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HUMAN ANATOMY
LECTURE SEVENTEEN
LYMPHATIC SYSTEM
LYMPHATIC SYSTEM
FUNCTIONS
• Fluid balance - extra interstitial fluid
(from capillaries) enters
lymphatic vessels - now called lymph
• Fat absorption - absorbs fat from
digestive tract (villi) into lacteals
• Defense - microorganisms and other
foreign substances are filtered from the
lymph by lymph nodes
Lymphatic system consists of:
• lymph - fluid component
• lacteals - remove fat from digestive tract
• lymphatic vessels - carry lymph
• lymphoid tissues and organs - tonsils,
lymph nodes, spleen, thymus gland
LYMPHATIC VESSELS
• Carry lymph in one direction - from tissues to circulatory system
• Fluid moves from extra cellular space into lymphatic capillaries
- tiny, closed ended vessels with very thin walls of simple squamous
epithelium
- overlapping squamous cells act as valves to prevent backflow
- found in all body tissues except CNS, bone marrow and tissues
without blood vessels (epidermis, cartilage)
• Lymphatic capillaries join to form lymphatic vessels
- similar to small veins with one-way valves
- superficial lymphatics and deep lymphatics collect lymph from
capillaries
• Lymph drains into the cisterna chyli (saclike chamber) of the thoracic duct and into
the left subclavian vein - from abdomen, pelvis, lower limbs
• Lymph from head, neck, chest, upper limbs drains into the right lymphatic duct and
empties into the right subclavian vein
LYMPH ORGANS
• Made up of lymphatic tissue consisting of many lymphocytes held
by fine reticular fibers
• Lymphocytes are formed in the red
bone marrow and act as part of the
immune system by increasing in
number when exposed to
microorganisms
TONSILS
• Large lymphatic nodules on walls of
pharynx
• 3 kinds:
phayngeal - near internal opening
of nasal cavity
palatine - on each side of posterior
opening of oral cavity “tonsils”
lingual - posterior surface of tongue
• Form protective ring around
opening of oral and nasal cavities
LYMPH NODES
• Small, round nodules distributed along lymphatic vessels - lymph passes
through before entering blood
• Three aggregations of nodes: - inguinal nodes in the groin
- axillary nodes in the armpits
- cervical nodes in the neck
• Surrounded by a dense connective tissue capsule and divided by trabeculae
into compartments of lymphatic tissue (lymphocytes) and lymph sinuses
(spaces containing macrophages within fibrous network)
• As lymph travels through the node (i) immune system may be activated to
produce more lymphocytes
(ii) removal of microorganisms by
macrophages
SPLEEN
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Contains the largest amount of lymphatic tissue in the body
Located in the left, superior corner of abdominal cavity
Surrounded by a capsule of collagen and elastic fibers
Contain two kinds of lymphatic tissue:
White pulp - surrounds arteries within the spleen, resemble lymph nodes
Red pulp - associated with the veins, contains large number of macrophages
• Cells detect and respond to foreign substances in the blood and destroy worn out
RBC’s as blood passes through the red pulp
• Stores iron as RBC’s broken down
• Initiates immune response in response to antigens in the blood
• Acts as a resevoir for blood - can let blood out in an emergency (ie/ hemorrgage)
THYMUS
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Located in superior mediastium just posterior to the sternum
Capsule divides it into two thymic lobes separated by the septa
Each lobule consists of a dense cortex and a central medulla
Lymphocytes (T cells) divide in the cortex and move to the medulla –
where they mature and eventually move into the blood