Week 3 - F - Physiology 6(a) - Anti-diuretic hormone Flashcards
What is the osmolarity of the tubular fluid leaving the ascending loop of Henle and entering the distal tubule?
Concentration - 100mosmol/l
What is the surrounding omsolarity of interstitial fluid around the proximal distal convoluted tubule?
300mosmol/l is the omsolarity of the surrounding interstitium
The distal tubule then empties into the collecting duct Once it passes from cortex into medulla, what is the collecting duct exposed to?
It is exposed to the corticomedullary gradient of the surrounding interstitium - 300 to 1200 as you go deeper
What are the major sites for regulation of ion and water balance in the nephron?
This would be the distal tubule and the collecting duct
What is the major site for reabsorption of salt and water?
This is the proximal convoluted tubule
What does the rate of fluid flowing into the proximal tubule to leaving change by?
Flows in at 125ml/min and then due to tubular reabsorption leaves at 45ml/min
The regulation of the salt and ion concentration is due to hormones, what are the sites that the hormones act on in the nephron?
The distal and the convoluted tubule
What are the 4 primary hormones that regulate the ion and water reabsorption in the nephron?
- ADH (vasopressin) 2. Aldosterone 3. ANP (Atrial-natriuretic hormone) 4. Parathyroid hormone
What is the role of ADH in the nephron? What does it cause to the urine?
It promotes the reabsorption of water therefore changing the volume and concentration of urine produced
What does aldosterone cause? (one thing reabsorbed, 2 things secreted)
Cause the reabsorption of sodium and the secretion of hydrogen and potassium
What does atrial natriuretic hormone cause? What does parthyorid hormone cause in the kidneys?
Causes decreased sodium reabsorption Parathyroid hormone causes increased calcium absorption and decreased phosphate absorption
What does parathyroid hormone cause in the gut and bone?
In gut and bone Gut - absorption of calcium and phosphate Bone - increased bone resroption leading to increased calcium and phosphate
In the basal state (resting conditions), what is the permability of the distal tubule to urea and water?
Distal tubule has a low permeability to urea and water - Urea is therefore concentrated in the tubular fluid (which helps to establish the osmotic gradient within the medulla
The late distal collecting duct has a low ion permability however a high permeability to water What is this permeability to water influenced by?
It is influenced by the circulating levels of ADH
Where is ADH synthesised and what is its other name?
ADH is synthesised in the supraoptic and paraventricular nuclei in the hypothalamus ADH is also known as (arginine) vasopressin
What other hormone is synthesised in the supraoptic and paraventricular nuclei in the hypothalamus?
Oxytocin
Both ADH and oxytocin are transported where to be stored until release?
Transported to the posterior pituitary to be stored until release
Once the axon potentials from the hypothalamus are fired to the posterior pituitary, which chemical is the release of ADH (and oxytocin) dependent on?
Calcium dependent release
What is the primary reason for the release of ADH?
An increase in plasma omsolarity so that ADH can caused increased water reabsorption in the collecting duct and distal tubule
Where are the two vasopressin receptors and which type is where?
Type 1 vasopressin receptor is on smooth muscle Type 2 vasopressin receptor is at the basolateral membrane of the tubular cell
Once vasopressin binds to the basolateral V2 receptor, what occurs?
An increase in intracellular cyclic AMP which causes the increased concentration of aquaporins at the apical membrane
What does the increased concentration of aquaporins at the apical membrane of the distal tubule cause?
This causes the increased permability of the apical membrane to water
High levels of vasopressin increases permability of tubular cells, low levels lowers permeability of tubular cells to water Summarise what happens when there is an increase in plasma omsolarity?
Hypothalamus sends neurons to elicit Ca2+ dependent release of ADH ADH binds to V2 (vasopressin 2) receptors on the basolateral tubular cell membrane This causes an increase in intracellular cyclicAMP which causes an increase in the concentration of aquaporins at the apical membrane The aquaporins increase the permability of the tubular cell to water
describe the volumes of urine produced in high and low levels of ADH?
High ADH level - small and concentrated levels of urine Low ADH levels - large volume and dilute levels of urine
What does dehydration cause to the ADH production and how?
Dehydration causes a high serum osmolarity leading to an increased production of ADH which will promote the reabsorption of water in the distal convoluted tubule and the collecting duct
When there is increased ADH concentration, the tubular lumen is permeable to water, what therefore happens during the corticomedullary gradient as the collecting duct extends into the medulla?
This promotes the omsotic gradient of water into from the tubular cells via aquaporins and into the intersitium
What further modification happens to the urine once it reaches the pelvicalcyeal system?
No further modification once the urine has eft the kidneys
In presence of minimal levels of ADH, how does the corticomedullary gradient affect the water flow?
Since their is minimal, the distal convoluted tubule / collecting duct is not permable to water and therefore no water flows and a large dilute volume of urine is produced
How does the ADH affect the solute concentration of the tubules?
ADH does not have an effect on this concentration
What are the cells detecting the change in osmolarity of the plamsa in the hypothalamus known as?
Known as hypothalamic osmoreceptors
Hypothalamic osmoreceptors cause increased hypothalmic neurons leading to increase ADH and increased thirst This decreases urinary output overall decreasing plasma omsolarity and increasing plasma volume What does a decrease in ECF volume cause to the blood pressure?
This cause a decrease in arterial blood pressure
Left atrial volume receptors only kicks in a significant arterial BP drop (aka someone with a bad haemorrhage) In response to a significant decrease in ECF volume, this is picked up by stretch receptors in the left atrium of thee heart and this will signal to hypothalamic neurones to promote secretion of ADH What does the ADH cause to smooth muscle of arteriole and what does this cause?
ADH binds to V1 (vasopressin) receptors on smooth muscle causing contraction and this leads to an increased TPR of arterioles
What is Vessel resistance equal to?
The vessel resistance is resistance is proportional to the length of vessel and viscosity of the blood but inproportional to the radius of the vessel to the power of 4 - therefore when there is vasoconstriction causing constricted arterioles this increases TPR causing increased MABP
Name the condition where there is a continual excess diuresis due to water loss? What are the two types?
This is Diabetes insipidus (cranial or nephrogenic)
HowDiabetes insipidus is diagnosed by a water deprivation test How can you tell from cranial and nephrogenic?
Give a vasopressin test If cranial, this will cause a water reabsorption If nephrogenic there will be no change in urine production
What is the treatment of cranial diabetes insipidus? What is the treatment of nephrogenic diabetes insipidus?
Cranial - desmopressin Nephrogenic - give thiazide diuretics (has a paradoxical effect causing increased reabsorption of water in the proximal tubule)
What drug prescribed for bipolar disorder can cause it if on this treatment long term?
Lithium
What in cigarretes stimulates ADH release? What (say on nights out) inhibits ADH release?
Nicotine stimulates, alcohol inhibits
