LO 15 Flashcards
What are the structural elements of the lymphatic system?
- Lymph
- Lymphatic vessels
- Lymph nodes
- Thymus
- Tonsils
- Spleen
Describe lymph
- Blood plasma filters out of capillaries into the tiny spaces between cells of tissues (blood pressure is the ‘force’ that promotes this) – fluid now called interstitial fluid (IF)
- IF that isn’t reabsorbed by blood vessels drains into lymphatic capillaries – fluid now called lymph
- Lymph carries protein molecules & other substances back to the blood
Describe lymphatic vessels
- Permit one-way movement of lymph towards heart
- Collect excess IF (as lymph) and returns it to the blood stream via veins
- Two types - Lymphatic capillaries & Lymphatic ducts
Describe lymphatic capillaries
- Microscopic, blind-ended (open at one end) tubes found in tissue spaces wherever blood capillaries are (except bone, teeth, bone marrow and CNS)
- Walls are simple squamous epithelium and are very porous/permeable due to structure
- Called ‘lacteals’ in the intestinal wall (Digestive System)
- Edges of cells loosely overlap each other = one-way ‘swinging doors’
- Fluid pressure in interstitial fluid determines if fluid will move into or out of lymphatic capillaries
- When fluid pressure is greater in interstitial spaces than in lymphatic capillaries, ‘doors’ are pushed open and fluid moves in
- When fluid pressure is greater inside the lymphatic capillary than in interstitial spaces, doors are pushed shut, preventing lymph from leaking backwards
Describe the lymphatic ducts`
- Right lymphatic duct - Drains lymph from right upper extremity, right side of head, neck, and upper torso
- Thoracic Duct - Largest lymphatic vessel
Drains lymph from the rest of the body; A structure called cisterna chyli found along its course (storage area for lymph moving towards entering the venous system)
Describe lymph nodes
- Filter lymph
- Located in clusters along the pathway of lymphatic vessels where they converge to form larger trunks
- Functions include defense and WBC formation
Describe the flow of lymph in a lymph node
- Into node via several afferent lymph vessels and drained
- Away from node by a single efferent lymph vessel
Describe the lymph nodes role in immunity
- If any antigens/pathogens are detected in the lymph entering the lymph node, various WBCs in the lymph node will go out into the circulation and attack them
- Other immune system cells are made to fight the infection and “sent” to the lymph nodes. The increased numbers of immune system cells fighting the infection will make the node expand and become “swollen.”
Describe the structure of the thymus
- Lymphoid tissue organ located in mediastinum
- Total weight of 35 to 40 g (just over an ounce)
- Completes most of its work in childhood. In adults, lymphoid tissue is largely replaced by fat and connective tissue in a process called involution
Describe the function of the thymus
- Plays a vital and central role in immunity
- Maturation/development of T lymphocytes, or T cells
- Secretes hormones called thymosins which arouse the body’s response to an infection
Describe the tonsils
- Composed of three masses of lymphoid tissue around the openings of the mouth and throat
- Palatine tonsils (“the tonsils”) – largest, most often infected
- Pharyngeal tonsils (adenoids)
- Lingual tonsils
Describe the function of the tonsils
- Function is to gather & remove pathogens entering pharynx (via respiratory or digestive system)
- Subject to chronic infection
- Enlargement of pharyngeal tonsils may impair breathing as they’re located near posterior opening of the nasal cavity
Describe the structure of the spleen
- Largest lymphoid organ in body
- Located in upper left quadrant of abdomen
- Often injured by trauma to abdomen
- Surgical removal called splenectomy
Describe the function of the spleen
- Filtration & phagocytosis of bacteria and other pathogens
- Destroys old RBCs and stores breakdown products (e.g. iron) which can be ‘reused’
- Acts as a blood reservoir
Give a brief overview of the lymphatic system
- Allows exchange of substances, such as excess fluid and protein molecules, that cannot occur in the circulatory system’s capillary beds
- Filters out harmful substances from the lymph before returning it to the blood - Acts as sewer system of the body
Describe the function of the immune system
- Protects the body from pathologic bacteria, foreign tissue cells, and cancerous cells
- Made up of the lymphatic system, specialized cells and ‘free-floating’ molecules
What are the 2 types of immunity?
- Non-specific - general protection against pathogens, toxins, & chemicals
- Specific
What structures/functions are part of non-specific immunity?
- Skin
- Tears; saliva & mucus membranes/mucus
- Inflammation
How does skin act as a structure of non-specific immunity?
- Mechanical barrier - ‘first line of defense’
- recall keratin & secretions of skin
How do tears; saliva & mucus membranes/mucus act as structures of non-specific immunity
- Wash eyes; trap & kill bacteria
How does inflammation act as a function of non-specific immunity?
- Tissue damage attracts immune cells to site of injury
- Increases local blood flow
- Increases vascular permeability
- Promotes movement of WBCs to site of injury or infection & prevents spread of damage to other tissues
Describe the inflammatory response
- A generalized response to an invader, such as bacteria that are causing tissue damage
- This triggers release of immune factors from immune cells - attracts WBCs; causes increased blood flow (site becomes warm and reddened) and increased vascular permeability (site swells with associated discomfort)
- These immune factor-mediated changes help phagocytic WBCs reach the site and enter the affected tissue
Describe specific immunity
- Protection against invaders due to the ability of the body to recognize, respond to, and remember specific harmful substances or bacteria
- Is antigen-specific: immune response recognizes and is a directed against specific pathogens
- Is systemic: immunity is not restricted to the initial area of infection
- Has memory: if the body is ever exposed to the same pathogen, the immune response will be even stronger than it was to previous exposure(s)
Specific immunity can be either ____________
- Natural Immunity (exposure to pathogen is not deliberate)
- Artificial/Acquired Immunity (exposure to pathogen is deliberate)
(There are active and passive forms of each of the above)
Describe natural immunity
- Inherited immunity to certain diseases from birth
- Exposure to pathogen is not deliberate
- Can be active or passive
1. Active – active disease promotes immunity (production of antibodies)
2. Passive – mother passes immunity (antibodies) to fetus through placenta or breast milk
Describe artificial/acquired immunity
- Exposure to pathogen is deliberate (vaccine)
- Can be active or passive
- Active – vaccination ‘stimulates’ antibody production leading to immunity
- Passive – immune ‘material’ (antibodies) developed in another individual is given to a non-immune person
Immune system molecules consist of ______
- Antibodies
- Complement proteins
Describe antibodies
- Protein compounds with specific combining sites
- Combining sites attach antibodies to specific antigens, forming an antigen–antibody complex
- Inactivation of antigens in this way is called humoral or antibody-mediated immunity
- Antigen–antibody complexes have various modes of action
What 4 things can antigen-antibody complexes do?
- Neutralize toxins
- Clump or agglutinate enemy cells
- Promote phagocytosis
- Complement fixation
Describe complement proteins
- Group of at least 14 plasma proteins normally present in blood in an inactive state
- Complement fixation
1. Important mechanism of action for antibodies
2. Causes cell lysis by permitting entry of water through ‘defects’ (holes) created in the plasma membrane (e.g. cell bursts due to an increase in internal osmotic pressure)
The primary cells of the immune system are _________ and _________
- Phagocytes
- Lymphocytes
What do phagocytes and lymphocytes do?
- These cells recognize invading/foreign substances/cells and neutralize/destroy them
- Communicate with each other to coordinate immune response
Describe phagocytes
- Ingest and destroy foreign cells or other harmful substances via phagocytosis
- They are chiefly macrophages - Neutrophils>macrophages (Kupffer’s cells (liver) & Dust cells (lungs))
Describe lymphocytes
- Most numerous of immune system cells
- They are either B cells or T cells
- Both B cells and T cells originate from hemocytoblasts in the red bone marrow and whether they develop into B or T cells depends on where in the body the cell ‘matures’ (e.g. where it becomes immunocompetent)
Describe B cells
- Primitive (original) stem cells migrate from bone marrow and go through two stages of development
First stage
1. stem cells develop into immature B cells
2. occurs in liver & bone marrow before birth/during childhood, and in the bone marrow only in adults
3. immature B cells are small lymphocytes with specific antibody molecules (which they have synthesized) in their plasma membranes
4. immature B cells migrate from liver/bone marrow to primarily lymph nodes (also liver & spleen)
5. undergo mitosis to make clones of themselves containing their specific antibody
Second Stage
1. Migrated immature B cell develops into activated B cell only if it comes in contact with its specific antigen (that will bind to its surface antibodies)
2. Activated B cell, by dividing repeatedly (mitosis), forms two clones of the original B cell
1. Plasma cells - secrete antibodies into blood to form an ‘army’ of protection against antigen
2. Memory cells - are stored in lymph nodes as an ‘emergency supply’ and then if subsequent exposure to the antigen that activated B cell occurs, memory cells quickly become plasma cells and secrete antibodies
Describe the function of B cells
- Indirectly, they produce humoral immunity by secreting antibodies into the blood
- Activated B cells develop into plasma cells
- Plasma cells secrete antibodies into the blood
- Circulating antibodies produce humoral immunity
Describe the development of T cells
First stage
1. Stem cells from bone marrow migrate to thymus gland several months before & after birth
2. In the thymus gland, stem cells begin development into T cells
3. T cells have protein molecules on their cytoplasmic membrane shaped to bind to only one kind of antigen
4. T cells migrate from thymus to lymph nodes (also to liver & spleen)
Second stage
1. Occurs only if a specific antigen binds to T cell’s surface proteins
2. Antigen is presented by macrophage that has ingested antigen (T cell must recognize antigen AND macrophage)
3. T cells develop into sensitized T cells 🡪 cell-mediated immunity
Describe the function of T cells
- Provide cell-mediated immunity
- Kill invading cells directly by releasing a substance that poisons cells
- Release chemicals that attract and activate macrophages to kill cells by phagocytosis
Describe humoral immunity
- Immunity conferred by the action of antibodies
- Activated B cells 🡪 plasma cells and memory cells
Describe cell-mediated immunity
- Immunity conferred by the action of cells
- Activated/Sensitized T cells
- Kill invading cells directly by releasing substances called lymphotoxins or lymphokines that attract and activate macrophages to kill cells by phagocytosis
