6: The Immune System Flashcards
what is the lymphatic system
comprised of several organs and tissues: lymphatic tissue, bone marrow, lymph, lymphatic vessels
protects us against disease
lymphoid cells respond to environmental pathogens, toxins, abnormal body cells such as cancers
pathogens that cause disease
viruses, bacteria, fungi, parasites
4 parts to lymphatic system
lymph = the fluid, similar to plasma but much less proteins
lymphatic vessels = the lymphatics, carry lymph from peripheral tissue to venous system
lymphoid tissues and organs
lymphoid cells (lymphocytes, phagocytes)
function of the lymphatic system
produce, maintain and distribute lymphocytes
return of fluid and solutes from peripheral tissues to blood
distribution of hormones, nutrients and waste products from tissue or origin to circulation
production and distribution of lymphocytes
lymphatic production occurs in: lymphoid tissues, lymphoid organs and red bone marrow
lymphocyte distribution: travel through lymphatic vessels and capillaries, they detect problems and travel into sites of injury or infection
difference between lymphatic vessels and blood capillaries
lymphatic vessels start as blind pockets rather than tubes
they have larger diameters and thinners walls
flat and irregular in section
lymph trunks and ducts
from the lymphatic vessels, lymph passes through lymph nodes and then into lymph trunks
lymph trunks include the lumbar, intestinal bronchomediastinal, subclavian and jugular trunks
lymph trunks then marge to form either the thoracic duct or the right lymphatic duct
thoracic duct much larger
types of lymphocytes
T cells: thymus-dependent, cell mediated immunity
B cells: bone marrow derived, antibody mediated immunity
NK cells: natural killer cells, also bone marrow derived, immunological surveillance
lymphatic organs and tissues
primary lymphatic organs are where immune cells become immunocompetent: thymus and red bone marrow
secondary lymphatic organs and tissues are where cells do their job of fighting germs and foreign substances: lymph nodes, spleen, lymphoid nodules
lymph nodes
efferent lymphatic vessels take lymph fluid out and away from lymph nodes
afferent lymphatic vessels take fluid into lymph nodes
route: afferent lymphatic vessels, subscapular sinus, trabecular sinus, medullary sinus, efferent lymphatic vessels
lymphoid nodules
no fibrous capsule
in lumen or gut and in tonsils
lymph organs vs lymphoid nodules
lymph organs (the nodes, thymus and spleen) are separated from surrounding tissues by a fibrous capsule
lymphoid nodules are bundles of lymphoid tissue without fibrous capsule e.g. tonsils, appendix
formation and flow of lymph
interstitial fluid: blood plasma is filtered from blood capillaries into interstitial spaces to become interstitial fluid
lymphatic capillaries: absorb interstitial fluid (now called lymph) and pass lymph to afferent lymphatic vessels
afferent vessels: carry lymph from capillaries to nodes
lymph nodes: remove foreign substances through filtering lymph, phagocytosis and immune reactions
efferent lymphatic vessels: carry lymph from nodes
valves: ensure one way flow of lymph
lymphatic vessels: pass lymph to lymphatic ducts
ducts: empty lymph into the junction of jugular and subclavian veins of the CV system
lymph node circulation
flows through lymph node in a network of sinuses
- from subscapular space: contains macrophages and dendritic cells
- through outer cortex: contains B cells within germinal centres
- through deep cortex: dominated by T cells
- through the core medulla: contains B cells and plasma cells, organised into medullary cords
- finally into hilum and efferent lymphatics
lymph node functions
a filter to purify lymph before it returns to venous circulation
removes debris, pathogens, 99% of antigens
lymph node distribution
lymph nodes of gut, trachea, lungs and thoracic duct - protect against pathogens in digestive and respiratory systems
lymph nodes in glands - groin and base of neck, swell in response to inflammation
lymphadenopathy = chronic or excessive enlargement of lymph nodes may indicate infections, endocrine disorders of cancer
innate vs adaptive immune responses
innate = non-specific immune defences, born with it, doesn’t change, block or attack any potential pathogen, present from birth, no memory
adaptive = specific immune responses, adapts and changes, specific to particular pathogens, identify attack and develop immunity to specific antigen, acquired in response to antigens
there are 7 non-specific defences
- physical barriers
prevent approach of and deny access to pathogens
respiratory tract - mucus
eyes - tears contain antibodies and lysozyme enzyme
skin - barrier, sweat, sebum
digestive tract - acidity, low pH, enzymes
genitourinary tract - urine acidity, lysozyme
- phagocytic cells
remove debris and pathogens
microphages: neutrophils and eosinophils, leave the bloodstream, enter peripheral tissues to fight infections
macrophages: large phagocytic cells derived from monocytes, distributed through whole body, make up monocyte-macrophage system, may be fixed or free
activated macrophages respond to pathogens in several ways - engulf and destroy them with lysosome, bind to pathogen so other cells destroy it, or release toxic chemicals into interstitial fluid
- immunological surveillance (NK cells)
destroy abnormal cells
when recognising and binding to abnormal cells, NK cells line up their Golgi apparatus and secrete perforin
creates pores and perforates surface of target cells so it burst
- interferons (antiviral)
increase resistance of cells to viral infection
slows spread of disease
non-specific response to viral infection
interferons = proteins (cytokines) released by activated lymphocytes and macrophages
alpha-interferons = produced by leukocytes, stimulate NK cells
beta-interferons = secreted by fibrocytes, slow inflammation
gamma-interferons = secreted by T cells and NK cells, stimulate macrophage activity
- complement system
attacks and breaks down cell walls, attracts phagocytes, stimulates inflammation
enhances ability of antibodies and phagocytic cells to clear pathogens from an organism
11 complement proteins named C1 to C11
complement antibody action
a chain reaction
2 pathways of activation: classical (fast) or alternative (slow)
conversion of inactive protein C3 to C3b
forms pores in bacterial cell wall causing destruction of bacteria (MAC = membrane attack complex)
effects of complement activation: attraction of phagocytes, enhancement of phagocytosis by opsonization, stimulation of inflammation, destruction of target cell membrane (MAC)
- inflammation
numerous effects:
increased blood flow
mast cells in local tissue release histamine
phagocytes (neutrophils) move to site
neutrophils remove debris
activation of fibrinogen
all leads to tissue repair
- fever
mobilises defences, accelerates repairs, inhibits pathogens
increase in body temp due to release of pyrogens
pyrogen = any material that causes the hypothalamus to raise body temp
specific immunity
specific immunity is acquired upon exposure to specific antigens, creating memory, specificity and tolerance
cell mediated immunity = T cells only recognise fragments of antigenic proteins that are processed and presented in a certain way
humoral (antibody-mediated) immunity = B cells can recognise and bind to antigens in lymph, interstitial fluid or blood plasma
MHC proteins (major histocompatibility complex)
used to distinguish self and non-self
class I: on all nucleated cells (one tether to surface of cell)
class II: on antigen-presenting cells (APCs) and lymphocytes (two tethers to surface of cell)
recognition of infection
the specific immune repones operates by recognising foreign antigens either
- free living (exogenous)
- inside host cells (endogenous)
antigen expression vs antigen presentation
antigen expression: via class I MHC proteins on cell membrane of infected somatic cells
antigen presentation: via class II MHC proteins on the cells involved with specific immunity (APCs and lymphocytes)
types of T cells
cytotoxic T cells: cell mediated immunity, destroys virally infected cells, T cell receptor binds to antigen held by MHC I with help of CD8 and helper T cell, clonal selection takes place
helper T cells: stimulate function of T and B cells, T cell receptor binds to antigen held by MHC II with help of CD4 protein, helper cell becomes active and can go through clonal selection
suppressor (or regulatory) T cells: inhibit function of T cells and B cells
how killer T cells work
- cytotoxic T cell releases granzymes that cause apoptosis (burst) of infected cell, released microbes are destroyed by phagocyte
- cytotoxic T cell releases perforins that cause cytolysis, microbes destroyed by granulysin
cell mediated response
- antigen is engulfed and presented by a macrophage
- undifferentiated T cells with specific receptors recognise the antigen
- cytotoxic T cells migrate to focus on infection
- T cells differentiate into cytotoxic T cells and memory cells
- several stages of mitosis occur
- cytotoxic T cells release perforin and/or lymphotoxin
humoral immunity
mediated by B cells
attack antigens by producing specific antibodies
5 types of antibodies
antibody has variable segment at end and constant segment in middle
5 types of antibodies
IgG = most common, accounts for 80% of all antibodies, placental transfer at birth
IgA = glandular secretions e.g. mucus, salvia, breastmilk, tears
IgM = first set of antibodies to be produced in response to infection
IgD = on surface of B cells as antigen receptors
IgE = involved in hypersensitivity
forms of immunity
immunity - respond to threats on an individualised basis
innate = no prior exposure or antibody production needed
acquired = produced by prior exposure or antibody production
passive = transfer of antibody from another person (natural i.e. mum or induced i.e. injection)
active = produced by antibodies that develop in response to antigens (induced i.e. injection of antigens, or natural i.e. after exposure)
immunopathology = what happens when the immune system goes wrong
allergy = overly reactive to substance that is well-tolerated by most others, tissue damage occurs, hypersensitivity, too much IgE
autoimmune disease = immune system fails to display self-tolerance and instead attacks own body tisssues
transplant rejection = body recognises organ/tissue as non-self and mounts immune response, usually treated with immunosuppressants
disease of immune system = SCID (severe combined immunodeficiency syndrome), HIV turns to AIDs
immunopathology = what happens when the immune system goes wrong
allergy = overly reactive to substance that is well-tolerated by most others, tissue damage occurs, hypersensitivity, too much IgE
autoimmune disease = immune system fails to display self-tolerance and instead attacks own body tisssues
transplant rejection = body recognises organ/tissue as non-self and mounts immune response, usually treated with immunosuppressants
disease of immune system = SCID (severe combined immunodeficiency syndrome), HIV turns to AIDs
