Lymphatic Microanatomy 1 and 2 Flashcards
what does the interstitial fluid become once it is in the lymphatic vessels
lymph
describe lymphatic capillaries
-collect interstitial fluid with large molecules, including antigens and cells
-more permeable than blood capillaries
-thin walls that are formed by cells that overlap without tight junctions
what are lymphatic collecting vessels
-formed from lymphatic capillaries
-contain valves and unite to form major trunks or ducts
describe lymph nodes
filter lymph
collecting lymphatic vessels go through at least one before reaching the venous system
antigens are removed as part of the immune response
where are the tracheal trunks found
along the right and left ventromedial surface of the trachea
where are the lumbar trunks found
efferent vessels of the medial iliac, caudal mesenteric and lumbar lymph nodes
where are the intestinal trunk found
confluence of efferent vessels of the cranial mesenteric lymph nodes
where are the celiac trunks found
confluence of efferent vessels associated to the celiac trunk
where are the cisterna chyli found
located as an irregular, sac-like dilation of a large lymph trunk between the right side of the aorta and the right crus of the diaphragm, extending from L2 or L3 vertebrae to last thoracic vertebrae
where is the thoracic duct found
extension of cisterna chyli into the thoracic cavity
runs between the azygous vein and aorta
where is the right lymphatic duct found
confluence of efferent vessels of the cranial mediastinal and cranial sternal lymph nodes, empty into the caudal vena cava
where does hematopoiesis take place
bone marrow
what is the innate immune response
-no requirement for previous exposure
-non-specific response
-immediate and rapid response
-provides first line of defense
ONCE ANTIGENS BIND TO THE RECEPTOR, THEY TRIGGER THE INNATE IMMUNE RESPONSE
what is the adaptive immune response
-recognition of diverse antigens
-delayed response
-after previous exposure the response is quicker
what are the main cells involved in the adaptive immune response
lymphocytes
what are lymhocytes T
-have t cell receptors (Tc and Th)
-involved in cell mediated immune response
-generated in the bone marrow but differentiate and get educated in the thymus
what are lymphocytes B
-have B cell receptors (BCR)
-involved in humoral (antibodies) immune response
-activated directly by antigens and pAPCs
-only nonmyeloid cells that can function as APCs to activate lymphocytes T
-generated in the bone marrow
what are natural killer cells
-third type of lymphocytes that work similar to the cells of the innate immune response
-once activated, respond to kill cells like lymphocytes Tc
what can function as APC
any type of infected cells
what do APCs do
break down and conjugate fragments to MHC 1 which locate on the cell surface –> results in the activation of lymphocytes Tc
what results in the activation of lymphocytes Th
pAPCs break down the antigen and conjugate fragments to MHC 2, which locate on the cell surface
what activates lymphocytes B
antigens or dendritic cells (pAPCs)
what do lymphocytes Tc (CD8+) do?
-destroy infected cells and pathogens by secreting proteins that create channels of the cell’s plasma membrane and induce fragmentation of DNA
—> leads to apoptosis or lysis
what do lymphocytes Th (CD4+) do?
secrete cytokines that help enable or help the activation of lymphocytes B and Tc
what are the 2 subtypes of lymphocytes B?
plasma cells and memory B cells
what are plasma cells
synthesize and secrete antibodies
what are memory b cells
plasma cells that remain in the body and respond more quickly during next encounter with the antigen
—> dormant (need reactivation)
what are primary organs (where immune cells develop)?
bone marrow
thymus
what are secondary organs (where most of the immune response is initiated)?
-lymph nodes
-spleen
-lymphoid tissue
what is the parenchyma in the bone marrow?
HSCs and differentiating hematopoietic cells
what is the stroma in the bone marrow?
reticular cells, reticular fibers and adipocytes
what is the function of the bone marrow?
-hematopoiesis
-produces lymphocytes B
describe what happens in the bone marrow
-circulating lymphocytes can return and reside there
-with age, adipocytes replace 50% of the bone marrow and the efficiency of hematopoiesis decreases
what are blood sinusoids in the bone marrow
site of cellular and molecular exchange between circulation and hematopoietic compartment
describe the thymus
-education and differentiation of lymphocytes T
-gets smaller during puberty
describe the stroma in the thymus
-made of CT (collagen fibers and fibroblasts)
-trabeculae divides the parenchyma in incomplete lobes, which unite at the center
-contain blood vessels, efferent lymphatic vessels and nerves
describe what breaks up the cortex and medulla in the thymus
corticomedullary junction
describe the cortex in the thymus
-closely packed developing lymphocytes T which occupy spaces within an extensive meshwork of epithelioreticular cells (ERCs)
what are ERCs
specialized cells with features of both epithelial and reticular cells
their cytoplasmic processes contribute to form a framework
describe the blood thymus barrier in the cortex of the thymus
-prevents the lymphocytes T from contact with antigens
-education needs a clean environment –> absent of different antigens
-formed by the wall of blood vessels
describe the corticomedullary junction
-made of ERCs, which form the barrier between the cortex and medulla
-contain blood vessels, arterioles, and venules
what are high endothelial venules (HEV)?
-specialized post-capillary venule –> diapedesis and recirculation
-site for entrance and exit of lymphocytes
-found in most lymphoid organs except spleen
describe the medulla of the thymus
-loosely packed mature lymphocytes T with extensive meshwork of ERCs
name the 3 steps of education and final differentiation of lymphocytes T
1) lymphocytes are selected in the cortex based on their affinity to bind MHC
2) lymphocytes are selected in the medulla based on their affinity to bind tissue specific antigens
3) finally selected lymphocytes differentiate into Tc or Th and leave the medulla through the HEVs
what is positive selection and when does it occur in the thymus
lymphocytes that do not bind are induced to die (death by neglect)
occurs in step 1
what is negative selection and when does it occur in the thymus
lymphocytes that bind with too strong affinity are induced to die
occurs in step 2
what are lymph nodes and what do they do
-encapsulated lymphatic organs that are interposed along lymphatic vessels
-filters through which lymph percolates on its way to the blood vascular system
what makes up the stroma in lymph nodes
capsule
trabeculae
reticular tissue
describe the capsule in the stroma in lymph nodes
dense CT
describe the trabeculae in the stroma in lymph nodes
dense CT that forms a gross framework
describe the reticular tissue in the stroma in lymph nodes
reticular cells and reticular fibers that form a fine supporting meshwork
describe the deep cortex in lymph nodes
where lymphocytes T are mixed in with dendritic cells
describe the flow of lymph and blood into the lymph node
1) afferent lymphatic vessels
2) subcapsular sinus
3) trabecular sinus
4) medullary sinus
5) efferent lymphatic vessels
describe the stroma of the spleen
-capsule of dense CT
-trabeculae extending from the capsule into the parenchyma, contain blood and lymphatic vessels
-contain myoblasts –> help discharge RBCs into the blood
what 2 things make up the parenchyma of the spleen
white pulp and red pulp
describe the white pulp of the spleen
lymphoid nodules randomly scattered, secondary lymphoid organ
describe the red pulp of the spleen
embeds the white pulp and contains splenic sinuses
describe the process of formation of lymphatic nodules
1) APCs activate lymphocytes Th in PALS
2) lymphocytes Th help activate lymphocytes B, which expand and push PALS to the sides
3) lymphocytes B proliferate to form plasma and memory cells, which go into the blood
what are the 2 regions of red pulp in the spleen
-splenic cords
-splenic sinuses
describe the splenic cords
meshwork of reticular cells and reticular fibers
macrophages phagocytize damage RBCs
megakaryocytes form platelets
describe the splenic sinuses
spaces lined by endothelial cells
processes of macrophages extend between endothelial cells to monitor antigens in the blood
what is open circulation (humans)?
dump blood into cords of red pulp
what is closed circulation (dogs and rats)?
dump blood directly into the sinuses
describe diffuse lymphatic tissue
-no cortex or medulla
-not surrounded by CT capsule
-made of randomly packed lymphocytes
-after contact with antigen, lymphocytes travel to regional lymph nodes, where they undergo proliferation and differentiation
-progeny of these cells return to lamina propria as effector lymphocytes B and T
