apL2 - blood

• define blood

  red liquid that circulates in the arteries and veins, carrying oxygen to and carbon dioxide from the tissues of the body.
• state the composition of blood.

  55% plasma

  45% cellular content

  cellular content comprises of:

  • erythrocytes
  • leukocytes (white blood cells)
  • thrombocytes (platelets)
• list the constituents of plasma.

  90%-92% water plus dissolved substances including:

  plasma proteins

  prothrombin (a clotting factor)

  gamma globulin which contains immunoglobulins (part of the immune system)

  mineral salts

  nutrient materials

  organic waste products

  hormones

  gases
• describe the formation and life cycle of erythrocytes

  erythropoiesis = development of erythrocytes

  formed in red bone marrow from haemocytoblasts

  life span in circulation approximately 120 days

  follows two main lines of development:

  1. maturation of the cell - requires presence of vitamin B12 and folic acid, intrinsic factor.
  2. formation of hemoglobin - globin is a complex protein, haem is an iron containing substance synthesized inside developing erythrocytes in red bone marrow, function of haemoglobin.
• describe the structure and function of erythrocytes.

  structure:

  Bi-concave, non-nucleated discs

  contains cytoplasm and haemoglobin

  function:

  transport oxyhaemoglobin to all body cells

  transport carbon dioxide to lung for excretion
• list the types of leukocytes.

  basophil

  neutrophil

  eosinophil

  monocyte

  macrophage

  lymphocyte (T cell and B cell)
• describe the structure and function of granular leukocytes.

  40%-75% neutrophils (take up both dyed staining purple)

  0%-1% basophils (alkaline methylene blue)

  1%-5% eosinophils (red acid dye eosin)

  names represents the dyes they take up when stained in the laboratory.
• describe the structure and function of non-granular leukocytes.

  monocytes and macrophages:

  large mononuclear cells

  some circulate in blood and are actively motile and phagocytic

  are mobilized along with neutrophils

  some monocytes migrate into the tissues where they develop into macrophages.
• describe the physiology of erythropoiesis.

  bone marrow produces erythrocytes at the rate they are destroyed to maintain numbers.

  primary stimulus is hypoxia (deficient supply of oxygen to tissues) caused by hemorrhage and excessive hemolysis.

  hypoxia stimulates the production of the hormone erythropoietin this stimulates the production of erythrocytes.

  erythropoietin also regulates the normal production of erythrocytes.
• describe what haemolysis is.

  the breakdown of erythrocytes.

  performed by the reticuloendothelial (phagocytic) cells of the spleen, liver, bone marrow.

  all have the ability to break down haemoglobin into amino acids.

  iron reused in bone marrow, remainder of substances are excreted.
• describe the function of neutropils.

  body's first line of defence against bacterial infections

  seek out and ingest bacteria

  remove waste products such as cell debris

  pass from the blood stream through capillary walls into infected tissue

  actively phagocytic

  form cytoplasmic extensions called pseudopodia around microbes
• describe the function of basophils.

  secrete histamine which causes vasodilation therefore, increasing permeability of capillary walls.

  this assists the movement of phagocytes and protective substances such as antibodies into tissue spaces. they are also released following injury or allergic response.
• describe the function of eosinophils.

  protect the body against foreign materials particularly parasites.

  found in increased numbers in allergic reactions such as hay fever and asthma. they neutralize histamine and plasminogen.
• describe the structure and function of non-granular leukocytes (T and B lymphocytes).

  associated with the protection of the body against antigens

  develop from haemocytoblasts in red bone marrow then spread to the blood stream to lymphoid tissue elsewhere in the body where they become activated.

  able to respond to antigens

  T and B lymphocytes function independently but usually in collaboration.
• describe the function of T-lymphocytes.

  activated in the thymus gland

  some will then circulate in blood

  some will settle in lymphoid tissue

  mainly in lymph nodes, spleen and aggregated glands in the walls of the intestines.
• what are examples of antigens against which T-lymphocytes react:

  cancer cells

  fungi

  bacteria that live inside cells e.g., TB
• describe B-lymphocytes:

  are activated in lymphoid tissue in the walls of the intestines

  some will then circulate the blood

  some will settle in the lymphoid tissue

  mainly found in lymph nodes, spleen and aggregated glands in the walls of the intestines.

  B-lymphocytes usually target bacterial antigens circulating in blood.
• what are some blood clotting factors:

  I - fibrinogen

  II - prothrombin

  III - tissue factor

  IV - calcium

  V - labile factor, proaccelerin, Ac - globulin

  VII - stable factor

  VIII - AHG, antihaemophiliac factor A

  XIII - fibrin stabilising factor
• what is haemostasis?

  the body's natural process that stops bleeding and prevents further blood loss after an injury

  vasoconstriction (reduces blood flow and blood loss), blood vessels reduce in size.

  platelet adhesion and formation of a soft "plug" (primary hemostasis)

  clot formation (secondary haemostasis)

  clot dissolution (fibrinolysis) and healing.
• explain primary haemostasis:

  initiated by the exposure of collagen fibres in the tunica media (when the tunica media is damaged).

  platelets adhere to blood vessel wall through the intermediary of von willebrands factor.

  activation occurs: activated platelets attract circulating fibrinogen, they also attract other platelets (a process inhibited by aspirin).

  haemostatic plug formed mainly of platelets and fibrinogen.
• explain secondary haemostasis:

  the conversion of fibrinogen in the soft plug into fibrin

  prothrombin (factor II) converted to thrombin

  thrombin acts on fibrinogen (factor I) converting it to fibrin

  fibrin cross-links under the influence of factor XIII and shrinks, providing a strong insoluble mesh which traps blood cells.
• explain the blood clotting process:

  clot formed

  bleeding stopped

  plasminogen converted to plasmin by activators released from the damaged endothelial cells
• explain how the removal of a clot takes place:

  plasmin initiates breakdown of fibrin into soluble products

  soluble products treated as waste, seen as foreign, and removed by phagocytes

  healing of damaged vessels takes plalce.
• what are the functions of blood?

  1. oxygen from the lungs to the cells and tissues of the body.
  2. carbon dioxide to be excreted by the lungs.
  3. metabolites and waste products to the excretory organs.
  4. hormones secreted by endocrine glands to target glands and tissues.
  5. heat produced by active organs to less active tissues.
  6. protective substances e.g., antibodies (immunoglobulins) to areas of infection.
  7. materials necessary for haemostasis.
  8. regulation of electrolyte balance
  9. maintains a pH of approx 7.4