The Kidneys: Structure and Function

Question 1

10 functions of the kidney?

Answer 1

1. Water and salt balance
2. Maintenance of:
   • Plasma volume
   • Plasma osmolarity
3. Acid-base balance
4. Excretion of:
   • Metabolic waste products, e.g:
   • Exogenous foreign compounds, e.g:
5. Secretion of:
   • Renin (control of ABP)
   • Erythropoietin (RBC production)
6. Conversion of vitamin D into its active form (calcitriol), which allows Ca2+ absorption from the GI tract

Question 2

Primary function of the kidney?

Answer 2

Regulation of the following factors of the body fluids:
• Volume
• Composition
• Osmolarity

Question 3

Explain homeostasis and how this applies to water and ion balance

Answer 3

Balance concept of any substance (input = output), e.g:
• Water balance variable inc. thirst (input) and urinary loss (output)
• Na+, K+, H+, Ca+, Cl-, PO42-

Question 4

2 constituents of the urinary system and their functions?

Answer 4

1. Kidneys produce urine
2. Structures that store and carry the urine from the kidneys to the outside for elimination

IMAGE

Question 5

Describe the divisions and structure of the kidney

Answer 5

1. Renal cortex and medulla (consists of pyramids)

2. Renal pelvis continues into the ureter

Question 6

What is the nephron?

Answer 6

Functional unit of the kidney with each being composed of ~1 million neprhons

Question 7

Functional mechanisms of the nephron?

Answer 7

1. Filtration
2. Reabsorption
3. Secretion

Question 8

Label the regions of the nephron?

Answer 8

IMAGE

Question 9

2 types of nephron?

Answer 9

1. Juxtamedullary (~20%)

2. Cortical (~80%)

Question 10

Label the image of the nephron?

Answer 10

IMAGE

Question 11

Label the image of the Bowman’s capsule and glomerulus?

Answer 11

IMAGE

Question 12

Label the juxtaglomerular apparatus?

Answer 12

IMAGE

Question 13

What is urine?

Answer 13

Modified filtrate of the blood

Question 14

Kidney components that allow production of urine?

Answer 14

1. Filtration system
2. Rich blood supply
3. Mechanisms for urine modification:
   • Reabsorption
   • Secretion

Question 15

Renal PROCESSES that allows production of urine?

Answer 15

1. Glomerular filtration
2. Tubular reabsorption
3. Tubular secretion

Within the renal tubule, substance are added/removed as the urinary filtrate moves from the proximal to distal end

Question 16

What happens to the plasma that enters the glomerulus?

Answer 16

20% is filtered

80% is not filtered and leaves via the efferent arteriole

Question 17

Label the image of the glomerulus and the kidney tubule?

Answer 17

IMAGE

Question 18

Equation for the rate of excretion?

Answer 18

Filtration (GF) + Secretion (TS) = Reabsorption (TR) + Excretion

OR

Rate of excretion = rate of filtration + rate of secretion + rate of reabsorption

Question 19

How are movements of substances within the kidney described?

Answer 19

In terms of concentration x flow

Question 20

Calculate:

• Rate of filtration of a substance?

Answer 20

Rate of filtration of X =
mass of X filtered into the Bowman’s capsule per unit time

For a freely filterable substance (X):
Rate of filtration of X = [X]plasma x GFR

GFR = glomerular filtration rate

Question 21

Calculate:

• Rate of excretion of a substance?

Answer 21

Rate of excretion of X =
mass of X excreted per unit time

Rate of excretion of X = [X]urine x Vu

Vu = urine flow rate

Question 22

Calculate:

• Rate of reabsorption of a substance?

Answer 22

If rate of filtration > rate of excretion, net reabsorption of the substance has occurred

Rate of reabsorption of X = rate of filtration of X - rate of excretion of X

Question 23

Calculate:

• Rate of secretion of a substance?

Answer 23

If rate of filtrated < rate of excretion, net secretion of that substance has occured

Rate of secretion of X = rate of excretion of X - rate of filtration of X

Question 24

How are the rates of filtration and excretion measured?

Answer 24

Relatively easy

Question 25

How are the rates of reabsorption and secretion measured?

Answer 25

Reflect tubular modification of the filtrate, i.e: they are obtained as the DIFFERENCE between filtration and excretion

Question 26

Calculate the typical renal chloride balance?

Answer 26

Cl- filtered
= [Cl-]plasma x GFR
= 110 mmol/L x 0.12 L/min
= 13.2 mmol/min

Cl- excreted
= [Cl-]urine x Vu
= 200 mmol/L x 0.001 L/min
= 0.2 mmol/min

Thus, rate of filtration is > rate of excretion and so net reabsorption of Cl- has occurred

Cl- reabsorbed
= 13.2 - 0.2
= 13 mmol/min