4.1 - Communicable diseases

What is a pathogen?

A microorganism that causes disease

What organisms can cause diseases?

Bacteria, fungi, viruses and protoctista

What is bacteria?

a member of a large group of unicellular microorganisms that have cell walls but lack organelles and an organized nucleus, including some that can cause disease.

What is fungi?

Microscopic plant parasites that include molds, mildews, and yeast.

What is virus?

a tiny, nonliving, particle that enters and reproduces inside a living cell

How does bacteria cause disease?

by destroying living cells or by releasing chemicals that upset homeostasis

How does bacteria reproduce?

binary fission and they reproduce rapidly

How does fungi cause disease?

Digest living cells and destroy or produce toxins.

How does fungi reproduce?

spores

How do viruses cause disease?

by directly destroying living cells or by affecting cellular processes in ways that upset homeostasis

How do viruses reproduce?

Viruses can reproduce only by infecting living cells

What is a protoctista?

a group of eukaryotic organisms with a wide variety of feeding methods

How does protoctista cause disease?

They don't take over the genetic material of the host, they just digest the cell as they reproduce and spread.

Give some of examples of protoctista diseases

malaria, potato/tomato late blight

Give some of examples of bacterial diseases

Tuberculosis, bacterial meningitis and ring rot

Give some of examples of viral diseases

HIV/AIDS, influenza and TMZ

Give some of examples of fungal diseases

black sigatoka (bananas), ringworm (cattle), athlete's foot (humans).

What is a physical disease?

All diseases with the exception of some
mental diseases can be classified as this. They
cause permanent or temporary damage to the
body.

What is an infectious disease?

A disease that is contagious an can be transmitted from host to host via the chain of infection.

What is a genetic disease?

An inherited medical condition caused by a DNA abnormality.

What is a degenerate disease?

Non infectious diseases caused by ageing and
the inability of the body to carry out effective
repairs and regeneration

Define direct transmission

Pathogens are passed from one person to another by direct body contact as in sexual contact or by close personal contact.

Define indirect transmission

When a infectious disease spreads through the air or makes contact .with contaminated objects

Define transmission

The movement of an infectious agent to a new host from another host or source.

Define vector

a carrier, usually an arthropod, which transmits an infective agent from one host to another

How does climate affect disease?

pathogens can grow and reproduce more rapidly in warm and moist conditions

enzymes are closer to optimum and rate of reaction is faster - more ESCs formed

cooler climates reduce ability to grow and reproduce

greater variety of diseases found in warmer climates and infection is more likely

What is the first line of defence?

Skin, mucous membranes, expulsive reflexes and chemical secretions

Explain how skin acts a first line of defence

Skin posses an outer layer of dry, dead, hardened
cells filled with keratin, which is a tough fibrous protein
This layer of cells acts as a physical barrier to
pathogens. There are secretions of sebum that contain fatty acids which have antimicrobial properties
Evaporation of sweat from the skin leaves behind a
salt residue. The lack of moisture, low pH and high salinity
creates an inhospitable environment for the growth of microorganisms

Explain how mucous membranes acts a first line of defence

Mucous membranes line the gut, airways and reproductive system. The mucous membrane consists of epithelial cells and mucus-secreting cells like goblet cells
Mucus contains lots of glycoproteins with long carbohydrate chains. These chains are what make mucus sticky. Viruses, bacteria, pollen and dust float about in the air that we breathe in. Mucus in the airways can trap these particles. The particles are then moved towards the back of the throat by cilia

Explain how expulsive reflexes acts a first line of defence

When a pathogen irritates the lining of an airway it can trigger an expulsive reflex; a cough or sneeze. Both a cough and sneeze result in a sudden expulsion of air. This expelled air contains secretions from the respiratory tract along with the foreign particles that have entered

Explain how chemical secretions acts a first line of defence

Lysozymes are antimicrobial enzymes that breakdown the cell wall of bacteria. These special enzymes are found in body fluids such as blood, tears, sweat, and breast milk. Hydrochloric acid is produced by the cells that line the stomach

Explain how inflammation acts a first line of defence

The surrounding area of a wound can sometimes become swollen, warm and painful to touch; this is described as inflammation. It occurs via chemical signaling molecules which cause the migration of phagocytes into the tissue and increased blood flow. Body cells called mast cells respond to tissue damage by secreting the cell signaling molecule, histamine

What is inflammation?

A condition in which the body reacts to injury, irritation, or infection.

Explain blood clotting

The process is called the coagulation cascade that
involves a set of complex of reactions
Principle events: clotting factors cause platelets to
become sticky and adhere to the damaged region
which forms a solid plug
Clotting factors trigger the conversion of the inactive
prothrombin into the activated enzyme thrombin
Thrombin catalyses the conversion of soluble plasma
protein fibrinogen into an insoluble fibrous form called
fibrin
Fibrin strands form a mesh of fibres around the platelet
plug that traps the blood cells to form a temporarily
blood clot

What are the types of physical defences in plants?

Cellulose cell wall, lignin thickening, waxy cuticles, bark, stomatal closure and callose

How does cellulose cell wall act as a physical defense?

It acts as a physical barrier but also contains a variety of chemical defences that can be activated when a pathogen is detected

How does lignin act as a physical defense?

It is waterproof and completely indigestible

How do waxy cuticles act as a physical defense?

These prevent water collecting on the cell surfaces as pathogens require water to survive

How does bark act as a physical defense?

It contains a variety of chemical defences

How does stomatal closure act as a physical defense?

Stomata is a point of entry for pathogens

How does callose act as a physical defense?

It is a large polysaccharide that is deposited in sieve tubes and it blocks the flows of sieve tubes, this can prevent pathogens spreading around the plant

What are the active defences of plants?

Production of chemicals, oxidative bursts and deposition of callose

What is a terpenoid?

A range of essential oils that have antibacterial and antifungal properties

What is a phenol?

They have antibacterial and antifungal properties. They binds to salivary proteins and digestive enzymes deactivating the enzymes.

What is a secondary defence?

One that is used to combat pathogens that have entered the body

What is opsonin?

Protein molecules that attach to the antigens on
the surface of a pathogen. They are a type of antibody. The are not very specific so can attach to a variety
of pathogens. Their role is to enhance the ability of phagocytic cells to bind and engulf the pathogen

What is a phagocyte?

Specialised cells in the blood and tissue fluid that
engulf and digest the pathogens

What are the different types of phagocytes?

neutrophils and macrophages

What is neutrophils?

It is the most common type of phagocyte and it is manufactured in the bone marrow. It travels in the blood but often squeezed out into tissue fluid. They are short lived and contain a large number of lysosomes. They engulf and digest the pathogen. They die after digesting pathogens and collect in the area of infection forming pus

Explain the process of phagocytosis for neutrophils

Neutrophil binds to the opsonin attached to the antigen of the pathogen. The pathogen is engulfed by endocytosis forming a phagosome. Lysosomes and release lytic enzyme into it. After digestion, the harmless products can be absorbed into the cell

What is a lysosome?

membranous sac of hydrolytic enzymes that can digest macromolecules

What is a macrophage?

A large cell that can ingest and destroy dying cells or cellular debris. Travel in the blood as monocytes and many found in lymph nodes where they mature
into macrophages. When a macrophage engulfs a pathogen, it does not fully digest it. The antigen is saved and moved to a special protein complex on the surface of the cell - the cell becomes an antigen-presenting cell

Describe the structure and location of the receptor and suggest how this helps phagocytes to carry out their role:

can bind of opsonin or an antigen

Describe the structure and location of the lobed nucleus and suggest how this helps lobed nucleus to carry out their role

allows the cell to squeeze through narrow gaps

Describe the structure and location of the cytoskeleton and suggest how this helps lobed nucleus to carry out their role

helps the cell to change shape so it can engulf the pathogen and to move lysosomes and vacuoles around the cell

Describe the structure and location of the lysosomes containing lysin and suggest how this helps lobed nucleus to carry out their role

enzymes that can hydrolyse bacterial cell walls

Describe the structure and location of the many mitochondria and suggest how this helps lobed nucleus to carry out their role

to release energy for the process

Describe the structure and location of ribosomes and suggest how this helps lobed nucleus to carry out their role

to make the enzymes required

How does phagocytosis lead to antigen?

1.Phagosome/vesicle fuses with lysosome
2.(Virus) destroyed by lysozymes/hydrolytic enzymes 3.Peptides/antigen (from virus) are displayed on the cell membrane

What is antigen presentation?

The antigen presenting cell moves around the body where it can come into contact with specific cells that can activate the full immune response. They are the T lymphocytes and the B lymphocytes. The can only be 1 T and B cell with the correct recognition site for the antigen

What is clonal selection?

the process through which immature B and T Cells go through so that only certain types are permitted to mature

What is specific immune response?

The specific immune response is triggered by the detection of antigens found on pathogens or foreign tissues. This makes white blood cells called B-lymphocytes to make specific antibodies that can identify and attach to the antigens and destroy the pathogen. This response can lead to long lasting immunity.

What are the cells produced in the immune response?

T and B lymphocytes

What are the 4 types of T cells?

T-helper, killer/cytotoxic T cells, memory T cells, suppressor T cells.

What are T helper cells?

They release cytokines (chemical messenger) that stimulate B cells to develop and stimulate phagocytes

What are T killer cells?

cells that attack and destroy our own body cells that are infected by a pathogen

What are T memory cells?

Cells that remain in the blood for a long time, providing long-term immunity.

What are T regulatory cells?

They shut down the immune response after the pathogen has been successfully removed. They also play a role in preventing autoimmunity

What are the types of B cells?

Plasma cells and memory B cells

What are plasma cells?

Cells which secrete antibodies (usually) into blood plasma. They only survive for a few days - lead to destruction of pathogen.

What are B memory cells?

Cells that remain in the blood for a long time, providing long-term immunity.

What is cell signalling?

The specific immune response involves the coordinated
action of a range of cells

What are the types of cytokines?

monokines, interleukins and interferon

What are monokines?

They released by macrophages. Some of these attract neutrophils by chemotaxis and others stimulate B cells to differentiate and release antibodies

What are interleukins?

They released by T cells and macrophages which can stimulate clonal expansion and the differentiation of B and T cells

What is interferon?

Many cells can release this chemical which inhibits viral replication and simulates the activity of T killer cells

What is the T lymphocyte response?

T lymphocytes are white blood cells which contain receptors on their cell surface. Different T cells have different shaped receptors on their surface (so they will each bind to a different-shaped antigen). When a particular T cell binds to a complementary antigen (e.g. on a antigen-presenting cell or on a pathogen), the T cell will become activated - this is called clonal selection. Once it is activated, the T cell divides by mitosis to produce clones of itself - this is called clonal expansion

What is B lymphocyte response

B cells are activated when chemicals are released from T helper cells. They are also activated when the antibody molecules on their cell surface bind to a complementary antigen. Different B cells have different shaped antibodies on their surface, so only the B cells with the correct-shaped antibodies will be activated. Once they are activated, the B cells divide by mitosis and differentiate into two kinds of cell - plasma cells and memory cells.

What are anitbodies?

Immunoglobulins- complex proteins produced by
the plasma cells
Released in response to infection
They have a region with a specific shape that is
complementary to the antigen
Antibodies attach to antigens and render them
harmless

What is the structure of an antibody?

Y shaped molecule, four polypeptide chains: two heavy identical chains and two light identical chains held together by a disulfide bond, four constant regions (C), and four variable regions (V)

What are the features of an antibody?

-Has two 'heavy' polypeptide chains bonded
by disulfide bonds to two 'light' polypeptide chains
-Each polypeptide chain has a constant
region and variable region
-The constant regions do not vary between antibodies
The variable regions of the antibodies are different for
each antibody. The variable region is where the
antibody attaches to the antigen to form
an antigen-antibody complex
-At the end of the variable region is a site called
the antigen-binding site.
- The 'hinge' region gives flexibility to the antibody
molecule which allows the antigen-binding site to be
placed at different angles when binding to antigens

What are the 3 main groups of antibodies?

opsonins, agglutinins, anti-toxins

Explain opsonization

what an antibody coats an antigen to facilitate its recognition by the immune system

What are other opsonins-neutralisation?

Others are produced as part of the specific immune
response and bind to specific antigens
They bind to the antigen and render it useless - this
is caused neutralisation
This prevents the pathogen from being able to
enter the host cell

What are antitoxins?

Antibodies can act as anti-toxins by binding to toxins produced by pathogens

What is agglutination?

Each antibody has two identical binding sites so can cross link pathogens. This causes the pathogens to clump together (agglutinate). This reduces the chance that the pathogens will spread through the body and makes it possible for phagocytes to engulf several pathogens at one time

What is a primary response?

When an infecting agent is detected for the
first time it takes a few days before the number of antibodies in the blood is enough to combat the infection successfully

What is a secondary response?

B and T memory cells remain in the blood. They will recognise the antigen from before and be able to start
production of antibodies sooner- it is usually quick enough to prevent any symptoms being detected by the host

What is active immunity?

the immunity that results from the production of antibodies by the immune system in response to the presence of an antigen.

What is artificial immunity?

Immunity that is acquired when a person receives a vaccine.

What's an example of natural active immunity?

Chicken pox

What's an example of artificial passive immunity?

Hepatitis A and B

What's an example of artificial active immunity?

Influenza

What is natural immunity?

Immunity achieved through normal life processes

What is passive immunity?

the short-term immunity that results from the introduction of antibodies from another person or animal.

What is a vaccination?

injection of a weakened form of a pathogen to produce immunity

What forms of antigenic material can a vaccine contain?

Harmless or attenuated (weakened) version of
the pathogenic organism
Dead pathogen
Just the antigens
A toxoid (harmless version of a toxin)

What is herd immunity and why is it important?

The majority of vaccinated individuals protect the minority of unvaccinated individuals by reducing the chances that an unvaccinated individual will come into contact with an infected person. As herd immunity decreases, there is more opportunity for a chain of transmission to be maintained because there is increased likelihood that an infected individual will come into contact with an unvaccinated individual. Strong herd immunity is important to give protection to vulnerable people, such as newborn babies, unvaccinated children and those too sick to be vaccinated.

What is ring vaccination?

Ring vaccination is used when a new case of a disease is reported. Ring vaccination involves vaccinating all the people in the immediate vicinity of the new case. It is used in many parts of the world to control the spread of livestock disease.

What are the challenges of eradicating disease?

Pathogens mutate- antigens change shape
Unstable political situations -perhaps resulting in civil unrest or wars
Lack of public health facilities (poor infrastructure, few trained personnel, limited financial resources)