Water & Electrolytes

Question 1

How are water balance & electrolyte levels maintained in the body?

Answer 1

• Antidiuretic hormone (ADH)
• Renin-angiotensin-aldosterone system (RAAS)
• Atrial natriuretic hormone/peptide (ANH/ANP): Lowers BP & controls electrolyte homeostasis

Question 2

What are electrolytes?

Answer 2

Minerals which carry an electrical charge

e.g. Na+, Ca2+, K+ etc..

Question 3

How does antidiuretic hormone work?

Answer 3

Acts on distal convoluted tubules (in kidney) and collecting ducts to increase water permeability for reabsorption.

ADH High = High Reabsorption
ADH Low = Low Reabsorption

Question 4

How does the renin-angiotensin-aldosterone system (RAAS) work?

Answer 4

Promotes reabsorption of Na+ (and water) in distal convoluted tubule (DCT) in kidney.

Potent vasoconstrictor -> Increases BP

Question 5

How does atrial natriuretic hormone/peptide (ANH/ANP) work?

Answer 5

Increases EXCRETION of Na+ & Water

OPPOSITE EFFECTS TO ALDOSTERONE/RAAS

Question 6

What is the disorder when ADH is HYPO-secreted?

Answer 6

Diabetes insipidus

• Little reabsorption, very dilute urine