The Lymphatic System - includes specialized vessels and organs Returns escaped fluids back to blood Monitors fluids for pathogens and mobilizes defenses

Lymphatic Characteristics Not all plasma lost by capillaries returns directly to blood stream Lymph—excess fluid (+ cell debris, viruses, bacteria, cancer cells if present) Lymphatic vessels deliver lymph one-way toward heart ‘milked’ by skeletal muscle Smooth muscle in largest vessels Valves like veins

Lymphatic Capillaries weave between tissue cells and blood capillaries Minivalves let fluid in, but not out

Lymphatic Vessels collect lymph from capillaries Carry lymph to and from lymph nodes Return lymph to veins near heart

Fewer efferent than afferent = slow flow, better filter Lymph Nodes are organs that filter (clean up) lymph, house defense cells Macrophages—engulf and destroy foreign substances Lymphocytes—provide immune response to antigens Fewer efferent than afferent = slow flow, better filter

Participating… Fluid from plasma that does not return directly to the bloodstream in capillary beds is known as ___________ that may also contain pathogens. Lymph __________ may be ‘milked’ like veins by skeletal muscle. Lymph __________ filter the lymph slowly because ________ vessels enter than exit each one. lymph vessels nodes more

Other Lymphoid Organs don’t filter lymph, but do maintain lymphocytes for defense Spleen – filters, stores, and recycles blood Thymus – programs lymphocytes for immune functions Tonsils – filters mucus in throat Peyer’s patches – filters mucus of intestinal lining

Body Defenses and the Immune System Body in constant contact with bacteria, fungi, and viruses 2 defense systems Innate (nonspecific) defense system – responds immediately to various invaders Adaptive (specific) defense system – delayed response to specific invaders Both work in concert

Immune System Pathogens = any harmful or disease-causing microorganism Figure 12.6

Innate Body Defenses Table 12.1 (1 of 2)

First Line of Defense = Surface Membrane Barriers Skin and mucous membranes Physical barriers – pathogens can’t get through

Skin and mucous membranes also fight with chemicals Acidic pH of skin, vaginal secretions, and stomach kill or inhibit bacteria Sebum contains antibiotics Lysozymes in saliva and lacrimal fluid Digestive enzymes of stomach Mucus in respiratory and digestive systems

Second Line of Defense = Internal Cells and Chemicals (still innate defenses) Phagocytes (like neutrophils, macrophages) Engulf (phagocytize) foreign material into a vacuole Digest with lysosomes

Second Line of Defense = Internal Cells and Chemicals (still innate defenses) Natural killer (NK) cells – release deadly chemicals against ‘non-self’ cells Can kill cancer cells and virus-infected cells

WBCs – neutrophils, macrophages Second Line of Defense = Internal Cells and Chemicals (still innate defenses) Inflammatory response Triggered by tissue damage Chemicals (like histamine) released Dilate blood vessels Attract WBCs Clot forms Helps protect and heal Pathogens trapped and killed by WBCs Repair begins WBCs – neutrophils, macrophages

Second Line of Defense = Internal Cells and Chemicals (still innate defenses) Antimicrobial proteins Interferon – given off by infected cells as a warning Prevents viral replication (among other things) Complement proteins – pierce and lyse invaders

Second Line of Defense = Internal Cells and Chemicals (still innate defenses) Fever Hypothalamus reset by pyrogens (secreted by WBCs) Inhibits bacterial growth and speeds tissue repair

Summary of Nonspecific Body Defenses Table 12.1 (2 of 2)

Participating… Which of the following are part of the internal defenses of the innate immune system? A. Phagocytes B. Natural killer cells C. Inflammatory response D. Antimicrobial proteins E. Fever F. Mucus membranes

Third Line of Defense = Adaptive Defense System Third Line of Defense = Adaptive Defense System responds to specific pathogens Antigen specific—identifies pathogen-specific ‘nonself’ antigens (proteins, nucleic acids, pollen, microbes, etc.) Systemic—pathogen can be identified anywhere in the body Memory—subsequent exposure = quick & strong response

Adaptive Defense System: Third Line of Defense Humoral immunity = antibody-mediated immunity Big proteins (antibodies) in body fluids trap pathogens Cellular immunity = cell-mediated immunity Living immune cells attack virus-infected cells, cancer cells, and cells of foreign grafts

Cells of Adaptive Defense Lymphocytes respond to specific antigens B lymphocytes (B cells) – ‘mature’ in Bone marrow; make antibodies T lymphocytes (T cells) – ‘mature’ in Thymus; help B cells and attack nonself antigen cells Macrophages – eat invaders and present foreign antigens to T cells among other functions. ‘mature’ = become immunocompetent, i.e. capable of binding with antigens

B cells inhabit lymph nodes ‘awaiting’ their antigen Antigen binding to specific B cell in lymph node The Chosen One! B cells only bind directly with ‘free’ antigens = small viruses and toxins Figure 12.12, step 1

Humoral Immune Response Antigen Antigen binding to specific B cell in lymph node ‘Chosen’ B cell rapidly divides into clone army B lymphoblasts Figure 12.12, step 2

2 types of B cells are produced from clones… Primary Response (initial encounter with antigen) Antigen Antigen binding to specific B cell in lymph node 1. Plasma cells make antibodies 2. Memory B cells Primary Exposure – Peak antibody levels in 10 days Figure 12.12, step 3

Because of memory cells, secondary response is fast and massive! Primary Response (initial encounter with antigen) Antigen Proliferation to form a clone Plasma cells Subsequent challenge by same antigen Memory B cell Memory B cells Secreted antibody molecules Secondary Response (can be years later) 2-3 day peak at much higher levels! Figure 12.12

Have you had your flu shot? … me neither Vaccines eliminate slow primary response! Figure 12.13

Participating… Humoral immunity relies on the production of ______________ by B-cells. B-cells are activated by binding with free ___________ present in the lymph. Memory B-cells protect against secondary infections. How does a secondary response to infection compare with the primary response? antibodies antigens Faster and Stronger! Primary Response (initial encounter with antigen) Antigen Plasma cells Memory B cell Memory B cells Secondary Response (can be years later)

Immunoglobin (antibody) Classes Table 12.2

Antibody Function Figure 12.16

Cellular (Cell-Mediated) Immune Response Unlike B cells, antigens must be ‘presented’ by macrophages to activate T cells

Cellular (Cell-Mediated) Immune Response T cells cloned like B cells, but T cell clones = Cytotoxic (killer) T cells – bind and kill cells with toxic chemicals Helper T cells – recruit other immune cells Prod B cells to make antibodies (among others) Memory T cells, too!

Cytotoxic (killer) T cells release perforins that puncture cell membranes…ouch! Figure 12.18

Participating… In the cellular immune response, ___________ are activated by ______________ that present antigens from digested pathogens. As a result, _________ T-cells are generated that attack infected or pathogenic cells and _________ are stimulated to make antibodies. T-cells macrophages cytotoxic B-cells

Summary of Adaptive Immune Response Figure 12.19

Summary of Adaptive Immune Response Figure 12.19 (1 of 2)

Summary of Adaptive Immune Response Figure 12.19 (2 of 2)