BackCardiovascular System and Blood: Structure, Function, and Clinical Relevance
Study Guide - Smart Notes
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Cardiovascular System
Introduction and Overview
The cardiovascular system is essential for maintaining homeostasis by transporting nutrients, gases, hormones, and waste products throughout the body. It consists of the heart, blood vessels, and blood.
Heart: Pumps blood throughout the body.
Blood Vessels: Arteries, veins, and capillaries that transport blood.
Blood: Delivers nutrients and removes waste from tissues.
Functions of the Cardiovascular System
Transport: Moves oxygen, nutrients, hormones, and waste products.
Protection: White blood cells defend against pathogens; platelets help in clotting.
Regulation: Maintains pH, temperature, and fluid balance.
Relation to the Circulatory System
The cardiovascular system is part of the larger circulatory system, which also includes the lymphatic system (transports lymph and aids in immune function).
Blood and lymphatic vessels are separate but have similar locations.
Lymphatic fluid eventually drains into the cardiovascular system.
Components of Blood
What is Blood?
Blood is a type of connective tissue with cells suspended in an extracellular matrix (plasma). It is denser and more viscous than water, opaque, and ranges from scarlet to dull red in color. Average volume: 4-5 liters in females, 5-6 liters in males. Normal pH: 7.35–7.45.
Main Parts of Blood
Plasma (fluid part): ~55% of blood volume
Formed elements (cellular part): ~45% of blood volume
Plasma
91–92% water
Contains:
Gases: O2, CO2
Electrolytes: Na+, K+, Ca2+, Cl-
Nutrients: Glucose, amino acids, fatty acids
Waste: Urea, creatinine
Proteins: Albumin, globulins, fibrinogen
Enzymes and clotting factors
Serum
Serum is plasma minus the clotting factors.
Contains water, electrolytes, nutrients, waste, proteins, and enzymes.
Formed Elements
Red blood cells (RBCs)/Erythrocytes: ~99% of blood cells
White blood cells (WBCs)/Leukocytes: ~1% of blood cells
Platelets/Thrombocytes: Cell fragments involved in clotting
Red Blood Cells (RBCs)/Erythrocytes
Structure and Function
RBCs are biconcave discs, increasing surface area for gas exchange and flexibility. They lack nuclei and organelles, cannot reproduce, and have a lifespan of about 120 days.
Normal count: 4.8 million/μL (females), 5.4 million/μL (males)
Function: Carry oxygen (O2) and carbon dioxide (CO2)
Hemoglobin
Hemoglobin: Oxygen and carbon dioxide-carrying protein; about 1/3 of RBC weight
Gives blood its red color
Heme: Iron-containing molecule that binds O2 (forms oxyhemoglobin) and CO2 (forms carbaminohemoglobin)
Blood Groups and Blood Types
Antigens and Blood Group Classification
Blood groups are determined by genetically inherited antigens (glycoproteins and glycolipids) on the surface of RBCs. The two major blood group systems are ABO and Rh.
ABO Blood Group: Based on presence/absence of A and B antigens
Rh Blood Group: Based on presence/absence of Rh (D) antigen
ABO Blood Types
Type | Antigen(s) Present |
|---|---|
A | A antigen |
B | B antigen |
AB | Both A and B antigens |
O | Neither A nor B antigen |
Rh Blood Types
Type | Rh Antigen Present? |
|---|---|
Rh+ | Yes |
Rh- | No |
Combined ABO and Rh Types
Type | Antigens Present |
|---|---|
A- | A antigen only |
B- | B antigen only |
AB- | A and B antigens only |
O- | No antigens |
A+ | A and Rh antigens |
B+ | B and Rh antigens |
AB+ | A, B, and Rh antigens |
O+ | Rh antigen only |
Antigens and Antibodies
Definitions and Roles
Antigen (Ag): Any substance that can stimulate an immune response; present on RBCs and other cells.
Antibody (Ab): Protein produced in response to an antigen; highly specific and binds to the antigen to neutralize or mark it for destruction.
Antibody Specificity and Blood Types
Antibodies in plasma are specific to antigens not present on the individual's own RBCs.
For example, type A blood has anti-B antibodies; type B has anti-A antibodies; type AB has neither; type O has both anti-A and anti-B antibodies.
Antigen-Antibody Patterns
Blood Type | Antigen(s) on RBC | Antibody(ies) in Plasma |
|---|---|---|
A | A | Anti-B |
B | B | Anti-A |
AB | A and B | None |
O | None | Anti-A and Anti-B |
Transfusions and Antigen-Antibody Reactions
Transfusion Principles
Transfusion: Transfer of whole blood or blood components.
Recipient antibodies must not react with donor antigens to avoid agglutination.
Agglutination and Its Dangers
Agglutination: Clumping of RBCs due to antibody-antigen reaction.
Can block small blood vessels, reduce blood flow, and cause kidney failure due to hemoglobin release.
Transfusion Compatibility Table
Recipient | Antigens on RBC | Antibodies in Plasma | Possible Donors |
|---|---|---|---|
A+ | A, Rh | Anti-B | A+, A-, O+, O- |
A- | A | Anti-B, Anti-Rh | A-, O- |
B+ | B, Rh | Anti-A | B+, B-, O+, O- |
B- | B | Anti-A, Anti-Rh | B-, O- |
AB+ | A, B, Rh | None | All types (universal recipient) |
AB- | A, B | Anti-Rh | AB-, A-, B-, O- |
O+ | Rh | Anti-A, Anti-B | O+, O- |
O- | None | Anti-A, Anti-B, Anti-Rh | O- (universal donor) |
Rh Factor and Hemolytic Disease
Normally, blood plasma does not contain anti-Rh antibodies.
If an Rh- person receives Rh+ blood, they may develop anti-Rh antibodies, which can cause problems in future transfusions or pregnancy (hemolytic disease of the newborn).
White Blood Cells (WBCs)/Leukocytes
Types and Functions
WBCs are involved in immune defense and are classified as granulocytes or agranulocytes.
Granulocytes:
Neutrophils: Phagocytize bacteria
Eosinophils: Combat parasites and allergens
Basophils: Release histamine in allergic reactions
Agranulocytes:
Lymphocytes: B cells (antibody production), T cells (cell-mediated immunity)
Monocytes: Phagocytize pathogens and debris
Platelets/Thrombocytes
Structure and Role
Cell fragments derived from megakaryocytes
Essential for blood clotting (hemostasis)
Hemostasis
Mechanisms of Hemostasis
Hemostasis is the process that stops bleeding when a blood vessel is damaged. It involves three main mechanisms:
Vascular spasm: Constriction of blood vessels to reduce blood flow
Platelet plug formation: Platelets adhere to the site of injury and aggregate
Blood clotting (coagulation): Formation of a fibrin mesh that stabilizes the platelet plug
Blood Clotting Cascade (Simplified)
Formation of prothrombinase (requires calcium)
Prothrombinase converts prothrombin to thrombin
Thrombin converts fibrinogen to fibrin
Fibrin forms the mesh that stabilizes the clot
Equation:
Clinical Relevance
Disorders of hemostasis can lead to excessive bleeding or unwanted clot formation (thrombosis).
Summary Table: Blood Components
Component | Percentage | Main Function |
|---|---|---|
Plasma | ~55% | Transport of nutrients, hormones, waste; maintains osmotic balance |
RBCs | ~45% | Transport of O2 and CO2 |
WBCs | ~1% | Immune defense |
Platelets | ~1% | Blood clotting |
Example
If a patient with type O- blood needs a transfusion, only O- blood can be given to avoid agglutination and immune reaction.
Additional info: The notes also briefly mention hemolytic disease of the newborn (HDN), which occurs when an Rh- mother develops anti-Rh antibodies that attack the RBCs of an Rh+ fetus. This can be prevented by administering anti-Rh immunoglobulin (RhoGAM) to the mother.
