Blood Composition and Hematocrit

Major Components of Blood

Blood is a specialized connective tissue composed of several key components, each with distinct functions essential for homeostasis and transport.

• Plasma: The liquid matrix of blood, making up about 55% of total blood volume. It is 90% water by volume and contains dissolved proteins, nutrients, electrolytes, and waste products.

• Buffy Coat: A thin, whitish layer between plasma and red blood cells in centrifuged blood, containing leukocytes (white blood cells) and platelets.

• Red Blood Cells (RBCs): Also called erythrocytes, these cells are responsible for oxygen transport and make up about 45% of blood volume (the hematocrit).

Normal Hematocrit Ranges:

• Men: 47% (average)

• Women: 42% (average)

Plasma Composition

• Proteins: Albumin (main contributor to osmotic pressure), fibrinogen (clotting), globulins (immune function)

• Solutes: Glucose, chloride, electrolytes, antibodies

Red Blood Cells (Erythrocytes)

Structure and Function

Erythrocytes are highly specialized for oxygen transport. Their unique structure maximizes efficiency in gas exchange.

• Biconcave disc shape: Increases surface area for gas exchange and allows flexibility to squeeze through capillaries.

• Flexible membrane: Enables passage through narrow vessels.

• Lack of nucleus and organelles: Maximizes space for hemoglobin, the oxygen-carrying protein.

Production Site: Erythrocytes are produced in the bone marrow by a process called erythropoiesis.

Regulation: The hormone erythropoietin (EPO), produced mainly by the kidneys, stimulates RBC production in response to low oxygen levels.

White Blood Cells (Leukocytes)

Types and Functions

Leukocytes are the immune cells of blood, divided into two main groups based on the presence of cytoplasmic granules.

• Granulocytes: Contain visible granules in the cytoplasm.

  • Neutrophils: Multilobed nucleus, pale red and blue granules; phagocytize bacteria.

  • Eosinophils: Bilobed nucleus, red cytoplasmic granules; kill parasitic worms, involved in allergy and asthma.

  • Basophils: Bilobed nucleus, purplish-black granules; release histamine and other mediators of inflammation.

• Agranulocytes: Lack visible cytoplasmic granules.

  • Lymphocytes: Large spherical nucleus, thin rim of pale blue cytoplasm; mount immune response by direct cell attack or via antibodies.

  • Monocytes: Kidney-shaped nucleus, abundant pale blue cytoplasm; phagocytosis, develop into macrophages.

Platelets

Structure and Function

• Platelets are cell fragments derived from megakaryocytes in the bone marrow.

• They are not true cells, as they lack a nucleus.

• Essential for blood clotting (hemostasis).

Blood Typing and Transfusion

ABO and Rh Blood Groups

Blood types are determined by the presence or absence of specific antigens on the surface of RBCs and corresponding antibodies in plasma.

• Antigens: A, B, Rh (D)

• Antibodies: Anti-A, Anti-B, Anti-Rh

Blood Transfusion Compatibility

Universal Donor: Type O- blood has no A, B, or Rh antigens, so it does not trigger agglutination in recipients.

Universal Recipient: Type AB+ blood has all antigens, so it does not form antibodies against A, B, or Rh.

Hemolytic Disease of the Newborn

• Occurs when an Rh- mother carries an Rh+ fetus.

• The mother's immune system may produce anti-Rh antibodies that attack fetal RBCs in subsequent pregnancies.

• This is not a problem for Rh+ mothers, as they do not form anti-Rh antibodies.

Blood Typing Procedure

• Blood samples are mixed with anti-A and anti-B antibodies.

• Clumping (agglutination) indicates the presence of the corresponding antigen.

• Example: If clumping occurs with anti-A but not anti-B, the blood type is A.

Blood Histology

Microscopic Identification

• Erythrocytes: Small, biconcave, pink-staining cells without nuclei.

• Platelets: Tiny, purple-staining cell fragments.

• Leukocytes: Larger cells with distinct nuclei; classified by nuclear shape and cytoplasmic granules.

Granulocytes: Neutrophils, eosinophils, basophils

Agranulocytes: Lymphocytes, monocytes

Key Terms and Definitions

• Hematocrit: The percentage of blood volume occupied by red blood cells.

• Plasma: The liquid, non-cellular portion of blood.

• Buffy Coat: The thin layer of leukocytes and platelets between plasma and RBCs after centrifugation.

• Erythrocyte: Red blood cell, responsible for oxygen transport.

• Leukocyte: White blood cell, involved in immune defense.

• Platelet: Cell fragment involved in clotting.

• Antigen: A molecule on the surface of cells that can trigger an immune response.

• Antibody: A protein produced by the immune system that binds to specific antigens.

• Agglutination: Clumping of cells due to antigen-antibody interactions.

Summary Table: Blood Cell Types and Functions

Additional info: This guide expands on the provided notes with definitions, context, and tables for clarity and completeness, suitable for exam preparation in a college-level Anatomy & Physiology course.