Pituitary Gland Overview

The sella turcica is a depression in the sphenoid bone, a bone located at the base of the skull.

The infundibular stalk connects the pituitary gland to the base of the brain. It acts as a passageway for hormones and blood vessels.

The diaphragma sellae, like a roof, covers the pituitary gland and helps to hold it in place.

The hypophyseal veins are responsible for draining the blood from both parts of the pituitary gland - the pars distalis and pars nervosa.

The pars distalis is a major part of the pituitary gland and belongs to the adenohypophysis.

Fenestrated capillaries are specialized blood vessels with pores that allow for easy exchange of hormones and nutrients within the pituitary gland.

Somatotropes are cells in the adenohypophysis that produce growth hormone, which is essential for growth and development.

Thyrotropes, gonadotropes, and corticotropes are cells of the adenohypophysis involved in regulating thyroid function, reproduction, and stress response.

Thyrotropes are basophilic adenohypophysis cells that produce thyroid stimulating hormone.

Thyroid stimulating hormone's release is regulated by thyrotropin releasing hormone (TRH) from the hypothalamus.

Gonadotropes are basophilic adenohypophysis cells that produce follicle stimulating hormone and luteinizing hormone.

The release of follicle stimulating hormone and luteinizing hormone is regulated by gonadotropin releasing hormone (GnRH) from the hypothalamus.

Corticotropes are basophilic adenohypophysis cells that produce proopiomelanocortin.

Proopiomelanocortin is cleaved into adrenocorticotropic hormone (ACTH) and beta-lipotrophic hormone.

The release of proopiomelanocortin is regulated by corticotropin releasing hormone (CRH) from the hypothalamus.

ACTH and beta-lipotrophic hormone are produced by the cleavage of proopiomelanocortin.

Specialized cells resembling astrocytes found in the posterior pituitary, supporting the neurosecretory fibers.

Stored hormones like oxytocin and ADH accumulate in these dilations within the axon terminals of neurosecretory cells.

The neurohypophysis releases two hormones: oxytocin and ADH. These hormones are produced in the supraoptic and paraventricular nuclei of the hypothalamus.

The pineal gland, located in the brain, is connected to the third ventricle. It is covered by a thin membrane continuous with the pia mater.

The pineal gland's main cell type, pinealocytes, are characterized by their large size and crenated nuclei. These cells are responsible for producing melatonin.

Along with hormones, neurophysin is synthesized, but it is cleaved in the axon terminal before release.

The pineal gland also contains glial cells and pineal concretions, which are mineral deposits that can be seen on a CT scan.

The pineal gland is crucial for regulating circadian rhythm and sleep-wake cycles.

T3 is the more active form of thyroid hormone, produced from T4 in the kidney, liver, and heart.

Thyroid stimulating hormone (TSH) regulates all stages of T3 and T4 synthesis.

T3 and T4 regulate metabolic rate, heat production, and tissue growth.

Parafollicular cells, found in the thyroid gland, produce calcitonin.

Calcitonin lowers blood calcium levels by inhibiting osteoclasts and increasing renal/intestinal calcium excretion.

The parathyroid glands, located on the dorsal surface of the thyroid gland, are essential for life.

Principal cells of the parathyroid glands produce parathyroid hormone (PTH).

Oxyphil cells are larger than principal cells and have an unknown function.

The zona fasciculata is a layer within the adrenal cortex responsible for producing cortisol, a glucocorticoid. Its cells are arranged in straight columns that run radially.

The cells of the zona fasciculata are dependent on adrenocorticotropic hormone (ACTH) for their regulation.

The zona fasciculata cells contain abundant smooth endoplasmic reticulum (sER), which helps in steroid hormone synthesis.

The mitochondria of zona fasciculata cells have a unique structure called tubulovesicular cristae, which are important for steroid hormone production.

The zona reticularis is the inner layer of the adrenal cortex, producing dehydroepiandosterone, a gonadocorticoid.

The zona reticularis cells are arranged in a network, with smaller, darker cells that contain lipofuscin inclusions.

The zona reticularis cells also depend on adrenocorticotropic hormone (ACTH) for regulation.

Dehydroepiandosterone (DHEA), a gonadocorticoid produced by the zona reticularis, has a role in sex hormone production.

The pineal gland, a small endocrine gland located deep within the brain, primarily produces melatonin, which plays a crucial role in regulating sleep-wake cycles, adjusting to changes in day length, and influencing seasonal affective disorder. It also produces serotonin and other peptides involved in various physiological processes.

The thyroid gland is a butterfly-shaped endocrine gland situated at the level of the larynx. It consists of two lateral lobes interconnected by an isthmus. The functional unit of the thyroid gland is spherical follicles filled with colloid and lined by follicular cells. These follicular cells form a simple cuboidal epithelium.

The thyroid gland receives its primary blood supply from the superior and inferior thyroid arteries. These arteries deliver blood to a network of fenestrated capillaries, facilitating efficient exchange of substances between the blood and the thyroid tissue. The veins from the thyroid gland form a rich plexus, and the gland has good lymphatic drainage.

Thyroid follicular cells are responsible for synthesizing and releasing thyroid hormones, primarily thyroxin (T4) and triiodothyronine (T3). These cells are unique within the endocrine system because they store their secretory product extracellularly within the colloid of the follicles.

The production and storage of thyroid hormones involve a multi-step process. Follicular cells actively concentrate iodine from the blood using ATPase transporters. The endoplasmic reticulum synthesizes thyroglobulin proteins. In the Golgi apparatus, these proteins are further modified, and then released into the follicle lumen. Thyroid peroxidase, an enzyme, facilitates the coupling of iodine to tyrosine residues in thyroglobulin. This coupling leads to the formation of MIT and DIT, which further combine to synthesize T3 and T4. These hormones are then stored as colloid within the lumen.

The synthesis and release of both T3 and T4 are tightly regulated by the hypothalamus-pituitary axis. This feedback system involves the hypothalamus releasing TRH (thyrotropin-releasing hormone), which stimulates the pituitary gland to produce TSH (thyroid-stimulating hormone). TSH then acts on the thyroid gland to stimulate the synthesis and release of T3 and T4.