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D3.3.7 (HL)—Kidney role

The kidney maintains homeostasis by filtering blood, removing wastes and regulating water, ions and solute concentration in human physiology in human physiology.

Syllabus
First assessment 2025
Objective
D3.3.7
Level
HL

Exam analysis

Chance of appearing11%of analysed past papers
Latest appearanceNovember 2023
Most common paperPaper2
Typical marks1–8

Common command terms

  • Explain
  • State
  • Deduce
  • Outline
  • Identify

Recent exam appearances

November 2023Paper2 ["HL"] · TZ26(b)[ 5 ]D3.3.7 (HL)—Kidney role
November 2023Paper1 ["HL"] · TZ238[ 1 ]D3.3.7 (HL)—Kidney role
May 2023Paper2 ["HL"] · TZ22(d)[ 3 ]D3.3.7 (HL)—Kidney role
November 2022Paper1 ["HL"] · TZ038[ 1 ]D3.3.7 (HL)—Kidney role
May 2022Paper2 ["HL"] · TZ28(b)[ 7 ]D3.3.7 (HL)—Kidney role
Practice this objective

Coverage 2013–2023 · Updated 16 Jul 2026

Kidneys Perform Excretion and Osmoregulation

HL only

Kidneys regulate blood composition by excreting metabolic wastes and by osmoregulating water and dissolved ions.

Process Meaning Kidney outcome
Excretion Removal of metabolic waste and unwanted substances Urea and other unwanted solutes leave in urine
Osmoregulation Regulation of osmotic concentration Nephrons adjust water and ion reabsorption, changing urine volume and concentration

Osmoticconcentrationisexpressedinosmolesperlitre(osmolL−1).Osmotic concentration is expressed in osmoles per litre (osmol L⁻¹).

When body water is scarce, increased water reabsorption produces a smaller volume of more concentrated urine while urea is still excreted.

Excretion and egestion are different: kidneys remove substances from blood, whereas egestion removes undigested material from the gut.

Kidney role

HL only

Assessment in practice

1–7 marks
How it is assessed

This objective is assessed through structured response, commonly using Explain / State / Deduce.

Command terms

Explain / State / Deduce / Outline / Identify

What earns marks

Build the answer around this relationship: Kidneys remove wastes while conserving useful substances.

Representative question

Question 1

[Maximum number: 8]

Explain the role of the kidney in osmoregulation.

Retrieve the HL Homeostasis Route

HL only

HL D3.3 adds kidney and circulation mechanisms. The route is still feedback logic: nephrons filter and reabsorb, the loop of Henle builds a gradient, ADH changes collecting duct permeability, and blood vessels redistribute flow according to activity.

  • excretion removes urea; osmoregulation adjusts water and ions
  • glomerulus filters and proximal tubule selectively reabsorbs
  • medulla gradient and aquaporins conserve water
  • vasodilation and vasoconstriction redirect flow by activity

HL Kidney and Blood-Flow Control

HL only

HL homeostasis transfer is about structure-function precision. In kidney answers, say where filtration, reabsorption, salt pumping, water movement, ADH, and aquaporins happen. In blood-flow answers, say which vessels dilate or constrict and how activity changes tissue demand.

  • Distinguish excretion from osmoregulation and locate filtration/reabsorption in the nephron.
  • Explain the loop of Henle and ADH using permeability, salt movement, aquaporins, and concentrated urine.
  • Explain blood redistribution using vasoconstriction, vasodilation, exercise, epinephrine, and tissue demand.

Concept essentials

  • Kidneys remove wastes while conserving useful substances.
  • Filtration produces filtrate from blood plasma in nephrons.
  • Selective reabsorption returns needed substances to the blood.