Hormonal control of the kidney Flashcards
What us the % of sodium reabsorbed in:
a) The PCT
b) Thick ascending limb
c) DCT
d) Top of collecting duct
e) bottom of collecting duct
a) PCT: 60-70% reabsorbed
b) TAL: 25% reabsorbed
c) DCT: 6% reabsorbed
d) T CD: 2% reabsorbed
e) B CD: <1% reabsorbed
What does RAAS stand for?
Renin-Angiotensin-Aldosterone-System
What is renin?
Renin is an enzyme contained within specialised smooth muscle cells in the walls of afferent and efferent arterioles
How is renin stimulated? (3)
> Reduced perfusion pressure in the afferent arteriole
Increased sympathetic nerve activity in fibres innervating efferent and efferent arterioles
Decreased Na+ concentration flowing through DCT
What is the role of a renal baroreceptor?
Decrease renal perfusion (pressure in vessels sensed by renin-secreting cells) leading to increased renin release
What is the role of a catecholamines?
Beta-adrenoreceptor stimulation leads to increased renin release
What is the role of macula densa mechanisms?
Sense a decrease in Na+ delivery to distal tubule, ;ending to increased renin release
How does renin effect the function of blood volume and pressure? (8)
- Angiotensinogen + Renin
- Angiotensin 1
- Angiontensin 2
- Adrenal gland
- Aldosterone
- Increased Na+ and H2O reabsorption in distal tubes
- Homeostasis blood pressure volume (low vol or high pressure)
- Change will occur
What is angiotensin 2 and what does it stimulate (2)?
Angiotensin 2 increases blood pressure by constricting arterioles
- Stimulates reabsorption of Na+
- Stimulates the release of the hormone aldosterone from the adrenal gland, acts of DCT to increase Na+ and H2O reabsorption. Blood vol. and pressure increase
What is aldosterone?
Steroid hormone released from zona glomerulosa of adrenal cortex
What is the function of aldosterone? (2)
- Increases in plasma K+ and angiotensin 2 or decreases in plasma Na+ lead to elevated levels of aldosterone
- Acts via intracellular receptors in the DCT to increase Na+ channels - water follows
What are the consequences of aldosterone? (3)
Na+ retention
K+ loss
H+ loss
What is the Na+ largely controlled by?
Aldosterone
What happens when there is a decrease in blood pressure in the RAAS? (3)
- Reduced pressure near DCT stimulates release of renin from juxtaglomerular apparatus
- RAAS acts to increase permeability in the collecting duct, increasing blood volume and causing vasoconstriction
- Result is elevation in blood pressure
How does RAAS contribute to aldosterone production? (2)
- Angiotensin 2 causes adrenal gland to secrete aldosterone
- Helps to increase reabsorption of Na+
How does the RAAS contribute to volume sensors?
Renin rebased in response to low body fluid osmolality, low blood volume, low blood pressure
What is the effect of ADH/vasopressin? (2)
- Acts on the DCT to regulate filtrate volume and osmolality
- Changes in osmolality of body fluids are sensed by osmoreceptors in the hypothalamus which trigger release of ADH from stores in posterior pituitary
What senses a decrease in blood volume?
Cardiopulmonary baroreceptors - increase ADH release
How does ADH regulate water loss? (2)
Increase permeability to water in collecting duct
Produces concentrated urine
What is the primary function of ADH?
Regulate extracellular fluid volume by affecting renal handling of water - acts on V2 receptors on renal collecting ducts
What happens when ADh is at high and low levels?
High levels of ADH: More water is reabsorbed and less is excited
Low levels of ADH: Large volume of water are excreted (hydrated)
What are the 2 modes of action from ADH stimulation?
V1 - vasoconstriction - increased arterial pressure
V2 - renal fluid reabsorption - increased blood volume - increased arterial pressure
What is ANP?
Atrial natriuretic peptide - hormone released in response to an increase in blood volume and pressure
Where is ANP released?
Released by cardiac atrial cells when stretched - volume overload
What is the effect of ANP? (4)
> Opposes the RAAS and inhibits the release of renin
Causes Na+ and water loss by inhibiting aldosterone
Increases GFR
Also acts as a vasodilator
What does ANP counteract?
Counteracts the vasoconstrictor actions of sympathetic renal nerves and angiotensin 2
What is the purpose of ANP?
Promotes sodium excretion and water excretion to counteract changes in blood volume and pressure
