Chapter 17: The Cardiovascular System – Blood (Anatomy & Physiology Study Notes)

Chapter 17: The Cardiovascular System – Blood

Overview of Blood

Blood is a vital connective tissue that plays essential roles in transport, regulation, and protection within the human body. It consists of plasma and formed elements, each contributing to the overall function and health of the organism.

• Transport: Blood carries oxygen (O2), carbon dioxide (CO2), nutrients, hormones, and enzymes throughout the body.

• Regulation: Blood helps maintain body temperature, pH balance, and fluid volume.

• Protection: Blood prevents blood loss through clotting and defends against microbes, toxins, and infection via immune cells.

Components of Blood

Blood is composed of a liquid matrix called plasma and cellular elements known as formed elements.

• Plasma: The straw-colored, liquid portion of blood, making up about 55% of total blood volume. It contains water, electrolytes, proteins, nutrients, gases, and waste products.

• Formed Elements: These include erythrocytes (red blood cells, RBCs), leukocytes (white blood cells, WBCs), and thrombocytes (platelets).

When blood is centrifuged, it separates into:

• Plasma (about 55%)

• Buffy coat (<1%, contains WBCs and platelets)

• Erythrocytes (about 45%)

The percentage of erythrocytes is called the hematocrit (average: 42% in females, 47% in males).

Plasma Composition

Plasma is about 90% water and contains over 100 dissolved solutes:

• Electrolytes: Na+, K+, Ca2+, Cl-, HCO3-

• Proteins (8%):

  • Albumin: 60% of plasma proteins; maintains osmotic pressure.

  • Globulins: Transport proteins and antibodies.

  • Fibrinogen: Involved in blood clotting.

• Nitrogenous substances: Urea, uric acid, creatinine

• Nutrients: Glucose, amino acids, fatty acids

• Gases: O2, CO2

• Hormones: Steroid and thyroid hormones

Formed Elements of Blood

Erythrocytes (Red Blood Cells)

Erythrocytes are specialized for the transport of respiratory gases. Their unique structure and composition enable efficient oxygen and carbon dioxide exchange.

• Shape: Biconcave discs, 7.5 μm in diameter, providing a large surface area for gas exchange.

• Composition: 97% hemoglobin by volume (excluding water).

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

• Count: Approximately 5 million per cubic millimeter of blood.

Hemoglobin Structure and Function

Hemoglobin (Hb) is the protein responsible for oxygen transport in erythrocytes.

• Composed of four polypeptide chains (globin) and four heme groups.

• Each heme group binds one O2 molecule; thus, one Hb can carry four O2 molecules.

• Types:

  • Oxyhemoglobin: Hb saturated with O2

  • Deoxyhemoglobin: Hb after releasing O2

  • Carbaminohemoglobin: Hb bound to CO2

Erythropoiesis (Production of RBCs)

Erythropoiesis is the process of RBC formation, occurring in the red bone marrow.

• Starts from myeloid stem cells, progressing through several stages to mature erythrocytes.

• Regulated by erythropoietin (EPO), a hormone produced by the kidneys in response to low oxygen levels.

• Requirements: Iron (Fe2+), vitamin B12, and folic acid for DNA synthesis.

Equation for Oxygen Transport:

$\text{Hb} + 4\text{O}_2 \rightarrow \text{Hb(O}_2)_4$

Life Cycle and Degradation of Erythrocytes

• Average lifespan: 100–120 days.

• Old RBCs are engulfed by macrophages; iron is salvaged, and heme is degraded to bilirubin (excreted in bile).

Erythrocyte Disorders

• Anemia: Reduced oxygen-carrying capacity due to blood loss, insufficient RBC production, or excessive RBC destruction.

• Polycythemia: Excess RBCs, increasing blood viscosity; can be due to bone marrow cancer or induced (blood doping).

Leukocytes (White Blood Cells)

Leukocytes are the only complete cells in blood and are essential for immune defense.

• Account for less than 1% of blood volume (4,800–11,000 per μL).

• Function outside the bloodstream, defending against pathogens and cleaning up debris.

Types of Leukocytes

• Granulocytes: Contain visible granules; include neutrophils, eosinophils, and basophils.

• Agranulocytes: Lack visible granules; include lymphocytes and monocytes.

Type	Relative Percentage	Main Function
Neutrophils	50–70%	Phagocytosis of bacteria
Eosinophils	1–4%	Combat parasitic infections; modulate allergic responses
Basophils	0.1%	Release histamine and heparin; involved in inflammation
Lymphocytes	20–45%	Immune response; antibody production
Monocytes	4–8%	Phagocytosis; become macrophages in tissues

Leukopoiesis (Production of WBCs)

• Regulated by interleukins (IL-1, IL-2, etc.) and colony-stimulating factors (CSFs).

• Lymphoid stem cells produce lymphocytes; myeloid stem cells produce other WBCs.

Leukocyte Disorders

• Leukemia: Cancerous overproduction of abnormal WBCs.

• Leukopenia: Abnormally low WBC count.

• Mononucleosis: Viral disease (Epstein-Barr virus) with excess lymphocytes.

Platelets (Thrombocytes)

Platelets are cell fragments essential for blood clotting (hemostasis).

• Derived from megakaryocytes in bone marrow.

• Contain granules with enzymes, ADP, and platelet-derived growth factor (PDGF).

• Normal count: 150,000–400,000 per μL.

Hemostasis (Prevention of Blood Loss)

Hemostasis is the process that stops bleeding and involves three main steps:

1. Vascular Spasm: Vasoconstriction reduces blood flow.

2. Platelet Plug Formation: Platelets adhere to exposed collagen and release chemicals to attract more platelets.

3. Coagulation (Blood Clotting): Formation of a fibrin mesh that traps blood cells.

Coagulation Cascade:

• Intrinsic and extrinsic pathways lead to formation of prothrombin activator.

• Prothrombin activator converts prothrombin to thrombin.

• Thrombin converts fibrinogen to fibrin, forming the clot.

$\text{Prothrombin} \xrightarrow{\text{Prothrombin Activator}} \text{Thrombin}$ $\text{Fibrinogen} \xrightarrow{\text{Thrombin}} \text{Fibrin}$

Clot Retraction and Fibrinolysis

• Clot Retraction: Actin and myosin in platelets contract to stabilize the clot.

• Fibrinolysis: Plasminogen is converted to plasmin, which digests fibrin and dissolves the clot.

Hemostasis Disorders

• Thromboembolic Disorders: Formation of undesirable clots (thrombus, embolus).

• Bleeding Disorders: Thrombocytopenia (low platelets), impaired liver function, hemophilias (deficiency of clotting factors).

Blood Transfusion and Blood Groups

Blood Transfusion

• Transfusion of whole blood or packed RBCs restores oxygen-carrying capacity.

• Blood is often separated into components for targeted therapy.

• Isotonic saline may be used in emergencies if blood is unavailable.

Blood Groups and Typing

Blood groups are determined by the presence or absence of specific antigens on the surface of RBCs.

• ABO System:

  • Type A: A antigen, anti-B antibody

  • Type B: B antigen, anti-A antibody

  • Type AB: A and B antigens, no antibodies

  • Type O: No antigens, anti-A and anti-B antibodies

• Rh System: Rh+ has Rh antigen; Rh- does not.

Blood Group	Antigens Present	Antibodies Present
A	A	Anti-B
B	B	Anti-A
AB	A and B	None
O	None	Anti-A and Anti-B

Transfusion Reactions

• Occur when mismatched blood is transfused, leading to agglutination and hemolysis.

Blood Tests and Clinical Insights

• Complete Blood Count (CBC): Measures RBCs, WBCs, platelets, hemoglobin, and hematocrit.

• Comprehensive Metabolic Panel (CMP): Assesses metabolic and organ function.

• Prothrombin Time: Evaluates clotting ability.

Developmental Aspects of Blood

• Blood cell formation begins in the yolk sac, liver, and spleen during fetal development; bone marrow takes over by the seventh month.

• Fetal hemoglobin (HbF) has a higher affinity for oxygen than adult hemoglobin (HbA).

Additional info: The notes above expand on brief points and fill in missing context for clarity and completeness, including inferred details about blood cell formation, clinical tests, and the coagulation cascade.