Biochemistry Renal Function Flashcards Preview

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Flashcards in Biochemistry Renal Function Deck (31):
1

• Glomerular function tests

o Urea
o Creatinine
o eGFR

2

Functions of the kidney

Excretion of metabolic waste products
Water and solute homeostasis
Synthetic activity

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Synthetic activity of the kidney

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

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Inulin

gold standard renal function test

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Glomerular filtration Rate (GFR) Definition

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

6

GFR depends

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

7


Proximal Tubule:

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

8

High glycosuria: 2 causes

1. Renal glomerular disease - High glucose blood levels
2. Renal tubular disease - Defect in renal

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Counter-current multiplication →


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

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Counter-current exchange →

• Passive
• Distal tubule and collecting duct

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Distal Tubule

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

12

Renin-aldosterone system: Triggers


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

13

Renin-aldosterone system: Detection of stimuli at

Kidney – juxtaglomerular apparatus

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Renin-aldosterone system: Triggers release of

Renin

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Renin-aldosterone system: Renin pathway

Renin substrate stimulates Angiotensin I (inactive)
Angiotensin I stimulates Angiotensin II release

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Renin-aldosterone system: Angiotensin II action

Stimulates thirst
Causes Vasoconstriction
Aldosterone secretion

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Renin-aldosterone system: Vaso-constriction causes

Increased perfusion pressures

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Renin-aldosterone system:Aldosterone action

Renal sodium and water retention

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Renin-aldosterone system: Aldosterone secretion

High potassium
Angiotensin I

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

Increased perfusion pressure

21

Antidiuretic Hormone: Stimulants

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

22

Antidiuretic Hormone: Stimulants act on the

• Hypothalamus – Supra-optic and Para-ventricular nuclei

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Antidiuretic Hormone: Stimulant of hypothalamus

ADH release

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Antidiuretic Hormone: ADH action on the kidney

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

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Antidiuretic Hormone: Relying on ADH solely?

Reabsorb water and cause hyponatraemia – decreases osmolaity

26

Urea – breakdown of proteins increases

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

27

Glomerular Function Tests →

Serum creatinine concentration proportional to 1/GFR

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Direct estimates of GFR:

Measured Creatinine Clearance

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

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Indirect estimates of GFR:

eGFR

30

eGFR

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

31

eGFR


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

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