L11 – Structure and Function of the Lymphatic System Flashcards
3 components of the lymphatic system?
Lymph, lymphatic organs, lymphatic vessels
3 function of lymphatic system?
- Fluid balance (maintain homeostasis): recover fluid lost from blood capillaries
- Defense (immunity):
i) Carries away larger particles (e.g. bacteria, viruses) to be filtered, destroyed in lymph nodes
ii) Guards against pathogens - Fat absorption via intestinal lacteals:
- Chyle = lymph + lipids
- Transport the fats into venous circulation
5 Histological features of lymph vessels that differ from normal blood vessels/ capillaries? (think endothelium, basal lamina, lumen…)
- Blind ended
- Single layer of Loosely overlapped endothelial cells
- No tight junction, incomplete/ absent basal laminae
- Larger lumen than blood capillaries
- Large lymph vessels have Bicuspid valves (unidirectional flow)
Distribution of lymphatic capillaries?
throughout the body except in nonvascular tissues, splenic pulp and bone marrow.
Particularly abundant within dermis of skin, mucous membranes
List the sequence of drainage of lymph from interstitial fluid* to the venous circulation? (2 pathways)
Interstitial fluid > afferent lymphatic vessel (multiple) > lymph node > efferent lymphatic vessel (1 or 2) > various lymphatic trunks: drain into 2 lymphatic DUCTS
1) 75%, Left upper body + lower body (intestinal + lumbar into Cisterna chyli) into Thoracic duct > Left venous angle > Left brachiocephalic vein
2) 25%, right upper body into right lymphatic duct > Right venous angle> Right brachiocephalic vein
List all the lymphatic trunks and the areas they each drain? (5) (their names literally say where they drain!)
§ L/R Lumbar – lower limbs, pelvis, kidneys, adrenal glands and abdominal wall
§ Intestinal – organs in the abdominal cavity
§ L/R Bronchomediastinal – thoracic wall, lungs and heart
§ L/R Subclavian – upper limbs
§ L/R Jugular – head and neck
List all the lymphatic trunks and their accompanying blood vessels?
§ L/R Lumbar – Aorta and its branches
§ Intestinal – Aorta and its branches
§ L/R Bronchomediastinal – independent of blood vessels
§ L/R Subclavian – Subclavian vein
§ L/R Jugular – Internal jugular vein
3 mechanisms that provide pressure differences to drive lymph flow? (very similar to venous blood flow!)
- Skeletal muscle pump
- Respiratory pump
- Smooth muscle wall in tunica media and adventitia of large lymphatic vessels
What vessels form the venous angles?
junction of internal jugular and subclavian veins
2 types of lymphedema and causes?
Primary = developmental abnormality of lymph nodes, rare and inherited condition
Secondary = surgery/ radiation therapy/ tumour compression…etc cause scar tissue formation and failure of lymph vessels to regenrate
Cause and symptoms of Filariasis?
- invasion of the lymphatic vessels by filarioidea
- severe swelling in legs and genitals (elephantiasis)
Define the primary lymphatic organs and function?
The organs where lymphoid stem cells are divided and matured into immunocompetent B and T cells
§ Red bone Marrow (B cells)
§ Thymus (T cells)
Define secondary lymphatic organs and function?
where immunocompetent cells populate and initiate immune responses
§ Lymph nodes
§ Spleen
§ Mucosa-associated lymphatic tissue (MALT)
- Peyer’s patch - Tonsils
Location and gross structure/shape of thymus?
Location - in the mediastinum between sternum and the aorta
- two lobes being encapsulated separately and connected by connective tissue
- adhere to the fibrous pericardium
Change in the size of thymus over lifetime?
Size
- largest in the early part of life, particularly around puberty
- the functional portion atrophies with age and is replaced by fatty infiltrations
Describe the gross internal structure of the thymus?
Connective tissue capsule extends into thymus
» form trabeculae** subdividing the thymus into incomplete lobules**:
Each lobule has:
Cortex
Medulla
Describe the difference in staining between cortex and medulla of thymus lobules. (staining: think about the cells that reside there/ lifecycle of lymphocytes!)
1) Cortex
- dark-staining outer part of the lobule with densely packed immature lymphocytes
2) Medulla
- light-staining central part of lobule with mature lymphocytes
Mature lymphocytes have less dense nucleus + more cytoplasm = less staining
Describe the change in thymus parenchyma with aging?
cellular portion of thymus is gradually replaced by connective tissue and adipose cells.
List the cells in the cortex of lobules in the thymus?
§ large number of T cells
§ scattered epithelial reticular cells
§ dendritic cells and macrophages
Function of epithelial reticular cells in the lobules of the thymus?
Depends on location:
1) Cortex of lobule:
i) serve as a framework to “educate” the pre-T cells to develop self- antigen recognition in Positive Selection
ii) Produce thymic hormones***
2) Medulla of lobule:
- cluster to form Hassall’s corpuscles***
- assist in T cell “education” too
List the cells in the medulla of lobules in the thymus?
§ mature T cells
§ reticular epithelial cells
§ dendritic cells and macrophages
Define the neoplasm of thymic epithelium and its presentation?
Thymoma
- Non-symptom: 1/3 to 1/2 patients have no symptoms
- Symptoms: compression of the surrounding organs or associated autoimmune disorder (myasthenia gravis)
List the 4 layers of lymph nodes?
Capsule
Cortex
Paracortex
Medulla
Describe the structure of the lymph node capsule?
- connective tissue with trabeculae extensions into the node
» form subcapsular and trabecular sinuses - afferent lymphatic vessels penetrate the capsule
Function of the lymph node cortex?
Contain primary and secondary lymphoid follicles:
1) Primary lymphoid follicles
- absence of immune stimulation
- evenly distributed dark-staining inactive B cells
2) Secondary lymphoid follicles
- under antigenic stimulation
- sites of plasma cell and memory B cell formation
Function of the medulla of lymph nodes?
Contain medullary sinuses and medullary cords
> Connect trabecular sinuses with efferent lymph vessels at the Hilum
The cortex and paracortex both have primary and secondary lymphoid follicles. T or F?
False
Paracortex has no lymphoid follicles
3 functions of lymph nodes?
§ lymph filtration
§ phagocytosis of bacteria or foreign substances
§ lymphocytes production, storage, activation and recirculation
Describe the flow of lymph through the lymph nodes? Which layers are for immune defense?
Several afferent vessel Subcapsular sinus Trabecular sinus Medullary sinus 1-2 Efferent lymph vessels
All 3 sinuses have reticular fibers, macrophages and lymphocytes for immune defence
Why are there more afferent lymph vessels into lymph nodes than efferent?
Lower number of efferent vessels to slow down lymph flow
> > more time for filtration and immune defense
Compare the cells that populate the cortex vs paracortex of lymph nodes?
Cortex = B cells mainly, some dendritic cells and macrophages as APCs
,has primary and secondary lymphoid follicles
Paracortex = T cells and dendritic cells, no lymphoid follicles
Distinguish the cells that populate the secondary lymphoid follicles in LN?
- germinal center:
dendritic cells and macrophages activated B cells in various stages of maturation - peripheral zone (mantle zone):
inactive B cells with condensed nuclei and little cytoplasm
Function of the lymph node paracortex?
- absence of lymphoid follicles = no B cell production
- T cells and dendritic cells
»_space; expands in T cell dominated immune responses - postcapillary high endothelial venules (HEVs) ***
Describe the ultrastructure of the medulla of lymph nodes?
- Medullar cords separated by sinuses
- More lymphocytes in cords
- B cells and plasma cells migrated from cortex embed between reticular fibers in medulla
Function of HEVs in Lymph nodes? What are the histological layers of HEV?
High endothelial venules @ paracortex of LN
- Postcapillary venules lined by cuboidal** endothelium,THICK basal lamina and sparse tunica adventitia
(endothelium has specialized lymphocyte homeoreceptors) - Shortcut Passage of lymphocytes between bloodstream and LN and surrounding tissue
Describe difference between metastatic LN and Infected LN?
Metastatic = enlarged, firm, nontender lymph nodes fixed to underlying structures
Infected = Soft, tender, moveable
Define sentinel lymph nodes?
first lymph node encountered in the path of lymph drainage from a particular organ.
guard rest of body from dissemination of tumour cells or microbes
Differentiate the change in function of the spleen over lifetime?
- blood-forming organ in foetal life
- blood-destroying organ in postnatal life
- filters blood from blood-borne antigens and microorganisms
Describe the gross structure of the spleen with anatomical divisions?
fibrous capsule with trabeculae extension
White pulp:
- extends from central to marginal zones
- contains follicles,periarterial lymphatic sheath (PALS)
Red pulp: (major, 90% volume)
- at the periphery
- Contains splenic sinuses and splenic cords (Billroth cords)
Describe the anatomical structures and functions of the red pulp of the spleen.
90% splenic volume
Mechanical filtration of blood via macrophages
Splenic cords:
- Reticular fibers form matrix of WBC surrounding sinuses
- Macrophages destroy RBC
Splenic siuses:
- Drain into splenic vein branches
- Lined by discontinuous endothelium
Describe the anatomical structures and functions of the white pulp of the spleen.
- periarterial lymphatic sheath (PALS): T cells wrapping terminal end of central artery
- Lymphoid follicles:
i) Germinal center for B-cell proliferation under Ag stimulation
ii) Activated B cells and plasma cells move to germinal center - Marginal zone:
Junction between red and white pulp - Trap antigens by macrophages and lymphocytes
List the locations in the body where MALT is found?
Unencapsulated lymphoid tissue
> > in walls of GI, Resp, Reproductive, Urinary tracts + skin
e. g.
- gut-associated lymphoid tissue (GALT)
- tonsils (palatine,nasopharyngeal,lingual and tubal)
Describe the ultrastructure of MALT?
- Close to epithelial surface, unencapsulated
- Follicles in lamina propria and submucosa»_space; lymphocyte activation and proliferation
- Has APCs (dendritic, macrophages)
What are the 2 types of GALT in the gut?
Peyer’s patches @ ileum
Isolated lymphoid follicles @ throughout intestines
Describe the special cell types and functions of Peyer’s Patches?
1) specialized epithelial cells (M cells)
- phagocytose luminal antigens
- transport antigens to act as APC to lymphocytes & macrophages at follicles
2) Lymphoid follicles
- B and T cells, macrophages and plasma cells
Which layer of the intestine is GALT resided?
in the lamina propria & submucosa of ileum
Name of the ring of MALT at the oro- and nasopharynx?
Waldeyer’s ring
surrounds the openings into the digestive and respiratory tracts
List the tonsils that make up Waldeyer’s ring? Structure of these tonsils?
§ anteroinferiorly by the lingual tonsil
§ laterally by the tubal and palatine tonsils
§ posterosuperiorly by the pharyngeal tonsil
- partially encapsulated + lymphatic follicles with germinal centers
Where is the lingual tonsil located?
lamina propria of the root of the tongue
Describe the epithelium, capsule and ultrastructure of the lingual tonsils?
stratified squamous nonkaratinized epithelium with invaginations»_space; deep tonsillar crypts
incomplete capsule
primary or secondary lymphoid follicles
Location of palatine tonsils?
either side of pharynx between palatopharyngeal and palatoglossal arches
Describe the epithelium, capsule and ultrastructure of the palatine tonsils?
stratified squamous nonkaratinized epithelium with invaginations»_space; deep tonsillar crypts
incomplete capsule
mainly secondary lymphoid follicles, some primary
Compare the Aetiology and appearance of tonsils in acute vs chronic tonsillitis?
Acute:
Viral or bacterial cause
Enlarged, red and inflammed tonsils
Chronic:
repeated acute attacks
Small and fibrosed
Treatment options for tonsilitis?
Treat pathogen with antibiotics (viral usually self resolve)
Indicate tonsillectomy* for airway obstruction + dysphagia and dysphonia in chronic tosilitis (>3 months)
List the structural features that distinguish pharyngeal tonsil from lingual or palatine tonsils?
- pseudostratifed ciliated columnar goblet cell / respiratory epithelium (NOT NKSS)
- NO DEEP CRYPTS
- Mostly secondary lymphoid follicles
Sequence of arterial blood flow into spleen?
Splenic artery (hilum)
» trabecular arteries
» central arteries
» Periarterial lymphatic sheath (PALS) to penetrate lymphatic nodule
» pencillar artery/arterioles and terminal macrophage-sheathed capillaries
» splenic sinuses
Sequence of venous blood flow out of spleen?
splenic sinusoids/ sinuses» pulp veins»_space; trabecular veins»_space; splenic veins
If diffuse lymphoid tissues are filled with eosinophils, what does that indicate?
Chronic inflammation
Hypersensitivity reactions
