- Fluid balance - Na

Question 1

fluid balance

Answer 1

1. isomotic fluiding fluiding leaving proximal tubule becomes progressively more concentrated in the descenfing limb
2. removal of solute through thick ascending limb creates hyposomtic fluid
3. hormones control distal nephron permeability to water and solutes
4. urine osmolarirty depends on reapsorbtion in the collecting duct

Question 2

Na+ balance

Answer 2

kidneys control Na+ reabsorption to maintain ECF volume & blood pressure

Question 3

Na+ balance 2

Answer 3

• Na+ and ECF anions (HCO3- + Cl-) contribute 90% of the ECF osmotic activity
• Under normal conditions, the ECF can “retain” enough water to maintain osmolarity at 300 mOsm/L
– Add more salt to ECFretain more water = 300 mOsm/L • IncreasesECFvolume(bloodvolume)&bloodpressure
– Lose salt from ECFlose water = 300 mOsm/L
• Decreases ECF volume (blood volume & blood pressure)

Question 4

Sources of Na+ input & output

Answer 4

To maintain a constant salt load, salt intake must equal salt output

Question 5

Na+ reabsorption

Answer 5

• Nearly all Na+ is reabsorbed from the filtrate
• It is reabsorbed along the length of the tubule and plays different roles at each sit
* Descending limb of loop of Henle is the only place Na+ is not reabsorbed

Question 6

Hormonal control – Na+ reabsorption

Answer 6

8% of Na+ reabsorption is hormonally controlled
– Distal convoluted tubule & collecting duct
– Renin-angiotensin-aldosterone system (RAAS) • Reabsorbs Na+ (increases blood volume & pressure)
– Natriuretic peptides
• Inhibits Na+ reabsorption (decreases blood volume & pressure)

Question 7

Response to decrease in Na+ load

Answer 7

decrease Na > dc. arterial pressure >
1. > grf > net filtration
2. increase aldosterone > inc. na reabsorption
both lead to
dec exrection of na+ and accompanying cl- and fluid
> inc. conservation of nacl and accompanying fluid

Question 8

haemorrohage recap

Answer 8

The baroreceptor response causes the constriction of the afferent arteriole which dec. GFR

Question 9

RAAS - aldosterone

Answer 9

Na+ reabsorption in the distal tubule & collecting duct is controlled by the hormone aldosterone

• ## aldorsterone promotes the insertion of additional Na+ channels & pumps in the tubular cell membrane

Question 10

RAAS stimulation

Answer 10

RAAS is stimulated by cells of the juxtaglomerular apparatus
• RAAS begins with the secretion of renin by the granular cells
• Renin secretion is stimulated by:
1. dec. stretch of the granular cells (ie. dec. blood pressure in the afferent arteriole)
2. dec. NaCl in the distal tubule (detected by macula densa cells)
3. Baroreceptor reflex (sympathetic stimulation of granular cells)

Question 11

renin

Answer 11

trigers release of aldosterone

Question 12

RAAS

Answer 12

1. Granular cells secrete renin
2. Renin activates angiotensinogen into angiotensin I
   – Angiotensinogen is a plasma protein (high concentrations but inactive)
3. In lungs: Angiotensin I converted into angiotensin II by angiotensin-converting enzyme (ACE)
4. Angiotensin II triggers release of aldosterone (hormone) from adrenal cortex
5. Aldosterone stimulates Na+ reabsorption from distal tubule and collecting duct
6. Water follows Na+ into ECF to restore blood volume & pressure

Question 13

Natriuretic peptides (NP)

Answer 13

• Stimulates Na+ & water excretion to lower blood volume & pressure
• Producedbycardiomyocytesinthe – Atria (atrial natriuretic peptide - ANP)
- normal physiology
– Ventricles (brain natriuretic peptide – BNP)
- heart failure
• NP release is triggered by stretch of the heart chamber (inc. blood volume & pressure)