BIOL2260 - Lymphatic System

Lymphatic system functions

1. Transport and house lymphocytes and other immune cells

2. Return excess fluid in body tissue to blood to maintain blood volume

Components of the lymphatic system

-Lymph

-Lymphoid vessels

-Lymphoid organs

-Lymphoid tissues

Lymph

The fluid transported within lymph vessels

Components of lymph

-Water

-Dissolved solutes

-Small amounts of proteins

-Immune cells

-Cell debris

-Microorganisms

-Cancer cells

Primary lymphoid structures (organs)

Involved in formation and maturation of lymphocytes; thymus and red bone marrow

Secondary lymphoid structures (organs)

Do not form lymphocytes, but house them and other immune cells that are the sites of immune response initiation; lymph nodes, spleen, tonsils, lymphatic nodules, and MALT

Lymphoid tissues

A reticular CT matrix dominated by lymphocytes inside of lymphoid organs and nodules

Lymphoid nodules/follicles

Unencapsulated patches of lymphoid tissue that contain clusters of immune cells found throughout the body and contain germinal centers

Germinal centers

Location in lymphoid tissues where B-cells mature

Thymus

Gland located in the anterior chest that matures and produces T-cells; larger in children, then disappears and turns into adipose tissue post-puberty

Red bone marrow

Located in the spongy bone of some bone (e.g., flat bones of skull and head of femur); holds hematocytes to differentiate into formed elements (blood cells) and matures B-cells

Hematopoiesis

Formation of formed elements, which includes T-cells and B-cells

Thymocytes

Immature T-cells that migrate to the thymus to complete maturation

Tonsils

Secondary lymphoid structures in the pharynx that provide surveillance of inhaled and ingested substances; made of multiple lymphoid nodules

Tonsillar crypts

Invaginations in tonsils that trap foreign materials

Pharyngeal tonsil

Tonsil located in the posterior nasopharynx (superior to visible pharynx)

Adenoids

Pharyngeal tonsil when enlarged

Palantine tonsils

Paired tonsils located in posterolateral oral cavity

Lingual tonsil

Tonsil located on the posterior tongue

Lymph nodes

Small, oval, encapsulated structures that filter lymph and removes unwanted substances; located along pathways of lymph vessels

Cervical lymph nodes

Located in the neck and receives lymph from the head and neck

Axillary lymph nodes

Located in the armpit and receives lymph from the breasts, axilla, and arms

Inguinal lymph nodes

Located in the groin and receive lymph from the pelvis and legs

Afferent lymphatic vessels

Multiple entry vessels that bring lymph into the lymph node

Efferent lymphatic vessels

Singular exit vessels that bring lymph out of the lymph node

Pressure inside lymph node

Multiple afferent vessels creates more pressure when combined into one efferent vessel to push through the remainder of the lymph pathway

Hilum of lymph node

The back end of the lymph node where efferent vessels enter/leave

Capsule of lymph node

Outer layer of the lymph node that is made out of dense CT

Trabeculae of lymph node

Extensions of the capsule that subdivides the lymph node into internal compartments (cortex and medulla)

Cortex

Outer layer of the lymph node

Medulla

Inner layer of the lymph node

Immune cells in lymph nodes

Macrophages remove foreign debris from lymph and lymphocytes initiate immune response and proliferate in germinal centers

Spleen

The largest lymphoid organ that has one convex side and one concave side; located in the upper left abdominal quadrant, lateral to the left kidney, and posterolateral to the stomach

Hilum of spleen

Indention in the posterior concave side where the splenic artery and splenic vein enter/leave

Capsule of spleen

Surrounding of the spleen made up of CT

Trabeculae of spleen

Extensions of the capsule that internally divide the spleen into red and white pulp

White pulp

Clusters of T-, B-cells, and macrophages around a central artery

Red pulp

Storage site for platelets and monocytes, and destroys erythrocytes

MALT (mucosa-associated lymphoid tissues)

Aggregations of lymphoid tissue in the lamina propria of mucous membranes that helps to defend against foreign substances; found in the GI/GU, respiratory, and genital tracts

Peyer's patches

Large aggregations of lymphoid nodules within the wall of the ileum of the small intestine

Flow of lymph

Goes through larger sized vessels:

1. Capillaries

2. Collecting vessels

3. Trunks

4. Ducts

Hydrostatic pressure

The pressure that is exhibited on fluid that is not moving, which pushes it into the lymphatic capillary; caused by gravity

Movement of lymph

-Muscular contractions from skeletal muscle

-Respiratory pump (diaphragm)

-Pulsating movement of blood in nearby arteries

-Contraction of smooth muscle in nearby BV

Lymphatic capillaries

Small, closed-ended vessels that absorb interstitial fluid (fluid between BV and lymphatic vessels) and larger than circulatory capillaries; found around most capillaries and brain meninges (glymphatic system); contain flaps between cells to prevent backflow

Anchoring filaments

Hold lymphatic capillaries (endothelial cells) to nearby structures to prevent vessel collapse

Lymphatic collecting vessels

Vessels that are fed by lymphatic capillaries and located adjacent to arteries and veins; have all 3 tunics and valves to prevent backflow of lymph

Lymphatic trunks

Vessels that are fed by lymphatic vessels, preceded by lymph nodes in some cases

Jugular trunks

Drains from head and neck

Subclavian trunks

Drains breasts, superficial thoracic wall, and arms

Bronchomediastinal trunks

Drains deep thoracic structures (i.e., heart, lungs, etc.)

Intestinal trunks

Drains most abdominal structures (i.e., small intestines, colon, etc.)

Lumbar trunks

Drains abdominopelvic wall, pelvic organs, and legs

Lymphatic ducts

The largest lymphatic vessels that are fed by lymphatic trunks; return lymph to venous circulation

Right lymphatic duct

Located near the right right side of the head, neck, thorax, and right arm; delivers lymph to the right subclavian and right internal jugular veins

Thoracic duct

The largest lymphatic vessel that runs from the diaphragm to the junction of the left subclavian and left internal veins; drains the left side of the head, neck, thorax, left arm, all of the abdomen, pelvis, and both legs

Cisterna chyli

Saclike structure of the base of the thoracic duct that is a reservoir for lymph from the lower body and abdomen before the thoracic duct