Which of the following is incorrect about the human endocrine system ?

Options

A. Hormone are non-nutrient chemical substances that only act as extracellular messengers and are produced in trace amounts.
B. The pars distalis region of a gland situated in the sella turcica, is responsible for secretion of the hormone which includes ovulation.
C. Diabetes mellitus is a disorder caused due to decreased secretion of hormones from the alpha cells of the lslet of Langerhans of the pancreas.
D. The juxtaglomerular cells of the kidney produce a steroid hormone celled erythropoietin, which stimulates erythropoiesis.

Answer

To determine which statement is incorrect about the human endocrine system, we will analyze each statement provided.

### Step-by-Step Solution:

1. **Understanding Hormones**:
- Hormones are defined as non-nutrient chemical substances that act as extracellular messengers. They are produced in trace amounts and are secreted directly into the bloodstream by ductless glands (endocrine glands).
- **Hint**: Remember that hormones are messengers that travel through the blood to target organs.

2. **Pituitary Gland and Ovulation Hormones**:
- The pituitary gland is located in the sella turcica and is divided into two parts: the anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis). The anterior pituitary secretes hormones such as LH (Luteinizing Hormone), which is responsible for ovulation.
- **Hint**: Focus on the functions of the anterior pituitary and its role in reproductive hormones.

3. **Diabetes Mellitus**:
- Diabetes mellitus is primarily caused by a deficiency of insulin, which is secreted by the beta cells of the islets of Langerhans in the pancreas. The alpha cells secrete glucagon, which raises blood glucose levels but is not responsible for diabetes.
- **Hint**: Recall the roles of alpha and beta cells in the pancreas and their relation to diabetes.

4. **Erythropoietin Production**:
- The juxtaglomerular cells of the kidneys produce erythropoietin, which stimulates erythropoiesis (the production of red blood cells). This statement is correct.
- **Hint**: Erythropoietin is crucial for red blood cell production; think about its source and function.

5. **Identifying the Incorrect Statement**:
- The statement regarding diabetes mellitus being caused by the secretion of alpha cells is incorrect. Diabetes is due to the deficiency of insulin from beta cells, not glucagon from alpha cells.
- **Conclusion**: The incorrect statement is that "Diabetes mellitus is caused by the secretion of alpha cells in the islet of Langerhans of the pancreas." This is option C.

### Final Answer:
The incorrect statement about the human endocrine system is option C: "Diabetes mellitus is caused by the secretion of alpha cells in the islet of Langerhans of the pancreas."