Blood Composition, Blood Tests, and the Lymphatic & Immune Systems: Study Notes

Blood Composition

Plasma Components

The plasma is the liquid portion of blood, making up about 55% of total blood volume. It serves as a transport medium for nutrients, hormones, and waste products.

• Globulin: A group of proteins involved in immune responses and transport of substances.

• Fibrinogen: A plasma protein essential for blood clotting.

• Albumin: The most abundant plasma protein, maintaining osmotic pressure and transporting substances.

Formed Elements

The formed elements are the cellular components of blood, including:

• Erythrocytes (Red Blood Cells): Transport oxygen and carbon dioxide using hemoglobin.

• Leukocytes (White Blood Cells): Defend the body against infection. Types include:

  • Neutrophils: Most abundant, phagocytize bacteria.

  • Eosinophils: Combat parasites and modulate allergic responses.

  • Basophils: Release histamine in allergic reactions.

  • Monocytes: Differentiate into macrophages, phagocytize pathogens and debris.

  • Lymphocytes: Include B cells (produce antibodies) and T cells (cell-mediated immunity).

• Platelets (Thrombocytes): Cell fragments involved in blood clotting.

Blood Tests and Blood Typing

Common Blood Tests

• Differential WBC Count: Measures the percentage of each type of white blood cell.

• Hematocrit (Packed Cell Volume): Percentage of blood volume occupied by red blood cells.

• RBC Count: Number of red blood cells per unit volume of blood.

• Hemoglobin Concentration: Amount of hemoglobin in blood, indicating oxygen-carrying capacity.

• Mean Corpuscular Volume (MCV): Average volume of individual red blood cells. Formula: $\text{MCV} = \frac{\text{Hematocrit (\%)}}{\text{RBC count (millions/\mu L)}} \times 10$

• Mean Corpuscular Hemoglobin (MCH): Average amount of hemoglobin per red blood cell. Formula: $\text{MCH} = \frac{\text{Hemoglobin (g/dL)}}{\text{RBC count (millions/\mu L)}} \times 10$

Blood Typing

• ABO Blood Groups: Determined by presence of A and B antigens on RBCs.

• Rh Blood Groups: Determined by presence (+) or absence (−) of Rh antigen (D antigen).

• Antibodies (Agglutinins): Present in plasma, react with foreign antigens.

Clinical Significance

• Anemia: Reduced oxygen-carrying capacity of blood due to low RBCs or hemoglobin.

• Iron Deficiency Anemia: Caused by insufficient iron for hemoglobin synthesis.

• Pernicious Anemia: Due to vitamin B12 deficiency.

• Polycythemia: Increased RBC count, raising blood viscosity.

The Lymphatic & Immune Systems

Functions of the Lymphatic System

• Returns excess interstitial fluid to the bloodstream.

• Absorbs dietary fats from the digestive tract (via lacteals).

• Defends the body against pathogens and foreign substances.

Lymphatic Capillaries and Vessels

• Lymphatic Capillaries: Small, blind-ended vessels that absorb interstitial fluid.

• Lacteals: Specialized lymphatic capillaries in the small intestine that absorb fats.

• Lymphatic Vessels: Transport lymph toward the heart, include collecting vessels and trunks.

• Lymphatic Trunks: Large vessels that drain lymph from major body regions.

Reticular Tissue

• Reticular Cells: Produce reticular fibers, forming a supportive network in lymphoid organs.

• Reticular Fibers: Provide structural support for lymphocytes and other immune cells.

Lymphatic Organs

• Lymph Nodes: Filter lymph and house lymphocytes. Structure includes:

  • Afferent and efferent lymphatic vessels (entry and exit points for lymph).

  • Capsule (outer covering), cortex (outer region), and medulla (inner region).

  • Subcapsular (cortical) sinus, secondary follicles, germinal centers, and trabeculae.

• Spleen: Largest lymphatic organ, filters blood, removes old RBCs, and stores platelets. Structure includes:

  • Capsule, trabeculae, hilum, red pulp (RBC removal), white pulp (immune function).

  • Venous (splenic) sinuses, splenic cords (Billroth's cords), central arteries, and secondary follicles.

• Thymus: Site of T cell maturation. Structure includes:

  • Capsule, lobules, cortex (immature T cells), medulla (mature T cells), and thymic (Hassall's) corpuscles.

• MALT (Mucosa-associated Lymphatic Tissue): Lymphoid tissue in mucous membranes, including:

  • Lymphoid follicles in the tongue, tonsils, appendix, and bronchi.

  • Peyer's patches in the small intestine.

Table: Comparison of Major Lymphatic Organs

Organ	Main Function	Key Structures
Lymph Node	Filters lymph, immune surveillance	Capsule, cortex, medulla, germinal centers
Spleen	Filters blood, removes old RBCs, immune response	Capsule, red pulp, white pulp, hilum
Thymus	T cell maturation	Capsule, lobules, cortex, medulla, Hassall's corpuscles
MALT	Protects mucosal surfaces	Lymphoid follicles, Peyer's patches, tonsils

Example: A patient with swollen lymph nodes may be fighting an infection, as lymph nodes trap and destroy pathogens.

Additional info: The lymphatic system is closely integrated with the circulatory and immune systems, playing a vital role in fluid balance and defense against disease.