Chapter 22 Flashcards
Immunity
The ability to ward off damage or disease through our defenses.
Susceptibility
Vulnerability or lack of resistance to damage or disease.
What are the two general types of immunity? Describe them:
- Innate (nonspecific) immunity: does not involve specific recognition of a microbe and acts against all microbes in the same way. Among the components of innate immunity are the first line of defense (the physical and chemical barriers of the skin and mucous membranes) and the second line of defense (antimicrobial substances, natural killer cells, phagocytes, inflammation, and fever). Innate immune responses represent immunity’s early warning system and are designed to prevent microbes from entering the body and to help eliminate those that do gain access.
- Adaptive (specific) immunity: defenses that involve specific recognition of a microbe once it has breached the innate immunity defenses. Is based on a specific response to a specific microbe. Adaptive immunity involves lymphocytes (a type of white blood cell) called T lymphocytes (T cells) and B lymphocytes (B cells). The lymphatic system is responsible for adaptive immunity.
Lymphatic (or lymphoid) system
Consists of lymph, lymphatic vessels, lymphatic tissues, and red bone marrow. Assists in circulating body fluids and helps defend the body against disease-causing agents.
Lymph
Interstitial fluid that is located within lymphatic vessels and lymphatic tissue.
Lymphatic tissue
A specialized form of reticular connective tissue that contains large numbers of lymphocytes.
What are the three primary functions of the lymphatic system?
- Drains excess interstitial fluid
- Transports dietary lipids
- Carries out immune responses
Lymphatic capillaries
Where lymphatic vessels begin. Are located in the spaces between cells, and are closed at one end. Unite to form larger lymphatic vessels.
What are the two main differences between lymphatic capillaries and blood capillaries?
- Lymphatic capillaries have greater permeability than blood capillaries and thus can absorb large molecules such as proteins and lipids.
- Lymphatic capillaries are slightly larger in diameter than blood capillaries and have a unique one-way structure that permits interstitial fluid to flow into them but not out.
Lacteals
Specialized lymphatic capillaries in the small intestine that carry dietary lipids into lymphatic vessels and ultimately into the blood. The presence of these lipids causes the lymph draining from the small intestine to appear creamy white, and this lymph is called chyle.
Describe the route of lymph
Blood capillaries (blood) → interstitial spaces (interstitial fluid) → lymphatic capillaries (lymph) → lymphatic vessels (lymph) → lymphatic trunks or ducts (lymph) → junction of the internal jugular and subclavian veins (blood).
What are the five principal lymph trunks? Describe them:
- Lumbar trunks: drain lymph from the lower limbs, the wall and viscera of the pelvis, the kidneys, the adrenal glands, and the abdominal wall.
- Intestinal trunk: drain lymph from the stomach, intestines, pancreas, spleen, and part of the liver.
- Bronchomediastinal trunks: drain lymph from the thoracic wall, lung, and heart.
- Subclavian trunks: drain the upper limbs.
- Jugular trunks: drain the head and neck.
True or false: lymphatic vessels contain valves
True. This ensures the one-way movement of lymph.
What two pumps help maintain the flow of lymph?
- Respiratory pump
- Skeletal muscle pump
What two groups can lymphatic organs and tissues be classified into based on their functions?
- Primary lymphatic organs: sites where stem cells divide and become immunocompetent, that is, capable of mounting an immune response. Include the red bone marrow and the thymus.
- Secondary lymphatic organs and tissues: sites where most immune responses occur. Include lymph nodes, the spleen, and lymphatic nodules (follicles).
Thymus
A bilobed organ located in the mediastinum between the sternum and the aorta. A connective tissue capsule encloses each lobe separately. Trabeculae divide each lobe into lobules.
Trabeculae
Extensions of the capsule.
What two components does each thymic lobule consist of? Describe them:
- Cortex: composed of large numbers of T cells and scattered dendritic cells, epithelial cells, and macrophages.
- Medulla: consists of widely scattered, more mature T cells, epithelial cells, dendritic cells, and macrophages.
Thymic (Hassall’s) corpuscles
Clusters of epithelial cells that become arranged into concentric layers of flat cells and become filled with keratohyalin granules and keratin. May serve as sites of T cell death in the medulla.
Lymph nodes
Located along lymphatic vessels. Are covered by a capsule of dense connective tissue that extends into the node. Trabeculae divide the node into compartments, provide support, and provide a route for blood vessels into the interior of a node. Lymph nodes function as a type of filter.
What two parts can the functional part of the lymph node be divided into?
- Cortex
- Medulla
What two parts does the cortex of the lymph node consist of? Describe them:
- Outer cortex: contains lymphatic nodules (follicles); contains B cells, follicular dendritic cells, and macrophages.
- Inner cortex: does not contain lymphatic nodules (follicles); contains T cells and dendritic cells.
Lymphatic nodules (follicles)
Egg-shaped aggregates of B cells.
What are the two types of lymphatic nodules (follicles)? Describe them:
- Primary lymphatic nodule: consists mainly of B cells. When these B cells recognize an antigen, they develop into secondary lymphatic nodules.
- Secondary lymphatic nodule: form in response to an antigen (a foreign substance) and are sites of plasma cell and memory B cell formation.
Medulla (of the lymph node)
Contains B cells, plasma cells, and macrophages.
Describe the route of lymph through a lymph node
Afferent lymphatic vessel → subcapsular sinus → trabecular sinus → medullary sinus → efferent lymphatic vessel
Hilum
A slight depression on one side of the lymph nodes that efferent lymphatic vessels emerge from. Blood vessels also enter and leave lymph nodes here.
Spleen
Is the largest single mass of lymphatic tissue in the body. Is a soft, encapsulated organ of variable size. The spleen is located in the left hypochondriac region between the stomach and diaphragm.
What are the two different kinds of tissue within the spleen? Describe them:
- White pulp: is lymphatic tissue, consisting mostly of lymphocytes and macrophages arranged around central arteries.
- Red pulp: consists of blood-filled venous sinuses and splenic cords (or Billroth’s cords). Veins are closely associated with the red pulp.
Splenic cords (Billroth’s cords)
Cords of splenic tissue. Consist of red blood cells, macrophages, lymphocytes, plasma cells, and granulocytes.
Lymphatic nodules within the mucous membranes lining the gastrointestinal, urinary, and reproductive tracts and the respiratory airways are also referred to as ______.
Mucosaassociated lymphatic tissue (MALT)
Tonsils
Aggregations of lymphatic nodules in specific parts of the body. Participate in immune responses against inhaled or ingested foreign substances.
What is the difference between the pharyngeal tonsil, palatine tonsils, and lingual tonsils?
Pharyngeal tonsil: is embedded in the posterior wall of the nasopharynx.
Palatine tonsils: lie at the posterior region of the oral cavity, one on either side; these are the tonsils commonly removed in a tonsillectomy.
Lingual tonsils: located at the base of the tongue, may also require removal during a tonsillectomy.
How does the epidermis of the skin function in the first line of defence?
Forms physical barrier to entrance of microbes.
How do the mucous membranes function in the first line of defence?
Inhibit entrance of many microbes, but not as effective as intact skin.
How does mucus function in the first line of defence?
Traps microbes in respiratory and gastrointestinal tracts.
How do hairs function in the first line of defence?
Filter out microbes and dust in nose.
How do cilia function in the first line of defence?
Together with mucus, trap and remove microbes and dust from upper respiratory tract.
How does the lacrimal apparatus function in the first line of defence?
Tears dilute and wash away irritating substances and microbes.
How does saliva function in the first line of defence?
Washes microbes from surfaces of teeth and mucous membranes of mouth.
How does urine function in the first line of defence?
Washes microbes from urethra.
How does defecation and vomiting function in the first line of defence?
Expel microbes from body.
How does sebum function in the first line of defence?
Forms protective acidic film over skin surface that inhibits growth of many microbes.
How does lysozyme function in the first line of defence?
Antimicrobial substance in perspiration, tears, saliva, nasal secretions, and tissue fluids.
How does gastric juice function in the first line of defence?
Destroys bacteria and most toxins in
stomach.
How do vaginal secretions function in the first line of defence?
Slight acidity discourages bacterial growth; flush microbes out of vagina
What are the four main types of anti-microbial substances?
- Interferons (IFNs)
- Complement system
- Iron-building proteins
- Antimicrobial proteins (AMPs)
How do interferons (IFNs) function in the second line of defence?
Protect uninfected host cells from viral infection.
How does the complement system function in the second line of defence?
Causes cytolysis of microbes; promotes phagocytosis; contributes to inflammation.
How do iron-building proteins function in the second line of defence?
Inhibit growth of certain bacteria by reducing amount of available iron.
How do antimicrobial proteins (AMPs) function in the second line of defence?
Have broad-spectrum antimicrobial activities and attract dendritic cells and mast cells.
How do natural killer (NK) cells function in the second line of defence?
Kill infected target cells by releasing granules that contain perforin and granzymes; phagocytes then kill released microbes.
Perforin
A proteins that inserts into the plasma membrane of the target cell and creates channels (perforations) in the membrane.
Cytolysis
The process of extracellular fluid flowing into the target cell, causing the cell to burst.
Phagocytosis
The ingestion of microbes or other particles such as cellular debris.
What are the five phases of phagocytosis?
- Chemotaxis
- Adherence
- Ingestion (pseudopods engulf the microbe - when they come together they fuse and surround the microorganism with a sac called a phagosome)
- Digestion (the phagosome merges with lysosomes to form a phagolysosome; the phagosome part of the phagolysosome can form lethal oxidants in a process called oxidate burst)
- Killing (after the chemical onslaught, any materials that cannot be degraded further remain in structures called residual bodies)
What are the three basic stages of the inflammatory response?
- Vasodilation and increased permeability of blood vessels.
- Emigration (movement) of phagocytes from the blood into interstitial fluid.
- Tissue repair
Epitopes (antigenic determinants)
Small parts of a large antigen molecule that act as a trigger for immune responses. Most antigens have several epitopes that induce the production of different antibodies or activate different T cells.
What are the seven steps involved in the processing and presenting of an exogenous antigen by an antigen-presenting cell?
- Ingestion of the antigen.
- Digestion of antigen into peptide fragments.
- Synthesis of MHC-II molecules.
- Packaging of MHC-II molecules.
- Fusion of vesicles.
- Binding of peptide fragments to MHC-II molecules.
- Insertion of antigen-MHC-II complexes into the plasma membrane.
What are the five steps involved in the processing and presenting of an endogenous antigen by an infected body cell?
- Digestion of antigen into peptide fragments.
- Synthesis of MHC-I molecules.
- Binding of peptide fragments to MHC-I molecules.
- Packaging of antigen-MHC-I molecules.
- Insertion of antigen-MHC-I complexes into the plasma membrane.
What are the two principal mechanisms that cytotoxic T cells have for killing infected target cells?
- Cytotoxic T cells, using receptors on their surfaces, recognize and bind to infected target cells that have microbial antigens displayed on their surface. The cytotoxic T cell then releases granzymes, protein-digesting enzymes that trigger apoptosis. Once the infected cell is destroyed, the released microbes are killed by phagocytes.
- Alternatively, cytotoxic T cells bind to infected body cells and release two proteins from their granules: perforin and granulysin. Perforin inserts into the plasma membrane of the target cell and creates channels in the membrane. As a result, extracellular fluid flows into the target cell and cytolysis (cell bursting) occurs. Other granules in cytotoxic T cells release granulysin, which enters through the channels and destroys the microbes by creating holes in their plasma membranes. Cytotoxic T cells may also destroy target cells by releasing a toxic molecule called lymphotoxin, which activates enzymes in the target cell. These enzymes cause the target cell’s DNA to fragment, and the cell dies. In addition, cytotoxic T cells secrete gamma-interferon, which attracts and activates phagocytic cells, and macrophage migration inhibition factor, which prevents migration of phagocytes from the infection site. After detaching from a target cell, a cytotoxic T cell can seek out and destroy another target cell.
B-cell receptors (BCRs)
What an antigen binds to during activation of a B cell.
Antibodies belong to a group of glycoproteins called globulins, and for this reason they are also known as ______. Most antibodies contain four polypeptide chains. Two of the chains are identical to each other and are called ______; each consists of about 450 amino acids. Short carbohydrate chains are attached to each heavy polypeptide chain. The two other polypeptide chains, also identical to each other, are called ______, and each consists of about 220 amino acids. A disulfide bond (S—S) holds each light chain to a heavy chain. Two disulfide bonds also link the midregion of the two heavy chains; this part of the antibody displays considerable flexibility and is called the ______. Because the antibody “arms” can move somewhat as the hinge region bends, an antibody can assume either a T shape or a Y shape. Beyond the hinge region, parts of the two heavy chains form the ______.
Immunoglobulins (Igs); heavy (H) chains; light (L) chains; hinge region; stem region
IgG
Most abundant, about 80% of all antibodies in blood; found in blood, lymph, and intestines; monomer (one-unit) structure. Protects against bacteria and viruses by enhancing phagocytosis, neutralizing toxins, and triggering complement system. Is the only class of antibody to cross placenta from mother to fetus, conferring considerable immune protection in newborns.
IgA
Found mainly in sweat, tears, saliva, mucus, breast milk, and gastrointestinal secretions. Smaller quantities are present in blood and lymph. Makes up 10–15% of all antibodies in blood; occurs as monomers and dimers (two units). Levels decrease during stress, lowering resistance to infection. Provides localized protection of mucous membranes against bacteria and viruses.
IgM
About 5–10% of all antibodies in blood; also found in lymph. Occurs as pentamers (five units); first antibody class to be secreted by plasma cells after initial exposure to any antigen. Activates complement and causes agglutination and lysis of microbes. Also present as monomers on surfaces of B cells, where they serve as antigen receptors. In blood plasma, anti-A and anti-B antibodies of ABO blood group, which bind to A and B antigens during incompatible blood transfusions, are also IgM antibodies.
IgD
Mainly found on surfaces of B cells as antigen receptors, where it occurs as monomers; involved in activation of B cells. About 0.2% of all antibodies in blood.
IgE
Less than 0.1% of all antibodies in blood; occurs as monomers; located on mast cells and basophils. Involved in allergic and hypersensitivity reactions; provides protection against parasitic worms.
What are the five steps in which a cascade of reactions occurs in complement activation?
- Inactivated C3 splits into activated C3a and C3b.
- C3b binds to the surface of a microbe and receptors on phagocytes attach to the C3b. Thus C3b enhances phagocytosis by coating a microbe, a process called opsonization. Opsonization promotes attachment of a phagocyte to a microbe.
- C3b also initiates a series of reactions that bring about cytolysis. First, C3b splits C5. The C5b fragment then binds to C6 and C7, which attach to the plasma membrane of an invading microbe. Then C8 and several C9 molecules join the other complement proteins and together form a cylinder-shaped membrane attack complex, which inserts into the plasma membrane.
- The membrane attack complex creates channels in the plasma membrane that result in cytolysis, the bursting of the microbial cells due to the inflow of extracellular fluid through the channels.
- C3a and C5a bind to mast cells and cause them to release histamine that increases blood vessel permeability during inflammation. C5a also attracts phagocytes to the site of inflammation (chemotaxis).
Primary response
After an initial contact with an antigen, no antibodies are present for a period of several days. Then, a slow rise in the antibody titer occurs, first IgM and then IgG, followed by a gradual decline in antibody titer.
Secondary response
After subsequent encounters, the antibody titer is far greater than during a primary response and consists mainly of IgG antibodies. Is an accelerated and more intense response. Antibodies produced during a secondary response have an even higher affinity for the antigen than those produced during a primary response, and thus they are more successful in disposing of it.
Positive selection
Allows recognition of self-MHC proteins.
Negative selection
Provides self-tolerance of your own peptides and other self-antigens.
What two ways does negative selection occur? Describe them:
- Deletion: self-reactive T cells undergo apoptosis and die.
- Anergy: T cells remain alive but are unresponsive to antigenic stimulation.
