Physio 2

Question 1

what exists in the same concentration in plasma and ultrafiltrate?

Answer 1

organic and inorganic anionic and cationic solutes

Question 2

glomerular filtration rate (GFR)

Answer 2

125 ml/min or 180 L per day. filters entire ECF volume every 2 hours.

Question 3

filtration rate formula

Answer 3

Kf[(Pgc-Pbs)-(piGC-piBS)]

Kf is the filtration coefficient of the glomerular capillary and is the product of capillary hydraulic conductivity and the surface area available for filtration. (Pgc-Pbs) is the difference in hydrostatic pressure inside the glomerular capillary and bowmans space. The pi is the difference in oncotic pressure in the same areas. O

Question 4

how does Pgc change over the course of the glomerular capillary?

Answer 4

about 45-50 mmHg at the beginning and about 41-47mmHg at the end. decrease occurs despite a decrease of plasma volume, and is due to post capillary efferent arteriole constriction

Question 5

changes in piGC over course of glomerular capillary

Answer 5

25 mmHg at the beginning and 35 mmHg at the end. due to plasma filtration and concentration of the plasma protein

Question 6

glomerular barrier to filtration

Answer 6

endothelial cells of the glomerular capillaries restrict passage of cellular elements into bowmans space. capillary basement membrane restricts filtration of solutes larger than 1 kDa. an anionic charge favors filtration of cations and restricts filtration of anionic proteins. Podocytes of visceral epithelial layer of bowman’s capsule have foot processes covering capillaries. foot processes are separated by filtration slits where anionic charge further restricts filtration of anionic proteins, but not smaller organic/inorganic anions

Question 7

what does removal of negative charge from the glomerular barrier do?

Answer 7

increases the passage of anions. this occurs in nephrotic serum nephritis

Question 8

renal hemodynamics

Answer 8

GFR remains constant and the rate and volume of urine excretion varies according to the rate and volume of fluid consumed, which changes the volume and solute concentration of the ECF

Question 9

what happens when RPF increases?>

Answer 9

GFR increases and filtration fraction decreases.

FF = GFR / RPF

Question 10

fluid reabsorption in the post glomerular peritubular capillaries

Answer 10

starling forces drive reabsorption from the interstitial space into the peritubular capillaries. peritubular capillary oncotic pressure difference driving fluid absorption exceeds the peritubular capillary hydrostatic pressure difference opposing fluid absorption

Question 11

pathway of fluid reabsorption

Answer 11

lumenal tubular fluid -> tubule cell -> interstitial fluid -> peritubular capillary plasma

Question 12

what can measuring the GFR show?

Answer 12

can provide an index of the number of functioning nephrons in kidney disease. renal failure begins when GFR decreases to below 20 ml/min or a loss of function of 85% of the nephrons.

Question 13

renal clearance of a substance

Answer 13

virtual volume of plasma from which a solute is completely removed from the plasma by the kidney per unit of time. measured as ml/min.

Question 14

GFR calculation

Answer 14

GFR = Us x V/Ps

Us x V is amount of solute excreted / time
Ps x GFR is amount of solute filtered / time
Amount of solute filtered / time = amount of solute excreted / time

Question 15

solutes used to measure GFR

Answer 15

exogenous: Insulin. given by IV infusion, measured accurately in plasma and urine
endogenous: creatinine. in the absence of strenuous exercise or disease, a constant amount of creatinine / time diffuses from skeltal muscle to plasma

Question 16

solute clearance from the plasma by the kidney

Answer 16

formula: Cs - (Us x V)/Ps

Question 17

clearance ratios

Answer 17

a solute clearance less than the clearance of insulin/creatinine indicates that the solute is not freely filtered at the glomerulus, or , if freely filtered, net solute reabsorption has occurred. solute clearance greater than insulin / creatinine shows net solute secretion

Question 18

fractional excretion of water

Answer 18

fraction of the glomerular filtrate not reabsorbed from the tubular fluid along the nephron and therefore appearing as urine.

FEh20 = V / GFR

Question 19

fractional excretion of solute

Answer 19

fraction of filtered solute that appears in the urine. estimated as a ratio of clearance to GFR

Question 20

autoregulation of renal blood flow

Answer 20

maintained relatively constant over MAPs which maintains a constant GFR. due to myogenic response of renal vasculature in response to pressure changes. tubuloglomerular feedback at the macula densa cells sensing an increase or decrease in GFR and providing increased or decreased resistance. Autoregulation of renal blood flow is intrinsic to kidney and occurs in the absence of autonomic innervation to the kidneys

Question 21

glomerular filtration

Answer 21

process by which plasma is filtered across the glomerular capillaries to form a protein-free ultrafiltrate in bowman’s space. driven by differences in starling forces drive the net efflux.