Role of kidneys in fluid regulation Flashcards
what are the roles of the kidney in homeostasis
- role of kidney in volume regulation
- fluid balance
- electrolyte balance - control of acid base balance by kidneys
define fluid balance
the amount of water gained by the body each day equals the amount lost
what is electrolyte balance
the ion gan each day equals ion loss
what is acid base balance
h+ gain is offset by H+ loss
what does the renal system integrate with to maintain homeostasis
cardiovascular system and respiratory system
describe the actions of antidiuretic hormone
- interacts with V2 receptors on basolateral surface of principal cells in collecting duct of tubule
- results in increased permeability of collecting duct to h2o by insertion of AQP2 water channels on apical surface
- maximal ADH leads to production of low amounts of concentrated urine
what is adh released in response to
released in response to changes in plasma osmolality and effective circulating volume
- these changes are detected by osmoreceptors and baroreceptors
describe the volume regulation by ADH during dehydration
- increased plasma osmolality stimulates osmoreceptors in the hypothalamus which trigger ADH release
- so, more water reabsorbed from collecting ducts in kidney back into circulation
- this leads to increased effective circulating volume - increased osmolality also stimulates a second group of osmoreceptors in the hypothalamus which trigger thirst
- promotes water intake which enters circulation
- this also increases ECV
describe the role of plasma osmolality in volume regulation
- sensors= osmoreceptors
- efferent pathways= ADH and thirst
- effector= kidney and brain
- what is affected= renal excretion of water and water intake
describe the effectors and sensors in effective circulating volume
- sensors= baroreceptors
- efferent pathways= ADH, RAAS, ANP, sympathetic NS
- effector= short term: heart and blood vessels, long term: kidney
- what is affected= short term: blood pressure, long term: na+ excretion
what are baroreceptors
central vascular sensors that detect changes in ECV
- low pressure blood volume receptors- large systemic veins
- cardiac atria
- pulmonary vasculature - high pressure atrial stretch receptors- carotid sinus
- aortic arch
- renal afferent arteriole - sensors in the CNS and liver
describe the control of ECV
- Feedback control of ECV exists- mediated by baroreceptor stimulation
- changes in ECV trigger 4 parallel effector pathways which act on kidney: RAAS, sympathetic NS, ADH release and ANP release
- together these change renal haemodynamics and na+ transport by renal tubule cells
- ECV regulation= na+ regulation
describe the renin angiotensin aldosterone system
- principal factor controlling plasma ANG II levels is renin release from the JGA
- decreased ECV stimulates renin release via:
- decreased renal perfusion pressure detected in the afferent arteriole (renal baroreceptor)
- decreased na+ conc in distal tubule detected by macula densa cells (renal Na+ sensor)
- decreased systemic blood pressure also triggers effects of sympathetic NS supplying the JGA
what are all of the actions of AngII designed to do
all the actions of AngII are designed to increase ECV
what are the important actions of AngII
- enhances tubular na+ transport in the kidney- this promotes na+ and water reabsorption from the tubule
- stimulation of aldosterone release from adrenal cortex- so more na+ and water is reabsorbed from distal tubule/collecting duct
- acts on the hypothalamus to stimulate thirst and ADH release into circulation
- water intake adds to ECV
- ADH increases water reabsorption from collecting duct - vasoconstriction of renal `and other systemic vessels- so systemic blood pressure increases
- causes renal cell hypertrophy- so more protein synthesis of Na+ transporters and channels
what are all of the actions of aldosterone designed to do
designed to increase ECV ( in collaboration with AngII)
what are the important actions of aldosterone
- stimulates na+ reabsorption in the distal tubule and collecting duct
- also exerts indirect negative feedback on the RAAS by increasing ECV and lowering plasma k+ concs
- important in conserving na+ and water but also important in preventing large variation in plasma K+ levels by causing its excretion out of kidney
describe the volume regulation pathway of RAAS
- lower ECV
- detected by renal baroreceptors and renal na+ sensors
- activation of the RAAS
- angiotensin II and aldosterone release
- reduced Na+ excretion by the kidney and increased renal na+ reabsorption
- higher ECV
describe the volume regulation pathway of the ANS
- low ECV
- detected by peripheral baroreceptors
- signals to hypothalamus in brain
- activation of the autonomic (sympathetic) NS
- direct effects on renal haemodynamics and activation of the RAAS
- reduced Na+ excretion by kidney and increased renal na+ reabsorption
- increasing ECV
describe the volume regulation pathway of ADH
- low ECV
- detected by peripheral baroreceptors
- signals to hypothalamus in brain
- release of ADH into circulation
- increased water reabsorption in kidney
- increased ECV
or - low ECV= high plasma osmolality
- detected by osmoreceptors in hypothalamus
- release of ADH into circulation
- increased water reabsorption in kidney
- increased ECV
what is the role of atrial natriuretic peptide (ANP)
all designed to lower ECV
describe how ANP lowers ECV
- atrial myocytes synthesise and store ANP
- increased ECV causes atrial stretch which leads to ANP release into circulation
- ANP promotes natriuresis (increases na+ excretion from kidney)
- also causes vasodilation so increases blood flow, leading to increase in GFR
- so more na+ excreted - more na+ reaches the macula densa so renin release by JGA is reduced
- reduces effects of AngII - overall effect= inhibits actions of renin and opposes effects of AngII
what feedback system is the renal system involved in
renal system interacts with cardiovascular system to provide volume balance
