Flashcards in The distal tubule, collecting ducts and urination Deck (26)
what are the major sites for regulation of ion and water balance?
the distal tubule and the collecting duct
what structures do hormones have an effect on?
Hormones only influence the cells of the distal tubule and collecting duct- no effect on proximal tubule or loop of henle
what hormone increases waster reabsorption?
Antidiuretic hormone (ADH) - also known as vasopressin and so it decreases urine production
what hormone increases Na+reabsorption ,and H+,K+ secretion?
what decreases Na+ reabsorption?
atrial natriuretic hormone
what increases Ca2+ and decreases PO4-3?
what is the distal tubule's permeability to water when there is no ADH in the blood?
low permeability to water
what two segments can the distal tubule and the collecting duct be split into?
what occurs in the early distal tubule?
Na+-K+-2Cl- transport (NaCl reabsorption)
what occurs in the late distal tubule?
(+ aldosterone: K+ secretion when K+ secretory cells are activated)
what part of the collecting duct is similar to the late distal tubule?
Early collecting duct
what properties does the late collecting duct have?
(a) a low ion permeability
(b) permeability to water (and urea) influenced by ADH (antidiuretic hormone)
where is ADH synthesised and stored?
supraoptic nucleus in the hypothalamus and the nerve terminals are stored in granules in the posterior pituitary
what happens when action potentials down the nerves lead to Ca2+ -dependant exocytosis?
ADH is released into blood
what is the plasma half life of ADH?
what effect does ADH have on water permeability of the collecting duct?
Increases permeability of
luminal membrane to H2O
by inserting new
water channels (aquaporins)
what happens in the presence of maximal ADH plasma?
water moves from the collecting duct lumen along the osmotic gradient into the medullary interstitial fluid thus enabling hypertonic urine formation
what is the permeability of water and the type of urine produced when there is high levels of ADH (dehydrated)?
-high water permeability -hypertonic urine (up to 1400 mosmol/l)
what is the permeability of water and the type of urine produced when there is low levels of ADH (over hydrated)?
-low water permeability
- hypotonic urine (< 50 mosmol/l)
what happens as plasma ADH increases?
-urine osmolarity increases
-urine volume decreases
what effect does ADH have on salt reabsorption?
No effect- it only effects water reabsorption
what process is urine emptied from the bladder?
how does urine move to the bladder?
Once urine has been formed by the kidneys it is propelled by peristaltic contractions through the ureters to the bladder for temporary storage
what is micturition or urination governed by?
1. The micturation reflex
2. Voluntary control
how does the micturation reflex work?
The urinary bladder can accommodate up to 250-400 ml of urine before stretch receptors in within its wall initiate the micturation reflex. This reflex causes involuntary emptying of the bladder by simultaneous bladder contraction and opening of both the internal and external urethral sphincters