Adenohypophysis – Function, Hormones and Disorders
The adenohypophysis is the anterior lobe of the pituitary gland and produces vital hormones that regulate numerous body functions including growth, metabolism, and reproduction.
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The adenohypophysis is the anterior lobe of the pituitary gland and produces vital hormones that regulate numerous body functions including growth, metabolism, and reproduction.
What is the Adenohypophysis?
The adenohypophysis, also known as the anterior pituitary gland, is the glandular front portion of the pituitary gland – a small, pea-sized endocrine organ located at the base of the brain. It plays a central role in regulating the body's hormonal system. The pituitary gland rests in a bony cavity of the skull base called the sella turcica and is divided into two main parts: the adenohypophysis (anterior lobe) and the neurohypophysis (posterior lobe).
The adenohypophysis accounts for approximately 80% of the total pituitary gland. As a true endocrine gland, it synthesizes and secretes hormones directly into the bloodstream. Its activity is regulated by releasing and inhibiting hormones produced by the hypothalamus, which reach the adenohypophysis via a specialized portal blood vessel system.
Structure of the Adenohypophysis
The adenohypophysis is divided into three zones:
- Pars distalis: The largest region, responsible for the production of most anterior pituitary hormones.
- Pars tuberalis: A narrow zone that wraps around the pituitary stalk.
- Pars intermedia: A thin intermediate zone between the anterior and posterior lobes, which is only rudimentary in humans.
Within the pars distalis, several specialized cell types produce distinct hormones, including somatotrophs, thyrotrophs, gonadotrophs, corticotrophs, and lactotrophs.
Hormones of the Adenohypophysis
The adenohypophysis produces six key hormones:
- GH (Growth Hormone / Somatotropin): Stimulates growth, cell proliferation, and metabolic processes.
- TSH (Thyroid-Stimulating Hormone): Triggers the thyroid gland to produce thyroid hormones.
- ACTH (Adrenocorticotropic Hormone): Stimulates the adrenal cortex to release cortisol and other corticosteroids.
- FSH (Follicle-Stimulating Hormone): Regulates the maturation of germ cells in the ovaries and testes.
- LH (Luteinizing Hormone): Triggers ovulation and promotes sex hormone production.
- Prolactin (PRL): Stimulates milk production in the mammary glands after childbirth.
Regulation and Feedback Loops
Hormone production in the adenohypophysis is governed by a precise feedback loop: the hypothalamus releases stimulating hormones (such as CRH, TRH, GnRH, or GHRH) that travel to the adenohypophysis and trigger hormone release. These hormones then activate target organs like the thyroid, adrenal glands, or gonads. The resulting hormone levels feed back to inhibit the hypothalamus and adenohypophysis – a principle known as negative feedback.
Diseases of the Adenohypophysis
Disorders of the adenohypophysis can result in hormone overproduction or deficiency and affect multiple organ systems:
- Pituitary adenoma: A benign tumor of the adenohypophysis that may cause hormone overproduction (e.g., prolactinoma, acromegaly) or, through compression, hormone deficiency.
- Hypopituitarism: Partial or complete loss of anterior pituitary hormone production, caused by tumors, radiation, trauma, or other damage.
- Acromegaly: Excess growth hormone secretion in adults, leading to coarsening of facial features and enlargement of hands and feet.
- Cushing's disease (pituitary form): Excess ACTH production by an adenoma, resulting in elevated cortisol levels.
- Prolactinoma: The most common pituitary tumor, causing elevated prolactin levels with menstrual irregularities or galactorrhea.
Diagnosis of Adenohypophysis Disorders
Diagnostic workup typically includes:
- Blood tests to measure hormone levels (basal and stimulated endocrine tests)
- MRI (Magnetic Resonance Imaging) of the brain to visualize the pituitary gland
- Visual field testing (perimetry) if a tumor is suspected to compress the optic nerves
Treatment
Treatment depends on the underlying condition:
- Hormone replacement therapy for deficiency states (e.g., cortisol, thyroid hormones, growth hormone)
- Medication, such as dopamine agonists for prolactinoma
- Surgical removal of pituitary adenomas (usually via transsphenoidal approach through the nasal sinuses)
- Radiation therapy as an adjunct treatment option
References
- Melmed S. et al. – Williams Textbook of Endocrinology, 14th Edition (2020). Elsevier.
- Molitch M.E. – Diagnosis and Treatment of Pituitary Adenomas: A Review. JAMA. 2017;317(5):516–524.
- World Health Organization (WHO) – Classification of Tumours of Endocrine Organs, 4th Edition (2017). IARC Press, Lyon.
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