Collecting duct Flashcards
Function of collecting duct?
Similar distal
Acid balance
Regulate H2O and salt reabsorption
Water moves out to hypertonic interstitium
What hormone effects collecting ducts?
Vasopressin (ADH)
Effect of vasopressin (ADH)?
Promote AQP2
How is water reabsorbed in collecting duct?
1) Dilute (hypotonic) fluid enters collecting duct
2) Passes through increasing concentration gradient (hypertonic) in medullary interstitium
3) Cells have tight junctions the collecting duct is impermeable to water
4a) Absence of vasopressin collecting duct is impermeable to water (lots of urine produced)
4b) With vasopressin becomes permeable water is reabsorbed
Collecting duct becomes permeable to urea
Increase water reabsorption through oncotic pressure
How does urea increase water reabsorption?
Oncotic pressure
What 2 factors influence conc gradient?
1) Efficiency reabsorption
2) Length loop of Henle
Where is ADH (vasopressin) synthesised?
secreted from?
Synthesised- hypothalamus
Secreted- posterior pituitary
What controls realse ADH?
Osmoreceptors
Function of osmoreceptors?
Detect changes in osmolarity
If increased
Release ADH
Does alcohol increase or decrease release ADH?
Decrease
Does nicotine increase or decrease release ADH?
Increase
Is half life of ADH (vasopressin) short or long?
Why
Short
Allow quick adaptations
What does ADH do?
Allow expression AQP2 on apical membrane
How is water reabsorbed in collecting duct?
1) AQP2 in vesicles
2) ADH stimulate excretion of AQP2
3) Water absorbed through AQP2 channels on apical membrane
4) Use AQP3 and AQP4 channels on basolateral membrane
State 2 effects of ADH?
1) Increase expression AQP2 channels- water reabsorption
2) Cause arteriolar constriction- restore bp
What stimulates osmoreceptors?
Increase plasma osmolarity
Decrease ECF
What does stimulation of osmoreceptors lead to?
Secretion ADH
Increase H2O absorption
Why is urea important?
Used produce concentrated urine
How does urea allow production of concentrated urine?
Interstitium try keep high urea
Stop osmotic effect water moving back into collecting duct
Location of baroreceptors (2)?
Aortic arch
Carotid sinus
Name 2 factors stimulate ADH?
Osmolality
Decreased ECF
Explain baroreceptor reflex?
1) Baroreceptors detect decrease in ECF
2) Increase aldosterone via RAAS
3) Decrease rate of firing
4) ADH secretion due to less stimulation of hypothalamus
4) Increased permeability of collecting ducts
5) More water reabsorbed
What is more sensitive baro or osmorecptors?
Osmoreceptors
What is baroreceptor reflex if high BP?
Increased baroreceptor firing
Decrease vasopression secretion
