Renal 2 Flashcards
What is the first step of urine formation
Filtration of plasma from glomerular capillaries into the kidney tubules
What remains in blood during filtration
RBCs and plasma proteins
What makes up filtrate
Plasma and dissolved solutes
How much of the plasma that enters bowman’s capsule is filtered
20% (filtration fraction)
80% continues to peritubular capillaries
Not all can be filtered (would turn to sludge)
How much of CO do kidneys receive
~ 20%
1L/min
How much of blood that kidney recieves is plasma
60%
.6L/min
How much of plasma is filtered
20% of the 60%
.12L/min
What is normal minute filtration rate
125 ml/min
Where do the bowman’s capsule and glomerulus exist within
The renal corpuscle
What is the triple filtration barrier
- Glomerular capillary endothelial cells (fenestrated)
- Basal lamina (Extracellular matrix)
- Podocyte endfeet)
What are podocytes
- tiny extensions that form end feet that cover glomerular capillary walls
- can contract or retract feet
Mesangial cells
Supportive connective tissue cell
- contract and reduce surface area
What can mesangial cells and podocytes do
Influence filtration
What 3 pressures govern filtration from glomerular capillaries into renal tubes
- Hydrostatic pressure
- Colloid osmotic (oncotic) pressure
- Bowman’s capsule hydrostatic pressure
Hydrostatic pressure
Pressure of blood in glomerular capillaries
- favours filtration (determines how much pushed out)
- ~55 mmHg
Colloid osmotic (oncotic) pressure
Pressure gradient due to presence of plasma proteins and opposes filtration
~30 mmHg
How does the presence of plasma proteins oppose filtration
Remain with glomerulus and water attracted to excess protein (pulls in)
Bowman’s capsule hydrostatic pressure
Fluid pressure of the small structure of nephron on the capillaries
opposes filtration
~15 mmHg
Calculation of net filtration pressure
Hydrostatic - oncotic - fluid pressure=
What is a glomerular filtration rate (GFR)
Volume of fluid that filters from the glomerular capillaries into the bowman’s capsules per unit time (usually /min)
What is normal GFR
~125mL/min or 180L/day
How many times do the kidneys filter our entire plasma volume in a day
Plasma volume 3L
60 times per day
If not reabsorbed how quickly would we run out of plasma
24 mins
What 2 factors influence GFR
Net Filtration pressure and filtration coefficient
What 2 things determine the filtration coefficient
Slit surface area and filtration barrier permeability
What is GFR constant over
Wide range of blood pressures
What is GFR primarily regulated by
Renal arterioles (afferent and efferent)
- more at afferent
Autoregulation maintains a nearly constant GFR between what mean arterial blood pressures
80-180
How do the afferent and efferent arterioles regulate GFR
Vasoconstriction and vasodilation
What does vasoconstriction of afferent arteriole cause
Increases resistance, decreased renal blood flow, decreased capillary blood pressure, decreased GFR
What is dependent on overall resistance
Renal blood flow
What is overall resistance determined by
Resistance in both afferent and efferent arterioles
What happens with increased resistance in efferent arteriole
Decreased renal blood flow, increased capillary blood pressure, increased GFR
- blood polls in glomerulus
What would happen if afferent arteriole resistance decreased and efferent stayed the same
RBF would increase, hydrostatic pressure increase, GFR increase
What are 2 auto regulatory mechanisms that maintain stable GFR in face of BP fluctuations
- Myogenic response of afferent arterioles (Myogenic autoregulation)
- Tubuloglomerular feedback
What does the auto regulatory mechanisms protect
The filtration barriers from high BP that would cause damage
What is Myogenic autoregulation
Constriction in responses to stretch of the vascular smooth muscle caused by increased blood flow
What is tubuloglomerular feedback
Local control pathway in which fluid flows through the tubule portion of the nephron influences GFR
Juxtaglomerular apparatus
Where nephron loops back on itself so ascending limb of loop of henle passes between afferent and efferent arterioles
What do the macula densa cells do
Sense increased amount of flow
What do the macula densa cells do
Sense distal tubule flow and release paracrine signals that affect afferent and efferent arteriole diameter
What do granular cells do
Secrete an enzyme involved in salt and water balance
How do macula densa cells sense change
Possibly increased NaCl transport or increased cilia movement
What other 2 factors influence GFR
Sympathetic neurons
Hormones
How do sympathetic neurons influence GFR
Release norepinephrine that acts on a1 adrenergic receptors on both afferent and efferent arterioles leading to vasoconstriction
How do sympathetic neurons and hormones influence GFR
Integrating centers outside kidneys can override the local control mechanisms by altering resistance or filtration coefficient
When does sympathetic activation alter GFR
Sharp rapid drop in blood pressure
Ex) hemorrhage or sever dehydration
What hormones influence GFR
Angiotensin II, vasoconstrictor
Prostaglandins, vasodilators
How else can the hormones alter the filtration coefficient
Act on podocytes and/or mesangial cells
How do hormones affect podocytes
Change size of filtration slits altering permeability
How do mesangial cells alter the filtration coefficient
Contraction of these cells alter capillary surface area available
