Blood
Let’s take a quick look at... Human blood.
The main components of human blood are:
Plasma - The liquid component of the blood
Red blood cells (erythrocytes) - Carry oxygen from the lungs to the rest of the body
White blood cells (leukocytes) - Help fight infections and aid in the immune process.
Platelets (thrombocytes) - Help in blood clotting
Plasma consists mostly of water (90%), with proteins, ions, nutrients, and wastes mixed in. It can be isolated by spinning a tube of whole blood at high speeds in a centrifuge. The denser cells and platelets move to the bottom of the tube, forming red and white layers, while the plasma remains at the top, forming a yellow layer.
Red blood cells (RBCs) are responsible for carrying oxygen to the body tissues and carbon dioxide away from the tissues. Their small size and biconcave shape increase the surface area-to-volume ratio, improving gas exchange. When mature, RBCs and do not contain mitochondria or a nucleus. Lack of mitochondria keeps the RBCs from using any of the oxygen they’re carrying, which maximises the amount delivered to tissues of the body. Lack of a nucleus makes additional space for haemoglobin, a key protein used in oxygen transport.
White blood cells (WBCs) are a key part of the immune system, which helps the body defend itself against infection. Different types of WBCs fight foreign invaders such as bacteria and viruses. Some types of WBCs make antibodies, which are special proteins that recognise foreign materials and help the body get rid of them. Blood contains far fewer WBCs than RBCs. The WBC count (the number of cells in a given amount of blood) in someone with an infection often is higher than usual because more WBCs are being made or are entering the bloodstream to fight the infection.
Oh, one last thing. Blood is red. Let’s just be perfectly clear on that point!!! I’ve written a post on that :)