Human Anatomy & Physiology: Chapter 12 - Blood

12.1: Introduction to the Blood

  • Definition of Blood: A type of connective tissue with a fluid matrix known as plasma.
  • Components of Circulatory System: Composed of blood, heart, and blood vessels.
  • Functions of Blood:
    • Transport: Transports substances throughout the body, such as:
    • Nutrients from the digestive tract to body cells.
    • Oxygen from the lungs to body cells and carbon dioxide from cells to the lungs.
    • Hormones from endocrine glands to target organs.
    • Metabolic wastes (e.g., urea, uric acid) from cells to kidneys for excretion.
    • Regulation:
    • Helps maintain fluid and electrolyte balance.
    • Regulates body temperature by absorbing and distributing heat.
    • Maintains normal pH in body tissues by acting as a buffer system.
    • Protection:
    • Prevents blood loss by initiating clotting mechanisms.
    • Prevents infection through white blood cells, antibodies, and complement proteins.
  • Formed Elements of Blood:
    • Comprised of:
    • Red blood cells (RBCs): Primarily responsible for carrying oxygen from the lungs to the body tissues and carbon dioxide from the tissues back to the lungs.
    • White blood cells (WBCs): Crucial components of the immune system, defending the body against pathogens, foreign invaders, and abnormal cells.
    • Platelets (thrombocytes): Small, irregular-shaped cell fragments essential for hemostasis, forming plugs to seal breaks in blood vessels and participating in blood clotting.
    • These cellular components are produced in the red bone marrow through a process called hematopoiesis.

Blood Volume and Composition

  • Plasma Composition: A mixture of water, amino acids, proteins, carbohydrates, lipids, vitamins, hormones, electrolytes, and cellular wastes.
  • Normal Blood pH: Ranges from pH 7.35 to 7.45.
  • Hematocrit (HCT): Percentage of formed elements in blood, normally around 45% (mainly red blood cells).
  • Plasma constitutes 55% of blood volume.
  • White blood cells and platelets are less than 1% of blood volume.
  • Average Blood Volume: Approximately 5.3 quarts (5 liters) in an average-sized adult.

12.2: Formed Elements

Red Blood Cells (Erythrocytes, RBCs)
  • Shape and Structure: Biconcave disks that provide flexibility and increased surface area for gas exchange.
  • Development:
    • RBCs discard their nuclei and organelles during development, preventing reproduction and protein production.
  • Hemoglobin Composition:
    • RBCs consist of one-third hemoglobin, responsible for oxygen transport.
    • Oxyhemoglobin (oxygen-bound hemoglobin) gives blood a bright red color; deoxyhemoglobin (oxygen released) appears darker.
  • Energy Production: RBCs produce ATP through glycolysis and lack mitochondria, meaning they do not utilize the oxygen they transport.
Red Blood Cell Counts
  • Normal Counts:
    • Adult Males: 4,700,000 to 6,100,000 cells/microliter (\muL).
    • Adult Females: 4,200,000 to 5,400,000 cells/\muL.
  • Health Implications: The number of RBCs influences the blood's oxygen-carrying capacity and overall health.
Red Blood Cell Production and Its Control
  • Erythropoiesis: The process of red blood cell production.
    • In embryos and fetuses, occurs in yolk sac, liver, and spleen; after birth, occurs in red bone marrow (hematopoiesis).
  • Origin: Produced from hematopoietic stem cells (hemocytoblasts), undergoing several stages before maturation.
  • Lifespan of RBCs: Approximately 120 days.
  • Regulation: Constant RBC levels maintained by a negative feedback mechanism involving erythropoietin released by kidneys and liver in response to low oxygen levels.
  • Polycythemia: Condition with an excessive increase in RBCs, leading to viscous, slow-moving blood and oxygen deficiency.
Dietary Factors Affecting RBC Production
  • Nutritional Requirements:
    • Vitamins and folic acid for DNA synthesis, crucial for cell reproduction in hematopoietic tissues.
    • Iron for hemoglobin synthesis, primarily sourced from recycling old RBCs.
  • Anemia: A deficiency in RBCs or hemoglobin reduces blood's oxygen-carrying capacity.
Types of Anemia
  • Hemorrhagic Anemia: Due to blood loss (hemorrhage).
  • Hemolytic Anemia: Caused by destruction of RBCs due to infections or transfusion incompatibility.
  • Pernicious Anemia: Due to vitamin B12 absorption failure due to lack of intrinsic factor.
  • Aplastic Anemia: Resulting from destruction of bone marrow.
  • Iron-Deficiency Anemia: Caused by insufficient iron intake or chronic blood loss.
  • Sickle Cell Anemia: A genetic disorder causing abnormal hemoglobin structure.
Breakdown of Red Blood Cells
  • RBC Aging: RBCs become fragile, often damaged in narrow capillaries.
  • Phagocytosis: Damaged RBCs are engulfed by macrophages in the liver and spleen.
  • Hemoglobin Breakdown:
    • Components of hemoglobin decompose into heme and globin.
    • Heme is converted into iron (stored or recycled) and biliverdin (converted to bilirubin, excreted in bile).
    • Globin is broken down into amino acids for reuse.
Life Cycle of a Red Blood Cell
  1. Nutrients absorbed by the intestine.
  2. Blood transports absorbed nutrients.
  3. Nutrients and erythropoietin foster RBC production in red bone marrow.
  4. RBCs circulate for about 120 days.
  5. Macrophages break down old RBCs in the liver and spleen.
  6. Hemoglobin decomposed into globin and heme.
  7. Iron is either stored or recycled for new RBCs; pigments converted to biliverdin and bilirubin, expelled as urine.

12.3: Plasma

  • Definition: Clear, straw-colored liquid part of blood where cells and platelets are suspended.
  • Composition: Primarily water (92%) with various dissolved substances.
  • Functions of Plasma:
    • Transports nutrients and gases.
    • Regulates fluid and electrolyte balance.
    • Maintains optimal pH.
Plasma Proteins
  • Categories: 3 main groups of plasma proteins.
  1. Albumins (60% of total plasma proteins): Synthesized in the liver; help maintain colloid osmotic pressure.
  2. Globulins (36% of total plasma proteins):
    • Alpha and beta globulins (from liver): transport lipids and fat-soluble vitamins.
    • Gamma globulins (from lymphatic tissues): constitute antibodies for immunity.
  3. Fibrinogen (4% of total plasma proteins): Key role in blood coagulation, also produced in the liver.
Gases and Nutrients in Plasma
  • Blood Gases: Primarily oxygen and carbon dioxide.
  • Nutrients in Plasma:
    • Include amino acids, simple sugars, nucleotides, lipids, vitamins, and minerals from digestive absorption.
  • Glucose Utilization: Can be converted to glycogen or fat in the liver or used for energy.
  • Transport of Lipids: Lipids bind to proteins due to their insolubility in plasma water.
Nonprotein Nitrogenous Substances
  • Nature: Compounds containing nitrogen not classified as proteins.
  • Examples: Amino acids, urea, uric acid, creatine, creatinine.
  • Source: Products of metabolism (dietary) or breakdown of proteins and nucleic acids.
Plasma Electrolytes
  • Substances: Include sodium, potassium, calcium, magnesium, chloride, bicarbonate, phosphate, and sulfate ions.
  • Key Roles: Vital for maintaining osmotic pressure and pH balance in plasma.

12.4: Hemostasis

  • Definition: The process of stopping bleeding after blood vessel injury.
  • Mechanisms of Hemostasis:
  1. Vascular Spasm (Vasospasm): Contraction of blood vessel muscles upon injury, lasting approximately 30 minutes.
  2. Platelet Plug Formation: Platelets adhere to damaged areas and each other, forming a plug.
  3. Blood Coagulation: A series of reactions leading to blood clot formation, essential for effectively stopping bleeding.
Vascular Spasm
  • Process: Immediate response to vessel injury causing temporary constriction of the vessel to reduce blood loss.
  • Serotonin Release: Platelets release serotonin to maintain vasoconstriction.
Platelet Plug Formation
  • Adhesion: Platelets adhere to rough tissues exposed within damaged blood vessels, sticking together to form a network, particularly effective in small vessels.
Blood Coagulation
  • Process:
    • Involves the release of tissue thromboplastin by damaged tissues, initiating a cascade of clotting factors.
    • Lead to the conversion of prothrombin to thrombin, which then converts fibrinogen to fibrin, a protein that forms a network to trap blood cells.
  • Positive Feedback Mechanism: Enhances clotting response based on the extent of tissue damage.
Clot Dissolution and Abnormal Clot Formation
  • Fibrinolysis: The process of clot dissolution post-repair.
  • Thrombus Formation: Abnormal clot solidifying in a vessel can be perilous, leading to conditions like coronary thrombosis or pulmonary embolism.

12.5: Blood Groups and Transfusions

  • Historical Context: Understanding blood groups is crucial for successful transfusions and compatibility.
  • Blood Compatibility Testing includes:
    • ABO Blood Type Testing: Assesses presence or absence of A and B antigens.
    • Rh Factor Testing: Ensures compatibility regarding Rh antigens.
    • Cross-Matching: Involves mixing donor RBCs with recipient serum to check for agglutination.
Antigens and Antibodies
  • Definition:
    • Antigen: A substance that triggers immune response.
    • Antibody: A protein produced to combat specific antigens.
  • Transfusion Reaction: Occurs when antibodies in the recipient react against incompatible antigens, causing agglutination, and can lead to severe consequences.
ABO Blood Groups
  • Classification: Based on presence or absence of antigens A and B on RBCs.
  • Types of Blood:
    • A: A antigens with anti-B antibodies.
    • B: B antigens with anti-A antibodies.
    • AB: Both A and B antigens; universal recipient, no antibodies.
    • O: No antigens; universal donor, possesses both antibodies.
Universal Donor and Recipient
  • Universal Recipient: Type AB can receive RBCs from any blood type (no anti-A or anti-B antibodies).
  • Universal Donor: Type O can be transfused to any type without causing agglutination.
Rh Blood Group
  • Identification: Rh system includes multiple antigens; most prevalent is Antigen D.
    • Rh-positive: Presence of D antigen.
    • Rh-negative: Absence of D antigen; can develop antibodies if exposed to Rh-positive blood.
  • Erythroblastosis Fetalis: Condition resulting from Rh incompatibility during pregnancy, preventable with RhoGAM administration.