salt and water balance Flashcards
describe the structure of the colon:
- epithelium is flat with no villi
- contains crypts extending deep into the epithelium
- many mucus secreting goblet cells throughout epithelium
what is a benefit of having deep crypts ?
- can act as capillaries to suck water out of feces
- more water is absorbed
what is a benefit of having goblet cells throughout the epithelium ?
eases passage of feces
what does water absorption in the crypts cause ?
capillary suction pressure
how does capillary suction work?
capillary action of crypts causes suction
this helps remove water from feces
Na + H20 absorbed
how much water does a normal stool contain ?
65-85% of water
how much water is in diarrhea ?
> 85%
how much bacteria is found within stools ?
40-50% of solid matter
what pH is a stool ?
what gives it this characteristic ?
5-6 / acidic
short chain fatty acid production
what is an example of materials found in stools ?
- sloughed enterocytes
- bile salts
- electrolytes
what is the absorption of water powered by ?
powered by the absorption of ions
mainly Na
where is the greatest amount of water absorbed ?
small intestine - jejunum
how are ions absorbed ?
most diffuse slowly through passive diffusion
calcium + iron are incompletely absorbed so are regulated
what are the 2 types of water transport in cells ?
how do they occur ?
- paracellular
occur via tight junctions between cells - transcellular
across cell membranes via aquaporins
what is standing gradient osmosis ?
what is it driven by ?
term used to describe the reabsorption of water against osmotic gradient at the colon
Na
how does transport of Na vary in the small intestine ?
in small intestine Na is :
- counter transported in exchange for H+
- co-transported with amino acids + monosaccharides
- co- transported with Cl
how is Na transported in the colon ?
- restricted movement through ion channels
- Cl is counter transported with HCO3 due to electrical potential created by Na transport
what happens to intracellular sodium ?
actively transported into intercellular space by Na/K ATPase transport in plasma membrane
what causes the fluid to be hypertonic ?
high conc of ions in the intercellular space
how is hydrostatic pressure increased ?
increased by water as it distends the intracellular channels
list 3 types of colonic disorders :
- diarrhea
- constipation
- irritable bowel syndrome
what are the 3 types of diarrhoea ?
- congenital diarrhoea
- bacterial infection of the gut
- osmotic diarrhoea
what is constipation due to ?
slow movement of faeces
causes too much water to be absorbed
= hard faeces
what is irritable bowel syndrome ?
combination of diarrhoea + constipation
causes abdominal pain
what happens to the osmotic gradient in osmotic diarrhoea ?
it is reversed
>350 mosmoles being reabsorbed
what happens in congenital diarrhoea
Cl/HCO3 exchange is lacking
what happens in bacterial induced diarrhoea ?
enhanced secretion of electrolytes + water
what happens in osmotic diarrhoea ?
- failure to absorb nonelectrolytes
- there is a hypermotility of intestine = rapid flow of intestinal contents passing the absorptive epithelium
where is most of the bacteria found in the GI tract ?
large intestine
where does the microbiome come from ?
- breast feeding
- diet
- exercise
- disease
- drugs
- ageing
what are the benefits of a microbiome ?
- help extract energy from food
- produce essential vitamins
- regulate immune system
- regulate glucose + metabolism levels
what has gut bacteria been linked to ?
- insulin resistance
- lipid metabolism
- obesity - gut bacteria contribute to it
