Body Fluid Volume and Osmoregulation Flashcards
What is another name for ADH?
ADH = anti diuretic hormone
Vasopressin
Where is ADH synthesised?
In the hypothalamus
Where is ADH released?
From the terminals of hypothalamic neurones found within the posterior pituitary
What does ADH increase the expression of?
AQP2
How does ADH increase the expression of AQP2?
ADH interacts with V2 receptor
Triggering adenylyl cyclase to produce cAMP
cAMP promotes nucleus transcription and PKA (protein kinase A)
Describe osmolality across the nephron
High in the proximal tubule
Highest in the loop of Henle
Lower in the collecting duct
Describe flow rate in the nephron with no ADH present
Highest at the start of the proximal tubule and then decreasing
Describe osmolality in the nephron
High in the proximal tubule
Highest in the loop of Henle
Lower in the convoluted tubule
Then increasing to be as high as the loop of Henle
Compare flow in the nephron with ADH and without
With ADH present flow decrease across the nephron in the same way but to a much greater extent
How do cells survive the very high osmolality in the nephron?
They have adapted to have a range of organic osmolytes within the cells
This includes sorbitol, inositol, glycerophosphororylchlorine and betaine
What is diabetes insipidus?
Loss of ADH secretion or loss of kidney sensitivity to ADH
What would cause a loss of sensitivity to ADH?
Nephrogenic diabetes insipidus
Problem with the V2 receptors
What are the symptoms of diabetes insipidus?
Unable to produce concentrated urine
Polyuria
Dehydration
What is central diabetes insipidus?
Caused by head injury, tumours or infection
Treated with desmopressin (ADH analogue)
Some treatment with thiazides
What causes nephrogenic diabetes insipidus?
Toxicity
Hyperglycaemia
Genetic mutations
How is nephrogenic diabetes insipidus treated?
Thiazide diuretic
Low salt diet
What is SIADH?
Syndromes in inappropriate ADH
What cause SIADH?
Most commonly a head injury
What are the symptoms of SIADH?
Inappropriately high levels of ADH
Concentrated urea
How is SIADH treated?
With Urea
What is the body’s mechanism against thirst?
Increase of osmolality of the plasma
Osmolality detected by anteroventral third ventricle AV3V
AV3V neurones extend into the hypothalamus, increasing thirst
What happens if you drink sea water?
Dehydration
1kg of sea water require 1.4L of water to clear
What is the maximum urine concentration?
1400mOsm
How much urine must be produced to secrete 1400 mOsm?
1 litre
What is a hyperosmolar hyperglycaemic state?
Hyperosmolality caused by high blood glucose levels
Leads to strong thirst
Can also cause altered mental status, seizures and increases blood viscosity
What does the body regulate with regards to volume of water?
The effective circulating volume
What is the juxtaglomerular apparatus?
The complex of late distal tubule and renal different arteriole
What is the macula densa?
Thickening of the wall of the early distal tubule
What system increases the effective circulating volume?
Renin-angiotensin-aldosterone system
What are the two triggers for aldosterone release?
Angiotensin II
Hyperkalaemia
What is spironolactone?
Blocks the effect of aldosterone
How is the renin angiotensin system inhibited?
ACE inhibitors
AT1 receptor antagonists
Aldosterone receptor antagonists
Renin inhibition
What is the main receptor for angiotensin II?
AT1 receptor
What is the AT1 receptor coupled to?
Gq
What are the five actions of angiotensin II on circulating volume?
Vasoconstriction
Increase Na+/H+ exchange in the proximal tubule
Increase in aldosterone release from the adrenal cortex, increasing distal Na+ absorption
Cause ADH release
Cause thirst
What produces renin?
Granule cells
What regulates renin production?
Sympathetic innervation of granule cells
What are the effects of activating sympathetic innervation of the afferent arteriole?
Vasoconstriction upstream of granule cells causes decreased pressure sensed by them, results in a fall in blood pressure
Direct stimulation of renin release by granule cells
Afferent arteriole vasoconstriction reduces GFR
What is the neurotransmitter in the nerves of the afferent arteriole?
Noradrenaline
What causes vasoconstriction?
Alpha 1 adrenoreceptors that are Gq coupled
What receptors are found on the granule cells?
Beta 1 adrenoreceptors that are Gs coupled
What is another stimulus of renin release?
Decreased Na+ delivery to the distal tubule
A result of decreased venous tone and greater fluid loss from the filtrate
What is atrial natriuretic peptide?
ANP
Released in response to increased venous return
Decreases the activity of Na+/K+/ATPase
Increases renal excretion of Na+
What works the same as atrial natriuretic peptide?
Renal natriuretic, produced in the kidney
What is the primary effect of ADH?
To drop osmolality
