Physiology week 11 (exam 3)

Lymphatic System

Overview and Functions

The lymphatic system is a network of vessels, tissues, and organs that play a crucial role in fluid balance and immune defense. It consists of lymphatic vessels (lymphatics), lymphoid tissue, lymph nodes, and lymphoid organs such as the tonsils, thymus, and spleen.

• Fluid Transport: Transports tissue fluid (lymph) that has leaked out of the vascular system and returns it to the blood vessels.

• Immune Protection: Removes foreign material (e.g., bacteria) from the lymphatic stream, helping to protect the body.

Lymphatic Vessels and Circulation

• Lymphatic Capillaries: Pick up leaked fluid and carry it through larger vessels.

• Lymphatic Vessels and Trunks: Transport lymph toward the heart.

• Right Lymphatic Duct: Drains lymph from the right upper extremity, head, and thorax.

• Large Thoracic Duct: Receives lymph from the rest of the body.

• Cisterna Chyli: Receives lymph from the digestive organs.

• One-way System: Lymph flows only toward the heart.

• Lymph Nodes: Filter lymph as it passes through.

Immune Response

General Concepts

The immune response is the collection of the body's defenses against various threats, including pathogens and foreign substances.

• Innate (Nonspecific) Defenses: Surface barriers (skin, mucous membranes), phagocytes, inflammation, fever.

• Adaptive (Specific) Defenses: "Lock-and-key" recognition for foreign molecules, involving lymphocytes and antibodies.

Adaptive Immune System

Characteristics

The adaptive immune system provides highly specific and long-lasting protection against pathogens.

• Memory: Ability to remember and respond more rapidly to previously encountered antigens.

• Specificity: Targets specific antigens with high accuracy.

• Self-Tolerance: Distinguishes self from non-self to prevent attacking the body's own tissues.

Antigens and Immune Response

• Antigens: Substances capable of provoking an immune response; recognized by lymphocytes and white blood cells.

• Immunocompetent Lymphocytes: Can bind to one or a few similar antigens, demonstrating specificity.

Autoimmunity

• The immune system can distinguish self from foreign antigens.

• Sometimes, the immune system attacks the body's own tissues, leading to autoimmune diseases such as Multiple Sclerosis, Myasthenia Gravis, Rheumatoid Arthritis, and Diabetes Mellitus.

Organs, Cells, and Cell Interactions

Lymphoid Organs and Tissues

• Primary Lymphoid Organs: Thymus and red bone marrow (sites of lymphocyte maturation).

• Secondary Lymphoid Organs and Tissues: All other lymphoid tissues (e.g., lymph nodes, spleen).

B and T Lymphocytes

• B Lymphocytes: Originate and mature in the red bone marrow; become immunocompetent and self-tolerant.

• T Lymphocytes: Originate in the red bone marrow, mature in the thymus.

Clonal Selection

• When an antigen binds to a specific cell-surface receptor, B and T cells are cloned with antigen receptor.

• Clones become memory cells or effector/regulatory cells.

Comparison of B and T Lymphocytes

Table: Properties of B and T Lymphocytes

Properties	B Lymphocytes	T Lymphocytes
Type of Immune Response	Humoral immunity (antibody-mediated immunity)	Cellular immunity (cell-mediated immunity)
Site of Maturation	Red bone marrow	Thymus
Effector Cells	Plasma cells (antibody-secreting cells)	Cytotoxic T cells, helper T cells, regulatory T cells
Memory Cell Formation	Yes	Yes
Functions	Plasma cells produce antibodies that neutralize antigens and tag antigens for destruction	Cytotoxic T cells attack infected cells and tumor cells; Helper T cells activate B cells and other T cells

Antibodies

Structure and Function

Antibodies (immunoglobulins) are proteins produced by effector B cells (plasma cells) and are essential for humoral immunity.

• Made up of gamma globulins: IgA, IgD, IgE, IgG, IgM.

• All antibodies share a basic structure but differ in functionality.

Antibody Monomers

• Four polypeptide chains bound together by disulfide bridges.

• Composed of heavy chains and light chains.

• Constant (C) region and variable (V) region.

• Y-shaped structure, uniquely shaped to fit one specific antibody's antigen-binding site.

Example: Antibody-Antigen Binding

• Antibodies bind to antigens with high specificity, neutralizing pathogens or marking them for destruction by other immune cells.