renal 3 - filtration Flashcards
which two processes involve entry into renal lumen
glomerular filtration and tubular secretion
which two processes involve entry out of the renal lumen
tubular reabsorption and excretion of urine
formula for amount excreted
amount filtered+amount secreted-amount reabsorbed
what are the 3 layers of the glomerular capillary
fenestrated endothelium
basement membrane
podocytes with filtration slits
why cant large proteins or albumin go through filtration (3 reason)
- too large for pores
- pores&BM are negative, they repel negative proteins
- podocyte slits remain covered with find semiporous membranes (nephrins podocins)
what are nephrins and podocins
proteins that determine what can pass through the podocyte slits
what is the ultrafiltrate
the filtrate that passed through the capillary and has nearly identical composition to the plasma (besides RBC and proteins)
what is proteinuria
when there is protein in the filtrate
what could cause proteinurea
issues with nephrins and podocins
is net glomerular filtration always positive or negative and why
always positive because you are pushing things out into the bowmans space
what is PBS and what is its role towards filtration
fluid pressure in bowmans space
opposed filtration
what is piBS
osmotic force due to proteins in bowmans space
BUT ITS 0 because there are no proteins in the bowmans space
overall, what is the difference with P and pi
P is the fluid pressure
pi is the opposing osmotic force
what is PGC and what is its role towards filtration
glomerular capillary blood pressure
favors filtration
what is piGC and what is its role towards filtration
osmotic force due to proteins in plasma
opposing filtration
what is the net glomerular filtration pressure
PGC-PBS-piGC
which direction does PGC go
capillary–>bowman
which direction does PBS go
bowman–>capillary
which direction does piGC go
bowman–>capillary
which direction does piBS go
none cause pretty much zero
otherwise it would go towards to bowmans space
which has the highest pressure (PBS PGC piBS piGC)
PGC
what does Glomerular filtration pressure initate
urine formation by forcing protein ree filtrate from plasma out of the glomerulus into bowmans space
what is filtration fraction (and the %)
only 20% of the plasma entering the afferent arteriole is iltered
what % of the filtered volume is excreted
less than 1%
what % of the filtered volume is reabsorbed
19% (20% filtered, 1% remains)
what is flomerular filtration rate (GFR)
the volume of fluid filtered from the glomerulus into the bowmans space per unit time
what is GFR for human
125mL/min
180L/day
for 70kg man
which 4 factors influence GFR
- net glomerular filtration pressure
- permeability of corpuscular membrane
- surface area for filtration
- neural and endocrine control
how does GFR change with changes in arterial pressure or renal blood flow?
it remains constant so that you don’t damage the nephrons
how do you do autoregulation of GFR
change renal blood vessel resistance (compensate for changes in BP)
how do you change the arteriol resistance
myogenic response of afferent arteriole (smooth muscle)
or the tubuloglomerular feedback effect
what is the tubuloglomerular feedback effect
increase flow causes constriction of the afferent arteriol to reduce GFR
how is the tubuloglomerular feedback effect regulated
- paracrine actions of the juxtaglomerular apparatus (cells close to glomerulus)
- paracrine control of afferent arteriole resistance
what range of blood pressures does autoregulation maintain a nearly constrant GFR
80-180mm Hg
what is mean arteriol blood pressure formula
2/3 diastolic pressure + 1/3 systolic pressure
why does autoregulation of glomerular filtration rate take place in a small range of blood pressures
it doesnt
it is a wide range so that your body can handle a large fluctuation of blood pressure
where does most resistance change occur
afferent arterioles
what happens (to GFR, capillary BP and blood flow) when you increase resistance in afferent arteriole
decrease GFR
decrease capillary BP
decrease renal blood flow
increase flow to other organs
what happens (to GFR, capillary BP and blood flow) when you increase resistance in efferent arteriole
increase GFR
increase capillary BP
decrease renal blood flow
increase flow to other organs
what are two ways to decrease GFR
constrict afferent arteriole
dilate efferent arteriole
what are two ways to increase GFR
dilate afferent arteriole
constrict efferent arteriole
what is myogenic response of GFR regulation
similar to autoregulation in other systemic arterioles
what does autoregulation mean
mean arteriole pressure is fluctuating but this helps keep it constant
what is a role of the juxtaglomerular apparatus
tubuloglomerular feedback
what does increased tubular flow cause to afferent arteriole and why
constrict afferent to reduce GFR
how is tubuloglomerular feedback regulated
paracrine control of afferent arterioles by the juxtaglomerular apparatus
how does afferent smooth muscle react with an increase in BP
smooth muscle cells in the wall of the arteriole are stretched and respond by contracting to resist the pressure, resulting in little change in flow
how does afferent smooth muscle react with an decrease in BP
smooth muscle cells relax to lower resistance, allowing a continued blood flow
what kind of GFR regulation is not autoregulated
hormones and autonomic neurons
how do hormones and autonomic neurons work
not autoregulate
they change resistance in arterioles
what are the components of the juxtaglomerular apparatus
macula densa and juxtaglomerular cells
what/where are the macula densa
cells on the wall of the distal convoluted tubule
what do macula densa sense
can sense increased fluid flow through distal tubule (senses [Na+] and [Cl-])
what do macula densa secrete and what does this cause
secrete vasoactive compounds with paracrine effects on afferent arteriol resistance
this signals to JG cells (controls GFR)
what do juxtaglomerular cells do
secrete renin
where are juxtaglomerular cells
on the wall of the afferent arteriole
what are granular cells
juxtaglomerular cells
what are mesangial cells
similar to smooth muscle, help with muscle contraction
are mesangial cells part of the juxtaglomerular apparatus
noooo
what 4 factors control GFR
- myogenic arteriole reflex
- neuro-endocrine input on arterioles
- paracrine effects of macula densa
- mesangial cells
what happens with contraction of mesangial cells (surface area and GFR)
reduces surface area of glomerular capillaries
GFR decreased
what is the definition of filtered load
total amount of non protein or non protein bound surface filtered into bowman’s space
what is the formula of filtered load
GFRx[substance in plasma]
not protein, its stuff like glucose
what happens when substance excreted in urine
reabsorption
less is released than in the load
what happens when substance excreted in urine>filtered load
secretion
more is excreted than in the load
