The sella turcica, a term derived from Latin meaning “Turkish saddle,” is a distinct saddle-shaped depression located in the sphenoid bone at the base of the skull. Its formation includes a raised anterior border, the tuberculum sellae, and a posterior boundary, the dorsum sellae, with a central lower area known as the hypophyseal fossa where the gland rests.
The Pituitary Gland: Its Location and Structure
The structure residing within the sella turcica is the pituitary gland, also referred to as the hypophysis. This small gland is comparable in size to a pea or a kidney bean, typically weighing less than one gram. It is positioned at the base of the brain, directly beneath the hypothalamus.
The pituitary gland is composed of two primary parts, or lobes, each possessing distinct structural characteristics and developmental origins. The anterior pituitary, known as the adenohypophysis, is the larger of the two, accounting for approximately 80% of the gland’s total weight. This lobe consists of hormone-secreting epithelial cells and is connected to the hypothalamus via a network of blood vessels.
In contrast, the posterior pituitary, or neurohypophysis, is an extension of the hypothalamus itself. It is primarily composed of unmyelinated secretory neurons, which are nerve fibers rather than glandular tissue. These structural differences between the glandular anterior lobe and the neural posterior lobe are fundamental to their varied functions within the body.
The Pituitary Gland’s Vital Functions
The pituitary gland is often referred to as the “master gland” due to its extensive influence over numerous other endocrine glands and bodily processes. It orchestrates various physiological functions by producing and releasing hormones that act as chemical messengers throughout the body. This central role makes it indispensable for maintaining internal balance.
The anterior pituitary produces and releases several hormones that regulate growth, metabolism, reproduction, and stress response. These include growth hormone (GH), which affects muscle and bone health and fat distribution; thyroid-stimulating hormone (TSH), which prompts the thyroid gland to produce its own metabolic hormones; and adrenocorticotropic hormone (ACTH), which stimulates the adrenal glands to produce cortisol, involved in stress response and metabolism. Additionally, it secretes follicle-stimulating hormone (FSH) and luteinizing hormone (LH), collectively known as gonadotropins, which are crucial for reproductive functions in both males and females. Prolactin, another anterior pituitary hormone, stimulates breast milk production after childbirth and influences fertility.
The posterior pituitary, unlike the anterior lobe, does not produce its own hormones. Instead, it stores and releases two hormones that are synthesized by the hypothalamus. These include antidiuretic hormone (ADH), also known as vasopressin, which plays a role in regulating the body’s water balance and sodium levels by influencing kidney function. The other hormone is oxytocin, which is involved in uterine contractions during labor and facilitates breast milk release. It also contributes to social bonding.
Common Conditions Affecting the Sella Turcica
Given the confined space of the sella turcica, conditions that affect the pituitary gland can lead to significant health issues. The most common of these are pituitary tumors, known as adenomas, which are typically benign or noncancerous growths. These adenomas can cause problems either by their physical size, exerting pressure on surrounding structures, or by causing an imbalance in hormone production.
When pituitary adenomas grow large, exceeding 10 millimeters, they are termed macroadenomas. Their expansion can compress nearby structures, most notably the optic chiasm, which is located directly above the pituitary gland. Compression of the optic chiasm can lead to visual disturbances, such as blurred vision, double vision, or a characteristic loss of peripheral vision in both eyes.
Hypersecretion can lead to conditions like hyperpituitarism, where an excess of hormones causes various symptoms depending on the hormone involved. For instance, too much growth hormone can result in acromegaly in adults, while excess ACTH can lead to Cushing’s disease. Conversely, hypopituitarism occurs when the gland is underactive and does not produce enough hormones, leading to deficiencies that can affect growth, metabolism, and reproductive functions.