Defence Against Disease

Question 1

What is the main cause of infectious disease?

Answer 1

Pathogens

Question 2

5 examples of pathogens

Answer 2

Bacteria

Fungi

Protists (unicellular/multicellular eukaryotic organisms)

Viruses

Prions (infectious proteins)

Question 3

What are the three layers of the skin?

Answer 3

Epidermis, dermis, hypodermis

Question 4

On the skin, what layers prevent entry of microorganisms?

Answer 4

Keratin deposits that lay on dead cells on epidermis

Sebaceous Glands in dermis produce oils that keep skin at low pH —> preventing growth of bacteria

Question 5

What are mucous membranes?

Answer 5

Membranes that line the body cavities (digestive, urogenital, respiratory tract, salivary ducts, lacrimal ducts, mouth, not]se, mammary glands).

Produce mucus which traps potential pathogens entering the cavities.

Mucus contains the enzymes lysozyme—> attacks bacterial cell walls and kills bacteria.

Question 6

What are mechanical actins that help flush away the mucus along with trapped pathogens?

Answer 6

Respiratory epithilium: cilia that beat in a synchronised manner, coughing, sneezing

Tears

Urine

Question 7

What are commensal bacteria?

Answer 7

Naturally occurring bacteria on several parts of human body that outcompete pathogens for nutrience/space without harming the body.

Question 8

Describe the process of blood clotting to seal cuts in the skin

Answer 8

1. Activation and accumulation of platelets at site of injury
2. Platelets form a plug that seal opening
3. Platelets (and injured tissues) release clotting factors including Ca+, thromboplastin (plasma protein)

[clotting factors normally preset in inactive form, once activated they interact in a cascade of reactions]

4. Fibrin forms mesh over wound that entraps more platelets and red blood cells—> resulting in blood clotting. Over time clotting dries and forms a scab.

Question 9

What is the innate immune system?

Answer 9

Immunity present from birth that provides innate immunity.

Responsible for rapid, non-specific defence responses against pathogens encountered daily.

Question 10

What is the function of the innate immune system?

Answer 10

Prevents entry of pathogens/limits pathogenic spread if entered

Uses chemical and physical barriers provided by skin and mucous membranes&& generalised immune responses like phagocytosis

Not specific to any pathogen

Question 11

What is the adaptive immune system?

Answer 11

When the innate immune system is unable to control pathogens.

Slower and mediated by lymphocytes (white blood cell type).

Question 12

What are the main distinguishing features of the adaptive immune system?

Answer 12

• Specificity: directed toward a specific pathogen—> more effective
• Memory: ability to ‘remember’ pathogens—> ensures subsequent infection with same pathogen is faster and efficient

Question 13

Briefly, what is phagocytosis?

Answer 13

Process by which any foreign materials, including pathogens, and ingested, digested, and eliminated.

Question 14

What is phagocytosis mediated by?

Answer 14

Specialised leukocytes (white blood cells):

monocytes
neutrophils
macrophages

All cells capable of amoeboid movement and can migrate from blood to site of infection.

Question 15

Outline the 5 steps of phagocytosis

Answer 15

1. Recognition of pathogen by phagocytes. Receptor molecules on plasma membrane of phagocytes recognise and bind to pathogen triggering a chain of reactions that lead to pseudopolia formation
2. Pseudopodia encircle target microorganism, both protrusions seal, resulting in formation of phagosome vesicle
3. Phagosome undergoes phagosome maturation (series of stages)
4. Phagosome fuses with lysosomes forming phagolysosomes. These new structures contain digestive enzymes (originally present in lysosome)
5. There enzymes digest microbial components then released from cell

[non-specific secondary line of defence]

Question 16

What are lymphocytes?

Answer 16

A type of leukocyte (white blood cell)

Produced in bone marrow

Can be divided into T-lymphocytes (T-cells) that mature in thymus (primary lymphoid organ)

and B-lymphocytes (B-cells) mature in bone marrow.

Question 17

What is the lymphatic system comprised of?

Answer 17

Lymph: watery fluid derived from blood that moves through lymphatic system

lymphoid organs and tissues, and lymphatic vessels.

Question 18

What is the function of the lymphatic system?

Answer 18

To return fluid back to bloodstream
AND
Immune response of body as bone marrow and thymus (lymphoid organs) are regions where lymphocytes mature .

After reaching maturity, B-cells and T-cells migrate, some remain in circulation some concentrated in secondary lymphoid organs (spleen, tonsils, lymph nodes) where more likely to encounter antigens.

Question 19

What is an antigen?

Answer 19

Any substance that triggers the immune response resulting in production of antibodies against it. Most antigens are proteins.

Though pathogen is infectious agent, antigen in part of the pathogen that elicits the immune response.

Usually found on surface of pathogen(e.g. cell wall of baterium or coat of virus)

Question 20

What are self antigens?

Answer 20

Antigens that exist of the cells of our own body that help the immune system to identify and tolerate our cells (e.g. red blood cells, liver cells)

Question 21

What are B-lymphocytes response to antigens?

Answer 21

Produce antibodies that lead to hormonal immunity

High diversity = can recognise millions of antibodies—>produce highly specific antibodies

Question 22

What are antibodies?

Answer 22

Protein molecules that:

Identify
Bind to &
Neutralise

Antigens that enter the body

Y-shaped molecule w 2 heavy, 2 light chains

Question 23

What is the immune repose of T-lymphocytes to antigens?

Cell-mediated immunity

Answer 23

2 types:
- helper T-cells
- cytotoxic T-cells

Helper: helps immune system by activating other components

Cytotoxic: kill infected cells

Question 24

What determines blood group?

Answer 24

The presence or absence of specific polysaccharide antigens on the surface of erythrocytes (red blood cells):

E.g. A: Antibody in plasma Anti-B and antigen on red blood cell A antigen

O: Antibody A and B but no antigens

Question 25

What is the Rhesus factor?

Answer 25

RhD can be either -ive or +ive depending on the presence or absence of the RhD antigen.

+ive if present, -ive if absent.

Question 26

Activation of B & T lymphocytes

Answer 26

For every antigen, there is a B & T cell specific to it.

Until the B and T cells present in secondary lymphoid organs encounter a specific antigen, they are naive.

Once they encounter one, they become effector cells.

Question 27

What is the activation process of helper T-cells?

Answer 27

Phagocytes that digest a pathogen retain fragments of it.
Antigen-presenting cells present these fragments to specific helper T-cells, activating them:

• increase in number of T-cells that recognise antigen
• activates B-cells specific to the same antigen
• activates cytotoxic T-cells specific to same antigen

Question 28

What is the activation process of B-cells?

Answer 28

Depends on 2 integrated events:

1. When receptor on surface of B-cell recognises and binds to specific antigen
2. Stimulation by an activated T-helper cell that recognises same antigen

Question 29

Multiplication of B-cells

Answer 29

1. Activated B-cell undergoes repeated mitotic divisions to create many clones of itself: ** clonal selection theory**
2. Once B-cell activated, multiplies and differentiates to form plasma cells and memory cells
3. Each plasma cell produces and releases thousands of specific antibodies that circulate in blood

primary immune response is first response

Question 30

What is clonal selection theory?

Answer 30

That a pre-selected B-cell specific to the antigen divides (mitosis) to form clones which all recognise the same antigen

Question 31

What are memory cells?

Answer 31

Small percentage of B-cells become memory cells

Long-lived and persist in blood stream and lymph nodes & retain a memory of the antigen

Lie dormant until body in re-infected with same antigen so can quickly differentiate to form plasma cells (that produce antibodies)

secondary immune response