Human Physiology - Cardiovascular System and Blood

Chapters Overview

  • The content covers the following chapters in Human Physiology:

    • Cardiovascular System

    • Blood

    • Endocrine System

The Cardiovascular System Overview

  • Components:

    • Blood

    • Heart

    • Blood vessels

  • Functionality:

    • Cells cannot move to acquire oxygen, nutrients, or eliminate carbon dioxide and wastes; these functions are performed by blood and interstitial fluid.

    • Blood: A liquid connective tissue comprising cells suspended in a liquid extracellular matrix (blood plasma).

    • Interstitial Fluid: Fluid that bathes body cells, renewed continuously by blood.

  • Transport Mechanism:

    • Oxygen (O2) transported from lungs to cells; nutrients from digestive tract to cells through diffusion from blood to interstitial fluid to body cells.

    • Carbon dioxide (CO2) and wastes travel from cells to interstitial fluid and then to blood for elimination through lungs, kidneys, and skin.

Waste Excretion via Four Major Body Systems

  • Urinary System:

    • Removes nitrogenous wastes, excess salts, and water via kidneys.

  • Respiratory System:

    • Excretes carbon dioxide and water vapor through lungs.

  • Digestive System:

    • Eliminates undigested food, bacteria, and metabolic byproducts such as bilirubin through feces; does not excrete nitrogenous wastes.

  • Integumentary System:

    • Excretes water, salts, and small amounts of urea through sweat glands.

  • Lymphatic System:

    • Returns interstitial fluid to the bloodstream as lymph, thus maintaining fluid balance and preventing edema.

Functions of Blood

  • Categorized Functions:

    • Transportation:

      • Delivers oxygen from lungs to cells.

      • Exchanges carbon dioxide from cells to lungs.

      • Transports nutrients and hormones to cells and nitrogenous wastes to be excreted from the body, particularly through the kidneys.

    • Regulation:

      • Maintaining homeostasis of body fluids.

      • Blood maintains pH using buffer systems (bicarbonate, proteins, hemoglobin).

      • Regulation of body temperature through heat absorption and blood flow adjustments to the skin; vasodilation for heat loss and vasoconstriction for heat preservation.

      • Regulation of interstitial fluid concentration by adjusting fluid movement across capillaries.

    • Protection:

      • Ability to clot and prevent excessive blood loss upon injury.

      • Leukocytes (white blood cells): protection against disease and infections through phagocytosis and immunological responses (innate and adaptive immunity).

      • Proteins like antibodies and complement play roles in enhancing pathogen destruction.

Components of Blood

  • Whole Blood Composition:

    • Blood Plasma: A liquid matrix containing dissolved substances.

    • Formed Elements: Cells and cell fragments:

      • Red Blood Cells (RBCs): Carry oxygen and carbon dioxide.

      • White Blood Cells (WBCs): Immune function.

      • Platelets: Fragments critical for hemostasis.

Blood Composition Details

  • Centrifugation separates blood into:

    • Plasma: Forms the upper layer (55% of blood volume).

    • Formed Elements: 45% of blood volume, with RBCs making up over 99%, while WBCs and platelets account for less than 1% and form a buffy coat in between.

  • The Hematocrit: Percentage of total blood volume composed of RBCs; normal ranges:

    • Males: 40% to 54%

    • Females: 38% to 46%

Blood Plasma Composition

  • Composition:

    • 91.5% water, 8.5% solutes (7% proteins by weight).

  • Main Plasma Proteins:

    • Albumins: 54% (regulates colloid osmotic pressure).

    • Globulins: 38% (transport hormones and fight infections).

    • Fibrinogen: 7% (converts to fibrin during clotting).

  • Electrolytes: Sodium (Na⁺), Chloride (Cl⁻), Bicarbonate (HCO₃⁻) are crucial for maintaining balance, excitability, and acid-base homeostasis.

  • Metabolic Waste Products: Urea, uric acid, creatinine, ammonia, and bilirubin.

Blood Formed Elements Overview

  • Red Blood Cells (Erythrocytes):

    • Specialized for transport of O2 and CO2.

    • Contain hemoglobin, lack nuclei, and have a biconcave shape to enhance surface area for gas exchange.

  • White Blood Cells (Leukocytes):

    • Five major types (detailed on the following pages).

  • Platelets (Thrombocytes):

    • Anucleate fragments from megakaryocytes; essential for hemostasis by forming plugs at injury sites.

Hematocrit Explanation

  • Definition: Clinical measurement reflecting the volume percentage of RBCs in blood. Abnormal levels can indicate dehydration or conditions like anemia and polycythemia.

  • Values: Average is approximately 45% for a healthy adult.

Erythropoiesis Overview

  • Definition: The process of RBC formation in red bone marrow, beginning from pluripotent hematopoietic stem cells.

    • Divides into stages involving proerythroblasts and reticulocytes.

  • Stimuli for Increased Erythropoiesis: Hypoxia, hemorrhage, or iron deficiency.

Negative Feedback Regulation of Erythropoiesis

  • Oxygen Supply Feedback Mechanism:

    • Hypoxia recognized by kidneys → Increased EPO → Enhanced RBC production → Restoration of oxygen delivery.

  • EPO Role: Critical hormone produced from kidneys under low oxygen conditions, stimulating RBC production.

Required Components for Erythropoiesis

  • Essential: Iron ions, globin proteins, vitamin B₁₂, folate, and EPO. Deficiencies can lead to anemia or excessive RBC production (polycythemia).

Structure of Hemoglobin

  • Composition: 4 polypeptide chains with heme groups (Fe²⁺) that bind oxygen.

  • Functionality: Higher oxygen affinity variants (e.g., fetal hemoglobin).

Gas Exchange Functions of Blood

  • Oxygen Transport: 98.5% bound to hemoglobin and 1.5% dissolved in plasma.

  • Carbon Dioxide Transport: 70% as bicarbonate (HCO₃⁻), 23% as carbaminohemoglobin, and 7% dissolved.

White Blood Cells (Leukocytes) Overview

  • General Functions: Protect against pathogens with a normal count of 5,000-10,000 cells/µL. They lack hemoglobin but contain nuclei.

  • Types: Granulocytes (neutrophils, eosinophils, basophils) and agranulocytes (lymphocytes and monocytes).

Importance of WBC Dynamics

  • Movement to Sites of Infection: Emigration (diapedesis) through capillary walls, following chemotactic signals.

Hemostasis Overview

  • Definition: Sequence of responses to stop bleeding following vessel injury.

Hemostasis Mechanisms

  1. Vascular Spasm: Immediate vessel constriction, following injury; reduces blood flow.

  2. Platelet Plug Formation: Adhesion and activation of platelets to form a plug.

  3. Coagulation: Enzymatic cascade converting fibrinogen to fibrin, stabilizing the plug.

Platelet Plug Formation Steps

  • Step 1: Adhesion to exposed collagen.

  • Step 2: Activation releases mediators (e.g., ADP, TXA₂).

  • Step 3: Aggregation to seal breaks.

Coagulation Process Overview

  • Clotting Cascade: Transforming blood into a gel-like scaffold; fibrin threads stabilize the aggregate.

Clotting Pathways

  • Extrinsic Pathway: Quick response to external damage.

  • Intrinsic Pathway: Internal damage causing a slower response with a cascade of clotting factors.

Common Pathway in Coagulation

  • Activation of prothrombinase converts prothrombin to thrombin, converting fibrinogen to fibrin, completing the clotting process.

ABO and Rh Blood Group Systems

  • Blood Group Systems: Involvement of antigens and corresponding antibodies (agglutinins).

  • Significance of Antigens: Critical for blood transfusion safety; mismatched transfusions can lead to severe reactions.

Importance of Blood Compatibility Testing and Procedures

  • Types of Tests: Blood typing for ABO and Rh among others; positive agglutination indicates the presence of specific antigens.

  • Clinical Relevance: Necessary for safe transfusion and intervention in emergencies or surgeries.

Conclusion

  • Every aspect of blood functions, from transport to homeostasis, plays a critical role in maintaining overall physiological balance in the human body.