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D3.3.11 (HL)—Blood supply changes

Blood supply changes during exercise redistribute flow so more blood reaches skin for heat removal in human physiology in human physiology.

Syllabus
First assessment 2025
Objective
D3.3.11
Level
HL

Exam analysis

Chance of appearing1%of analysed past papers
Latest appearanceMay 2025
Most common paperPaper1A
Typical marks1

Common command terms

  • Identify

Recent exam appearances

May 2025Paper1A ["HL"] · TZ332[ 1 ]D3.3.11 (HL)—Blood supply changes
Practice this objective

Coverage 2025–2025 · Updated 16 Jul 2026

Activity Redistributes Blood among Organs

HL only

Arteriolar vasodilation and vasoconstriction redistribute blood so organ supply matches changing metabolic activity while vital functions continue.

State Skeletal muscle Gut Brain Kidneys
Sleep Lower flow to most muscle groups than when awake Depends on digestive activity Total flow changes little, though regions such as hypothalamus/brainstem can rise during REM Maintained for excretion and osmoregulation; lying down can raise renal flow
Vigorous exercise Strongly increased Reduced as blood is redirected Kept relatively stable Reduced during prolonged vigorous exercise, but regulation limits disruption
Wakeful rest Lower than during exercise Increased after a meal for digestion and absorption Kept relatively stable Fairly constant overall; posture can alter flow

Locally active tissues dilate their arterioles, while sympathetic/epinephrine signals can constrict vessels to less immediately required organs and dilate those supplying skeletal muscle.

During vigorous exercise, skeletal-muscle flow rises while gut and renal flow fall; this supplies respiration where demand is greatest.

Redistribution is relative, not complete shut-off. Brain and kidney perfusion must remain sufficient for neural control, excretion and osmoregulation.

Blood supply changes

HL only

Assessment in practice

1 marks
How it is assessed

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

Command terms

Identify

What earns marks

Build the answer around this relationship: Exercise increases heat production in muscles.

Representative question

Question 1

[Maximum number: 1]

What is a reason for the changes in blood flow during exercise?

A

Increased blood flow to the kidneys removes waste products from exercise.

B

Blood flow to the brain decreases so that blood is diverted to the kidneys.

C

Increased blood flow to the skin removes heat.

D

Increased blood flow to the digestive system provides more glucose to muscles.

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

  • Exercise increases heat production in muscles.
  • More blood flow to the skin helps transfer heat to the environment.
  • Blood redistribution supports thermoregulation during activity.