Microorganisms Characteristics and Immune Response: Pathogens, Transmission, and MRI

Bacteria

Prokaryotic cells

Bacteria Size

0.5-5 µm

How Bacteria Cause Disease

Releasing toxins and damaging host cells

Fungi

Eukaryotic cells

Fungi Size

5-15 µm

How Fungi Cause Disease

Releasing enzymes that digest tissue and spreading via spores

Protoctists (Protists)

Eukaryotic

Protoctists Size

1 µm - 2 mm

Protoctists Characteristics

Often parasitic

Example Protoctist Diseases

Malaria, toxoplasmosis

Viruses

Acellular (not prokaryotic or eukaryotic)

Viruses Size

20-350 nm

Virus Structure

Contain DNA or RNA in protein coat (capsid)

Virus Replication

Replicate only inside host cells

Bacterial Diseases

Chlamydia, Gonorrhoea, Tuberculosis

Viral Diseases

Common cold, Mumps, Measles

Fungal Diseases

Yeast infections

Protoctist Diseases

Malaria (Plasmodium), Toxoplasmosis

Prion Diseases

CJD (Creutzfeldt-Jakob disease)

Direct Transmission

Physical contact, Sexual contact, Sharing needles

Indirect Transmission

Airborne droplets, Contaminated surfaces (fomites)

Vehicle Transmission

Contaminated food or water

Vector Transmission

Carried by organisms (e.g. mosquitoes)

Factors Increasing Spread of Disease

Poor sanitation, Lack of social distancing, Limited access to healthcare, High population density / close contact

Antigen

Molecule on surface of pathogen/cell, Recognised as non-self, Triggers immune response

Antibody

Protein produced by B lymphocytes, Specifically binds to a complementary antigen

Non-Specific Defences

Skin (physical barrier), Mucus traps pathogens, Cilia move mucus out of airways, Lysozyme destroys bacteria, Stomach acid kills pathogens, Phagocytosis (white blood cells engulf pathogens), Inflammation response

Specific Immune System

Two main branches: Cell-mediated immunity (T cells), Antibody-mediated immunity (B cells)

T Helper Cells

Activated by antigen-presenting cells, Release interleukins, Activate B cells + cytotoxic T cells

Cytotoxic T Cells

Destroy infected cells, Release perforin → makes holes in cell membrane

T Memory Cells

Provide faster secondary response

T Regulator Cells

Shut down immune response after infection, Prevent autoimmune reactions

B Cells

Produce antibodies

Antibody Functions

Neutralisation (block pathogens), Agglutination (clumping), Opsonisation (marking for phagocytosis)

B Memory Cells

Long-term immunity, Faster secondary response

How the Immune Response Works

Pathogen enters body, Antigens detected, T helper cells activated, B cells activated (clonal selection), Clonal expansion, Plasma cells produce antibodies, Memory cells formed

Injury

Damage to tissues caused by external force

Responses to Injury

Inflammation, Blood clotting, Temporary or permanent loss of function

Severe Outcomes of Injury

Haemorrhage (blood loss), Ischaemia (reduced oxygen supply), Organ failure (severe cases)

MRI Uses

Strong magnetic field, Radio waves, Produces internal body images

MRI Considerations

Metal implants/pacemakers, Patient medical history, Patient preparation (remove metal, explain procedure)