Chapter 11: The Cardiovascular System – Blood (Mini-Textbook Study Notes)

The Cardiovascular System: Blood

Introduction to the Cardiovascular System

The cardiovascular system is the body's internal transport network, consisting of the heart, blood, and blood vessels. Blood is essential for transporting nutrients, gases, waste products, and chemical messengers throughout the body. It is the first organ system to become fully operational during embryonic development.

• Major components: Heart, blood, blood vessels

• Primary functions of blood:

  • Transport of dissolved gases, nutrients, hormones, and metabolic wastes

  • Regulation of interstitial fluid pH and ion composition

  • Restriction of fluid loss at injury sites

  • Defense against toxins and pathogens

  • Stabilization of body temperature

Composition and Physical Characteristics of Blood

Blood Composition

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

• Plasma: Makes up about 55% of blood volume; contains water, plasma proteins, and other solutes.

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

• Blood volume: Adult males: 5–6 L; Adult females: 4–5 L

Physical Characteristics of Blood

• Temperature: 38°C (slightly above body temperature)

• Viscosity: Five times more viscous than water due to plasma proteins and formed elements

• pH: Slightly alkaline (7.35–7.45)

• Type: Connective tissue

Blood Collection and Analysis

• Venipuncture: Common method for collecting blood, usually from the median cubital vein

• Capillary collection: From fingertip or earlobe for blood smears

• Arterial puncture: Used to evaluate gas exchange at the lungs

Plasma and Plasma Proteins

Composition of Plasma

Plasma, along with interstitial fluid, forms most of the extracellular fluid in the body. It is composed of:

• Water: 92%

• Plasma proteins: 7%

• Other solutes: 1% (hormones, nutrients, gases)

Major Types of Plasma Proteins

• Albumins: ~60%; maintain osmotic pressure

• Globulins: ~35%; transport proteins and antibodies (immunoglobulins)

• Fibrinogen: ~4%; functions in blood clotting as precursor to fibrin

Most plasma proteins are synthesized by the liver, except antibodies (produced by lymphocytes).

Other Solutes in Plasma

• Organic nutrients: Lipids, carbohydrates, amino acids, vitamins

• Electrolytes: Na+, K+, Ca2+, Mg2+, Cl-, HCO3-, etc.

• Organic wastes: Urea, uric acid, creatinine, bilirubin, ammonium ions

Red Blood Cells (Erythrocytes)

Structure and Function

Red blood cells (RBCs) are specialized for oxygen and carbon dioxide transport. They account for 99.9% of formed elements and contain the pigment hemoglobin.

• Biconcave shape: Increases surface area for gas exchange and flexibility for capillary passage

• Lack organelles: No nucleus or mitochondria; rely on anaerobic metabolism

Hemoglobin Structure and Function

• Structure: Four globular protein subunits, each with a heme group containing iron

• Oxygen transport: O2 binds to heme; CO2 binds to globin

• Oxygen loading/unloading: High plasma O2 promotes loading (lungs); low plasma O2 and high CO2 promote unloading (tissues)

Red Blood Cell Life Cycle and Recycling

• Lifespan: ~120 days; cannot repair themselves

• Recycling: Macrophages in liver, spleen, and bone marrow engulf old RBCs; hemoglobin is broken down and components recycled

• Hemoglobin breakdown: Heme → biliverdin → bilirubin (excreted in bile); iron is stored or transported by transferrin

• Jaundice: Excess bilirubin causes yellowing of skin and eyes

Erythropoiesis (RBC Formation)

• Site: Red bone marrow in adults; yolk sac in embryo

• Requirements: Amino acids, iron, vitamin B12 (requires intrinsic factor for absorption)

• Stages: Hemocytoblast → myeloid stem cell → erythroblast → reticulocyte → erythrocyte

Regulation of Erythropoiesis

• Stimulus: Hypoxia (low tissue oxygen)

• Hormone: Erythropoietin (EPO) released by kidneys; stimulates RBC production in bone marrow

• Clinical relevance: EPO used in anemia treatment and blood doping

Blood Types and Transfusions

ABO and Rh Blood Groups

• Antigens: Surface markers on RBCs (A, B, Rh)

• Antibodies: Found in plasma; attack foreign antigens

• Blood types: A, B, AB, O; each can be Rh+ or Rh-

Transfusion Reactions

• Cross-reaction: Occurs if antibodies attack donor RBC antigens, causing agglutination and hemolysis

• Blood compatibility testing: Mixing blood with anti-A, anti-B, and anti-Rh antibodies to determine type

Universal Donors and Recipients

• Universal donor: Type O- (no A, B, or Rh antigens)

• Universal recipient: Type AB+ (no anti-A, anti-B, or anti-Rh antibodies)

White Blood Cells (Leukocytes)

Types and Functions

White blood cells defend the body against pathogens, remove toxins, and clean up damaged cells. They are classified as granulocytes or agranulocytes.

• Granulocytes: Neutrophils, eosinophils, basophils

• Agranulocytes: Lymphocytes, monocytes

Characteristics of WBCs

• Amoeboid movement

• Diapedesis (migration out of bloodstream)

• Positive chemotaxis (movement toward chemical signals)

• Phagocytosis (neutrophils, eosinophils, monocytes)

Types of White Blood Cells

• Neutrophils: 50–70%; first responders, phagocytize bacteria

• Eosinophils: 2–4%; attack parasites, involved in allergic reactions

• Basophils: <1%; release histamine and heparin, enhance inflammation

• Monocytes: 2–8%; become macrophages, aggressive phagocytes

• Lymphocytes: 20–40%; specific immunity, produce antibodies

Differential WBC Count

• Measures the percentage of each type of WBC in a blood sample

• Leukopenia: Low WBC count

• Leukocytosis: High WBC count

• Leukemia: Cancer of blood-forming tissues, abnormal WBCs

WBC Formation

• Originate from hemocytoblasts in red bone marrow

• Lymphoid stem cells → lymphocytes (regulated by thymosins, antigens)

• Myeloid stem cells → other formed elements (regulated by colony-stimulating factors, CSFs)

Platelets and Hemostasis

Platelets (Thrombocytes)

• Cell fragments derived from megakaryocytes

• Initiate clotting and help close injured blood vessels

• Circulate for 9–12 days; normal count: 150,000–500,000/μL

• Thrombocytopenia: Low platelet count; Thrombocytosis: High count

Hemostasis: Stopping Blood Loss

Hemostasis is the process of stopping bleeding and involves three phases:

• Vascular phase: Vascular spasm constricts vessel, endothelium becomes sticky

• Platelet phase: Platelets adhere to exposed collagen and each other, forming a plug

• Coagulation phase: Cascade of reactions converts fibrinogen to fibrin, forming a clot

Clotting Pathways

• Extrinsic pathway: Initiated by tissue factor from damaged tissues; rapid

• Intrinsic pathway: Initiated by exposure of blood to collagen; slower

• Common pathway: Both pathways activate Factor X, leading to conversion of prothrombin to thrombin, and fibrinogen to fibrin

Key factors: Calcium ions (Ca2+) and vitamin K are essential for clotting. Deficiency in either impairs the process.

Clot Retraction and Removal

• Platelets contract, pulling vessel edges together (clot retraction)

• Clot is dissolved by fibrinolysis (plasminogen → plasmin, which digests fibrin)

Summary Table: Major Formed Elements of Blood

Formed Element	Main Function	Relative Abundance
Red Blood Cells (Erythrocytes)	Transport O2 and CO2	~99.9% of formed elements
White Blood Cells (Leukocytes)	Defense against pathogens	~0.1% of formed elements
Platelets (Thrombocytes)	Clotting, vessel repair	~0.1% of formed elements

Key Equations and Concepts

• Hematocrit (%): $\text{Hematocrit} = \frac{\text{Volume of RBCs}}{\text{Total Blood Volume}} \times 100$

• Oxygen transport: $\text{Hb} + \text{O}_2 \rightleftharpoons \text{HbO}_2$

• Coagulation cascade: $\text{Prothrombin} \xrightarrow{\text{Prothrombinase}} \text{Thrombin}$ $\text{Fibrinogen} \xrightarrow{\text{Thrombin}} \text{Fibrin}$

Additional info: These notes provide a comprehensive overview of blood as a component of the cardiovascular system, suitable for ANP college students preparing for exams or seeking a concise reference.