Defense Against Disease Flashcards
What is the role of fibrin in the clotting process?
Fibrin forms a mesh that traps platelets and red blood cells, creating a stable blood clot that eventually dries and shrinks to form a scab.
How does thrombin contribute to forming a blood clot?
Thrombin converts fibrinogen, a soluble clotting factor, into insoluble fibrin.
What role does thromboplastin play in the clotting cascade?
Thromboplastin, with the help of calcium ions, converts prothrombin into its active form, thrombin.
What do platelets and injured tissues release during clotting, and why is this important?
They release clotting factors—including calcium ions and thromboplastin—which trigger a cascade of chemical reactions necessary for clot formation.
What is the initial step in blood clotting following a skin injury?
Platelets are activated and accumulate at the site of injury to form a plug.
Why is blood clotting an important defence mechanism?
Clotting quickly seals wounds or cuts, preventing pathogens from entering the body through these openings.
What function do commensal bacteria serve in our primary defence system?
They naturally reside on the skin, gut, mouth, and nose and can outcompete pathogenic organisms for nutrients and space.
How do gastric secretions contribute to defence against ingested pathogens?
The hydrochloric acid in gastric secretions creates a low pH that kills most microbes ingested with food.
What role do cilia play in defending the respiratory system?
Cilia on respiratory epithelial cells beat in a coordinated way to move mucus and trapped pathogens away from the lungs, facilitating their expulsion via coughing or sneezing.
In which body fluids is lysozyme found and what is its role?
Lysozyme is present in mucus, sweat, tears, and saliva, where it helps to kill bacteria.
How do mucous membranes trap and eliminate pathogens?
They produce sticky mucus that traps pathogens and contains lysozyme, an enzyme that attacks bacterial cell walls.
What are mucous membranes and where are they located?
They line the body cavities and parts open to the outside, including the digestive, urogenital, and respiratory tracts, as well as the mouth, nose, and other ducts.
What chemical defence does the skin offer against pathogens?
Sebaceous glands secrete oils that lower the skin’s pH, inhibiting bacterial growth.
How does the epidermis help prevent pathogen entry?
Its outer layers consist of dead cells with keratin deposits that form a tough, impermeable barrier.
What are the three layers of the skin?
The epidermis, dermis, and hypodermis.
What are the primary physical and chemical barriers that form the body’s first line of defence?
The skin and mucous membranes.
In what way can some pathogens be classified as parasites?
A: Some pathogens are obligate parasites, meaning they rely on their host for energy, nutrition, and other life functions.
What are prions and what is an example of a prion-caused disease?
Prions are infectious proteinaceous substances that cause neurodegenerative diseases, for example, bovine spongiform encephalopathy (mad cow disease).
What distinguishes viruses from other pathogens, and what diseases do they cause?
Viruses require a living cell to replicate. They cause diseases such as the common cold, influenza, measles, mumps, and COVID-19.
Define protists and list some diseases they cause.
Protists are diverse unicellular or multicellular eukaryotic organisms. The pathogenic ones can cause diseases like malaria, toxoplasmosis, and sleeping sickness.
What are fungi and which diseases are commonly associated with fungal pathogens?
Fungi are unicellular or multicellular eukaryotic organisms; a small percentage are pathogenic and can cause conditions such as ringworm, thrush, and athlete’s foot.
What are bacteria and what diseases can pathogenic bacteria cause?
Bacteria are unicellular, prokaryotic organisms found nearly everywhere. Although most are beneficial, some cause diseases like tuberculosis, plague, diphtheria, and cholera.
What are the main types of pathogens?
Bacteria, fungi, protists, viruses, and prions.
How do pathogens cause disease in the human body?
They invade and live parasitically in the body, and diseases occur when they pass from an infected host to a healthy individual.
What are pathogens?
Pathogens, also called infectious agents, are organisms that cause disease and serve as the starting points in the chain of infection.
amoeboid movement
A type of locomotion that involves the protrusion of pseudopodia.
Monocyte
Largest type of specialised white blood cells or leukocytes capable of amoeboid movement., defending the immune system by destroying or damaging pathogens, including viruses, bacteria and fungi.
Neutrophil
Most abundant type of specialised white blood cells or leukocytes capable of amoeboid movement. of white blood cells, They are usually the first line of defence against pathogens, targeting mainly bacteria and fungi.
Macrophages
A type of white blood cell that engulfs and kills microorganisms, removes dead cells, and stimulates the action of other immune system cells.
Pseudopodia
Literally ‘false feet’, they are temporary arm-like projections or extensions used for movement and feeding.
What is the primary role of the immune system?
To protect the body from pathogens and foreign substances by distinguishing self from non-self.
What are the two main branches of the immune system?
The innate immune system and the adaptive immune system.
What is innate immunity?
Immunity present from birth that provides rapid, non-specific defence against pathogens.
How does the innate immune system respond to pathogens?
It uses physical and chemical barriers—such as the skin, mucous membranes, and phagocytosis—to prevent or limit pathogen spread.
Is the response of the innate immune system specific to particular pathogens?
No, it responds in a similar manner to any potential pathogen without tailoring the response.
What triggers the adaptive immune system?
It is activated when the innate immune system is unable to fully control an infection.
Which cells mediate the adaptive immune response?
Lymphocytes, a type of white blood cell.
What is one key feature that distinguishes the adaptive immune system from the innate immune system?
Specificity—it targets particular pathogens with a tailored response.
What is another important feature of the adaptive immune system?
Memory—the system “remembers” pathogens for a faster, enhanced response during subsequent infections.
Do the innate and adaptive immune systems work independently?
No, they constantly communicate and work together to provide an effective immune response.
What is phagocytosis?
A process where specialized white blood cells ingest and digest foreign material, including pathogens.
Which cells are known as professional phagocytes?
Monocytes, neutrophils, and macrophages.
What kind of movement allows phagocytes to reach the site of an infection?
Amoeboid movement, which enables them to migrate from the blood to the affected tissues.
What is the first step in the process of phagocytosis?
Recognition of the pathogen by receptor molecules on the plasma membrane of phagocytes.
After recognition, how do phagocytes begin to engulf the pathogen?
They extend pseudopodia that bind to and surround the pathogen.
What structure is formed when pseudopodia encircle the pathogen?
A vesicle called a phagosome.
What happens during phagosome maturation?
The phagosome undergoes changes preparing it for fusion with lysosomes.
What is formed when the phagosome fuses with lysosomes?
A phagolysosome.
What role do the lysosomal enzymes play in phagocytosis?
They digest the microbial components inside the phagolysosome.
What is the end result of phagocytosis?
The pathogen is broken down, and its components are released from the cell.
How would you compare the speed of the innate immune response with that of the adaptive immune response?
The innate immune response is rapid and immediate, whereas the adaptive response is slower to develop.
What advantage does immunological memory provide?
It allows for a faster and more effective response upon re-infection with the same pathogen.
Why is distinguishing self from non-self critical for the immune system?
It prevents the immune system from attacking the body’s own cells while targeting foreign invaders.
What general defence mechanisms are employed by the innate immune system?
Physical barriers (skin and mucous membranes) and generalised cellular responses like phagocytosis.
How does the adaptive immune system complement the innate immune system?
It provides a specific, long-lasting response that targets pathogens more effectively when the innate defences are insufficient.
Which immunity retains memory?
Adaptive immunity retains a memory of the pathogen ensuring a more effective and enhanced immune response on subsequent exposure to the same pathogen.
What are naive lymphocytes?
Lymphocytes (B-cells and T-cells) that have not yet encountered their specific antigen.
What are effector cells in the context of lymphocytes?
Lymphocytes that have encountered their specific antigen and become activated to mount an immune response.
What is the significance of having a specific B-cell and T-cell for every antigen?
It ensures that the immune system can recognize and respond to an enormous variety of antigens with precision.
How do lymphocytes become activated from their naive state?
They encounter their specific antigen in the secondary lymphoid organs, which triggers their conversion into effector cells.
What role do phagocytes play in activating helper T-cells?
They digest pathogens and retain fragments (antigens) that are later presented by antigen-presenting cells (APCs) to helper T-cells.
What is the function of antigen-presenting cells (APCs) in the immune response?
APCs display antigen fragments on their surface to activate specific helper T-cells.
What happens when a helper T-cell is activated?
It increases in number (clonal expansion), activates B-cells specific to the same antigen, and also activates cytotoxic T-cells.
How does the activation of helper T-cells contribute to the overall immune response?
By coordinating the activation of both B-cells (for antibody production) and cytotoxic T-cells (for killing infected cells).
What are the two integrated events required for B-cell activation?
First, the B-cell receptor must bind to its specific antigen; second, an activated helper T-cell that recognizes the same antigen must provide additional stimulation.
What is the clonal selection theory?
The theory that once a B-cell is activated by its specific antigen, it divides repeatedly to produce clones, all of which recognize the same antigen.
What occurs during the multiplication of activated B-cells?
They undergo repeated mitotic divisions to form many clones that are all specific to the antigen encountered.
What are plasma cells and what is their function?
Plasma cells are differentiated B-cells that produce and secrete large quantities of antibodies specific to the antigen.
What role do antibodies play in the immune response?
They bind to antigens, neutralizing them or marking them for destruction by other immune cells.
What are memory B-cells and why are they important?
Memory B-cells are long-lived cells that remain in the bloodstream and lymph nodes, “remembering” the antigen for a rapid response upon reinfection.
What is the primary immune response?
The initial immune response upon first exposure to an antigen, which is slower and less robust because it relies on the activation of naive lymphocytes.
What characterizes the secondary immune response?
A faster and stronger response upon re-exposure to the same antigen due to the rapid activation of memory B-cells.
How does the activation of helper T-cells lead to clonal expansion?
Once activated, helper T-cells multiply, increasing the pool of cells available to activate B-cells and cytotoxic T-cells that recognize the same antigen.
In the activation process, what indicates that a B-cell has successfully recognized an antigen?
The B-cell receptor on its surface binds specifically to the antigen.
Why is the stimulation by an activated helper T-cell critical for B-cell activation?
It provides a necessary second signal that ensures the B-cell is activated only in the presence of the correct antigen, thereby preventing inappropriate responses.
What is the overall result of the interaction between T-lymphocytes and B-lymphocytes?
The coordinated activation and clonal expansion of lymphocytes lead to the production of antibodies, elimination of the pathogen, and establishment of immunological memory.
How does the immune system “remember” an antigen for future protection?
Through the formation of memory B-cells, which remain dormant until the same antigen is encountered again.
What does the term “clonal expansion” refer to in the context of B-cell activation?
It refers to the process where a single activated B-cell divides to produce many identical clones that all recognize the same antigen.
How do plasma cells and memory cells differ in their roles?
Plasma cells produce antibodies to fight the current infection, while memory cells provide long-term immunity by “remembering” the antigen for future responses.
What triggers the transition from a primary to a secondary immune response?
The presence of memory B-cells generated during the primary response, which rapidly differentiate into plasma cells upon re-exposure to the antigen.
What is the significance of having both humoral and cell-mediated responses during an immune reaction?
It ensures that the body can neutralize free pathogens with antibodies (humoral immunity) and eliminate infected cells via cytotoxic T-cells (cell-mediated immunity).
Why is the described process considered a simplified version of lymphocyte activation?
Because the complete process involves additional complex signalling pathways and interactions that are beyond the scope of this overview.
