Unit
- Location and structure: The pituitary gland sits in the sella turcica of the sphenoid bone, connected to the hypothalamus via the pituitary stalk. It consists of the anterior adenohypophysis and posterior neurohypophysis, each derived from different embryologic tissues and responsible for distinct hormonal secretions. The gland is about the size of a pea but exerts control over multiple endocrine axes.
- Anterior lobe cell types: Five specialized cell types produce specific hormones: somatotrophs (growth hormone), lactotrophs (prolactin), corticotrophs (adrenocorticotropic hormone), thyrotrophs (thyroid-stimulating hormone), and gonadotrophs (luteinizing hormone and follicle-stimulating hormone). Each cell type responds to hypothalamic releasing factors and is subject to negative feedback.
- Posterior lobe function: The posterior pituitary stores and releases oxytocin and antidiuretic hormone (ADH), which are synthesized in hypothalamic nuclei and transported via axons. ADH regulates water balance by acting on kidney collecting ducts; oxytocin stimulates uterine contractions and milk ejection.
- Blood supply: The hypophyseal portal system delivers hypothalamic hormones directly to the anterior pituitary. This venous network ensures rapid communication between the hypothalamus and pituitary, allowing precise control of hormone release. The posterior pituitary receives arterial blood from the inferior hypophyseal arteries.
- Pituitary stalk: The infundibulum connects the hypothalamus to the pituitary gland, carrying both axons for posterior hormones and portal blood vessels. Damage to the stalk can disrupt both anterior and posterior pituitary function, leading to panhypopituitarism or diabetes insipidus.
- Surrounding anatomy: The pituitary is adjacent to the optic chiasm superiorly, the cavernous sinuses laterally, and the sphenoid sinus inferiorly. Enlargement of the pituitary can compress these structures, causing visual field defects, cranial nerve palsies, or cerebrospinal fluid leaks.
- Embryology: The anterior pituitary arises from oral ectoderm (Rathke pouch), while the posterior pituitary develops from neuroectoderm. This dual origin contributes to the difference in hormone synthesis and regulation between the two lobes.
- Age-related changes: Pituitary size and function change across the lifespan. In children, the gland is smaller; during pregnancy, the anterior pituitary enlarges due to lactotroph hyperplasia. Aging leads to decreased growth hormone secretion and altered gonadal feedback.
- Hypothalamic releasing factors: The hypothalamus synthesizes corticotropin-releasing hormone (CRH), thyrotropin-releasing hormone (TRH), growth hormone-releasing hormone (GHRH), and gonadotropin-releasing hormone (GnRH). These enter the portal blood to stimulate respective anterior pituitary cells. Inhibitory factors like dopamine and somatostatin also travel via the portal system to modulate prolactin and growth hormone release, respectively.
- Feedback regulation loops: Peripheral target gland hormones such as cortisol, thyroid hormone, and sex steroids act on the hypothalamus and pituitary to inhibit further release of releasing hormones and tropic hormones. For example, elevated cortisol suppresses CRH and ACTH secretion through negative feedback, preventing excessive adrenal activity and maintaining hormonal balance.
- Common pituitary disorders: Adenomas are the most frequent pituitary pathology, often causing hormone hypersecretion (e.g., prolactinoma, acromegaly, Cushing disease) or mass effects. Other conditions include hypopituitarism from stalk compression, Sheehan syndrome postpartum, and empty sella syndrome, each requiring specific diagnostic and therapeutic approaches.
Scope of Practice
Role: Endocrinologist in Pituitary Diagnosis and Management
Within scope:
- Interpreting pituitary imaging and laboratory results
- Prescribing hormone replacement and suppressive therapies
- Coordinating multidisciplinary teams for complex cases
Outside scope:
- Performing transsphenoidal surgery
- Administering radiotherapy
- Providing intraoperative monitoring
Quick Revision
- The pituitary gland comprises anterior and posterior lobes with distinct embryologic origins and functions.
- Anterior lobe produces six key hormones via five cell types, regulated by hypothalamic factors and feedback loops.
- Posterior lobe stores ADH and oxytocin synthesized in the hypothalamus.
- The hypophyseal portal system enables rapid hypothalamic-pituitary communication.
Disclaimer
Educational use only. Not intended for practical surgery, incisions, or other surgical procedures. It does not qualify you to perform physical operations.