renal blood flow, Lect 2

Question 1

kidneys receive what percentage of the CO

Answer 1

• 25%, needed to support filtration

Question 2

how much filtrate is formed per day

Answer 2

180 L

Question 3

equation of filtration fraction

Answer 3

FF=GFR/RPF

Question 4

equation for renal plasma flow

Answer 4

RPF = (1-Hct)RBF

Question 5

sympathetic nerves cause vasoconstriction via what receptors? What effect does this have on RBF and GFR

Answer 5

• alpha 1 receptors
• decrease RBF and GFR

Question 6

name the factors that cause vasoconstriction and decrease RBF and GFR

Answer 6

• sympathetic innervation of alpha 1 receptors
• angiotensin II (effects on GFR are variable)
• ADH
• ATP
• endothelin

Question 7

effect on angiotensin II on afferent and efferent arterioles

Answer 7

angiotensin II constricts both afferent and efferent arterioles however the efferent arteriole is more sensitive

Question 8

list the compounds that vasodilate and increase RBF and GFR

Answer 8

• atrial natriuretic peptide
• glucocorticoids
• NO
• prostaglandins (PGE₂, PGI₂)

Question 9

autoregulation of RBF and GFR

Answer 9

constant blood flow and GFR at different arterial pressures

• range arterial pressures: 80-180 mmHg

Question 10

autoregulation of RBF and GFR can be overridden by

Answer 10

large increases in sympathetic tone

Question 11

two mechanisms which cause autoregulation of RBF and GFR

Answer 11

• myogenic mechanism
• tubuloglomerular feedback (“flow-dependent”)

Question 12

myogenic mechanism

Answer 12

• intrinsic to vascular smooth muscle cells; contract in response to stretch
• affects RBF and GFR mainly by changing resistance of afferent arteriole

Question 13

Tubuloglomerular feedback

Answer 13

• increasing GFR increases NaCl delivery to LOH; sensed by the macula densa which causes the resistance of the afferent arteriole to increase thereby decreasing RBF and GFR
• function: maintains constancy of salt load delivered to distal tubule

Question 14

signal used in tubuloglomerular feedback

Answer 14

adenosine

Question 15

describe the fluid in bowman’s capsule

Answer 15

• a protein-free filtrate of blood plasma
  
  • all small-MW solutes that are not protein-bound appear in filtrate in the same concentrations as in blood plasma

Question 16

list the route of filtrate from capillary lumen into urinary space

Answer 16

1. fenestrae
2. basal lamina
3. filtration slits (between pedicels of podocytes)

Question 17

substances to be filtered are seperated by what characteristics

Answer 17

• size (MW)
• electrical charge
  
  • basal lamina and slits coated with negative charges
  • proteins usually have (-) charge and are repelled

Question 18

what are the main barriers to protein being filtered

Answer 18

• basal lamina
• filtration slits

Question 19

describe GFR using the starling equation

Answer 19

• GFR = K_f[(P_GC - P_BC) - (π_GC - π_BC)]
  
  • π_BC: oncotic pressure in bowman’s capsule is approximately zero bc no proteins in BC
  • K_f= filtration coefficient
  • [(P_GC - P_BC) - (π_GC - π_BC)] = net filtration pressure

Question 20

K_f

Answer 20

filtration rate produced by each mmHg of net filtration pressure

Question 21

compare K_f for glomerular capillaries vs capillaries in skin and muscle

Answer 21

K_f for glomerular capillaries is 50-100 greater than that for capillaries in skin and muscle

Question 22

K_f can be altered by what type of cells

Answer 22

mesangial cells

• relaxation of glomerular mesangial cells increase glomerular surface area and results in an increase in GFR
• Angtiotensin II reduces Kf

Question 23

equation calculating GFR using Kf

Answer 23

GFR = Kf x NFP

• net filtration pressure
• GFR = Kf (P_GC - P_BC - π_GC)

Question 24

what is P_GC

Answer 24

blood pressure in glomerular capillary

• driving force for GFR

Question 25

P_BC

Answer 25

back pressure in bowman's capsule * diminishes GFR

Question 26

π_GC

Answer 26

oncotic pressure of glomerular capillary blood * due to proteins unable to cross barrier; retards GFR * increases as plasma diverted into BC

Question 27

Glomerular capillary pressure remains constant as blood moves from the afferent arteriole into the efferent arteriole. What NFP paramter changes

Answer 27

the oncotic pressure in the glomerular capillary increases from 20 mmHg in the afferent arteriole to 35 mmHg in the efferent arteriole

Question 28

equation for Net filtration pressure (NFP)

Answer 28

* NFP = (P_GC + π_BC) - (P_BC + π_GC) * note π_BC = 0

Question 29

vasoconstriction of the afferent arteriole has what effect on GFR? Vasoconstriction of the efferent arteriole has what effect on GFR

Answer 29

* afferent: decreases P_GC -\> Decreases GFR * efferent: increases P_GC -\> Increases GFR

Question 30

what happens to P_GC and RBF when afferent and efferent arteriolar resistances both increase

Answer 30

* P_GC: no effect * RBF: dramatic decrease

Question 31

name a situation which would cause a increase in bowman's capsule pressure. what effect does this have of GFR

Answer 31

* increase in intratubular pressure due to obstruction of tubule or extrarenal urinary system * decrease in GFR