Chapter 22: The Lymphatic System and Immunity Flashcards
What are the 3 primary functions of the lymphatic system?
- Drains excess interstitial fluid - takes it from tissue spaces and returns it to blood
- Transports dietary lipids
- Carries out immune responses
What is the difference between lymph and interstitial fluid?
Lymph is located within lymphatic vessels and tissues whereas ISF is located between cells
How is lymph circulated?
Lymphatic capillairies coverage to form larger lymphatic vessels, which resemble small veins in structure but have thinner walls are more valves
Lymph passes from capillaries, into vesicles and then through through lymph nodes, organs consisting of masses of B and T cells
Define lacteals
Specialized lymphatic capillaries in the small intestine that carry dietary lipids into lympthic vessels and ultimately into the blood
The presence of this lipids cause lymph training from the small intestine to appear creamy white, known as chyle (usually clear, pale-yellow fluid)
What are lymph trunks? What are the 2 main channels they drain into?
As lymphatic vessels exit lymph nodes they unite to form lymph trunks - they then drain into:
- Thoracic duct - begins as a dilation called the cistern chyli anterior to the 2nd lumber vertebrae and is the main duct for return of lymph to blood; it drains into venous blood at junction of the left internal jugular and left subclavian veins
- Right lymphatic duct - received lymph from right jugular, right subclavian, and right bronchomediastinal trunks (received from upper right side of body)
How is lymph formed?
Components of blood plasma filter freely through the capillary walls to form ISF but more fluid filters out of the capillaries the returns to them by reabsorption, the excess fluid (3L/day) drains into the lymphatic vessels and becomes lymph
Describe the flow of lymph
Blood capillaries (blood) –> interstitial vessels (lymph) –> lymphatic ducts (lymph) –> junction of the internal jugular and subclavian veins (blood)
Which two pumps aid in maintaining the flow of lymph?
The same as the ones that aid in the return of venous blood to heart:
Skeletal muscle pump - milking of skeletal muscles compresses lymphatic vessels and forces lymph toward the junction of the internal jugular and subclavian veins
Respiratory pump - lymph flows fro the abdomen region, where the pressure is higher, toward the thoracic region, where it is lower during inhalation and during exhalation valves in the tissues prevent back flow
Primary vs. secondary lymphatic organs
Primary - sites where stem cells divide and become immunocompetent, located in red bone marrow (mature B cells) and thymus (mature T cells)
Secondary - sites where most immune responses occur, involve organs (lymph nodes, spleen and thymus) as well as tissue (lymphatic nodules)
Briefly describe the thymus
Located in mediastinum between sternum and aorta
Has a connective tissue capsule that separates two lobes
Trabecular divide each lobe into lobules
Cortex is composed of large numbers of T cells - surviving T cells enter the medulla
Define Hassall’s corpuscles
aka thymic corpuscles
Clusters of epithelial cells that become arranged into concentric layers of flat cells that degenerate and become filled with keratohyalin granules and keratin
They may serve as sites of T cell death in the medulla
Briefly describe the structure of a lymph node
Bean shaped, scattered throughout the body, and covered by a capsule of dense connective tissue that extends into the node
Trabeculae divide node into compartments, provide support, and provide a route for blood vessels into the interior of a node
Describe the inner and outer cortex of a lymph node
The outer cortex contains aggregates of B cells called lympthatic nodules - after B cells in a primary lymphatic nodule recognizes an antigen it develops into a secondary lymphatic nodule which contains B cells, follicular dendritic cells, and macrophages; follicular dendritic cells paired with antigen cause B cells to proliferate into antibody-producing plasma cells
The inner cortex contains mainly T cells and dendritic cells that ender a lymph node from other tissues; dendritic cells present antigen to T cells, causing their proliferation
What cells are found in the lymph nodes medulla?
B cells, antibody producing plasma cells, and macrophages
Describe the flow of lymph through a lymph node
Flows in one direction only - acts as a filter; foreign substances are trapped within the sinuses of the node and destroyed by macrophages and lymphocytes
It flows in through afferent lymphatic vessels into sinuses and then drains into one or two efferent lymphatic vessels that carry it out of the node
Efferent lymphatic vessels emerge from one side of the node in a depression alled a hilum
Describe the spleen and the difference between white and red pulp
Spleen is the largest single mass of lympthatic tissue in the body and is located in the hypochondriac region between the stomach and diaphragm
White pulp - lymphatic tissue, consisting of lymphocytes and macrophages arranged around branches of the splenic artery called central arteries
Red pulp - consists of blood-filled venous sinuses and cords of splenic tissue called splenic cords that consists of RBCs, macrophages, lymphocytes, plasma cells, and granulocytes
Describe the structure of lymphatic nodules
Egg-shaped masses of lymphatic tissue that are not surrounded by a capsule and are scattered throughout the lamina propria of mucous membranes and thus are also referred to as mucosa-associated lymphatic tissue (MALT)
The aggregation of lymphatic nodules in the oral cavity is referred to as ______. List the 5 single nodules.
tonsils
Pharyngeal tonsil (adenoid) - embedded in posterior wall of nasopharynx Palatine tonsils (x2) - posterior region of the oral cavity, one on either side Lingual tonsils (x2) - located at base of lounge
What is the first line of defense against pathogens? Describe its defences.
The skin and mucous membranes
- Epidermis provides a physical barrier
- Mucus traps microbes and foreign substances
- Hairs trap and filter microbes
- Cilia in respiratory tract moves microbes to throat to be coughed or sneezed out
- lacrimal apparatus in eyes drains tears away in response to irritants and contain lysozyme that breaks down bacteria
- Saliva washes microbes from the moth
- Flow of urine retards microbial colonization of the urinary system
- Sebum forms a protective film over the surface of the skin
What is the second line of defence?
Internal secondary defences include:
- antimicrobial substances
- Natural killer cells and phagocytes
- Inflammation
What are the 4 types of antimicrobial substances that discourage microbial growth?
- Interferons - protect uninfected host cells from viral infections
- Complement system - causes cytolysis of microbes; promotes phagocytosis; contributes to inflammation
- Iron-binding proteins - inhibit growth of certain bacteria by reducing amount of available iron
- Antimicrobial proteins - have broad-range antimicrobial activities and attract dendritic cells and mast cells
How do natural killer cells attack microbes?
Binding of NK cell to target cells causes release of granules that contain perforin and granzymes
Perforin causes cytolysis (cell burst) or granzymes cause apoptosis/self-destruction
Phagocytes (neutrophils and macrophages) perform phagocytosis, the ingestion of microbes and cellular debris
Describe the 5 phases in phagocytosis
- chemotaxis - chemically stimulate movement of phagocytes to site of damage
- Adherence - attachment of phagocyte to microbe
- Ingestion - plasma membrane of phagocyte extends projections called pseudopods and engulf microbe; when the pods meet they surround the microorganism in a phagosome
- Digestion - phagosome enters cytoplasm and merges with lysosomes to form a single, larger structure called a phagolysome and lysozyme breaks down cells walls
- Killing - chemical onslaught by lysozyme and digestive enzymes kill microbes
