12 - Communicable diseases Flashcards
Pathogens
Pathogens are microorganisms that cause diseases.
they live within the Host and also cause damage by taking nutrition from them.
There are 4 types of pathogens
Bacteria
TB
Bacterial meningitis
Ringrot
Their presence can cause diseases by damaging cells or by releasing waste products to the host.
In plants bacteria lives within the vascular tissues and cause blackening and death of these tissues
Viruses
HIV / AIDS
Influenza
Tobacco Mosaic Virus (TMV)
Viruses invade cells and take over the genetic machinery and other organelles of the cell
Then they cause the cell to create more copies of the virus
The host cell eventually bursts releasing many new viruses which can affect the healthy cells
Protoctista
Malaria
Blight
These enter the cell and feed on the contents so that they can grow
Fungi
Black sigatoka
Athlete’s foot
Ringworm
Fungus can send out specialise reproductive hyphae which grow on the surface of the skin to release spores
Direct Transmission
Passing a pathogen from host to new host with no middle vector
Indirect transmission
Passing off and pathogen from host to a new host via a vector
Transmission
Passing a pathogen from an infected individual to an uninfected individual
Vector
An organism that carries a pathogen from one host to another
Diseases and climate
Many fungi and bacteria can grow and reproduce quicker in warm and waste conditions therefore they tend to be more common in warmer climates. In cooler conditions these pathogens are damaged and even killed by cold weather
Passive defences
Passive defences are present before the infection and their role is to prevent the entry and spread of the pathogen
Plant defences (physical)
Cellulose cell wall acts as a physical barrier
Lignin thickening of the cell wall
Waxy cuticle prevent water collecting on the surface
Bark contains chemicals
Callose : a large polysaccharide that is deposited in the sieve tubes
Plant defences (chemical)
Some chemicals such as terpenes and tannins in bark are present before an infection however because it requires a lot of energy they are not produced until after the plant detects takes an infection
Active Defence
Cell walls becoming thickened and are strengthened with additional cellulose.
Callose is deposited between the plant cell wall and membrane near the pathogen so that the pathogen cannot penetrate the barrier and infect the cell
Necrosis
Deliberate cell suicide
Canker
A sunken necrotic lesion in the woody tissue it causes death of the cambium tissue in the bath
Inflammation
Swelling and redness of tissue caused by infection
Mucous membrane
Specialised epithelial tissue that is covered by mucus
Primary defences
Those that prevent pathogens entering the body
The Skin
The skin is the body’s main primary defence. The outer layer of the skin or the epidermis, consists of layers of cells. These cells are called keratinocytes.
These cells are produced by mitosis at the base of the epidermis. As they migrate, they dry out and the cytoplasm is replaced by the protein keratin. This process is called keratinisation. By the time the cells reach the surface, they are no longer available. The layer of dead skin acts as an effective barrier to pathogens.
Blood clotting
The body must prevent excess blood loss by forming a clot, making a temporary seal to prevent infection and repair the skin.
Many clotting factors are released platelets and from damaged tissue. These factors activate an enzyme cascade.
Skin repair
Once the clot is formed, it begins to dry out and form a scab. The scab shrinks and dries, which makes a temporary seal, where the skin under repairs.
Phagocytes
First line of the secondary defence. Specialised cells in the blood and tissue fluid engulf and digest the pathogens.
Antigen presenting cell
A cell that isolates the antigen from a pathogen and places it on the plasma membrane so that it can be recognised by other cells in the immune system
Neutrophil
A type of white blood cells that engulfs foreign matter and traps it the phagosome which fuses with lysosomes to digest the foreign matter.
Opsonins
Protein that binds to the antigen on a pathogen and then allow phagocytes to bind.
Stages of phagocytosis
Neutrophil binds to the opsonin attached to the antigen of the pathogen.
The pathogen is engulfed by endocytosis forming a phagosome.
Lysosomes fuse to the phagosome and release lyric enzymes into it.
After digestion, the harmless products can be absorbed into the cells.
Interleukin
Signally molecules that are used to stimulate the immune response
Antibodies
Specific proteins released by plasma cells that can attach to pathogenic antigens
T helper cells
Release cytokines that stimulate the B cells to develop and stimulate phagocytosis
T killer cells
Cells which can attack and kill host-body cells that display the foreign antigen.
T memory cells
Cells that remain in the blood which require long-term immunity
T regulator cells
Cells which shut down the immune response after the pathogen has successfully been removed
Plasma cells
These produce antibodies to a particular antigen and release them into circulation
B memory cells
These live for a long time and provide the immunological memory.
B effector cells
These divide to form the plasma cell clones
How antibodies defend the bodyCell mediated immunity
1) The antibody of the antigen-antibody complex acts as an opsonin so the complex is easily engulfed by phagocytes.
2) Most pathogens can no longer effectively invade the host cells once they are part of an antigen-antibody complex.
3) Antibodies act as agglutinins causing pathogens carrying antigen-antibody complexes to clump together. This helps prevent them spreading through the body and makes it easier for phagocytes to engulf a number of pathogens at the same time
4) Antibodies can act as anti-toxins binding to the toxins produced by the pathogens and making them harmless
Clonal Expansion
An increase in the number of cells by mitotic cell division
Cell mediated immunity
The T lymphocytes respond to the cells of an organism that have been changed in some way, by antigen processing or mutation and cells from transplanted tissues. It is particularly important against viruses and early cancers.
How does cell mediated immunity occurs
1) In the non-specific defence system, pathogens go through phagocytosis. They process the antigens from the surface of the pathogen to form antigen-presenting cells.
2) The receptors on some of the T helper cells fit the antigens. These T helper cells become activated and produce interleukin, which stimulate more T cells to divide rapidly by mitosis. They form clones of identical activated T helper cells that all carry the right antigen to bind to a particular pathogen.
3) The cloned T cells may:
- Develop into T memory cells, which give rapid responses, if the pathogens invade the body again
- Produce interleukins to stimulate phagocytosis
Humoral Immunity
In humoral immunity the body responds to antigens found outside the cells, and to APC’s.
The humoral immune system produces antibodies that are soluble in the blood and tissue fluid and are not attached to cells.
B lymphocytes have antibodies on their cell-surface membrane and there are millions of different types each with their own antibodies.
When a pathogen enters the body it will carry specific antigens or produce toxins that act as antigens. A B cell with the complementary antibodies will bind to the antigens on the pathogens. The B cell engulfs and processes the antigens to become an APC.
How does humoral immunity occur
1) Activated T helper cells bind to the B cell APC. This is clonal selection - the point at which the B cell with correct antibody to overcome a particular is selected for cloning.
2) Interleukins produced by the activated T helper cells activate the B cells
3) The activated B cell divides by mitosis to give clones of plasma cells and B memory cells. This is clonal expansion
4) Cloned plasma cells produce antibodies that fit the antigens on the surface of the pathogen, bind to the antigens and disable them or act as opsonins or agglutinins. This is the PRIMARY immune response and it can take days even weeks to be fully effective against a particular pathogen. This is why we get symptoms before the primary response is fully operational.
5) Some cloned B cells develop into B memory cells. If the body is infected by the same pathogen again, the B memory cells divide to form plasma cell clones. These produce the right antibody and wipe out the pathogen quickly before it can cause the symptoms of disease. This is the SECONDARY immune response.
Structure of antibodies
Antibody molecules are Y-shaped and have two distinct regions
They consist of four polypeptide chains
They have a variable region which has a specific to the shape of antigen.
They also have a constant region which is the same in all antibodies
They are Y shaped like a proteins called immunoglobulins, which bind to a specific antigen on the pathogen that has triggered the immune response.
The chains are hard together by disulfide bridges and they are also disulfide bridges within the polypeptide chain holding them in shape.
Antibodies bind to antigens with a protein-based lock and key mechanism which is complementary between the active site of the enzyme and substrate
The variable region
The binding site of 110 amino acids on both heavy and light chain
How do antibodies defend the body
The antibody of the antigen-antibody complex acts as an opsonin so the complex is easily engulfed and digested by the phagocytes.
Most pathogens can no longer effectively invade the host cells once they are part of an antig- antibody complex.
Antibodies act as agglutininins causing pathogens carrying antigen-antibody complexes to clump together. This helps prevent them spreading though the whole body and it easier for the phagocytes to engulf a number of pathogens at the same time.
Antibodies can act as anti-toxins, binding to the toxins produced by pathogens making them harmless
Natural Active Immunity
When you first meet a pathogen your immune system is activated and antibodies are formed, which results in the destruction of the antigen.
The immune system produces T and B memory cells so if you meet a pathogen for a second time your immune system recognises and destroys the pathogen immediately.
It is known as ‘natural’ as your body acts by itself to produce these antibodies.
Natural Passive Immunity
The immune system of a new-born baby cannot make antibodies for the first few months.
Some antibodies are passed from the mother to the fetus while the baby is in the uterus, so it has some immunities from birth.
The first milk a mother makes called colostrum, is very high in antibodies.
The infant gut allows these proteins to pass into the bloodstream without being digested.
These antibodies last until the immune system of the baby begin to make its own.
Artificial Passive Immunity
For certain fatal disease, antibodies are formed n one individual, extracted and then are injected into the bloodstream of another individual.
Artificial Active Immunity
The immune system of the body is stimulated to make its own antibodies to a safe form or an antigen (vaccine), which is injected into the bloodstream.
The antigen is not usually the normal live pathogen, as this could cause disease and have fatal results.
Formation of a vaccine
The pathogen is made safe in one of these ways so that the antigens are intact but there is no risk of infection.
Small amounts of the safe antigen, are injected into the blood.
The primary immune response is triggered by the foreign antigens and your body produces antibodies and memory cells as if you were infected with a live pathogens.
If you come into contact with a live pathogen, the secondary immune response is triggered and you destroy the pathogen rapidly before you suffer symptoms of the disease.
Autoimmune diseases
Sometimes the immune system stops recognising ‘self’ cells and starts to attack healthy body tissue. This known as an
autoimmune disease.
There are around 80 different types of autoimmune diseases that can cause chronic inflammation or the complete breakdown and destruction of healthy tissue.
.
Type 1 diabetes
Affected body parts:
The insulin secreting cells of the pancreas
Treatment:
Insulin injection
Pancreas transplant
Immunosuppresant drugs
Rheumatoid arthritis
Affected body parts:
Joints (hands, wrists, ankles and feet)
Treatment: No cure Anti-inflammatory drugs Steroids Immunosuppresants Pain relief
Lupus
Affected body parts:
Skin/Joints
Can attack any organ
Treatment: No cure Anti-inflammatory drugs Steroids Immunosuppresants
Sources of medicines
Penicillin was first widely used, effective, safe antibiotic capable or curing bacterial diseases.
It comes from mould.
Alexander Fleming saw what mould did to his bacteria but could not extract enough to test its potential.
It need Florey and Chain to develop an industrial process for making the drug.
Personalised Medicine
Sequencing technology and molecular modelling have huge potential for future medicine.
It is possible to screen the genomes of pants or microorganisms to identify potential medicinal compounds from DNA sequences.
It may be possible to sequence the genes from individuals with a particular condition and develop specific drugs for the conditions.
Synthetic Biology
The development of new molecules (enzymes). = synthetic biology
It is also used to design and construct new devices and systems that may be useful in research, healthcare or in manufacturing.
Some fruits and vegetables have specific health benefits.
Penicillin
Source: Extracted from mould growing on melons
Action: Antibiotic
Docetaxel/Paclitaxel
Source: Derived from yew tress
Action: Treatment of breast cancer
Aspirin
Source: Based on willow bark
Action: Pain-killer, anti-coagulant
Prialt
Source: Derived from the venom of a cone snail
Action: New pain-killing drug - x1000 more effective than morphine
Vancomycin
Source: Derived form soil fungus
Action: One of our most powerful antibiotics
Digoxin
Source: Originally extracted from foxgloves
Action: Powerful heart drug used to treat atrial fibrillation and heart failure
Antibiotic Dilemma
Antibiotics interfere with the metabolism of bacteria without affecting the metabolism of human cells = selective toxicity.
Antibiotics are becoming a less effective in the treatment of bacteria diseases as they are becoming resistant.
Antibiotic Resistance
MRSA and C.difficile
An antibiotic works because a bacterium has a binding site for the drug. If a random mutation occurs during bacterial reproduction, that new bacteria may not be affected by the antibiotics , therefore these ones will reproduce and survive
