts.

d. Consequently, although still hypotonic in humans, saliva is closer to isotonic, with higher concentrations of Na+ and Cl.

COLON:

a. K+ channels are present in the luminal as well as the basolateral membrane of the enterocytes of the colon, so K+ is secreted into the colon.

b. In addition, K+ moves passively down its electrochemical gradient.

c. The accumulation of K+ in the colon is partially offset by H+–K+ ATPase in the luminal membrane of cells in the distal colon, with resulting active transport of K+ into the cells. Nevertheless, loss of ileal or colonic fluids in chronic diarrhea can lead to severe hypokalemia. Q

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