Week 8 - the lymphatic system and immunity Flashcards
What are the lymphatic and immune systems responsible for?
- They are responsible for protecting us against foreign substances and infections
What are the three barriers of defence in the human body?
- To block invaders out, i.e. skin and mucous membranes
- Inducing inflammatory response
- Production of antibodies
What is the relationship between the immune system and the lymphatic system?
- The immune system is closely associated with the lymphatic system
- The two terms are often used interchangeably and refer to the bodies ability to defend against pathogens
What does the lympatic system consist of?
- It consists of a network of vessels that penetrate nearly every tissue in the body, and a collection of tissues and organs that produce immune cells
What are the main functions of the immune/ lymphatic sytem system?
- Fluid recovery - absorbs excess fluid from tissue spaces and returns it to blood stream via lympatic vessels
- Immunity - fluid recovered by lymph vessels contains foreign cells and chemicals from tissues, it passes through the lymph nodes which contain immune cells which detect pathogens and activate a protective immune response
- Lipid absorption - lacteals are lymphatic vessels located in the small intestine which aborb dietary lipids that are not absorbed by capillaries
What is the lypmatic system composed of?
- Lymph (recovery fluid)
- Lympatic vessels (to transport the lymph)
- Lymphatic tissue (lympocytes and macrophages)
- Lymphatic organs (concentrated with immune cells)
What is lymph?
- It originates as blood plasma that leaks from the capillaries to become interstitial fluid
- Once in the lymphatic system the interstitial fluid is called lymph but has a similar composition to the original intersitial fluid
Describe the structure of lymphatic vessels
- Similarly to veins, lypmpahtic vessels also contain valves
- They have tunica interna and tunica media
- Their walls are thinner and they have more valves than veins
- There is a continual recycling of fluid from blood to lymph
Describe the course that lymph takes through the lymphatic system on the way back to the bloodstream
- Lymphatic capillaries
- Collecting vessels
- Lymphatic trunks
- Collecting ducts
- Subclavian veins
- The lymphatic capillaries join together to form the collecting vessels
Where are collecting vessels typically found in relation to other structures?
- Collecting vessels are typically found alongside veins and arteries
Where are lymph nodes located?
- There are several lymph nodes in the lymphatic system, interspersed along the collecting vessels, which receive and filter the lymph
What do collecting vessels join together to form?
- Collecting vessels join to form large lymphatic trunks with each draining a larger portion of the body
Give some examples of the main lymphatic trunks
- The main lymphatic trunks include:
- Lumbar trunk
- Intestinal trunk
- intercostal trunk
- Bronchomediastinal trunk
- Subclavian trunk
- Jugular trunk
What do the lymphatic trunks join together to form?
- Lymphatic trunks join together to form the two collecting ducts:
- Thoracic duct
- Right lymphatic duct
Describe the thoracic duct
- This duct is larger than the right lymphatic duct and receives lymph from the abdomen, lower extremities and left side of the upper body
- It begins as a sac in the abdominal cavity called the cisterna chyli which serves as a temporary holding area for lymph which then passes through the diaphragm
Describe the right lymphatic duct
- Right lymphatic duct begins in the right thoracic cavity and receives lymph drainage from the right side of the upper body and thoracic area
How is the flow of lymph assisted?
- Flow is lymph is assisted by rhythmic contractions of the lymphatic vessels
- Similar to veins, lymphatic vessels are also assisted by skeletal muscles which squeeze them to force the movement of lymph
What are primary lymphatic organs?
- The primary lymphatic organs are red bone marrow and the thymus - they are the sites of the production and maturation of lymphocytes (WBCs)
What is red bone marrow responsible for?
- Red bone marrow is the site of blood cell production, some of the white blood cells produced in the marrow include:
- Neutrophils
- Basophils
- Eosinophils
- Monocytes
- Lymphocytes
What are the types of lymphocyte and why are they named in this way?
- There are B lymphocytes and T lymphocytes
- Red bone marrow is the site of maturation for B lymphocytes and the thymus is the site of maturation for T lymphocytes
Describe the location and role of the thymus gland in the lymphatic system
- Thymus gland is a small lymphoid organ situated in the mediastinum, which extends upwards into the midline of the neck
- Most active in children
- Gland is a member of both the lymphatic and endocrine systems
- It produces thymic hormones such as thymosin, which aids in the maturation of T lymphocytes
- Immature T lymphocytes travel from the bone marrow to the thymus via the blood stream
What are the secondary lymphatic organs?
- Secondary lymphatic organs play an important role in the immune system and it includes:
- Spleen
- Lymph nodes
- Tonsils
- Appendix
Describe the spleen as a secondary lymphatic organ
- It is the bodys largest lymphatic organ and is situated in the upper quadrant of the abdomen
- Composed of two tissue types:
- Red pulp - consists of sinuses and erythrocytes
- White pulp - consists of lymphocytes and macrophages
- Similar to lymph nodes, the spleen monitors the composition of pathogens in the blood
- Lymphocytes and macrophages respond rapidly to foreign antigens in the blood and activate immune reactions
Describe the lymph nodes as secondary lymphatic organs
- They are small structures located along the lymphatic vessels
- They have two main functions:
- Cleanse the lymph
- Alert the immune system to pathogens
- Lymph nodes are situated in each cavity of the body except the dorsal cavity
- When body fights infection lymph nodes quickly multiply and swell
- Physicians often detect the bodys reaction to infected by feeling for swollen or tender lymph nodes
Describe the tonsils as secondary lymphatic organs
- They are patches of lypmatic tissue situated at the entrance to the pharynx where they guard against ingested and inhaled pathogens
- There are three pairs of tonsils:
- Pharyngeal tonsil
- Palatine tonsil
- Lingual tonsil
Describe Peyer’s patches as secondary lymphatic organs
- They are located in the wall of the intestine and the appendix and they are attached to the cecum of the large intestine
- They intercept pathogens that enter the body through the intestinal tract
Define the term “immunity”
- Immunity is the ability to resist damage from foreign substances
What are the different categories of immunity?
- Immuity is categorised as either innate immunity or adaptive immunity
Briefly outline innate immunity
- The body recognises and destroys specific foreign substances but the response to them is the same each time
Briefly outline adaptive immunity
- The body recognises and destroys foreign substances but the response to them improves every time
What do the main componets of innate immunity include?
- Mechanical mechanisms that prevent the entry of microbes into the body
- Chemical mediators that act directly against the microorganism
- Cells involved in phagocytosis
What are examples of physical barriers in the innate immunity?
- The skin and mucous membranes provide a barrier for microorganisms to enter the body and spread through tissues
Describe how the skin acts as an external barrier in the innate immune response
What is a concern if the skin is broken?
- Sebaceous glands in the skin produce sweat and sebum which help protect the skin because they both contain antiseptic molecules that destroy the cell wall of bacteria
- When the skin is broken one of the most urgent treatment concerns is the prevention of infection
Describe how mucous membranes act as an external barrier in innate immunity
- Digestive, respiratory, urinary and reproductive tracts are all exposed to the external environment making them succeptible to invasion by pathogens
- They are protected by mucous membranes
Give an example of mucous membranes acting as an external barrier in the innate immune response
- In the respiratory tract ciliated mucous membranes sweep microbes trapped in the mucous to the back of the larynx where they are swallowed
Besides mucous membranes, what other mechanisms in the respiratory tract act as barriers in innate immunity?
- Coughing and sneezing are additional mechanisms that remove microorganisms
What is the role of inflammation in innate immunity?
- Inflammation is a local defensive response to tissue injury including trauma and infection
What are the main functions of inflammation in innate immunity?
- The main functions of inflammation in the innate immune response include:
- To reduce the spread of pathogens
- To remove debris of damaged tissue
- To initiate tissue repair
What are the signs of inflammation in the innate immune response?
- Swelling
- Redness
- Heat
- Pain
What is the “complement system” in innate immunity?
- It is a biochemical cascade of the immune system that helps remove pathogens and promotes healing
- This system is referred to as a non-specific defence which is activated by antibody-antigen complexes
What does the complement system require in order to work?
- It requires the cooperation of several plasma proteins that work together to result in cytolysis by disrupting the target cell’s plasma membrane
What are interferons in innate immunity?
- Interferons are glycoproteins secreted by cells that have been invaded by viruses
What is the function of interferons in innate immunity?
- Their main function is to interfere with viral growth by diffusing into neighbouring cells and stimulating them to produce antiviral proteins which prevent the multiplication of viruses within them
What are leukocytes and how are they divided in innate immunity?
- They are the primary cells of the immune system and are divided into six types:
- Neutrophils
- Eosinophils
- Basophils
- Lymphocytes
- Monocytes
- Dendritic cells
What is the term phagocyte used to describe in innate immunity?
- Phagocytes are classified as a functional group of leukocytes who engulf and ingest their targets by phagocytosis
- This group includes:
- Neutrophils
- Eosinophils
- Monocytes
- Macrophages
What is the term cytotoxic cells used to mean in innate immunity?
- Cytotoxic cells are a second functional group that destroys their target cells, this group includes:
- Eosinophils
- Specific types of lymphocytes
What are neutrophils in innate immunity?
- Motile cells
- Destroy cells by phagocytosis and digestion
- Similar to leukocytes in that they are synthesised in bone marrow
- Release cytokines
What are eosinophils in innate immunity?
- They phagocytose:
- antigen-antibody complexes
- allergen
- inflammatory chemicals
- Attach to large parasites and release substances from their granules that destroy parasites
What are basophils in innate immunity?
- Secrete heparin and histamine which aid in the motility of other leukocytes
- Release mediators that contribute to inflammation
What are lymphocytes in innate immunity?
- Key cells that mediate acquired immunity
- Natural killer (NK) cells are a type of lymphocyte that atach and lyse host cells that have either become infected or have become cancerous
- NK cell recognises abnormal cell it releases perforins which perforate the cell surface and destroys the cell
What are dendritic cells in innate immunity?
- They activate lymphocytes
- Responsible for recongising and capturing antigens, they then migrate to secondary lymphoid tissues and present the antigens to lymphocytes
What are monocytes in innate immunity?
- They are precursors to macrophages
- Once monocytes exit the blood they enlarge and differentiate into macrophages
What is adaptive immunity?
- This part of the immune system directly targets attacking microbes and the immune defenses respond to antigens
What are antigens and epitopes?
- An antigen is any molecule that triggers an immune response
- Only specific regions of an antigen molecule, called epitopes, stimulate immune responses
- Generally our immune system doesn’t respond to our own antigens and if it does it is called an autoimmune disease
What is meant by the term allergenic response?
- An immune response to harmless antigens such as pollen is known as an allergic response
What does the immune system consist of?
- It is not an organ, it consists of a group of distributed cells that recognise foreign substances and act to neutralise or destroy them
What are the two characteristics that differentiate the adaptive response from the innate immune response?
- Specificity - the ability of the adaptive immune system to recognise a specific antigen
- Memory - the ability to remember previous encounters with a speicifc antigen and induce a more rapid response next time
- In innate immunity, each time the body is exposed to an antigen the response is the same due to a lack of specificity and memory of previous encounters
How are lymphocytes important in adaptive immunity?
- Specific immunity is dependant upon B lymphocytes and T lymphocyte (B/T cells)
- Both B and T cells recognise target antigen-bearing cells although they both use different mechanisms
What is the role of B lymphocytes in adaptive immunity?
- Mainly responsible for humoral immunity (antibody-mediated immunity)
- Produce antibodies which are proteins that bind with and neutralise specific antigens
- When antibodies bind to viruses they can prevent the virus from infecting cells
- When antibodies bind to toxins they stimulate neutralisation
What cells do B lymphocytes produce?
- B lymphocytes produce plasma and memory cells
Describe the production of plasma cells in the adaptive immune response
- B cells have specific surface receptors allowing them to detect certain antigens
- B cells are distributed through lymph nodes, spleen and tonsils
- B cells inactive until they enounter an antigen on a foreign cell
- Macrophages and T cells act as antigen presenting cells (APCs) and interact with B lymphocytes
- B cells bind to the antigen which activates the B cell
- B cells multiply into a large homogeneous group (clone)
- Majority of these clone cells are plasma cells which secrete antibodies to bind to the epitope
What are memory cells?
- Once B cells active, some of the clones become long-lived memory cells
- Memory cells record information about the foreign antigen so antibodies can be made more quickly upon second exposure
What are the different classes of antibody?
- Antibodies aka immunoglobulins
- Several different classes:
- IgA
- IgG
- IgE
- IgM
What is the function of antibodies in the adaptive immune system?
- Attach to surface of foreign antigen to make it more easily phagocytosed by neutrophils, monocytes and macrophages
- Antibodies which bind and inactive toxins are known as antitoxins
- Antibodies can bind to surface of microbes and prevent them from entering host cells
- Antibodies can stimulate the complement system
What are T lymphocytes responsible for?
- T cells are responsible for defending the body against intracellular pathogens
- Referred to as cell-mediated immunity
What is the relationship between T cells and macrophages?
- Macrophages are responsible for phagocytosing invading microbes and digesting it into molecular fragments
- Macrophages display the epitopes of antigens to T cells
What classes of cell does cell-mediated immunity involve?
- It involves:
- Cytotoxic T cells
- Helper T cells
- Suppressor T cells
- Memory T cells
What are cytotoxic T cells responsible for in cell-mediated immunity?
- They migrate to the site of infection and carry out the attack on virally infected cells and tumor cells be secreting perforins to perforate the cells resulting in lysis
What are T helper cells responsible for in cell-mediated immunity?
- Promote the action of cytotoxic cells and play a role in humoral immunity (unlike other T cells which are only involved in cell-mediated immunity)
- These cells are targeted in a HIV infection
What are suppressor T cells responsible for in cell-mediated immunity?
- They limit the cell-mediated attack and stimulate other T cells and B cells
What are memory T cells responsible for in cell-mediated immunity?
- They are antigen-specific T cells that persist long-term after an infection has resolved
- They are descended from cytotoxic T cells
- Responsible for memory in cell-mediated immunity
Define the term acquired immunity
- Acquired immunity responsed are antigen-specific responses in which the body recognises a foreign substance and reacts to it
How can acquired immunity be divided?
- Can be subdivided into active and passive acquired immunity
When does active immunity occur?
Describe two situations in which it may occur
- Occurs when body’s exposed to a pathogen and produces its own antibodies
- Can occur naturally, when a pathogen invades the body, and artificially when given vaccinations containing disabled or killed microorganisms
How do vaccinations occur in acquired active immunity?
- In vaccinations the antigens have been modified so that they stimulate an immune response but won’t cause symptoms of disease
- E.g. MMR vaccination against measels, mumps and rubella
What is passive acquired immunity?
- It is temporary immunity that results from acquiring antibodies produced by another individual
Describe different examples of passive acquired immunity
- Transfer of antibodies from mother to foetus across placenta
- Baby acquired antibodies through milk after birth
- Injection of immune serum obtained from another individual that produced antibodies - this is artificial passive immunity
What is the difference between active and passive immunity?
- Passive immunity generally lasts 2-3 weeks or until the acquired antibody is degraded
- Active immunity occurs indefinitely
Name one Immunodeficiency disease
- Acquired Immunodeficiency disease (AIDS) is a life threatening disease
What is AIDS and can be the result of this disease?
- AIDS is a collection of symptoms and infections resulting from damage to the immune system caused the the human immunodeficiency virus (HIV)
- The late stage of AIDS leaves individuals prone to infection and tumors
How does HIV cause AIDS and what is the effect on the immune system?
- HIV is a retrovirus that mainly infects components of the human immune system such as T helper cells (CH4+ T Cells), macrohpages and dendritic cells
- HIV destroys CH4+ cells which are fundamental for correct functioning of the immune system, cell-mediated immunity is lost resulting in AIDS
What are the strains of HIV involved in causing AIDS?
- HIV-1 is responsible for the majority of cases of AIDS
- HIV-2 is most prominent in West Africa
How does a HIV infection progress?
- It progresses over time from acute HIV infection to latent HIV infection then to early symptomatic HIV infection before finally to AIDS
How is AIDS identified?
- It is mainly identified by the amount of CH4+ T cells in the blood and the presence of certain infections
How is HIV transmitted?
- Transmitted through direct contact of a mucous membrane or the bloodstream from an infected person to a non-infected person
- Transmission can occur through exchange of blood, vaginal fluid, semem and breast milk
How is a HIV infection treated?
- Currently there are no cures
- Treatments exist to slow the progression of the virus
Name three autoimmune diseases
- Vitiligo
- Multiple sclerosis
- Juvenile-onset diabetes
What is vitiligo ?
- Autoimmune disorder in which the immune system targets and destroys melanocytes - pigment making cells
- Causes irregular white patches on the surface of the skin which can affect different parts of the body
What is multiple sclerosis?
- Chronic degenerative disorder of the central nervous system
- Immune system attacks and destroys myelin in the CNS
- Causes multiple scars on the myelin sheath resulting in the loss of nerve function
What is juvenile-onset diabetes?
- Autoimmune disorder in which the beta cells of the pancreas are attacked thus insulin is not produced
What is the immune response to allergies known as?
What are the two types of this?
- Referred to as hypersensitivity or sensitivity to the antigen
- Immediate hypersensitivity and delayed hypersensitivity
What is immediate hypersensitivity?
- Immune response to an allergy
- Immediate hypersensitivity is induced by antibodies and occurs within minutes of exposure to the allergen (antigen)
What is delayed hypersensitivity? Regarding the immune system
- Delayed hypersensitivity reactions are induced by helper T cells and macrophages
- May take several days to develop
What is type 1 hypersensitivity, how is it mediated and what are the symptoms?
- Type 1 hypersensitivity is an allergic reaction caused by re-exposure to a specific allergen
- Mediated by IgE antibodies and the release of histamines
- Can be local or systemic and symptoms can range from mild irritation to sudden death from anaphylactic shock
