Which statement is TRUE?
The anterior pituitary is not a true endocrine gland because it only stores hormones made by the hypothalamus.
The anterior pituitary receives neural stimulation to produce and secrete its hormones.
The posterior pituitary is strictly part of the neural system.
The posterior pituitary is not a true endocrine gland because it only stores hormones made by the hypothalamus.
The Correct Answer and Explanation is :
Correct Answer:
The posterior pituitary is not a true endocrine gland because it only stores hormones made by the hypothalamus.
Explanation:
The pituitary gland is divided into two parts: the anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis). Each part has distinct structures and functions in the endocrine system.
1. The Posterior Pituitary:
The posterior pituitary is not a true endocrine gland because it does not synthesize its own hormones. Instead, it acts as a storage site for hormones produced by the hypothalamus. Specifically:
- Oxytocin and antidiuretic hormone (ADH, also called vasopressin) are synthesized in the hypothalamic nuclei (paraventricular and supraoptic nuclei).
- These hormones travel down axons in the hypothalamo-hypophyseal tract to the posterior pituitary, where they are stored and released into the bloodstream in response to neural signals.
Because the posterior pituitary only stores and releases hormones made elsewhere, it is not classified as a true endocrine gland.
2. The Anterior Pituitary:
The anterior pituitary is a true endocrine gland because it synthesizes and secretes its own hormones. It is regulated by hypothalamic hormones delivered via the hypophyseal portal system. Examples of anterior pituitary hormones include:
- Growth hormone (GH)
- Prolactin (PRL)
- Thyroid-stimulating hormone (TSH)
- Adrenocorticotropic hormone (ACTH)
- Follicle-stimulating hormone (FSH)
- Luteinizing hormone (LH)
The anterior pituitary does not receive direct neural stimulation but instead relies on hormonal signals from the hypothalamus.
Conclusion:
The posterior pituitary’s role as a hormone reservoir differentiates it from true endocrine glands, which produce and secrete hormones. Understanding this distinction clarifies the roles of the pituitary divisions in endocrine regulation.