Unit 6 Immune System Flashcards
1
Q
what is the immune system and its roles
A
- Big multicellular organisms provide lots of environments for other, smaller organisms to proliferate in
- Ability of the body to fight off these invaders is called immunity (immunis = exempt)
- Key features of the immune system
- Lymphoid tissues and immune cells
- Chemicals that coordinate and execute function
- Three maior functions of the immune system
1. Protecting the body - Microbes = bacteria, viruses, fungi, protozoa
- Parasites = worms, etc.
- Toxins produced by microbes
- Other foreign proteins or substances (e.g. allergens)
2. Removes dead/damaged tissue and cells - Immune cells scavenge extracellular compartments
3. Tries to recognize and remove abnormal cells - Cells that are unable to control growth may be detected by the immune system
2
Q
diseases in the immune system
A
- When the immune system does not perform normally you can get a variety of pathologies
- Examples:
1. Incorrect responses - Autoimmunity
2. Overactive responses - Allergies
3. Lack of response - Immunodeficiency
3
Q
what are pathogens
A
- Pathogens are disease-causing agents
- We will look at two different types of pathogens
1. Bacteria
2. Viruses - These require slightly different responses from the immune system
4
Q
Bacteria
A
- Can be intracellular and extracellular
- Cells surrounded by a cell membrane & usually a cell wall
- Can survive & reproduce outside host
- Most can be killed by drugs –> antibiotics
5
Q
Viruses
A
- Intracellular pathogens
- Not cells –> nucleic acid core with protein coat –> cannot reproduce alone
- Some have envelope derived from host cell membrane
- Cannot be killed by antibiotics
- Some treated with antiviral drugs
- Once inside host, virus nucleic acid takes over
- New viral particles can either rupture host cell or bud off from host cell
6
Q
lymphoid organs and lymph
A
- Immune system organs are called lymphoid organs because lymphocytes are found there
- The lymphoid organs are connected by blood vessels and the lymph vessels
- Carry lymph –> clear fluid
- Essentially extracellular fluid that has left capillaries & filter through tissue
- Lymph is a conduit for immunologically active cells to travel through
- Lymph nodes (bean-shaped) are located at strategic positions
- Knee, groin, elbow, shoulder, neck
- Regions of the body outside lymphoid organs –> periphery
7
Q
types of lymphoid organs
A
- primary lymphoid organs
- Secondary lymphoid organs
8
Q
primary lymphoid organs
A
- Organs where lymphocytes develop
- Bone marrow –> all blood cells originate here
- B lymphocytes (cells) mature here
- Thymus –> T lymphocytes (cells) mature here
- not thyroid
9
Q
secondary lymphoid organs
A
- Organs where lymphocytes interact and initiate responses
- Spleen, lymph nodes, tonsils, and Gut Associated Lymphoid Tissue (GALT)
- Filter blood and lymph –> for pathogens & pathogen containing lymphocytes
- Structure of secondary lymphoid organs reflects this function:
- Afferent lymph vessel brings in lymphocytes from periphery
- Efferent lymph vessel allows them to keep circulating
- Pulp inside the lymph node allows mixing of lymphocytes and other leukocytes
- Arteries and veins to supply nutrients & O2, plus non-lymphocytic leukocytes
- Spleen and lymph nodes surrounded by a fibrous wall –> encapsulated
- Tonsils and GALT are unencapsulated tissues –> diffuse
10
Q
types of leukocytes
A
- Main players in the immune system
- Larger in size than RBC and less numerous (7000 per ml vs 5x10° RBC)
- Able to leave the blood stream and function extravascularly (in the tissues)
- They have a various lifespan –> some alive for a few hours and others for several months
- Six main types of cells:
1. Eosinophils
2. Basophils (Mast cells)
3. Neutrophils
4. Monocytes (Macrophages)
5. Lymphocytes
6. Dendritic cells
11
Q
subdivisions by function/ morphology
A
- Granulocyte
- Have prominent cytoplasmic granules
- Eosinophils, basophils & neutrophils + mast cells - Phagocytes
- Can engulf and ingest pathogens
- Neutrophils, macrophages, dendritic cells - Cytotoxic Cells
- Kill other cells, even self-cells
- Eosinophils & some lymphocytes - Antigen presenting cells (APCS)
- Display fragments of pathogens on cell surface (antigen)
- Some lymphocytes, dendritic cells & macrophages
12
Q
what are antigens and antibodies
A
- Antigen (Ag - antibody generator) –> substances that are recognized by an antibody and induces an immune
response - Antibodies (Ab) –> proteins that bind specifically to Ag’s and target pathogens for destruction
13
Q
Eosinophils
A
- cytotoxic granulocytes with bright pink staining granules
- Role in defence against parasites & function in allergic response
- Few in peripheral circulation, only live for 6-12 hours
- Found in digestive tract, lungs, genital tract, and skin
- Respond by binding to an antibody-coated parasite and degranulate –> spew granule contents
- Granule contents (toxic enzymes & oxidative chemicals) damage and kill parasites –> cytotoxic
- Eosinophils also degranulate in allergic responses
14
Q
Basophils
A
- granulocytes involved in allergic responses
- Have large dark blue staining granules (granulocyte)
- Basophils in blood (rare in numbers), mast cells in tissue –> found in digestive tract, lungs & skin
- Granules contain histamine, heparin, cytokines
- In allergic responses cells also degranulate
15
Q
neutrophils
A
- granulocytes that are phagocytic
- Most abundant leukocyte (50-70% of total leukocytes)
- Live 1-2 days & can ingest 5-20 bacteria
- Can leave circulatory system to attack pathogens in tissues
- Granules contain cytokines that cause fever and start other inflammatory responses
16
Q
monocytes
A
- Monocytes are precursor cells of tissue macrophages and are uncommon in blood (1-6% of leukocytes)
- Estimated in the blood for 8 hours –> move into tissues to become macrophages
- Macrophages are large ameboid cells and function as scavengers by phagocytosing old red blood cells and dead neutrophils
- Can phagocytose up to 100 bacteria
- Have a role in adaptive immune response –> phagocytosed pathogens are digested, and fragments are placed on the cell surface (APCs)
17
Q
lymphocytes
A
- Key players in the adaptive immune response
- Make up 20-30% of all leukocytes
- Only 5% of them are in the circulation –> most are found in lymphoid tissues
- 10^12 per individual at any given time
- They all look alike under a microscope, but have fundamental differences in function
- NK Cell in innate immunity
-T and B lymphocytes in adaptive immunity
-when B lymphocytes are activated they become plasma cells
18
Q
dendritic cells
A
- Phagocytic antigen presenting cells (APCs)
- Have long thin processes (like dendrites on a neuron)
- Found in skin and other organs
- They recognize and engulf pathogens
- Pathogens are digested and placed on cell surface
- “Activated” cells then migrate to secondary lymphoid organs to present the antigens to lymphocytes
19
Q
haematopoiesis
A
- All blood cells are produced in the bone marrow
- Derived from pluripotent hematopoietic stem cells
- Give rise to uncommitted stem cells
- These give rise to committed progenitor cells –> develop into each cell type
- The path taken is guided by cytokines
20
Q
types of lymphocytes
A
- B lymphocytes (B cells)
- T lymphocytes (T cells)
21
Q
B lymphocytes
A
- Produced in the bone marrow (easy to remember their name –> but NOT why they are called B Cells)
- Letter “B” derived from research in chickens
- The B cells leave the bone marrow and mature/develop in the Bursa of Fabricius –> an invagination of the colon
- Mammals do not have a bursa –> “B” is often translated as the “bursa equivalent”
Produce antibodies –> can be found on the cell surface as receptors or free Ab’s in the plasma
22
Q
T lymphocytes
A
- Produced in the bone marrow but mature/develop in the thymus (easy to remember their name –> and it IS why they are called T cells)
- Use contact-dependent signalling (cell-to-cell communication) via the T-cell receptor expressed on the T cell membrane –> can only bind to MHC-antigen complexes
- T-cell receptor cannot bind to free Ag
