Veins carry blood towards from the heart.
thin muscle and elastic fibres
veins have valves which act to stop the blood from going in the wrong direction.
body muscles surround the veins so that when they contract to move the body, they also squeeze the veins and push the blood along the vessel.
Capillaries link Arteries with Veins
the wall of a capillary
is only one cell thick
they exchange materials between the blood and other body cells.
The exchange of materials between the blood and the body can only occur through capillaries.
A collection of capillaries is known as a capillary bed.
red blood cells
white blood cells
red blood cell
white blood cell
contain haemoglobin, a molecule specially designed to hold oxygen and carry it to cells that need it.
can change shape to an amazing extent, without breaking, as it squeezes single file through the capillaries.
a biconcave disc that is round and flat without a nucleus
there are many different types and all contain a big nucleus.
the two main ones are the lymphocytes and the macrophages.
some lymphocytes fight disease by making antibodies to destroy invaders by dissolving them.
other lymphocytes make antitoxins to break down poisons.
macrophages ‘eat’ and digest micro-organisms .
Platelets are bits of cell broken off larger cells.
Platelets produce tiny fibrinogen fibres to form a net. This net traps other blood cells to form a blood clot.
A straw-coloured liquid that carries the cells and the platelets which help blood clot.