Control And Abnormalities Of Body Water

Question 1

How is volume regulation maintained in the body?

Answer 1

Retaining sodium (and water with it)

Question 2

What is osmoregulation?

Answer 2

Preventing shifts of water between the ECF and ICF

Question 3

How is the osmolarity of the ECF adjusted?

Answer 3

Adding or removing water in the body (thirst mechanism or kidney)

Question 4

What is the only site of regulated water loss?

Answer 4

Renal tubule

Question 5

What happens to the urine if there’s a water excess?

Answer 5

Large volume of dilute urine

Question 6

What happens to the urine if there’s a water deficit?

Answer 6

Small volume of concentrated urine

Question 7

What are the two ways the kidney osmoregulate?

Answer 7

Concentrate interstitial fluid in the medulla, dilute urine in ascending limb and distal tubule

Question 8

What is the threshold for urine concentration?

Answer 8

50 - 1200 mOsm/L

Question 9

What are the concentration difference between the interstitial fluid and tubular fluid in the proximal tubule?

Answer 9

Isotonic

Question 10

Where do you get the max concentration of both the interstitial and tubular fluid?

Answer 10

Bend of the loop of henle

Question 11

Where do you get the maximum dilution of the tubular fluid?

Answer 11

Distal tubule

Question 12

What is the osmoregulatory hormone?

Answer 12

ADH

Question 13

What does lack of ADH in the collecting duct mean?

Answer 13

It’s impermeable to water and therefore maximally dilute urine is secreted

Question 14

What urine osmolality is meant to signify the presence of ADH?

Answer 14

> 100mOsm/Kg

Question 15

At maximum ADH levels what is the limit of water reabsorption set by?

Answer 15

The osmolality of the medullary interstitial fluid

Question 16

What is ADH’s mechanism of action?

Answer 16

Vasopressin V2 receptors act on principal cells and get them to make and insert aquaporin 2 channels into the membrane

Question 17

What do V1 receptors on vascular smooth muscle lead to?

Answer 17

Vasoconstriction but only significant with very high ADH levels

Question 18

How does a net water loss change ECF osmolality?

Answer 18

Increase

Question 19

What is the normal ECF osmolality range?

Answer 19

285-295 mOsm/Kg

Question 20

Where are changes in osmolality detected?

Answer 20

Osmoreceptors in the anterior hypothalamus

Question 21

Where do the osmoreceptors project to?

Answer 21

Magnocellular neurons of the paraventricular and supraoptic nucleus of the hypothalamus

Or thirst centres

Question 22

What do the paraventricular and supraoptic nucleus release?

Answer 22

ADH

Question 23

Where do the paraventricular and supraoptic nuclei release ADH from?

Answer 23

The axon terminus in the posterior pituitary glands

Question 24

What is the threshold for ADH release?

Answer 24

280-285 mOsm/Kg

Question 25

Above the range, what do small changes in osmolality lead to?

Answer 25

Large changes in ADH secretion

Question 26

When do you get a strong desire to drink?

Answer 26

Plasma osmolality > 295 mOsm/Kg

Question 27

What else can thirst be stimulated by?

Answer 27

Large drops in blood volume/ pressure and angiotensin 2 acting on hypothalamus

Question 28

What is the main determinant of ECF osmolality?

Answer 28

Plasma [Na+]

Question 29

What formula do you use to estimate plasma osmolarity?

Answer 29

2[Na+] + 2[K+] + [glucose] + [urea]

Question 30

What is hypernatraemia?

Answer 30

Too little water (too much sodium)

Question 31

What are the causes of hypernatraemia?

Answer 31

Gain of sodium or loss of water (more common)

Question 32

How can you gain sodium?

Answer 32

Iatrogenic, excess ingestion, excess mineralocorticoid activity

Question 33

What does iatrogenic mean?

Answer 33

Unintended side effect of medical treatment

Question 34

What can cause a loss of water?

Answer 34

Extrarenal losses (dehydration/infection) Renal losses (osmotic diuresis/ diabetes insipidus)

Question 35

What is osmotic diuresis?

Answer 35

Impaired tubular fluid dilation meaning the osmotic gradient is off so water reabsorption is decreased

Question 36

What causes diabetes insipidus?

Answer 36

Lack of effective ADH- either due to a failure of secretion (central) or a lack of renal response (nephrogenic)

Question 37

What does hypoosmotic hypernatraemia signify?

Answer 37

Water excess

Question 38

When does pseudohyponatraemia occur?

Answer 38

When some other solute conc is high enough that sodium has to be reduced to maintain electro neutrality

Question 39

What can cause syndrome of inappropriate ADH secretion?

Answer 39

CNS damage/ disease and ectopic ADH production by tumour

Question 40

What does syndrome of inappropriate ADH secretion cause?

Answer 40

Hyponatraemia and high urine osmolarity

Question 41

Which is more powerful- low volume/ pressure or osmotic signals?

Answer 41

Low volume/ pressure

Question 42

What happens in kidneys in congestive heart failure?

Answer 42

RAAS -> sodium/ water retention (volume expansion) -> ineffective because dodgy starling forces -> oedema