Summary
Arteries carry blood away from the heart, veins return it and capillaries exchange materials.
In depth
Arteries have thick elastic and muscular walls; veins have thinner walls, larger lumen and valves; capillaries are one cell thick for exchange. Blood pressure falls from arteries to veins. Muscle contractions help return blood.
Vessel structure suits function: arteries withstand pressure; capillaries allow exchange; veins act as reservoirs. Vasoconstriction and vasodilation regulate flow.
Key idea: total capillary area is huge but blood moves slowly there to allow exchange.
Arteries have a thick muscular wall and elastic tissue that smooths pulsatile flow and allows recoil; arterioles control resistance. Capillaries are about 8 micrometres wide, with walls of single endothelial cells, and may be continuous, fenestrated (kidney, intestine) or sinusoidal (liver). Veins have thin walls, large lumens and valves, and rely on skeletal muscle pumps and breathing to return blood. Veins hold about 60 percent of blood volume.
At the arterial end of a capillary, hydrostatic pressure pushes fluid out, and at the venous end, oncotic pressure of plasma proteins pulls much back; the remainder goes to the lymph. Varicose veins result from faulty valves, and oedema from excess fluid leaving vessels. Endothelium also secretes nitric oxide to relax vessels.
Key idea: structure matches function, with thick walls for pressure and thin walls for exchange.
Frequently asked questions
What is Blood Vessels?
Arteries carry blood away from the heart, veins return it and capillaries exchange materials.
Which area of biology covers Blood Vessels, and how advanced is it?
Blood Vessels is one of the 51 topics in Human Physiology. It is rated Beginner, so it suits learners who are starting out in biology. Related topics in this area include Fluid Compartments, Circulatory System, Gas Exchange in Alveoli.
Can you give an example of Blood Vessels?
Varicose veins have faulty valves.
What should I learn before Blood Vessels?
Blood Vessels is a Beginner topic, so no earlier topic is required. Other Beginner topics in Human Physiology that pair well with it include Homeostasis, Tissues and Organs, Skeletal System.
What topics are related to Blood Vessels?
The closest topics to Blood Vessels are Fluid Compartments, Circulatory System, Gas Exchange in Alveoli, Lymphatic System. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Blood Vessels?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Blood Vessels. To practise the whole of Human Physiology, use the Human Physiology quiz.
How is Blood Vessels different from Fluid Compartments?
Blood Vessels: Arteries carry blood away from the heart, veins return it and capillaries exchange materials. Fluid Compartments: Body water is divided into intracellular and extracellular fluid, with distinct ion compositions. Read both side by side and note what each one explains.
How should I study Blood Vessels step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Fluid Compartments and explain the difference aloud. Finally, take the Human Physiology quiz and come back to this page for any question you miss.