anatomy 20.2

Master control center of the endocrine system

Hypothalamus.

Regulated by the hypothalamus

Most endocrine activity.

Three ways hypothalamus controls endocrine function

Through anterior pituitary, posterior pituitary, and autonomic nervous system.

How hypothalamus controls anterior pituitary

Hypothalamic cells secrete regulatory hormones that influence the secretory activity of the anterior pituitary.

Regulatory hormones

Hormones secreted by the hypothalamus into the blood that regulate the secretion of most anterior pituitary hormones.

Types of hypothalamic regulatory hormones

Releasing hormones (RH) and inhibiting hormones (IH).

Function of releasing hormones (RH)

Stimulate the production and secretion of specific anterior pituitary hormones.

Function of inhibiting hormones (IH)

Deter or decrease the production and secretion of specific anterior pituitary hormones.

Indirect control of other endocrine organs

The anterior pituitary secretes hormones that influence many endocrine organs, controlled by the hypothalamus.

Corticotropin-releasing hormone (CRH)

A hypothalamic releasing hormone that increases secretion of adrenocorticotropic hormone (ACTH) from the anterior pituitary.

Effectors of CRH

Corticotropic cells in the pars distalis of the anterior pituitary.

Gonadotropin-releasing hormone (GnRH)

A hypothalamic releasing hormone that increases secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH).

Effectors of GnRH

Gonadotropic cells in the pars distalis of the anterior pituitary.

Growth hormone-releasing hormone (GHRH)

A hypothalamic releasing hormone that increases secretion of growth hormone (GH), also called somatocrinin.

Effectors of GHRH

Somatotropic cells in the pars distalis of the anterior pituitary.

Prolactin-releasing hormone (PRH)

A hypothalamic releasing hormone that increases secretion of prolactin (PRL).

Effectors of PRH

Mammotropic cells in the pars distalis of the anterior pituitary.

Thyrotropin-releasing hormone (TRH)

A hypothalamic releasing hormone that increases secretion of thyroid-stimulating hormone (TSH).

Effectors of TRH

Thyrotropic cells in the pars distalis of the anterior pituitary.

Growth hormone-inhibiting hormone (GHIH)

A hypothalamic inhibiting hormone that decreases secretion of growth hormone (GH), also called somatostatin.

Effectors of GHIH

Somatotropic cells in the pars distalis of the anterior pituitary.

Prolactin-inhibiting hormone (PIH)

A hypothalamic inhibiting hormone that decreases secretion of prolactin (PRL), also called dopamine.

Effectors of PIH

Mammotropic cells in the pars distalis of the anterior pituitary.

Disorders from abnormal secretion of hypothalamic regulatory hormones

Examples include Addison disease, Cushing syndrome, Kallmann syndrome, growth hormone deficiency, and others.

Hormones produced by the hypothalamus stored in the posterior pituitary

Antidiuretic hormone (ADH) and oxytocin (OT).

Does the posterior pituitary synthesize ADH and oxytocin?

No, these hormones are produced by the hypothalamus and transported to the posterior pituitary.

Function of posterior pituitary with ADH and oxytocin

Releases these hormones into the blood.

How hypothalamus controls adrenal medulla

Directly oversees stimulation and hormone secretion through the sympathetic nervous system.

Stimulus for adrenal medulla to secrete hormones

Stimulation by the sympathetic nervous system.

Do all endocrine cells require hypothalamic regulation?

No, some endocrine cells secrete hormones without hypothalamic input.

Example of hormone secretion without hypothalamic input

Parathyroid glands secrete hormones in response to ion concentration in the blood.