Week 5 Flashcards
What are the three components of the lymphatic system?
Lymphatic vessels
Lymph
Lymphoid tissues & organs
What are the key functions of the lymphatic system?
Circulatory function
Returns fluid that has leaked from the vascular system to the blood
Transport of nutrients, hormones, wastes
Immunity
Lymphocytes housed within lymphoid organs are activated by immune responses
Some lymphoid organs also contain macrophages, which engulf foreign material
What are the lymphatic vessels?
An elaborate network of drainage vessels that transport protein-rich interstitial fluid back to the bloodstream
Lymphatic capillaries drain the interstitial spaces of most tissues
When the interstitial fluid enters these vessels, it is called lymph
What is the flow of lymph?
Lymphatic capillaries –>lymphatic collecting vessels –>lymphatic trunks –>lymphatic ducts
What are lymphatic collecting vessels?
Thin-walled vessels that drain lymphatic capillaries
Possess numerous valves (beaded appearance)
In general, superficial lymphatic vessels (those in the skin and subcutaneous tissues) follow veins and eventually drain into deep lymphatic vessels
Deep lymphatic vessels follow arteries
What are lymphatic trunks?
Are formed by large collecting vessels
Named for the regions that they drain
Which lymphatic ducts drain into the thoracic duct or Rt lymphatic duct near the junction of subclavian and int. jugular veins?
Jugular trunks (x2) Subclavian trunks (x2) Bronchomediastinal trunks (x2)
Which lymphatic trunks drain into the cisterna chyli?
Lumbar trunks (x2) Intestinal trunk (x1)
What is the thoracic duct?
Major vessel of the lymphatic system
38 - 45 cm long, 3-5 mm in diameter
What is the pathway of the thoracic duct?
Formed by the convergence of the lumbar & intestinal trunks (anterior to L1/2 vertebrae)
In 50% of people, it begins as an enlarged sac, the cisterna chyli
Cisterna (L. ‘box’), chyli (Gr. ‘juice’)
Ascends through the aortic hiatus into the posterior mediastinum
Enters the venous system at the junction of the Lt internal jugular and Lt subclavian veins
Receives lymph from the Lt jugular, subclavian & bronchomediastinal trunk before entering junction
What is the right lymphatic duct?
~ 1.25 cm long
Drains Rt upper limb, Rt side of head and thorax
What is the pathway of the right lymphatic duct?
Formed by lymphatic trunks draining the right upper quadrant of the body:
Rt jugular, subclavian & bronchomediastinal trunks
Enters the venous system at the junction of the Rt internal jugular and Rt subclavian veins
What does the lymphatic system rely on to prevent back flow?
Lymphatic system lacks a pump
Relies on valves to prevent backflow
What are the factors affecting lymphatic flow?
Rhythmic contraction of lymphatic vessels (smooth m.) & pulsations of nearby arteries
Intermittent pressure on lymphatic vessels
e.g. skeletal m. contraction, movement of viscera
Pressure changes in the thorax during respiration
Flow is almost negligible in an immobile limb
e.g. swelling of feet after a long plane trip
What are the 3 lymphoid cells?
Consist of lymphocytes, auxiliary immune cells and supporting cells
What are lymphocytes?
T cells: cellular adaptive immunity
~75% circulating lymphocytes
Subtypes: cytotoxic, helper, regulatory T cells
B cells: humoral adaptive immunity
Subtypes: plasma, memory cells
Natural Killer cells: innate (nonspecific) immunity
Induce apoptosis of virus- or cancer-infected cells
What are auxiliary immune cells?
MACROPHAGES
Widely distributed throughout lymphoid organs
Functions include:
Phagocytosis
Enhancement of inflammatory response
Presentation of antigens to T cells
DENDRITIC CELLS
Mobile, antigen-presenting cells
Possess wispy cellular extensions for antigen capture & phagocytosis
Migrate to lymph nodes and present antigens to naïve lymphocytes (initiates adaptive immune response
What are supporting cells?
Reticular cells: fibroblast-like cells that produce a connective tissue stroma (L. ‘bed covering’) for lymphoid tissues and organs