Week 6 - Urine formation

Question 1

Where does filtration start to occur in the kidney

Answer 1

Glomerulus

Question 2

What components make up the filtration membrane of the capillary, basement membrane and Bowman’s capsule epithelium that helps with filtration?

Answer 2

Capillary endothelial layer contains many pores called fenestrations, the basement membrane has spaces between it’s fibers, and the Bowman’s capsule epithelial layer has podocytes that wrap around capillaries of the glomerulus and have filtration slits.

Question 3

What is Renal Fraction and what is it for resting healthy adults

Answer 3

% of total cardiac output that enters the kidneys

21%

Question 4

Glomerular filtration rate (GFR)

Answer 4

The amount of filtrate (plasma) that enters the Bowman’s capsule

Worked out by the following:

Renal blood flow rate (RBFR): CO x 21% (renal fraction) = ___mL/min

Renal plasma flow rate (RPFR): RBFR x 55% (amount of plasma in the blood) = ___mL/min

GFR: RPFR x 19% (filtration rate) = ___ mL/min or ___L/day

Question 5

Renal blood flow rate (per min)

Answer 5

CO x Renal Fraction (5600mL/min x 21%)

Question 6

What would a person’s renal blood flow rate be with a CO of 5600 mL?

Answer 6

5600 mL x 21%
= 1176 mL/min passes through the kidneys for a resting healthy adult

Question 7

Renal plasma flow rate

Answer 7

Renal blood flow rate x amount of plasma in the blood

1175 mL x 55% = 650 mL/min

Question 8

Filtration pressures (3)

Answer 8

Glomerular capillary pressure, capsular hydrostatic pressure, blood colloid osmotic pressure

Question 9

Glomerular capillary pressure

Answer 9

Outward pressure of blood in the capillaries, which forces solutes and fluid out of the capillaries (50 mm Hg)

Question 10

Capsular hydrostatic pressure

Answer 10

Inward pressure of the filtrate in the Bowman’s capsule pressing back on the capillaries (10 mm Hg)

Question 11

Blood colloid osmotic pressure

Answer 11

As water leaves capillaries through osmosis, plasma proteins are left behind because they are too big. This then makes a high concentration of plasma proteins at the end of the capillaries, drawing more water in through osmosis (30 mm Hg)

Question 12

Final filtration pressure

Answer 12

50 - 10 - 30 = 10 mm Hg

Question 13

Regulation of the GFR is maintained through auto-regulation, what are the other two mechanisms that regulate GFR?

Answer 13

Myogenic mechanism and Tubuloglomerular mechanism

Question 14

The mechanism that changes BP in the blood vessels to maintain GFR

Answer 14

Myogenic mechanism - Blood vessels constrict or dilate to maintain the pressure within the arterioles and capillaries.

Question 15

Tubuloglomerular mechanism

Answer 15

An adaptive mechanism that links the rate of glomerular filtration to the concentration of salt in the tubule fluid at the macula densa

Question 16

What happens to GFR when the afferent arteriole diameter decreases

Answer 16

GFR decreases

Question 17

What happens to GFR when the efferent arteriole diameter increases

Answer 17

GFR decreases

Question 18

What type of reabsorption occurs at the PCT and how much filtrate is reduced by the end of PCT?

Answer 18

Active and selective reabsorption, filtrate is reduced by 65% at the end of PCT

Question 19

What is reabsorbed in the PCT? (5)

Answer 19

Electrolytes, virtually all nutrients (glucose, amino acids, vitamins, some ions), water, lipid-soluble solutes, urea

Question 20

Primary Active Transport

Answer 20

Uses ATP to transport molecules across a cell membrane

Na+/K+ pump

Question 21

Secondary Active Transport

Answer 21

Doesn’t use ATP to transport molecules across a cell membrane

Symport through sodium travelling down it’s gradient after it has been actively transported across the cell through Na+/K+ pump

Question 22

Passive Transport (diffusion)

Answer 22

Molecule does not require another molecule to transport

Lipid-soluble substances, various ions and urea

Question 23

Countercurrent Multiplier

Answer 23

Countercurrent multiplication in the kidneys is the process of using energy to generate an osmotic gradient that enables you to reabsorb water from the tubular fluid and produce concentrated urine

Question 24

Where in the nephron loop is water permeable?

Answer 24

The descending limb

Question 25

Where in the nephron loop is water impermeable and pumps out salt?

Answer 25

The ascending limb

Question 26

What is the osmolarity level at the cortex of the kidney?

Answer 26

300

Question 27

What is the osmolarity level at the inner medulla of the kidney?

Answer 27

1200

Question 28

What does a higher osmolality level mean?

Answer 28

High concentration of dissolved particles of chemicals and minerals such as sodium and other electrolytes in the filtrate. Low osmolality (300) means it is more dilute.

Question 29

What percentage of our cardiac output goes to the kidneys?

Answer 29

21%

Question 30

The first membrane molecules cross over from the renal tubule during tubular reabsorption is called:

Answer 30

Apical Membrane

Question 31

What is the opening called for the renal artery and vein to enter the kidney?

Answer 31

Hilum

Question 32

The majority of reabsorption occurs in the:

Answer 32

Proximal convoluted tubule (65% reduced by the end of PCT)