03.1 Reabsorption, Filtration and Clearance Flashcards
How are the peritubular capillaries organised in cortical nephrons?
Loose and disorganised
Where are the juxtamedullary nephrons located?
Inner cortex
How are the peritubular capillaries arranged in juxtamedullary nephrons?
Vasa recta - straight and longer than the loop of Henle
What are the proportions of cortical to juxtamedullary nephrons?
90% Cortical nephrons
10% Juxtamedullary
How much blood is filtered at once in the glomerulus?
20% filtered, 80% exits via efferent arteriole.
What property of the basement membrane between capillary endothelium and the podocytes of the Bowman’s capsule is important during filtration?
The glycoproteins have a negative charge hence they repel proteins therefore proteins stay in the blood.
Which have a higher clearance rate per given size, anions or cations?
Cations (positive ions) have a higher clearance rate than anions (negative ions).
What are the three filtration pressures that act at the glomerulus and state whether they favour of oppose filtration?
Hydrostatic pressure in plasma - favours filtration
Hydrostatic pressure in the tubule - opposes filtration
Oncotic pressure in the plasma - opposes filtration
Name the two methods of filtration autoregulation?
Myogenic.
Tubuloglomerular feedback.
What is the myogenic autoregulation response to a rise in blood pressure?
Increased blood pressure is detected by smooth muscle which contracts to reduce blood flow.
What is the tubuloglomerular feedback mechanism response to an increase in blood pressure?
Increased BP leads to an increase in filtration and hence an increase in sodium and chloride in the tubule.
Macula densa senses these electrolytes and causes the juxtaglomerular apparatus to release adenosine.
Adenosine causes vasoconstriction of the afferent arteriole.
What is the tubuloglomerular feedback mechanism response to a decrease in blood pressure?
Decreased BP leads to decreased filtration and therefore decreased sodium and chloride in the tubule.
Macula densa senses these electrolytes and causes the juxtaglomerular apparatus to release prostaglandin.
Prostaglandins causes vasodilatation of the afferent arteriole.
Where are cortical nephrons located?
Outer cortex
Describe the reabsorption that occurs in the proximal convoluted tubule.
Bulk transport.
Isosmotic reabsorption.
What transporter is on the basolateral membrane of PCT cells?
NaKATPase
What transporters can be found on the apical membrane of PCT cells?
Na-H Antiporter
Na-Glucose Symporter
What transporters can be found on the apical membrane of the cells of the Loop of Henle?
NaK2Cl Symporter
What transporters can be found on the apical membrane of early DCT cells?
NaCl Symporter
What transporters can be found on the apical membrane of late DCT and Collecting duct cells?
ENaC
What do the kidneys actively secrete?
Hydrogen ions
Potassium
Organic cations and anions (drugs)
How do you calculate glomerular filtration rate?
Measure a substance in the urine.
The substance cannot be altered in any way in the nephron (cannot be reabsorbed or secreted).
What is a substance that can be given IV to calculate GFR accurately?
Inulin.
What is clearance of a substance?
The volume of plasma from which substance x can be completely cleared to the urine per unit time.
What is the equation for clearance of substance x?
Cx = (Ux x V)/Px
Where C is clearance, Ux is the urine concentration of substance x, V is the urine flow rate and Px is the plasma concentration of substance x.
What is Tm?
Transport maximum for a substance, once exceeded the substance stays in the urine.
