IB Biology HL: C3.2 - defence against disease

pathogens

disease causing organisms or agent which can infect humans

how do pathogens cause disease

• enter the body (broken skin, respiratory track)

• multiplication; reproduce rapidly ( binary fission/viruses into cells)

primary defence definition

non-specific, first line of defence that prevents pathogens from entering the body, consisting primarily of the skin and mucous membranes

primary defenses of immune systems

mucous and skin; physical and chemical barrier to pathogens

saliva, ph difference on skin/vagina, nasal hairs,

skin as a primary defence

physical barrier:

• keratin

• cell shedding: makes it hard for pathogens to attach

Chemical barrier

• sebum: low ph

• sweat: low ph

mucus membrane as a primary defence

• goblet cell which produce mucus. contains lysosomes, antibacteria enzymes (hydrolyses cell walls)

• cilliated epitheal cells which sweep mucus upwards, out of lungs

disease

a disruption to the normal function of the body, often caused by harmfull microorganisms

blood clotting definition

physical process which seals cuts to prevent blood loss and pathogen entry

blood clotting process

• broken skin, collagen is exposed

• platelets adhere to collagen, forms a platelet plug

• platelets release clotting factors

• cascade happens

• fibrinogen is converted to fibrin by thrombin

• traps erythrocytes, forming a stable clot

innate immune system

part of the immune system which rapidly reacts to broad categories to pathogens, and which doesn’t change during an organism’s life. Only phagocytes are needed to be known

innate immunity

The first line of defence against pathogens including physical barriers and non-specific defence mechanisms which respond rapidly.

adaptive immune system

A specialised response to infection mediated by lymphocytes, resulting in immunological memory. Response is much slower

why are adaptive immune system responses stronger and longer lastinf

• specificity ( very specific )

• memory ( “remebers” pathogens it encounters, leading to a faster and stronger response in case of repeat,)

phagocytes

main type of innate immune cell, which can perform phagocytosis, and capable of amoeboid movement

phagocytosis definition

Phagocytosis is the process by which any foreign material, including pathogens, is engulfed ingested and digested, resulting in its elimination.

pseudopodia

Literally ‘false feet’, pseudopodia are temporary arm-like projections or extensions used for movement and feeding.

phagocytosis process

1. pathogen is recognised by phagocytes: receptor molecules on plasma membranes recognise and bind to the pathogen

2. pseudopodia are formed and encircle target organism. both protrusions seal, and form a vesicle called phagosome

3. phagosome undergoes maturation

4. phagosome fuses with lysosomes, forming phagolysosomes, which contain digestive enzymes

5. the enzymes digest bacterial components, which are then released in the cell.

amoeboid movement

A type of locomotion that involves the protrusion of pseudopodia. Movement of phagocytes, nothing more about it needs to be known

lymphocytes

type of white blood cell. Can be divided into T-lymphocytes or B-lymphocytes

adaptive vs innate immune system

• rapid response vs slow response

• both protect body against pathogens

• stays the same vs adapts and improves over time

• involves phagocytes vs involves lymphocites

• more general vs more specialised

the lymphatic system

A system comprising the lymph, lymphoid organs and tissues, and lymphatic vessels. The lymphatic system plays an important role in the immune response of the body.

T-lymphocytes

Type of white blood cell, lymphocyte, that is made in the bone marrow and matures in the thymus. Also known as T-cells. Can be helper T-cells or cytotoxic T-cells. Both play essential roles in the adaptive immune system.

T-lymphocyte maturation in thymus

any immature T-lymphocyte which reacts with proteins present in the body are killed by the thymus glands as they will cause autoimmune responses.

B-lymphocytes

Type of white blood cell that is made and matures in the bone marrow, the lymph and are responsible for producing antibodies. Also known as a B-cell. There are a lot of them, and each make a specific type of antibody

antigen

A foreign substance which elicits an immune response; can be a toxin, allergen or part of a pathogen.

self antigens

Antigens that exist on the cells of our own bodies and that help the immune system to identify and tolerate these cells.

B-lymphocytes immune response

recognises antigen by receptor, produces antibodies → leads to humoral immunity

humoral immunity

A type of adaptive immune response mediated by antibodies secreted from plasma cells.

Helper T-lymphocytes

“help” the immune system by activation other components

cytotoxic/killer T-lymphocytes

kill infected cells (viral infection or cancer response). Cell mediated immunity

why can there be reactions to blood donated from another group

blood can have A, B, or Rh antigens, and if own body doesn’t have these types immune system will react by producing antibodies to the antigen that they don’t have.

antibodies

a globular protein called an immunoglobulin. 4 polypeptide chain held by disulphide bridges and forming a Y shaped molecule. top of the '“arms” contain an antigen binding site. Can be free, or on the surface membrane of B-cells.

agglutination

process by in which how antibodies which attack to antigens, causing them to stick together, making them easier to get phagocise.

immune system complement proteins

will bind to any pathogens which have antibodies, making small holes and causing lysis

How do we recognise self from non self ?

cells are recognised by glycoproteins called and major histocompatibility complex (MHC). Lympocytes can recognise them, and so leave our cells alone

How are B-cells activated

• B-cells need to come into contact with the antigen

• Activated T-cells for that antigen need to come into contact with B-cells

only then are proper antibodies produced

Whole immune system process

• B-cell in lymph detects antigen using it’s antibodies on it’s surface: they become antigen specific

• macrophages perform phagocytosis, secrete citokines which activates rest of immune system. digest

• macrophages present the antigen externally on an MHC on their cell membrane

• this is antigen presentation

• if helper T-cells detect their corresponding antigen on an MHC antigen, they realise shit gets serious and activates

• if an antigen specific b cell meets an activated T-cell, it realises again shit gets serious and become activated

• first the B-cells perform mitosis to be present in sufficient quantities

• then produce specific antibodies

• at the end, some T-cells and B-cells that used to be activated are now memory cells: whole immune process occurs again can occur much more quickly. Immune