Cardiovascular System and Blood: Structure, Function, and Blood Typing

Cardiovascular System

Introduction and Composition

The cardiovascular system is essential for maintaining homeostasis in the body by transporting blood, nutrients, gases, and waste products. 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; blood clotting prevents excessive bleeding.

• 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. The lymphatic system returns fluid to the blood and is involved in immune responses.

Components of Blood

Overview

Blood is a specialized connective tissue composed of cells suspended in plasma. It is denser and more viscous than water, with a pH of 7.35–7.45. Average blood volume is 4–5 liters in females and 5–6 liters in males.

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+, etc.

  • Nutrients: Glucose, amino acids, vitamins

  • Waste: Urea, creatinine, CO2

  • Proteins: Albumin, globulins, antibodies, fibrinogen

  • Enzymes: Catalyze chemical reactions

  • Clotting factors: Help stop bleeding

Serum

• Plasma minus clotting factors

• Contains similar components as plasma except for clotting proteins

Formed Elements

• Red Blood Cells (RBCs)/Erythrocytes: ~99% of formed elements

• White Blood Cells (WBCs)/Leukocytes: ~1% of formed elements

• Platelets/Thrombocytes: ~1% of formed elements

Red Blood Cells (RBCs) / Erythrocytes

Structure and Function

• Biconcave discs: Increase surface area for gas exchange and flexibility

• No nucleus or organelles: Cannot divide or repair

• Hemoglobin: Oxygen and carbon dioxide carrying protein; gives blood its red color

• Normal count: 4.8 million/μL (females), 5.4 million/μL (males)

• Lifespan: ~120 days

Hemoglobin

• Comprises about 1/3 of RBC weight

• Heme molecule: Binds oxygen (oxyhemoglobin) and carbon dioxide (carbaminohemoglobin)

Blood Groups and Blood Types

Antigens and Blood Typing

Blood types are determined by the presence or absence of specific antigens on the surface of RBCs. The two major blood group systems are ABO and Rh.

ABO Blood Group

Type	Antigen(s) Present
A	A antigen
B	B antigen
AB	A and B antigens
O	Neither A nor B antigen

Rh Blood Group

Type	Rh Antigen Present?
Rh+	Yes
Rh-	No

Combined ABO and Rh Types

Type	Antigens Present
A+	A antigen, Rh antigen
B+	B antigen, Rh antigen
AB+	A and B antigens, Rh antigen
O+	Rh antigen only
A-	A antigen only
B-	B antigen only
AB-	A and B antigens only
O-	No antigens

Antigens and Antibodies

Definitions and Roles

• Antigen (Ag): Any substance that can stimulate an immune response; found on RBC surfaces.

• Antibody (Ab): Protein produced in response to an antigen; found in plasma.

• Antibodies are highly specific and only bind to their target antigen.

Patterns in Blood Plasma

RBC Antigen	Plasma Antibody
A	Anti-B
B	Anti-A
AB	Neither
O	Both anti-A and anti-B

Under normal circumstances, plasma does not contain anti-Rh antibodies unless exposed to Rh antigen.

Agglutination

• Agglutination: Clumping of RBCs when antibodies bind to their specific antigens.

• Can block blood vessels and cause tissue damage or kidney failure.

Transfusions and Antigen-Antibody Reactions

Transfusion Principles

• Transfusion: Transfer of whole blood or blood components.

• Recipient antibodies must not react with donor antigens.

• Universal donor: O- (no antigens)

• Universal recipient: AB+ (no antibodies)

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
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-

Rh Antigen Exposure and Hemolytic Disease

• Rh- individuals can develop anti-Rh antibodies after exposure to Rh+ blood.

• Hemolytic disease of the newborn (HDN): Occurs when Rh- mother produces antibodies against Rh+ fetal blood.

• Prevention: Administration of anti-Rh immunoglobulin (Rho(D) immune globulin) to Rh- mothers.

White Blood Cells (WBCs) / Leukocytes

Types and Functions

• Granulocytes:

  • Neutrophils: Phagocytosis of bacteria

  • Eosinophils: Combat parasites, modulate allergic responses

  • Basophils: Release histamine, involved in inflammation

• Agranulocytes:

  • Lymphocytes: Immune response (B cells, T cells)

  • Monocytes: Phagocytosis, become macrophages

WBC Count and Clinical Significance

• Normal WBC count varies; abnormal counts may indicate infection, inflammation, or disease (e.g., leukemia).

Platelets / Thrombocytes

Role in Hemostasis

• Platelets: Small cell fragments involved in blood clotting.

• Normal count: 150,000–400,000/μL

Hemostasis Mechanisms

1. Vascular spasm: Constriction of blood vessels to reduce blood flow.

2. Platelet plug formation: Platelets adhere to damaged vessel and aggregate.

3. Coagulation: Formation of a stable blood clot via clotting factors. Key equation: $\text{Prothrombinase} + \text{Prothrombin} \rightarrow \text{Thrombin}$ $\text{Thrombin} + \text{Fibrinogen} \rightarrow \text{Fibrin (clot)}$

Summary Table: Blood Components

Component	Function
Plasma	Transport of nutrients, hormones, waste
RBCs	Oxygen and CO2 transport
WBCs	Immune defense
Platelets	Blood clotting

Example Application

Blood transfusions require careful matching of donor and recipient blood types to prevent agglutination and immune reactions. Understanding blood components and their functions is essential for clinical practice and research in physiology and medicine.

Additional info: Some explanations and tables have been expanded for clarity and completeness based on standard academic knowledge.