Immune System Flashcards
What are the 3 functions of the immune system?
- Scavenge dead, dying body cells
- Destroy abnormal cells
- Protect from pathogen and foreign molecules
Describe the skin
- Largest organ in the body
- pH = 5.6-6.4
- pH of 3-5 cause by oil/sweat inhibits growth of many microorganisms and prevents excessive water loss
What are the 3 layers of skin?
- Epidermis - hard and tough stratified squamous epithelium
- Dermis - dense connective tissue
- Hypodermis - lies below these 2 regions and is made of subcutaneous and adipose tissue
What are the 4 types of cell in the epidermis?
- Keratinocytes - produce keratin to make skin tough - resistant to weak acids and bases, bacterial enzymes and toxins
- Melanocytes - produce melanin to absorb sunlight (cause pigmentation)
- Merkel Cells - touch receptors
- Tactile (Dendritic) Cells - antigen-presenting
What are the 5 layers of the epidermis?
- Stratum Corneum (OUTER)
- Stratum Lucidum
- Stratum Granulosum
- Stratum Spinosum
- Stratum Basale (INNER)
Describe the Stratum Corneum
- Contains 20-30 layers of dead cells that account for 3/4 of epidermis thickness
- Flat membranous sacs filled with keratin that protect the skin from abrasion and penetration
- Glycolipids in extracellular space to provide a waterproof coating
Describe the Stratum Lucidum
- Thin and translucent
- Considered to be a subdivision of the superficial Stratum Corneum
- Consistsof 2/3 rows of clear, flat, dead keratinocytes with indistinct boundaries
Describe the Stratum Granulosum
- 4-6 layers of flattened cells with organelles deteriorating as a result of keratinisation
- Cytoplasm is full of lamellar granules which is a major factor in slowing water loss across the epidermis
- Keratohyaline granules help form keratin in the upper layers
Describe the Stratum Spinosum
- Several layers thick
- Cells contain thick bundles of intermediate filaments made of pre-keratin
Describe the Stratum Basale
- Attached to the dermis
- Consists of 1 row of actively mitotic stem cells
Describe the dermis
- 15-40 x thicker than the epidermis
- Provides structural support for the epidermis
- Contains matrix of blood vessels, nerve endings, muscles etc
- Wrinkling takes place in the dermis
What are the 2 layers of the dermis?
- Papillary - has dermal papillae (peg-like projections containing pain receptors, touch receptors and/or capillary loops that provide nutrients)
- Reticular - dense, irregular connective tissue, blood vessels, sweat glands and lamellar corpuscles
Describe skin pigmentation
- Skin colour reflects amount of pigments (melanin and carotene) in the skin and oxygenation of Hb
- Melanin produced by melanocytes
- Production of melanin is stimulated by sunlight exposure
- Protects the skin by absorbing UV radiation
- Skin colour can be affected by emotional state and diseases
Give 2 examples of diseases that affect skin colour
- Jaundice - yellowing of the skin and whites of the eyes caused by a number of diseases (e.g. alcoholic liver disease, gallstones, hepatitis)
- Erythema - redness of skin caused by injury, infection or inflammation
Give 7 ways that the skin protects from pathogens
- Removal of particles by cilia in nasopharynx
- Commensals
- Vaginal acids
- Flushing of urinary tract
- Rapid change in pH of gut
- Mucous lining trachea
- Lysozymes in tears and other secretions
Describe hair
- Produced by hair follicles
- Consist of heavily keratinised cells
- Have a central medulla, cortex, outer cuticle and root and shaft portions
- Hair colour reflects amount and kind of melanin present
- Hair follicles consist of inner epithelial root sheath and outer peripheral connective tissue sheath derived from the dermis
Describe sweat glands
- Called eccrine (merocrine) sweat glands
- Distributed over the entire body surface
- Main function = control body temp
- Sebaceous glands excrete sebum (lubricant to keep skin soft and moist)
What are the 4 main types of microorganisms?
- Bacteria
- Viruses
- Microscopic fungi
- Protectants
What is the function of gram staining?
Differentiates between gram positive and gram negative bacteria
How else can bacteria be classified?
- Heterotrophs - consume organic matter (cause illness by attacking cells)
- Autotrophs - synthesise own organic matter
What are 2 ways that bacteria can harm other cells?
- Damage tissues in affected host
- Release harmful toxins
What is used to cure bacterial infections?
Antibiotics
What are infectious diseases?
Diseases caused by bacteria that can be passed from one person to another
Give 5 ways that bacteria can be passed on
- In air
- Contact with animals
- Contaminated food
- Touch
- Water
Describe viruses
- Noncellular
- Nucleic acid core surrounded by a protein coat
- When viruses infect living cells, they make numerous copies of themselves and can evolve
- In most viral infections, viruses attack and destroy cells in the body, leading to outbreak of disease
What are the 3 main lines of defence?
- Surface barriers (innate)
- Internal defences (innate)
- Adaptive defences
Describe surface barriers
- Intact skin
- Mucous membranes (nasal cavity, saliva etc)
Describe internal defences
- Phagocytes
- Natural killer cells
- Inflammatory response
- Anti-microbial chemicals
- Fever
Describe adaptive defences
Humoral Immunity - antibodies and memory cells
Cellular Immunity - activation of phagocytes, lymphocytes and cytokines
Describe the innate defence system
- Responds within minutes
- Second line of defence (internal defences) gets called into action when first line has been breached
- Non-specific defences
What is the main internal defence?
Inflammation
What is involved in inflammation?
- Macrophages
- Mast cells
- WBC
- Chemicals that kill pathogens and help repair tissue
What are the 2 types of effects of inflammation?
- Local = clearly beneficial (e.g. destruction of invading microorganisms) but at other times appear to serve no function
- Systemic = fever, malaise (feeling ill) and leucocytosis (increased number of WBC)
Give 3 examples of inflammation triggers
- Physical trauma
- Intense heat
- Invasion of viruses
Describe the mechanism of a fever
- Pathogen activate leucocyte release
- This stimulates the hypothalamus to produce prostaglandins which cause a high fever (temp)
What are the 4 stages of inflammation?
- Leucocytosis - neutrophils enter blood from bone marrow
- Margination - neutrophils cling to the capillary wall
- Diapedesis - neutrophils flatten and squeeze out of the capillary wall
- Chemotaxis - neutrophils follow the chemical trail to the injury site
Give 3 beneficial effects of inflammation
- Entry of antibodies
- Fibrin formation (facilitates phagocytosis)
- Stimulates immune response
Give 4 harmful effects of inflammation
- Destruction of normal tissue
- Swelling, heat, redness and pain
- Inappropriate inflammatory response
- Can be temporary limitation of joint movements
What causes swelling, heat, redness and pain during inflammation?
- Vasodilation
- Increased permeability of capillaries
What is the function of phagocytes?
Confront pathogens that get through the skin/mucosa
What are the 5 types of leucocytes?
- Neutrophils (60-70%)
- Lymphocytes (20-30%)
- Monocytes (1-6%)
- Eosinophils (1-3%)
- Basophils (<1%)
Describe neutrophils
- Formed from stem cells
- Initiate inflammation
- Release chemicals to kill cells during phagocytosis
Give 3 types of phagocyte
- WBC
- Macrophage
- Natural Killer Cells
Describe macrophages
- Produced by differentiation of monocytes
- Detect, engulf and destroy pathogens and apoptic cells
- Can be free or fixed
- Large, irregular shapes
Describe natural killer cells
Lymphocytes that play an important role in host rejection of tumours and virally infected cells (e.g. cancer) by depositing fluid and chemicals into the cell until it bursts
Define phagocytosis
The taking in/engulfing of extracellular substances by enclosing them in a vesicle
(a type of endocytosis)
Describe the process of phagocytosis
- Phagocyte engulfs the substance to form a phagosome
- The phagosome fuses with a lysosome to form a phagolysosome
How do neutrophils and macrophages kill ingested prey?
- Encloses the prey in a vesicle to form a phagosome
- Acidify it and digest its contents with lysosomal enzymes
- This is known as the cellular counterattack
What are interferons?
- Proteins released by virus-infected cells that bind to nearby cell membranes and release proteins that interfere with the ability of viruses to multiply
- Genetically engineered interferons are used to treat several disorders (e.g. hepatitis C, genital warts, multiple sclerosis)
What are complements?
- A major mechanism for destroying foreign substances
- Its activation unleashes inflammatory chemicals that amplify the inflammatory process
- Complement proteins form a complex transmembrane pore (similar to action of natural killer cells)
What are the 3 pathways in which complements are activated?
- Classical
- Alternative
- Mannose-binding lectin
How do natural killer cells work?
- Killer cells bind to the target cell, causing vesicles loaded with Perforin molecules to move to the plasma membrane of the killer cell and release the content into the intercellular space of the target cell
- The perforin molecules insert into the plasma membrane of the target cell, forming a pore that admits water and ruptures the cell
Describe the adaptive defence system
- Attacks specific cells
- Takes longer to be called to action
- When it fails or is disabled, it can cause diseases (e.g. cancer, AIDS)
- Must be primed by an initial exposure to a specific foreign substance (antigen)
Describe active and passive immunity
Active Immunity = can recognise cells that have already been dealt with in the past and not let them back in
Passive Immunity = passed down from parents (naturally acquired)
What are the 3 important aspects of adaptive immunity?
- Lymphocytes
- Antibodies
- Macrophages
What is another name for humoral immunity?
Antibody mediated immunity
What is an antigen?
A toxin/ foreign substance that triggers an immune response in the body, particularly the production of antibodies
Describe humoral immunity
- Provided by antibodies present in the body’s humors (fluids e.g. blood, lymph)
- Antibodies bind to extracellular targets, bacteria, bacterial toxins and viruses; this inactivates them temporarily and marks them for destruction by phagocytes or complements
- Antibodies are specific to a particular antigen
What are haptens?
Smaller than antigens and have to be attached to a large carrier (e.g. protein) to trigger an immune response
What are self and non-self antigens?
Self = recognised proteins of the body Non-self = foreign substances that will be attacked
What are B and T cells?
- Lymphocytes
- B = humoral immunity
- T = cell-mediated immunity
What determines the specificity of B and T cells?
- Their ability to recognise antigenic determinants
- Their surfaces are covered with 10,000 to 100,000 lymphocyte antigen receptors
Describe the difference of the receptors on B and T cells
B = receptor is an immunoglobulin (Y-shaped and a membrane-bound antibody); all receptors are identical so they only bind with 1 type of antigen T = recognise antigen fragments housed in membrane proteins called MHC proteins
What are MHC proteins?
Major Histocompatibility Complex proteins
What distinguishes between self and non-self antigens?
Lymphocytes, depending on specificity of lymphocyte antigen receptors
What are the 2 regions of receptors?
- Constant region = same for all antigen receptors
2. Variable region = specific for an antigen
Where do B and T cells originate and mature?
Bone marrow and thymus (lymphoid organs)
What must B and T cells accomplish to become immunocompetent?
- Generate a viable lymphocyte antigen receptor
2. Survive apoptosis
How do B cells respond to antigens?
They produce proteins called antibodies/ immunoglobulins which are antigen specific
How do T cells respond to antigens?
They directly attack the cells that carry antigens; they recognise the foreign cells and flag down the B cells to come and destroy them
How do T cells recognise antigens?
They bind to MHC proteins on an antigen-presenting cell (e.g. dendritic cell) - this is known as positive selection
What is clonal expansion?
When an antigen binds to a lymphocyte receptor, the cell divides, making many clones
Describe the movement of T cells
- They migrate to the thymus
- In the outermost cortex, the T cells form new T cell antigen receptors and then migrate to the medulla to test these new receptors
What is negative selection?
If T cells fail to recognise a protein, it is tested for recognition of self-antigens
What are self-tolerant T cells?
Immature T cells that do not recognise the body’s own antigens
What happens if lymphocytes attach to the body’s own cells?
Autoimmune diseases
What are the 3 components of the lymphatic system?
Lymph vessels
Lymph nodes
Organs
What are the main lymphoid organs/tissues?
Spleen
Thymus
Tonsils
Lymphoid tissues
What are the 5 functions of lymphatic system?
- Absorption of excess fluid
- Returning excess fluid to the blood stream
- Absorption of fat (small intestine)
- Immune system function
- Transport cells and chemicals around the body
What are the functions of the right lymphatic duct and thoracic duct?
Right Lymphatic = drains lymph from right arm and right side of head and thorax
Thoracic = receives lymph from rest of body
Describe the movement of lymphatic fluid
Lymph capillaries –> Lymphatic vessles –> Thoracic ducts
What do lymphoid cells consist of?
Immune system cells found in lymphoid tissues and supporting cells that form the scaffolding for those tissues
What is the function of lymphoid tissue?
Traps antigens and provides signals that sustain lymphocytes
Describe lymph nodes
- Clustered along the lymphatic vessels
- Large clusters of lymph nodes occur near the body surface in the inguinal, axillary and cervical regions; places where the collecting lymphatic vessels converge to form trunks
What are the 2 main functions of lymph nodes?
- Remove foreign material from the lymphatic stream (e.g. bacteria and tumour cells)
- Produce lymphocytes
What is a reservoir?
Place where the microbe lives and replicates
e.g. people, equipment, water, food, animals
What is a portal of exit?
Place where the microbe leaves the reservoir
e.g. coughing, sneezing, bleeding, faeces
What is a portal of entry?
Entry point (e.g. wound, mucosa of mouth, catheters, IV line)
What is a susceptible host?
Non-immune person
e.g. immune deficiency, babies, elderly, immunosuppressant drugs
