Blood Composition and Function

• Blood is a connective tissue comprised of plasma (55%) and formed elements(45%).
• Plasma is the liquid component, constituting 90% water and contains proteins, salts, nutrients, gases, wastes, and hormones.
• The liver produces plasma proteins.
• Erythrocytes, leukocytes, and platelets are the 3 types of formed elements

Plasma Composition (55%)

• Water: Serves as a solvent for transporting substances.
• Ions: Includes sodium, potassium, calcium, magnesium, chloride, and bicarbonate. Plays a role in osmotic balance, pH buffering and regulation of membrane permeability.
• Plasma Proteins: Includes albumin for osmotic balance and pH buffering; fibrinogen is for clotting; immunoglobulins (antibodies) are for defense.
• Substances Transported by Blood: Includes nutrients like glucose, fatty acids, and vitamins, waste products of metabolism, respiratory gases (O₂ and CO₂), and hormones.

Cellular Elements Composition (45%)

• Erythrocytes: 5-6 million per mm3 of blood; involved in transporting oxygen and carbon dioxide.
• Leukocytes: 5,000-10,000 per mm3 in blood; involved in defense and immunity.
• Platelets: 250,000-400,000 per mm3 of blood; for blood clotting.

Formed Elements Detail

• Erythrocytes (Red Blood Cells)
  • Description: Biconcave, anucleate disc, salmon-colored; diameter 7-8 µm.
  • Count: 4-6 million per mm3 of blood
  • Development and Lifespan: 5-9 days development, 100-120 days lifespan
  • Function: Transports oxygen and carbon dioxide.
• Leukocytes (White Blood Cells)
  • Description: Spherical, nucleated cells.
  • Count: 4800-11,000 per mm3 of blood
  • Granulocytes: Neutrophils, Eosinophils, Basophils.
  • Agranulocytes: Lymphocytes, Monocytes.

Granulocytes

• Neutrophils
  • Description: Nucleus multi-lobed; inconspicuous cytoplasmic granules; diameter 12-14 µm.
  • Count: 3000-7000 per mm3 of blood.
  • Development and Lifespan: 7-11 days, 6 hours to a few days.
  • Function: Destroys bacteria by phagocytosis.
• Eosinophils
  • Description: Nucleus bilobed; red cytoplasmic granules; diameter 12-15 µm.
  • Count: 100-400 per mm3 of blood.
  • Development and Lifespan: 7-11 days, about 5 days.
  • Function: Turns off allergic responses and kills parasites.
• Basophils
  • Description: Nucleus bilobed; large blue-purple cytoplasmic granules; diameter 10-14 µm.
  • Count: 20-50 per mm3 of blood.
  • Development and Lifespan: 3-7 days, a few hours to a few days.
  • Function: Releases histamine and other mediators of inflammation.

Agranulocytes

• Lymphocytes
  • Description: Nucleus spherical or indented; pale blue cytoplasm; diameter 5-17 µm.
  • Count: 1500-3000 per mm3 of blood.
  • Development and Lifespan: Days to weeks development, hours to years lifespan.
  • Function: Mounts immune response by direct cell attack (T cells) or via antibodies (B cells).
• Monocytes
  • Description: Nucleus U- or kidney-shaped; gray-blue cytoplasm; diameter 14-24 µm.
  • Count: 100-700 per mm3 of blood.
  • Development and Lifespan: 2-3 days, months lifespan.
  • Function: Phagocytosis; develop into macrophages in tissues.

Platelets

• Description: Discoid cytoplasmic fragments containing granules; stain deep purple; diameter 2-4 µm.
• Count: 150,000-500,000 per mm3 of blood.
• Development and Lifespan: 4-5 days, 5-10 days lifespan.
• Function: Seals small tears in blood vessels, instrumental in blood clotting.
• RBCs, also called erythrocytes, are the most abundant.
• Flexible, oval, biconcave disk
• The normal range is 4.5 – 5.5 million /mm³ (µL) of blood
• Life span is 100-120 days.
• They are destroyed in the spleen.
• It is a bag of hemoglobin to carries O2 and some CO2
• Does not have organelles such as nucleus, mitochondria, ER or golgi apparatus.
• Originates in the red bone marrow.
• Each RBC carries 250 million hemoglobin.

RBC Abnormalities

• Polycythemia: Increased number of RBC; may result from bone marrow cancer or living at high altitude due to less oxygen.
• Anemia: Decrease in RBC number due to iron deficiency, abnormal kidney function, or Vitamin B12 deficiency.
• Leukocytes, also called WBCs, are less abundant than RBCs which are nucleated cells.
• Normal range: 5000-11,000/mm³ of blood.
• Involved in body's immunity/defense.
• Exhibit diapedesis (ability to move in and out from blood vessels) and amoeboid motion (move through tissues).
• Classified into granulocytes and agranulocytes based on whether they carry granules in their cytoplasm.
• Neutrophil, eosinophil, and basophil are granulocytes distinguishable via Write's stain and nuclear shape.
• Neutrophil: Most abundant; 3-6 lobed nucleus; light purple color cell and fine granules.
• Granulocytes (WBC): Eosinophil constitute 2-4% of WBCs; nucleus is blobbed or number 8 shape; Cytoplasmic granules are orange-red; role in eukaryotic parasitic defense (worms); involved in allergy and asthma.
• Basophil: Less than 1% of WBC population, least abundant; possesses a "U" or "S" shape nucleus; cytoplasm contains deep purple coarse granules; histamine granules are involved in allergic and inflammatory reactions.
• Agranulocytes (WBC): Lack visible cytoplasmic granules; have normal shaped nucleus; more abundant in spleen, thymus, and lymph nodes than blood. Comprising Lymphocytes and Monocytes.
• Lymphocytes: Smallest leukocytes; size of RBC; nucleus occupies most space in cytoplasm; blue-purple color; B cells produce antibodies, T cells destroy graft, virus, tumor cells.
• Monocytes: Largest of all leukocytes; double the size of RBC; constitute 3-8% of leukocyte population; convert to macrophage during infection and perform "phagocytosis"; increase in number during infection.

WBC Abormalities

• Leukocytosis: High WBC count; indicates bacterial/viral infection or hemorrhage.
• Leukopenia: Low WBC count; lower than 4000/mm3.
• Leukemia: Uncontrolled proliferation of immature WBC accompanied by reduction of RBC and platelets.
• Platelets: Not cells, but fragments of megakaryocytes formed in bone marrow.
• Have an irregular size and shape make up 1% of whole blood.
• Are important for blood clot formation, and also called thrombocytes.

Hematocrit

• Hematocrit or Packed Cell Volume (PCV) measures RBC percentage.
• Whole blood separates via centrifuge into plasma (55% by vol), red blood cells (45%), and a buffy coat (1% of white blood cells and platelets).
• Hematocrit is approximately 47% in males and 42% in females.

Blood Typing

• Blood classification is determined the antigens (glycoprotein) on the RBC cell membrane.
• Plasma contains "antibody" or "agglutinin" against these antigens.
• There are 3 antigen types (A, B, O) for four blood types.
• The major blood types are A, B, AB, and O.
• People with blood type A have B antibodies and vice versa.
• Type AB has no antibodies.
• Type O has both A and B antibodies.
• Blood typing is important for transfusion, grafting.
• Mismatched blood will cause agglutination (clumping) of RBCs, which can have fatal consequences.

ABO Blood Typing

• Blood Type A: Has A antigen, B antibody, can receive blood from A or O.
• Blood Type B: Has B antigen, A antibody, can receive blood from B or O.
• Blood Type AB: Has both A and B antigens, no antibody, can receive blood from all types.
• Blood Type O: Has no antigen, A and B antibodies, only can receive blood from O.
• Rh Factor: Another antigen in RBC is Rh protein, found in 85% of US population (Rh+).
• Unlike ABO groups, no preformed Rh antibodies exist.
• Rh- people slowly sensitize upon receiving Rh+ blood.
• Transfusions should match Rh factor.
• Pregnancy with Rh+/Rh- couple can cause complications.