The Lymphatic System

“the body’s drains”

Principle Organs/Tissues• Lymph (lymphatic fluid)

• Lymphatic vessels

• Lymph nodes (glands)

• Tonsils

• Thymus

• Spleen

• Peyer’s patches

Principle Functions

• Fluid balance (returns water, proteins, etc. from tissues back to blood)

• Immunity

• Transports lipids from the digestive tract

• Lacteals (lymph capillaries)

in intestine transport fatty lymph called chyle

What does the lymphatic system do?

• As blood circulates small amounts of fluid gets left behind in tissues

• If allowed to build up this could cause edema(swelling)

• Lymph vessels collect fluid and return it to veins

Lymph

• Interstitial fluid is fluid which surrounds cells

• Once it drains into lymph vessels it is called lymph

• Lymph is clear and watery

Lymphatic Capillaries• Lymphatic vessels begin as “blind

end” vessels called lymphatic capillaries

• Those originating in the small intestines are called lacteals

• All lymph vessels drain into either the thoracic duct or right lymphatic duct.

Structure of Lymphatic Vessels

• Vessels have thinner walls than veins (same tunicas as veins)

• Contain many valves, giving them a beaded appearance

• lymph nodes present at certain intervals

• Small openings between endothelial cells allow for high permeability to large substances

Circulation of Lymph

• Solutes and water constantly leak out of capillaries into interstitial fluid

• These are reabsorbed by lymph vessels and returned to blood

• Lymphatic vessels absorb excess fat preventing increased viscosity of blood

Lymphatic Pump• Lymph is kept moving by two

(lymphokinetic)actions– Breathing– Skeletal muscle movement

• Inspiration causes intraabdominal pressure while decrease thoracic pressure allowing lymph to move up thoracic duct

• Other factors that increase lypmh flow – Physical activity– Postural changes– Massage– Arterial pulsations

Structure of Lymph Nodes

• Lymph nodes are biological filters

• Fibrous trabecula created sinuses where fluid “percolates”

• Sinuses are lined with recticuloendothelial cells that are capable of phagocytosis

Major Lymph Node Locations

• Preauricular- located in front of ear

• Submental and submaxillary- floor of the mouth

• Superficial cervical- in the neck• Superficial cubital,

supratrochlear- above bend in elbow

• Axillary- underarm and chest• Inguinal- groin

Functions of Lymph Nodes

• Filtration and Phagocytosis– Cells phagocytose

microorganisms and other foreign particles

– During infections nodes become swollen and tender, called adenitis

– Tumors can block flow causing edema

• Hematopoesis– Maturation of some

lymphocytes and monocytes occur in lymph nodes

Role of a lymph node in a skin infection. Yellow areas represent dead and dying cells (pus). Black dots around the yellow areas represent bacteria.

The Tonsils

• Are a mass of lymphoid tissue

• First line of defense against infection

• The pharyngeal tonsils are called adenoids

pharyngeal

palatine

lingual

The Thymus

• Located above the heart

• Plays a role in lymphocyte development

• Releases thymosin that helps in T cell maturation

The Spleen

• Located above the left kidney behind the stomach

• Functions

– Defense- phagocytosis of microorganisms

– Hematopoesis- monocytes and lymphocytes maturation

– Red blood cell and platelet destruction, hemoglobin is recycled

– Blood Reservoir