Hormones Secreted by the Anterior Pituitary
The correct answer is E: 1,2, and 3 (LH, Prolactin, and TSH are secreted by the anterior pituitary, while ADH is secreted by the posterior pituitary).
Anterior Pituitary Hormones
The anterior pituitary (adenohypophysis) secretes several key hormones that regulate various physiological processes throughout the body. According to current evidence, these hormones include:
Luteinizing Hormone (LH): A gonadotropin that plays a crucial role in reproduction. In females, LH triggers ovulation and stimulates the corpus luteum to produce progesterone. In males, LH stimulates Leydig cells to produce testosterone 1.
Prolactin (PRL): Primarily responsible for stimulating milk production in the mammary glands during lactation. Prolactin levels are highest in the first 2 years of life, fall to a nadir in mid-childhood, and rise again during adolescence 1, 2.
Thyroid-Stimulating Hormone (TSH): Stimulates the thyroid gland to produce thyroid hormones (T3 and T4), which regulate metabolism 1.
Other anterior pituitary hormones (not listed in the question options but important to note):
- Growth Hormone (GH): Regulates growth and metabolism
- Adrenocorticotropic Hormone (ACTH): Stimulates the adrenal cortex to produce cortisol
- Follicle-Stimulating Hormone (FSH): Another gonadotropin that stimulates follicular development in females and spermatogenesis in males
Posterior Pituitary Hormones
The posterior pituitary (neurohypophysis) does not produce hormones but stores and releases:
- Antidiuretic Hormone (ADH/Vasopressin): Regulates water retention by the kidneys. The posterior pituitary gland consists of axonal terminations of neurons whose cell bodies are located in the hypothalamus 1.
- Oxytocin: Stimulates uterine contractions during childbirth and milk ejection during breastfeeding.
Anatomical and Functional Distinction
The hypothalamic-pituitary axis consists of two separate neuroendocrine organs:
- The anterior pituitary system secretes hormones under the influence of hypothalamic trophic factors 1, 3.
- The posterior pituitary system releases hormones that are actually produced in the hypothalamus and transported to the posterior pituitary for storage and release 1.
Clinical Relevance
Understanding which hormones are secreted by which part of the pituitary is crucial for diagnosing and managing pituitary disorders:
- Hyperprolactinemia (elevated prolactin) can result from prolactinomas or medications, and may present with galactorrhea, amenorrhea, or hypogonadism 1.
- Central hypothyroidism presents with low TSH and low free T4, indicating pituitary dysfunction 1.
- Hypogonadotropic hypogonadism presents with low LH/FSH and subsequent low sex hormones 1.
This anatomical and functional distinction is important for understanding the pathophysiology of conditions like hypophysitis, which can affect anterior pituitary hormones (TSH, ACTH, gonadotropins) but typically spares posterior pituitary function 1.