Glomerular Filtration & Renal Blood Flow Flashcards
T or F?
Things bigger than 50,000 daltons typically are too big to be filtered in the glomerulus
False
It’s anything greater than 60,000 (such as albumin)
What are the 3 layers that filtrate must pass through in the glomerulus?
1) Fenestrated capillary endothelium (isn’t too selective of what it lets pass)
2) Negatively charged basal lamina
3) Tubular podocyte epithelium
Which 2 layers are primarily responsible for the molecular sieving of the glomerulus?
The basal lamina (which is negatively charged) and the tubular epithelial podocytes
What are the Starling forces that drive and oppose glomerular filtration?
Drive: Hydrostatic pressure caused by blood pressure
Oppose: 1) Hydrostatic pressure of tubule (Pt)
2) Net osmotic force (Pigc)
What is the Starling equation for GFR?
What do the different variables represent?
GFR=K(Pgc-Pt-Pigc)
K is a constant that is affected by hydraulic conductivity and total glomerular surface area
Pgc is the hydrostatic pressure created by BP
Pt is hydrostatic pressure in tubule
Pigc is the oncotic pressure
State the typical magnitude of each of the Starling forces and the resultant net filtration pressure.
Pgc = 46 mm. Pt = 10 mm. Pigc = 30mm
NFP = the sum = 6 mm.
How does the body autoregulate for changes in MAP to maintain a constant GFR?
Inside what ranges of pressure can this autoregulation do its job?
It is vital to maintain a constant GFR to keep homeostasis and all of the balances where they should be. The afferent arterioles are able to adapt to changes in MAP by either constricting or dilating to make sure that the flow to the glomerulus remains constant.
This autoregulation occurs only from about 75-150 mmHg, which is why malignant hypertension can be very dangerous.
How do the kidneys and arterioles respond to hypovolemia (different response from autoregulation)
In hypovolemia, the total renal blood flow is decreased. As a response, both the afferent and efferent arterioles constrict to make sure the glomerulus gets proper blood flow. The hypovolemic response trumps the autoregulation mechanism.
*Thus, whereas with low blood pressure the afferent arteriole dilates, in hypovolemia the afferent and efferent arterioles actually constrict.
What role do renal prostaglandins play in hypovolemic conditions?
Since we know in hypovolemia the afferent and efferent arterioles constrict, the kidney has to do something to prevent ischemic events.
Renal prostaglandins oppose the actions of AII and cause the afferent arterioles to dilate. They do not oppose or take away the hypovolemic mechanisms, they just make sure the kidney gets adequate blood flow
Where are renal prostaglandins produced and what are they released in response to?
Produced in the renal interstitial cells in the medulla.
Released in response to AII, act on AFFERENT arteriole to cause vasodilation.
Where are granular cells located in the kidney and what do they secrete?
They are located in the afferent arteriole and they secrete renin.
