Test 5 - renal Flashcards
What are the 3 barriers of glomerular filtration?
Glomerular capillary endothelium
Glomerular basement membrane
Visceral epithelium (podocytes)
How large are the fenestrations in the glomerular capillary endothelium?
~100nm
Is the glomerular basemement membrane positively or negatively charged?
negatively
How large are the filtration slits in the visceral epithelium (podocytes)?
~40nm
What is renal blood flow? What is percentage of renal blood flow?
Renal blood flow is the fraction of blood the kidneys recieve from total cardiac output
20%
What is renal plasma flow?
Renal plasma flow (RPF)
RPF = RBF x (1 - hematocrit)
What is normal glomerular filtration rate?
~125 mL/min
What are the 4 starling forces that govern movement of fluids across the glomerulus? Which force is negligible?
Glomerular Hydrostatic Pressure
Glomerular Oncotic pressure
Bowman’s Capsular Hydrostatic Pressure
Bowman’s Capsular Oncotic Pressure (negligible)
What is the filtration coefficient?
the product of hydraulic permeability (permeability of the capillary) and surface area (of the capillary)
Where is the macula densa? What does it interact with?
The junction between the loop of Henle and the DCT that courses between the afferent and efferent arterioles
Smooth muscle in the afferent arteriole: Granular cells
What do granular cells and the macula densa form? What are its functions?
the juxtaglomerular apparatus
regulation of GFR and systemic blood volume and pressure
What in the juxtaglomerular apparatus secretes renin?
granular cells (smooth muscle in the afferent arteriole)
How does the JGA work? (two functions based on Cl- concentation in the nephron)
tubuloglomerular feedback:
Macula densa senses the amount of Cl- via the NKCC transporter on the macula densa. If Cl- levels are high, the macula densa signals smooth muscle in the afferent arteriole via adenosine to contract, decreasing GHP and thus GFR
Renin response:
Macula densa senses the amount of Cl- via the NKCC transporter on the macula densa. If Cl- levels are low (volume loss), the macula densa signals granular cells in the afferent arteriole via PGE2 to vasodilate and secrete renin
What are the 3 factors that mediate renal autoregulation (RBF and GFR)
Myogenic reflex
tubuloglomerular feedback
neurohormonal factors
Describe tubuloglomerular feedback
Macula densa senses the amount of Cl- via the NKCC transporter on the macula densa. Increased GHP leads to an increase in Cl- levels. The macula densa senses this increase and signals smooth muscle in the afferent arteriole via adenosine to contract, decreasing GHP and thus GFR
Describe myogenic reflex
An autoregulatory range allows for flow to remain constant through afferent arterioles. As pressure increases within the autoregulatory range, smooth muscle contracts in an attempt to maintain steady flow. As pressure decrease within the autoregulatory range, smooth muscle relaxes in an attempt to maintain steady flow.
Describe neurohormonal factors (RAAS components) in regulating RBF and GFR
Renin converts angiotensinogin (liver) to angiotensin I. ACE (lungs and kidney) convert angiotensin I to angiotensin II. Angiotensin II does a lot of stuff
Secretion of renin is regulated by 3 things. What are they?
Intrarenal baroreceptors
macula densa
renal sympathetic nerves
How do intrarenal baroreceptors regulate renin secretion? What would happen if the baroreceptors sensed a fall in pressure?
the granular cells in the JGA are baroreceptors that monitor afferent arteriole pressure.
A fall in pressure would result in the secretion of renin
How does the macula densa regulate renin secretion? What would happen if the macula densa sensed a fall in tubular Cl-?
Macula densa senses the amount of Cl- via the NKCC transporter on the macula densa.
If Cl- levels are low (volume loss), the macula densa signals granular cells in the afferent arteriole via PGE2 to secrete renin
How do renal sympathetic nerves regulate renin release?
vascular baroreceptors sense low BP —> increased sympathetic tone to kidney —> renin release by granular cells
What are the 4 major actions of angiotensin II?
- Vasoconstriction
- contsticts arterioles throughout the body
- Na+ balance
- Na+ reabsorption in PCT
- stimulates aldosterone release –> Na+ reabsorption in the distal nephron
- Water balance
- stimulates ADH release –> H2O reabsorption distal nephron
- stimulates thirst
- Effects on GFR
- low dose, no effect little effect on GFR as it mostly works on efferent arteriole
- High dose, decrease in GFR as it constricts afferent and efferent arterioles
Describe the SNS control over the kidney during hypotension
During hypotension, SNS causes vasoconstriction, which diverts blood from the kidney to other vital organs. This minimizes the loss of water and salt
At rest, is the sympathetic tone to the kidney low?
you betcha