Blood composition

There are two main components of blood: cells, or

Blood cells

Composed of three main cell types: erythrocytes, leucocytes & platelets.

Erythrocytes

• Most numerous cells (5.5x10'^12^'/L).
• No mitochondria
• No nucleus
• Lifespan 120 days
• Contains haemoglobin, with four subunits with a polypeptide globin chain and an iron containing haem group. Adult haemoglobin has two alpha and two beta chains.
• Binds reversibly to four O2 molecules.

Leukocytes

Check out the immune pages for more on these... 4-10x10'^9^'/L (20x10'^9^'/L in newborn)

Lymphocytes

• Agranulocyte, which means that they have clear cytoplasm under a H&E stain.
• Made from lymphoblasts
• Two types: B and T cells.
• Make antibodies (immunoglobulins)
• Allows immunological memory (for vaccines etc)

Monocytes

• Found in blood and bone marrow, are the precursors of macrophages, which are found in connective tissue and ingest foreign bacteria.
• After formation in marrow they circulate for around 72 hours before entering tissues.

Neutrophils

• A granulocyte - meaning the cells go grainy under a H&E stain.
• Life span 10 hours
• Phagocytose bacteria
• Secrete cytokines and chemotaxins
• Important in the inflammatory response.
• Made from myeloblasts in bone marrow

Eosinophils

• Granulocyte
• Ingest foreign particles.
• Cover surfaces within the body.
• Involved in allergic responses

Basophils

• Granulocyte
• Contain histamine (causes vasodilation, contraction of smooth muscle, mediates inflammation) and heparin (anticoagulant).
• Ingests foreign particles.

Platelets

• 140-400x10'^9^'/L
• Small, vesicle like structures.
• Formed from megakaryocytes in the bone marrow.
• Contain dense granules and receptors from ADP and collagen.
• Lifespan of 4 days.

Blood Fluid

Plasma, mainly composed of water, blood proteins and inorganic electrolytes

Plasma proteins

Albumin

• Determines oncotic pressure (the pressure difference between the blood and the lymph/ tissue fluid).
• Lack of albumin results in oedema, liver disease and nephritic syndrome.

Immunoglobins

• Also known as antibodies, these are produced by plasma cells, which are differentiated B lymphocytes.
• IgG
• IgA
• IgM
• IgE (GAME)
• Produced in response to non-self antigens.

Others

• Coagulation factors - fibrinogen, prothrombin and plasminogen.
• Carrier proteins and hormones

Inorganic electrolytes

• Ca²⁺
• Na⁺
• K⁺
• Mg²⁺
• Cl^-
• CO₃^2-
• PO₄^3-
• Fe^2+/3+