Question

Do chylomicrons enter the capillaries that are around the enterocytes? If not, how do they gain access to systemic blood circulation?

a) Yes, they enter directly into capillaries.
b) No, they enter lymphatic vessels first and then enter the bloodstream.
c) No, they are absorbed by the stomach lining.
d) Yes, they are transported through the hepatic portal system.

Answer 1

Chylomicrons enter the lacteals in the small intestine, not directly into the capillaries. They travel through the lymphatic system and enter systemic circulation via the thoracic duct and subclavian vein.

Step-by-step explanation:

No, chylomicrons do not enter directly into the capillaries surrounding the enterocytes. Instead, after they are synthesized in the intestinal cells, they are too large to pass through the basement membranes of blood capillaries. Therefore, chylomicrons enter the lacteals, which are specialized lymphatic capillaries present in the small intestine. These lacteals merge to form larger lymphatic vessels, which transport the chylomicrons through the lymphatic system.

Eventually, the chylomicrons reach the thoracic duct, which empties into the subclavian vein of the circulatory system. Here, they enter the systemic blood circulation. Once the chylomicrons are in the bloodstream, lipoprotein lipase can break down the triglycerides they carry into free fatty acids and glycerol. These can then pass through the capillary walls to tissues where they'll be used for energy or stored in adipose tissue.