E n d o c r i n e S y s t e m

Section 2, Chapter 13

Pituitary Gland (Hypophysis)Location: Lies at the base of the brain in the sella turcica, connected to hypothalamus by a pituitary stalk (infundibulum)

2 Lobes:Anterior pituitary (adenohypophysis) Posterior pituitary(neurohypophysis)

Control of Pituitary Gland

Releasing hormones secreted from hypothalamus regulates the anterior lobe.

Nerve impulses from hypothalamus regulate the posterior lobe.

Anterior Pituitary Gland Posterior Pituitary Gland

Anterior Pituitary GlandHypophyseal Portal System –• Releasing hormones secreted by the hypothalamus are conveyed to

the anterior gland through Hypophyseal portal veins.

• Releasing hormones act on specific target cells within the anterior pituitary gland

• In response, the pituitary gland secretes tropic hormones that travel throughout the body acting on distant target cells.

Tropic hormone = hormones that have other endocrine glands as their target

Example of hypophyseal pathway

Releasing Hormone:Thyroid releasing Hormone (TRH) secreted from hypothalamus

Tropic Hormone:Thyroid Stimulating Hormone (TSH) is secreted from the anterior pituitary

Target Cells:Thyroid Hormone (Thyroxine) is secreted from thyroid glands

Anterior Pituitary Hormones 1. Growth Hormone (somatotropin)

Target Cells: • Epithelial and Connective Tissue• Adipose Tissue• Liver

Actions of GH: • Promotes cell growth and division, especially in

skeletal muscles and chondrocytes• Promotes breakdown and use of fat for energy• Liver: promotes breakdown of glycogen for energy

Hypothalamic Control of GH:• Growth Hormone Releasing Hormone (GHRH):

promotes GH secretions

• Somatostatin: inhibits GH secretion

Growth Hormone Disorders

Hypopituitary Dwarfism• Insufficient GH during development• GH therapy may treat condition if

administered before the epiphyseal plates ossify

Gigantism• Results from oversecretion of GH in childhood• Usually caused by a tumor of the pituitary gland

Anterior Pituitary Hormones 2. Thyroid Stimulating Hormone (thyrotropin)

Hypothalamic Control of TSH: Thyroid Releasing Hormone

Target Cells: Thyroid Gland

Actions: TSH promotes secretions of thyroid hormones(T3 & T4)

Under normal conditions, T3 and T4 inhibit further secretions of TRH and TSH

Thyroid Hormones and Negative Feedback

Iodine obtained from the diet is essential for thyroid hormone (T3 & T4) synthesis

TRH & TSH continually stimulate the thyroid gland without inhibition.

Goiter = enlarged thyroid gland

An Iodine deficiency prevents the formation of Thyroid Hormones.

Anterior Pituitary Hormones 3. Prolactin (mammotropin)

Hypothalamic Control of PRL: • Prolactin Releasing Factor: promotes secretion of prolactin• Prolacting Release Inhibiting Hormone: inhibits PRL secretion

Target Cells: Mammary Glands

Actions: Prolactin promotes milk production

3. Adrenocorticotropic Hormone (ACTH)

Anterior Pituitary Hormones

Hypothalamic Control of ACTH: Corticotropin Releasing Hormone

Target Cells: Adrenal Cortex

Actions: ACTH promotes secretions of hormones from the adrenal cortex (e.g. cortisol)

Anterior Pituitary Hormones 4. Follicle Stimulating Hormone (FSH) 5. Luteinizing Hormone (LH)

Hypothalamic Control: Gonadotropin Releasing Hormone (GRH)

Target Cells: GonadsMale: testes Female: Ovaries

4 & 5 = gonadotropes

Actions of gonadotropes: Follicle Stimulating Hormone:

Female = promotes development of ovarian folliclesMale = promotes development of sperm

Luteinizing Hormone:Female = promotes the secretion of estrogens and progesteroneMale = promotes the production of testosterone

Figure 13.15 Hormones released from the hypothalamus, the corresponding hormones released from the anterior lobe of the pituitary gland, and their target organs.

Posterior Pituitary GlandStructurally consists of neurosecretory cells

Hormones are produced by the hypothalamus, then released from the posterior pituitary gland.

Posterior Pituitary Hormones1. Antidiuretic Hormone (ADH) (also called vasopressin)

Target Cells: Kidneys & Blood Vessels

Actions of ADH depend the receptors to which it bindsV1 receptors• Located within blood vessels• ADH, in high concentrations promotes vasoconstriction• May prevent a drop in blood pressure with profuse bleeding

V2 receptors• Located within tubules of kidneys• ADH promotes water reabsorption at the kidneys, and thus

decreases water loss.

• Alcohol inhibits ADH secretion, which explains its role as a diuretic.

Posterior Pituitary Hormones2. Oxytocin

Actions of OxytocinFemales: • stimulates smooth muscle contractions in the uterus during delivery• Promotes ejection of milk from mammary glands

Males: Function is unknown

End of Section 2, Chapter 13.