7 - Integration of salt and water balance Flashcards
Ang 2 actions of AT1 and AT2 receptors?
AT1 - aldosterone release - efferent arteriole and peripheral vasoconstriction - thirst - ADH release - prox Na+ reabs AT2 - vasodilation
How does aldosterone cause action
Steroid hormone so enters cell, binds to MR receptor, enters nucleus and influences gene expression to increase ENaC channels and Na/K ATPase to increase Na reabs and K secretion
What stimulates aldosterone secretion
High K+ and ang 2
Spironolactone?
MR anatagonist used to treat essential HT
Mediators of ECF volume?
RAAS and symp
How are changes in ECF volume compensated?
Changes in Na+ reabsorption
Decreased ECF vol is compensated for by increasing renal reabs of Na+
What causes an increase in renal Na+ reabsorption?
- most importantly the renin-ang-aldosterone system
- sympathetic nervous system
- and less importantly ADH
What causes less Na+ reabsorption?
- ANP
- reduced RAA and SNS activity
- dopamine
- prostaglandins
How does ANP work?
- Atrial natriuretic peptide is released from the atria in response to increased atrial stretch
- anp then binds to receptors to increase cGMP
- ANP causes reduced Na+ reabsorption in the distal tubules and the outer medullary collecting ducts by blocking ENaC and inhibiting Na/K ATPase
- inhibits both aldosterone and renin release
- vasodilates the afferent arteriole to increase GFR
Effects of dopamine?
Dopamine is released by neurons in the proximal tubule and inhibits the Na/K ATPase and the Na/H exchanger in the proximal tubule
Why does the ECF osmolality need to stay constant?
Symptoms of hypo/hyperosmolality include headache, nausea, confusion, lethargy, weakness, seizures
Hyponatremia?
Low sodium in the blood
- can occur when you consume too much water that your kidneys can’t excrete enough and you dilute your ECF and Na+ conc
What happens with dehydration
(what’s changing, where’s it being sensed, what are the signals, what are the effectors and what is the response)
What happens with dehydration
- increased osmol (incr Na+ or reduced fluid)
- supraoptic and paraventricular neurons/osmoreceptors in the hypothal
- hypothal increases ADH
- binds to V2 receptor in collecting duct epithelium
- insertion of aquaporins into the apical/tubular lumen
- increased water reabsorption
What if dehydration is so bad that volume decreases by 10%?
- stimulate/reduce stretch of cardio-pulmonary receptor afferents to the pituitary
- reduced stretch of atria and reduced ANP release
