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)