Biochemistry Renal Function

Question 1

• Glomerular function tests

Answer 1

o Urea
o Creatinine
o eGFR

Question 2

Functions of the kidney

Answer 2

Excretion of metabolic waste products
Water and solute homeostasis
Synthetic activity

Question 3

Synthetic activity of the kidney

Answer 3

• Renin
• 1,25 (OH)2 vit D
• Erythropoietin

Question 4

Inulin

Answer 4

gold standard renal function test

Question 5

Glomerular filtration Rate (GFR) Definition

Answer 5

The quantity of glomerular filtrate formed each minute in all nephrons of both kidneys

Question 6

GFR depends

Answer 6

• Number of functioning nephrons
• Glomerular function (acute)
• Intra-capillary pressure (shock)
• Tubular luminal pressure (BPH – outflow block)

Question 7

Proximal Tubule:

Answer 7

• Bulk reclamation of solutes
o 70% Na, K, Ca, Cl
o 100% HCO3-, Glucose, Urate, Amino Acids
• Isosmotic reabsorption of water (70%)

Question 8

High glycosuria: 2 causes

Answer 8

1. Renal glomerular disease - High glucose blood levels

2. Renal tubular disease - Defect in renal

Question 9

Counter-current multiplication →

Answer 9

• Active
• Loop of Henle
• Dilutes urine
• Generates hypertonic medulla

Question 10

Counter-current exchange →

Answer 10

• Passive

* Distal tubule and collecting duct

Question 11

Distal Tubule

Answer 11

• Homeostatic solute adjustment
→ Sodium – hydrogen exchange
→ Sodium – potassium exchange
• Isosmotic water reabsorption

Question 12

Renin-aldosterone system: Triggers

Answer 12

Low arterial pressure (via carotid sinus detection)
Low sodium intake
Low renal blood flow
High potassium –promotes sodium potassium exchange (potassium excretion)

Question 13

Renin-aldosterone system: Detection of stimuli at

Answer 13

Kidney – juxtaglomerular apparatus

Question 14

Renin-aldosterone system: Triggers release of

Answer 14

Renin

Question 15

Renin-aldosterone system: Renin pathway

Answer 15

Renin substrate stimulates Angiotensin I (inactive)

Angiotensin I stimulates Angiotensin II release

Question 16

Renin-aldosterone system: Angiotensin II action

Answer 16

Stimulates thirst
Causes Vasoconstriction
Aldosterone secretion

Question 17

Renin-aldosterone system: Vaso-constriction causes

Answer 17

Increased perfusion pressures

Question 18

Renin-aldosterone system:Aldosterone action

Answer 18

Renal sodium and water retention

Question 19

Renin-aldosterone system: Aldosterone secretion

Answer 19

High potassium

Angiotensin I

Question 20

Renin-aldosterone system: Inhibition of R-A-A

Answer 20

Increased perfusion pressure

Question 21

Antidiuretic Hormone: Stimulants

Answer 21

• Drugs e.g. opiates, chlorpropamide
• Stress e.g. pain and nausea
• Decreased blood volume (stretch receptors and baroreceptors)
• Increased plasma osmolality

Question 22

Antidiuretic Hormone: Stimulants act on the

Answer 22

• Hypothalamus – Supra-optic and Para-ventricular nuclei

Question 23

Antidiuretic Hormone: Stimulant of hypothalamus

Answer 23

ADH release

Question 24

Antidiuretic Hormone: ADH action on the kidney

Answer 24

Increased water permeability

Causing increased water reabsorption and decreased plasma osmolality (negative feedback)

Question 25

Antidiuretic Hormone: Relying on ADH solely?

Answer 25

Reabsorb water and cause hyponatraemia – decreases osmolaity

Question 26

Urea – breakdown of proteins increases

Answer 26

o Poor nutrition = urea is low (conserve proteins) | o Gastrointestinal bleed – urea increases as globulin presence and so urea increases

Question 27

Glomerular Function Tests →

Answer 27

Serum creatinine concentration proportional to 1/GFR

Question 28

Direct estimates of GFR:

Answer 28

Measured Creatinine Clearance CCL = Urine [creatinine] x (Urine volume/collection time) Serum [creatinine]

Question 29

Indirect estimates of GFR:

Answer 29

eGFR

Question 30

eGFR

Answer 30

Creatinine production rate is related to muscle mass, which can be estimated from age and sex

Question 31

eGFR

Answer 31

1.86 x (serum [creatinine] x 0.0113) -1.154 x age (age) -0.203 * x 0.742 if female * x 1.21 if African