7. Glomerular Filtration and Renal Blood Flow Flashcards
For the starling forces in the glomerulus and bowman’s capsule, the osmotic pressure in the bowmans capsule ( Pi BC) is normally zero. What are the other 3 forces?
Glomerular hydrostatic pressure favors filtration
Bowmans capsule hydrostatic pressure (PBC) opposes filtration
Glomerular capillary osmotic pressure (Pi GC) opposes filtration (absorption)
What is the calculation for filtration?
Kf (Pgc - Pbc - Pi gc)
what means the same as colloid osmotic pressure?
oncotic pressure
The ultrafiltration coefficient (Kf) can be calculated by multiplying hydraulic conductivity (permeability/#pores in endothelium) Lp and?
surface area for filtration (Sf)
The two factors involved in calculating Kf (Sf and Lp) multiplied by the PUF (capillary ultrafiltration pressure or the starling forces) will equal?
GFR
so if Lp or Sf increase, so does GFR
If PUF increases so does GFR
What three things can alter the Pgc?
renal arterial blood pressure
afferent arteriolar resistance
efferent arteriolar resistance
The ultrafiltration coefficient (Kf) only changes due to kidney disease and deficiency in glycocalyx. What role do the glomerular mesangial cells play in the ultrafiltration coefficient?
glomerular mesangial cells contract, which influences/ decreases the glomerular surface area, which decreases GFR
Hydrostatic pressure is highest in the renal artery and lowest in the renal vein (normal). Where are the two sites of regulation, seen by a large drop in pressure due to fluid getting filtered out?
at the afferent and efferent arterioles where fluid is filtered out
** relatively high hydrostatic P in glomerular capillary**
When the fluid is being filtered out leaving all the plasma proteins in the blood, this increase its concentration leading to an increase in what ?
oncotic GC (Pi gc)
At the afferent arteriole, Pgc and Pigc are 60 and 25 respectivley, but at the glomerular capillary and efferent arteriole, what occurs?
the oncotic gc pressure increases d/t increase in plasma concentration and the hydrostatic gc will drop only 1-2mmHg
PUF (filtration) remains greater when the blood flow is higher and more of the glomerular capillary is exposed to a net driving force for filtration, which increases?
surface area for filtration
When there is constriction at the afferent arteriole what occurs to the GFR and PUF (starling forces)?
gfr and puf will decrease
When there is dilation at the afferent arteriole what occurs to the gfr and puf?
gfr and puf will increase
When there is constriction at the efferent arteriole what occurs to the gfr and puf?
gfr and puf will increase
When there is dilation at the efferent arteriole what occurs to the gfr and puf?
gfr and puf will decrease
During any dilation and constriction what will occur to renal blood flow?
during dilation at either afferent or efferent, the RBF will increase as opposed to during constriciton RBF will decrease in both.
The kidney consumes about 7 times more blood compared to the brain… this is due primarily to?
O2 consumption which is related to the high Na+ reabsorption in the tubules (possitive correlation)
What are three physiological controls of glomerular filtration and rbf, more focused on changing glomerular hydrostatic pressure and glomerular capillary oncotic pressure?
- vasoactive signals
- hormones
- sympathetics
Intrinsic control of the kidney occurs via what two mechanisms?
autoregulation
tubuloglomerular feedback
Extrinsic control (bigger/systemic things) of the kidney occurs via what three mechanisms?
sympathetic nerves
hormones
composition of blood
Renal blood vessels are richly innervated by sympathetics with strong stimuli which constrict arterioles and decrease rbf/gfr. Local sympathetics and circulating catecholamines active ______ receptors, which are more prevelent in the ______ arteriole.
Alpha 1 receptors which are more prevelent in the afferent arterioles
PGE2 (increases rbf), NO (increase rbf), ANP (increase gfr) and what other two are common vasodilators of arterioles?
bradykinin (increases both) and dopamine (increases rbf)
Glomerulartubular balance increases reabsorption rate within the renal tubes when ?
GFR rises (= inc Na)
Autoregulation maintains rbg and gfr wihtin narrow limits across wide ranges of blood pressures. The local reflex (myogenic) cause smooth muscle contraction to inc BP, while the tubuloglomerular feedback does what?
physiological feedback via juxtaglomerular apparatus (JGA)
changes in tube, feeback to glomerulus
bloodflow autoregulation maintains a stable GFR during what range of arterial pressure changes?
80-170mmHg
below 80 gfr/rbf dec
above 170 gfr same and rbf inc.
The local myogenic reflex senses and resists stretch due to high blood pressure and smooth m contracts in 1-2s. What is more common at the afferent compared to efferent?
afferent arteriolar experiences more constriction while the efferent experiences dilation
The tubuloglomerular feedback uses the juxtaglomerular apparatus which consists of what 3 things?
- macula densa cells
- juxtaglomerular (granular) cells - renin
- Extraglomerular mesangial (lacis) cells
The tubuloglomerular feedback sense the concentration of NaCl/ salt in the blood. it feeds back signal to adjust arteriolar resistance as needed when salt is too high/low. What do the macula densa do?
signal to JG cells when decrease Nacl to release renin and talked to the glomerulus when salt is too high to lessen the amount of blood intake
What is the main job of the tubuloglomerular feeback ?
to maintain constant Na delivery to the distal convoluted tubule and maintain a constant GFR
The macula densa signaling has 4 major steps. The first is increased delivery of NaCl to macula densa tranported via NaCl2K (nKCC2) which leads to an increase in ATP and adenosine. what are steps 3 and 4?
the increase in ATP signals vasoconstriction of the afferent arteriole which decrease GFR so there is less Na in the distal tubule.
What occurs when there is an increased renal perfusion pressure?
signals via macula densa results in vasoconstriction of afferent arteriole to decrease GFR, mediated by adenosine
What occurs when there is a decreased renal perfusion pressure?
Decreased gfr, decrease NaCl delivery to macula densa, signals to JG to secrete renin, makes angiotensinII to restore BP.
*Results in efferent arteriolar vasoconstriction and afferent arteriolar dilation via NO
What are factors that increase sensistivity of TGF (tubuloglomerular feedback)? (5)
volume contraction adenosine PGE2 thromboxane Ang II
What are factors that decrease sensistivity of TGF? (6)
volume expansion ANP NO cAMP PGI2 High protein diet (in Nacl reabsorption so flow)
Afferent arteriole vasodilation via protaglandins, bradykinin, NO, dopamine and ANP results in what regarding rbf, gfr and peritubular capillary hydrostatic pressure?
increases gfr rbf and P
Afferent arteriole vasoconstriction via ace-inhibitors causes?
rbf, gfr, and peritubular pressure to decrease
Efferent arteriole vasodilation via sympathetics causes?
rbf to increase, gfr to decrease and peritubular pressure to increase
Efferent arteriole vasoconstriction via angiotensinII causes?
decrease in rbf, increase or same gfr, and decrease in peritubular pressure (hydrostatic)
