Endocrine control of body fluid volume and composition Flashcards Preview

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Flashcards in Endocrine control of body fluid volume and composition Deck (51):
1

How does the osmolarity of the tubular fluid leaving the loop of henle compare to that of the surrounding interstitial fluid?

Hypo-osmotic

2

Where does the distal tubule drain to?

Collecting duct (cortical)

3

How does the interstitial fluid change as the collecting duct progresses?

Increasing osmolarity (collecting duct drills down into medulla)

4

Where in the nephron is ion and water balance mainly regulated?

Distal tubule and collecting duct

5

Where does most reabsorption of ions occur?

Proximal tubule BUT the remaining ions are essential for salt balance

6

What is the main mechanism of salt and water regulation?

Hormonal

7

Where do the hormones acting on the kidney act?

Distal tubule and collecting duct
(do NOT act on proximal tubule or loop of Henle)

8

How permeable is the distal tubule to water and urea? What effect does this have?

Not very (unless ADH levels are high)
Urea is concentrated in the tubular fluid which helps maintain the corticomedullary gradient

9

Describe what happens in the early and late parts of the distal tubule with regard to ion absorption

Early
- Sodium, chlorine and potassium triple co-transporter (i.e salt reabsorption)
Late
- Calcium reabsorption
- Hydrogen secretion
- Sodium reabsorption
- Potassium reabsorption

10

Is it the early or late distal tubule that is stimulated by hormones?

Late

11

Describe what happens in the early and late collecting duct with regard to ion absorption

Early
- Sodium reabsorption
- Potassium reabsorption
- Hydrogen secretion
- Calcium reabsorption
Late
- Low ion permeability
- Permeability to water varies with respect to ADH

12

Describe vasopressin secretion

Peptide hormone synthesised (supraoptic and paraventricular nuclei) in the hypothalamus >
Transported down nerves >
Stored in the posterior pituitary >
Released into blood in response to calcium dependent exocytosis (induced by action potentials)

13

Peptide hormones have a long half life. T/F

False - short half life

14

How does ADH increase the permeability of the collecting duct to water?

ADH binds to type 2 vasopressin receptors on the basolateral membranes of tubular cells >
Increase in intracellular cyclic AMP >
Increased expression of aquaporins (water channels) at the apical membrane >
Increased permeability to water

15

How is hypertonic urine formed?

In the presence of high ADH water moves from the collecting duct to the interstitial fluid along the osmotic gradient

16

How is hypotonic urine formed?

In the presence of low ADH water cannot leave the collecting duct and so is retained in the urine

17

Tubular fluid equilibrates with interstitial fluid via aquaporins under which condition?

High ADH

18

The collecting duct is impermeable to water so none is reabsorbed under which condition?

Low ADH

19

ADH affects salt and water reabsorption. T/F

False - ADH only has a direct effect on water reabsorption

20

Describe the ADH hormone axis

Increase in plasma osmolarity >
Hypothalamic osmoreceptors >
Increase in thirst and ADH secretion >
ADH causes vasoconstriction + increased distal tubular and collecting duct permeability to water >
Decreased urine output >
Increased plasma volume and decreased plasma osmolarity

21

When are left atrial volume receptors stimulated to produce ADH?

When there is a massive drop in ECF thus blood pressure and eventually decreased atrial stretch

22

How can diabetes insipidus be classified?

Central
Nephrogenic

23

Is diabetes insipidus hereditary?

Usually

24

What are the symptoms of diabetes insipidus?

Large volumes of dilute urine
Constant thirst

25

How is diabetes insipidus managed?

ADH replacement

26

What medication (long term) induces diabetes insipidus?

Lithium as is used in bipolar disorder

27

What controls feedforward ADH secretion?

Stretch receptors in the GI tract

28

What effect do nicotine (i.e smoking) and alcohol have on ADH secretion?

Nicotine - increase ADH
Alcohol - decrease ADH

Nb - ecstasy also decreases ADH and thus poses a massive dehydration risk

29

How does the tubular osmolarity change across the length of the nephron

Proximal tubule - low
Loop of Henle - high then low
Distal tubule - low (may rise if increased ADH)
Collecting duct - low (may rise if increased ADH)

30

What type of hormone is aldosterone and where is it secreted form?

Steroid
Adrenal cortex

31

What mnemonics can be used to remember the hormones secreted from the adrenal gland?

Get my = glomerulosa - mineralocorticoids (aldosterone)
Freaking gun = fasiculata - glucocorticoids (cortisol)
Right away = reticularis - androgens (sex hormones)
Magic = medulla - adrenaline, etc (magic rush)

32

When is aldosterone secreted?

Directly in response to rising potassium
Indirectly in response to falling sodium
Indirectly as part of the renin-angiotensin-aldosterone system

33

What effect does aldosterone have?

Increases sodium reabsorption
Increases potassium secretion

Nb - remember water follows salt so inc sodium helps to increased plasma volume

34

What happens if a patient is not producing aldosterone?

Eventually leads to death due to low fluid volumes

35

Where is potassium reabsorbed? How much potassium is excreted in the urine?

90% within the proximal tubule and 10% within the distal tubule. None

36

How is potassium reabsorption affected by aldosterone?

Increase in potassium is detected by the adrenal cortex >
Aldosterone release >
Increased secretion of potassium

37

Decreasing sodium indirectly stimulates aldosterone release how?

Lowered sodium levels detected within the juxtaglomerular apparatus stimulates the renin-angiotensin-aldosterone system

38

Explain RAAS

Lowered ECF, sodium and BP >
Kidneys detect and secrete renin >
Renin acts on angiotensiogen (secreted by the liver) to covert it to angiotensin I >
Angiotensin I is converted to angiotensin II by angiotensin converting enzyme (ACE) in the lungs >
Angiotensin II acts on the adrenal cortex to stimulate aldosterone >
Aldosterone acts on the liver to decrease potassium and increase sodium reabsorption >
Increased salt causing increased water retention and thus fluid repletion

39

What does angiotensin II do?

Increases thirst
Stimulates aldosterone release
Increases ADH
Causes arteriolar vasoconstriction

40

How does the juxtaglomerular apparatus effect the RAAS?

Granular cells in the juxtaglomerular apparatus release renin in response to
- decreased afferent blood pressure
- decreased salt concentration
- direct sympathetic stimulation

41

How does aldosterone increase sodium reabsorption at the distal tubule and collecting duct?

Promotes increased expression of apical sodium channels
Increases number and activity of basolateral sodium potassium ATPases

42

Abnormal activity of the RAAS causes what?

Hypertension

43

What is the cause of fluid retention in congestive heart failure?

RAAS

44

Where is atrial natriuretic peptide/hormone produced and stored?

Left atrium produces and atrial muscle cells store

45

What is atrial natriuretic peptide released?

In response to mechanical stretch of the left atrium due to increased circulating plasma volume

46

What does atrial natriuretic peptide do?

Increases excretion of sodium hence diuresis and thus reduction in circulating plasma volume
Decreases activity of RAAS
Arteriolar vasodilation
Decreases sympathetic stimulation

47

Which two mechanisms control micturation?

Micturation reflex
Voluntary control

48

What initiates the micturation reflex?

Stretch receptors in the bladder wall

49

What is the micturation reflex?

Involuntary contraction of the detrusor and relaxation of the internal urethral sphincter

50

How can micturation be stopped by voluntary control?

Central pathways cause the relaxation of the detrusor and contraction of internal
Voluntary contraction of external sphincter and levator ani

51

What is the difference between water diuresis and osmotic diuresis?

Water - increased urine flow but no increased salt excretion
Osmotic - increase in urine flow is a result of primary increase in salt excretion

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