C3.2 Defence against disease

What do pathogens cause?

Infectious diseases

Pathogens

Infectious disease-causing organism

Infectious disease

Can be passed from 1 organism to another

Types of pathogens

1. Viruses

2. Bacteria

3. Fungi

4. Protists

Do archae cause disease in humans?

No

What does careful observation lead to?

Improtant progress

Example of careful observation leading to important progress

CO during 19th-century epidemics of childbed fever (due to an infection after childbirth) in Vienna + cholera in London led to breakthroughs in the control of infectious disease

• CO led to break thrus in disease control

Primary defence system

Non specific

• Skin

• Mucous membranes

How does the skin defend against pathogens?

Acts as a physical AND chemical barrier to pathogens

How does the skin act as a physical barrier to pathogens?

• Outer layer covered in dead cells = tough → difficult for pathogens to penetrate

• Forms scabs → prevents pathogens from entering when the skin is damaged

• Natural MO on the skin compete w harmful pathogens for nutrients

How does the skin act as a chemical barrier to pathogens?

Sebaceous glands produce antimicrobial secretions (sebum) → kills bacteria

How does sebum defend against pathogens?

Maintains skin moisture + lowers the pH

• Low pH inhibits growth of bacteria + fungi

Where are mucous membranes found?

Skin openings

• Eg nose, reproductive organs, airways

How do mucous membranes defend against pathogens?

Secrete mucus → traps pathogens

• Cilia on lining of MM waft them

What happens to the trapped pathogens by mucus / cilia?

• Swallowed → destroyed by HCl

• Or expelled by coughing

What does mucus contain that helps it destroy pathogens?

Lysozyme = anti-bacterial enzymes

• Break down bacterial CW (chatgpt)

Why can antibiotics be used to treat bacterial infections but not viral infections?

Bacteria have peptidoglycan cell walls

• Viruses don’t

Purpose of blood clotting

Seal cuts in skin to:

• Prevent excess bleeding

• Prevent pathogen entry

Clotting factors

• Proteins in the blood

• Control bleeding

• Released by platelets

How is a clot formed?

1. Platelets release clotting factors

2. Cascade pathway →

3. Rapid conversion of fibrinogen (soluble) to fibrin (insoluble) by thrombin

4. Erythrocytes (RBC) trapped

5. Blood clot hardens → forms scab

More detailed explanation of the clotting cascade

1. Platelets attach to injury site + release clotting factors

2. Cause prothrombin → thrombin (enzyme)

3. Thrombin converts fibrinogen (soluble) → fibrin (insoluble)

4. Fibrin forms a mesh → traps platelets + RBC → clot

Thrombin

Catalyses clotting process

Fibrinogen

• Soluble protein

• Circulates in blood plasma

Fibrin

• Insoluble protein

• Forms scabs

2 types of immunse system

1. Innate

2. Adaptive

Innate immune system

• Responds to broad categories of pathogen

• Doesn’t change during an organism’s life

Adaptive immune system

• Responds in a specific way to particular pathogens

• Builds up a memory of pathogens encountered, so the immune response becomes more effective

How does the adaptive IS make the immune response more effective?

Builds up a memory of pathogens encountered

Defence against pathogens levels

2 types of blood cells

1. RBC (erythrocytes)

2. WBC (leucocytes)

   • Phagocytes (engulf)

   • Lymphocytes (produce antibodies)

2 types of lymphocytes

1. B cells

2. T cells

Which type of WBC does the innate vs adaptive IS use?

• Innate- phagocytes (engulf)

• Adaptive- lymphocytes (build memory)

Compare innate vs adaptive immune systems

INNATE

• Phagocytes

• Constant thru out organism's life

• Not specific (attack any foreign body)

ADAPTIVE

• Lymphocytes

• Builds memory / immunity thr out organism’s life

• Specific (diff response for each pathogen(

Phagocytes (or macrophage)

WBC part of innate immune system

• Non specific

Infection control by phagocytes

1. Move from blood to inflection site via amoeboid movement

2. Phagocytes recognize pathogens

3. Phagocytes engulf pathogens by endocytosis

4. Phagocytes digest them using enzymes from lysosomes

When a phagocyte responds to the presence of a pathogen, the following events happen:

1. Enzymatic digestion

2. Exocytosis

3. Phagocytosis

4. Vacuole formation

5. Endocytosis

Which of the following would be the correct order of events?

1. Endocytosis / phagocytosis

2. Vesicle formation

3. Enzymatic digestion

   • L release digestive E

4. Exocytosis

   • Waste

1. Vesicle forms around pathogen

2. Lysosome fuses with vesicle

3. Digestive enzymes destroy pathogens

Lymphocytes

• WBC

• In adaptive immune system

• Produce antibodies

Where are lymphocytes found?

Both:

1. Circulate in the blood

2. Contained in lymph nodes

An invdividual has a v large no of what type of lymphocyte?

B-lymphocytes

What does each B-lymphocyte make?

A specific type of antibody

Antibody

• Protein produced by lymphocytes in response to an antigen

• It recognizes a specific antigen + binds to it as part of an immune response

What happens when antibodies bind to antigens on pathogens?

1. Tag it for destruction by other immune cells

2. Or prevent it from binding with other host cells

What are antibodies specific to?

Antigens

• So need diff lymphocyte types to make lots of diff antibodies

Antigens

• Recognition molecules that trigger antibody production

• Glycoproteins or other proteins

• Usually located on the outer surfaces of pathogens

Where are antigens usually located?

Outer surfaces of pathogens

What do antigens that are recognised as non-self stimulate?

An immune response

• Specifically antibody production by B-lymphocytes

Example of antigens stimulating an immune response (erythrocytes)

Antigens on the surface of RBC may stimulate antibody production if transfused into a person with a diff blood group

ABO blood types, antigens, antibodies

B lymphocytes = B cells

Helper T-lymphocytes = T helper cells

2 roles of the (antigen specific) B cells

1. Produce antibodies

2. Become memory cells

B cells can only produce AB + become memory cells only when…

They have been activated

What does the activation of B cells require

Both:

• Direct interaction with the specific antigen

• Contact with a helper T-cell that has also become activated by the same type of antigen (Contact w activated T cell)

Process of activating B cells by T cells

1. Pathogen engulfed by phagocyte (say entire phagocytosis process)

2. Antigen (from destroyed pathogen) presents itself outside the phagocyte

3. T helper cell binds to antigen → becomes activated

4. Activated T cell binds to specific B cell

5. B cell activated

What happens after B lymphocytes are activated?

Activated B cells multiply to form clones of antibody-secreting plasma B cells

Plasma B cells

• Activated B-cells first divide by mitosis to produce large no of plasma B-cells

• Capable of producing the same type of antibody.

Thru what process to activated B cells divide?

Mitosis

Why do activated B cells need to divide?

• Bc relatively small no. of B-cells that respond to a specific antigen

• So divide to produce sufficient quantities of antibody

2 types of cells activated B cells divide into?

• Plasma B cells (produce AB)

• Memory cells (for immunity)

What happens when activated B cells differentiate into plasma cells?

• Grow

• Produce organelles for AB production (eg rough ER, golgi)

What specific type of cell produces antibodies?

Plasma B cell

• Plasma cell produce AB → circulate blood stream

Is the activation of B cells etc part of adaptive or innate immunity?

Adaptive

Cell division pathway

Immunity

The ability to eliminate an infectious disease from the body

What is immunity a consequence of?

Retaining memory cells

How long to memory cells remain in the body?

Years

• LT

Memory cells

• Lymphocytes that can specific antibodies needed to fight the infection

• Survive in the LT

Purpose of memory cells

Produce a rapid response if pathogen is detected again

• Faster + stronger response (more ABs, produced more quickly)

HIV full form

Human immunodeficiency virus

How is HIV transmitted?

Via body fluids:

1. Sexual intercourse (unprotected w infected person)

2. Blood donation

3. Sharing of needles w infected person

4. Breast milk (mother to child) if mother infected

NOT by casual contact (hugging, touching)

Consequence of HIV

AIDS

• Acquired immunodeficiency syndrome

• HIV destorys T cells + body ability to fight of other pathogens

• cant produce AB