The distal tubule, collecting ducts and urination

Question 1

what are the major sites for regulation of ion and water balance?

Answer 1

the distal tubule and the collecting duct

Question 2

what structures do hormones have an effect on?

Answer 2

Hormones only influence the cells of the distal tubule and collecting duct- no effect on proximal tubule or loop of henle

Question 3

what hormone increases waster reabsorption?

Answer 3

Antidiuretic hormone (ADH) - also known as vasopressin and so it decreases urine production

Question 4

what hormone increases Na+reabsorption ,and H+,K+ secretion?

Answer 4

Aldosterone

Question 5

what decreases Na+ reabsorption?

Answer 5

atrial natriuretic hormone

Question 6

what increases Ca2+ and decreases PO4-3?

Answer 6

parathyroid hormone

Question 7

what is the distal tubule’s permeability to water when there is no ADH in the blood?

Answer 7

low permeability to water

Question 8

what two segments can the distal tubule and the collecting duct be split into?

Answer 8

• early

- late

Question 9

what occurs in the early distal tubule?

Answer 9

Na+-K+-2Cl- transport (NaCl reabsorption)

Question 10

what occurs in the late distal tubule?

Answer 10

Ca2+ reabsorption
H+ secretion	
Na+ reabsorption
K+ reabsorption
(+ aldosterone: K+ secretion when K+ secretory cells are activated)

Question 11

what part of the collecting duct is similar to the late distal tubule?

Answer 11

Early collecting duct

Question 12

what properties does the late collecting duct have?

Answer 12

(a) a low ion permeability

b) permeability to water (and urea) influenced by ADH (antidiuretic hormone

Question 13

where is ADH synthesised and stored?

Answer 13

supraoptic nucleus in the hypothalamus and the nerve terminals are stored in granules in the posterior pituitary

Question 14

what happens when action potentials down the nerves lead to Ca2+ -dependant exocytosis?

Answer 14

ADH is released into blood

Question 15

what is the plasma half life of ADH?

Answer 15

10-15 minutes

Question 16

what effect does ADH have on water permeability of the collecting duct?

Answer 16

Increases permeability of
luminal membrane to H2O
by inserting new
water channels (aquaporins)

Question 17

what happens in the presence of maximal ADH plasma?

Answer 17

water moves from the collecting duct lumen along the osmotic gradient into the medullary interstitial fluid thus enabling hypertonic urine formation

Question 18

what is the permeability of water and the type of urine produced when there is high levels of ADH (dehydrated)?

Answer 18

-high water permeability -hypertonic urine (up to 1400 mosmol/l)

Question 19

what is the permeability of water and the type of urine produced when there is low levels of ADH (over hydrated)?

Answer 19

• low water permeability

- hypotonic urine (< 50 mosmol/l)

Question 20

what happens as plasma ADH increases?

Answer 20

• urine osmolarity increases

- urine volume decreases

Question 21

what effect does ADH have on salt reabsorption?

Answer 21

No effect- it only effects water reabsorption

Question 22

what process is urine emptied from the bladder?

Answer 22

micturition

Question 23

how does urine move to the bladder?

Answer 23

Once urine has been formed by the kidneys it is propelled by peristaltic contractions through the ureters to the bladder for temporary storage

Question 24

what is micturition or urination governed by?

Answer 24

1. The micturation reflex

2. Voluntary control

Question 25

how does the micturation reflex work?

Answer 25

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

Question 26

how does the voluntary control work?

Answer 26

Micturation can be voluntarily prevented by deliberate tightening of the external sphincter and surrounding pelvic diaphragm