Gastrin is a hormone secreted into the __________ by the ___________.
Blood; stomach
Lumen; stomach
Lumen; pancreas
Blood; small intestine
To determine the correct answer, we need to understand the function of gastrin and where it is secreted. Gastrin is a hormone involved in the regulation of gastric acid secretion and gastric motility.
To find the answer, we can start by breaking down the options provided.
Option 1: Gastrin is secreted into the blood by the stomach.
Option 2: Gastrin is secreted into the lumen of the stomach.
Option 3: Gastrin is secreted into the lumen of the pancreas.
Option 4: Gastrin is secreted into the blood by the small intestine.
We know that gastrin is involved in regulating stomach-related functions, so it is unlikely to be secreted by the pancreas or small intestine.
Next, let's analyze the remaining two options. Gastrin functions within the stomach, so it would make sense for it to be secreted into the lumen of the stomach where it can directly interact with the gastric mucosa. On the other hand, if it was secreted into the blood, it would then need to be transported to the stomach to exert its effects, which seems less efficient.
Therefore, the correct answer is:
Gastrin is a hormone secreted into the lumen of the stomach.