Intro to Life Processes - Chapter 7

All about the lymphatic and immune systems

Lymphatic system

consists of the lymphatic vessels and lymphatic organs

Homeostasis Functions - Lymphatic system

• lymphatic capillaries absorb excess interstitial fluid

• lymphatic capillaries absorb fats from the digestive tract and transport them to the bloodstream

• lymphoid organs help defend the body against disease

Lymphatic vessels

form a one-way system of vessels that move fluid from tissues to the cardiovascular system

Lymph

fluid inside lymphatic vessels

Interstitial fluid

• the primary component of lymph

• mostly water, but also contains solutes (nutrients, electrolytes, and oxygen) derived from blood plasma

• Additionally, interstitial fluid contains cellular products (hormones, enzymes, and cellular waste)

Lymphatic organs

divided into primary and secondary lymphatic organs

Primary Lymphatic Organs

red bone marrow and the thymus

Secondary lymphatic organs

the lymph nodes and the spleen

Red bone marrow

produces all types of blood cells

• children have red bone marrow in most bones

• adults have red bone marrow in the sternum, vertebrae, ribs, pelvic girdle, humerus, femur

• produces red blood cells and five types of white blood cells: neutrophils, eosinophils, basophils, lymphocytes, monocytes

Lymphocytes

divided into B cells and T cells

B cells (B lymphocytes)

mature in the bone marrow

• any B cell that reacts to body cells is destroyed in the bone marrow and does not enter circulation to prevent autoimmune disorders

T cells (T lymphocytes)

mature in the thymus

Thymus

soft-bodied and bilobed organ located in the cavity between the trachea and the sternum which decreases in size as children grow into adulthood

Thymus functions

• produce hormones (like thymosin - aids in the maturation of t lymphocytes)

• maturation site of T lymphocytes: only ~5% of these cells ever leave the thymus

• to leave the thymus, T cells have to demonstrate that they can attack a pathogen and that they will not attack body cells

• without mature T cells, the body cannot adequately respond to specific infections

Spleen

• filters blood

• largest lymphatic organ, located in the upper left part of the abdominal cavity

• within the spleen, macrophages engulf pathogens and debris

Lymph nodes

• occur along lymphatic vessels

• each of their multiple compartments are filled with lymph, and lymphocytes and macrophages (which attack pathogens and cancer cells)

Immunity

the capability of killing or removing foreign substances, pathogens, and cancer cells

• innate (non-specific immunity)

• adaptive immunity

Innate (non-specific) immunity

• include physical and chemical barriers

• serve as a first line of defense against infection by pathogens

Physical Barriers - innate immunity

• skin: prevents the entry of microbes

• mucous membranes: trap invading pathogens

Chemical Barriers - innate immunity

• perspiration, saliva, and tears: contain lysozyme (antibacterial enzyme)

• acidic pH: stomach and vagina

• microbiome: beneficial bacteria in our systems

Inflammatory Response

• second line of defense

• employs neutrophils and macrophages to surround and kill invading pathogens

• symptoms of IR: redness, heat, swelling, pain

• excess fluid from leaky capillaries causes swelling (which presses on nerves) and pain

• these summon white blood cells to the region

• neutrophils are the first WBCs to arrive, and they phagocytize (eat) debris, dead cells, and bacteria

• if neutrophils are overwhelmed, they released cytokines

• monocytes are longer-lived cells that become macrophages

Histamine

a chemical mediator released by damaged tissue cells and mast cells which cause the capillaries to dilate and become more permeable

Cytokines

proteins that attract more WBCs, including monocytes

Macrophages

more powerful phagocytes than neutrophils

Complement system

composed by a number of blood plasma proteins that increased the immune response of one or more specific immune responses

Complement proteins can…

• trigger mast cells to release histamine

• attract phagocytes to a specific location

• bind directly to bacteria can cause them to burst

Interferons

proteins produced by virus-infected cells that cause uninfected cells to prepare for viral infection by producing substance that interfere with viral replication

Antigen

a large protein structure that the immune system recognizes as a foreign body

Fragments that can be antigenic

bacteria, viruses, molds, parasitic worms

Adaptive defenses

primarily depend on B and T cells (B and T lymphocytes)

• each lymphocyte has a single kind of receptor to combine with a specific antigen (like a lock and key)

Adaptive Immunity Pathways

cell-mediated immunity and antibody-mediated (humoral) immunity

Cell-mediated immunity

T-cells target and destroy any cells that present a specific antigen

• helper t cells may come into contact with an antigen and release cytokines to call cytotoxic T cells to the area

• cytotoxic t cells either phagocytize or trigger apoptosis in infected cells

Antibody-mediated (humoral) immunity

an antigen binds with a B cell’s receptor

• the B cell then undergoes rapid clonal expansion, creating B memory cells, and plasma cells

• the plasma cells created secrete antibodies for the original antigen

Antibody Structure

Y-shaped with two antigen binding sites

Antibody function

many antibodies will bind with the antigens, covering the offending molecule so that it can’t bind

• antibodies then call for other white blood cells

Antibody classes

IgG, IgM, IgA, IgD, IgE

IgG

• main antibody type in circulation

• crosses the placenta from mother to fetus

• binds to pathogens

• activates compliments

• enhances phagocytosis by WBCs

IgM

• found in circulation

• largest antibody

• first antibody formed by newborns

• first antibody formed in any new infection

• activates compliment and clumps cells

IgA

• main antibody in saliva and breast milk

• prevents pathogens from attaching to epithelial cells in the digestive and respiratory tracts

IgD

• antibody found on the surface of immature B cells

• signifies readiness of B cells

IgE

• antibody found as antigen receptors on mast cells

• responsible for immediate allergic response and protection against certain parasitic worms

Cytotoxic T Cells

specialized T lymphocytes with storage vacuoles that contain perforins and storage vacuoles that contain granzymes

Granzymes

an enzyme that causes apoptosis

Helper T cells

specialized T lymphocytes that regulate immunity by secreting cytokines

• B lymphocytes cannot be activated without T cell help

• HIV (which causes AIDS) attacks T cells, which leaves patients vulnerable to opportunistic infections, which may eventually cause death

Memory T cells

remain within the body and can jump-start an immune response to an antigen previously present in the body

Active immunity

occurs when an individual produces antibodies against an antigen

• develops naturally after a person is infected with a pathogen

• can be artificially developed by exposure to the antigen

Passive immunity

occurs when an individual is given prepared antibodies via an injection

• commonly achieved in infants from IgG antibodies that have crossed the placenta from their mother

Immunization

involves the use of vaccines to expose the immune system to the antigen

• part of active immunity

Vaccine

substances that contain an antigen to which the immune system responds

AIDS

• acquired immunodeficiency syndrome

• inability of the acquired immune system to respond to opportunistic pathogens because of a low helper T cell count; caused by HIV

HIV

• human immunodeficiency virus

• virus that infects and destroys T helper cells and macrophages; causes AIDS if untreated

Opportunistic infection

an infection that can only occur because the patient’s immune system is compromised

Allergies

a hypersensitivity to a substance, like pollen, food, animal hair, or mold, that would ordinarily do no harm to the body

Allergen

an antigen that elicits an allergic response

Immediate allergic response

• response within seconds to be exposed to an allergen

• caused by IgE antibodies attached to receptors on mast cells and basophils

Anaphylactic shock

• an immediate allergic response that occurs when an antigen enters the bloodstream

• characterized by a life-threatening sudden drop in blood pressure due to the increased permeability of capillaries in the response to a flood of histamine

• often treated with epinephrine

Delayed allergic response

immune response initiated by T cells at the site where an allergen contacts the body

• used to test for tuberculosis (TB)

SCID

• severe combined immunodeficiency disease

• characterized by both the antibody and cell-mediated immune responses being either inadequate or lacking

• has been successfully treated with bone marrow transplant and or gene therapy

Autoimmune Disease

• occurs when cytotoxic T cells or antibodies attack the body’s own tissues

• exact cause is unknown, but it appears to have both genetic and environmental components

• women more likely to develop autoimmune disorders than men

Rheumatic fever

antibodies introduced into throat to fight the streptococcal infection also react with the heart muscle

• causes an inflammatory response in the heart that damages the heart muscle and valves

Rheumatoid arthritis

causes chronically inflamed joints

• antibodies, compliments, neutrophils, activated T cells, and macrophages all attack the cartilage of the joints

SLE

• systemic lupus erythematosus

• various symptoms including facial rash, fever, and joint pain

• patients produce high levels of anti-DNA antibodies, which interferes with tissues throughout the body

• damage to the central nervous system, heart, and kidneys can be fatal

Myasthenia gravis

antibodies attach to muscle cells

• causes muscle weakness and eventual death from respiratory failure