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 Gland

Hypophyseal 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 • 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: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

Hypothalamic Control of GH:

• Growth Hormone Releasing Hormone (GHRH):

promotes GH secretions

• Somatostatin: inhibits GH secretion

• 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

Growth Hormone Disorders

Gigantism

• Results from oversecretion of GH in childhood

• Usually caused by a tumor of the pituitary gland

Hypopituitary Dwarfism

• Insufficient GH during development

• GH therapy may treat condition if

administered before the epiphyseal

plates ossify

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 hormonesActions: 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.

An Iodine deficiency prevents the

formation of Thyroid Hormones.

Goiter = enlarged thyroid gland

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 GlandsTarget 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 CortexTarget 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: Gonads

Male: testes Female: Ovaries

4 & 5 = gonadotropes

Male: testes Female: Ovaries

Actions of gonadotropes:

Follicle Stimulating Hormone:

Female = promotes development of ovarian follicles

Male = promotes development of sperm

Luteinizing Hormone:

Female = promotes the secretion of estrogens and progesterone

Male = 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 Gland

Structurally 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 binds

V1 receptors

• Located within blood vessels• 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 Oxytocin

Females:

• stimulates smooth muscle contractions in the uterus during delivery

• Promotes ejection of milk from mammary glands

Males: Function is unknownMales: Function is unknown

End of Section 2, Chapter 13.