Which membrane is in the way if you try to reach the lesser peritoneal sac and head of the pancreas after penetrating the greater peritoneal sac?
**Core Concept**
The question is testing the student's knowledge of the peritoneal cavity and its related structures. The lesser peritoneal sac, also known as the omental bursa, is a small cavity that contains the head of the pancreas, the duodenum, and the proximal part of the bile duct. It is enclosed by the greater omentum, which is a fold of peritoneum that hangs down from the greater curvature of the stomach.
**Why the Correct Answer is Right**
The correct answer is the **Ceck's capsule**, also known as the **lesser omentum's posterior layer**. This layer of the peritoneum forms the posterior wall of the lesser peritoneal sac and separates it from the greater peritoneal sac. To reach the lesser peritoneal sac and the head of the pancreas, one must first penetrate the greater omentum and then the lesser omentum's posterior layer, which is the Ceck's capsule.
**Why Each Wrong Option is Incorrect**
* **Option A:** The **greater omentum** is indeed a fold of peritoneum that hangs down from the greater curvature of the stomach, but it is not the specific membrane that is in the way when trying to reach the lesser peritoneal sac and the head of the pancreas.
* **Option B:** The **mesentery of the small intestine** is a fold of peritoneum that attaches the small intestine to the back of the abdominal wall, but it is not directly related to the lesser peritoneal sac or the head of the pancreas.
* **Option D:** The **parietal peritoneum** is a layer of peritoneum that lines the abdominal cavity, but it is not the specific membrane that is in the way when trying to reach the lesser peritoneal sac and the head of the pancreas.
**Clinical Pearl / High-Yield Fact**
It is essential to remember that the lesser omentum's posterior layer, also known as Ceck's capsule, forms the posterior wall of the lesser peritoneal sac and separates it from the greater peritoneal sac. This knowledge is crucial when performing surgical procedures in the upper abdomen, such as pancreatectomy or cholecystectomy.
**Correct Answer:** C. Ceck's capsule