T3 L10 Regulation of homeostasis by the kidney: fluid balance Flashcards
What is the role of the kidney in volume regulation?
Fluid balance
Electrolyte balance
What is fluid balance?
The amount of water gained by the body each day equals the amount lost
What is electrolyte balance?
The ion gain each day equals the ion loss
What increases the permeability of the collecting duct?
ADH
What is ADH?
Most important hormone that regulates water balance
Nonapeptide with Mw of over 1000
Known as vasopressin or 8-arginine vasopressin (AVP)
Plasma half life is 10-15 minutes
What does ADH act on?
On V2 receptors on the basal membrane of principal cells in the collecting duct.
This leads to the inserted of AQP 2 into the apical surface
What happens when there is maximal ADH release?
There is the production of low amounts of concentrated urine
When causes ADH to be released?
Changes in plasma osmolality and effective circulating volume
What are changes in plasma osmolality detected by?
Osmoreceptors in hypothalamus
What are changes in effective circulating volume detected by?
Baroreceptors
What happens in dehydration?
1) There is an increase in plasma osmolality
2) Stimulates osmoreceptors in hypothalamus
3) Triggers ADH release
4) More water reabsorbed from collecting ducts back into circulation
5) Increases effective circulating volume
What happens if there is increased osmolality?
Stimulates a group of osmoreceptors in hypothalamus
Triggers thirst
Promotes water intake which enters circulation
Increases effective circulating volume
Describe the efferent pathway affected by plasma osmolality
ADH - effector is the kidney. Causes renal excretion of water
Thirst - effector is the brain. Causes water intake
Where are baroreceptors found?
Carotid sinus
Aortic arch
Renal afferent arteriole
Atria of heart
What are the efferent pathways affected by ECV?
ADH
RAAS
ANP
Sympathetic nervous system
What is the effector for ECV in the short term?
Heart & blood vessels
Affects blood pressure
What is the effector for ECV in the long term?
Kidney
Affects sodium excretion
Where are low pressure blood volume baroreceptors found?
Large systemic veins
Cardiac atria
Pulmonary vasculature
Where are high pressure blood volume baroreceptors found?
Carotid sinus
Aortic arch
Renal afferent arteriole
What is the renal baroreceptor?
The renal afferent arteriole
What is feedback control of ECV mediated by?
Baroreceptor stimulation
What 4 parallel effector pathways are triggered by changes in ECV?
RAAS
Sympathetic nervous system
ADH release
ANP release
What do the 4 parallel effector pathways change when triggered by ECV?
They change renal haemodynamics & sodium transport by renal tubule cells
What is RAAS?
The principal factor controlling plasma Ang II levels is renin release from the juxtaglomerular cells
How does a decreased ECV stimulate renin release?
Decrease renal perfusion pressure detected in the afferent arteriole - renal baroreceptor
Decreased sodium concentration in the distal tubule detected by the macula dense cells
Decreased systemic blood pressure triggers effects of the sympathetic nervous system supplying JGA
What are the important actions of angiotensin II?
All of the actions designed to increase ECV
1) Enhances tubular sodium transport in the kidney
2) Stimulation of aldosterone release from adrenal cortex
3) Acts on hypothalamus to stimulate thirst & ADH release into circulation
4) Vasoconstriction of renal & other systemic vessels
What does the stimulation of aldosterone release from the adrenal cortex lead to?
More sodium & water is reabsorbed from the distal tubule / collecting duct
What does vasoconstriction of renal & other systemic vessels do?
Increase systemic blood pressure
What are the longer term effects of angiotensin II?
Causes renal cell hypertrophy
More protein synthesis of sodium transporters & channels
What are the important actions of aldosterone?
All the actions are designed to increase ECV in collaboration with angiotensin II
Stimulates sodium reabsorption & potassium excretion in distal tubule & collecting duct
Exerts indirect negative feedback on RAAS by increasing ECV & lowering plasma K+ concentration
Important to conserve sodium & water & prevent large variations in plasma K+ levels
What is the volume regulation pathway for RAAS?
1) Decrease in ECV
2) Detected by renal baroreceptors & renal sodium sensors
3) Activation of RAAS - angiotensin II & aldosterone
4) Reduced sodium excretion by kidney
Increased renal sodium reabsorption
5) Increase in ECV
What is the volume regulation pathway for ANS?
1) Decrease in ECV
2) Detected by peripheral baroreceptors
3) Signals to hypothalamus in brain
4) Activation of autonomic sympathetic NS
5) Reduced sodium excretion by kidney
Increased renal sodium reabsorption
6) Increase in ECV
What is the volume regulation pathway for ADH?
1) Decrease in ECV
2) Detected by peripheral baroreceptors
3) Signals to hypothalamus in brain
4) Release of ADH into circulation
5) Increased water consumption in the kidney
6) Increase in ECV
1) Decrease in ECV = increase in plasma osmolality
2) Detected by osmoreceptors in hypothalamus
3) Release of ADH into circulation
4) Increased water reabsorption in the kidney
5) Increase in ECV
What are the actions of ANP?
All actions designed to lower ECV
Atrial myocytes synthesis & store ANP
Increased ECV causes atrial stretch leading to ANP release into circulation
ANP promotes natriuresis
Renal vasodilation –> increased blood flow –> increase in GFR -> more Na+ excreted
More Na+ reaches macula dense –> renin release by JGA is reduced –> reduces effect of Any II
Overall effect is to inhibit the actions of renin & oppose effects of Ang II
