Glomerular Filtration (in-depth)

Question 1

3 processes necessary for body to filter blood + retain important materials

Answer 1

1. filtration
2. reabsorption
3. secretion

Question 2

glomerular filtration

Answer 2

• occurs in glomerulus

- mechanical process - depends on opposing pressures (in mmHg) btwn glomerular capsule and capillary beds

Question 3

blood hydrostatic pressure (HP)

Answer 3

• amount of pressure in blood inside capillaries
• this pressure is what drives fluid + solutes out of capillaries
• varies person to person (higher BP means higher HP)

Question 4

3 ways of regulating GFR

Answer 4

1. renal autoregulation
2. nervous system control
3. renin-angiotensin-aldosterone system

Question 5

glomerular filtration rt (GFR)

Answer 5

• amount of blood glomerulus filters over time
• higher if arterial BP in kidneys is higher
• lower if osmotic pressure is higher due to dehydration

Question 6

normal GFR

Answer 6

120-125 mL/min or 180L/day

Question 7

renal autoregulation of GFR

Answer 7

• this is how GFR is controlled in normal situations
• kidneys control diameter of efferent and afferent arterioles
• allows for GFR to remain constant even as arterial pressure in body changes

Question 8

nervous system control of GFR

Answer 8

• how GFR is controlled during emergencies (sympathetic NS activated)
• epinephrine causes sympathetic nerve fibers narrow afferent arterioles to divert blood from kidneys to other vital organs
• this decreases GFR (should only be a short time so as not to cause kidney damage)

Question 9

colloid osmotic pressure (COP)

Answer 9

aka oncotic pressure

• opposes HP
• pressure that drives fluids back into capillaries (draws water out of filtrate
• depends on amt of proteins in plasma

Question 10

net filtration pressure (NFP)

Answer 10

NFP = HP - (COP + CP)

- when filtrate enters PCT, pressure of filtrate = NFP

Question 11

normal range of COP

Answer 11

25-32 mmHg

anything outside this range can damage glomerulus

Question 12

3 ways GFR is regulated

Answer 12

1. renal autoregulation of GFR
2. nervous system control
3. RAA system

Question 13

RAA system

Answer 13

aka renin-angiotensin-aldosterone system

• enzyme response when body’s BP drops too low
• triggers thirst mechanism + release of aldosterone

Question 14

what happens if GFR is too high

Answer 14

• filtration rate is too fast

- this means body can’t sufficiently reabsorb needed substances (necessary things are being excreted in urine)

Question 15

what happens if GFR is too low

Answer 15

• filtration rate is too slow

- this means nearly all filtrate is being reabsorbed into blood stream, including waste that needs to be excreted

Question 16

angiotensin

Answer 16

• pre-enzyme produced by liver

- floats freely in blood

Question 17

renin

Answer 17

• enzyme released from juxtaglomerular (JG) cells of nephron

- converts angiotensin into angiontensin I

Question 18

angiotensin I

Answer 18

converted to angiotensin II in lungs

Question 19

angiotensin II

Answer 19

• triggers thirst mechanism in hypothalamus (water ingested –> raises arterial BP back to healthy level)
• vasoconstrictor (increases peripheral BP)
• causes release of aldosterone
• converted from angiotensin I in lungs

Question 20

aldosterone

Answer 20

• hormone released by adrenal glands
• causes renal tubules in nephron to reabsorb more sodium ions
• those Na+ ions are dissolved in water, so it causes increased water retention / reabsorption from filtrate

Question 21

capsular pressure

Answer 21

• the mechanical pressure from the recoil inside glomerular arterioles (from their elasticity).
• opposes blood hydrostatic pressure and drives fluid back into the glomerular capillaries.