Lymphatic capillary

Lymphatic capillaries are microscopic, blind-ended vessels composed of a single layer of overlapping endothelial cells. They represent the origin of the lymphatic system, collecting interstitial fluid, proteins, and immune cells from tissues.

Location: Lymphatic capillaries are present in nearly all tissues, except for:

• The central nervous system (although meningeal lymphatics exist)

• Bone marrow

• Avascular tissues such as cartilage, cornea, and epidermis

Structure: Lymphatic capillaries are blind-ended sacs with thin endothelial walls. The endothelial cells overlap like flaps, functioning as one-way valves that permit fluid entry while preventing backflow. Anchoring filaments attach the vessels to surrounding connective tissue, preventing collapse under interstitial pressure. They lack a basement membrane, which facilitates the easy entry of fluid, macromolecules, and immune cells.

Functions:

• Serve as the initial site of lymph formation.

• Collect interstitial fluid, proteins, cellular debris, and immune cells from tissues.

• Include specialized forms in the small intestine called lacteals, which absorb dietary fats in the form of chylomicrons.

Clinical Relevance:

• Edema: Obstruction or dysfunction of lymphatic capillaries contributes to tissue swelling.

• Infection entry: Pathogens can enter through lymphatic capillaries and spread to regional lymph nodes.

• Nutrient absorption: Intestinal lacteals are essential for lipid absorption during digestion.