Functional Anatomy of Lymphatic

System

Lymphatic System protects body against foreign material assists in circulation of body fluids between

cells and bloodstream transports dietary fats

Lymphatic System (cont.)

Consists of:- lymph- network of vessels- lymph nodes and nodules - tonsils- spleen - thymus gland- bone marrow

Lymph (lympha = clear fluid)

derived from tissue fluid contains more white blood cells than plasma enters node through afferent lymphatic vessels flows through node in one direction

Lymph (cont.)

flows through sinuses in lymph node cortex and then into the medulla

exits the lymph node through efferent lymphatic vessels

must be returned to blood stream to maintain blood volume and pressure

Lymph Capillaries

microscopic closed-ended vessels located next to blood capillaries in tissue spaces larger diameter than blood capillaries are very permeable and collect tissue fluid and

proteins lymph capillaries merge to form larger lymph

vessels

Lymph Vessels

resemble veins but have thinner walls and more valves

ends of endothelial cells overlap

- act as one-way valves allowing interstitial fluid to flow in but not out

attached to surrounding tissue by anchoring filaments

Lymph Vessels (cont.) no pump for lymph

Lymph is kept moving by:

- constriction of vessels

- skeletal muscle pump

- respiratory pump at intervals along vessels lymph flows into

lymph nodes lymphatic vessels unite to form lymph trunks

Lymph Trunks

formed by lymphatic vessels uniting large tubes empty their lymph into lymphatic ducts

Lymphatic Ducts

Lymph empties into two conducting ducts:- the thoracic duct (left lymphatic duct)- the right lymphatic duct

Lymph from these ducts enters the blood stream via the left subclavian vein and the right subclavian vein

Thoracic Duct(left lymphatic duct)

about 15-18 inches (38-45 cm) in length begins as a dilation called the cisterna chyli main collecting duct of lymphatic system receives lymph from lower body and upper

left quadrant empties into the left subclavian vein

Cisterna Chyli

large lymph vessel formed by the union of lymph vessels from

lower body located anterior to the second lumbar

vertebra continues superiorly as thoracic duct

Right Lymphatic Duct about 0.5 inches (1.5 cm) in length receives lymph from upper right quadrant empties into the right subclavian vein

Lymph Nodes oval or bean-shaped masses of lymphatic tissue aid in defense and white blood cell formation located along length of lymphatic vessels scattered throughout the body usually in clusters

Lymph Nodes (cont.) covered by a capsule contain capsular extensions called

trabeculae (form partitions within node) internal to capsule are reticular fibers and

fibroblasts- form framework of a lymph node

Two main regions of a lymph node:- cortex - medulla

cortex

medulla

trabeculae

germinalcenter

lymphatic vessel

valve

arteriolevein

Cortex

outer region directly beneath the capsule contains densely packed lymphocytes

arranged in masses called follicles

- outer rim of follicle contains T cells, macrophages, and follicular dendritic cells (aid in T cell activation)

Medulla

inner region lymphocytes are arranged in strands called

medullary cords

- contain macrophages and plasma cells

Biological Filtration

as lymph passes through a node bacteria and other foreign materials are trapped by reticular fibers within the node

- bacteria are then phagocytized by macrophages

Biological Filtration (cont.)

plasma cells produce antibodies to antigens in the lymph

antibodies, lymphocytes, and monocytes are eventually returned to the blood via subclavian veins

Major Lymph Nodes

cervical axillary inguinal mesenteric

Cervical

located in neck area filter lymph from head and neck

Axillary

located in armpits filter lymph from hand, arm, breast

Inguinal

located in groin area filter lymph from lower extremities and

external genital organs

Mesenteric

located in abdominal peritoneum aid in infection control after abdominal

surgery filter lymph from abdominal cavity

Metastasis process by which bacteria or body cells are

spread from one body part to another through lymphatic or circulatory systems

cancer cells migrate to nearby nodes, eg. breast cancer to axillary nodes - chemotherapy is necessary once metastasis occurs

Diffuse Lymphatic Tissue

not enclosed by a capsule consists of reticular connective tissue that

contains lymphatic nodules Found in:

- small amounts in almost every organ, especially mucous membranes that line tracts of body

Isolated Lymphatic Nodules(B cells)

oval-shaped concentrations of lymphatic tissue most are solitary, small, and discrete Scattered in lamina propria of mucous

membranes of:

- gastrointestinal tract

- respiratory airways

- urinary and reproductive tract

Isolated Lymphatic Nodules (B cells) (cont.)

when activated by antigens they differentiate into plasma cells and produce antibodies against specific antigens

plasma cells secrete IgA antibodies

- provide protection against bacterial and viral infections in lumen of tracts

Isolated Lymphatic Nodules (B cells) (cont.)

located in mucus membranes of gastrointestinal tract

Examples:

- tonsils

- ileum of small intestine (Peyer’s patches)

- appendix

Tonsils

aggregations of large lymphatic nodules embedded in mucous membrane located beneath epithelium of pharynx and

oral cavities protect nasal and oral cavities Three types:

- nasopharyngeal tonsils- palatine tonsils- lingual tonsils

Nasopharyngeal Tonsils

commonly called adenoids Located:

- behind nose

- on roof of posterior wall of pharynx

- posterior opening of nasal cavity

Palatine Tonsils

usually referred to as the “tonsils” Location:

- back of mouth

- lateral walls of pharynx most commonly removed - tonsillectomy

Lingual Tonsils

base of tongue first line of defense from exterior

Spleen largest lymphatic organ located in upper left abdominal quadrant between fundus of stomach and diaphragm 5-6 inches long, 2-3 inches wide resembles a large lymph node filters blood

Structure of Spleen

capsule

- covering of dense connective tissue hilum

- depression on medial surface

- nerves and arteries enter spleen, veins and lymphatic vessel exit

Structure of Spleen (cont.)

trabeculae

- extensions of capsule, form partitions within the spleen

pulp

- tissue inside

- divided into red and white

White Pulp

consists of lymphatic tissue mostly lymphocytes arranged around central

arteries

Red Pulp

Consists of:

- venous sinuses filled with blood

- cords of splenic tissue

consists of red blood cells, macrophages, lymphocytes, plasma cells, and granulocytes

Functions of Spleen phagocytosis of bacteria and worn out or

damaged red blood cells and platelets stores and releases blood in times of demand,

e.g., hemorrhage functions in immunity as a site of B cell

proliferation into plasma cells does not filter lymph because it has no afferent

lymphatic vessels or lymph sinuses

Thymus Gland

two-lobed organ located in upper part of chest along trachea inferior to thyroid gland, posterior to sternum largest and most active during prenatal

period and infancy after puberty it decreases in size

Thymus Gland (cont.)

composed of lymphatic tissue subdivided into lobules immature T cells originating in the bone

marrow migrate to thymus via blood in thymus, cells develop into mature T

cells for release into circulation thymic hormones aid in maturation of T cells

Thymus Gland (cont.)

mature T cells travel to lymph nodes, spleen, and diffuse lymphatic tissues where they reside

responsible for cell-mediated immune responses

Removal of Thymus(thymectomy)

can be removed but decreased T-cell production results

possible acute susceptibility to infection

Removal of Spleen(splenectomy)

can be removed other organs, e.g. the liver and bone marrow

can compensate for it increased susceptibility to disease may result