Lymphatic System Flashcards
The lymphatic system consists of lymph, ________________, lymphoid tissues and organs, and _________________
Lymphatics
Lymphocytes
The primary function of the lymphatic system is the production, maintenance, and distrubution of __________________
Lymphocytes
The lymphatic vascular system is a system of thin-walled endothelial channels that collect excess interstitial fluid from the tissue spaces and returns it to the blood as _____________
Lymph
Unlike the circulatory system, lymph flows in _______ direction towards the _________
One
Heart
At the _______________ end of the capillary microvasculature, the rate of tissue fluid generally exceeds fluid reuptake
Venous
At the venous end of the microvasculature, the blood pressure is ___________ (less than, greater than) that of the tissue fluid, forcing some fluid to return to the capillaries
Less than
Explain this figure.
At the arterial end of the microvasculature, blood pressure and hypertonicity is higher than that of the tissue fluid, forcing fluid out of the capillary and into the surrounding tissue; however, at the venuous end of the microvasculature, blood pressure and hypertonicity is lower than that of the tissue fluid, forcing fluid into the capillary
What happens to fluid that is not reabsorbed by capillaries?
Excess fluid is drained by lymph capillaries and converies into progressively larger lymphatic vessels
________________ __________ carry lymph from peripheral tissues
Lymphatic vessels
Lymphatic _____________________ originate in the various tissues and are thin, close-ended vessels that consist of a single layer of endothelium
Capillaries
Lymphatic capillaries converge into larger lymphatic vessels with structures similar to those of veins except that they have _______________ walls and lack a clear-cut separation between ________________
Thinner
Tunics
To what does the V point?
Lymphatic valve
Two sets of lymphatic vessels collect lymph. What are they?
Superficial lymphatics
Deep lymphatics
Lymphatic vessels ultimately end up as two large trunks. What are they?
Thoracic duct
Right lymphatic duct
The ______________ duct empties lymph into the junction of the left jugular vein with the left subclavian vein, accounting for 75%of all lymph drainage
Thoracic duct
The ___________ duct empties into the confluence of the right subclavian fvein and the right internal jugular vein, accounting for approximately 25% of lymph collection
Right lymphatic duct
What are some characteristics of lymphoid tissues?
They are composed of connective tissues and contain a rich supply of lymphocytes
Lymphoid tissues are composed of ____________ and a rich network of reticular or _____________ fibers supporting lymphocytes
Free cells
Type III collagen
Reticular fibers in lymphoid tissues are produced by fibroblast-derived cells called ________________ _______________
Reticular cells
In lymphoid tissues, fibroblast-like reticular cells produce and secrete reticulin fibers to which many cells loosely attach, including ____________ and __________________
Macrophages
Lymphocytes
What is the largest lymphoid organ?
Mucosa-associated lymphoid tissue (MALT)
Mucosa-associated lymphoid tissue (MALT) can be found in what types of sites?
Sites exposed to the external environment
What are two specific types of MALT discussed in class?
Tonsils
Peyer’s patches (GI)
The _____________ are large nodules in the walls of the pharynx of which most people contain five
Tonsils
What are the five tonsils named?
Left and right palatine tonsils
Paryngeal tonsil
Lingual tonsils (two)
Tonsils contain several lymphoid nodules that are collectively covered by _______________ ______________ _____________ ______________ on one side and a ___________ _______________ ___________ _______________ on the other
Stratified squamous keratinized epithelium
Dense connective tissue capsule
___________________ _________ are pockets or folds that occur naturally in the tonils
Tonsillar cypts
The average adult tonsil has between __ and __ crypts
10 and 20
Crypts in the tonsils are usually small and debris-free; however, on some occassions, ____________ ________ may develop
Tonsil stones
What often occurs to the epithelium surrounding tonsillar crypts?
It often vecomes infiltrated with lymphocytes and neutrophils, becoming difficult to recognize histologically
Where would you find Peyer’s patches?
Ileum
The ileum is lined by an absorptive simple _______________ epithelium and intraepithelial lymphocytes are frequently present between cells
Columnar
______________ __________ are small, oval lymphoid organs covered by a capsule
Lymph nodes
The capsule of a lymph node is composed of what type of connective tissue?
Dense irregular connective tissue
A changing population of immune cells is suspended on what type of fibers in lymph nodes?
Reticular fibers
All lymph node cells are arranged in the stroma of reticulin fivers and reticular cells to form three major regions within each lymph node. What are these regions?
- An outer cortex containing the nodules
- A deeper extension of the cortex called the paracortex, which lacks nodules
- A medulla with prominent draining sinusoids adjacent to the hilum
A lymph node has a convex surface where ____________________ lymphatics enter and a concave depression, the __________, where an _____________________ lymphatic leaves and where an artery, vein, and nerve penetrate
Afferent
Hilum
Efferent
___________________ _____________________ have a dark and light zone sthat form in the lymph node follicles (lymphoid nodules) and are a site of ___ cell activation and proliferation
Germinal centers
The paracortex is densely packed with __________________
Lymphocytes
The medulla of the lymph node has two major components. What are they?
- Medullary cords
- Medullary sinuses
What are medullary cords?
They are branched cordlike masses of lymphoid tissue extending from the paracortex and contain T and B lymphocytes and many plasma cells
What are medullary sinuses?
They are dilated spaces lined by discontinous endothelium that separate the medullary cords; the lumens of medullary sinuses include a meshwork of processes from reticular cells, which represent a final lymp filter
The cortex contains the _________________ _________, immediately inside the capsule, that receives lymph from the afferent lymphatics
Subcapsular sinus
What lymphoid organ is lobular and posterior to the sternum with no lymphatic nodules?
Thymus
The functional tissues of the thymus are the __________________
Lobules
Each thymus lobule is surrounded by a connective tissue of _________________ _____________ _______________; an ______________ _____________ of densely packed lymphocytes; and a _____________ _______________ of loosely packed cells
Epithelial reticular cells
Outer cortex
Central medulla
The thymus cortex and medulla play different roles in the development of _____________
T cells
The thymus is the site of T lymphocyte differentiation and the selective removal of T cells reactive against self-antigens, a key part of inducing _________________ __________ _____________
Central self-tolerance
In _______________ ________________, developing thymocytes are chosen depending upon whether their T cell receptors can recognize and bind antigens on the MHC molecules properly; if they are unable to do so, they are removed
Positive selection
_______________ _________________ removes thymocytes that are capable of strongly binding with “self” MHC peptides.
Negative selection
Where does positive selection occur?
Thymic cortex
Where does negative selection occur?
Thymic medulla
About 98% of thymocytes die during the development processes in the thymus by failing either positive selection or negative selection, whereas the other 2% survive and leave the thymus to become mature immunocompetent ___ _________
T cells
The thymus cortex is composed mainly of _______________ (cells) supported by a network of finel-branched _______________ _______________ ________________ that are continuous with a similar network in the medulla
Thymocytes
Epithelial reticular cells
The ________________ is the location of the earliest events in thymocyte development, where T cell receptor gene rearrangement and positive selection occur
Cortex
How are lobes divided in the thymus?
Via connective tissue septa
What are the two key identifying features of the thymus?
- Lack of lymphatic nodules
- Hassall’s corpuscles
_______________ ______________ are layered whorls of epithelial cells that increase in number throughout life; they are the remains of epithelial tubes, which grow out of the third _____________ pouches of the embryo; however, their function remains unknown as there are no such structures in mice
Hassall’s corpuscles
Pharyngeal
Where are Hassall’s corpuscles located?
Thymic medulla
Fewer lymphocytes are present in the thymic __________________
Medulla
Thymocytes that reach the medulla have successfully undergone T-cell receptor gene rearrangement and positive selection and have been exposed to a limited degree of negative selection; the medulla is specialized to allow thymocytes to undergo additional rounds of _______________ ______________ to remove auto-reactive T cells from the mature repertoire
Negative selection
What happens to the thymus as one progresses from childhood to adulthood?
- The thymus enlarges during childhood but begins to atrophy at puberty; the thymus is thus highly active at birth and early childhood, but after puberty, thymic activity declines and fewer lymphocytes remain
- Relatedly the structure of the thymus is reduced - the cortex and medulla become difficult to distinguish from the capsule
What are the three crucial functions of the spleen?
- The removal of abnormal blood cells
- The storage of iron recycled from red blood cells
- The initiation of immune responses by B cells and T cells
The spleen is an oval-shaped organ encapsulated with a _____________ _____________ connective tissue with lymphatic nodules distributed throughout
Dense irregular
There are two primary “pulps” of the spleen. What are they?
White pulp or spots that are composed of lymphocytes
Red pulp or spots that are spaced in between white pulp and contain sinuses and cords of red blood cells
What is the white pulp of the spleen?
An accumulation of lymphocytes
The white pulp contain germinal centers, regions of _____ _______ proliferation and differentiation, and ___________ ____________, which brings blood from the splenic artery for filtration
B cell
Central arteries
