Red Blood Cells
Blood as a transport system
- The role of blood in the body is to act as a transport system carrying useful substances to every cell of the body, and carrying harmful waste substances to other organs for processing and/or excretion
- It also plays a vital role in transferring heat from “active” organs to cooler parts of the body (such as the extremities – hands and feet)
- Blood consists predominantly of red blood cells and plasma
- Over half of the volume of the blood is made up of plasma
- The majority of the other half is made up of red blood cells
- Less than 1% of blood contains white blood cells and platelets
- Blood consists predominantly of red blood cells and plasma
- It also plays a vital role in transferring heat from “active” organs to cooler parts of the body (such as the extremities – hands and feet)
Blood micrograph
Composition of human blood
Red blood cells carry oxygen
- Red blood cells are specialised cells that carry oxygen from the lungs to cells throughout the body
- The structure of red blood cells are adapted for this function in 3 key ways
- Red blood cells are small with a 'biconcave disk' shape which gives them a large surface area to volume ratio to maximise diffusion of oxygen in and out
- They are full of haemoglobin, a protein that binds to oxygen to form oxyhaemoglobin
- They have no nucleus which allows more space for haemoglobin to be packed in
- Their small size and flexibility allows them to pass through capillaries
Red blood cells
Blood Plasma
- Plasma is a straw coloured liquid which the other components of the blood are suspended within
- Plasma is important for the transport of many substances including:
- Red blood cells, white blood cells and platelets
- Water
- Carbon dioxide - the waste product of cellular respiration
- Digested food and mineral ions - absorbed from the small intestine and delivered to cells around the body
- Urea - the waste substance produced in the breakdown of proteins by the liver. Urea is dissolved in the plasma and transported to the kidneys
- Hormones - chemical messengers released into the blood from the endocrine organs (glands) and delivered to target tissues/organs of the body
- Antibodies - which are special proteins to help fight infection
- Heat energy - created in respiration (an exothermic reaction), heat energy is transferred to cooler parts of the body or to the skin where heat can be lost