Blood groups, transfusions and the lymphatic system

Blood groups and blood transfusions

•       Involves blood, or a blood product, from a donor being injected directly into the patient’s bloodstream.

Why would someone need a blood transfusion?

⚬      To replace excessive blood loss, e.g. surgery, injury, or medical conditions

⚬      Some types of anaemia

⚬      Conditions that affect the blood, e.g. leukaemia (bone cancer), haemophilia etc.

•       Whole blood transfusion:

⚬      Severe traumatic haemorrhage (severe blood loss).

•       Red blood cell transfusion:

⚬      Spinning blood at very high speed in a centrifuge.

⚬      Treat low haemoglobin or red cell count, anaemia, heart disease.

•       Platelet transfusion:

⚬      Treat low platelet count (thrombocytopaenia).

⚬      Caused by chemotherapy, bone marrow transplantation, major surgery, liver disease, severe trauma, some medications.

•       Plasma transfusion:

⚬      Fresh frozen plasma (all blood cells are taken out).

⚬      Replace missing or low levels of blood proteins.

⚬      Liver disease, heart surgery, severe blood lost, severe burns.

•       Cryoprecipitate:

⚬      Contains clotting factors (factor VIII, Factor XIII and von Willebrand factor) and fibrinogen.

⚬      Thawing fresh frozen plasma and then collecting the cold-insoluble proteins (precipitate); refrozen for storage.

⚬      Low levels of clotting proteins for conditions like Haemophilia A (lack factor VIII) and von Willebrand disease (lack this factor).

Autologous transfusions

•       When patient’s own blood is used.

•       Collected prior to surgery that may require a transfusion.

•       Advantage: eliminate the risk of transmission of disease and most possible side effects of the usual transfusions.

ABO blood groups

•       The surface of red blood cells are coated with sugar and protein molecules that can stimulate the immune system.

•       These surface molecules are called antigens.

•       Blood groups are determined by the antigens on the red blood cells:

•       antigen A or antigen B

•       On the surface of the red blood cells a person can either have antigen A, antigen B, both antigens or neither antigen.

Antigens and immune system

•       The immune system recognises the antigens that are found on its own cells, but it will produce antibodies for any antigens that are not normally found in the body (as part of our immune response).

•       An antigen is defined as any substance capable of causing the formation of antibodies when introduced into the tissues.

Antibodies

•       Antibody: a substance produced by a type of specialised white blood cell in response to a specific antigen.

•       Antibodies circulate in the blood plasma.

•       The antibody is a protein and therefore has a complementary shape to a specific antigen.

•       The specific antibody will combine with the specific antigen to neutralise or destroy it (forms a complex = lock-and-key).

Agglutination

•       Circulating antibodies form a complex with foreign antigens.

•       These antibodies will form a complex with more than one foreign red blood cell; forming a clump. This process is called agglutination.

•       Agglutination: The clumping together of microorganisms or red blood cells

Agglutination and phagocytosis

•       Foreign red blood cells that are clumped together are then removed from the blood by circulating white blood cells through the process of phagocytosis.

Rhesus blood groups

•       The Rh blood group is due to a type of protein antigens found on the surface of red blood cells - called the D antigen.

•       A person who is Rh positive has the D-antigen and someone who is Rh negative does not have the D-antigen.

Blood groups and transfusions

•       It is important to know the blood type of the recipient (person receiving the transfusion).

•       This is to avoid complications of being transfused with blood that triggers an immune response.

•       If a Rh-negative person receives Rh-positive blood, they will produce antibodies that will react to the donated blood.

•       An individual with blood type B will have anti-A antibodies circulating in their plasma.

•       If this person is mistakenly given blood type A from a donor this will cause an immune reaction called agglutination.

•       Blood type A red blood cells have the A-antigen.

•       The anti-A antibodies in the recipient's blood will bind to the A antigens from the donor blood forming an antigen-antibody complex.

•       Clumping the foreign blood together.

•       Universal donor:

⚬      Blood type that can be donated to any recipient.

•       Universal recipient:

⚬      Individuals who can receive blood from any type of donor blood.

Lymphatic system

Body fluids

•       Water makes up about 60% (by weight) of the human body.

•       Water, together with important dissolved substances, form the various fluids of the body.

•       Fluid contained inside the cells is called intracellular fluid.

•       Fluid outside cells is extracellular fluid:

⚬      Between the cells there are microscopic spaces filled with fluid, known as tissue fluid (or interstitial fluid or intercellular fluid)

⚬      Blood plasma

Tissue bed

•       Capillaries are the link between arteries and veins.

•       They are microscopic blood vessels that form a network to carry blood close to nearly every cell in the body.

•       The function of the capillaries is to take the blood close to individual cells and to allow substances to be exchanged between cells and the blood.

•       Capillary walls are permeable to substances such as water, inorganic ions, glucose, amino acids, urea and lactic acid.

•       Capillary walls are relatively impermeable to large molecules, such as plasma proteins, and red blood cells.

•       The most important way materials pass between the blood and the tissue fluid is by diffusion, due to concentration gradients.

-       A second way in which materials move from the blood plasma to tissue fluid (or vice versa) is due to blood pressure.

-       The blood pressure at the arterial end of the capillaries is relatively high, and fluid with dissolved substances is forced out through the permeable capillary walls.

-       The plasma which is forced out of the capillaries, becomes part of the tissue fluid.

•       As capillaries are very narrow blood vessels, they offer high resistance to blood flow.

•       At the venous end of the capillaries, blood pressure is relatively low, and because the proteins in the blood plasma create a high osmotic pressure, much of the fluid returns to the capillaries at the venous end.

Role of lymphatic system

•       During a 24-hour period the difference in volume between fluid leaving the capillaries and fluid returning to the capillaries is about 3L.

•       If this fluid was allowed to accumulate, the tissues would swell and start to interfere with cell function.

•       It is removed by the lymphatic system.

•       A system of lymph capillaries drains away the excess fluid in the tissue bed.

•       The fluid is now known as lymph.

•       One-way transport system that carries excess fluid away from the tissues back to the circulatory system.

•       Drain excess fluid from the tissue bed and return it to the circulatory system

•       Role in internal defence against disease-causing organisms.

Consists of:

⚬      Lymph (fluid)

⚬      Lymph capillaries

⚬      Lymphatic vessels

⚬      Lymph nodes (lymphoid tissue)

Lymph capillaries

•       They are blind-ended tubes in the spaces between the cells of most tissues.

•       Slightly larger than blood capillaries.

•       More permeable than blood capillaries: proteins and disease-causing organisms in the tissue fluid can easily pass through the walls of the lymph capillaries into the lymph.

Lymph vessels

•       The network of lymph capillaries join to larger lymphatic vessels.

•       Structurally similar to veins:

-       Lined by layer of endothelial cells

-       Thin layer of smooth muscle

-       Have valves to prevent backflow of lymph, which allows the lymphatic system to function without a central pump (unlike the circulatory system)

•       Lymph movement occurs despite low pressure due to smooth muscle action, valves and compression during contraction of adjacent skeletal muscle.

•       The lymphatic vessels join up into larger and larger vessels, which eventually join into two large ducts =

-       thoracic duct

-       right lymphatic duct

-       These ducts empty their contents into the subclavian veins (brings blood back to the heart)

-       Thus, any tissue fluid that does not directly pass back into the capillaries in the tissue bed is returned to the blood via the lymphatic system.

Lymph nodes

•       At intervals along the lymphatic vessels are structures called lymph nodes.

•       Most numerous in the neck, armpits, groin and around the alimentary canal.

•       Bean shaped (1mm - 25mm)

•       Capsule of connective tissue

•       Within are masses of lymphoid tissue that contain:

•       Lymphocytes (B-cells and T-cells)

•       Macrophages (phagocytes)

•       Criss-cross of mesh fibres

•       Lymph entering the lymph nodes contains cell debris, foreign particles and micro-organisms (some of which may cause disease).

•       Lymph is filtered in the lymph node = larger particles, such as bacteria, are trapped in the mesh – macrophages + phagocytosis.

•      When infections occur the formation of lymphocytes increases – lymph nodes become swollen.

Blood clotting

•       Minimise blood loss when blood vessel is damaged.

•       Prevent entry of pathogens (disease causing organisms) into the blood.

•       During a small injury to a blood vessel, a platelet plug may be sufficient. (4)

•       In a larger injury a blood clot may be required. (5)

Clotting process

1.     Vasocontriction:

Localised contraction of smooth muscle in small blood vessels is called vasoconstriction.

Decreases blood flow to minimise blood loss and allows time for other responses.

2.    Formation of platelet plug:

Platelet Activation:

As soon as a blood vessel wall is damaged, a series of reactions activates platelets so that they stick to the injured area of the blood vessel.

The platelets change shape from round to spiny.

Platelet Plug:

Blood vessels that are damaged create a rough surface for platelets to stick.

This attracts other platelets forming a platelet plug.

Chemicals are continued to be released that enhance vasoconstriction

3.  Coagulation (blood clot)

This is a complex process which involves a large number of chemical substances called clotting factors, in the blood plasma.

Your blood plasma contains many dissolved substances, including relatively large plasma proteins.

Fibrinogen:

Soluble plasma protein

Inactive form

Platelets release a chemical that triggers a complex chemical pathway that causes fibrinogen to change its structure.

The fibrinogen is converted into threadlike proteins fibres called fibrin (insoluble).

Fibrin threads then form a mesh over the top of the platelet plug, that entraps red blood cell, platelets and plasma to form the clot itself.

The fibrin threads stick to the damaged blood vessel wall and thus anchors the clot in place.

4.  Clot retraction

Fibrin meshwork shrinks and becomes denser and stronger – pulls the edges of the damaged blood vessel closer together.

Tissue repair takes place.

Fluid, called serum, is squeezed from the fibrin meshwork – clot dries and forms a scab.