Renal physiology 2 Flashcards
how much( in %) of renal plasma flow gets filtrated?
~25%
~125 ml/min
~180 L/day
what is the main driver of glomerular filtration?
Glomerular blood hydrostatic pressure(GBHP)
net filtration pressure
determines how much water and small dissolved solutes leaves the blood
what are the forces driving plasma filtration?
glomerular blood hydrostatic pressure(GBHP)
what are the forces opposing the filtration of plasma?
capsular hydrostatic pressure(CHP)
Blood colloid osmotic pressure(BCOP)
capsular hydrostatic pressure(CHP)
the pressure exerted on the plasma filtrate by the elastic recoil of the glomerular capsule
what is the normal capsular hydrostatic pressure(CHP) value?
~ 15 mmHg
Blood colloid osmotic pressure (BCOP)
the osmotic force of the proteins left in the plasma: the proteins exert an increasing osmotic “pull” on the water in the plasma filtrate
(Water wants to move in from the capsule to dilute the plasma)
what is the normal BCOP?
~30 mmHg
what is the normal net filtration pressure (NFP)?
~10 mmHg
what is the normal glomerular blood hydrostatic pressure(GBHP)?
~ 55mmHg
what is the relationship between renal pressure and urine output?
directly proportional
Higher pressure-> more urine output
what is the relationship between renal pressure and glomerular filtration rate?
Glomerular filtration rate is relatively constant as blood flow to kidney is tightly regulated even if the pressure is increased
autoregulation in the kidney(2 mechanisms)
glomerular filtration rate and blood flow is tightly regulated
Autoregulation happens in 2 ways:
-Myogenic autoregulation: Elevations in transmural pressure induce contraction of preglomerular arterioles, predominantly at the level of afferent arterioles.
-Tubuloglomerular feedback: It senses changes in the amount of sodium chloride in the tubular fluid reaching the macula densa cells in the distal tubule and adjusts the diameter of the afferent arteriole accordingly. Tubuloglomerular feedback serves as an effective autoregulatory mechanism because the sodium chloride concentration of the fluid reaching the macula densa is dependent on flow rate, which in turn, is related to the GFR and glomerular capillary pressure.
how can increases and decreases in arterial blood pressure be buffered with the help of myogenic autoregulation?
increase in arterial pressure can be buffered by vasoconstriction of the afferent arteriole:
constriction of afferent arteriole-> decrease in renal blood flow-> decrease in glomerular pressure
decreases in pressure can be buffered by vasoconstriction of efferent arteriole:
constriction of efferent arteriole-> decrease in renal blood flow-> increase in glomerular pressure
what are the different mechanisms for regulation of glomerular filtration rate?
– Autoregulation: myogenic autoregulation or tubuloglomerular
feedback
– Neural: Increased sympathetic nerve activity leads to vasoconstriction of the afferent arterioles.
– Hormonal:
* Production of Angiotension II ->vasoconstriction of afferent and efferent arterioles
* Stretching of Atria of the heart stimulates Atrial Natriuretic Peptide production-> relaxation of mesangial cells, increasing the surface area available for filtration
tubuloglomerular feedback
Tubuloglomerular feedback: It senses changes in the AMOUNT( NOT CONCENTRATION) of sodium chloride in the tubular fluid reaching the macula densa cells in the distal tubule and adjusts the diameter of the afferent arteriole accordingly
what types of epithelium are there in different parts of the nephron?
what is the main difference between juxta-medullary and cortical nephrons?
Cortical nephrons produce dilute urine only
Juxtamedullary nephron produces BOTH dilute and concentrated urine
where does the largest amount of solute and water reabsorption occur?
proximal convoluted tubule
where does the largest amount of solute and water reabsorption occur?
proximal convoluted tubule
how much glomerular filtrate is reabsorbed in the proximal convoluted tubule?
~60%
How much NaCl and water is reabsorbed in the proximal convoluted tubule?
~60%
How much glucose is reabsorbed in the proximal convoluted tubule?
~100%
what helps increase the surface area for reabsorption in the proximal convoluted tubule?
brush border(microvilli)
how does absorption occur in the proximal convoluted tubule?
Na+ K+ ATPase pumps Na+ into the interstitial space, creating a Na+ gradient.
Na+ Glucose symporter brings Na+ and Glucose into the cell from the tubule
Glucose diffuses down its concentration gradient from the tubule cells into the blood
Na+diffuses into the blood
Cl- follows to balance charge
Water follows by osmosis
how does absorption occur in the proximal convoluted tubule?
Na+ K+ ATPase pumps Na+ into the interstitial space, creating a Na+ gradient.
Na+ Glucose symporter brings Na+ and Glucose into the cell from the tubule
Glucose diffuses down its concentration gradient
what type of absorption happens in the proximal convoluted tubule?
Isoosmotic
Osmolarity of the filtrate does not change
what processes happen in the descending loop of Henle?
Low permeability to ions
High permeability to water
Because the interstitial fluid is highly concentrated in the medulla of the kidney water moves out of the tubule via osmosis.
By the bottom of the loop of Henle, the filtrate is very concentrated(1200 mOsmol/L)
What is the permeability to ions and water of the descending loop of Henle?
Low permeability to ions and urea
High permeability to water
what processes happen in the ascending loop of Henle(particularly in the thick limb)?
This segment is impermeable to water and highly permeable to ions
Na+ K+ and Cl- actively reabsorbed
the tubular content becomes more dilute with the osmolarity of 100 mOsmol/L at the top of the loop of Henle( as it enters the early distal tubule segment)
what is the osmolarity of the filtrate at the bottom of the descending loop of Henle?
1200 mOsmol/L
what is the osmolarity of the filtrate at the top of the ascending loop of Henle?
100 mOsmol/L
How does the flow in ascending and descending tubule influence each other?
descending limb is impermeable to Ions (NaCl)
Ascending limb is impermeable to water and highly permeable to ions
Interstitial fluid is incredibly concentrated at the tip of the medulla
Ions that move out of the ascending limb provide the gradient for the water to move out from the descending limb
Loop of Henle-countercurrent mechanism
the flows of ions and water in descending and ascending tubules support each other
This is further supported by the blood flow in the vasa recta. The tubule and arteriole flows are going in opposite directions. Interstitial fluid is NOT diluted as H2O moves out of the descending loop and into the capillaries. So do the ions from the ascending loop.
what processes take place in the distal tubule and collecting duct?
Additional NaCl is reabsorbed here
In the absence of ADH( antidiuretic hormone) this section is also impermeable to water and results in the production of a dilute urine
reabsorption of Na+ and secretion of K+
what is the osmolarity of the filtrate produced in the renal corpuscle?
the same as the plasma
~300 mOsmol/L
Has the same composition as the plasma but does not contain plasma proteins
what is the osmolarity of the filtrate produced in the renal corpuscle?
the same as the plasma
~300 mOsmol/L
Has the same composition as the plasma but does not contain plasma proteins
what parts of the kidney tubules have the same osmolarity of ~300 mOsmol/L?
Afferent arteriole= efferent arteriole= glomerulus=renal capsule= proximal convoluted tubule
what effect does an increased NaCl lvl in the distal convoluted tubule have on the GFR?
decreased GFR
what effect does an increased sympathetic activity in the kidney have on GFR?
decreased GFR
what effect does an increased ANP have on GFR?
increased GFR
what vessel does ANP predominantly act on?
afferent arteriole
what vessels does Angiotensin 2 predominantly act on?
both afferent and efferent arterioles
what vessel does NaCl in the distal convoluted tubule predominantly act on?
afferent arteriole
