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Blood vessels

Detail level

A network of tubes carrying blood between the heart and the body: arteries carry it away from the heart, veins bring it back, and tiny capillaries exchange materials with tissues.

MedlinePlus counts three components: arteries, veins, and capillaries (tiny vessels that connect small arteries to small veins and whose thin walls allow the exchange of substances). Arteries and veins share a three-layered wall, and the vein wall is thinner because its pressure is lower, and veins have valves that prevent backflow of blood.

The left ventricle pumps blood at high pressure through the aorta to the arteries, which branch into arterioles that regulate flow into the capillaries, then venules collect it and then larger veins return it to the heart through the superior and inferior venae cavae. Oxygen-rich blood remains in the pulmonary veins and oxygen-poor blood in the pulmonary artery, an exception to the general rule. The middle layer of the wall is muscular and regulates the vessel's diameter and blood pressure (SEER).

In one minute123

What is it?
The network of arteries, veins and capillaries that carries blood around the body.
Who is usually affected?
Concerns everyone; and they are affected by blood pressure, diabetes and smoking.
Acute or chronic?
They change over time and are affected by chronic diseases.
Main symptoms
Varies by disease: leg pain, swelling, weak pulse, signs of stroke.
Red flags?
Yes: signs of stroke or severe chest pain are an emergency.
Preventable?
Controlling blood pressure, sugar and lipids, quitting smoking, and physical activity.

What are they?

Blood vessels are the system that carries blood around the body. MedlinePlus mentions three components: arteries, veins and capillaries.

According to the NHLBI: "Veins bring blood to the heart, and arteries take blood away from the heart", and they connect the heart to the rest of the circulatory system.

Sources12

Types and roles

TypeFunctionNote
ArteriesCarry blood from the heart to tissues and organs (MedlinePlus)Systemic arteries carry oxygen-rich blood, whereas the pulmonary artery carries oxygen-poor blood to the lungs
CapillariesTiny vessels that connect small arteries to small veins, and their thin walls allow exchange of substances between tissues and bloodTheir density varies with tissue activity; they are abundant in skeletal muscle and absent from the epidermis of the skin (SEER)
VeinsReturn blood and waste to the heartVeins have valves that keep blood moving towards the heart, which matters especially in the limbs

How it works

  1. 1
    PumpingThe left ventricle generates the high pressure needed to push blood around the body through the aorta (NHLBI).
  2. 2
    BranchingLarge arteries branch into smaller arterioles that regulate blood flow into the capillaries (SEER).
  3. 3
    ExchangeIn the capillaries, tissues exchange substances with the blood.
  4. 4
    ReturnVenules gather into larger veins that return oxygen-poor blood to the heart through the superior and inferior venae cavae (NHLBI).
  5. 5
    The lungsThe pulmonary artery carries it to the lungs, and it returns oxygen-rich through the pulmonary veins to the left atrium.

The wall of an artery and vein has three layers: the inner, the middle muscular layer, which is the thickest and regulates the vessel's diameter and blood pressure, and the outer, of connective tissue. The vein wall is thinner and less rigid because its pressure is lower (SEER).

The heart muscle itself is nourished by the coronary arteries that branch from the aorta, and the coronary veins return its blood to the right atrium (NHLBI).

Sources23

Links to other organs

The heart
  • The blood pump that pushes it through the arteries and receives it from the veins.
The lungs
  • Blood passes through them via the pulmonary artery and pulmonary veins to pick up oxygen.
Blood pressure
  • It is the force of blood against the artery walls; sustained high levels damage the vessel walls and contribute to heart attacks, strokes, heart failure and chronic kidney disease (NHLBI).
Sources24

Conditions that affect them

MedlinePlus lists vessel diseases: aneurysm, atherosclerosis (plaque build-up), clots (including deep vein thrombosis and pulmonary embolism), coronary and carotid artery disease, Raynaud's phenomenon, stroke, varicose veins, and vasculitis.

The NIDDK notes that chronic diabetes damages blood vessels and nerves, raising the risk of heart disease and stroke.

Tests used to study them

MedlinePlus mentions among heart and vessel tests: ultrasound of vessels (such as the carotid artery) and coronary angiography. It counts "heart health tests" among the topics related to vascular disease.

Sources67

Keeping them healthy

  • Not smoking or quitting.
  • Regular physical activity according to the World Health Organization's guidelines.
  • A balanced diet low in salt and unhealthy fats.
  • Controlling blood pressure, sugar and blood lipids.
Strength of evidence: Strong evidence

Why this rating: The relationship between smoking, high blood pressure, sugar and lipids and cardiovascular disease is established by large, consistent studies, and lowering them is part of the World Health Organization's guidelines.

High confidence that the true effect is close to the estimate; usually based on large, consistent randomised trials or systematic reviews of them.

Sources891011

When do you need urgent help?

Call emergency services now 998

  • Signs of sudden stroke (weakness, slurred speech, change in vision) or severe chest pain: call an ambulance immediately.1213

Educational content only — no diagnosis, and no substitute for a clinician.

References

  1. 1
    MedlinePlus. Vascular Diseases. medlineplus.gov/vasculardiseases.html
    Health agencies & guidelines · Accessed 2026-10-06
  2. 2
    NHLBI. How the Heart Works — How Blood Flows through the Heart. www.nhlbi.nih.gov/health/heart/blood-flow
    Health agencies & guidelines · Accessed 2026-10-06
  3. 3
    NCI SEER Training. Classification & Structure of Blood Vessels. training.seer.cancer.gov/anatomy/cardiovascular/blood/classification.html
    Educational & historical references · Accessed 2026-10-06
  4. 4 Health agencies & guidelines · Accessed 2026-10-06
  5. 5 Health agencies & guidelines · Accessed 2026-10-03
  6. 6
    MedlinePlus. Heart and vascular services. medlineplus.gov/ency/article/007459.htm
    Health agencies & guidelines · Accessed 2026-10-06
  7. 7
    NHLBI / NIH. Heart Tests. www.nhlbi.nih.gov/health/heart-tests
    Health agencies & guidelines · Accessed 2026-10-04
  8. 8
    WHO. Cardiovascular diseases (CVDs) — Fact sheet. www.who.int/news-room/fact-sheets/detail/cardiovascular-diseases-(cvds)
    Health agencies & guidelines · Accessed 2026-10-04
  9. 9
    WHO. Physical activity — Fact sheet. www.who.int/news-room/fact-sheets/detail/physical-activity
    Health agencies & guidelines · Accessed 2026-10-03
  10. 10 Health agencies & guidelines · Accessed 2026-10-03
  11. 11 Health agencies & guidelines · Accessed 2026-10-04
  12. 12
    NHS. Stroke — Symptoms. www.nhs.uk/conditions/stroke/symptoms/
    Health agencies & guidelines · Accessed 2026-10-03
  13. 13 Health agencies & guidelines · Accessed 2026-10-03

Review status: Edited content · Last updated:

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Educational content only — no diagnosis, and no substitute for a clinician.

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