filtration, reabsorption, and secretion (midterm 3)

Question 1

what is GFR

Answer 1

glomerular filtration rate, the rate of fluid extraction from the glomerular capillaries into Bowman’ capsule (~180 L/day - ~ 2 mL/min into Bowman’s)

Question 2

what are the 3 major layers of the glomerular capillary membranes (most cap membranes only have 2!)

Answer 2

• the endothelium of the capillary
• a basement membrane
• a layer of epithelial cells (podocytes) surrounding the outer surface of the capillary basement membrane

Question 3

what is filtered in glomerular filtration and at what rate compared to water

Answer 3

• Sodium, glucose, and inulin are filtered as freely as water
• Myoglobin is filtered 75% as rapidly as water; albumin 0.5% as water

Question 4

what is the equation for GFR

Answer 4

Kf (filtration coefficient) x (PG - PB - πG + πB)
PG = glomerular hydrostatic pressure
PB = Bowman’s capsule hydrostatic pressure
πG = glomerular capillary colloid osmotic pressure
πB = Bowman’s capsule colloid osmotic pressure

Question 5

what is net filtration favored by

Answer 5

glomerular hydrostatic pressure (PG) and Bowman’s capsule colloid osmotic pressure ( πB)
- typically, πB ~ 0 because there is no protein transport into Bowman’s capsule

Question 6

what is the major determinant of GFR

Answer 6

PG - increased PG = increased GFR

Question 7

what is PB usually and what does it do to GFR

Answer 7

18 mmHg - reduces GFR

Question 8

what happens to GFR with πG

Answer 8

increased πG = decreased GFR

Question 9

what are the three things glomerular hydrostatic pressure is determined by

Answer 9

• Arterial pressure (increased arterial pressure increases glomerular hydrostatic pressure and GFR)
• Afferent arteriolar resistance (increased resistance reduces glomerular hydrostatic pressure and decreases GFR)
• Efferent arteriolar resistance (increased resistance (up to a point!) reduces glomerular capillary outflow, increases glomerular hydrostatic pressure and increases GFR)

Question 10

what is the total renal blood flow of a 70 kg person

Answer 10

1200 mL/min (21% of cardiac output)

Question 11

in normal vs renal tissue, what is the correlation between BF and metabolic demand

Answer 11

normal: BF = metabolic demand
renal: BF > renal metabolic demand

Question 12

what do vasoconstrictors do to GFR

Answer 12

they decrease blood flow and therefore decrease GFR

norepinephrine, epinephrine

Question 13

what do vasodilators do to GFR

Answer 13

they decrease renal vasculature resistance, increase BF, and increase GFR

Question 14

what does increased sympathetic stimulation do to GFR

Answer 14

decreases renal arterial diameter, decreases BF, decreases GFR

Question 15

what is tubuloglomerular feedback

Answer 15

changes in sodium chloride concentration causes changes in the macula densa, that then control renal arteriolar resistance (graph on pg 13 of notes/ desktop)

Question 16

what is urinary excretion rate equal to

Answer 16

filtration rate minus reabsorption rate plus secretion rate

Question 17

how do glomerular filtration and tubular reabsorption compare to urinary excretion

Answer 17

they are very large relative to it

Question 18

are glomerular filtration and tubular reabsorption selective

Answer 18

glomerular filtration is non-selective

tubular reabsorption and secretion is highly selective

Question 19

what does filtration lead to

Answer 19

reabsorption

Question 20

what are the transport mechanisms during reabsorption

Answer 20

tubular epithelium -> interstitial space -> peritubular capillary endothelium

Question 21

what is primary active transport through the tubular membrane linked to

Answer 21

the hydrolysis of ATP via
- Sodium-potassium ATPase
- Hydrogen ATPase
- Hydrogen-potassium ATPase
- Calcium ATPase

Question 22

what does secondary active transport through the tubular membrane involve

Answer 22

Na+/glucose co-transport
Na+/amino acid co-transport
Na+/H+ counter-transport

Question 23

do active transport and passive transport have limits

Answer 23

active transport has a maximum limit
passive transport has no limit

Question 24

what is passive transport determined by

Answer 24

electrochemical gradient
membrane permeability
fluid retention time within the tubule

Question 25

what does sodium transport do

Answer 25

drives water reabsorption by osmosis

Question 26

what is the concentration of molecules along the nephron a result of

Answer 26

the individual molecules' transport and the transport of water

Question 27

what is the concentration of sodium, glucose, and creatine/urea along the nephron + how they are transported

Answer 27

- Sodium is highly transported, but its concentration does not change as water is also highly removed - Glucose concentration falls dramatically, as it is transported much more quickly than water - Creatinine and urea increase in concentration and urea is not reabsorbed

Question 28

what are the three segments of the loop of Henle

Answer 28

- descending thin segment (highly permeable to water) - ascending thin segment - thick ascending segment (thick epithelial cells capable of active reabsorption of sodium, chloride, and potassium - ~ 25% of these filtered molecules are reabsorbed here)

Question 29

how is the distal tubule of a nephron similar to the loop of Henle

Answer 29

they both reabsorb most ions including sodium, potassium and chloride, but are impermeable to water and urea

Question 30

what two cell types do the late distal tubule and cortical collecting tubule contain

Answer 30

- principal cells, which reabsorb sodium and water and as secrete potassium - intercalated cells, which reabsorb potassium and secrete hydrogen

Question 31

what is glomerulotubular balance

Answer 31

increased GFR => increased tubular resistance (proximal tubular reabsorption is 65% of GFR)

Question 32

what is the equation for tubular reabsorption and what does everything stand for

Answer 32

Kf x (-Pc + Pif + πc - πif) - Peritubular hydrostatic pressure (Pc) - Renal interstitium hydrostatic pressure (Pif) - Peritubular colloid osmotic pressure (πc) - Renal interstitium colloid osmotic pressure (πif)

Question 33

what are Pc and πc functions of and what do they do to absorption

Answer 33

Pc = f(Pa) (increased Pa, increased Pc => decreased reabsorption and Pc = f(Ra, E) (decreased Ra, E (resistance of afferent and efferent arterioles), increased Pc => decreased reabsorption) πc = f(πA) (increased πA, increased πc => increased reabsorption) and πc = f(FF) (increased filtration fraction, increased plasma F, increased plasma (protein), increased πc => increased reabsorption

Question 34

what is the effect of arterial pressure regulation between 75 and 160 mmHg

Answer 34

only a slight effect on renal BF and GFR

Question 35

what happens when GFR auto regulation is impaired

Answer 35

arterial pressure can cause large increases in GFR and a greater effect on sodium and water excretion