renal 2 Flashcards
what is filtration?
filtration of plasma from the glomerular capillaries into the kidney tubules is the first step in urine formation
-RBCs and plasma proteins remain in the blood, plasma and dissolved solutes make up filtrate
-of all the plasma that enters into the Bowman’s capsule, only 20% is filtered (filtration fraction), 80% continues on to the peritubular capillaries
what is the equation for filtration?
what is the renal corpuscle?
what is the triple filtration barrier?
what are mesangial cell?
-supportive and connective tissue cells
-can influence filtration by reducing surface area (by contracting)
what are the three pressures govern filtration from glomerular capillaries into the renal tubules?
-hydrostatic pressure
-colloid osmotic pressure
-bowman’s capsule hydrostatic pressure
what is hydrostatic pressure?
hydrostatic pressure of blood in the glomerular capillaries favors filtration (55mm Hg) (overall blood pressure)
what is colloid osmotic (oncotic) pressure?
colloid osmotic pressure of the blood is the pressure gradient due to the presence of plasma proteins and opposes filtration (30 mmHg)
what is bowmans capsule hydrostatic pressure?
(fluid pressure) opposes filtration (15mmHg)
what is GFR?
glomerular filtration rate
-the volume of fluid that filters from the glomerular capillaries into the bowman’s capsules per unit time
how much plasma does GFR in a day?
-normally 125 ml/min or 180L/day
-our plasma volume is about 3L meaning the kidneys filter our entire plasma volume approximately 60 times per day
-if it was not reabsorbed we would run out of plasma in about 24 minutes
GFR is ____________
RELATIVELY CONSTANT
-relatively constant over a wide range of blood pressures
what is GFR primarily regulated by ____________
renal arterioles (afferent and efferent)
how does the GFR remain relatively constant?
-renal blood flow is dependent on overall resistance, which is determined by the resistance in both the afferent and efferent arterioles
-if afferent arteriole resistance decreased and efferent stayed the same then RBF would increase, hydrostatic pressure increase and GFR increase
REGULATION MAINLY OCCURS AT THE AFFERENT ARTERIOLES
what happens for the GFR to decrease and increase?
what is the GFR autoregulation?
two auto-regulatory mechanisms maintain a relatively stable GFR in the face of normal blood pressure fluctuations
-to protect the filtration barriers from high blood pressure that would cause damage
what are the two mechanisms of autoregulation of GFR?
-myogenic response of the afferent arterioles (myogenic autoregulation)
-tubuloglomerular feedback
what is myogenic autoregulation?
contraction in response to stretch of the vascular smooth muscle
what is the graph of myogenic autoregulation?
what is tubuloglomerular feedback?
-local control pathway in which fluid flow through the tubule portion of the nephron influences GFR
what is the tubuloglomerular feedback graph?
increased NaCl transport in macula densa cells/increased cilia movement
what other two factors can influence GFR? and how is it allowed?
-sympathetic neurons
-hormones
-integrating centers outside the kidneys are capable of overriding the local control mechanisms by altering resistance or filtration coefficient
how can sympathetic neurons influence GFR?
-sympathetic neurons release norepinephrine that acts on a1 adrenergic receptors on both afferent and efferent arterioles leading to vasoconstriction
-sympathetic activation only really alters GFR when there is a sharp rapid drop in blood pressure (ex: hemorrhage or severe dehydration when water needs to be conserved)
how do hormones influence GFR?
-two important hormones that modulate arterioles resistance are angiotensin II, which is a potent vasoconstrictor and prostaglandins, which act as vasodilators
-these hormones are also believed to alter the filtration coefficient by acting on podocytes and/or mesangial cells
-modulation of podocytes changes the size of the filtration slits altering permeability for filtration
-contraction of mesangial cells alters capillary surface area available for filtration
