The immune system Flashcards
- Our body defends itself against —–
pathogens
* These are recognised as being nonself – foreign molecules
Organs of the immune system
-The lymphoid tissues are an essential part of the defence system
* The thymus
* The spleen
* The lymph nodes
* The lymphoid tissues scattered throughout the gastrointestinal, respiratory and urinary tracts
Types of immunity
- Immunity occurs when an organism has sufficient
defences to successfully avoid the effects of biological invasion by a pathogen - Two major types of immunity in humans: the innate and the acquired/adaptive
- The innate and adaptive mechanisms operate together as a coordinated defence system
The innate immune system
- Nonspecific – applied to any potential harmful pathogen
- Inherited mechanisms
- Act very rapidly
- Consists of
- Physical barriers
- Mechanical barriers
- Chemical barriers
- Blood cells.
Two lines of innate defence
1st line - the physical and chemical barriers
2nd line - involves immune cells and proteins to nonspecifically recognize and eliminate any pathogen that enters the body
Physical barriers of innate
*Includes the skin and mucosal membranes
* Acts as a physical barrier to prevent infectious organisms and other matter from entering the body
* Acts as a chemical barrier
* Sweat is bactericidal
* Skin has weak spots
* Various orifices that connect the internal body to the outside
* Mouth, nose urethral opening, anus
The skin
-The physical barrier of the skin: Bacteria rarely penetrate intact skin, which has about 30 cell layers; by the same token, broken skin increases the risk of infection.
-The saltiness and dryness of skin: This environment may not be hospitable to the growth of the bacterium.
-The presence of normal flora: Bacteria and fungi that normally live and sometimes reproduce in great numbers on our body surfaces without causing disease will compete with pathogens for space and nutrients.
Mechanical/chemical barriers
- Cilia, coughing, sneezing and tears
- Cilia move dirt, microorganisms and mucus away to the adenoids (made of lymphatic tissue)
- Mucus is a viscous substance secreted by mucous membranes
- Mucus traps microorganisms so they can be removed by the beating of cilia
- Sneezing and coughing work by expelling any microorganisms or irritants out of the body and into the external atmosphere
- Tears are also a mechanical barrier. They also contain a a bactericidal enzyme- Lysozyme
- An enzyme made by cells of the mucous membranes that attacks the cell walls of many bacteria, causing them to lyse (burst open).
- Defensins - toxic to a wide range of pathogens, including bacteria, microbial eukaryotes, and enveloped viruses
- insert themselves into the cell membranes of these organisms and make the membranes permeable, thus killing the invaders
- also produced in phagocytes, where they kill pathogens ingested by phagocytosis
- Gastric juice in the stomach is a deadly environment for many bacteria because of the hydrochloric acid and proteases that are secreted into it
Specialised proteins and cells
- Complement proteins
- Proteins attach to specific components on the surface of a microbe or to an antibody that has already bound to the microbe’s surface.
- Binding helps phagocytes recognize and destroy the microbe
- Activate the inflammatory response and attract phagocytes to the site of infection
- Complement proteins lyse invading cells
what are Interferons
- Signalling proteins
- Increase the resistance of neighbouring cells to infections
- A class of cytokines
- Particularly important against viruses
- Bind to receptors on the cell membranes of uninfected cells
- Stimulate a signalling pathway that inhibits viral reproduction if the cells are subsequently infected
what is Phagocytes
- Some phagocytes travel freely in the circulatory and lymphatic systems
- Others can move out of blood vessels and adhere to certain tissues
what is Natural killer cells
- A class of lymphocytes
- Can distinguish virusinfected cells and some tumour cells from their normal counterparts and initiate apoptosis (programmed cell death )
- Interact with the adaptive defence mechanisms by
lysing antibody—labelled target cells
what are Dendritic cells
- Phagocytes present in tissues exposed to the environment
- skin and the linings of the digestive and respiratory tracts, blood
- Act as messengers between the innate and adaptive immune systems
- Can endocytose microbes, viruses, and even remnants of the virusinfected host cells
- Once inside a dendritic cell, these particles are digested to fragments
- Dendritic cell “presents” an antigenic fragment on its surface, with MHC class II proteins
- Dendritic cells secrete signals that activate cells of the adaptive immune system
Inflammation
- Isolates the damaged area to stop the spread of the damage
- Recruits cells and molecules to the damaged location to kill the invader
- Promotes healing
- The first responders to tissue damage are mast cells
- Adhere to the skin and the linings of organs
- Release numerous chemical signals
- Tumor necrosis factor, a cytokine protein that kills target cells and activates immune cells.
- Prostaglandins, fatty acid derivatives involved in various responses, including the widening of blood vessels. Interact with nerve endings and are partly
responsible for the pain caused by inflammation. - Histamine, an amino acid derivative that causes dilation of blood vessels, as well as itchy, watery eyes and rashes seen with some types of allergic reactions.
The adaptive immune system
- Aimed at specific pathogens
- Activated by the innate immune system
- Slower to develop than the innate defences
- Longer lasting
- Involves the following:
- Antibody proteins
- Other proteins that recognise, bind to and aid destruction of specific viruses and bacteria
- Memory cells
Classes of antibodi
