Comprehensive Study Guide on Blood Tissue, Plasma, and Formed Elements

General Characteristics of Blood

• Definition: Blood is the only fluid tissue in the human body.
• Proportion of Body Weight: In adults, blood accounts for $7-9\%$ of total body weight.
• Volume by Gender:
  • Male: Approximately $5-6\,L$.
  • Female: Approximately $4-5\,L$.
• Separation Process: When whole blood is withdrawn and placed in a tube to be centrifuged, it separates into two primary components:
  • Plasma ($55\%$): The liquid portion.
  • Formed Elements ($45\%$): The cellular portion.

Blood Plasma Composition and functions

• Water ($90\%$ of plasma): Acts as a solvent for carrying other substances and absorbs heat.
• Salts (Electrolytes):
  • Constituents: Sodium ($Na^+$), Potassium ($K^+$), Calcium ($Ca^{2+}$), Magnesium ($Mg^{2+}$), Chloride ($Cl^-$), and Bicarbonate ($HCO_3^-$).
  • Major Functions: Maintains osmotic balance, pH buffering, and regulation of membrane permeability.
• Plasma Proteins ($7\%$ of plasma volume):
  • Production: All plasma proteins are produced in the liver.
  • Albumin ($60\%$ of proteins): Regulates osmotic pressure of cells.
  • Globulins ($35\%$ of proteins):
    • Transport Globulins: Include hormone-binding proteins, metalloproteins, and steroid-binding proteins (alpha and beta types).
    • Gamma Globulins: Antibodies used for defense.
  • Fibrinogen ($4\%$ of proteins): Large molecules that form long, insoluble strands of fibrin to produce blood clots.
• Substances Transported by Blood:
  • Nutrients: Glucose, fatty acids, vitamins, and amino acids.
  • Metabolic Waste Products: Urea and uric acid.
  • Respiratory Gases: Oxygen ($O_2$) and carbon dioxide ($CO_2$).
  • Hormones: Various signaling molecules.

Plasma Nutrients and Gases

• Nutrients:
  • Amino Acids: Building blocks of proteins.
  • Monosaccharides: Sugars that are stored as glycogen in the liver or converted to fat.
  • Lipoproteins:
    • Chylomicrons: Responsible for carrying fat to muscle and adipose cells.
    • Very Low-Density Lipoprotein (VLDL): Transporting lipids.
    • Low-Density Lipoprotein (LDL): Often referred to as bad cholesterol.
    • High-Density Lipoprotein (HDL): Carries chylomicron remnants back to the liver and disposes of cholesterol by secreting it into bile.
• Gases:
  • Oxygen ($O_2$): Required for cellular respiration.
  • Carbon Dioxide ($CO_2$): A byproduct of cellular respiration.
  • Nitrogen ($N_2$): Presence is noted, but its biological use is currently unknown.

Formed Elements: Erythrocytes (Red Blood Cells)

• Prevalence: $4-6\text{ million}$ per $mm^3$ of blood; they comprise $99.9\%$ of the formed elements.
• Anatomy:
  • Salmon-colored biconcave disks.
  • Anucleate (lacking a nucleus).
  • Most organelles have been ejected; they are essentially "sacs of hemoglobin."
  • Size: Approximately $7-8.4\,\mu m$ in diameter and $2.31-2.85\,\mu m$ in thickness.
• Function: Transport oxygen bound to hemoglobin molecules and assist in the transport of small amounts of carbon dioxide.
• Hemoglobin ($Hgb$):
  • Male Levels: $14-16\,g/dL$.
  • Female Levels: $12-14\,g/dL$.
  • Each RBC contains approximately $250\text{ million}$ hemoglobin molecules.
  • Hemoglobin F ($Hgb\ F$): The specific form found in newborns.
• Lifespan: Approximately $100-120\text{ days}$.
• Related Conditions:
  • Anemia: Condition of reduced oxygen-carrying capacity.
  • Hemophilia: Genetic bleeding disorder.
  • Sickle Cell Anemia ($Hgb\ S$): Caused by a single Valine substitution in the hemoglobin chain, resulting in sickled RBC shapes.

Erythrocyte Life Cycle and Phagocytosis

• Elimination: Worn-out RBCs are eliminated by phagocytes (macrophages) in the spleen, liver, or red bone marrow.
• Breakdown Process:
  1. Globin: Broken down into amino acids and reused for protein synthesis.
  2. Heme: Broken down into iron ($Fe^{3+}$) and biliverdin.
  3. Iron Recycling: $Fe^{3+}$ binds to Transferrin in the blood. It is transported to the liver and stored as Ferritin, or sent to the red bone marrow for Erythropoiesis.
  4. Pigment Conversion: Biliverdin is converted to Bilirubin. Bilirubin is secreted into bile and enters the small intestine.
  5. Excretion: Bacteria in the large intestine convert bilirubin into Urobilinogen. Some is excreted as Urobilin in urine (via kidneys), while the rest is converted to Stercobilin and excreted in feces.

Control of Erythrocyte Production

• Mechanism: Negative feedback loop maintained by the hormone Erythropoietin.
• Stimulus: Reduced oxygen levels in the blood ($O_2$ deficiency), decreased RBC count, or increased tissue demands for oxygen.
• Organ Response: The kidneys (specifically peritubular capillaries) release erythropoietin.
• Target: Erythropoietin stimulates the Red Bone Marrow to enhance erythropoiesis (RBC production).
• Outcome: Increased RBC count raises the oxygen-carrying ability of the blood, restoring normal oxygen levels.

Blood Typing and Hemolytic Disease

• ABO Blood Groups: Determined by the presence or absence of carbohydrate antigens on the surface of the RBC.
  • Type A: Has A antigens and Anti-B antibodies.
  • Type B: Has B antigens and Anti-A antibodies.
  • Type AB: Has both A and B antigens and neither antibody (Universal recipient for cells).
  • Type O: Has neither A nor B antigens and both Anti-A and Anti-B antibodies (Universal donor for cells).
• Rh Blood Group:
  • Rh+: RBCs possess the Rh antigen.
  • Rh-: RBCs lack the Rh antigen.
  • Under normal conditions, plasma does not contain Anti-Rh antibodies.
• Hemolytic Disease of the Newborn (HDN): Occurs if an Rh- mother is pregnant with an Rh+ fetus. If fetal blood contacts the mother during birth, she develops Anti-Rh antibodies. This affects the second Rh+ baby as the antibodies can cross the placenta.

Leukocytes (White Blood Cells)

• Standard Count: $4,000-11,000\text{ cells/mm}^3$.
• Function: Crucial for body defense against disease.
• Diapedesis: The ability of WBCs to move into and out of blood vessels to reach infected tissues.
• Abnormal Levels:
  • Leukocytosis: WBC count over $10,000\text{ cells/mm}^3$ (e.g., appendicitis).
  • Leukopenia: WBC count less than $5,000\text{ cells/mm}^3$ (e.g., typhoid fever, flu, measles, AIDS).
  • Leukemia: Abnormal, excessive production of immature leukocytes.

Types of Leukocytes: Granulocytes

• Characteristics: Contain specialized granules (specific and azurophilic) and lobed nuclei.
• Neutrophils ($60-70\%$ of WBCs):
  • Stains pale pink; nucleus has $3-7$ lobes.
  • Barr Body: An inactive X chromosome found in neutrophils of females.
  • Function: Active phagocytes for acute or short-term infections.
• Eosinophils ($2-4\%$ of WBCs):
  • Also called acidophils; stain deep red with a figure-8 or bilobed nucleus.
  • Function: Kill parasitic worms and increase during allergy attacks. They release enzymes to counteract inflammatory effects of neutrophils/mast cells.
• Basophils ($< 1\%$ of WBCs):
  • Stain deep blue; U- or S-shaped nucleus.
  • Function: Release Histamine (a vasodilator for inflammation) and Heparin (an anticoagulant).

Types of Leukocytes: Agranulocytes

• Characteristics: Lack visible cytoplasmic granules (though azurophilic granules are present but do not stain) and have spherical or kidney-shaped nuclei.
• Lymphocytes ($20-25\%$ of WBCs):
  • Smallest WBC; large dark purple nucleus with a thin rim of blue cytoplasm.
  • Function: Part of the immune system. Includes B Lymphocytes (produce antibodies) and T Lymphocytes (fight tumors/viruses and graft rejection).
  • They are capable of mitosis and can re-enter circulation.
• Monocytes ($2-8\%$ of WBCs):
  • Largest WBC; abundant gray-blue cytoplasm with a kidney-shaped nucleus.
  • Function: Become Macrophages in tissues for long-term "clean-up." Increased numbers are seen in chronic infections like tuberculosis, typhoid fever, and malaria.

Platelets (Thrombocytes)

• Origin: Derived from fragments of large multinucleated cells called Megakaryocytes.
• Counts:
  • Normal Range: $150,000-400,000\,mm^3$ (or $130,000-360,000\,\mu L$).
• Function: Essential for blood clotting; they initiate the clotting cascade by clinging to broken vessel areas.
• Lifespan: Circulate for $9-12\text{ days}$.
• Clinical terms:
  • Thrombocytopenia: Abnormally low platelet count.
  • Thrombocytosis: Abnormally high platelet count.