**Question:** Duodenum and Jejunum secrete ALL EXCEPT

A. Glucagon
B. Insulin
C. Thyroxine
D. Cortisol

**Core Concept:**

The small intestine, also known as the GI tract, comprises the duodenum and jejunum. These regions play crucial roles in digestion, nutrient absorption, and hormone secretion. The pancreas, a nearby organ, is responsible for secreting hormones like glucagon and insulin to regulate blood glucose levels, whereas the thyroid gland produces thyroxine to control overall body functions. Cortisol is a hormone secreted by the adrenal glands in response to stress, and its secretion is not associated with the small intestine.

**Why the Correct Answer is Right:**

The correct answer, **D.** Cortisol, is right because cortisol is a hormone produced by the adrenal glands, which are located above the kidneys. Cortisol plays a vital role in the body's stress response and is not secreted by the duodenum or jejunum. In contrast, the duodenum and jejunum secrete hormones related to digestion and glucose regulation, such as glucagon (increases blood glucose) and insulin (decreases blood glucose). Thyroxine (thyroid hormone), produced by the thyroid gland, is another hormone not secreted by the duodenum or jejunum.

**Why Each Wrong Option is Incorrect:**

A. Glucagon: Although glucagon is involved in blood glucose regulation, it is produced by alpha cells in the pancreas, not the duodenum or jejunum.

B. Insulin: Similar to glucagon, insulin is secreted by beta cells in the pancreas, not the duodenum or jejunum.

C. Thyroxine: As mentioned before, thyroxine is produced by the thyroid gland, not the duodenum or jejunum.

**Clinical Pearl:**

Understanding the anatomy, physiology, and hormone secretion patterns is crucial for medical students and practicing physicians alike. This knowledge ensures accurate diagnosis, treatment, and communication with patients regarding their health conditions. Moreover, it highlights the importance of recognizing the distinct roles of various organs and glands in maintaining physiological homeostasis, such as glucose and thyroid hormone regulation by the pancreas and thyroid gland, respectively.