Week 6 Bioscience

Question 1

1. Lymphatic System

Answer 1

Components
- lymphatic capillaries & vessels
- lymph nodes
- lymph Functions
- circulates body fluids
- removes foreign materials from body fluids
- transports WBC

Question 2

Lymph

Answer 2

A white-milky protein containing fluid à excess interstitial fluid (ISF).

Question 3

Lymphatic Capillaries

Answer 3

Are remarkably permeable.
* contain flaplike minivalves that permit the entry of interstitial fluid, WBC and foreign materials into lymphatic capillaries

Question 4

Lymphatic Vessels

Answer 4

Carry lymph from peripheral tissues → back to the blood (venous circulation).
This circulation of lymph (excess interstitial fluid)
* regulates interstitial fluid volume
* maintains blood volume & blood pressure
* transports white blood cells & foreign materials to lymph nodes

Question 5

Lymph Nodes

Answer 5

• Located along lymphatic vessels
• Trap foreign materials = “filter lymph”
• Contain white blood cells that:
• directly destroy foreign materials
• activate an immune response to destroy foreign materials

Question 6

2. Lymphoid Organs and Tissues

Answer 6

Primary Lymphoid Organs
* Contain stem cells that differentiate into the various WBC of the lymphoid system, e.g., red bone marrow & thymus

Secondary Lymphoid Organs and Tissues
* Contain WBC
* Sites where foreign materials become trapped & destroyed or an immune response generated, e.g., lymph nodes, spleen, appendix & tonsils

Question 7

3. White Blood Cells (WBC)

Answer 7

• Many different types:
• neutrophils, macrophages, mast cells, basophils, eosinophils, lymphocytes (natural killer cells, T cells & B cells)
• Found in blood, lymph, lymphoid organs and tissues
• Protect the body from foreign materials

Question 8

4. Cytokines

Answer 8

• Produced and secreted by WBC
• Chemical messengers that recruit and/or activate WBC, e.g., interferons, IL-1 & IL-2

Question 9

Immune Defences

Answer 9

The body is armed with two main immune defences:
* Innate (non-specific) defences
* Adaptive (specific) defences

These defences:
* involve the lymphoid system, the body’s surface barriers and protective proteins
* prevent foreign materials from entering the body
* attack and destroy foreign materials that do enter the body

Question 10

Innate Defences

Answer 10

• Present at birth
• Provide immediate protection against any type of foreign material (non-specific)
• Always work in the same way
• Aim to prevent foreign materials from:
• entering the body
• spreading throughout the body

Question 11

First Line of Defence = Surface Barriers

Answer 11

• Prevent foreign materials from entering the body
• Include physical and chemical barriers that function to:
• form a formidable barrier
• trap & remove foreign materials
• expel foreign materials
• destroy foreign materials

Question 12

Physical Barriers

Answer 12

• Intact skin & mucous membranes that line internal passageways
• epithelial cells form a formidable barrier
• Accessory structures
• hairs (skin & nose) → trap foreign materials
• cilia of the “mucociliary escalator” → move foreign materials from the respiratory tract towards the throat
• Normal flora
• colonise areas of the skin, upper respiratory tract and parts of the digestive, urinary & reproductive tracts
• prevent pathogen colonisation by consuming essential nutrients & taking up space - pathogens unable to attach to body cells/tissues

Question 13

Chemical Barriers

Answer 13

• Sweat, saliva and tears
• cleanse body surfaces & contain lysozyme → destroys bacteria
• Sebum
• acidic skin secretion → inhibits pathogen growth & toxic to some bacteria
• Mucus
• traps foreign materials in respiratory and digestive tracts
• Gastric juice
• • hydrochloric acid & pepsin → destroy ingested foreign materials

Question 14

Second Line of Defence = Internal Defences

Answer 14

• Prevent foreign materials from spreading throughout the body
• Involves:
• macrophages & neutrophils
• natural killer (NK) cells
• interferons
• complement
• pyrogens
• inflammatory response

Question 15

Macrophages and Neutrophils

Answer 15

Phagocytose (ingest) and destroy all types of foreign materials via lysosomal enzymes.

Question 16

Natural Killer (NK) Cells

Answer 16

• Destroy virus-infected cells & cancerous cells
• Recognise, adhere to and destroy target cells via the release of perforins and granzymes
• perforins → create pores in the target cell membrane, allowing entry of granzymes
• granzymes → induce apoptosis (program the cell to die)

Question 17

Interferons

Answer 17

• A group of specific cytokines produced by white blood cells and virus-infected cells
• Inhibit viral replication
• Activate macrophages and NK cells to destroy virus-infected cells and cancerous cells

Question 18

Complement

Answer 18

A large group of proteins that:
* recruit macrophages and neutrophils to the site of enemy invasion
* enhance phagocytosis by opsonisation → coat foreign material making it easier for phagocytes to identify & more palatable “tasty”
* directly destroy cellular targets, (e.g., bacteria & mismatched RBC) by forming a membrane attack complex (MAC) = hole → cell lysis
* enhance an inflammatory response

Question 19

Inflammation

Answer 19

The inflammatory response aims to:
1. Localise and contain foreign material at an injury site
2. Dispose of foreign materials and cellular debris → this involves macrophages, neutrophils & complement
3. Repair the damaged tissue

Question 20

Fever

Answer 20

Pyrogens → a group of proteins that reset the body’s hypothalamic thermostat & increase body temperature
e.g. IL-1 interferons bacterial toxins

Mild or moderate fevers can be beneficial
→ inhibit the growth of some bacteria & viruses
→ ↑ cell metabolism - accelerates immune defences

Question 21

Summary - Innate defences

Answer 21

The body’s innate defences provide:
* immediate protection against any type of foreign material
* prevent the entry of foreign material into the body
* quickly contain and eliminate foreign materials that do enter

Question 22

Adaptive Defences

Answer 22

• Are acquired - develop throughout life
• Provide protection against a specific foreign invader
• Are systemic → not restricted to the initial infection site
• Remember invaders = “immunological memory”

Question 23

Antigens (Ag)

Answer 23

An antigen is a molecule capable of inducing an immune response (third line of defence), e.g.
* viral and bacterial proteins or polysaccharides
* bacterial toxins
* pollen, egg white, peanut lectin
* transplanted tissues/organs
* tumour cell proteins
* transfused blood cells

Question 24

T cells and B cells

Answer 24

• Antigen Presenting Cells (APC = macrophages or dendritic cells) phagocytose and present antigens to T cells → activates T cells
• Activated T cells → activate B cells
• Activated T and B cells mount an immune response towards the antigen

Question 25

Immunocompetence

Answer 25

(i.e., the ability to recognise and bind one specific antigen) * Each T & B lymphocyte displays a unique surface receptor that recognises and binds one specific antigen. - T cells → membrane bound T cell receptor (TcR) - B cells → membrane bound antibody receptor

Question 26

Self-tolerance

Answer 26

(i.e., the ability to recognise “self-antigens” from “non-self-antigens”) * During their maturation T & B cells are educated to recognise self from non-self (foreign) antigens - B cell maturation occurs in the bone marrow - T cell maturation occurs in the thymus * If T & B cells fail to recognise self-antigens and attack normal body cells/tissues → autoimmune disease

Question 27

Immunological Memory

Answer 27

(i.e., the ability to remember antigens) The first time an antigen invades the body a primary immune response, which produces a population of memory T and B cells, is generated. Memory cells: * “remember” antigens * launch a faster, stronger counterattack called a secondary immune response

Question 28

An immune response involves two interconnected responses:

Answer 28

* Cellular immune response → mediated by cytotoxic T cells * Humoral immune response → mediated by B cells

Question 29

Activated TC cells proliferate to produce many antigen-specific:

Answer 29

→ effector TC cells → memory TC cells

Question 30

A cellular and humoral immune response begins with the activation of a Helper T cell (TH).

Answer 30

* TcR binds to a specific antigen presented by an APC → TH activated * Activated TH cell proliferates to produce many antigen-specific: → effector TH cells → memory TH cells * Effector TH cells secrete cytokines (e.g., IL-2) à helps activate cytotoxic T cells (Tc) and B cells and thus “turn on” a cellular and a humoral immune response

Question 31

Activated B cells proliferate & differentiate to produce many:

Answer 31

- plasma cells → secrete Ag-specific antibodies - memory B cells

Question 32

Primary vs Secondary Immune Response

Answer 32

First antigen exposure produces a primary immune response * A small, slow, short-lived response that doesn’t protect from illness → humoral response produces a small amount of antibody → IgM is produced first, then IgG * Produces thousands of long-lived antigen-specific memory T and B cells Subsequent antigen encounters produce a secondary immune response. * Activated memory T and B cells rapidly produce a powerful, long-lasting response that protects from illness → humoral response produces a large amount of IgG antibody * Effectiveness is one of the basic principals behind the development of vaccines

Question 33

Vaccines

Answer 33

* Expose an individual to an antigen → inactive or attenuated (weak) antigen * Provide the first antigen encounter → activate a primary immune response & generate memory T and B cells → prime the body for a secondary immune response

Question 34

Disorders of immune function

Answer 34

* Immunodeficiency diseases * Autoimmune diseases * Hypersensitivities

Question 35

Immunodeficiency diseases

Answer 35

Occur when the body’s immune defences are compromised or absent and unable to mount an effective immune response. * Severe combined immunodeficiency (SCID) syndromes → no T & B cells * Acquired immunodeficiency syndrome (AIDS) → Human Immunodeficiency Virus (HIV) primarily infects & destroys TH cells → No TH cells = no cellular or humoral immune response

Question 36

Autoimmune Diseases

Answer 36

Occur when the body’s immune defences target normal cells and tissues, e.g., Rheumatoid arthritis, Type I diabetes and Multiple sclerosis. * self-reactive cytotoxic T cells destroy normal body cells * self-reactive B cells differentiate into plasma cells that secrete self-reactive antibodies = autoantibodies

Question 37

Hypersensitivities (allergies)

Answer 37

Occurs when the body’s immune defences respond to a harmless antigen that is perceived as a threat. Immediate Hypersensitivity * Acute, rapid allergic reaction * The antigen is called an allergen * Mediated by allergen-specific IgE antibodies - allergen binds to IgE on mast cells & basophils → triggers the release of histamine which: * stimulates bronchoconstriction, mucus production & vasodilation * increases blood vessel permeability