BLOOD

• • Blood transports everything that must be carried from one place to another, such as:
  • Nutrients
  • Wastes
  • Hormones
  • Body heat
• The blood is composed of plasma (55%) and formed elements (45%). The formed elements are made up of red blood cells (RBC), white blood cells (WBC), and platelets.
• Physical Characteristics of the blood:

  • Sticky, opaque fluid
  • Heavier and thicker than water
  • Color range
  • xygen-rich blood is scarlet red
  • Oxygen-poor blood is dull red or purple
  • Metallic, salty taste
  • Blood pH is slightly alkaline, between 7.35 and 7.45
  • Blood temperature is slightly higher than body temperature, at 38ºC or 100.4ºF
• • Blood volume
  • About 5–6 liters, or about 6 quarts, of blood are found in a healthy adult
  • Blood makes up 8 percent of body weight
• Components of blood includes the following: A. Plasma B. Formed Elements b.1 Red Blood Cells b.2 White blood cells b.3 Platelet
• Plasma

  • 90 percent water
  • Straw-colored fluid
  • Includes many dissolved substances:
  • Nutrients
  • Salts (electrolytes)
  • Respiratory gases
  • Hormones
  • Plasma proteins
  • Waste products
• Plasma proteins: - Most abundant solutes in plasma - Most are made by the liver
• (Plasma Proteins) Albumin — an important blood buffer and contributes to osmotic
• (Plasma Proteins) Clotting proteins—help to stem blood loss when a blood vessel is injured
• (Plasma Proteins) Antibodies — help protect the body from pathogens
• Erythrocytes (Red Blood Cells or RBCs) - Main function is to carry oxygen
• • RBCs differ from other blood cells
  • Anucleate (no nucleus)
  • Contain few organelles; lack mitochondria
  • Essentially bags of hemoglobin (Hb)
  • Shaped like biconcave discs
• Normal count is 5 million RBCs per cubic millimeter (mm3 ) of blood
• • Hemoglobin is an iron-bearing protein
  • Binds oxygen
  • Each hemoglobin molecule can bind 4 oxygen molecules
  • Each erythrocyte has 250 million hemoglobin molecules
  • Normal blood contains 12–18 g of hemoglobin per 100 milliliters (ml) of blood
• Homeostatic imbalance of RBC

  - Anemia is a decrease in the oxygen-carrying ability of the blood due to:

  • Lower-than-normal number of RBCs
  • Abnormal or deficient hemoglobin content in the RBCs
  • Sickle cell anemia (SCA) results from abnormally shaped hemoglobin
• Polycythemia

  • Disorder resulting from excessive or abnormal increase of RBCs due to:
  • Bone marrow cancer (polycythemia vera)
  • Life at higher altitudes (secondary polycythemia)
• Increase in RBCs slows blood flow and increases blood viscosity
• Leukocytes (White Blood Cells or WBCs) - Crucial in body’s defense against disease - Complete cells, with nucleus and organelles - Able to move into and out of blood vessels (diapedesis) - Respond to chemicals released by damaged tissues (known as positive chemotaxis) - Move by amoeboid motion - 4,800 to 10,800 WBCs per mm3 of blood
• (Clinical Correlation)

  Leukocytosis - WBC count above 11,000 cells per mm3 of blood - Generally indicates an infection
• Leukopenia - Abnormally low WBC count - Commonly caused by certain drugs, such as corticosteroids and anticancer agents

  Leukemia - Bone marrow becomes cancerous - Numerous immature WBC are produced
• (Types of leukocytes) Granulocytes - Granules in their cytoplasm can be stained - Possess lobed nuclei - Include neutrophils, eosinophils, and basophils
• (Types of Leukocytes)

  Agranulocytes - Lack visible cytoplasmic granules - Nuclei are spherical, oval, or kidney-shaped - Include lymphocytes and monocytes
• (Types pf Granulocytes)

  Neutrophils

  • Most numerous WBC
  • Multilobed nucleus
  • Cytoplasm stains pink and contains fine granules
  • Function as phagocytes at active sites of infection
  • Numbers increase during infection
  • 3,000–7,000 neutrophils per mm3 of blood (40–70% of WBCs)
• (Types of Granulocytes)

  Eosnophils

  • Nucleus stains blue-red
  • Brick-red cytoplasmic granules
  • Function is to kill parasitic worms and play a role in allergy attacks
  • 100–400 eosinophils per mm3 of blood (1–4 percent of WBCs)
• (Types pf Granulocytes)

  Basophils - Rarest of the WBCs - Large histamine-containing granules that stain dark blue - Contain heparin (anticoagulant) - 20–50 basophils per mm3 of blood (0–1 percent of WBCs)
• (Types of Agranulocytes) Lymphocytes - Large, dark purple nucleus - Slightly larger than RBCs - Reside in lymphatic tissues - Play a role in immune response - 1,500–3,000 lymphocytes per mm3 of blood (20–45% of WBCs)
• (Types of Agranulocytes)

  Monocytes

  • Largest of the white blood cells
  • Distinctive U- or kidney-shaped nucleus
  • Function as macrophages when they migrate into tissues
  • Important in fighting chronic infection
  • 100–700 monocytes per mm3 of blood (4–8 percent of WBCs)
• Platelets

  • Fragments of megakaryocytes (multinucleate cells)
  • Needed for the clotting process
  • Normal platelet count is 300,000 platelets per mm3 of blood
• Hematopoiesis is the process of blood cell formation

  • Occurs in red bone marrow (myeloid tissue)
  • All blood cells are derived from a common stem cell (hemocytoblast)
• Hemocytoblasts form two types of descendants

  • Lymphoid stem cell, which produces lymphocytes
  • Myeloid stem cell, which can produce all other formed elements
• Since RBCs are anucleate, they are unable to divide, grow, or synthesize proteins

  • RBCs wear out in 100 to 120 days
  • When worn out, RBCs are eliminated by phagocytes in the spleen or liver
  • Lost cells are replaced by division of hemocytoblasts in the red bone marrow
• Formation of Red Blood Cells

  • Rate of RBC production is controlled by a hormone called erythropoietin
  • Kidneys produce most erythropoietin as a response to reduced oxygen levels in the blood
  • Homeostasis is maintained by negative feedback from blood oxygen levels
• Formation of White Blood Cells and Platelets

  • WBC and platelet production is controlled by hormones
  • Colony stimulating factors (CSFs) and interleukins prompt bone marrow to generate leukocytes
  • Thrombopoietin stimulates production of platelets from megakaryocytes
• Hemostasis is the process of stopping the bleeding that results from a break in a blood vessel

  • Blood usually clots within 3 to 6 minutes
  • The clot remains as endothelium regenerates
  • The clot is broken down after tissue repair
• Hemostasis involves three phases

  • Vascular spasms
  • Platelet plug formation
  • Coagulation (blood clotting)
• Step 1: Vascular Spasms

  • Immediate response to blood vessel injury
  • Vasoconstriction causes blood vessel to spasm
  • Spasms narrow the blood vessel, decreasing blood loss
• Step 2: Platelet Plug Formation

  • Collagen fibers are exposed by a break in a blood vessel
  • Platelets become “sticky” and cling to fibers
  • Anchored platelets release chemicals to attract more platelets
  • Platelets pile up to form a platelet plug (white thrombus)
• Step 3: Coagulation

  • Injured tissues release tissue factor (TF)
  • PF3 (a phospholipid) interacts with TF, blood protein clotting factors, and calcium ions to trigger a clotting cascade
  • Prothrombin activator converts prothrombin to thrombin (an enzyme)
  • Thrombin joins fibrinogen proteins into hairlike molecules of insoluble fibrin
  • Fibrin forms a meshwork (the basis for a clot)
  • Within the hour, serum is squeezed from the clot as it retracts
  • Serum is plasma minus clotting proteins
• (Disorders of Hemostasis) (7.4.2 Undesirable Clotting) 7.4.2.1 Thrombus

  • A clot in an unbroken blood vessel
  • Can be deadly in areas such as the lungs
• (7.4.1 Disorders of Hemostasis) (7.4.2 Undesirable Clotting)

  Embolus

  • A thrombus that breaks away and floats freely in the bloodstream
  • Can later clog vessels in critical areas such as the brain