Renal Glomerular Filtration Flashcards
What is GFR?
Glomerular filtration rate
Rate of formation of filtrate in Bowman’s space
What are the four determinants of GFR?
- Intraglomerular (capillary) pressure
- Capsular pressure
- Oncotic pressure
- Glomerular permeability and surface area
What three factors are involved in the regulation of GFR?
- Autoregulation
- Tubuloglomerular feedback
- Neurohormonal influences
What is normal GFR?
80-125 ml/min
How do glomerular capillaries differ from peripheral capillaries?
Capillaries in the kidney are bound on both sides by arterioles (the aferent and the efferent), rather than an arteriole and a venule.
How is pressure within the glomerular capillary adjusted?
Tone of afferent or efferent arterioles
Which is relatively higher, glomerular or systemic blood pressure
Glomerular, this is good because we want fluid to to pushed out into Bowman’s space
What is intraglomerular pressure?
Pressure within the glomerular capillary
What is capsular pressure?
Pressure in Bowman’s space that opposes fluid movement out of the glomerular capillary
What is trans glomerular pressure?
The difference between the intra-glomerular pressure and capsular pressure.
What limits the filtration in the glomerulus to about 20% of the plasma?
Oncotic pressure
When does glomerular filtration stop?
When oncotic pressure exceeds transglomerular pressure
What affects GFR, increased permeability or decreased permeability?
Decreased permeability can reduce GFR
What is least likely to have an effect on GFR?
Glomerular permeability and surface area
How does the kidney maintain GFR despite variations in systemic blood pressure under physiologic conditions?
Changes in pre- and post-capillary arteriolar resistance, which produces a constant intra-glomerular pressure
What is the mean arterial pressure of the glomerulus?
60mmHg
How does the afferent arteriole respond to an increase in systemic blood pressure?
Afferent arteriole tone increases to prevent the increased pressure from reaching the capillary
How does the afferent arteriole respond to decreases in systemic blood pressure?
Afferent arteriolar tone decreases to allow more of the systemic blood pressure into the capillary
What is meant by the term autoregulation of GFR?
Increases/decreases in tone of afferent arteriole
What is tubuloglomerular feedback?
Changes in GFR in response to changes in tubular flow rates - mediated by the macula densa and the juxtaglomerular apparatus
What ion does the macula densa sense?
Chloride ions
How does the macula densa respond to changes in chloride concentrations?
When chloride delivery increases (increase in GFR), response initiated to decrease GFR, and vice verse.
What is effective circulating volume?
Volume of arteriole blood effectively perfusing tissue
What effect does nor-epinephrine and epinephrine have on the kidney?
Increased renin release and tubular sodium re-absorption
What effect does the renin-angiotensin system have on the kidneys?
Vasoconstriction systemically (to increase blood pressure) and vasoconstriction of both afferent(less) and efferent(more) arterioles to increase intra-glomerular pressure at the expense of reduced blood flow to the kidneys (a shunt).
Define renal blood flow
Rate of blood flowing through kidney
Define renal plasma flow
Rate of plasma (blood - RBCs) flowing through kidney
Define filtration fraction
Portion of plasma that becomes filtrate
What makes up the glomerular filter?
- Vascular endothelium
- Glomerular basement membrane
- Podocyte
(4. Mesangial cells)
What determines glomerulus permeability?
- Pore size
2. Charge (negative - opposites attract therefore filtering positive substances well)
How are major fluctuations in GFR handled?
Renin-angiotensin-aldosterone system
How does the body respond to an increase in effective circulating volume?
- Atrial natriuretic peptide (from dilated atria)
2. Dopamine (vasodilation)
