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
