Blood is the fluid medium in which materials are transported around the body via blood vessels
- An average adult human contains roughly 5 – 6 litres of blood (approximately 77 mls per kilogram)
When blood is fractionated by centrifugation, three key elements become apparent
- Fractionated blood contains roughly 55% plasma, 45% red blood cells and less than 1% forms a buffy coat
Plasma
- Consists mainly of water, which dissolves materials and functions as a transport medium
- Contains electrolytes (minerals that carry a charge), which are important for maintaining fluid balance and blood pH
- Proteins in the blood plasma maintain osmotic potential (albumin), transport lipids (globulin) and help clot (fibrinogen)
- Blood plasma also functions to transport various materials needed by the body and wastes produced by body cells
Red Blood Cells
- Red blood cells (erythrocytes) are responsible for transporting oxygen around the body
- Oxygen is bound to haemoglobin at the lungs and released from the red blood cell at respiring body tissues
Buffy Coat
- The buffy coat is the fraction of a blood sample that contains white blood cells and platelets
- White blood cells (leukocytes) are involved in the body’s immune defence (eliminating infections)
- Platelets (thrombocytes) are involved in blood clotting (repairing damaged vessels to prevent blood loss)
Composition of Human Blood
Composition of Blood Plasma
Various materials are transported in the plasma for use by the body, including:
Nutrients – needed by cells to make chemical energy (e.g. glucose)
Antibodies – involved in pathogen identification and elimination
Carbon dioxide – waste produced as a by-product of cell respiration
Hormones – chemical messengers that move through the bloodstream
Oxygen – required by body tissues in order to respire aerobically
Urea – compound that is excreted to remove nitrogen from the body
Heat – not a molecule, but still an important component of blood plasma
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