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Renal Physiology > K5 - The Distal Tubule, Collecting Ducts and Urination > Flashcards

K5 - The Distal Tubule, Collecting Ducts and Urination Flashcards

1
Q

What is the tubular fluid leaving the loop of henle and entering the distal tubules relationship to plasma?

A

hypo-osmotic

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2
Q

what is the concentration of the surrounding interstitial fluid of the renal cortex?

A

300mosmol/l

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3
Q

the distal tubule empties into where?

A

collecting duct

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4
Q

What is very important for salt balance?

A

residual load

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5
Q

what hormones regular ion and water balance?

A
  • antidiuretic hormone (ADH)
  • aldosterone
  • atrial natriuretic hormone
  • parathyroid hormone
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6
Q

How does ADH regulate water balance?

A

Water reabsorption increases

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7
Q

How does aldosterone regulate ion balance?

A

Na+ reabsorption increases

H+/K+ secretion increases

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8
Q

How does the atrial natriuretic hormone regulate ion balance?

A

Na+ reabsorption decreases

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9
Q

How does parathyroid hormone (PTH) regulate ion channel?

A

Ca2+ reabsorption increases and PO4 3- reabsorption decreases

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10
Q

What does the distal tubule have low permeability to?

A

water and urea

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11
Q

Where is urea concentrated in?

A

tubular fluid

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12
Q

what occurs in the early distal tubule?

A

Na+, K+ and 2Cl- transport

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13
Q

what occurs in the late distal tubule?

A

Ca2+ reabsorption
H+ secretion
Na+ reabsorption
K+ reabsorption

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14
Q

What part of the collecting duct has low ion permeability and permeability to water influenced by ADH?

A

the late collecting duct

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15
Q

what is synthesised by the supraoptic nucleus in the hypothalamus?

A

octapeptide

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16
Q

Where does ADH secretion occur?

A

posterior pituitary

17
Q

where is ADH stored?

A

In granules in the posterior pituitary

18
Q

When is ADH released into the blood?

A

When action potentials down the nerves lead to Ca2+ dependent exocytosis

19
Q

What is the plasma half life of ADH secretion?

A

10-15 mins

20
Q

Describe the effect of ADH on water permeability of the collecting duct?

A
  1. ADH acts on type 2 vasopressin receptor on basolateral membrane
  2. Once bound ATP is converted into cyclic AMP
  3. this increases the aquaporins at the luminal membrane therefore more water is reabsorbed to the blood
21
Q

If there is no ADH in the blood what happens to the aquaporin concentration at the luminal membrane?

A

they become internalised back into the cytoplasm and therefore reduce the permeability of the cells for water reabsorption

22
Q

What enables hypertonic urine formation?

A

In the presence of maximal [ADH]plasma water moves from the collecting duct lumen along the osmotic gradient into the medullary interstitial fluid

23
Q

What does High ADH cause?

A
  • high water permeability down osmotic gradient,

- concentrated urine

24
Q

what enables hypotonic urine?

A
  • low ADH
  • low water permeability down osmotic gradient,
  • dilute urine
25
Q

what effect does ADH have on salt balance?

A

no effect

26
Q

what are the features of the Proximal tubule and descending loop of Henle?

A
  • Na+ reabsorbed by transcellular mechanisms (**PT only)
  • Water moves between inter-cellular junctions
  • These produce net fluid reabsorption
  • Na+ and water coupling
27
Q

what are the properties of the Ascending Loop of Henlé and Distal Tubule?

A
  • Low water permeability of epithelium (ADH-dependent)
  • Na+ & Cl- reabsorption
    These produce dilution of urine
  • Na+ & Cl- coupling
28
Q

What are the properties if the collecting duct?

A
  • Modulation of water / urea permeability

- This contributes to determination of final urine osmolarity

29
Q

What are the properties of the Distal Tubule / Collecting Duct?

A

Site of hormone action (ADH, Aldosterone, Atrial Natriuretic Peptide

30
Q

Where is urine temporarily stored?

A

Where is urine temporarily stored?

In the bladder

31
Q

What is the name for the process of the bladder emptying?

A

Micturation or urination

32
Q

What two mechanisms is micturition governed by?

A
  1. The micturition reflex

2. Voluntary control

33
Q

How many ml of urine can the urinary bladder accommodate before stretch receptors within its wall initiate the micturition reflex?

A

250- 400ml

34
Q

what is the micturation reflex?

A

stretch receptors within walls of bladder are stretched leading to involuntary emptying of the bladder by simultaneous bladder contraction and the opening of both internal and external urethral sphincters

35
Q

how can micturation reflex be voluntary prevented?

A

By deliberate tightening of the external sphincter and surrounding pelvic diaphragm

Renal Physiology (8 decks)

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