Chapter 21: The Lymphatic System Overview

Functions of the lymphatic system

This system transports and houses lymphocytes and other immune cells, returns excess fluid from tissues into the blood, which maintains blood volume.

Components of the lymphatic system

It is made of lymph vessels, lymphoid tissues, and lymphoid organs.

Lymph fluid

Lymph fluid is fluid that has left the blood and has not been reabsorbed. Moves from interstitial spaces into the lymphatic capillaries.

Contents of lymph fluid

Lymph fluid contains water, dissolved solutes, and small amounts of proteins. May have cell debris, pathogens, or cancer cells.

Lymphatic capillaries

Lymph capillaries are small, closed-ended vessels found amongst most blood capillaries.

Absence of lymphatic capillaries

You do not find them in avascular tissues, red bone marrow, the spleen, or the CNS.

Function of lymphatic capillaries

They absorb interstitial fluid.

Lacteals

In the GI tract, they are called lacteals, and they absorb lipid-soluble substances from the GI tract.

Fluid movement into lymphatic capillaries

Hydrostatic pressure in interstitial fluid pushes fluid into lymphatic capillaries.

Drainage of lymphatic capillaries

They are moved into larger and larger lymphatic vessels: Capillaries -> vessels -> trunks -> ducts.

Drainage into lymphatic vessels

Capillaries drain into the vessels.

Location of lymphatic vessels

Found next to arteries and veins.

Structure of lymphatic vessels

Contains tunica intima, media, and externa. They also have valves.

Movement of fluid in lymphatic vessels

Uses skeletal muscle and respiration as well as the pulsations of nearby arteries or the contraction of smooth muscle in nearby organs.

Drainage of lymph vessels

Drains into lymphatic trunks.

Drainage into lymphatic trunks

Lymphatic vessels drain into lymphatic trunks.

Association of lymphatic trunks

Draining specific areas of the body.

Drainage into lymphatic ducts

Lymphatic trunks drain into lymphatic ducts.

Function of lymphatic ducts

They bring lymph back to venous blood circulation.

Right lymphatic duct

It is near the clavicle and drains the upper right quadrant of the body.

Thoracic duct

It is the larger duct that drains the rest of the body.

Primary lymphoid structures

Formation and maturation of lymphocytes.

Secondary lymphoid structures

House lymphocytes and other immune cells. It is where the immune response is initiated.

Primary lymphoid structures examples

Red bone marrow and thymus.

Secondary lymphoid structures examples

Lymph nodes, spleen, tonsils, and lymphatic nodules.

MALT

Mucosa-associated lymphoid tissue.

Red Bone Marrow

A primary lymphoid structure located in spongy bone where hematopoiesis occurs.

Thymus

A primary lymphoid structure located in the mediastinum where T-lymphocytes mature.

Thymus in Adults vs. Children

It is large in children but replaced by fat in adults.

Cortex of Thymus

Contains immature T-lymphocytes.

Medulla of Thymus

Contains mature T-lymphocytes.

Lymph Nodes

Secondary lymphoid structures found along the pathways of lymph vessels in clusters.

Function of Lymph Nodes

They filter lymph and remove unwanted substances.

Lymph Fluid Entry and Exit

Afferent lymphatic vessels bring fluid in, and efferent vessels bring fluid out.

Cortex of Lymph Nodes

Contains lymphoid nodules, which house lymphocytes and macrophages.

Medulla of Lymph Nodes

Contains immune cells.

Spleen

A secondary lymphoid structure located in the left upper quadrant.

Associated Vessels of Spleen

Splenic artery and vein.

White Pulp of Spleen

Clusters of lymphocytes and macrophages around a central artery.

Red Pulp of Spleen

Contains other formed elements and is where RBCs and platelets are stored.

Functions of Spleen

Filters blood, eats foreign particles, clears defective erythrocytes and platelets, and stores erythrocytes and platelets.

Fetal Function of Spleen

This is where blood cells are made in the first 5 months of fetal development.

Tonsils

Secondary lymphoid structures found in many locations including the nasopharynx and oral cavity.

Function of Tonsils

Function in immune surveillance; tonsillar crypts trap material.

Lymphoid Nodules

Clusters of lymphoid cells with some ECM.

Diffuse Lymphoid Nodules vs. MALT

Diffuse is when they are scattered; they are MALT when clustered into larger structures.

Location of MALT

Found in GI, respiratory, genital, and urinary tracts; called Peyer patches in the small intestine.

Lymphedema

Condition where interstitial fluid accumulates because lymphatic drainage is blocked.

Causes of Lymphedema

Can be caused by trauma to an area, infection of lymph vessels, or tumors.

Signs and Symptoms of Lymphedema

Swelling, pain, and can interfere with wound healing and response to infection.

Management Options for Lymphedema

Can be controlled using compression garments, exercise, and massage.