What is the source of Follicle Stimulating Hormone (FSH)?

Follicle Stimulating Hormone (FSH) Production

Follicle stimulating hormone (FSH) is produced by the pituitary gland (answer D). This is clearly established in the medical literature and is fundamental to understanding reproductive endocrinology.

Anatomical and Physiological Basis

FSH is specifically produced by the anterior lobe of the pituitary gland, which functions as a distinct endocrine organ with specific cell populations and secretory products 1. The pituitary gland, often referred to as the "master gland" of the body, plays a central role in governing homeostasis, maintaining reproductive function, and directing the activity of other glands 1.

Pituitary Hormone Production

• The anterior pituitary produces several key hormones:
  • Thyroid stimulating hormone (TSH)
  • Corticotropin (ACTH)
  • Luteinizing hormone (LH)
  • Follicle stimulating hormone (FSH)
  • Growth hormone (GH)
  • Prolactin

Regulation of FSH Production

The production of FSH is regulated by the hypothalamus via the hypothalamic-pituitary-gonadal axis 2, 3:

1. The hypothalamus secretes gonadotropin-releasing hormone (GnRH)
2. GnRH stimulates the pituitary gland to produce FSH
3. In women, a sustained midcycle increase in estradiol causes an increase in hypothalamic secretion of GnRH
4. This hormone then stimulates the pituitary gland to increase LH secretion and, with an increase in progesterone and estradiol, FSH levels increase

Structure and Function of FSH

FSH is a glycoprotein hormone with a heterodimeric structure composed of two non-covalently associated subunits containing several heterogeneous oligosaccharide residues 4. These oligosaccharide residues play an important role in both the in-vivo and in-vitro bioactivity of the hormone.

Biological Role of FSH

• In females: FSH is crucial for follicular development and maturation in the ovaries 5
• In males: FSH acts on Sertoli cells in the testes and contributes to spermatogenesis, although interestingly, FSH-deficient males can still be fertile despite having small testes 5

Clinical Relevance

FSH measurements are important in clinical practice for:

1. Diagnosing reproductive disorders
2. Monitoring ovarian function
3. Assessing pituitary function
4. Evaluating infertility
5. Guiding assisted reproductive technologies

For example, FSH levels >40 IU/L on two occasions at least 4 months apart, along with amenorrhea before age 40, are diagnostic criteria for premature ovarian insufficiency (POI) 3.

Therapeutic Applications

Recombinant FSH preparations are used clinically for:

• Treatment of anovulatory infertility in women
• Controlled ovarian stimulation in assisted reproductive technologies
• Treatment of male hypogonadotropic hypogonadism 6

In conclusion, FSH is definitively produced by the pituitary gland, not by the thyroid, adrenal medulla, or adrenal cortex.