Body Fluid Compartments and Water Balance: MET Flashcards
what should water balance be like in a healthy person?
0 ! inputs should = outputs
why is water needed in the digestive system? (5)
- hydrolysis
- facilitates absorption (brings products of digestion closer to proximity of microvilli)
-
propulsion of gut contents
- water moves nutrients, hormones, antibodies and oxygen through the blood steam and lymphatic system - used in process of mucus production
5. proteins and enzymes in our cells function more efficiently at low viscosity solutions
which cells regulate water contents in the gut?
what is the mechanism of this?
secretory cells of the intestinal crpyts:
- CFTR channel within these cells controls this:
a) Cl- moves from ECF via Na/K/CL2 cotransporter (as does Na & K)
b) Cl- enters lumen through CFTR channel
c) Na+ is reabsorbed via Na/K ATPase
d) negative Cl- in lumen attracts Na by paracellular pathway (through cell gaps)
* *e) water follows the Na into the lumen**
differences between ECF and ICF?
ICF vs ECF
ICF
- very little Na+.
- Lots of K+ and PO43- (buffers acid / base situation)
- Lots of protein anions (think - sea with Na+ is ECF, banana tree: ICF).
ECF
- high Na+ and Cl-
- little K+
which 3 regulatory systems regulate body fluid?
1. CNS (hypothalamus - has osmoreceptors)
2. Hormones
- ADH: makes cells of CD & DT more permeable to water
- Angiotension II & Aldosterone: promotes urinary absorbtion of Na & Cl (and therefore water), when dehydrated)
- ANP (promotes exctetion of Na+ and Cl- to decrease BV)
3. Kidneys
explain the MoA of when thirst occurs - from
1. increase in plasma osmolality: (less water in plasma. solutes are concetrated)
a) decrease in saliva = dry mouth -> feedback into hypothalamus thirst center
b) osmoreceptors in hypothalamus -> feedback into hypothalamus thirst center
@ the hypothalamus thirst centre:
a) sensation of thirst -> decide to drink -> water moistens mouth / throat -> water absorbed in GI tract = decrease in plasma osmolality
2. Plasma volume decreases (less efficient feedback)
a) causes blood pressure to decrease -> feedback into hypothalamus thirst center. also triggers the renin-angiotensin mechanism.
similarity / differences between interstitial fluid and blood plasma?
Interstitial fluid & Plasma:
- same: electrolyte components (i.e. lots of K+, PO43-)
- differences: plasma as proteins like albumin and anions. IF does not !
describe mechanism of aldosterone working
(where made? released from? what does it cause to do? result?)
aldosterone:
released from: adrenal cortex
released when: reduced Na+ or increased K+
function: increases reabsorbtion of Na or increased K secretion
result: homeostatic plasma levels of Na+ and K+.
what is cellular mechanism of ADH binding to cell?
ADH binds to receptor on cell
- changes transcriptional activity of nucleus
- more aquaporin made & transported to membrane
- more water goes into cell via aquaporin from filtrate of urine
- water goes from cell into blood
how does atrial natruiretic peptide work? released from? releaed when?
Atrial natriuretic peptide (ANP)
released from: cardiac Atria
released when: increased blood volume (stretches atria)
function: promotes excretion of Na+ and Cl-, in turn decreases water reabsorbtion (brings blood volume back towards normal)(acts on hypothalamus and adrenal cortex up the mechanism.)
how does aldosterone make kidney cells recapture sodium?
- aldosterone binds to kidney cells
- causes to produce more
a) ENAC (Na channel) - can reabsorb more Na
b) Na/K pump ( pumps Na in / K out)
what can cause dehydration (2)
which population groups are more at risk of dehydration?
dehydation:
1. ICF and ECF long term water loss:
- lead to: weight loss, fever & confusion (neurons dont work well)
OR
2. Excess urine production
- occurs in both forms of diabetes
population: young people (not fully developed kidneys) and very old (decline of kidney function)
which bacterial dieasee is an acute diarrhoeal disease?
what can 80% of cases be treated successfully with?
what do severe cases need?
what can u add to water to kill off the bacteria?
Cholera - caused by Vibrio cholerae.
- -* 80% can be treated successfully with oral rehydration solution
- severe cases need IV fluids and antibiotics
- can treat water with chlorine / boil water
what type of bacteria is vibrio cholera?
gram negative comma shaped
how does cholera effect the secretory cells of the crypts?
- Vibrio cholerae releases toxins: has a Part A & Part B
- Part A incorporated into cell. binds to **adenylate cyclase, which in turn makes more cAMP
- too much cAMPtriggers CFTR to be constantly open AND blocks Na/CL symporter (so lots of Cl- is leaving cell and is not being reimbursed)
_- Cl leaves cell into gut = water follows
= secretory diarrhoea**_
what is MoA for when ORS treats cholera?
ORS MoA:
- ORS has Na, glucose and AA in it.
- Na & Gluocse transporters are still working with cholera
- Na prefers to be in ECF: leaves crpyt secretory cells
- pumped out via Na/K ATPase into ECF
- water follows = save water
how does lactose / sugar malbsorption cause diarrhoea?
- lactose has high osmotic power = attracts water into colon
- sugars = fermentation occurs on lactose - C02 & H2 released - bloating
what is hyperglycemia - why is it bad? explain the mechanism
hyperglycemia = high blood glucose
why bad?
- plasma and interstitial fluid is baso at equilibrium
- so high blood glucse = high interstitial glucose
- ECF Na & new glucose has high osmotic power = draws water from ICF (the cell) via aquaporins
- the water dilutes the Na & bit of glucose = hyponatraemia :( (low serum Na)
- kidneys: reabsorb Na BUT if too much glucose = excreted in urine.
- gluocose in urine has osmotic draw -> get osmotic diursesis bc water follows the glucose
= server water loss !
