If biliary pool is reduced, the bile acid synthesis/enterohepatic recycling of bile salts is:
**Core Concept**
Bile acid synthesis and enterohepatic recycling of bile salts depend on a sufficient biliary pool. The biliary pool is the amount of bile acids present in the bile, which are then recycled back to the liver through enterohepatic circulation. This process is essential for maintaining bile acid homeostasis.
**Why the Correct Answer is Right**
When the biliary pool is reduced, the liver senses a decrease in bile acid levels and responds by increasing the synthesis of new bile acids. This is achieved through the activation of the farnesoid X receptor (FXR) and the reduction of the expression of the bile acid synthesis enzyme, CYP7A1. The reduced bile acid levels also stimulate the intestinal release of fibroblast growth factor 19 (FGF19), which further inhibits CYP7A1 expression.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because a reduced biliary pool would not lead to an increase in bile acid synthesis. Instead, the liver would respond by increasing synthesis to compensate for the loss.
**Option B:** This option is incorrect because bile acid binding proteins, such as bile acid-binding protein (BABP), play a role in the transport and storage of bile acids, but they do not directly influence the synthesis or recycling of bile acids.
**Option C:** This option is incorrect because the enterohepatic circulation of bile salts is not directly affected by the size of the biliary pool. The enterohepatic circulation refers to the process by which bile acids are secreted into the intestine, reabsorbed, and returned to the liver.
**Option D:** This option is incorrect because the liver's response to a reduced biliary pool is not to decrease bile acid synthesis. Instead, the liver increases synthesis to compensate for the loss.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that the liver's response to a reduced biliary pool is to increase bile acid synthesis through the activation of FXR and the reduction of CYP7A1 expression. This is an important mechanism for maintaining bile acid homeostasis and preventing bile acid deficiency.
**Correct Answer:** C.