Lacteals (Intestinal Lymph Capillaries)

Lacteals are specialized lymphatic capillaries located within the intestinal villi of the small intestine. Their primary function is to absorb dietary lipids and lipid-soluble vitamins from digested food, a role that distinguishes them from other lymphatic capillaries in the body. The lymph collected by lacteals is milky white in appearance due to its high fat content and is known as chyle.

Structure

Each intestinal villus typically contains a single central lacteal that runs vertically through its core. These lacteals are blind-ended capillaries composed of thin, overlapping endothelial cells that allow the entry of macromolecules like fatty acids, while preventing backflow.

Structural Characteristics:

• Thin-walled: Composed of endothelium without a basement membrane, increasing permeability
• Blind-ended: Closed at the villus tip, allowing unidirectional flow
• Anchored: Attached to surrounding tissue by anchoring filaments to prevent collapse during absorption

Location

Lacteals are located exclusively in the small intestine, specifically within the lamina propria of the intestinal villi:

• Most prominent in the jejunum, where lipid absorption is greatest
• Less developed or absent in the large intestine

From each villus, the lacteal drains into larger lymphatic vessels in the submucosa, which ultimately feed into the mesenteric lymph nodes and then the intestinal trunk.

Function

Lacteals perform several critical physiological functions:

• Absorption of dietary lipids: Take up long-chain fatty acids and monoglycerides that are packaged into chylomicrons within enterocytes
• Transport of lipid-soluble vitamins: Absorb vitamins A, D, E, and K from the intestinal lumen
• Delivery to systemic circulation: Chyle passes from lacteals → mesenteric lymphatics → intestinal trunk → thoracic duct → left subclavian vein

Clinical Significance

Lacteals are essential to proper digestive and immune function and are involved in various pathological conditions:

• Chylous ascites: Obstruction or rupture of intestinal lymphatics (e.g., from trauma or lymphoma) can lead to leakage of chyle into the peritoneal cavity
• Malabsorption syndromes: Conditions like celiac disease or intestinal lymphangiectasia may impair lacteal function, reducing lipid and vitamin absorption
• Chylomicronemia syndromes: Disorders of lipid metabolism may affect lymphatic lipid transport
• Lymphatic imaging: Specialized contrast studies (lymphangiography) may help visualize lacteal dysfunction in suspected intestinal lymphatic disorders

Lacteals are a unique component of the lymphatic system, specialized for fat absorption rather than immune filtration. Their strategic position within the villi and their role in nutrient transport make them essential for digestive efficiency and metabolic balance.