pituitary gland

1. Section 2, Chapter 13

2. 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)

3. Control of Pituitary Gland
Anterior Pituitary Gland
Releasing hormones secreted from
hypothalamus regulates the anterior lobe.
Posterior Pituitary Gland
Nerve impulses from hypothalamus
regulate the posterior lobe.

4. 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
travel throughout the body acting on distant target cells.
Tropic hormone = hormones that have
other endocrine glands as their target

5. 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

6. Anterior Pituitary Hormones
1. Growth Hormone (somatotropin)
Hypothalamic Control of GH:
• Growth Hormone Releasing Hormone (GHRH):
promotes GH secretions
• Somatostatin: inhibits GH secretion
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

7. 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

8. 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)

9. Thyroid Hormones and
Negative Feedback
Under normal conditions, T3 and T4
inhibit further secretions of TRH and TSH
Iodine obtained from the diet is essential
for thyroid hormone (T3 & T4) synthesis

10. An Iodine deficiency prevents the
formation of Thyroid Hormones.
TRH & TSH continually stimulate the
thyroid gland without inhibition.
Goiter = enlarged thyroid gland

11. 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

12. Anterior Pituitary Hormones
3. Adrenocorticotropic Hormone (ACTH)
Hypothalamic Control of ACTH:
Corticotropin Releasing Hormone
Target Cells: Adrenal Cortex
Actions: ACTH promotes secretions of hormones
from the adrenal cortex (e.g. cortisol)

13. Anterior Pituitary Hormones
4. Follicle Stimulating Hormone (FSH)
4 & 5 = gonadotropes
5. Luteinizing Hormone (LH)
Hypothalamic Control:
Gonadotropin Releasing Hormone (GRH)
Target Cells: Gonads
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

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

15. Posterior Pituitary Gland
Structurally consists of neurosecretory cells
Hormones are produced by the hypothalamus,
then released from the posterior pituitary gland.

16. Posterior Pituitary Hormones
1. 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
• 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.

17. Posterior Pituitary Hormones
2. Oxytocin
Actions of Oxytocin
Females:
• stimulates smooth muscle contractions in the uterus during delivery
• Promotes ejection of milk from mammary glands
Males: Function is unknown

19. End of Section 2, Chapter 13.