salt and water balance

Question 1

describe the structure of the colon:

Answer 1

• epithelium is flat with no villi
• contains crypts extending deep into the epithelium
• many mucus secreting goblet cells throughout epithelium

Question 2

what is a benefit of having deep crypts ?

Answer 2

• can act as capillaries to suck water out of feces

- more water is absorbed

Question 3

what is a benefit of having goblet cells throughout the epithelium ?

Answer 3

eases passage of feces

Question 4

what does water absorption in the crypts cause ?

Answer 4

capillary suction pressure

Question 5

how does capillary suction work?

Answer 5

capillary action of crypts causes suction
this helps remove water from feces
Na + H20 absorbed

Question 6

how much water does a normal stool contain ?

Answer 6

65-85% of water

Question 7

how much water is in diarrhea ?

Answer 7

> 85%

Question 8

how much bacteria is found within stools ?

Answer 8

40-50% of solid matter

Question 9

what pH is a stool ?

what gives it this characteristic ?

Answer 9

5-6 / acidic

short chain fatty acid production

Question 10

what is an example of materials found in stools ?

Answer 10

• sloughed enterocytes
• bile salts
• electrolytes

Question 11

what is the absorption of water powered by ?

Answer 11

powered by the absorption of ions

mainly Na

Question 12

where is the greatest amount of water absorbed ?

Answer 12

small intestine - jejunum

Question 13

how are ions absorbed ?

Answer 13

most diffuse slowly through passive diffusion

calcium + iron are incompletely absorbed so are regulated

Question 14

what are the 2 types of water transport in cells ?

how do they occur ?

Answer 14

• paracellular
  occur via tight junctions between cells
• transcellular
  across cell membranes via aquaporins

Question 15

what is standing gradient osmosis ?

what is it driven by ?

Answer 15

term used to describe the reabsorption of water against osmotic gradient at the colon
Na

Question 16

how does transport of Na vary in the small intestine ?

Answer 16

in small intestine Na is :

• counter transported in exchange for H+
• co-transported with amino acids + monosaccharides
• co- transported with Cl

Question 17

how is Na transported in the colon ?

Answer 17

• restricted movement through ion channels

- Cl is counter transported with HCO3 due to electrical potential created by Na transport

Question 18

what happens to intracellular sodium ?

Answer 18

actively transported into intercellular space by Na/K ATPase transport in plasma membrane

Question 19

what causes the fluid to be hypertonic ?

Answer 19

high conc of ions in the intercellular space

Question 20

how is hydrostatic pressure increased ?

Answer 20

increased by water as it distends the intracellular channels

Question 21

list 3 types of colonic disorders :

Answer 21

• diarrhea
• constipation
• irritable bowel syndrome

Question 22

what are the 3 types of diarrhoea ?

Answer 22

• congenital diarrhoea
• bacterial infection of the gut
• osmotic diarrhoea

Question 23

what is constipation due to ?

Answer 23

slow movement of faeces
causes too much water to be absorbed
= hard faeces

Question 24

what is irritable bowel syndrome ?

Answer 24

combination of diarrhoea + constipation

causes abdominal pain

Question 25

what happens to the osmotic gradient in osmotic diarrhoea ?

Answer 25

it is reversed

>350 mosmoles being reabsorbed

Question 26

what happens in congenital diarrhoea

Answer 26

Cl/HCO3 exchange is lacking

Question 27

what happens in bacterial induced diarrhoea ?

Answer 27

enhanced secretion of electrolytes + water

Question 28

what happens in osmotic diarrhoea ?

Answer 28

• failure to absorb nonelectrolytes

- there is a hypermotility of intestine = rapid flow of intestinal contents passing the absorptive epithelium

Question 29

where is most of the bacteria found in the GI tract ?

Answer 29

large intestine

Question 30

where does the microbiome come from ?

Answer 30

• breast feeding
• diet
• exercise
• disease
• drugs
• ageing

Question 31

what are the benefits of a microbiome ?

Answer 31

• help extract energy from food
• produce essential vitamins
• regulate immune system
• regulate glucose + metabolism levels

Question 32

what has gut bacteria been linked to ?

Answer 32

• insulin resistance
• lipid metabolism
• obesity - gut bacteria contribute to it