Urine Production: Filtration

Question 1

what metabolic waste products are made in the liver?

Answer 1

urea
creatinine
bilirubin

Question 2

where is urea reabsorbed?

Answer 2

• most reabsorbed in PCT (30-40%)
• small amount in medullary collecting duct

Question 3

what is creatinine made from?

Answer 3

muscle breakdown

Question 4

how much creatinine is reabsorbed in the kidney?

Answer 4

none

Question 5

what is bilirubin made from?

Answer 5

breakdown of RBC

Question 6

name the steps of urine production

Answer 6

1. filtration in glomerulus
2. reabsorption in PCT
3. counter-current concentration in loop of Henle (& collecting duct)
4. secretion in DCT
5. excretion in collecting duct

Question 7

what is the first step of urine production?

Answer 7

filtration

Question 8

where does filtration occur?

Answer 8

glomerulus

Question 9

what is the osmolarity in the glomerulus?

Answer 9

300

Question 10

how much blood is in the kidney at all times?

Answer 10

20%

Question 11

glomerular filtration is based on ____

Answer 11

size

Question 12

the glomerulus is composed of…

Answer 12

fenestrated capillaries reinforced by basement membrane, and podocytes (slit pores)

Question 13

what is the normal glomerular filtration rate (GFR)?

Answer 13

~125 mL/min

Question 14

how does filtrate compare to plasma?

Answer 14

same but no protein

Question 15

what is the equation for filtered load?

Answer 15

plasma concentration x GFR

Question 16

what osmolarity is considered hypotonic?

Answer 16

less than 300 mmol

Question 17

what osmolarity is considered hypertonic?

Answer 17

more than 300 mmol

Question 18

what osmolarity is considered isotonic?

Answer 18

300 mmol

Question 19

what effect would a 50% decrease in efferent arteriolar resistance have on GFR?

Answer 19

substantial decrease

Question 20

with a chronic decrease in GFR by 50%, what changes in plasma concentration would you find for:
- creatinine
- K+
- glucose
- Na+
- phosphate
- H+

Answer 20

• creatinine increases until renal excretion of creatinine returns to normal
• glucose, K, Na, H stay constant (closely regulated)
• phosphate maintained until GFR below 20-30% of normal

Question 21

what changes would you expect in renal blood flow, GFR, and peritubular capillary hydrostatic P, from a 50% decrease in afferent arteriolar resistance and no change in arterial pressure?

Answer 21

• increase renal blood flow
• increase GFR
• increase peritubular capillary hydrostatic P

Question 22

what is the net pressure driving glomerular filtration given the following:
- glomerular capillaries hydrostatic P = 50mmHg
- Bowman’s space hydrostatic P = 12mmHg
- glomerular capillaries colloid osmotic P = 30mmHg
- no protein in glomerular ultrafiltrate

Answer 22

50 - 12 - 30 = 8mmHg

Question 23

what is the concentration of urea in tubular fluid at the end of the proximal tubule compared to the plasma?

Answer 23

higher than concentration of urea in the plasma

Question 24

how does urea reabsorption in the proximal tubule compare to in the cortical collecting collecting tubule?

Answer 24

PCT > collecting tubule
(40-50% in PCT; none in collecting tubule)

Question 25

what is the equation for net glomerular filtration pressure?

Answer 25

glomerular hydrostatic P - bowman’s hydrostatic P - glomerular osmotic P