The Immune System Lecture Summary

Learning Objectives

  • After completing this chapter, you should be able to:
      - 25.1 Define and spell the terms for this chapter.
      - 25.2 Identify the structures of the lymphatic system.
      - 25.3 Explain the functions of the immune system.
      - 25.4 Describe how the immune system changes during the life span of a child to an older adult.
      - 25.5 Identify key components to the immune response.
      - 25.6 Differentiate between types of immunity.
      - 25.7 Describe Common Pathology Associated With the Immune System.

The Immune System

  • The immune system is the body's defense system that protects against germs like bacteria, viruses, and fungi.

  • It includes:
      - Special cells
      - Tissues
      - Organs

  • The immune system functions to:
      - Identify and remove harmful invaders and damaged cells.
      - Involves processes that find and eliminate abnormal cells and foreign substances.
      - Includes foreign tissues such as transplants.

Immunology

  • An immunologist specializes in the treatment of the immune system, including the lymphatic system.

  • Immunology is the field of study that deals with the immune system.

Functions of the Immune System

  • The primary functions include:
      - Defending the body against harmful invaders like bacteria, viruses, fungi, and other pathogens.
      - Identifying and removing abnormal or damaged cells to prevent disease.
      - Working with the lymphatic system, where lymph nodes filter pathogens and house immune cells for protection.

Lymphatic System

  • The lymphatic system is a network of vessels, nodes, and organs that helps maintain fluid balance, remove waste, and support the immune system by transporting infection-fighting cells.

Components of the Lymphatic System

  • The main components include:
      - Interstitial Fluid (lymph fluid)
      - Lymph nodes
      - Lymph nodules
      - Thymus
      - Spleen
      - Bone marrow

Interstitial Fluid (Lymph)

  • Definition: Tissue fluid found between cells that, once collected and filtered, becomes lymph.

  • Characteristics:
      - Lymph is cleaned fluid that helps fight infection.
      - Moves through the body via muscle contractions, breathing, and vessel movement (not through a heart).

Lymph Nodes

  • Definition: Small, bean-shaped structures that filter lymph and help fight infections, crucial to the immune system.

  • Functions:
      - Filter harmful substances by removing bacteria, viruses, and toxins from lymph.
      - Contain immune cells like B cells, T cells, and macrophages to detect and attack infections.
      - Produce antibodies (B cells create antibodies to fight specific pathogens, known as humoral immunity).
      - Support cell-mediated immunity (T cells destroy infected or abnormal cells).
      - Aid in circulating lymph (enters through afferent vessels, gets filtered, exits via efferent vessels).

Examples of Lymph Nodes

  • Major lymph nodes include:
      - Cervical (neck)
      - Axillary (armpit)
      - Inguinal (groin)
      - Mesenteric (abdominal)

Spleen

  • Location: Upper left quadrant of abdomen.

  • Characteristics:
      - Largest lymphatic organ.
      - Blood passes through intricate meshwork of tiny blood vessels in the spleen before continuing to the liver.
      - Blood vessels in the spleen are lined with macrophages.

Tonsils

  • Location: Within the depressions of mucous membranes of the throat and pharynx.

  • Function:
      - Filter bacteria and aid in the formation of white blood cells.
      - Can become enlarged and infected if unable to properly filter bacteria and pathogens.

Bone Marrow

  • Definition: Contains stem cells that develop into all cells of the body in a process called hematopoiesis.

  • Characteristics:
      - Immune system cells become either mature cells of the immune system or precursors to cells that will mature elsewhere in the body.

Hematopoiesis: Blood Cell Production

  • Definition: The process of making blood cells in the bone marrow.

  • Importance:
      - Replaces old blood cells.
      - Helps carry oxygen, fight infections, and stop bleeding.

  • Types of Blood Cells Produced:
      - Red Blood Cells (RBCs): Carry oxygen.
      - White Blood Cells (WBCs): Fight infections.
      - Platelets: Help with blood clotting.

Thymus Gland

  • Location: Behind the sternum (breastbone).

  • Size: Large in children; shrinks (atrophies) after adolescence.

  • Functions:
      - Produces and develops T-cells to fight infections.
      - Immature cells from bone marrow mature in the thymus, helping distinguish normal T-cells from harmful ones.

The Immune System and the Life Span

The Child

  • Infants are incredibly vulnerable to disease and infection due to undeveloped immunity.

  • Immunizations begin at birth with hepatitis B and continue on an age-based schedule through 18 to 23 months.

  • The thymus gland grows from birth to puberty, producing and maturing T cells for the body’s defense.

Older Adults

  • Bone marrow becomes less productive with age.

  • The thymus gland continues to shrink.

  • Lymphatic and circulatory vessels in arms and legs begin to stiffen, complicating blood and fluid transport.

  • Overall immune response to microorganisms and pathogens begins to slow.

  • Older adults are more susceptible to harmful viruses and bacteria compared to younger individuals, with an increased likelihood of developing autoimmune diseases. Immunizations are strongly encouraged.

The Immune Response and the Body’s Defenses

  • Definition: Represents the collaboration of cells, tissues, and organs in the immune system to attack organisms and substances that invade the body systems and cause illness and disease.

Antigens vs. Antibodies

  • Antigens:
      - Foreign substances (like bacteria or viruses) that trigger an immune response.
      - The immune system recognizes them as harmful.

  • Antibodies (Immunoglobulins):
      - Proteins made by B Cells, not cells themselves.
      - Function: Attach to invaders (antigens) and mark them for destruction, akin to heat-seeking missiles locking onto enemy targets.

Leukocytes (White Blood Cells)

  • Definition: Cells that seek out and destroy harmful organisms.

  • Two types:
      - Lymphocytes:
        - Enable the body to recognize previous invading organisms.
      - Phagocytes:
        - Attack and ingest (engulf, or eat) invading organisms.

Types of White Blood Cells (WBCs)

  • There are five types of WBCs:
      - Lymphocytes (B Cells, T Cells, & Natural Killer Cells): Target specific threats.
      - Monocytes: Become macrophages to clean up invaders.
      - Neutrophils: First responders that attack bacteria.
      - Eosinophils: Fight parasites & allergens.
      - Basophils: Trigger inflammation & allergic responses.

B-Cells (A Type of Lymphocyte)

  • Functions:
      - Recognize invaders (antigens) and turn into plasma cells that produce antibodies to help fight specific infections.

T-Cells (A Type of Lymphocyte)

  • Functions:
      - Recognize invaders and attack infected cells directly. Help destroy virus-infected or harmful cells.

Monocytes (A Type of Phagocyte)

  • Functions:
      - Act as cleanup crew by engulfing and destroying pathogens, including those tagged by antibodies.

How Antibodies Help

  • Tag invaders for destruction by other immune cells.

  • Activate the complement system to help destroy bacteria, viruses, or infected cells.

Vaccines & Immunity

  • Definition: Vaccines introduce small, weakened, or inactive pieces of a virus or bacteria to train the immune system to recognize and respond without causing illness.

Immunity

  • Definition: The body's ability to recognize, resist, and defend against harmful invaders like bacteria, viruses, and toxins, helping prevent infections and diseases by activating the immune system.

Immunosuppressants

  • Definition: Medications that weaken the immune system.

  • Purpose:
      - Prevent organ rejection after transplants.
      - Treat autoimmune diseases where the immune system attacks the body.
      - Reduce immune response, which makes the patient vulnerable to illnesses.
      - Extreme stress can also suppress the immune system, compromising its ability to fight infections.

Types of Immunity

  • Innate Immunity:
      - Born with it, inherited from parents.
      - Provided mainly by external barriers (skin, mucous membranes).
      - Acts as the first line of defense against pathogens, capable of rendering many viruses and bacteria ineffective against humans.

  • Active Immunity:
      - Not inborn; develops after birth and is permanent, providing lifelong protection against diseases.
      - Includes:
        - Acquired Active Immunity: Developed from exposure to a live pathogen, leading to immunity post-primary immune response.
        - Artificially Acquired Active Immunity: Induced by vaccines, containing antigens stimulating a primary response without causing symptoms.

  • Passive Immunity:
      - Not permanent; only lasts temporarily such as antibodies passed to an infant through breast milk.
      - Provides short-term protection against infections during early years of childhood.

Common Pathology Associated With the Immune System

Immune Disorders

  • Immune system disorders may involve an inappropriate, excessive, or absent immune response.

  • Autoimmune diseases occur when the body mistakenly attacks healthy cells and tissues, perceiving them as foreign pathogens.

  • Disorders may be:
      - Inherited
      - Acquired through infection or illness
      - A result of specific drug treatments.

Acquired Immunodeficiency Syndrome (AIDS)

  • Definition: AIDS is caused by the Human Immunodeficiency Virus (HIV) and represents the final stage of HIV infection.

  • It results in a weakened immune system, making the body more vulnerable to infections and diseases.

  • It is characterized by the destruction of T-lymphocytes (T-cells), reducing the immune response.

HIV Transmission

  • Given through:
      - Unprotected sexual contact with an infected person.
      - Blood contact (through needle sharing, unscreened blood transfusions).
      - Mother-to-child transmission during pregnancy, birth, or breastfeeding.

Symptoms & Treatment of AIDS

  • Symptoms:
      - Early stage: Often asymptomatic for up to 10 years.
      - Advanced stage: Frequent infections (e.g., pneumonia, meningitis), unexplained weight loss, skin sores or ulcers, Kaposi’s sarcoma.

  • Treatment:
      - No cure available.
      - Antiretroviral drugs (ARVs) slow the progression of HIV.
      - Highly Active Antiretroviral Therapy (HAART) is crucial for virus management.

Understanding Allergies

  • Allergy: Abnormal immune response to harmless substances known as allergens.

  • The immune system overreacts by producing antibodies to attack these allergens.

  • Allergens may enter the body through:
      - Inhalation
      - Ingestion
      - Injection
      - Skin contact

  • Reactions can be:
      - Localized (e.g., skin rash, itching)
      - Systemic (affecting the entire body).

  • Common allergens include pollen, pet dander, peanuts, and bee stings.

Anaphylaxis

  • Definition: Life-threatening allergic reaction with symptoms such as airway swelling, a drop in blood pressure, and difficulty breathing.

  • Can lead to hypoxia (lack of oxygen) and is potentially fatal without immediate treatment.

  • Symptoms: Difficulty breathing, throat swelling, hives, dizziness, and nausea.

  • Requires emergency treatment, with epinephrine (EpiPen) crucial to reversing symptoms.

Cancer

  • Definition: A group of diseases characterized by uncontrolled cell growth.

  • Cancer cells grow uncontrollably and do not perform normal functions, utilizing the body's resources at the cost of healthy cells.

  • Can form tumors (masses of tissue) and potentially metastasize (spread) to other body parts.

Causes & Risk Factors of Cancer

  • Causes:
      - Mutations in DNA can lead to abnormal cell division.
      - Exposure to carcinogens that trigger mutations.
      - Activation of oncogenes, which control cell growth.

  • Risk Factors:
      - Suppressed immune system.
      - Exposure to radiation, tobacco, or environmental toxins.
      - Stressors from the environment.
      - Some viruses linked to cancer.

Symptoms of Cancer

  • Vary by type but may include:
      - Unexplained weight loss
      - Fever and fatigue
      - Lumps or swelling (in breast, prostate, uterus)
      - Shortness of breath (lung cancer) or hoarseness (throat cancer).

Stages of Cancer

  • Stage 0: Very early stage; cancer cells are few and haven't spread.

  • Stage I: Cancer grows deeper into tissues, may start spreading.

  • Stage II: Affects surrounding tissues but stays at the primary site.

  • Stage III: Cancer spreads to nearby tissues or lymph nodes.

  • Stage IV: Cancer has metastasized to other organs beyond the primary site.

  • Stage vs. Grade: Stage shows the extent of spread, while grade indicates the cell abnormality and growth pace.

Cancer Treatments

  • Surgery: Removes tumors and surrounding tissue.

  • Chemotherapy: Drugs slow growth, prevent spread, or kill cancer cells; side effects include nausea, hair loss, weight loss.

  • Radiation Therapy: Destroys cancer cells using high-energy rays.

  • Immunotherapy: Boosts immune system's ability to target cancer cells.

  • Treatment decisions depend on:
      - Type of cancer.
      - Stage and spread of disease.
      - Patient’s overall health.

Chronic Fatigue Syndrome (CFS)

  • Definition: Persistent fatigue not relieved by rest or sleep can last for months.

  • Cause: Unknown; believed to relate to various pre-existing or undiagnosed conditions.

  • Symptoms:
      - Severe fatigue lasting 6+ months
      - Low energy, feelings of depression or anxiety
      - Sleep disorders, flu-like symptoms (e.g., muscle aches, low-grade fever).

  • Treatment: Includes medications for depression/anxiety, sleep evaluation, a healthy diet and exercise, rest, and education on active participation in treatment.

Infectious Mononucleosis (Mono)

  • Definition: Viral infection caused by an increase in mononuclear WBCs, often spread through saliva, also known as the "kissing disease."

  • Cause: Epstein-Barr Virus (EBV), part of the Herpes virus family.

  • Symptoms:
      - Fever, fatigue, sore throat.
      - Night sweats, muscle weakness, headaches.
      - Swollen glands, spleen, and sometimes liver.

Treatment for Mono

  • No cure; symptoms are managed:
      - Pain relief (analgesics) and fever reducers (antipyretics).
      - Corticosteroids may be needed for severe throat swelling.
      - Rest and recovery can take weeks to months; untreated cases may lead to hepatitis or spleen enlargement.

Lymphedema

  • Definition: Occurs due to a damaged or dysfunctional lymphatic system, leading to fluid buildup and swelling.

  • Types:
      - Primary Lymphedema: Inherited and develops in stages.
      - Secondary Lymphedema: Caused by damage to the lymphatic system (e.g., surgery, radiation, infection, or injury).

Causes of Lymphedema

  • Developmental issues in the lymphatic system.

  • Damage from infections, injuries, or burns affecting lymph nodes.

  • Cancer treatments, including radiation or surgical removal of lymph nodes.

Treatments for Lymphedema

  • Management options (no cure):
      - Exercise to promote lymph fluid movement.
      - Compression therapy using stockings and bandages.
      - Massage to encourage lymph drainage.
      - Complete Decongestive Therapy (CDT) combines various treatments for best results.

Rheumatoid Arthritis (RA)

  • Definition: Chronic autoimmune disease characterized by the immune system attacking joint tissues, leading to pain and degeneration.

  • Causes: No known specific cause; family history increases risk significantly (4x).

  • Effects:
      - Severe pain and joint damage.
      - Reduced quality of life and potentially shorter life expectancy.

  • Treatment:
      - Anti-inflammatory medications for pain and swelling.
      - Rest and exercise to maintain joint function.
      - Disease-modifying antirheumatic drugs (DMARDs) need regular blood work due to potential severe side effects.

Systemic Lupus Erythematosus (SLE)

  • Definition: Autoimmune disease primarily affecting women, causing abnormal antibodies that attack own tissues.

  • Causes & Risk Factors:
      - Genetic predisposition increases risk especially with close family members affected;
      - Symptoms may mimic other diseases, complicating diagnosis.

  • Symptoms:
      - Joint pain and swelling.
      - Fatigue, fever, chills, headaches.
      - Skin issues: Hair loss, mouth sores, sensitivity to light, raised scaly rashes.

  • Management & Treatment:
      - No cure; chronic lifelong condition requiring control of immune response through medication (e.g., corticosteroids).
      - Periods of remission and relapse are common.