The Cardiovascular System and Blood: Structure, Function, and Clinical Relevance

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Cardiovascular System

Introduction to the Cardiovascular System

The cardiovascular system is essential for transporting substances throughout the body, maintaining homeostasis, and protecting against disease. It is a central topic in biological psychology due to its role in supporting brain and body function.

Components: The heart (pumps blood), blood vessels (transport blood), and blood (carries nutrients, gases, and waste).
Functions: Transport (nutrients, gases, hormones), protection (immune cells), and regulation (temperature, pH, fluid balance).
Relation to Homeostasis: Maintains stable internal conditions by distributing substances and removing waste.

Example: Oxygen is transported from the lungs to tissues, while carbon dioxide is carried back to the lungs for exhalation.

The Circulatory System

The cardiovascular system is part of the larger circulatory system, which also includes the lymphatic system.

Cardiovascular system: Moves blood through the body.
Lymphatic system: Moves lymph, returns fluid to the bloodstream, and supports immune function.

Additional info: The lymphatic system drains excess fluid from tissues and returns it to the cardiovascular system.

Components of Blood

What is Blood?

Blood is a specialized connective tissue composed of cells suspended in a liquid extracellular matrix (plasma).

Physical Properties: Denser and more viscous than water; opaque; color ranges from scarlet to dull red.
Volume: 4-5 liters in females, 5-6 liters in males.
pH: 7.35–7.45

Main Components of Blood

Plasma (fluid part): ~55% of blood volume.
Formed elements (cells): ~45% of blood volume (includes red blood cells, white blood cells, and platelets).

Plasma

Plasma is the liquid portion of blood, consisting mostly of water and dissolved substances.

91–92% water
Contains:
- Gases (O2, CO2)
- Electrolytes (ions such as Na+, K+, Ca2+)
- Nutrients (glucose, amino acids, fatty acids)
- Waste products (urea, uric acid, CO2)
- Proteins (albumin, antibodies, fibrinogen)
- Hormones and enzymes
- Clotting factors

Serum

Serum is plasma without the clotting factors.

Contains water, electrolytes, nutrients, waste, proteins (except clotting factors), hormones, and enzymes.

Formed Elements

The cellular portion of blood includes:

Red blood cells (RBCs)/Erythrocytes: ~99% of formed elements; transport oxygen and carbon dioxide.
White blood cells (WBCs)/Leukocytes:
- Platelets/Thrombocytes:

Red Blood Cells (RBCs)/Erythrocytes

Structure and Function

RBCs are specialized for gas transport.

Biconcave disc shape: Increases surface area for gas exchange and flexibility.
No nucleus or organelles: Cannot divide or repair themselves; lifespan ~120 days.
Hemoglobin: Protein that binds oxygen and carbon dioxide; gives blood its red color.
Normal counts: 4.8 million/μL (females), 5.4 million/μL (males).
2 million new RBCs produced per second.

Hemoglobin

About 1/3 of RBC weight is hemoglobin.
Heme group: Contains iron, binds oxygen (oxyhemoglobin) or carbon dioxide (carbaminohemoglobin).

Blood Groups and Blood Types

Antigens and Blood Groups

Blood groups are determined by antigens (genetically determined glycoproteins and glycolipids) on the surface of RBCs.

ABO Blood Group: Based on presence/absence of A and B antigens.
Rh Blood Group: Based on presence/absence of Rh (D) antigen.

Type	Antigens Present	Antibodies Present
A	A antigen	Anti-B antibody
B	B antigen	Anti-A antibody
AB	A and B antigens	Neither anti-A nor anti-B antibodies
O	Neither A nor B antigen	Both anti-A and anti-B antibodies

Rh Blood Types

Rh+: Rh antigen present on RBC surface.
Rh-: Rh antigen absent.

Combined ABO and Rh Types

Type	Antigens Present	Antibodies Present
A+	A, Rh	Anti-B
B-	B	Anti-A, anti-Rh (if exposed)
AB+	A, B, Rh	None
O-	None	Anti-A, anti-B, anti-Rh (if exposed)

Antigens and Antibodies

Definitions

Antigen (Ag): Any substance that can stimulate an immune response; on RBCs, determines blood type.
Antibody (Ab): Protein produced by the immune system in response to an antigen; binds specifically to that antigen.

Immune Specificity

Antibodies are highly specific; they only bind to the antigen that triggered their production.
Normally, the immune system does not attack self-antigens (autoimmunity is an exception).

Antigen-Antibody Reactions

When antibodies in plasma encounter their specific antigen on RBCs, they bind and cause agglutination (clumping of RBCs).
Agglutination can block blood vessels and cause hemolysis (destruction of RBCs), leading to serious complications such as kidney failure.

Transfusions and Antigen-Antibody Reactions

Blood Transfusions

Transfusions involve transferring whole blood or blood components from a donor to a recipient.
Used to treat anemia, blood loss, or clotting disorders.
Compatibility is crucial to avoid immune reactions.

Transfusion Compatibility

Recipient	Antigens on RBC	Antibodies in Plasma	Possible Donors
A+	A, Rh	Anti-B	A+, A-, O+, O-
B+	B, Rh	Anti-A	B+, B-, O+, O-
AB+	A, B, Rh	None	All types (universal recipient)
O-	None	Anti-A, Anti-B, Anti-Rh (if exposed)	O- (universal donor)

Rh Incompatibility

Normally, plasma does not contain anti-Rh antibodies.
If an Rh- person receives Rh+ blood, they may develop anti-Rh antibodies, causing problems in future transfusions or pregnancies.

Hemolytic Disease of the Newborn (HDN)

Occurs when an Rh- mother carries an Rh+ fetus.
Mother may develop anti-Rh antibodies that cross the placenta and attack fetal RBCs.
Prevention: Administration of Rho(D) immune globulin (RhoGAM) to Rh- mothers.

White Blood Cells (WBCs)/Leukocytes

Types and Functions

Granulocytes: Neutrophils, eosinophils, basophils (contain granules in cytoplasm).
Agranulocytes: Lymphocytes, monocytes (lack visible granules).
Function: Defend against infection, destroy foreign organisms, and remove debris.

Abnormal WBC Counts

High or low WBC counts can indicate infection, immune disorders, or blood diseases.

Platelets/Thrombocytes and Hemostasis

Platelets

Fragments of megakaryocytes; essential for blood clotting.
Help prevent blood loss by forming plugs in vessel injuries.

Hemostasis

Hemostasis is the process of stopping bleeding and involves three main steps:

Vascular spasm: Blood vessel constricts to reduce blood flow.
Platelet plug formation: Platelets adhere to the injury site and aggregate.
Coagulation (blood clotting): Fibrin forms a mesh that stabilizes the platelet plug.

Additional info: Clotting factors in plasma are essential for the coagulation cascade.

Summary Table: Blood Types and Transfusion Compatibility

Recipient	Antigens on RBC	Antibodies in Plasma	Possible Donors
A+	A, Rh	Anti-B	A+, A-, O+, O-
A-	A	Anti-B, anti-Rh (if exposed)	A-, O-
B+	B, Rh	Anti-A	B+, B-, O+, O-
B-	B	Anti-A, anti-Rh (if exposed)	B-, O-
AB+	A, B, Rh	None	All types (universal recipient)
AB-	A, B	Anti-Rh (if exposed)	AB-, A-, B-, O-
O+	Rh	Anti-A, Anti-B	O+, O-
O-	None	Anti-A, Anti-B, Anti-Rh (if exposed)	O- (universal donor)

Example: Type O- blood can be given to any recipient (universal donor), while AB+ can receive from any donor (universal recipient).