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 called erythropoietin, which stimulates erythropoiesis.

Answer

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

### Step-by-Step Solution:

1. **Statement Analysis**:
- **Statement 1**: "Hormones are non-nutrient chemical substances that only act as extracellular messengers and are produced in trace amounts."
- **Analysis**: Hormones are indeed non-nutrient chemical substances produced in trace amounts. However, they primarily act as intracellular messengers (within cells) rather than extracellular messengers (between cells). Therefore, this statement is incorrect due to the term "extracellular."

2. **Statement 2**: "The pars distalis is a region of a gland situated in the sella turcica responsible for secretion of the hormone which includes ovulation."
- **Analysis**: The pars distalis is part of the anterior pituitary gland, located in the sella turcica. It secretes hormones such as luteinizing hormone (LH), which is involved in the ovulation process. This statement is correct.

3. **Statement 3**: "Diabetes mellitus is a disorder caused due to the decreased secretion of hormones from the alpha cells of the islets of Langerhans of the pancreas."
- **Analysis**: Diabetes mellitus is primarily related to insulin deficiency or resistance, which is produced by the beta cells of the islets of Langerhans. The alpha cells produce glucagon, which raises blood glucose levels. The statement incorrectly attributes diabetes to decreased secretion from alpha cells when it is more related to beta cell dysfunction. Therefore, this statement is also incorrect.

4. **Statement 4**: "The juxtaglomerular cells of the kidney produce steroid hormone called erythropoietin which stimulates erythropoiesis."
- **Analysis**: Erythropoietin (EPO) is indeed produced by the juxtaglomerular cells of the kidneys and stimulates the production of red blood cells (erythropoiesis). This statement is correct.

### Conclusion:
The incorrect statements about the human endocrine system are **Statement 1** and **Statement 3**.