Chapters 7.1-7.5 Definitions

Lymphatic system

Returns excess interstitial fluid to blood and supports immunity

Immune system

Detects and destroys pathogens

Lymph

Interstitial fluid inside lymphatic vessels

Lacteals

Lymphatic capillaries that absorb dietary fats

Chyle

Lipid-rich lymph from intestines

Lymphedema

Swelling due to impaired lymph drainage

Thoracic duct

Drains most body lymph into left subclavian vein

Right lymphatic duct

Drains right upper body lymph

Lymph nodes

Filter lymph and activate immune cells

Primary lymphoid organs

Bone marrow and thymus

Barrier defences

Prevent pathogen entry

Skin barrier

Physical barrier of keratinised cells

Lysozyme

Enzyme that destroys bacterial cell walls

Mucus

Traps pathogens

Cilia

Move mucus and trapped microbes

Innate immunity

Rapid, non-specific immune response

Adaptive immunity

Specific immune response with memory

Phagocytosis

Engulfment and destruction of pathogens

Macrophages

Tissue phagocytes

Neutrophils

Fast-acting blood phagocytes

Monocytes

Precursors to macrophages

Natural killer (NK) cells

Kill infected or cancer cells

Pattern recognition receptors

Detect pathogen patterns

Cytokines

Immune signalling molecules

Chemokines

Attract immune cells

Interferons

Antiviral proteins

Complement system

Plasma proteins that enhance immunity

Inflammation

Redness, heat, swelling, pain, loss of function

Antigen

Molecule that triggers adaptive immunity

Epitope

Antigenic determinant

T cell receptor (TCR)

Recognises antigen on MHC

Antigen presentation

Display of antigen on MHC

MHC class I

Presents intracellular antigens

MHC class II

Presents extracellular antigens

Antigen-presenting cells

Macrophages, dendritic cells, B cells

Helper T cells (CD4⁺)

Activate immune cells

Cytotoxic T cells (CD8⁺)

Kill infected cells

Regulatory T cells

Suppress immune responses

Memory T cells

Provide long-term protection

Naïve T cell

Mature but unexposed T cell

Thymus

T cell maturation site

B cells

Produce antibodies

Plasma cells

Secrete antibodies

Memory B cells

Long-term antibody immunity

Central tolerance

Removal of self-reactive lymphocytes

Clonal selection

Expansion of antigen-specific lymphocytes

Humoral immunity

Antibody-mediated immunity

Antibody (immunoglobulin)

Binds antigens

Heavy chains

Large antibody chains

Light chains

Small antibody chains

Fc region

Constant region binding immune cells

IgM

First antibody produced

IgG

Main blood antibody and memory response

IgA

Secretions and breast milk antibody

IgE

Allergy and parasite antibody

IgD

B cell receptor antibody

Class switching

Change antibody class without changing specificity

Primary immune response

Slow first response

Secondary immune response

Faster stronger response

Opsonisation

Tagging pathogens for phagocytosis

Neutralisation

Blocking pathogen attachment

Mucosal immunity

Immunity at mucous membranes

M cells

Sample intestinal antigens

Seroconversion

Rise in antibodies and fall in pathogen load

Bacterial defence

Complement and phagocytosis

Viral defence

Interferons, NK cells, cytotoxic T cells

Parasitic defence

IgE and eosinophils

Fungal defence

Phagocytosis and complement

Antigenic variation

Pathogen changes surface antigens

Immune evasion

Pathogen avoids immune destruction

Hygiene hypothesis

Low pathogen exposure linked to allergies