Blood and Cardiovascular System

Blood and the Cardiovascular System

Overview of Blood

• Connective Tissue: Blood is classified as a specialized connective tissue that plays a crucial role in transporting nutrients, gases, and waste products throughout the body.

• Volume: The average adult human has approximately 5 liters of blood, which constitutes about 7-8% of total body weight.

• Components:

  • Plasma: Makes up about 55% of blood volume; consists of 90% water, electrolytes (like sodium and potassium), nutrients (such as glucose and amino acids), hormones (including insulin and cortisol), and plasma proteins (including albumin, fibrinogen, and globulins).

  • Formed elements:

  • Erythrocytes (Red Blood Cells): Approx. 45% of blood volume; contain hemoglobin which allows for oxygen transport.

  • Leukocytes (White Blood Cells): Less than 1% of blood volume (the buffy coat); crucial for immune response.

  • Platelets: Also part of the buffy coat; play a vital role in clotting.

Red Blood Cells (Erythrocytes)

• Structure: Biconcave discs that increase surface area for oxygen and carbon dioxide exchange, contributing to their efficiency in gas transport.

• Formation: Generated in the bone marrow through a process called erythropoiesis; requires Vitamin B12 and folic acid for proper DNA synthesis during cell division.

• Hemoglobin: Comprises about one-third of the cell's volume; it binds to oxygen in the lungs and releases it in tissues, as well as binding to carbon dioxide from the tissues back to the lungs.

• Types:

  • Oxyhemoglobin: Hemoglobin saturated with oxygen, typically of a bright red color.

  • Deoxyhemoglobin: Hemoglobin lacking oxygen, typically darker in color.

• Lifespan: RBCs have a lifespan of approximately 120 days, after which they are recycled by macrophages primarily in the liver and spleen.

• Regulation: The hormone erythropoietin, produced by the kidneys, regulates RBC production; normal counts are 4.6-6.2 million/mm³ in males and 4.2-5.4 million/mm³ in females.

White Blood Cells (Leukocytes)

• Types:

  • Granulocytes:

  • Neutrophils: Most abundant WBCs and first responders to infection; participate in phagocytosis to eliminate pathogens.

  • Eosinophils: Important in combating parasites and modulating allergic inflammatory responses.

  • Basophils: Release histamine and heparin; involved in allergic reactions and inflammatory processes.

  • Agranulocytes:

  • Monocytes: The largest type of WBC; differentiate into macrophages and dendritic cells that help in antigen presentation and phagocytosis.

  • Lymphocytes: Key components in the immune response; includes B cells (which produce antibodies) and T cells (which destroy virus-infected and tumor cells).

• Development: Leukocytes arise from multipotent stem cells in the bone marrow and differentiate into various types through several progenitor stages influenced by growth factors.

Platelets (Thrombocytes)

• Source: Derived from large bone marrow cells known as megakaryocytes, which fragment to release platelets into circulation.

• Function: Essential for maintaining hemostasis; they adhere to sites of vascular injury, forming a temporary platelet plug and releasing chemicals to activate coagulation pathways and recruit more platelets.

• Hemostasis Phases:

  1. Vasospasm: Initial contraction of the damaged blood vessel to reduce blood flow.

  2. Platelet Plug Formation: Platelets adhere to the exposed collagen fibers at the injury site and become activated, resulting in aggregation.

  3. Coagulation: Involves the activation of clotting factors leading to the transformation of fibrinogen into fibrin, resulting in a stable clot formation.

Blood Clotting Mechanism

• Intrinsic and Extrinsic Pathways: Activation of the clotting cascade in response to vessel injury involves the intrinsic pathway (activated by collagen exposure) and the extrinsic pathway (triggered by tissue factor from damaged tissues). Both converge at the common pathway to produce fibrin.

• Fibrinolysis: The process of breaking down clots after healing occurs, primarily through the action of plasmin, which dissolves fibrin.

Blood Types

• ABO System:

  • Type A: Has A antigens on the RBC surface and anti-B antibodies in the plasma.

  • Type B: Contains B antigens and anti-A antibodies.

  • Type AB: Universal recipient; has both A and B antigens, with no antibodies against A or B.

  • Type O: Universal donor; has no antigens but anti-A and anti-B antibodies.

• Rh Factor: Determines positive or negative blood types based on the presence (positive) or absence (negative) of antigen D on RBCs, important in transfusions and pregnancy.

Disorders of the Circulatory System

• Common disorders include heart disease, stroke, hypertension, and atherosclerosis, all of which can lead to severe health complications.

• Cholesterol Types:

  • LDL (Low-Density Lipoprotein): Often referred to as "bad" cholesterol; can deposit in arterial walls, contributing to plaque formation and increased cardiovascular risk.

  • HDL (High-Density Lipoprotein): Known as "good" cholesterol; helps to clear cholesterol from the bloodstream, providing protective cardiovascular effects.

Heart Anatomy and Function

• Chambers: The heart consists of four chambers: right atrium and ventricle handle deoxygenated blood, while the left atrium and ventricle handle oxygenated blood. Each chamber has distinct functions and blood flow pathways.

• Valves: Four main valves (tricuspid, pulmonary, mitral, and aortic) ensure unidirectional blood flow and prevent backflow during heart contractions.

• Conduction System:

  • Sinoatrial (SA) Node: Acts as the natural pacemaker of the heart, initiating electrical impulses that cause heart beats.

  • Atrioventricular (AV) Node: Delays electrical signals to ensure coordinated contraction of the atria and ventricles.

  • Purkinje fibers: Spread the impulse throughout the ventricles, causing contraction and efficient blood ejection.

Regulation of Heart Activity

• Nervous System Influence:

  • Parasympathetic Activity: Primarily via the vagus nerve, it decreases heart rate and promotes calm states.

  • Sympathetic Activity: Increases heart rate and force of contraction during stress or physical activity.

• Hormonal Regulation: Involves chemicals such as norepinephrine and epinephrine, which modulate heart rate and contractility in response to physical demands.

• Factors Affecting Heart Rate:

  • Temperature variations can influence heart rate; warmer conditions may increase heart rate.

  • Electrolytes: An excess of calcium can lead to an increased heart rate and contraction strength.

Blood Vessel Structure

• Components of Blood Vessels:

  • Tunica Interna: Inner layer composed of endothelial cells that provide a smooth surface to minimize turbulence.

  • Tunica Media: Middle layer containing smooth muscle and elastic fibers, regulating vessel diameter and blood pressure.

  • Tunica Externa: Outermost layer comprised of connective tissue, providing structural support and protection.

• Blood Pressure: Typically measured as systolic over diastolic (normal being 120/80 mmHg); influenced by factors such as blood volume, cardiac output, and peripheral resistance.