Lymphatic System: Functions, Structures, and Key Organs

Functions of the lymphatic system

Returns excess interstitial fluid to the blood, Transports absorbed lipids (fats) from the digestive system, Participates in immunity (defense against pathogens)

Plasma

Fluid portion of blood inside blood vessels

interstitial fluid

Fluid between cells (comes from plasma)

Lymph

Interstitial fluid once it enters lymphatic vessels

Lymphatic vessels order

Lymphatic capillaries, Collecting lymphatic vessels, Lymph trunks, Lymph ducts

Flow pathway of lymphatic vessels

Capillaries → collecting vessels → trunks → ducts → veins (subclavian + internal jugular junctions)

Lymphatic organs

Lymph nodes, Thymus, Spleen, Tonsils

Largest lymphatic organ

Spleen

Lymphatic capillaries structure

Located near blood capillaries, Highly permeable, Have 'mini-valves' that open when fluid pressure increases

Function of lymphatic capillaries

Take in tissue fluid, proteins, bacteria, etc.

Comparison of lymphatic capillaries to blood capillaries

More permeable, Can take in larger particles

Lacteals

Specialized lymph capillaries found in villi of the small intestine that absorb digested fats

Structure of collecting lymphatic vessels

Same 3 layers (tunics) as blood vessels, Thinner walls than veins, More valves than veins

Function of collecting lymphatic vessels

Transport lymph

Movement of lymph

Skeletal muscle pump, Nearby artery pulsations, Smooth muscle contraction

Two lymph ducts

Thoracic duct drains ¾ of the body; Right lymphatic duct drains ¼ of the body

thoracic duct drains into

left subclavian + left internal jugular vein

right lymphatic duct drains into

right subclavian + right internal jugular vein

Function of lymph nodes

Filters/cleans lymph (removes pathogens)

Regions with lymph nodes

Superficial: cervical, axillary, inguinal; Deep: tracheobronchial, aortic, iliac

Thymus location

Upper chest (behind sternum)

Function of the thymus

Site where T lymphocytes mature; Secretes thymic hormones

Effects of aging on the thymus

Shrinks (atrophies) and becomes less active because immune system is already developed

Functions of the spleen

Removes pathogens in blood, Destroys old/defective blood cells, Stores blood, Site of blood cell formation in fetus

Tonsils names and locations

Pharyngeal tonsil (1) - nasopharynx; Palatine tonsils (2) - sides of oropharynx; Lingual tonsil (1) - base of tongue

Fibrous capsule

outer covering

Trabeculae

inward extensions dividing node

Segments

compartments formed by trabeculae

Afferent vessels

bring lymph into node

Hilum

exit point

Efferent vessels

carry lymph out

Lymph nodes (loc + funct)

Location: throughout body (neck, armpit, groin, deep areas); Function: filter lymph

Thymus

Location: chest (mediastinum); Function: T-cell maturation

Spleen

Location: left upper abdomen; Function: filters blood, removes old RBCs

Tonsils

Location: pharynx; Function: protect against inhaled/ingested pathogens