Vessels and Blood Group Classification of Blood Groups

After completing this lesson, students should be able to: - Compare and contrast the 3 different types of blood vessels. - Name the key blood vessels in the heart. - Describe the blood flow in arteries and veins. - Explain how blood groups are named. - Name the 4 different blood groups and their antibodies. - Explain the appropriate blood to be used in a transfusion using the terms Antigen and Antibody. - Identify the different types of transfusions.

Blood is pumped by the heart into blood vessels which carry blood around the body.
There are three different types of blood vessels: arteries, veins, and capillaries.
Each type of blood vessel possesses a unique set of characteristics allowing it to perform its specific function.
Important Note: Blood vessels are not classified based on the type of blood (oxygenated or deoxygenated) they carry.

Direction of Flow: Arteries carry blood AWAY from the heart.
Pathways: Arteries direct blood into the capillaries by dividing into smaller vessels called arterioles.
Main Arteries Discussed: - Pulmonary Artery - Aorta
Structural Characteristics: - Must withstand high pressure, necessitating very thick walls. - Walls contain smooth muscles and elastic fibres. - Lumen size: Relatively small compared to veins.
Functional Mechanism: - When ventricles contract, the artery walls stretch to accommodate the extra blood. - When ventricles relax, the elastic walls recoil. This recoil keeps the blood moving and maintains blood pressure. - Crucial Distinction: The artery wall itself does not contract and relax; it stretches and recoils.
Control of Blood Flow: Flow to specific organs can be controlled via the processes of vasoconstriction and vasodilation to suit bodily needs.
Clinical Aspect: A normal coronary artery has a wide lumen; however, narrowing can occur due to the build-up of atherosclerotic plaque.

Direction of Flow: Veins carry blood TOWARDS the heart.
Pathways: Capillaries join into small veins called venules, which then join up to form larger veins.
Main Veins Discussed: - Superior Vena Cava - Inferior Vena Cava - Pulmonary Veins
Structural Characteristics: - Thin, inelastic walls with very little muscle due to the low and relatively constant pressure. - Lumen size: Relatively much larger than in arteries. - Presence of valves (flaps) to prevent the backflow of blood.
Functional Mechanism: - Veins typically lie between skeletal muscle groups. - Periodic contractions of these skeletal muscles help push venous blood along towards the heart.
Note on Diameter: Unlike arteries, veins are not able to change their diameter significantly.

Function: Capillaries serve as the link between arteries and veins.
Structure: - Microscopic vessels forming a dense network. - Walls are a single layer of cells (endothelium only) to facilitate efficient exchange. - They do not have to withstand high internal pressure.
Role in the Body: - They carry blood close to nearly every cell in the body. - They increase the Surface Area ( $SA$ ) for the exchange of substances (oxygen, nutrients, waste, carbon dioxide) between the blood and body cells.

Muscular Walls: - Arteries: Thick - Veins: Thin - Capillaries: None (one cell thick)
Elastic Walls (allowing for recoil): - Arteries: Yes - Veins: No - Capillaries: No
Valves Present: - Arteries: No - Veins: Yes - Capillaries: No
Lumen Size: - Arteries: Small - Veins: Large - Capillaries: Smallest
General Blood Flow Sequence: Heart $\rightarrow$ Arteries $\rightarrow$ Arterioles $\rightarrow$ Capillaries $\rightarrow$ Venules $\rightarrow$ Veins $\rightarrow$ Heart.

Based on systemic and pulmonary circulation diagrams, specific vessels connect as follows:

Pulmonary Circuit: Pulmonary artery (to lungs), Pulmonary vein (from lungs).
Major Systemic Vessels: - Aorta: Transports oxygenated blood to the body. - Vena Cava: Transports deoxygenated blood to the heart. - Liver: Hepatic artery (to liver), Hepatic vein (from liver), Hepatic portal vein (from stomach/intestines to liver). - Kidneys: Renal artery (to kidneys), Renal vein (from kidneys). - Gas Exchange Locations: Occurs in the lungs, upper body, liver, stomach/intestines, kidneys, and lower body.

Antigens: Protein molecules (identity markers) found on the surface of Red Blood Cells ( $RBCs$ ) that are able to stimulate an immune response (antibody production).
Antibodies: Found in the blood plasma; they are designed to react to foreign (non-self) antigens.
Antigen-Antibody Complex: Formed when antibodies combine with foreign antigens during an immune response.
The Two Antigens: Antigen A and Antigen B.
The Four Blood Groups: - Group A: Has Antigen A on RBCs; produces Anti-B antibodies. - Group B: Has Antigen B on RBCs; produces Anti-A antibodies. - Group AB: Has both Antigens A and B on RBCs; produces neither Anti-A nor Anti-B antibodies. - Group O: Has neither Antigen A nor B on RBCs; produces both Anti-A and Anti-B antibodies.

Agglutination: If a person is given incorrect blood, antibodies will attach to antigens causing blood cells to clump together.
Immune Attack: Leucocytes then attack these clumps and destroy the cells.
Recipient/Donor Rules: - Type A: Can receive A or O blood; cannot have B or AB blood. - Type B: Can receive B or O blood; cannot have A or AB blood. - Type AB (Universal Recipient): Can have any type of blood. - Type O (Universal Donor): Can only receive Type O blood.
Compatibility Table Specifics: - O-: Can donate to all (O-, O+, A-, A+, B-, B+, AB-, AB+). - AB+: Can receive from all (Universal Recipient). - B+: Can receive from B+, B-, O+, O-. Can donate to B+, AB+. - A-: Can receive from A-, O-. Can donate to A+, A-, AB+, AB-.

Whole Blood: - Description: Blood taken from a donor with chemicals added to prevent clotting. - Use: Cases of severe blood loss.
Red Cell Concentrates: - Description: Produced by centrifuging blood; heavy cells sink to the bottom while plasma remains on top. May have platelets/WBCs removed. - Use: Heart disease or severe anaemia.
Plasma: - Description: The liquid portion of blood containing clotting factors. - Use: Severe bleeding or liver disease (to provide extra clotting factors).
Platelet Concentrates: - Description: Concentrate containing only platelets. - Use: People with reduced or abnormal platelets.
Cryoprecipitate: - Description: Obtained by freezing plasma and thawing it slowly; the solid remains contain substances necessary for clotting. - Use: Treating some forms of haemophilia or severe bleeding.
Immunoglobulins: - Description: Proteins that act as antibodies extracted from plasma. - Use: Treating people who are deficient in antibodies.
Autologous Transfusion: - Description: Using the patient's own blood, collected prior to an operation. - Use: Treating blood loss after elective surgeries to reduce side effects from donated blood.