L07: Urine Concentration Dilution Flashcards
Whereabouts in the nephron does water get reabsorbed back into the blood
Descending limb of loop of henle
Collecting duct
What is the main determinant hormone of the urine concentration
ADH
What is ADH also known as
Vasopressin
Where is ADH synthesised
Hypothalamus
Where is ADH secreted from
Posterior pituitary gland
Where does ADH act on
Collecting duct
What does ADH do in term of express channels
It expresses aquaporin 2
Describe the process of absorption of water when ADH increases aquaporin 2 in the apical membrane
1) water moves in through AQP2 in the apical membrane
2) water then moves out of the cell though the basolateral membrane via aquaporin 3
What receptors do ADH bind to when they are released from the posterior pituitary gland
V2 receptors
What happens intracellular when ADH binds to V2 receptors
V2 receptors or coupled to Gs proteins
Gs proteins Stimulate adenylyl cyclase to create CAMP (2nd messenger)
CAMP stimulates the nucleus to transcribe AQP2 synthesis
CAMP then stimulate protein kinase A to insert the synthesised AQP2 into the apical membrane
Therefore what is the concentration of the urine like when there is ADH
Concentrated
Therefore what is the concentration of urine when there is no ADH
Dilute
What happens to the flow rate of urine when there is no ADH
High
What happens to the flow rate in the nephron when there is ADH
LOW as we are not producing urine
What does urea do in terms of osmolalility
Contribute to medullary osmolarity when it gets reabsorbed from the loop of henle
What happens to urine when there is low urea
Urine is dilute
What results in low urea
Protein starvation
What hormone regulators the expression of UT-A1 (urea transporter)
ADH
What receptor does ADH bind to stimulate the expression of UT-A1
V2 receptors the basolateral membrane
What happens intracellularly when ADH binds to V2 receptors
1) Gs is activated which stimulates adenylyl cyclase to produce CAMP
2) CAMP increases transcription and synthesis of UT-A1
3) CAMP stimulates protein kinase A to insert UT-A1 into the apical membrane
What is diabetes insipidus
Low ADH secretion
Or
Loss of ADH sensitivity due to loss of function of V2 receptors
What are the symptoms of diabetes insipidus
Polyuria Dehydration Hypo aloe is Polydipsia (drinking too much) Hypernatreamic
Due to the 2 different causes of diabetes insipidus, what are the 2 types of diabetes inspidus
Central diabetes insipidus
Nephrogenic diabetes insipidus
What is diabetes insipidus due to
Lack of secretion of ADH
What are the causes of central diabetes insipidus
Head injury
Tumours in pituitary gland
Infection
What is the treatment of central diabetes insipidus
Give ADH analogue called desmopressin to replace ADH
What is nephrogenic diabetes insipidus due to
Loss of sensitivity to ADH in V2 receptors
What are the causes of nephrogenic diabetes insipidus
Toxicity
Hypercalcaemia
Genetic mutation to V2 receptors
What is the treatment to nephrogenic diabetes insipidus
Thiazides diuretic: increase aquporin expression
Law salt diet
What does SIADH stand for
Syndromes inappropriate ADH
In terms of SIADH what are the levels of ADH like
High
What are the causes of SIADH
Head injury
What are the symptoms of SIADH
Concentrated urine
Hyponatremic because water dilutes sodium
What is the treatment for SIADH
Fluid restriction
Aquaretic drugs
What does aquoretic drugs cause
Water loss without salt loss
What is a aquaretic drug
V2 receptor antgonist
Where does aquaretic drugs act in the nephron
Late portion of the distal tubule
Collecting duct
Why do we administer a low salt diet to someone who has nephrogenic diabetes insipidus
They have a low sodium because they are losing a lot of water
To treat hypernatremia we tell them to restrict salt in the diet
