Lecture 60

Question 1

What is enterosystemic fluid cycle

Answer 1

The net movement of fluid into & out of the intestinal lumen

Question 2

Why is it very important to reabsorb secretions delivered to the proximal part of the SI

Answer 2

B/c secretory fluids from the accessory organs, stomach, & intestines make up a substantial fraction of ECF volume

Question 3

T/F: Herbivores have a larger vole of secretion than carnivores

Answer 3

T

Question 4

Where are the major reabsorptive sites for enterosystemic fluid

Answer 4

The distal SI & LI

Question 5

_____ lines the intestinal crypts & secretes fluid and electorlytes

Answer 5

Epithelial cells

Question 6

Why do apical membranes have Cl- channels

Answer 6

B/c Na follow Cl into the lumen which will cause water to follow Na into the membrane

Question 7

What transporters for intestinal secretions is found on the basolateral membrane

Answer 7

Na/KATPase
Na/K/2Cl cotransporters

Question 8

What causes Cl channels to open

Answer 8

Hormones & neurotransmitters binding to the basolateral membrane

Question 9

What does cholera do to the Cl channels & what does this cause

Answer 9

Cl channels stay open
The body loses a lot of Na, Cl, & H2O & it is very hard to reabsorb what has been lost

Question 10

What are the routes fluid & electrolytes can take for absorption

Answer 10

Transcellular routes
Paracellular routes

Question 11

What determines the routh fluids & electrolytes will take during absorption

Answer 11

The permeability of the tight junctions between the enterocytes

Question 12

What happens if the junctions are tight & where are tight junctions found

Answer 12

Makes it hard to travel paracellular so fluid & ions move transcellulary
Found in the stomach & colon

Question 13

What happens if the junctions are leaky & where are leaky junctions found

Answer 13

Ions & water move via paracellular routes
Found in the duodenum & jejunum

Question 14

T/F: The fluid that is absorbed is NEVER isosmotic

Answer 14

F

Question 15

What part does the jejunum play in absorption

Answer 15

• Is the major site for Na absorption
• Absorption occurs via Na dependent cotransporters in the enterocytes of apical membranes
• Monosaccharides, amino acids, & H+ exchange use the Na gradient
• After entering the enterocyte Na enters the blood via the Na/K pump

Question 16

What part does the Ileum play in abosrption

Answer 16

• Absorbs Na
• Cl/HCO3 exchange occurs in the enterocytes of the apical membrane
• There are Cl transporters in the enterocytes of the basolateral membrane
• Overal there is a net absorption of NaCl

Question 17

What part does the colon play in absorption

Answer 17

There is Na & K channels in the apical membrane
Synthesis of Na channels can occur b/c of aldosteron here

Question 18

What happens if aldosterone synthesizes Na channels

Answer 18

There is an increase in Na absorption & an increase in K secretion

Question 19

Why is aldosterone important in herbivores

Answer 19

Causes an increase in K secretion
K is high in plants so excess K needs to be moved out

Question 20

What happens to K during diarrhea & why

Answer 20

Increase in the loss of K
b/c of increased flow rates of the intestinal fluid

Question 21

What happens if there is a loss of large volumes of ECF type fluid from the GIT

Answer 21

Decreased ECF volume
Decrease intravascular volume
Decreased arterial pressure (which causes baroreceptor activation to restore BP)

Question 22

What are some issues or losses associated with severe diarrhea

Answer 22

Circulatory collapse
High HCO3 losses are relative to Cl loses which can leads to hyperchloremic metabolic acidosis w/ a normal anion gap
High K losses that lead to hypokalemia b/c K is lost from the ECF

Question 23

What happens when there is hyperchloremic metabolic acidosis w/ a normal anion gap

Answer 23

Loss of bicarb for the GIT signals the kidneys to reabsorb NaCl (b/c NaCl is lost when bicarb is lost)
This is activated by the RAAS system (stimulates Na/H exchangers)
Causes the kidneys to excrete more acid

Question 24

What is a main cause of diarrhea

Answer 24

Decreased surface are for absorption due to infections or inflammation of the SI

Question 25

What causes osmotic diarrhea

Answer 25

Non absorbable solutes cause water retention in the SI lumen which lead to a decrease in SA

Question 26

What causes secretory diarrhea

Answer 26

Excessive amounts os fluid being secreted by the crypt cells
Adenylyl cyclase has been permanently activated & cAMP levels are high