Lymphatic System (Immune System) and Respiratory Physiology: Study Notes

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Lymphatic System (Immune System)

Overview of the Lymphatic System

The lymphatic system is a crucial component of the immune system, responsible for defending the body against pathogens and maintaining fluid balance. It includes a network of lymphatic vessels, lymph nodes, and various immune cells.

Lymph: A clear fluid that circulates through lymphatic vessels, carrying immune cells and waste products.
Immune cells: Include lymphocytes (T cells, B cells), natural killer (NK) cells, macrophages, and dendritic cells.
Organs: Lymph nodes, spleen, thymus, tonsils, and bone marrow.

Key Immune Cells and Their Functions

T cells: Lymphocytes that mature in the thymus and are involved in cell-mediated immunity. Subtypes include helper T cells (activate other immune cells), cytotoxic T cells (kill infected cells), and regulatory T cells (suppress immune responses).
B cells: Lymphocytes that mature in the bone marrow and are responsible for humoral immunity by producing antibodies.
NK cells (Natural Killer cells): Lymphocytes that can destroy virus-infected cells and tumor cells without prior sensitization.
APCs (Antigen Presenting Cells): Cells such as dendritic cells and macrophages that process and present antigens to T cells, initiating an immune response.

Lines of Immune Defense

First line: Physical and chemical barriers (skin, mucous membranes, secretions).
Second line: Innate immune responses (phagocytes, inflammation, fever, complement system).
Third line: Adaptive immune responses (T cells and B cells, specific to pathogens).

Antibody Types and Functions

Antibodies (immunoglobulins) are proteins produced by B cells that bind to specific antigens. The main types include:

IgA: Found in mucous membranes, saliva, tears, and breast milk; protects body surfaces.
IgM: First antibody produced in response to infection; effective in agglutination and complement activation.
IgG: Most abundant antibody in blood; provides long-term protection and can cross the placenta.
IgE: Involved in allergic reactions and defense against parasitic infections.

Order of appearance: IgM appears first during an immune response, followed by IgG.

Cell Surface Markers

CD4: Marker found on helper T cells; recognizes antigens presented by MHC class II molecules.
CD8: Marker found on cytotoxic T cells; recognizes antigens presented by MHC class I molecules.

Major Histocompatibility Complex (MHC)

MHC I: Present on all nucleated cells; presents endogenous antigens to CD8+ cytotoxic T cells.
MHC II: Present on antigen-presenting cells; presents exogenous antigens to CD4+ helper T cells.

Immune Response to Bacteria

The immune system responds to bacterial infection through a coordinated sequence of events involving both innate and adaptive immunity. The response includes the activation of phagocytes, production of antibodies, and recruitment of T cells.

Interferons and Cytokines

Interferons: Proteins released by virus-infected cells to warn neighboring cells and enhance their antiviral defenses.
Interleukins: A group of cytokines that mediate communication between immune cells; for example, Interleukin-2 (IL-2) stimulates T cell proliferation.

Training of T Cells

T cells are "trained" in the thymus to recognize self from non-self antigens. This process is called thymic selection.
Only T cells that do not react strongly to self-antigens survive and mature.

Summary Table: Immune Cell Types and Functions

Cell Type	Main Function	Surface Marker
Helper T cell	Activate B cells and cytotoxic T cells	CD4
Cytotoxic T cell	Kill infected or cancerous cells	CD8
B cell	Produce antibodies	CD19, CD20
NK cell	Destroy virus-infected and tumor cells	CD16, CD56
APC	Present antigens to T cells	MHC II

Respiratory Physiology

Overview of Respiratory Function

The respiratory system is responsible for gas exchange, supplying oxygen to the body and removing carbon dioxide. It involves ventilation, diffusion, and transport of gases in the blood.

Hemoglobin and Oxygen Transport

Hemoglobin (Hb): A protein in red blood cells that binds oxygen for transport.
Fetal hemoglobin: Has a higher affinity for oxygen than adult hemoglobin, facilitating oxygen transfer from mother to fetus.
Bohr effect: The decrease in hemoglobin's oxygen affinity at lower pH (increased CO2), enhancing oxygen delivery to tissues.
Effect of BPG (2,3-bisphosphoglycerate): BPG decreases hemoglobin's affinity for oxygen, promoting oxygen release in tissues.

Respiratory Control Centers

Located in the medulla oblongata and pons of the brainstem.
Regulate the rate and depth of breathing in response to CO2, O2, and pH levels.

Types of Breathing

Quiet breathing: Normal, restful breathing involving the diaphragm and external intercostal muscles.
Forced breathing: Active process involving additional muscles (e.g., internal intercostals, abdominal muscles) during exercise or respiratory distress.

Respiratory Pathologies

Emphysema: Destruction of alveolar walls, reducing surface area for gas exchange.
Tuberculosis (TB): Infectious disease caused by Mycobacterium tuberculosis, affecting lung tissue.
Hypercapnia: Elevated CO2 levels in the blood, leading to increased respiratory drive.

Gas Exchange and Transport

Occurs in the alveoli of the lungs, where O2 diffuses into the blood and CO2 diffuses out.
Partial pressures of gases drive diffusion: moves from high to low partial pressure, as does .
Hemoglobin facilitates the transport of both O2 and CO2.

Equations and Concepts

Oxygen-Hemoglobin Dissociation Curve: Describes the relationship between the partial pressure of oxygen () and hemoglobin saturation.
Bohr Effect Equation:
CO2 Transport:

Summary Table: Effects of Various Factors on Oxygen-Hemoglobin Binding

Factor	Effect on O2 Binding
Increased CO2 (Bohr effect)	Decreases affinity
Decreased pH	Decreases affinity
Increased temperature	Decreases affinity
Increased BPG	Decreases affinity
Fetal hemoglobin	Increases affinity

Respiratory Zone

The respiratory zone includes respiratory bronchioles, alveolar ducts, and alveoli, where gas exchange occurs.

Additional info:

Sympathetic stimulation (e.g., epinephrine) dilates airways, while parasympathetic stimulation constricts them.
Albuterol is a beta-2 agonist used to relax airway smooth muscle in asthma.
Histamine causes bronchoconstriction and is involved in allergic responses.