The Lymphatic and Immune Systems Flashcards
What is the purpose of the lymphatic system?
it is responsible for recovering excess tissue fluid and returning it to the bloodstream in addition to housing and producing cells of the immune system, monitoring the body for pathogens, absorbing dietary lipids
What organs are included within the lymphatic system?
lymphatic vessels, lymphoid tissues, red bone marrow, tonsils, thymus, spleen, lymph nodes
What does the lymphatic system reabsorb?
water, electrolytes, nutrients, hormones, and other substances not reabsorbed by the capillaries - lymphatic vessels collect this excess fluid moving it to the subclavian vein of the shoulders where it is returned to the blood stream
What is the fluid absorbed by lymphatic vessels called?
lymph
What is the function of the lymph nodes?
filtration of lymph - macrophages within the lymph nodes phagocytize impurities and cleanse the lymph, monitoring for potential pathogens before the lymph reenters the blood stream
What is edema?
A collection of fluid in the tissues resulting in swelling and potential circulatory collapse from loss of blood volume - happens when the lymphatic system fails to collect excess fluid
What two cell types are vital to the immune system for monitoring?
macrophages and lymphocytes
What are lacteals?
located in the small intestine - special lymphatic vessels that absorb dietary fats, cholesterol, and fat-soluble vitamins
What are the three major components of the lymphatic system?
Lymphatic vessels, Lymphatic Tissues, Lymphatic Organs
What are Lymphatic vessels?
lymphatic capillaries converge to form collecting vessels which lead into lymph nodes and move node to node -
collecting vessels converge into 6 lymphatic trunks which are coordinated to different regions of the body -
lymphatic trunks converge into collecting ducts that empty into true blood vessels called the subclavian veins
What are Lymphatic tissues? Are there subtypes of these tissues?
these are aggregations of lymphocytes within connective tissues of various organs and in loose connective tissue lying below epithelia
subtypes: MALT (mucosa-associated lymphatic tissue), GALT (gut-associated lymphoid tissue), BALT (bronchus-associated lymphoid tissue)
Describe the significance of MALT.
mucosa-associated lymphatic tissue
mucous membranes line passages open to the exterior: digestive, respiratory, reproductive, urinary - which are subject to invasion of outside pathogens
MALT guards these openings against the entrance of pathogens - sometimes becoming concentrated into dense masses of lymphocytes called lymphatic nodules
What are Lymphatic organs?
A mass of lymphatic tissue that is enclosed in a fibrous capsule that separtes it from neighboring tissues/organs.
These organs hace a refined structure
e.g. red bone marrow, tonsils, thymus, lymph nodes, spleen
What types of cells are a part of the lymphatic-immune system?
Natural Killer (NK) Cells, B Lymphocytes (B Cells), Antigen-presenting Cells (APCs), T Lymphocytes (T Cells) - Helper (TH Cells), Cytoxic T (TC) Cells, Regulatory T (TR) Cells, Memory T Cells
Natural Killer (NK) Cells
nonspecific defenses in the body - retain no memory of a given pathogen
only attack host cells (of one’s own body) that are either cancerous or have been antigenically modified by viral infection
destroying precancerous cells - prevent growth of tumors
limit the spread of virus to new cells
~ 10 - 15% of the circulating blood lymphocytes
B Lymphocytes (B Cells)
small lymphocytes originating in the bone marrow where they become immunocompetent (where they develop antigen receptors enabling response to foreign antigens)
responsible for humoral (antibody-based) immunity
when stimulated by an antigenic challenge may have enlarged rough ER = plasma cell
may also become a memory B cell which serves to “remember” an antigen, reacting to known foreign bodies rapidly
What are T Cells? List the types of T Lymphocytes (T Cells)
small lymphocytes that achieve immunocompetence (antigen sensitivity) in the thymus - responsible for cell mediated immunity.
Helper, Cytotoxic, Regulatory, Memory
What is the function of Helper T (TH) Cells
recognize fragments (epitopes) presented by APCs - secrete lymphokines which activate humoral, and cellular immunity and inflammation
= coordinate nonspecific defense and both kinds of specific immunity
- target of HIV - results in highly immunocompromised state
What is the function of Cytotoxic T (CT) Cells?
directly attack and destroy foreign cells (bacteria and transplanted tissue) - release perforins that create a hole in the enemy membrane as well as granzymes which enter through the perforin-created hole to degrade the enzymes of the enemy cell.
What is the function of Regulatory T (TR) Cells?
prevent excess TH and TC response - preventing attacks against one’s own tissues
What is the function of Memory T Cells?
like Memory B Cells - preprogrammed to respond quickly in the case of reexposure to the same antigen that caused an original immune response
What is the function of APCs? What are the three types?
Antigen-Presenting Cells
these are cells that phagocytize antigens, digest them and then display antigenically active fragments of them (epitopes) on the plasma mem. surface
when a TH Cell recognizes one of these antigens it secretes lymphokines that activate humoral and cellular immunity (B and TC Cells) and inflammation
types: B Cells, Macrophages, Dendritic Cells
Where do macrophages develop?
typically from blood monocytes
Describe the organization of lymphatic vessels.
Lymphatic CAPILLARIES = single layer of endothelial cells form a sac - overlapping one another like shingles = very thin walled and irregular - anchored to tissues by anchoring filaments which help maintain patency
when tissue swells with fluid, endothelial flaps are pushed open and fluid enters the capillary, when pressure is higher in the capillary the flaps are shut
(cell gaps are so large that bacteria and cancer cells may enter)
fluid now in the capillaries is deemed lymph
capillaries form collecting vessels through anastamoses leading to larger collecting ducts (2 in the chest) that open into the subclavian veins
What is a lymphoid nodule?
Also called a lymphoid follicle - an area with considerable lymphocyte infiltration having a pale germinal center and a dark peripheral border with no capsule but rather a precise boundary
Describe Peyer’s Patches.
located on the abmesenteric side of the ileum - concentrated here to intercept bacterial infection from the large intestine to prevent spread into the small intestine.
Describe the epithelial specialization in the bronchi and intestines characterized in lymphatic tissue.
epithelium laying over lymphoid follicles changes from whatever is present surrounding the typical organ to a squamous epithelium of microfold (M) Cells which are APCs
What are the three types of tonsils?
Lingual, Palatine, Pharyngeal
Where are the Palatine Tonsils located? What are its characteristics?
Near the back of the oral cavity two structures located on the lateral walls of the mouth
having 10-12 deep crypts lined with lymphatic nodules (dense collections of lymphocytes) and trabeculae of fibrous connective tissue lined by stratified squamous epithelium
when inflamed (tonsillitis) - exhibit abundant neutrophils within their tissue
Where are the Lingual Tonsils located? What are its characteristics?
embedded at the back of the tongue, behind the vallate papillae
each of these having a single crypt and surface opening - crypts are deep and wide (distinguish against palatine tonsils) - covered with stratified squamous epithelium with a flimsy underlying capsule
*lingual glands have ducts that open into the base of each crypt of the lingual tonsils
Where are the Pharyngeal Tonsils located? What are its characteristics?
There is only one!
located medially behind the nasal cavity on the dorsal wall of the nasopharynx
covered by pseudostratified columnar epithelium, distinguishing it from lingual and palatine tonsils - may have scattered patches of stratified squamous epithelium, having the thinnest and most incomplete capsule among other tonsil types.
rather than having “crypts” these tonsils hace shallow folds or pleats of tissue
seromucous gland ducts open into the base of these “pleats”
inflammation among these tonsils are called adenoids
What is the anatomical location of the thymus?
within the mediastinum, superior to the heart, below the thyroid gland
surrounded by a fibrous capsule with trabeculae that penetrate into the gland and divide the parenchyme into polygonal lobules
each lobule has a dark cortex and lighter medulla and is connected to other lobules by cords of medullary tissue - exhibits thymic (Hassal) corpuscles (concentric flattened cells with degenerating central cells)
What organ does involution apply to?
the thymus - very large in a newborn extending across most of the diaphragm (often mistaken for lung), growing rapidly to age 1-2 and slowing until approx. age 14
then undergoing involution the thymus shrinks rapidly and is replaced with fat and fibrous tissue - shrinking so much that little remains at old age
What cells mature in the thymus?
lymphocyte class T Cells which are formed in the bone marrow and mature in the thymus
What is the process of T Cell maturation
residing in the cortex as immature T cells called thymocytes where they develop a surface receptor for antigens
once mature called immunocompetent T Cells - and tested through negative selection to ensure they do not attack our own antigens but still capable of recognizing antigens
only 2% of T Cells enter the medulla where they are stimulated by thymic hormones to multiply and colonize into large identical T Cells = positive selection
These cells now disperse and colonize in other organs of the body
Where do mature T Cells colonize within the body after positive selection?
bone marrow, lymph nodes, tonsils, mucous membranes, etc
What lymphatic organ is the most numerous?
Lymph nodes - approx. 450 in the adult body
Where are lymph nodes concentrated throughout the body?
neck, armpit, breast, groin, mesenteries, bend of the elbow and knee
How are lymph nodes organized in relation to one another as well as independently? How does lymphatic fluid enter the nodes?
form a series of in-line filters along the course of the lymphatic collecting vessels
lymph enters a node through afferent lymphatic vessels along the convex side of the node, moving through the nodal tissue, exiting via two-three efferent lymphatic vessels on the same convex region of the node
*nodes are the only organs that have afferent lymphatics as well as efferent
How do lymph nodes filter passing lymph?
macrophages phagocytize bacteria, APCs intercept and alert the immune system, T and B Cells carry out immune attacks on foreign disease agents - also adding lymphocytes to the lymph which will eventually make it’s way back into the blood
Describe the anatomy of a lymph node. What structure is unique to lymph nodes?
Trabeculae arise from the capsule, penetrating into the node to subdivide the parenchyma
- just below the capsule, lies the subcapsular sinus - the point where lymph from afferent vessels enters continually - washing away typical lymphocytes allowing the area to appear clear
Describe the components of the splenic cortex.
containing primary lymphoid nodules with pale germinal centers (secondary nodules) where B memory cells and plasma cells form.
lying between nodules are the cortical (radial) sinuses which deliver lymph to the medulla - sinuses = a network of reticular cells and adherent macrophages
Describe the components of the splenic paracortex.
where cortex mets medulla - containing mostly T cells - having a specialized vascular system - high endothelial venules
*activated T Cells (Helper T Cells) activated by APCs in the spleen will proliferate quickly under antigenic stimulation and be sent into the body through the efferent lymphatic system
Describe the components of the splenic medulla.
consists of large, twisting sinuses ensheathed in lymphocyte clusters aka medullary cords
What is the largest lymphatic organ?
The Spleen!
