THE LYMPHATIC SYSTEM

The Lymphatic System

Two Semi-Independent Parts1. Lymphatics (vessels)

Collects leaked plasma & proteins from bloodstream (lymph)

One way flow toward heart Minivalves

2. Lymphoid tissues & organs Immune functions

Lymph Nodes

Contain macrophages to digest bacteria

Contain lymphocytes B cells that generate

plasma cells (antibody-releasing cells)

T cells that destroy tumor cells

More afferent than efferent vessels

Lymphoid Organs

Spleen – filters worn erythrocytes, bacteria, viruses, & other debris

Thymus – Releases hormone thymosin during childhood to help T lymphocytes mature

Tonsils – Trap foreign pathogens entering throat

Peyer’s patches – capture & destroy bacteria in the small intestine

The Immune System

Two Types of Resistance:1. Nonspecific Resistance

General protection against many pathogens Immediate Present since birth (inherited)

2. Specific Resistance Develops in response to

contact with specific invaders

First Line of Defense: Barriers

Physical Barriers: Skin Hairs Mucous

Membranes Digestive Respiratory Urinary Reproductive

Cilia

First Line of Defense: Barriers

Chemical Barriers Acid secretions –

skin, vagina, stomach; kill bacteria

Sebum – oil of skin; toxic to bacteria

Lysozyme – enzymes in tears, saliva, and urine that destroys bacteria

Second Line of Defense: Cells

Nonspecific; Attack pathogens but don’t “remember” for next time.

Phagocytes – perform phagocytosis Neutrophils – first to enter infected tissues; kill

bacteria Macrophages – slower; BIG eaters

Second Line of Defense: Cells

Natural Killer Cells (Killer T cells) – Kills cancer cells Kills virus-infected body cells Lyses cell with perforin

Second Line of Defense: Inflammatory Response Triggered when tissues are injured Four Signs:

Redness Heat Swelling Pain

Second Line of Defense: Inflammatory Response

First Step: Alarm Injured cells release histamine & kinins causing:

Vasodilation – increases blood flow Leaky capillaries – causes edema Activated pain receptors – forces rest Chemotaxis – chemical gradient attracts

phagocytes and other white blood cells

Second Line of Defense: Inflammatory Response One hour later:

Neutrophils perform diapedesis and start clean-up

8-12 hours later: Monocytes become macrophages!

Second Line of Defense: Inflammatory Response Prevents the spread of infection Disposes of cell debris & pathogens Sets the stage for repair and healing

Second Line of Defense: Antimicrobial Chemicals Interferon –

protein released by virus-infected cells to prevent neighboring cells from reproducing new viruses

Urine

Second Line of Defense: Antimicrobial Chemicals Complement System

At least twenty proteins always circulating Activated by foreign antigens Release chemicals:

Vasodilators Chemotaxis Opsonization – cause foreign cell

membranes to become sticky (and yummy)

Second Line of Defense: Fever

White blood cells secrete pyrogens

Triggers hypothalamus to raise body temperature

Inhibits bacterial growth Stimulates phagocytosis Causes liver & spleen to store

iron, reducing availability for bacteria

Third Line of Defense: The Immune System Two parts (working simultaneously):

Humoral Immunity – (antibody-mediated), antibodies present in the body fluids

Cellular Immunity – (cell-mediated), lymphocytes defend the body

Specific Systemic Has memory

Overview: Antigens

Nonself antigens Self antigens – MHC

(major histocompatibility) complex

Overview: Antibodies

AKA immunoglobulins (Igs) Bind to specific antigen Inactivates by:

Activating complement proteins = cell lysis Binds to toxic secretions, rendering them

harmless Agglutination Causes precipitation of soluble antigens

Effects of Antibodies

Cell Overview: Lymphocytes

Formed from hemocytoblasts in bone marrow Mature by gaining immunocompetence (ability

to respond to specific antigen) In Bone marrow = B cells In Thymus = T cells

Cell Overview: Macrophages

Antigen Presentation – present fragments of the antigens they’ve eaten on cell surface, for T cells to recognize

Secrete monokines, that further activate T cells

Primary Humoral Response

Antigen binds to immature B lymphocyte causing clonal selection

Helper T cells activate B cells B cell makes clones!

Plasma cells (most) Make antibodies

Memory cells (few) Remember invader for

faster response in future

Clonal Selection/T cell activation

B cell cloning/Antibody Production

Secondary Humoral Response

Achieved by memory B Cells in response to the old antigen

Faster More prolonged More effective

Active Immunity

Active immunity – activation of B Cells Naturally – bacterial or viral infection Artificially – vaccine

Spared threat of the disease Still primes immune system for secondary response

Passive Immunity

Passive immunity – antibodies are transferred into the body\ Naturally – from mother to baby

through placenta or breastmilk Artificially – antivenin (snake bites),

antitoxin (botulism, rabies, tetanus) B cells are not challenged by

antigen Immunological memory does not

occur

Cellular Immune Response: Helper T cells Recruit other immune cells to join fight Cannot recognize free-floating antigen Macrophages present antigens: double

recognition (self & non-self)

Cellular Immune Response: Helper T cells Activation of Helper T cells:

Stimulates B cells & Killer T cells to grow/divide Attracts other white blood cells to area Enhances macrophage ability to eat & destroy Releases lymphokines – chemicals that help

destroy antigens

Cellular Immune Response: Other T cells Suppressor T Cells – slows

or stops the activity of B and T cells once the infection has been conquered

Memory T Cells – same as memory B cells

Killer T Cells (cytotoxic T cells)