Chapter 11: The Cardiovascular System – Blood (Essentials of Anatomy & Physiology)

The Cardiovascular System: Blood

Introduction to the Cardiovascular System

The cardiovascular system is composed of the heart, blood, and blood vessels. Blood plays a vital role in transporting essential substances throughout the body and maintaining homeostasis.

• Components: Heart, blood, blood vessels

• Functions of blood:

  • Transport of nutrients, oxygen, waste products, and chemical messengers

  • Regulation of pH and ion composition

  • Restriction of fluid loss at injury sites (hemostasis)

  • Defense against toxins and pathogens

  • Stabilization of body temperature

Composition of Blood

Blood is a specialized connective tissue with a liquid matrix called plasma and formed elements (cells and cell fragments).

• Plasma: Makes up about 55% of blood volume; consists of water (92%), plasma proteins (7%), and other solutes (1%).

• Formed elements: Make up about 45% of blood volume; include red blood cells (RBCs), white blood cells (WBCs), and platelets.

• Average blood volume: Males: 5–6 liters; Females: 4–6 liters

Major Types of Plasma Proteins

Plasma proteins are essential for maintaining osmotic pressure, transporting substances, and blood clotting.

Type	Percentage	Main Function
Albumins	~60%	Maintain osmotic pressure of plasma
Globulins	~35%	Transport proteins and antibodies
Fibrinogen	~4%	Blood clotting (forms fibrin)
Lipoproteins	Variable	Transport lipids

Note: Insulin is a hormone, not a major plasma protein.

Red Blood Cells (Erythrocytes)

Red blood cells (RBCs) are the most abundant formed elements and are responsible for transporting oxygen and carbon dioxide.

• Percentage of formed elements: ~99.9%

• Main component: Hemoglobin (Hb), which binds oxygen and carbon dioxide

• Color: Responsible for the red color of blood

• Life span: ~120 days; cannot repair themselves

• Production rate: ~1% replaced daily; ~3 million/sec enter circulation

Hemoglobin Structure and Function

• Structure: 4 subunits, each with a heme group containing an iron atom

• Oxygen binding: O2 binds to heme

• Carbon dioxide binding: CO2 binds to globin subunits

Anemia: A reduction in oxygen-carrying capacity due to low hematocrit or reduced hemoglobin. Symptoms include muscle fatigue and lack of energy.

Blood Cell Formation (Hematopoiesis)

Hematopoiesis is the process of blood cell formation, occurring primarily in the red bone marrow.

• Erythropoiesis: Formation of RBCs, stimulated by erythropoietin (EPO)

• EPO effects: Increases cell division and maturation of RBCs, raises hematocrit, and increases blood viscosity

• Blood doping: Artificially increasing RBC count to enhance athletic performance

Blood Types and the Rh System

Blood types are determined by the presence of specific antigens on the surface of RBCs. The major blood group antigens are A, B, and Rh (D).

• Antigens: Trigger antibody responses; determine compatibility for blood transfusions

• ABO system: Four main types: A, B, AB, O

• Rh system: Rh-positive (has D antigen) or Rh-negative (lacks D antigen)

Transfusion reactions: Occur if incompatible blood is transfused, due to antibodies attacking foreign antigens.

Example: A person with type A blood cannot safely receive type B blood because of the presence of anti-B antibodies in the recipient's plasma.

White Blood Cells (Leukocytes)

White blood cells (WBCs) defend the body against pathogens and remove toxins, wastes, and abnormal cells. They contain a nucleus and can leave the bloodstream to enter tissues.

• Categories:

  • Granulocytes: Neutrophils, eosinophils, basophils

  • Agranulocytes: Monocytes, lymphocytes

• Mnemonic: Never Let Monkeys Eat Bananas (Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils)

Type	Relative Abundance	Main Features
Neutrophils	50–70%	Phagocytic, multilobed nucleus, short lifespan (~10 hours)
Lymphocytes	20–40%	Specific immunity, produce antibodies, migrate in/out of tissues
Monocytes	2–8%	Large, kidney-shaped nucleus, aggressive phagocytes
Eosinophils	2–4%	Phagocytic, exocytotic, release anti-inflammatory enzymes, bilobed nucleus
Basophils	Release histamine (vasodilation) and heparin (anticoagulant), promote inflammation

Platelets (Thrombocytes) and Hemostasis

Platelets are cell fragments involved in clotting and the prevention of blood loss. They circulate for 9–12 days, with an average count of 350,000/μL.

• Low count: Thrombocytopenia (risk of bleeding)

• High count: Thrombocytosis (risk of clotting)

Hemostasis

Hemostasis is the process of stopping blood loss from damaged vessels. It involves three main phases:

1. Vascular phase: Blood vessel constriction

2. Platelet phase: Platelet plug formation

3. Coagulation phase: Formation of a stable blood clot (fibrin mesh)

Sample Quiz Questions (Concept Checks)

• Gas exchange efficiency in lungs: Evaluated by arterial puncture

• Primary plasma proteins: Albumin, globulin, fibrinogen (not insulin)

• Functions of blood: Transporting gases, regulating pH, defending against pathogens (not replacing Ca)

• Cellular composition: About 1/4 (1/3) of all cells in the human body are red blood cells

• Hemoglobin function: Carries oxygen and carbon dioxide (not nitrogen)

• Components of whole blood: Plasma and formed elements

• Hemoglobin structure: 4 subunits

• Blood type compatibility: Type A cannot receive type B due to anti-B antibodies in the recipient

• Eosinophils: Granulocytes, 2–4% of WBCs, bilobed nuclei, phagocytic, exocytotic, release anti-inflammatory enzymes

• Lymphocytes: Agranulocytes, 20–40% of WBCs, specific defenses, migrate in/out of tissues

Additional info: The notes above expand on the brief quiz questions and slide content, providing definitions, context, and examples for each major topic in the study of blood within the cardiovascular system.