Lesson 29: Topic 25 - Glomerular Filtration Flashcards
calculating glomerular filtration is determined by?
hydrostatic and osmotic pressures across the glomerular capillary and Bowman’s space
what pressure dictates filtration?
glomerular capillary blood pressure (Pgc) (55mmHg)
- driving pressure of the blood in the glomerular capillary to drive plasma into the Bowman space and across the glomerular capillaries
what pressures oppose filtration?
- bowman’s space fluid pressure (Pbs) (15mmHg)
- plasma protein osmotic pressure (Pi gc) (30mmHg)
why is there no osmotic pressure from the plasma proteins in bowman’s space?
because they cannot pass the barrier from the capillary into the bowman’s space
what is the NET glomerular filtration pressure?
= Pgc - Pbs - Pigc = 10mmHg
- positive number then indicated that there is filtration occurring across the glomerulus
is there reabsorption happening at the glomerulus capillary?
no, there is not a long capillary like there is in blood vessels. it is a very blunt filtration space
what is the glomerular filtration rate (GFR) equation?
GFR = net filtration pressure x Kf
what is net glomerular filtration pressures biggest determinant?
glomerular capillary blood pressure
what is glomerular filtration rate determined by?
- net filtration pressure (largely controlled by Pgc - glomerular capillary blood pressure)
- filtration co-efficient (Kf)
what is filtration co-efficient determined by?
- dependent on:
- surface area of capillaries
and - glomerular permeability (capillary pores)
true or false: glomerular permeability is a determinant of net glomerular filtration rate
true
what is plasma protein fluid pressure?
nothing. it is called plasma protein osmotic pressure. not fluid pressure
how does blood pressure affect GFR? (glomerular filtration rate)
- increased arterial blood pressure (increases blood flow into the glomerulus) –> increases glomerular capillary blood pressure –> increases net filtration pressure –> increases GFR
what is the indirect way of affecting GFR?
- we are going to alter the afferent arteriole (we can also use the efferent arteriole) by vasoconstricting or vasodilation but also by keeping MAP the same
ex1. vasoconstrict afferent arteriole (producing less blood being delivered to glomerulus) –> lowers glomerular capillary blood pressure –> lower net filtration pressure –> lower GFR
ex2. vasodilation = the oppose of ex1
if we vasoconstrict the efferent arteriole, does the afferent need to vasoconstrict?
no. there is typically no correlation. they are independent of each other
how is GFR affected if we vasoconstrict the efferent arteriole?
- increased glomerular capillary pressure (Pgc) (more blood accumulation in the glomerulus)–> increase glomerular filtration rate
how is GFR affected if we vasodilate the efferent arteriole?
- decreased glomerular capillary pressure (Pgc) –> decrease glomerular filtration rate
which of the indirect GFR affects will cause the greatest decrease in glomerular filtration rate?
afferent vasoconstriction (restricting the amount of blood flow entering glomerulus) and efferent vasodilation (opening the leak of blood)
does glomerular filtration rate (GFR) ALWAYS vary with changes in MAP?
yes
- if MAP increases –> glomerular capillary pressure (Pgc) Increases –> GFR increases
an increase in MAP is dangerous. what are the implications?
dangerous imbalance of fluids, electrolytes, and wastes (excess excretion)
- we need a regulatory mechanism to maintain a steady GFR
what is the regulatory mechanism to maintain a steady GFR?
- flow autoregulation
- juxtaglomerular (tubuloglomerular) feedback
how does the flow autoregulation in the kidneys work?
if we increase MAP, that is going to cause a myogenic response in the afferent arteriole. which will then immediately increase glomerular capillary pressure and increase GFR
- but then we have the reflex response. the myogenic response where the afferent arteriole is going to constrict and then it is going to help maintain glomerular capillary pressure (decrease it) and bring GFR to normal
juxtaglomerular feedback alter glomerular filtration rate based on?
the amount of sodium chloride concentration that is in the tubule
where does the juxtaglomerular feedback happen?
in the juxtaglomerular apparatus
where is the juxtaglomerular appartus?
at the intersection between where the afferent arteriole and the efferent arteriole meet
in the kidney, there is a sensor of NaCl. where is it?
in the macula densa cells that are inside the distal tubule
what are the macula densa cells?
they are specialized epithelial cells that sense distal tubule NaCl FLOW –> secrete paracrine factors that affect afferent arteriole diameter
what are granular cells?
specialized endothelium within afferent arteriole –> produce factors in response to macula dense factors and SNS
too much NaCl excreted in urine means that?
we have less ability to hold water
assuming the distal tubule detects a high NaCl concentration inside the distal tubule, it will be sensed by the Macula densa which will then secrete?
adenosine
what does adenosine do?
cause vasoconstriction of the afferent arteriole which will decrease glomerular pressure which will decrease GFR and then decrease the NaCl
- which will then help retain NaCl and water in the body
- negative feedback loop
assuming the distal tubule detects a low NaCl concentration inside the distal tubule, it will be sense by the Macula densa which will then secrete?
prostaglandin
low NaCl indicates?
low blood volume or low blood pressure
what does prostaglandin do?
induce afferent arteriole vasodilation –> increase blood flow to the capillary –> increase glomerular capillary pressure –> increase glomerular filtration rate
what does high GFR do?
high GFR helps retain NaCl and water in the body by increasing tubular reabsorption
if the GFR is too low then our kidneys are or are not function properly?
are not functioning properly
what happens to our Macula dense if we do not have sufficient sodium?
the sensor of macula densa (which regulates glomerular filtration rate) does not have sufficient sodium to work as a sensor to cause afferent arterial vasodilation or constriction to regulate GFR
how do we ensure that there is always enough NaCl for the macula densa to sense it?
because the negative feedback loop of the juxtaglomerular apparatus, the increase GFR helps retain NaCl and water in the body
why does someone urinate more when they drink coffee?
it blocks the rate of adenosine
- which then prevents afferent arteriole vasoconstriction from occurring which then increases glomerular capillary pressure and increases GFR
