Lymphatic System Overview and Functions

Lymphatic System Overview

• The lymphatic system is a vascular network of tubules and ducts.
• It collects, filters, and returns lymph to blood circulation.
• It is composed of organs working together to perform specific functions.
• It plays a critical role in the body's defense against disease.

Functions of the Lymphatic System

• Transports excess fluid from interstitial spaces back to the bloodstream.
• Lymph capillaries pick up excess interstitial fluid and proteins, returning them to venous blood.
• Absorbs lipids from the digestive system and transports them to the venous circulation.
• Defends against invading microorganisms and disease, filtering lymph in lymph nodes.
• Lymph nodes and other lymphatic organs filter lymph to remove microorganisms.
• Lymphatic organs contain lymphocytes that destroy invading organisms.

Components of the Lymphatic System

• Lymphatic capillaries
• Lymphatic vessels
• Lymphatic trunks
• Lymphatic ducts
• Lymphatic organs and tissues

Lymphatic Capillaries

• Begin as blind-ended lymph capillaries.
• Found throughout the body except the epidermis, central nervous system (CNS), cornea of the eye, and bones.
• The capillary walls are permeable to interstitial fluids, including proteins and cell debris.
• Lacteals are lymphatic capillaries that transport digested fats from the small intestine into blood.
• One-way valves prevent backflow of lymph.

Lymphatic Vessels

• Formed by merging lymphatic capillaries.
• Found alongside arteries and veins.
• Carry fluid away from tissue spaces and return it to the venous system.

Lymphatic Trunks and Ducts

• Small lymphatics form larger tributaries called lymphatic trunks.
• Lymphatic trunks combine to form two large lymphatic ducts:
  • Right lymphatic duct: Drains the upper right side of the body. (Head, neck, right upper extremity, right side of thorax) Empties into the right subclavian vein.
  • Thoracic duct: Drains the rest of the body. (Left side of the head, neck, and chest, the left upper extremity, and the entire body below the ribs) Empties into the left subclavian vein.

Flow of Lymph

• Lymph flows from lymphatic capillaries to lymphatic vessels to lymphatic trunks and then into lymphatic ducts.
• It joins the bloodstream at the junction of the jugular and subclavian veins.

Maintenance of Lymph Flow

• Aided by skeletal muscle contractions, compressing lymphatic vessels and moving lymph.
• Respiratory pump, during inhalation, creates pressure differences between the abdomen and thoracic cavity.
• Smooth muscle contraction in larger lymphatic vessels promotes lymph flow.
• Lymphatic valves prevent backflow.

Clinical Application of Lymphatic System

• Edema: Excessive accumulation of interstitial fluid due to lymphatic system obstruction (infected lymph node or blocked lymphatic vessels), lack of skeletal muscle contraction, or increased capillary blood pressure.
• Lymphatic filariasis (elephantiasis): Filarial worms carried by mosquitos block lymphatic flow, resulting in edema.
• Lymph node removal: (e.g., in cancer treatment)

Lymphatic Organs

• Thymus
• Lymph nodes
• Spleen
• Tonsils
• Bone marrow

Thymus

• Located between the sternum and heart.
• Contains T cells, epithelial cells, and macrophages.
• Site of T cell maturation before entering the bloodstream.
• Thymosin hormone stimulates thymus and other lymphoid tissue maturation.
  • Shrinks during adolescence.

Lymph Nodes

• Oval structures located along lymphatic vessels.
• Contains lymphocytes and macrophages.
• Filter lymph and remove foreign substances
• Heavily concentrated near mammary glands, axilla, and groin.
• Lymph enters through afferent vessels and leaves through efferent vessels.
• Proliferation of lymphocytes occurs in nodes.
• Phagocytosis: Destruction of foreign substances by macrophages.

Spleen

• Largest lymphatic organ in the body.
• Located in the left hypochondriac region, between the fundus of the stomach and diaphragm.
• White pulp: contains lymphocytes.
• Red pulp: filled with blood and splenic cords containing RBCs, macrophages, lymphocytes, plasma cells, and granulocytes.
• Functions: phagocytosis (removal of worn-out or defective blood cells), storage of blood, immune response, and in some cases erythropoiesis (blood cell production).

Mucosa-Associated Lymphoid Tissue (MALT)

• Lymphatic tissue not surrounded by capsules.
• Contains B and T lymphocytes.
• Important for early detection of invaders.
• Includes Peyer's patches (in the ileum of the small intestine) and tonsils.

Tonsils

• Lymphatic nodules embedded in mucous membranes at the junction of the oral cavity and pharynx.
• Includes pharyngeal, palatine, and lingual tonsils.
• Function: Protect against invasion of foreign substances in nasal and oral cavities.

Bone Marrow

• Soft, flexible tissue inside bones.
• Responsible for the production of blood cells (RBCs, WBCs, and platelets).
• Bone marrow stem cells play a vital role in immunity by generating lymphocytes.