Lymphatic System & Body Defenses: Structured Study Notes

Chapter 12 — Lymphatic System & Body Defenses

12.1 The Lymphatic System

The lymphatic system is a network of vessels, tissues, and organs that help maintain fluid balance and protect the body against infection and disease. It works closely with the circulatory and immune systems.

• Lymphatic vessels: Transport lymph, a fluid containing white blood cells and waste products.

• Lymphoid tissues and organs: Include lymph nodes, spleen, thymus, tonsils, Peyer's patches, and MALT (mucosa-associated lymphoid tissue).

• Functions:

  • Transport escaped fluids back to blood

  • Provide defense and disease resistance

Lymphatic Characteristics

• Lymph: Excess tissue fluid collected from interstitial spaces.

• Vessels:

  • One-way system: flows toward the heart

  • No pump; movement via:

    • Skeletal muscle "milking"

    • Smooth muscle contraction

Lymphatic Vessels & Flow

• Capillaries: Flap-like minivalves allow fluid entry.

• Collecting vessels: Carry lymph to nodes and veins.

• Major ducts:

  • Right lymphatic duct: Drains right upper quadrant

  • Thoracic duct: Drains rest of body

• Flow of Lymph:

$\text{Tissue Fluid} \rightarrow \text{Lymph Capillary} \rightarrow \text{Collecting Vessel} \rightarrow \text{Lymph Node} \rightarrow \text{Lymph Duct} \rightarrow \text{Blood}$

Lymph Nodes

• Filter lymph before returning to blood

• Contain:

  • Macrophages: Engulf foreign material

  • Lymphocytes: Immune response

• Structure:

  • Cortex: follicles

  • Medulla: macrophages

Other Lymphoid Organs

These organs have specialized immune functions and locations.

Organ	Location	Function
Spleen	Left abdomen	Filters blood, stores RBCs
Thymus	Low throat	Programs T cells
Tonsils	Pharynx	Trap bacteria
Peyer's patches	Small intestine	Capture/destroy bacteria
MALT	Digestive/Respiratory	Protects mucosa

Innate (Nonspecific) Defenses

The innate defense system provides immediate, general protection against pathogens. It is not specific to any particular pathogen.

First Line

• Skin & mucous membranes: physical barrier

• Protective secretions: sebum, mucus, saliva, HCl

Second Line

• Natural Killer (NK) cells: destroy infected/cancer cells

• Inflammation: redness, heat, swelling, pain

• Phagocytes: neutrophils/macrophages engulf pathogens

• Antimicrobial proteins: complement & interferon

• Fever: inhibits bacteria & speeds repair

12.2 Adaptive Defense System

The adaptive (specific) defense system targets particular pathogens and provides immunological memory for long-term protection.

Third Line of Defense

• Specific immunity: Antigen-specific, systemic, memory

• Types:

  • Humoral (B cells): Antibodies in fluids

  • Cell-mediated (T cells): Kills infected cells

Antigens & Self-Antigens

• Antigens: Trigger immune response

• Self-antigens: Recognized as safe by the body

Lymphocytes

• B cells: Plasma cells (produce antibodies), memory cells (long-term defense)

• T cells: Cytotoxic (kill), helper (recruit), regulatory (suppress)

• Macrophages: Antigen presentation & cytokine secretion

Humoral Response

1. Antigen binds B cell — clonal selection

2. Plasma cells produce antibodies

3. Memory cells — faster & stronger secondary response

Active vs Passive Immunity

• Active: Own antibodies (infection/vaccine)

• Passive: External antibodies (maternal/serum)

Antibodies (MADGE)

Antibodies are proteins produced by B cells that bind specific antigens. There are five main classes, each with distinct functions.

Class	Function
IgM	Complement fixation
IgA	Mucus secretions
IgD	B cell activation
IgG	Crosses placenta
IgE	Allergies

Cell-Mediated Immunity

• Cytotoxic T cells: Kill infected cells via perforin & granzymes

• Helper T cells: Recruit immune cells

• Regulatory T cells: Suppress immune activity

• Memory cells: Long-term immunity

Organ Transplants & Rejection

• Graft types:

  • Autograft: same person

  • Isograft: identical twin

  • Allograft: unrelated person

  • Xenograft: different species

• Success increases with closer tissue match

Disorders of Immunity

• Allergies: Immediate (IgE & histamine) vs delayed (cytokines)

• Immunodeficiencies: Congenital/acquired (e.g., AIDS)

• Autoimmune: Attacks self (e.g., MS, Type 1 diabetes, RA, SLE)

Developmental Aspects

• Lymphoid organs poorly developed at birth

• Newborns — passive maternal immunity

• Loss of lymphatics — severe edema

Interactive Quiz

Test your understanding of the lymphatic system and body defenses.

Multiple Choice

1. Which organ programs T lymphocytes?

   • A) Spleen

   • B) Bone marrow

   • C) Thymus

   • D) Tonsils

2. Thoracic duct drains lymph from:

   • A) Right arm & head

   • B) Entire body except right upper quadrant

   • C) Lower limbs only

   • D) Left arm only

3. Which antibody class is involved in allergic reactions?

   • A) IgM

   • B) IgA

   • C) IgD

   • D) IgE

Matching

Organ	Function
Spleen	Filters blood, stores blood
Thymus	Programs T cells
Tonsils	Traps bacteria in pharynx
Peyer's patches	Protects intestines

True / False

1. NK cells are part of the adaptive defense system. (T/F)

2. Passive immunity results in immunological memory. (T/F)

3. Xenografts are always unsuccessful. (T/F)

4. Haptens alone are strongly antigenic. (T/F)

Answer Key

• Multiple Choice:

  1. C) Thymus

  2. B) Entire body except right upper quadrant

  3. D) IgE

• Matching:

  1. F

  2. T

  3. F

  4. F

• True / False:

  1. F

  2. F

  3. T

  4. F

Additional info: These notes expand on the original bullet points with definitions, examples, and academic context for clarity and completeness.