In the villi of the small intestine, fatty acids are absorbed into the:
A. lacteals in combination with bile salts
B. capillary networks by active transport
C. capillary networks by osmosis
D. lacteals by osmosis
The correct answer and explanation is:
The correct answer is A. lacteals in combination with bile salts.
In the villi of the small intestine, fatty acids, along with other products of fat digestion, are absorbed into the lacteals, which are specialized lymphatic vessels found within the villi. This process involves the formation of micelles, which are tiny lipid-bile salt complexes that help in the transport of fat-soluble substances through the aqueous environment of the intestinal lumen.
Once fatty acids and monoglycerides enter the enterocytes (intestinal cells), they are reassembled into triglycerides within the smooth endoplasmic reticulum. These triglycerides, combined with cholesterol and proteins to form chylomicrons, are then transported to the lacteals. The chylomicrons are too large to enter the blood capillaries directly, so they enter the lymphatic system first. From there, they eventually make their way into the bloodstream via the thoracic duct.
The presence of bile salts is crucial for this process because they emulsify the fats in the intestine, breaking them down into smaller droplets and increasing the surface area for the action of digestive enzymes. This makes it easier for lipases to break down triglycerides into free fatty acids and monoglycerides, which can then be absorbed by the enterocytes.
This method of absorption is different from that of water-soluble nutrients like glucose or amino acids, which are absorbed directly into the blood capillaries by active transport or facilitated diffusion. In contrast, the absorption of fatty acids into the lacteals is a process that primarily involves the lymphatic system, which is essential for the transport of lipids and fat-soluble vitamins.
Thus, the absorption of fatty acids in the villi involves both lacteals and bile salts, making option A the correct answer.