Cells Flashcards
What is an antigen
Any part of an organism or substance that the body recognises as self or non self
Describe lymphocytes
Have different receptors capable of recognising one kind of antigen
When they encounter their complementary pathogen they replicate
Examples of non self
Pathogens- viruses,bacteria,parasites
Non self cells
Transplanted tissues
Various toxins
Abnormal body cells- cancer cells
Examples of first line of defence
Skin
Earwax
Stomach acid
Sweat
Tears
Examples of second line of defence
Attack pathogens but don’t remember for next time
-Leukocytes
-Complement system
-Inflammatory response
Process of phagocytosis
Chemical products of pathogens can be detected by phagocytes, attracting
them towards the pathogen. Excellent trackers.
• Phagocytes also have receptors on their surface membrane allowing them
to detect non-self materials.
• When anything non-self is encountered, the phagocyte forms a vesicle
known as a phagosome which engulfs the pathogen.
• Lysosomes form and move towards the phagosome. Lysosomes contain
lysozymes which hydrolyse pathogen cell walls, destroying them.
• The soluble components of the destroyed pathogens are absorbed into the
cytoplasm of the phagocyte.
• The phagocyte presents pathogenic antigens on its cell membrane.
What are B-lymphocytes
“B” because they mature in the bone marrow. They
are responsible for the humoral response, so called because B-cells
are associated with antibodies found in body fluids such as blood
plasma.
What are T-Lymphocytes
“T” because they mature in the thymus. These are
associated with the cell-mediated response. They respond only toantigens present on body cells
Process involving T-lymphocytes
• Pathogens invade body cells or are engulfed by phagocytosis.
• Body cells present the pathogen antigens on their own cell membrane.
• Receptors on a specific helper T-cell bind to the antigen.
• This attachment stimulates the T-cell to divide rapidly by mitosis, forming
clones of genetically identical cells.
• The cloned cells respond in 4 distinct ways:
• They develop into memory cells that enable a more rapid response to future
exposure to the same pathogen.
• They stimulate phagocytes to engulf pathogens by phagocytosis.
• They stimulate B-lymphocytes to divide and excrete their antibody.
• They activate cytotoxic T-cells, Killer T-cells, (TC cells)
What do Killer T-cells do?
Killer T cells produce a protein called perforin, (think perforate)
perforin creates holes in the cell membrane of pathogenic or infected cells.
What is passive immunity?
The introduction of exogenous antibodies. No direct
contact with pathogens or antigens needed. No memory cells are produced and there is no endogenous production of the antibody. Antibodies are not replaced when they are broken down, thus the effect is short-lived. Anti-venoms and antibodies passed through the placenta to the foetus are examples of passive immunity.
What is active immunity?
Produced by stimulating the endogenous production
of antibodies by ones own immune system. Direct contact with the pathogen or antigen is necessary. This kind of immunity takes time to develop and is generally long-lasting
What is natural active immunity?
The immunity results from direct contact with pathogens or antigens under the natural context. I.e. you catch a disease.
What is artificial active immunity?
The immune response is purposely induced by introduction of disease antigens, ideally without the individual suffering the symptoms of the disease.
Why might vaccination completely eradicate a disease?
• The vaccine won’t work for all individuals. Compromised immune systems etc.
• Individuals may contract the disease soon after vaccination, i.e. before immunity develops.
• Mutation. Why do pathogens evolve rapidly?
• Highly variable pathogens, e.g. common cold.
• Some pathogens are good at evading the immune system. HIV, or Cholera “hiding” in the intestines.
• Some people may object. The old “vaccines cause autism” argument.
