renal sodium and water regulation Flashcards
describe fluid compartments of the body
- water makes up 60% of males lean body weights
- water makes up 55% of females weight
- 2/3 intracellular; 1/3 extracellular
describe fluid percentage of plasma and interstitial fluid
- 7%= plasma fluid
- 28 % = interstitial fluid
describe factors causing water gain and water loss
-water gain= liquids, food ingestion, metabolically produced
- water loss= insensible loss (evaporation from skin/ lungs) ,sweat, faeces and urine
describe factors causing sodium chloride gain and loss
- gain= food
- loss= sweat, faeces, gastrointestinal tract, urine
how is sodium regulated?
- sodium actively reabsorbed in all tubules expect descending LOH and collecting duct
how is water regulated? what is it dependent on?
- occurs through diffusion
- dependent on Na levels
how does water move ?
- through aquaporin channel’s
- none in collecting duct
where does water change detection occur?
- in neurons in hypothalamus
describe what happens when high plasma osmolarity is detected
- sensation of thirst and ADH release
- fluid intake and increased water reabsorption
- water is gained
describe what happens when low plasma osmolarity is detected
- thirst and ADH release decrease
- decrease in water reabsorption
- water lost
what is ECF volume?
- extracellular fluid
- amount of fluid that is outside of the cells in the body
when does ECF volume decrease?
- reabsorb more sodium, thirst and ADH retains water
when does ECF volume increase?
- reabsorb less sodium and water reabsorption decreases
how is changes in sodium content signalled? what is sodium balance linked to?
- signalled by changes in ECF volume that perfuses our tissues
- linked to blood pressure and volume
describe sodium reabsorption
- active process achieved by Na+/ K+- ATPase pump (keeps Na levels low to allow downhill movement from lumen)
- mechanisms of Na+ movement across luminal membrane varies between tubules
when is Na+/k+ always used?
- for basolateral membrane
describe different transport in proximal tubule and cortical collecting duct
- PT= co- transport of organic molecules e.g. glucose, amino acids
- cortical CD= Na+ channels
describe the coupling of water reabsorption and sodium reabsorption
- Na reabsorption creates an osmotic difference> drives water reabsorption
- H20 moves through epithelial cells and into interstitial fluid
what does anti- diuretic hormone indicate?
-cascade of events within the cells that leads to an increased number of AQP2 channels in luminal membrane
- allows increased passive diffusion of H20 into cells
where does water exit? what are these not sensitive to compared to ADH?
- exits through AQP3
- not sensitive to vasopressin
describe aquaporins
- water channels that are activated and moved towards the cell wall to transport water out tubules+ back into body
- operate in collecting ducts
what stimulates the aquaporin channels?
- anti - diuretic hormone (vasopressin) stimulates them
what system does ADH use and what for?
- cAMP systems to cause insertion of aquaporins into membranes of cells of collecting duct
what does insertion of aquaporins in membrane of cells in CD cause?
- outflow of water out of collecting ducts to be reabsorbed
where does regulation of ADH release occur?
- posterior pituitary gland
- receives signals from baroreceptors and osmoreceptors
why is absorption control more important than GFR?
- more important for long term regulation of Na+ excretion
what 3 factors determine the rate of tubular Na+ reabsorption?
- aldosterone
- atrial natriuretic peptide
- local effect of bp on tubules
how does aldosterone and renin- angiotensin system start?
- release of renin converts peptide angiotensinogen to angiotensin 1
what happens to the angiotensin 1?
- converted to angiotensin II by angiotensin converting enzyme
- enzyme acts on adrenal glands, kidneys and brains (target cells)
what happens due to angiotensin converting enzyme?
- activation of receptors in adrenal gland stimulates aldosterone release
- increases Na+ and H20 reabsorption
- decrease in plasma volume ^ Na+ reabsorption
what is ANP and where is it synthesised and released?
- atrial natriuretic peptide
- synthesised in heart
- released by atrial myocytes
when is ANP released and what does an increase in ANP circulation cause?
- released in response to atria stretching when circulatory blood volume increases
- it works to increase Na+ excretion
what does regulation of bodily fluid osmolarity require?
- separation of water excretion from Na+ excretion
- allowed via osmoreceptors and ADH dependent water reabsorption without Na+ reabsorption into CDs
what role does renal system play in regulating bp?
- sodium and water key in regulating bp
describe local effects of blood pressure on tubules
- baroreceptors regulate blood pressure simultaneously regulating total body sodium
what is GFR affected by?
- volume of surface available
- filtration membrane permeability
- NFP (net filtration pressure)
- blood flow to glomerular capillaries
what is GFR directly proportion to? what does this mean?
- proportional to NFP
- increase in systemic blood pressure increases GFR
describe inputs controlling thirst- how are deficits compensated ?
- kidneys cannot create new Na+ or H20 so deficits must eventually be compensated by ingestion
what are diuretics? state an example
- promotes loss of Na+ H20
- can be used to control BP
- alcohol inhibits the release of vasopressin
what are osmotic diuretic
- carbs that are filtered but not reabsorbed
what are loop diuretics?
- most powerful as they inhibit the formation of medullar gradient through inhibiting Na+ reabsorption
what are hydrochlorothiazide diuretics?
- acts on distal collecting duct
what are spironolactone diuretics?
- example of an aldosterone receptor antagonist
- K+ in urine is from aldosterone- driven active tubular secretion into DCT and collecting duct
what happens to renal blood as exercise intensity increases?
- as exercise intensity increases renal blood flow decreases
when is GFR only affected?
- at exercise intensities above 50% of V02 max
what system is used during exercise and what does this cause?
- sympathetic to vasoconstrict renal arterioles and hence reduce blood flow
what else reduces renal blood flow during exercise?
- increase ADH release due to renin- angiotensin- aldosterone system
what do kidneys do during exercise?
- kidneys have higher workload to buffer hydrogen ions
- remove 2% lactate produced
how do kidneys maintain pH during exercise?
- loss of excess H+ in urine
- lactate removed
how do kidneys conserve water?
- through anti- diuretic hormone and Na+ reabsorption
- fluid regulatory hormones
what do kidneys excrete post exercise?
- excrete metabolites e.g. creatine for muscle breakdown
what is rhabdomyolysis?
- condition where skeletal muscle cell damage can cause acute renal failure and sometimes death
what increases the risk of rhabdomyolysis ?
- heat stress and dehydration
