Blood

• Blood


  A connective tissue consisting of plasma and formed elements. It is the body's only fluid tissue, composed of liquid plasma and formed elements.
• Formed elements of blood

  • Erythrocytes (red blood cells)
  • Leukocytes (white blood cells)
  • Platelets
• Hematocrit


  The percentage of red blood cells out of the total blood volume
• Physical characteristics of blood

  • Denser and more viscous (thicker) than water and feels slightly sticky
  • Temperature: 38°C (100.4°F), about 1°C higher than oral or rectal body temperature
  • Slightly alkaline pH ranging from 7.35 to 7.45 (average = 7.4)
  • Color varies with oxygen content - bright red when saturated, dark red when unsaturated
  • Constitutes about 20% of extracellular fluid, amounting to 8% of the total body mass
  • Volume: 5 to 6 liters (1.5 gal) in an average-sized adult male, 4 to 5 liters (1.2 gal) in an average-sized adult female
• Plasma


  Pale yellow fluid containing over 100 solutes, mostly water (91%) and proteins (7%)
• Plasma proteins


  • Albumin (58% of plasma proteins)
  • Globulins (38% of plasma proteins)
  • Fibrinogen (4% of plasma proteins)
• Albumin


  Helps maintain osmotic pressure
• Globulins


  Involved in immunity (antibodies and complement) and transport (bind to molecules such as hormones)
• Fibrinogen


  Converted to fibrin during clot formation
• Other substances in plasma

  • Ions (electrolytes): sodium, potassium, calcium, chloride, bicarbonate
  • Nutrients: glucose, carbohydrates, amino acids
  • Waste products: lactic acid, urea, creatinine
  • Respiratory gases: oxygen and carbon dioxide
• Functions of plasma components

  • Water: Acts as a solvent and suspending medium for blood components
  • Proteins: Maintain osmotic pressure, destroy foreign substances, transport molecules, and form clots
  • Ions: Involved in osmotic pressure, membrane potentials, and acid-base balance
  • Nutrients: Source of energy and "building blocks" of more complex molecules
  • Gases: Involved in aerobic respiration
  • Waste products: Breakdown products of protein metabolism and red blood cells
  • Regulatory substances: Catalyze chemical reactions and stimulate or inhibit many body functions
• Hematopoiesis


  Blood cell production
• Hematopoiesis before and after birth

  1. Fetus: Liver, thymus, spleen, lymph nodes, and red bone marrow

  2. After birth: Red bone marrow of the axial skeleton and girdles, epiphyses of the humerus and femur
• Hemocytoblasts


  Stem cells that give rise to all formed elements of blood
• Erythropoiesis (red blood cell production)

  1. Hemocytoblast transforms into proerythroblast

  2. Proerythroblasts develop into early erythroblasts

  3. Ribosome synthesis in early erythroblasts

  4. Hemoglobin accumulation in intermediate and late erythroblasts

  5. Ejection of nucleus from late erythroblasts and formation of reticulocytes

  6. Reticulocytes released into circulating blood and become mature erythrocytes
• Erythrocytes (red blood cells)


  • About 95% of formed elements, have no nuclei or organelles, biconcave discs dedicated to respiratory gas transport, filled with hemoglobin
• Hemoglobin (Hb)


  Protein that functions in gas transport, consists of globin (two alpha and two beta chains) and heme groups (each with an iron atom that can bind one oxygen molecule)
• One red blood cell contains 250 million hemoglobin groups, thus it can carry 1 billion molecules of oxygen
• Carbon dioxide transport and exchange

  1. Carbon dioxide diffuses into red blood cells and combines with water to form carbonic acid, which dissociates into hydrogen ions and bicarbonate ions

  2. Carbonic anhydrase in red blood cells reversibly catalyzes the conversion of carbon dioxide and water to carbonic acid and bicarbonate
• Heme


  Molecules that transport oxygen (Iron is required)
• Oxygen content


  Determines blood color - Oxygenated: bright red, Deoxygenated: darker red
• Globin


  Molecules that transport carbon dioxide
• Oxygen transport


  • Bound to hemoglobin ~98.5%
  • Dissolved in plasma ~1.5%
• Each Hb molecule binds four oxygen atoms in a rapid and reversible process
• Carbon dioxide transport


  • Dissolved in plasma ~7%
  • Transported as bicarbonate(HCO3–) ~70%
  • Chemically bound to hemoglobin ~23%
• Erythrocyte (RBC)


  • Life span of 100–120 days
  • Old RBCs become rigid and fragile, and their Hb begins to degenerate
  • Dying RBCs are engulfed by macrophages located in the spleen or liver
• Hemoglobin breakdown


  1. Heme and globin are separated and the iron is salvaged for reuse

  2. Globin chains are broken down to individual amino acids and are metabolized or used to build new proteins

  3. Iron released from heme is transported to the red bone marrow and is used to produce new hemoglobin

  4. Heme becomes bilirubin that is secreted in bile

  5. In the intestines bilirubin is converted by bacteria into other pigments
• Gives feces its brown color and urine its yellow color
• Formed elements in blood

  • RBCs
  • WBCs
• WBCs


  • Are complete cells
  • Less numerous than RBCs
  • Make up 1% of the total blood volume
  • Can leave capillaries via ameboid movement and move through tissue spaces
• Functions of WBCs


  • Protect the body against invading microorganisms
  • Remove dead cells and debris from tissues by phagocytosis
• Types of WBCs


  • Granulocytes (neutrophils, eosinophils, basophils)
  • Agranulocytes (lymphocytes, monocytes)
• Granulocytes


  • Contain cytoplasmic granules that stain specifically (acidic, basic, or both) with Wright's stain
  • Are larger and usually shorter-lived than RBCs
  • Have lobed nuclei
  • Are all phagocytic cells
• Neutrophils


  • Most common type of WBC
  • Have two types of granules that take up both acidic and basic dyes, giving the cytoplasm a lilac color
  • Contain peroxidases, hydrolytic enzymes, and defensins (antibiotic-like proteins)
  • Are the body's bacteria slayers
• Basophils


  • Account for 0.5% of WBCs
  • Have large, purplish-black (basophilic) granules that contain histamine (inflammatory chemical) and heparin (prevents clot formation)
• Eosinophils


  • Account for 1–4% of WBCs
  • Have red-staining, bilobed nuclei connected via a broad band of nuclear material
  • Have red to crimson (acidophilic) large, coarse, lysosome-like granules
  • Lessen the severity of allergies by reducing inflammation
  • Lead the body's counterattack against parasitic worms
• Agranulocytes


  • Lymphocytes and monocytes
  • Lack visible cytoplasmic granules
  • Are similar structurally, but are functionally distinct and unrelated cell types
  • Have spherical (lymphocytes) or kidney shaped (monocytes) nuclei
• Lymphocytes


  • Account for 25% or more of WBCs
  • Have large, dark-purple, circular nuclei with a thin rim of blue cytoplasm
  • Are found mostly enmeshed in lymphoid tissue (some circulate in the blood)
  • There are two types: T cells and B cells
• B cells


  • Stimulated by bacteria or toxins
  • Give rise to plasma cells, which produce antibodies
• T cells


  • Protect against viruses and other intracellular microorganisms
  • Attack and destroy the cells that are infected