Pituitary hormones- Chemistry, Secretion, Functions and Regulation. Anterior Pituitary hormones–GH, Pituitary tropic hormones (LH, FSH, TSH, ACTH and Prolactin).

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 The anterior pituitary gland, also known as the adenohypophysis, secretes several hormones, each with specific chemistry, secretion patterns, functions, and regulation. Here's an overview of the anterior pituitary hormones, including growth hormone (GH) and the pituitary tropic hormones (LH, FSH, TSH, ACTH, and Prolactin):

1. Growth Hormone (GH):

  • Chemistry: GH is a peptide hormone composed of a chain of amino acids.
  • Secretion: GH secretion is controlled by the hypothalamic hormone Growth Hormone-Releasing Hormone (GHRH) and inhibited by Growth Hormone-Inhibiting Hormone (GHIH) or somatostatin. GH secretion follows a pulsatile pattern and increases during sleep and in response to stress and exercise.
  • Functions: GH plays a crucial role in stimulating growth and development of bones and tissues, primarily during childhood and adolescence. It also promotes protein synthesis, fat metabolism, and maintenance of blood glucose levels.
  • Regulation: GH secretion is regulated by a negative feedback loop, with GH itself and insulin-like growth factors (IGFs) produced in response to GH inhibiting further GH release.

2. Pituitary Tropic Hormones:

  • These hormones are so named because they regulate the function of other endocrine glands or organs.

a. Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH):

  • Chemistry: LH and FSH are glycoprotein hormones.
  • Secretion: LH and FSH secretion are regulated by Gonadotropin-Releasing Hormone (GnRH) from the hypothalamus. They exhibit a pulsatile secretion pattern.
  • Functions: In females, LH and FSH regulate the menstrual cycle, ovulation, and support the development of ovarian follicles and the production of estrogen and progesterone. In males, LH stimulates the Leydig cells to produce testosterone, while FSH supports spermatogenesis.
  • Regulation: LH and FSH secretion is influenced by feedback from sex steroids (estrogens and androgens) and inhibin.

b. Thyroid-Stimulating Hormone (TSH):

  • Chemistry: TSH is a glycoprotein hormone.
  • Secretion: TSH secretion is controlled by Thyrotropin-Releasing Hormone (TRH) from the hypothalamus. It follows a pulsatile pattern.
  • Functions: TSH stimulates the thyroid gland to produce and release thyroid hormones (T3 and T4), which regulate metabolism and energy production in cells.
  • Regulation: TSH secretion is regulated by feedback from thyroid hormones. High levels of thyroid hormones inhibit TSH release, while low levels stimulate it.

c. Adrenocorticotropic Hormone (ACTH):

  • Chemistry: ACTH is a peptide hormone.
  • Secretion: ACTH secretion is controlled by Corticotropin-Releasing Hormone (CRH) from the hypothalamus. It follows a diurnal rhythm, peaking in the morning.
  • Functions: ACTH stimulates the adrenal cortex to produce and release glucocorticoid hormones, such as cortisol. These hormones are involved in regulating metabolism, immune responses, and the body's response to stress.
  • Regulation: ACTH secretion is regulated by negative feedback from cortisol levels in the blood.

d. Prolactin (PRL):

  • Chemistry: PRL is a peptide hormone.
  • Secretion: PRL secretion is primarily controlled by Prolactin-Inhibiting Hormone (PIH) or dopamine. It follows a diurnal pattern, with higher levels during sleep.
  • Functions: PRL is best known for its role in promoting lactation (milk production) in mammary glands. However, it also has multiple other functions, including immune system regulation and influence on reproductive behaviors.
  • Regulation: PRL secretion is regulated by a complex interplay of factors, including dopamine, estrogen, and suckling stimuli. Dopamine inhibits PRL release, while estrogen and suckling stimulate it.

In summary, the anterior pituitary hormones, including GH and the pituitary tropic hormones, play vital roles in regulating various physiological processes in the body. Their secretion, functions, and regulation are tightly controlled by the hypothalamus and feedback mechanisms to maintain hormonal balance and support overall health and homeostasis.

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