Chapter 11: The Cardiovascular System – Blood

Ch 11-1 Blood: Functions and Characteristics

Blood is a specialized connective tissue that plays a vital role in maintaining homeostasis by transporting substances, regulating body functions, and protecting the body.

• Functions of Blood:

  • Transportation: Delivers oxygen, nutrients, hormones, and removes waste products (e.g., carbon dioxide, urea).

  • Regulation: Maintains pH, body temperature, and fluid balance.

  • Protection: Defends against pathogens (via white blood cells and antibodies) and prevents blood loss (via clotting mechanisms).

  • Homeostasis: Maintains internal environment stability.

  • Buffering: Helps regulate acid-base balance through plasma proteins and bicarbonate ions.

• Physical Characteristics of Blood:

  • Temperature: Blood temperature is approximately 38°C (100.4°F), slightly higher than body temperature.

  • Viscosity: Blood is about 5 times more viscous than water due to the presence of cells and plasma proteins.

  • pH: Blood pH is tightly regulated between 7.35 and 7.45, making it slightly alkaline.

Ch 11-2 Plasma

Plasma is the liquid component of blood, making up about 55% of total blood volume. It serves as the medium for transporting cells and dissolved substances.

• Components of Plasma:

  • Water: ~92% of plasma; acts as a solvent and helps regulate temperature.

  • Plasma Proteins: ~7% of plasma; includes albumins, globulins, and fibrinogen.

  • Other Solutes: ~1%; includes electrolytes, nutrients, gases, hormones, and waste products.

• Major Plasma Proteins and Their Functions:

  • Albumins: Maintain osmotic pressure and transport substances such as fatty acids and hormones.

  • Globulins: Include antibodies (immunoglobulins) for immune defense and transport globulins for carrying ions, hormones, and lipids.

  • Fibrinogen: Essential for blood clotting; converted to fibrin during coagulation.

Ch 11-3 Red Blood Cells (RBCs)

Red blood cells, or erythrocytes, are the most abundant blood cells and are specialized for oxygen transport.

• RBC Count: There are approximately 4.5–6 million RBCs per microliter (µl) of blood; a single drop of blood contains millions of RBCs.

• Unique Characteristics:

  • Biconcave shape increases surface area for gas exchange.

  • Lack nuclei and most organelles, maximizing space for hemoglobin.

  • Flexible membrane allows passage through narrow capillaries.

• Hemoglobin and Oxygen Binding: The iron ion (Fe2+) in the heme group of hemoglobin binds oxygen molecules.

• RBC Lifespan and Recycling: Old RBCs are removed by the spleen and liver; iron and amino acids are recycled, while heme is converted to bilirubin.

• Erythropoiesis (RBC Formation):

  • Occurs in red bone marrow.

  • Requires vitamin B12 for DNA synthesis.

  • Stimulated by the hormone erythropoietin (EPO), which is released by the kidneys in response to low oxygen levels (hypoxia).

Ch 11-4 ABO Blood System

The ABO blood system classifies blood based on the presence or absence of specific antigens on the surface of RBCs and corresponding antibodies in plasma.

• Antigen: A molecule (usually a protein or carbohydrate) found on the surface of RBCs that can trigger an immune response.

• Antibody: A protein found in plasma that binds to specific antigens and can cause agglutination (clumping) if incompatible blood types are mixed.

• Blood Type Antigens: A, B, and D (Rh factor) antigens determine blood type.

• Agglutination: The clumping of RBCs when antibodies bind to their specific antigens; occurs during incompatible blood transfusions.

• Cause of Agglutination: When a person receives blood with antigens that their plasma antibodies recognize as foreign, the antibodies bind to the antigens, causing clumping and potential blockage of blood vessels.

Ch 11-5 White Blood Cells (WBCs)

White blood cells, or leukocytes, are immune cells that protect the body against infection and foreign invaders.

• Comparison of WBCs and RBCs:

• Characteristics of WBCs:

  • Can migrate out of the bloodstream (diapedesis).

  • Capable of amoeboid movement.

  • Attracted to chemical stimuli (chemotaxis).

  • Some can perform phagocytosis (engulf pathogens).

• WBCs in Order of Abundance (Differential Count):

• WBC Production: Produced in red bone marrow and lymphatic tissues.

Ch 11-6 Platelets

Platelets, or thrombocytes, are small, cell fragment structures essential for blood clotting.

• Description: Platelets are fragments of megakaryocytes, lack nuclei, and circulate in large numbers (150,000–400,000 per µl of blood).

• Function: Initiate clotting by forming a platelet plug and releasing chemicals that promote coagulation.

Ch 11-7 Hemostasis

Hemostasis is the process that stops bleeding and maintains blood in a fluid state within the vascular system.

• Definition: The cessation of bleeding through a series of steps that form a stable blood clot.

• Three Phases of Hemostasis:

  1. Vascular Phase: Blood vessel constricts to reduce blood flow.

  2. Platelet Phase: Platelets adhere to the injury site and form a temporary plug.

  3. Coagulation Phase: Fibrinogen is converted to fibrin, forming a stable clot.

• Extrinsic vs. Intrinsic Pathways:

  • Extrinsic Pathway: Triggered by external trauma that causes blood to escape from the vessel; involves tissue factor.

  • Intrinsic Pathway: Initiated by damage to the blood vessel itself; involves clotting factors within the blood.

• Clot Removal: Once tissue is repaired, clots are dissolved by the process of fibrinolysis, primarily through the action of the enzyme plasmin.

Example: If a person with type A negative blood receives type B positive blood, their anti-B and anti-D antibodies will cause agglutination, leading to a dangerous transfusion reaction.

Additional info: The process of erythropoiesis is regulated by oxygen levels in the blood; low oxygen stimulates the kidneys to release erythropoietin, increasing RBC production. The ABO and Rh blood group systems are the most clinically significant for transfusions.