L28 Regulation of Salt Balance Flashcards
What effect does excessive fluid ingestion have on ECF osmolality?
Excess fluid intake = ↓osmolality of ECF
What are some examples of events that ↑ ECF osmolality?
Fluid deprivation, excess solute ingestion, diarrhoea etc.
Which hypothalamic osmoreceptors detect ECF osmolality?
Supraoptic and paraventricular nuclei (regulate ADH)
Lateral preoptic (controls thirst)
True or false: The kidneys can produce up to 23 litres of urine per day
True.
True or false: The kidneys can produce as little as 300ml of urine per day
True.
What determines osmolality of ECF?
A) Water content
B) Salt content
C) Both A and B
D) Neither A nor B
C) Both A and B
Osmolality is determined not only by water content, but also by salt content
What is the major cation in ECF?
Na
True or false: Hypernatremia can result in hypotension
False.
↑Na = ↑H2O, therefore hypernatremia leads to hypertension
True or false hyponatremia can result in hypovolaemia
True.
↓Na = ↓H2O
This leads to hypovolaemia and hypotension
Why does water follow sodium?
Sodium increases osmolality of the fluid, so ↑Na in ECF will lead to ↑osmosis of water.
Water will diffuse out of a hypotonic solution into a hypertonic solution.
Hypertonic = greater osmolality = more solute
Increase ECF osmolality will lead to what response from the body?
↑ osmolality = ↑ Na
Therefore, need to increase water in ECF.
Responses: ADH secretion (↑ water retention) and thirst (↑ fluid intake)
Decrease ECF osmolality will lead to what response from the body?
↓ osmolality = ↓ Na
Therefore, ↓ water in ECF.
Responses: ADH suppression (↑ water excretion)
Define ‘effective circulating volume’
The component of blood which is perfusing the tissues
Not necessarily identical to the intravascular blood volume - e.g. congestive heart failure
True or false: Renin is an enzyme
True
Where is renin synthesised and stored?
Juxtaglomerular apparatus
True or false: Increasing the effective circulating volume stimulates release of renin
False.
↑ sympathetic activity
↓ afferent arteriolar pressure
↓ Na delivery at macula densa (end of the loop of Henle/start of distal tubule)
These are all reflective of a decrease in ECV (caused by ↓Na)
There are two mechanism of renin release:
- The __1__ releases __2__, which stimulates granular cells to release renin into blood.
- __3__ nerves via __4__ receptors
- macula densa
- prostaglandin I2 (PGI2)
- Sympathetic
- beta-adrenergic
Which agent in the RAA system is a decapeptide messenger?
Angiotensin I
Which agent in the RAA system is a plasma protein that is cleaved by renin?
Angiotensinogen
Which plasma endothelial enzyme converts angiotensin I to angiotensin II?
Angiotensin converting enzyme (ACE)
Which agent in the RAA system is an octapeptide, and the primary hormone in Na regulation?
Angiotensin II
What is angiotensin II broken down into?
Angiotensin III and inactive products. Broken down by plasma peptidases
In what ways does angiotensin II increase blood pressure?
- Vasoconstriction
- ↑Na reabsorption from proximal tubule
- Stimulates aldosterone secretion - ↑Na reabsorption from distal tubule
- Thirst
- ADH release (water retention)
Removal of which organ results in:
- ↑NaCl excretion via urine
- ↓Na in ECF
- ↓ ECF volume
- Circulatory collapse
Adrenal glands - loss of aldosterone
Death can be avoided by high Na diet and aldosterone replacement therapy
Which agent in the RAA system is synthesised and secreted from zona glomerulosa?
Aldosterone
Aldosterone is:
A) a glucocorticoid B) a mineralocorticoid C) an androgen D) synthesised from cholesterol E) Both B and D
E) Both B and D
Remember that it regulates body minerals, therefore is a mineralocorticoid.
Which of the following is a trigger for release of aldosterone?
A) ↑ plasma [K] B) ↓ plasma [K] C) ↑ plasma [Na] D) ↓ ECV E) Both B and C F) B, C and D G) Both A and D
G) Both A and D
Stimuli for aldosterone release include:
↑ plasma K concentration
↓ plasma Na concentration
↓ ECV
Aldosterone promotes:
A) Na reabsorption in collecting duct B) K secretion in collecting duct C) H secretion in collecting duct D) Na reabsorption in gut and sweat glands E) All of the above
E) All of the above
What are principal cells and intercalated cells?
Cells in collecting duct epithelium.
Principal cells: main Na reabsorbing cells. Site of action for aldosterone, K-sparing diuretics and spironolactone.
Intercalated cells: H secretion, bicarbonate reabsorption
Which 28 amino acid hormone is released in response to hypovolaemia?
Atrial natriuretic peptide
Atrial = released from atrial cell in response to atrial stretch
Natriuretic = causes ↑ Na excretion in urine
Which 32 amino acid hormone is produced in the kidney and has natriuretic properties?
Urodilatin
Almost identical to ANP (4 extra AAs), same actions, but is produced in kidney not the atria.
What are the actions of ANP and urodilatin?
- Inhibit collecting duct Na-K ATPase
- Inhibit aldosterone secretion
- Reduce renin secretion
- Promotes vasodilation of afferent arteriole to ↑ GFR (more filtrate = more Na lost)
Which natriuretic agent is synthesised in the proximal tubule and inhibits Na-K ATPase and Na-H antiport?
A) ANP B) BNP C) Urodilatin D) Dopamine E) Kinins F) Adrenomedullin
D) Dopamine
Which 52 amino acid peptide is synthesised in the kidney, increases GFR and decreases Na tubular reabsorption?
A) ANP B) BNP C) Urodilatin D) Dopamine E) Kinins F) Adrenomedullin
F) Adrenomedullin
Which of the following counteracts ADH and is produced by the enzyme kallikrein?
A) ANP B) BNP C) Urodilatin D) Dopamine E) Kinins F) Adrenomedullin
E) Kinins
