Body Systems - Lecture 11

Immune System

What is Immunity?

  • Immunity is the body's resistance to infection, including:

    • Viral invasions

    • Bacterial invasions

    • Fungal invasions

    • Protozoan invasions

Types of Defense: Specific vs. Nonspecific

  • Innate Nonspecific Immune System:

    • First and second lines of defense.

    • Lines of defense:

      1. Skin

      2. Bacteriostats (fluids)

      3. Cilia

      4. Mucus membranes

  • Cell-mediated responses:

    • Phagocytic cells (macrophages) surround and destroy any foreign matter, causing inflammation.

  • Inflammation:

    • Response to tissue damage, causing redness (due to red blood cells), swelling, and warmth at the site.

    • Increase in cells and fluids.

    • White blood cells (WBCs) rush to the site.

  • Fever:

    • An important defense mechanism.

Lymphocytes (WBCs)

  • Made in the bone marrow.

  • Travel in blood and lymph or stay in lymph organs (nodes, tonsils, spleen).

  • Two types:

    • B lymphocytes.

    • T lymphocytes.

  • Responsible for specific immunity.

B Cells

  • Mature in bone marrow and produce antibodies.

  • Contain protein markers to bind specific antigens.

  • Plasma cells and memory cells are produced.

Lymphatic System

  • Components:

    • Right lymphatic duct

    • Adenoids

    • Tonsil

    • Thoracic duct

    • Left subclavian vein

    • Thymus

    • Lymph nodes

    • Large intestine

    • Appendix

    • Spleen

    • Peyer's patches

    • Small intestine

    • Bone marrow

Lines of Defense

  • First line:

    • Mechanical barriers

    • Chemical barriers

  • Second line:

    • Inflammation response

    • Phagocytosis

    • Natural killer cells

  • Third line:

    • Specific immune responses

    • T cells and antibodies

B Cells and Antibodies

  • Once the immune system makes antibodies, the body can quickly respond to the same antigen upon second exposure.

  • Vaccines are based on this principle.

  • Each antibody has a specific antigen-binding site to attach to the invader.

Antibody-Mediated Immunity

  • Produced by plasma cells to bind to antigens, causing clumping.

  • Macrophages then destroy the antigens.

  • Antibodies surround the virus, preventing reproduction or transport throughout the body.

Antibody Functions

  • Antibodies are found in serum, lymph, and on the surfaces of B cells.

  • Antibodies bound to antigens can kill antigens by:

    • Activating the complement system (series of serum proteins).

    • Attracting phagocytes to destroy antigens.

    • Aggregating (clumping) with antigens in the membrane, forming a hole for fluid to rush in and lyse (burst) the microbe.

Primary and Secondary Immune Responses

  • Primary immune response:

    • Antigen exposure causes rapid division of plasma cells into antibodies.

    • Takes 7-14 days for maximum antibody production.

    • Many stimulated B cells become memory cells.

  • Secondary immune response:

    • Re-exposure to the same antigen.

    • Memory cells make antibodies in 2-6 days.

T Cells

  • Mature in the thymus and divide into three types:

    • Killer T cells: Kill antigen for cell-mediated immunity; also kill tumor cells.

    • Helper T cells: Interact with B cells to make antibodies.

    • Suppressor T cells: Interact with B cells to stop antibody production when enough antibodies are made.

  • Identical descendants of lymphocytes are clones, each having specific antigen-binding receptors.

  • Only the specific clone of the antibody will be stimulated to divide after exposure to the specific antigen.

  • Pathogen: A disease-causing microbe.

Vaccines

  • 1798: Jenner developed the first vaccine by injecting a boy with pus from cowpox to protect him against smallpox.

  • 1860: Pasteur developed the rabies vaccine.

  • Vaccines use dead or weakened microbes to induce specific immunity against the antigen.

    • Examples: polio, MMR, DPT, flu, HiB, Hep B.

  • Some microbes change antigen markers to evade antibodies.

    • Examples: flu, HIV (viruses), TB (bacteria), trypanosome (protist).

Types of Immunity

  • A. Inborn:

    • Resistance to nonhuman diseases.

  • B. Acquired:

    • Resistance developed after birth.

Acquired Immunity Subtypes

  • 1. Passive:

    • Antibody introduced, not in response to antigen; temporary.

      • a. Natural: From mother through the placenta and breast milk.

      • b. Artificial: Injections (e.g., gamma globulin for hepatitis A).

  • 2. Active:

    • Antibody made by the body in response to antigen; more permanent immunity.

      • a. Natural: Antibody made after infection/disease.

      • b. Artificial: Antibody made after vaccine of dead/weak antigen is injected.

Immune System Suppression and Disorders

  • Stress, drugs, HIV suppress immune system reactions.

  • Allergic reactions are caused by hypersensitivity (hyperactive immune response).

  • Autoimmunity: Antibody or T cells bind to "self" cells due to gene susceptibility & environment.

    • Examples: rheumatoid arthritis, Multiple Sclerosis, some cancers.

Allergens

  • Chemically alter HLA, and T cells attack own “foreign” cells, causing inflammation, rash, blisters from histamine release.

  • Can also cause constriction of breathing from blocked airways and death.

Respiratory System

Overview

  • Takes in oxygen from the air and expels carbon dioxide as waste.

  • Lungs are the main structures.

  • Air enters through the nose or mouth, moves down the throat, and passes through the trachea (windpipe) to the lungs.

  • Oxygen is taken into the blood, and carbon dioxide leaves the blood through small tubes called bronchi and tiny air sacs called alveoli.

Inhalation and Exhalation

  • Inhalation:

    • Intercostal muscles contract, lifting the rib cage up and out.

    • Diaphragm contracts and pulls downward.

    • Lungs expand, and air is sucked in.

  • Exhalation:

    • Intercostal muscles relax.

    • Diaphragm relaxes.

    • Ribs fall downward and inward.

    • Diaphragm moves back into a dome shape, squeezing lungs and pushing air out.

Circulatory System

Overview

  • Carries oxygen, nutrients, and waste throughout the body.

  • Composed of the heart, blood vessels, and blood.

  • Closed system – continuous movement.

Blood Flow

  • Blood moves from arteries to capillaries.

  • Arteries carry blood away from the heart.

  • In capillaries, oxygen and nutrients move from the blood to the body's cells.

  • Capillaries allow diffusion of materials in and out of the bloodstream.

    • Nutrients enter (digestion), waste is eliminated (excretory), and movement of air (respiratory).

  • Blood then moves from capillaries to veins.

  • Veins carry blood to the heart.

Structure of the Heart

  • 4 chambers:

    • Right atrium: collects deoxygenated blood from the body.

    • Right ventricle: pumps deoxygenated blood to the lungs.

    • Left atrium: collects oxygenated blood from the lungs.

    • Left ventricle: pumps oxygenated blood to the body.

  • Superior and Inferior vena cava:

    • Largest vein in the body.

    • Brings deoxygenated blood from parts of the body back to the heart.

  • Aorta:

    • Largest artery.

    • Moves oxygenated blood from the heart to the body.

  • Valves:

    • Separate the chambers and vessels.

    • Regulate when blood can enter and leave the chambers and vessels.

  • Pulmonary vein:

    • Brings oxygenated blood from the lungs to the heart.

  • Pulmonary artery:

    • Brings deoxygenated blood from the heart to the lungs.


Phagocytic cells (macrophages) surround and destroy any foreign matter, causing inflammation.