Session 3: Immune System Flashcards
What are nonspecific defences (innate immunity)?
First line of defense is intact skin, and mucous membranes and their secretions. Second line of defense is phagocytic white blood cells (which engulf foreign materials like bacteria), inflammation and fever, and antimicrobial substances (substances that kill microbes). Nonspecific defenses are present before any exposure to pathogens and are effective from the time of birth.
What are specific defense mechanism (adaptive/acquired immunity)?
Specific defence mechanisms are the third line of defense: specialized lymphocytes (B-cells and T-cells) and antibodies. Specific mechanisms develop after exposure to microbes, toxins, or other foreign substances.
Describe the first line of defence (skin).
The skin provides a physical barrier to the entry of pathogens and is rarely penetrated by microorganisms. Harmless microbes live on the skin, making it difficult for others to colonise - natural microflora of intact skin inhibits the growth of most pathogenic microbes. The skin continuously sheds old skin cells which can physically remove microbes. The skin also produces chemical secretions, which inhibit the growth of bacteria and fungi. If microorganisms enter the body (get past the skin) they face a range of other defences: the lining of the respiratory, urinary, reproductive, and gastrointestinal tracts have sticky mucus that traps microorganisms and expels them using cilia.
Describe the second line of defence.
A range of non-specific cellular and chemical defences inside the body inhibit or destroy pathogens. Non-specific defences react to the presence of any foreign body, regardless of its nature. White blood cells are involved in most of these responses.
Describe blood clotting.
When tissue is wounded, the blood quickly coagulates to prevent further blood loss and maintain the integrity of the circulatory system. A tear or puncture of a blood vessel initiates clotting in order to prevent blood loss and invasion of bacteria. Clot formation is triggered by the release of clotting factors from damaged cells. A hardened clot forms a scab which acts as a barrier against the entry of pathogens. Injury to the lining of a blood vessel exposes collagen fibres to the blood. Platelets stick to the collagen fibres. Platelet releases chemicals that make the surrounding platelets sticky. Platelets clump together, the platelet plug forms an emergency protection against blood loss. A fibrin clot reinforces the seal by trapping blood cells. The clot eventually dries to form a scab.
Describe phagocytes and the phagocytosis process
Phagocytes are white blood cells that ingest microbes by phagocytosis and dispose of them, there are three types: granulocytes (including neutrophils), monocytes, and lympocytes. Detection: phagocyte locates harmful microbes via their chemical signature (chemotaxis). The microbes stick to receptors on the phagocyte’s surface. Ingestion: The phagocyte wraps pseudopodia around the bacteria, engulfing them. Phagosome forms: A phagosome (phagocytic vesicle) is formed, enclosing the bacteria within a membrane. Fusion with lysosome: phagosome fuses with a lysosome (containing powerful enzymes that can destroy the bacteria). Digestion: The bacteria are broken down by enzymes into their chemical constituents. Discharge: indigestible material is discharged from the phagocyte.
Describe monocytes (type of phagocyte).
Monocytes are the largest type of immune cell, they circulate in the blood and move quickly to the site of infection. They differentiate into macrophages in body tissues and dendritic cells. Macrophages engulf cellular debris and pathogens, and help stimulate lymphocytes and other immune cells. They are able to replace their lysosomes and are thought to have a much longer active life to destroy multiple pathogens. Dendritic cells act as messengers between the innate and adaptive immune system, sampling cellular structures and presenting antigen fragments to lymphocytes in order to help develop longer term immunity.
Describe neutrophils.
Neutrophils are the most abundant type of phagocyte. They are unable to renew their lysosomes and die after having phagocytosed a few pathogens. The accumulated dead neutrophils forms the majority of pus).
What are three types of leukocytes?
Basophils - involved in the inflammation response by releasing histamine and heparin. Eosinophil - discharge destructive enzymes, often in response to parasitic infections. Mast cell – very similar role to basophils (store histamine and heparin), also involved in allergy and anaphylaxis.
What are natural killer cells?
Type of cellular innate defence: Natural Killer Cells circulate through the body and detect abnormal cells. They are a type of lymphocyte that release chemicals leading to cell death, inhibiting the spread of virally infected or cancerous cells. They are not adaptive and do not keep memory of pathogenic cell, they destroy any potential threats they come across.
What are the functions of inflammation?
To destroy the cause of the infection and remove it and its products from the body. If this fails, to limit the effects on the body by confining the infection to a small area. To replace or repair tissue damaged by the infection by improving blood flow. Inflammation can be either local or systemic (throughout the body).
What is the process of inflammation?
Bacteria enter, a blood clot forms, and chemicals are released by damaged cells (e.g. histamines and prostaglandins) which attract phagocytes to the infection. Blood vessels increase in diameter and permeability in the area of damage. This increases blood flow to the area and allows defensive substances to leak into tissue spaces. Phagocytes reach the damaged area within one hour of injury, they squeeze between cells of blood vessel walls to enter the region and destroy invading microbes. An abscess starts to form after a few days. This collection of dead phagocytes, damaged tissue and various body fluids is called pus. Functioning cells or supporting connective tissue cells create new tissue to replace dead or damaged cells.
Describe inflammatory responses.
The inflammatory response, pain, redness, heat, and swelling, is brought about by molecules released upon infection injury. Mast cells and basophils release histamine, which triggers blood vessels to dilate and become more permeable, which causes fluids to collect around an injury to dilute toxins. This causes swelling. They also produce heparin which acts as an anticoagulant, preventing the formation or extension of clots. Prostaglandins increase blood flow and can cause pain. Activated macrophages and neutrophils release cytokines, signalling molecules that enhance the immune response. The temperature of the tissues may rise, which can kill temperature-sensitive microbes.
What is the function of fever?
Fever is a systemic inflammatory response triggered by pyrogens released by macrophages and by toxins from pathogens. Fever is a defense mechanism that can destroy many types of microbes. Fever also helps fight viral infections by increasing interferon production, proteins that are produced by the body’s cells as a defensive response to viruses. While high fevers can be dangerous, some doctors recommend letting low fevers run their course without taking aspirin or ibuprofen.
Describe antimicrobial peptides and proteins.
Peptides and proteins function in innate defence by attacking pathogens or impeding their reproduction. Interferon proteins provide innate defence, interfering with viruses and helping activate macrophages. About 30 proteins make up the complement system, which causes lysis of invading cells and helps trigger inflammation.
