Blood and Blood Cells

LAB EXERCISE 37: Blood and Blood Cells

Overview of Blood

  • Definition: Blood is a type of connective tissue characterized by cells suspended in a liquid intercellular material.
  • Physical Properties:
    • Heavier than water, approximately 3-4 times thicker than water.
    • Comprises cellular components like red blood cells (erythrocytes), white blood cells (leukocytes), and platelets.

Components of Blood

Formed Elements

  • Erythrocytes (Red Blood Cells): Responsible for oxygen transport.
  • Leukocytes (White Blood Cells): Integral to the immune system and defense against pathogens.
  • Platelets: Essential for blood clotting.

Hematocrit (HCT) and Plasma Composition

  • Hematocrit (HCT): The percentage of blood volume occupied by cells; also known as Packed Cell Volume (PCV).
    • Typically around 45% of blood volume is made up of cells.
  • Plasma: Comprises the remaining 55% of blood and contains:
    • Water: 92% by weight
    • Proteins: 7% by weight, including major components such as:
    • Albumins (58%)
    • Globulins (37%)
    • Fibrinogen (4%)
    • Other Solutes: 1% by weight, including nutrients, gases, and waste products.

Blood Cell Counts

  • Erythrocytes: Average of 4.2-6.2 million per cubic mm.
  • Leukocytes: Between 5,000 - 10,000 per cubic mm. Breakdown:
    • Neutrophils: 60-70%
    • Lymphocytes: 20-25%
    • Monocytes: 3-8%
    • Eosinophils: 2-4%
    • Basophils: 0.5-1%
  • Platelets: 120,000 - 300,000 per cubic mm.

Functions of Blood

Transport

  • Erythrocytes:
    • Carry oxygen from the lungs to body tissues.
    • Transport carbon dioxide from tissues back to the lungs for expulsion.
  • Blood Plasma:
    • Transports absorbed nutrients from the gastrointestinal tract.
    • Transports hormones released by endocrine organs to their target cells.
    • Carries waste products from cells to organs like the kidneys for excretion.

Regulation of Body Functions

  • Temperature Regulation:

    • Plasma absorbs and distributes heat throughout the body.
    • Blood vessels dilate in dermis for cooling; constrict to conserve heat.

  • pH Regulation:

    • pH measures fluid acidity or alkalinity (neutral pH = 7; alkaline 7-14; acidic 0-7).
    • Blood plasma maintains a pH of 7.4, critical for cellular function.

  • Fluid Levels Regulation:

    • Maintains normal fluid levels; balances fluid exchange between blood plasma and interstitial fluid.
    • Prevents fluid loss to maintain blood pressure: excessive absorption raises blood pressure, while excessive fluid loss leads to low blood pressure and edema.

Immune Defense

  • Leukocytes provide protection against infections by mounting immune responses against pathogens and antigens.
  • Antibodies in plasma immobilize antigens until leukocytes can respond.
  • Platelets and blood proteins form clots to prevent blood loss after vessel damage.

Blood Cell Formation

  • Blood cells are produced in the bone marrow from stem cells known as hemocytoblasts or hematopoietic stem cells.
  • Differentiation pathway includes various progenitor types:
    • Common lymphoid progenitor (for lymphocytes)
    • Common myeloid progenitor (for erythrocytes and platelets)
    • Common granulocyte precursor (for granulocytes).

Characteristics of Erythrocytes

  • Mature erythrocytes lack nuclei and mitochondria, relying on glycolysis to produce ATP.
  • Lifespan: Approximately 100-120 days.
  • Efficient gas transport due to lack of nuclei allows more hemoglobin capacity.

Hemoglobin

  • Each erythrocyte contains about 280 million molecules of hemoglobin.
  • Functions:
    • Transports oxygen and carbon dioxide.
    • Responsible for the red color of arterial blood; oxygen-poor blood takes on a deep red color, often perceived as blue through skin layers.

Blood Typing

ABO Blood Types

  • Blood types are determined by surface antigens:
    • Type A: Has antigen A, anti-B antibodies.
    • Type B: Has antigen B, anti-A antibodies.
    • Type AB: Has both antigens A and B, no antibodies.
    • Type O: Has neither antigen, but possesses both anti-A and anti-B antibodies.

Rh Factor

  • Rh (Rhesus factor): Two types, Rh- (negative) and Rh+ (positive).
  • Importance: Rh- mothers may produce Rh+ antibodies, posing anemia risk to Rh+ fetuses. RhoGAM prevents antibody development.

Agglutination Reaction

  • Occurs when antigens and antibodies mismatch, causing clumping. This is a critical consideration for successful blood transfusions.

Leukocytes

  • Functions: Protects the body against disease and responds to infections.
  • Types of Leukocytes:
    • Granulocytes (have granules):
    • Neutrophils: Most abundant, first responders to infections (54%-62% of leukocytes).
    • Eosinophils: Target parasites and mediate allergic reactions (1-3%).
    • Basophils: Release chemicals during allergic responses (<1%).
    • Agranulocytes (minimal granulation):
    • Monocytes: Largest blood cells, differentiate into macrophages to engulf pathogens and debris (3-9%).
    • Lymphocytes: Include T-cells (immune response management) and B-cells (antibody production).

Platelets/Thrombocytes

  • Not complete cells; derived from megakaryocytes in bone marrow.
  • Function: Clotting mechanism to repair damaged vessels; lifespan of about 10 days.

Laboratory Procedures

  • Lab Report Requirements: Parts A, B, D, F are essential for the report.
  • Blood Typing Lab Activity: Utilize provided printouts to complete blood typing activity, fill in responses, and participate in discussions.