Lymphatic System Part III Flashcards
Regulate and carry out adaptive immunity
LYMPHOCYTES
In adult stem cells for all lymphocytes are located in the ____
red bone marrow
cells of the major lymphoid lineages mature and become functional in two different central or primary lymphoid organs:
B lymphocytes
T lymphocytes
remains and differentiate further in the bone marrow
B lymphocytes
progenitors move via circulation into the developing thymus
T lymphocytes
Long lived lymphocytes, 75% of the circulating lymphocytes
T LYMPHOCYTES
Recognize antigenic epitopes via surface protein complexes termed T-cell receptors (TCRs) which include two glycoproteins called alpha and beta chains, each of which are with variable regions produced similarly to those of immunoglobulins.
T LYMPHOCYTES
Surface receptors for antigens are monomers of IgM or IgD
B LYMPHOCYTES
Covered by about 150,000 B-cell receptors (BCRs)
B LYMPHOCYTES
Produced antibodies
B LYMPHOCYTES
A main function of the _____is induction of central tolerance, which along with regulatory T cells prevents autoimmunity.
THYMUS
has a vascularized connective tissue capsule that extends septa into the parenchyma, dividing the organ into many incompletely separated lobules. Each lobule has an outer darkly basophilic cortex surrounding a more lightly stained medulla
THYMUS
contains an extensive population of T lymphoblasts (or thymocytes), some newly arrived via venules, located among numerous macrophages and associated with the unique thymic epithelial cells (TECs) that have certain features of both epithelial and reticular cells.
thymic cortex
three major types of TECs in the cortex of the thymus:
form a layer, joined by desmosomes and occluding junctions, line the connective tissue of the capsule and septa and surround the microvasculature. This creates an isolated cortical compartment and, together with the vascular endothelial cells and pericytes, forms a blood-thymus barrier preventing unregulated exposure of thymocytes to antigens.
Squamous TECs
three major types of TECs in the cortex of the thymus:
with processes containing keratin tonofilaments joined by desmosomes, form a cytoreticulum to which macrophages and developing lymphocytes attach instead of to reticulin fibers. Importantly, these cells are APCs,
expressing MHC class II molecules in addition to MHC class I. They also secrete numerous cytokines for T-cell development and other immune functions, justifying this organ’s inclusion among endocrine glands.
stellate TECs
three major types of TECs in the cortex of the thymus:
express MHC class II molecules but form a sheetlike structure contributing to a functional corticomedullary barrier between these two regions of each lobule.
squamous cortical TECs
bean-shaped, encapsulated structures, generally only 10 mm by 2.5 cm in size, distributed throughout the body along the lymphatic vessels
LYMPH NODES
A total of _____ lymph nodes are present in the axillae (armpits) and groin, along the major vessels of the neck, and in the thorax and abdomen, and especially in the visceral mesenteries.
400-450
constitute a series of in-line filters of lymph that defend against the spread of microorganisms and tumor cells and provide enclosed environments for antigen presentation and the development of plasma cells secreting non-IgA antibodies.
Lymph nodes
Before merging with the bloodstream, all lymph is filtered and has antibodies added by at least _____.
one lymph node
three major regions within each lymph node:
- OUTER CORTEX
- PARACORTEX
- MEDULLA
three major regions within each lymph node:
containing the nodules
OUTER CORTEX
three major regions within each lymph node:
a deeper extension of cortex
PARACORTEX
three major regions within each lymph node:
lacks nodules
PARACORTEX
three major regions within each lymph node:
with prominent draining sinusoids adjacent to the hilum
MEDULLA
The CORTEX includes the following components:
Subcapsular sinus
Lymphoid nodules
immediately inside the capsule, receives lymph from the afferent lymphatics. From this space cortical sinuses (or trabecular sinuses) branch internally among the lymphoid nodules along trabeculae
Subcapsular sinus
These sinuses are lined by a very thin, discontinuous endothelium penetrated by reticulin fibers and processes of dendritic cells.
Subcapsular sinus
Lymph containing antigens, lymphocytes, and APCs passes through these sinuses and percolates easily into the surrounding lymphoid tissue
Subcapsular sinus
with or without germinal centers, consist largely of developing B lymphocytes and occupy much of the cortex not filled with helper T lymphocytes
Lymphoid nodules
Each nodule is organized around the long, interdigitating processes of FDCs, but these are not readily seen by routine light microscopy
Lymphoid nodules
Numerous macrophages are also present for removal of newly formed defective B cells that undergo apoptosis.
Lymphoid nodules,
does not have precise boundaries but can be distinguished from the outer cortex by its lack of nodules
paracortex
Unlike the superficial cortex, the ____ contains lymphoid tissue rich in T cells distinguishable by immunohistochemistry
paracortex
The medulla of a lymph node has two major components:
Medullary cords
Medullary sinuses
are branched cordlike masses of lymphoid tissue extending from the paracortex. They contain T and B lymphocytes and many plasma cells.
Medullary cords
are dilated spaces lined by discontinuous endothelium that separate the medullary cords
Medullary sinuses
The lumens of these sinuses include a meshwork of processes from reticular cells, which represent a final lymph filter.
Medullary sinuses
These sinuses contain many macrophages and sometimes neutrophils if the lymph node is draining an infected region.
Medullary sinuses
They are continuous with the cortical sinuses and converge at the hilum as the efferent lymphatic vessel .
Medullary sinuses
contains the largest single accumulation of lymphoid tissue in the body and is the only lymphoid organ involved in filtration of blood, making it an important organ in defense against blood-borne antigens
SPLEEN
It is also the main site of old erythrocyte destruction
SPLEEN
As is true of other secondary lymphoid organs, the _____is a production site of antibodies and activated lymphocytes, which here are delivered directly into the blood.
spleen
Located high in the left upper quadrant of the abdomen and typically about 12 × 7 × 3 cm in size
Spleen
Its volume varies with its content of blood and tends to decrease very slowly after puberty.
Spleen
The spleen is surrounded by a capsule of dense connective tissue from which emerge trabeculae to penetrate the parenchyma or ___
splenic pulp
_____ originate at the hilum, on the medial surface of the spleen, and carry branches of the splenic artery, vein, lymphatics, and nerves into the splenic pulp
Large trabeculae
