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 its total volume. It serves as a transport medium for nutrients, hormones, and waste products.

• Plasma Proteins: Essential for maintaining osmotic pressure, transporting substances, and blood clotting.

  • Globulin: Involved in immune responses and transport of lipids and fat-soluble vitamins.

  • Fibrinogen: Key protein in blood clotting.

  • Albumin: Maintains osmotic pressure and transports hormones, drugs, and other substances.

Formed Elements

Formed elements are the cellular components of blood, including erythrocytes, leukocytes, and platelets.

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

• Leukocytes (White Blood Cells): Defend the body against infection and disease.

  • Neutrophils (Polymorphonuclear Leukocytes): Phagocytize bacteria; most abundant WBC.

  • Eosinophils: Combat parasitic infections and modulate allergic responses.

  • Basophils: Release histamine and heparin during inflammatory responses.

  • Monocytes and Macrophages: Phagocytize pathogens and debris; monocytes mature into macrophages in tissues.

  • Lymphocytes (B & T cells): Mediate immune responses; B cells produce antibodies, T cells destroy infected cells.

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

Blood Tests and Blood Typing

Common Blood Tests

Blood tests are essential for diagnosing and monitoring various health conditions. They provide information about the components and function of blood.

• 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 using Hemocytometer: Determines the number of red blood cells per unit volume.

• Hemoglobin Concentration: Amount of hemoglobin in blood; indicates oxygen-carrying capacity.

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

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

• Mean Corpuscular Hemoglobin Concentration (MCHC): Average concentration of hemoglobin in a given volume of packed red blood cells. $\text{MCHC} = \frac{\text{Hemoglobin (g/dL)}}{\text{Hematocrit (\%)}} \times 100$

Blood Typing

• Blood Groups: Determined by the presence of specific antigens (A, B, AB, O) on the surface of red blood cells.

• Antibodies (Agglutinins): Proteins in plasma that react against incompatible blood antigens.

• Rh Factor: Presence (+) or absence (−) of the D antigen; important in transfusion and pregnancy.

Clinical Significance

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

• Iron Deficiency: Most common cause of anemia; results from insufficient iron for hemoglobin synthesis.

• Pernicious Anemia: Caused by vitamin B12 deficiency, often due to lack of intrinsic factor.

• Polycythemia: Increased RBC count; can be physiological (high altitude) or pathological.

The Lymphatic & Immune Systems

Functions of the Lymphatic System

The lymphatic system maintains fluid balance, absorbs dietary fats, and provides immune defense.

• Lymphatic Capillaries: Collect excess interstitial fluid (lymph) from tissues.

• Lymphatic Vessels: Transport lymph toward the heart; movement aided by skeletal muscle contraction and valves.

• Lymphatic Trunks: Drain lymph from large regions of the body.

Lymphatic Capillaries and Vessels

• Lymphatic Capillaries (including Lacteals): Specialized for absorption of dietary fats in the small intestine.

• Lymphatic Vessels (Lymphatic Collecting): Merge to form larger lymphatic trunks.

• Lymphatic Trunks: Drain lymph into two main ducts: the right lymphatic duct and the thoracic duct.

Reticular Tissue

• Reticular Cells and Reticular Fibers: Form a supportive network in lymphoid organs, aiding in filtration and immune cell housing.

Lymphatic Organs

• Lymph Nodes: Filter lymph and house lymphocytes and macrophages.

  • Structure: Afferent and efferent lymphatic vessels, capsule, subcapsular (cortical) sinus, cortex, secondary follicles, germinal center, corona, trabeculae, and trabecular sinus, medulla (cords and sinuses).

  • Function: Immune surveillance and activation of lymphocytes.

• Spleen: Largest lymphatic organ; filters blood, recycles old RBCs, and stores platelets.

  • Structure: Capsule, trabeculae, hilum, red pulp (filters blood), venous (splenic) sinuses, splenic (Billroth's) cords, white pulp (lymphatic tissue), secondary follicles, central arteries.

• Thymus: Site of T cell maturation; most active in childhood.

  • Structure: Capsule, lobules, cortex, medulla, thymic (Hassall's) corpuscles.

• MALT (Mucosa-associated Lymphatic Tissue): Lymphoid tissues in mucous membranes, including lymphoid follicles in the tongue, tonsils, appendix, and Peyer's patches in the small intestine.

Summary Table: Blood Cell Types and Functions

Cell Type	Relative Abundance	Main Function
Erythrocytes	~99% of formed elements	Transport oxygen and carbon dioxide
Neutrophils	50-70% of WBCs	Phagocytosis of bacteria
Eosinophils	2-4% of WBCs	Combat parasites, modulate allergies
Basophils	<1% of WBCs	Release histamine, mediate inflammation
Monocytes	3-8% of WBCs	Phagocytosis; become macrophages
Lymphocytes	20-40% of WBCs	Immune response (B and T cells)
Platelets	150,000-400,000/μL	Blood clotting

Example: A patient with a high neutrophil count may be fighting a bacterial infection, while a low lymphocyte count could indicate an immune deficiency.

Additional info: Some explanations and formulas were expanded for clarity and completeness based on standard Anatomy & Physiology curricula.