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D3.3.9 (HL)—Loop of Henle

The loop of Henle creates a medullary concentration gradient that allows water reabsorption and concentrated urine production in human physiology.

Syllabus
First assessment 2025
Objective
D3.3.9
Level
HL

Exam analysis

Chance of appearing5%of analysed past papers
Latest appearanceNovember 2022
Most common paperPaper1
Typical marks1

Common command terms

  • Identify
  • State

Recent exam appearances

November 2022Paper2 ["HL"] · TZ05(b)[ 1 ]D3.3.9 (HL)—Loop of Henle
May 2019Paper1 ["HL"] · TZ233[ 1 ]D3.3.9 (HL)—Loop of Henle
November 2016Paper1 ["HL"] · TZ039[ 1 ]D3.3.9 (HL)—Loop of Henle
May 2014Paper1 ["HL"] · TZ140[ 1 ]D3.3.9 (HL)—Loop of Henle
May 2013Paper1 ["HL"] · TZ239[ 1 ]D3.3.9 (HL)—Loop of Henle
Practice this objective

Coverage 2012–2022 · Updated 16 Jul 2026

The Loop of Henle Builds a Medullary Gradient

HL only

The loop of Henle uses differing permeabilities and ion transport to create a high solute concentration in the medulla, enabling later water conservation.

The descending limb loses water but has low ion permeability; the ascending limb pumps ions but is water-impermeable. Countercurrent multiplication amplifies the gradient.

For each limb ask whether water can cross and whether solute is transported before predicting fluid concentration.; identify the signal, controller and effector

As filtrate descends, water leaves into the concentrated medulla; as it ascends, ions leave while water stays, making filtrate dilute. This gives a concrete prediction from the stated condition.

The loop creates the gradient; it does not by itself determine the final urine volume. Interpret the result within the stated biological model and limits.

Loop of Henle

HL only

Assessment in practice

1 marks
How it is assessed

This objective is assessed through multiple choice, commonly using Identify / State.

Command terms

Identify / State

What earns marks

Build the answer around this relationship: The descending limb allows water to leave the filtrate.

Representative question

Question 1

[Maximum number: 1]

What is the function of the loop of Henle?

A

To reabsorb salt

B

To maintain a hypertonic solution in the medulla

C

To transport liquid from the collecting ducts to the convoluted tubules

D

To reabsorb glucose

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

  • The descending limb allows water to leave the filtrate.
  • The ascending limb removes salts and helps make the medulla hypertonic.
  • The medullary gradient supports water reabsorption from collecting ducts.