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\b[<Chyle> is intestinal <lymph> enriched with absorbed dietary <lipids>; its usual route ends in the venous circulation at the left jugulosubclavian junction.] The milky appearance after a fat-containing meal is chiefly due to suspended lipid-rich particles, now called <chylomicrons>.
Formation begins with <lipid digestion> in the <small intestine>. <Pancreatic lipase> helps hydrolyse dietary <triglycerides>; <bile salts> help the digestion products reach the intestinal absorptive surface in <mixed micelles>. <Enterocytes> take up the products, reconstruct much of the long-chain <triglyceride>, and package it with other <lipids> and <apolipoproteins> into <chylomicrons>. These leave the basolateral side of the <enterocytes> and enter the central <lacteals> of the <intestinal villi>. Thus the particles carried in <chyle> are not simply intact globules of a meal passing through an open hole from the intestinal lumen.<Anatomy and Physiology 2e by J. Gordon Betts and others/23.7 Chemical Digestion and Absorption: A Closer Look>[Lipid Absorption: micelles, enterocytes, chylomicrons and lacteals]{ref}
From the <lacteals>, <chyle> enters lymphatic channels in the intestinal wall and then collecting vessels in the <mesentery>. These vessels pass through <mesenteric lymph nodes>, with afferent vessels entering and efferent vessels leaving the nodes. Successive collectors join the intestinal lymphatic trunk or trunks. They usually communicate with the <cisterna chyli>, an expanded origin of the <thoracic duct> in the upper lumbar region, near the bodies of L1–L2 and to the right of the <aorta>. The <cisterna chyli> also receives lymph from lumbar trunks; the stream beyond it therefore contains material from more than the <intestine>. A conspicuous sac is not present in every individual.
The <thoracic duct> passes through the <aortic hiatus> of the <respiratory diaphragm> and ascends in the posterior <mediastinum>, typically between the <aorta> and <azygos vein>, behind the <oesophagus>. It crosses towards the left in the middle or upper <thorax>, continues to the root of the neck and arches to its terminal venous opening. The usual endpoint is the left venous angle, where the <left internal jugular vein> joins the <left subclavian vein>; terminal branches and the precise opening show anatomical variation. It is not normally the right venous angle or a direct entrance into the <portal vein>.<Anatomy, Thorax, Thoracic Duct (StatPearls)>[Structure and Course: cisterna chyli, thoracic course, left cervical arch and variable venous termination]{ref}
The flow is promoted by intrinsic contraction of collecting lymphatic vessels, movements of surrounding <muscles> and respiratory changes of <pressure>. <Lymphatic valves> limit backward movement. <Lymph nodes> are interposed biological structures, not pumps that propel every particle independently.<Anatomy and Physiology 2e by J. Gordon Betts and others/21.1 Anatomy of the Lymphatic and Immune Systems>[Lymphatic Capillaries; Larger Lymphatic Vessels, Trunks, and Ducts; lymph transport]{ref}
This route applies particularly to the long-chain dietary <lipids> carried by <chylomicrons>. Most absorbed <glucose> and <amino acids>, and much shorter-chain <fatty acid> material, follow portal vascular routes instead. Confusing these pathways would obscure the reason for asking separately about <chyle>. In a classical anatomical demonstration, the mesenteric channels of an appropriately fed animal appear white, and an injected or dissected preparation can trace their continuity towards the <thoracic duct>. The timing after a fatty meal matters: an empty-looking channel in a fasted preparation does not prove absence of a <lymphatic vessel>. The molecular account of <chylomicrons> is a modern explanation of the older gross observation.
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