Blood composition

• Blood as a transport system (part 1):

  • 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 as a transport system (part 2):

  • 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 micrograph:

  
• Composition of human blood:

  
• Red blood cells carry oxygen (part 1):

  • 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 carry oxygen (part 2):

  • 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 (part 1):

  • 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.
• Blood plasma (part 2):

  • 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.
  • Hormones - chemical messengers released into the blood from the endocrine organs (glands) and delivered to target tissues/organs of 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.
• Blood micrograph:

  
• Blood plasma transports:

  1. Soluble digestion products (glucose) from the small intestine to other organs.
  2. Cardon dioxide (produced by aerobic respiration) from the organs to the lungs to be breathed out.
  3. The waste-product urea from the liver to the kidneys to be excreted in urine.
• Red blood cells transport oxygen from the lungs to the body cells. They contain the oxygen-carrying molecule haemoglobin. Red blood cells have no nucleus, which means that they have more room for haemoglobin. Lastly, in the centre of the cell, there are dimples, call this shape a biconcave disc. Like this...

  
• This shape gives the red blood cells a greater surface area so that oxygen diffuses in and out rapidly. Like this...