blood

• The circulatory system is made up of

  three parts:

  The heart

  The blood vessels

  The blood
• The normal adult human has

  about 5 litres of blood
• Blood is composed of:

  Red blood cells

  White blood cells

  Platelets

  Plasma ( liquid part of

  blood)
• Plasma is a straw yellow liquid

  Plasma consists of mostly water with

  dissolved proteins ( plasma proteins), salts,

  nutrients and wastes e.g. urea
• Plasma transports dissolved nutrients,

  wastes, carbon dioxide, antibodies and

  proteins around the body
• All of the blood cells form in

  bone marrow.
• Bone marrow is found at the

  centre of most bones.
• They are biconcave disc shaped – increases the surface

  area for oxygen to bind
• red blood cells have no nucleus or mitochondrion at maturity
• Red blood cells have a red pigment called haemoglobin –

  oxygen binds to the haemoglobin
• The blood travels to the cells of the body and oxygen is

  released from haemoglobin into the cells.
• Rbc have flexible membranes to allow them to move

  through narrow blood vessels
• In vertebrates, every haemoglobin molecule has four binding sites for

  oxygen.

  When oxygen binds to haemoglobin it is called oxyhaemoglobin

  When oxyhaemoglobin reaches an area of the body where oxygen is low it

  easily loses the oxygen molecules to be used by the cells in respiration

  Oxyhaemoglobin is what makes red blood cells appear bright red
• White blood cells are larger and less

  numerous than rbc.
• White blood cells fight against infection.
• Some white blood cells (phagocytes)

  surround and engulf bacteria - phagocytosis
• Some white blood cells produce antibodies,

  which help to destroy invading organisms.
• White blood cells can be

  divided into two main

  groups:

  1. Monocytes

  2. Lymphocytes
• Monocytes are the largest

  white blood cells

  They have a large bean shaped

  nucleus

  Mature monocytes are called

  macrophages

  They engulf pathogens in a

  process called phagocytosis
• Lymphocytes have a large spherical nucleus

  They play a vital role in the specific defence system

  They are found circulating in the blood but in high concentrations in the

  spleen, tonsils and lymph nodes ( lymphatic system)

  Lymphocytes produce antibodies to fight pathogens
• Platelets are fragments of larger cells called

  megacytes
• Platelets help to clot the blood when a blood vessel

  gets damaged.
• They gather at the site of a wound and start a series

  of chemical reactions that result in the production of

  a fibrous protein called fibrin

  This forms a network of strands across the wound,

  which traps blood cells, forming a scab and plugging

  the wound

  This prevents loss of blood and it also prevents

  microorganisms getting into the blood.
• Leukemia is a broad term for cancers of blood

  cells

  It is thought to occur when some blood cells

  acquire changes in their DNA ( mutations)

  The mutations tell the cells to grow larger and

  at a faster rate

  Over time these abnormal cells crowd out

  healthy blood cells in the bone marrow, leading

  to fewer healthy white blood cells, red blood

  cells and platelets
• There is a large variety of blood groupings but the most common is the ABO groups

  and the rhesus factor

  The groupings are based on antigens that are found on the surface of red blood cells
• Blood with the rhesus antigen on the

  surface of the red blood cell is said to

  be rhesus positive ( RhD+) and blood

  without it is said to be rhesus negative (

  RhD - )
• Your blood type determines which blood

  types you can safely receive in a blood

  transfusion

  If someone is given an unsuitable type in a

  transfusion, there may be a severe allergic

  reaction, which can be fatal
• The person’s blood cells will agglutinate

  (stick together) forming clots that block the

  capillaries
• Patients cannot receive blood that

  contains antigens to the antibodies

  present in their blood

  For example: A person with type A blood

  can receive blood from other Type A and

  type O individuals. They cannot receive

  blood from Type B or AB!