L26 Absorption And Secretion

Question 1

What are three types of control of GI actions and secretions?

Answer 1

Hormonal, paracrine and neurocrine control.

Question 2

How many L of fluid is handle by the GI per day and what happens to them?

Answer 2

> 9L per day, most are absorbed in the SI and the remaining fluid is lost.

Question 3

How is the ECF vol regulated in the GI?

Answer 3

Adjustment of total body NaCl.

Question 4

How is the Na+ content maintained in steady state?

Answer 4

Na+ intake by GI tract = Na+ output by renal (and other) pathways

Question 5

What are the three main functions of the stomach?

Answer 5

1. Secretion
2. Motor - regulates food intake
3. Humoral - gastrin activity

Question 6

What are the distal secretions of the stomach?

Answer 6

1. Gastrin
2. Somatostatin
3. Pepsinogens

Question 7

What are the proximal secretions of the stomach?

Answer 7

1. HCl
2. Pepsinogens
3. Intrinsic factor
4. Mucins/HCO ions.

Question 8

What amounts of secretion is done by the stomach per day?

Answer 8

> 2l per day.

Question 9

Name the oxyntic glands and what they secrete?

Answer 9

1. Epithelial cells - HCO3
2. Mucous neck cells - Mucus
3. Parietal cells - HCl, intrinsic factors
4. Enterochromaffin-like cells histamine
5. Chief cells - pepsinogens
6. Enterochromaffin cells – serotonin, VIP, substance P.
7. D cells – somatostatin (H)

Question 10

What does G cells secrete?

Answer 10

Gastrin hormone

Question 11

What is the secretions and functions of parietal cells?

Answer 11

HCl which denatures proteins, activated pepsinogen and inhibits pathogens

Question 12

What is the structure of parietal cells in resting phase?

Answer 12

1. Cytoplasmic pool of tubulovesicular membrane on apical side
2. Contains acid secreting H,K-ATPase

Question 13

What are the cytoskeletal changes caused by stimulation of parietal cells?

Answer 13

1. Fusion of tubulovesicular and canalicular membranes.
2. 50-100x increase in surface area
3. Microvilli appearance
4. insertion of H,K-ATPase pump, K+ + Cl- channels

Question 14

What is the mechanism of gastric acid secretion in parietal cells?

Answer 14

1. H2CO3 in dissociated
2. H+ will be sectreted across the apical membrane through H+-K+ ATPase.(Cl- follows)
3. Bicarbonate ion is absorbed into the blood via Cl - HCO3 exchanger.
4. Secretion of HCl and absorption of HCO3 occurs.
5. K is recycled into lumen by K channels.

Question 15

How does regulation of HCl secretion occur?

Answer 15

1. Stimulation of H+ secretion: histamine, Ach and Gastrin
2. Inhibition : leading to low pH and secretion of somatostatin and prostaglandins. (Check)

Question 16

What are the key electrolytes that the SI and LI need to absorb?

Answer 16

Na+, K+, Cl-, HCO3-

Question 17

What are the primary sites for absorption of Na+, Cl-, K+ and HCO3-?

Answer 17

Duodenum and jejunum

Question 18

What do the crypt epithelial cells do?

Answer 18

They secrete fluid and electrolytes

Question 19

Do SI me LI have similar structures?

Question 20

What seperates the apical and basolateral membranes in polar cells? (Check)

Answer 20

Misnomer not tight junction

Question 21

How do both SI and LI absorb + secret solutes?

Answer 21

Via active and passive mechanisms.

Transcellular movement is usually active
Paracellular movement is generally passive

Question 22

How are ions transported into the cell from the blood in the intestines?

Answer 22

Na+K+Cl- cotransporter

Question 23

Something to do with Chlorine (up regulation of ATP)

Question 24

How is water secreted into the lumen of the intestines?

Answer 24

Na+ follows Cl- secretion passively (paracellularly) - water drawn following the movement of NaCl

Question 25

Cellular transport in jejunum

Question 26

What is the extra addition of cellular transport in ileum compared to the jejunum?

Question 27

Understand the sodium ions concentration gradient and the set up in the jejunum