Renal L5: Fluid balance (Na+) Flashcards
What are the 4 steps of the reabsorption process?
- Isosmotic fluid leaving the proximal tubule becomes progressively more concentrated in the descending limb
- Removal of solute in the thick ascending limb creates hyposmotic fluid
- Hormones control distal nephron permeability to water and solutes
- Urine osmolarity depends on reabsorption in the collecting duct
What is step 1 of the reabsorption process?
Isosmotic fluid leaving the proximal tubule becomes progressively more concentrated in the descending limb
What is step 2 of the reabsorption process? (after fluid becomes more concentrated in the descending limb)
Removal of solute in the thick ascending limb creates hyposmotic fluid
What is step 3 of the reabsorption process? (after the ascending limb creates hyposmotic fluid)
Hormones control distal nephron permeability to water and solutes
What is step 4 of the reabsorption process? (after hormones control permeability)
Urine osmolarity depends on reabsorption in the collecting duct
What are the 2 reasons why the kidney controls reabsorption?
maintain:
- ECF volume
- blood pressure
What is Na+ important?
one of main solutes of blood- contributes to osmotic activity
_______ and _____ anions (specifically _____ - + _______) contribute 90% of the ECF osmotic activity
Na+; ECF; HCO3; Cl-
Under normal conditions, the ECF can “retain” enough water to maintain osmolarity at _______ mOsm/L
300
Add more salt to ECF —> retain _____ (more/less) water = 300 mOsm/L. As a result, this _____ (increases/decreases) ECF volume (blood volume) & blood pressure
more; increases
Add more salt to ECF —> _____ (gain/lose) water = 300 mOsm/L. As a result, this _____ (increases/decreases) ECF volume (blood volume) & blood pressure
lose; decrease
ECF volume and blood pressure are _______ (directly proportional/inversely proportional)
directly proportional
If the average salt input is 10.5g/day, how much of it is lost from obligatory loss in sweat and faeces?
0.5g
If the average salt input is 10.5g/day, how much of it is lost from controlled excretion in urine?
10.0g
How is the majority of Na+ loss in the body?
controlled excretion in urine
With Na+ reabsorption, ______ (nearly all/none) of Na+ is reabsorbed from the _________
nearly all; filtrate
Why is Na+ reabsorption for other molecule reabsorption?
Na+ absorption creates a gradient and helps create the absorption for other molecules
Order from most to least % of Na+ being reabsorbed: proximal, Loop of Henle and distal tubule and collecting duct.
Proximal tubule > Loop of Henle > Distal tubule and collecting duct
What is the function of the proximal tubule?
Aids reabsorption of glucose, amino acids, water, Cl- and urea
What is the function of the Loop of Henle?
Allows production of urine of varying concentrations (for osmotic gradient)
What is the function of the distal tubule and collecting duct?
Regulates ECF volume (hormonally controlled)
To maintain a constant salt load, salt intake must equal salt ______.
output
What is the response to a decrease in Na+ load?
What if there is a large drop in blood pressure (eg. Haemorrhage)?
The baroreceptor response causes the constriction of the afferent arteriole which decrease GFR
Na+ reabsorption in the distal tubule & collecting duct is controlled by the hormone _______
aldosterone
Where does aldosterone control Na+ reabsorption?
distal tubule & collecting duct
How does aldosterone control Na+ reabsorption?
Aldosterone promotes the insertion of additional Na+ channels and pumps in the tubular cell membrane
Aldosterone is _______ type hormone and is ____ (hydrophillic/phobic) which means it ____ can/can’t cross a membrane and go into the cell
lipid; hydrophobic; can
What are the 5 steps of aldosterone in Na+ reabsorption?
- Aldosterone combines with a cytoplasmic receptor
- Hormone-receptor complex initiates transcription in the nucleus.
- New protein channels and pumps are made
- Aldosterone-induced proteins modify existing protein
- Result in increased Na+ reabsorption and K + secretion
What is step 1 of aldosterone in Na+ reabsorption?
Aldosterone combines with a cytoplasmic receptor
What is step 2 of aldosterone in Na+ reabsorption? (after combined with a cytoplasmic receptor)
Hormone-receptor complex initiates transcription in the nucleus.
What is step 3 of aldosterone in Na+ reabsorption? (after initiation of transcript in the nucleus)
New protein channels and pumps are made
What is step 4 of aldosterone in Na+ reabsorption? (after protein channels and pumps are made)
Aldosterone-induced proteins modify existing protein
What are 3 factors that renin secretion is stimulated by?
- decreased stretch of the granular cells (ie. decreased blood pressure in the afferent arteriole)
- decreased NaCl in the distal tubule (detected by macula densa cells)
- Baroreceptor reflex (sympathetic stimulation of granular cells)
What are other factors related to fluid balance which also bring out changes? List the 6 steps
- Granular cells secrete renin
- Renin activates angiotensinogen into angiotensin I – Angiotensinogen is a plasma protein (high concentrations but inactive)
- In lungs: Angiotensin I converted into angiotensin II by angiotensin-converting enzyme (ACE)
- Angiotensin II triggers release of aldosterone (hormone) from adrenal cortex
- Aldosterone stimulates Na+ reabsorption from distal tubule and collecting duct
- Water follows Na+ into ECF to restore blood volume & pressure
What happens when there is an increase in NaCl, ECF volume and atrial blood pressure?
The initial response to a drop in blood pressure involves the ______ system, when there is a Car accident with severe blood loss (10%) and a drop in blood volume &blood pressure. ECF osmolarity is normal
cardiovascular
The long term response to a drop in blood pressure involves the _____ system
renal
