Composition of the Blood Blood contains:- Red blood cells White blood cells Plasma Platelets

Oxygen is carried in the red blood cells. Carbon dioxide is carried in the plasma. The concentration of carbon dioxide carried in the plasma is limited since it combines with water to form an acid. Too much acid in the blood would lead to problems since blood functions best between pH 7.36 and Most carbon dioxide is transported in blood plasma as bicarbonate ions. (Some CO 2 is carried in the red blood cells attached to other molecules)

Soluble food such as glucose and amino acids are also transported dissolved in the plasma.

Function of Haemoglobin  Haemoglobin is found in red blood cells.  In high oxygen concentrations haemoglobin combines readily with oxygen to form oxyhaemoglobin  This happens in the lungs  In low oxygen concentrations, oxyhaemoglobin releases its oxygen to the body cells.  Blood with oxygen is bright red.  Haemoglobin carries oxygen to the tissues of the body.

high in oxygen low in oxygen Colour in the blood high in oxygen red and the blood low in oxygen blue.

So:- Haemoglobin + oxygen oxyhaemoglobin Association (in lungs) Dissociation (in tissues) Associate = to combine with oxygen Dissociate = to release oxygen

White Blood Cells Are less numerous than RBC’s They contain nuclei, can change shape and squeeze through tiny pores in capillary walls. They are suited to their function of defending the body since they can reach the site of infection outwith the circulation. Two types of white blood cell are monocytes and lymphocytes. lymphocytes monocytes

Phagocytosis Is the process by which bacteria are engulfed and destroyed by phagocytic cells such as monocytes and macrophages (Macrophages are cells that come from monocytes) The macrophage will engulf a bacterial cell and then digest it. During infection, 100’s of monocytes and macrophages migrate to the infected area and engulf many bacteria by phagocytosis. Dead bacteria and these cells often accumulate at a site of injury forming pus!

Bacterium giving out chemical macrophage Vacuole forming Trapped bacterium Lysosome (structure containing digestive enzymes) Lysosomes move towards and fuse with vacuole Bacteria being digested by enzymes from lysosomes

Immunity and Antibodies Immunity is an organism’s ability to resist infectious disease. Phagocytosis is an example of non- specific immune response since it provides general protection against a wide range of micro-organisms. Antibody production is an example of specific immune response as they are specific to a particular antigen.

ANTIGEN A molecule that is recognised as alien to the body by the body’s lymphocytes. ANTIBODY The presence of an antigen in the body stimulates the lymphocytes to produce antibodies. An antibody is a Y-shaped molecule. Each arm has a receptor site whose shape is specific to a particular antigen. When an antibody meets its complementary antigen, they combine at their specific sites like a lock and key and the antigen is rendered harmless. It will then be engulfed by phagocytosis.

Antibody Receptor sites

Antigens meet antibodies virusantigen Virus gains access to body & multiplies inside the cell Some viral particles become attached to their antigens to lymphocytes lymphocyte Lymphocytes respond to this antigen by multiplying and producing cells that mass produce a specific type of antibody Antigens combine with antibodies at receptor sites and become a harmless complex later engulfed by a phagocyte.

Primary and Secondary Responses When a person is infected by a disease- causing organism, the body responds by producing antibodies. This is the primary response. Because it takes a while before the antibodies appear, the primary response is often unable to prevent the person from suffering the disease.

If the person survives and are exposed to the same disease-causing antigen in the future, a secondary response happens. This happens because the body has memory cells which remember the antigen. This time the disease is usually prevented. During the secondary response –Antibody production is more rapid –The concentration of antibodies produced reaches a higher level –The higher concentration of antibodies is maintained for a longer time

Increasing concentration of antibodies First exposure to antigen Second exposure to antigen Time (days)Some later time in a person’s life (days) Primary Response Secondary Response