BIO 5406 Notes, 1/27/05
PITUITARY (Part 2).
VII. Anterior Pituitary.
A. Review.
B. Pars intermedia. [Hadley, pp. 165-186]
1. Found in amphibians, reptiles and most mammals.
a. Absent or rudimentary in birds, cetaceans, and adult humans.
b. Present in human fetus.
2. Size is correlated with ability to change color.
a. Very large in green anole (chameleon).
3. Produces melanocyte-stimulating hormone (a-MSH).
C. Melanocyte-stimulating hormone.
1. a-MSH -- 13 amino acids (fig. 8.1).
2. MSH controls skin pigmentation.
3. Target cells -- melanocytes in epidermal layer of skin (fig. 8.8).
a. Melanocytes secrete pigment, melanin, into surrounding
epidermal cells.
b. Synthesis of melanin by follicular melanocytes is responsible for
hair color.
c. Alterations in pigmentation due to environmental changes.
1. Important for camouflage.
2. Response to changing backgrounds (ex. green anole).
3. Seasonal changes (ex. snowshoe hare).
4. MSH causes production and dispersion of melanin ---->
darkening of skin.
a. Stimulates adenylate cyclase ----> increased cyclic AMP (fig. 8.15).
b. Controlled by hypothalamus.
1. Influenced by light.
2. Place frog on black background ----> increase MSH secretion(fig. 8.10).
5. Clinical study published in JAMA, Nov. 1991.
a. Injected synthetic MSH analog into 28 male volunteers.
b. Caused darkening of skin.
c. Proposed use -- protection of fair-skinned individuals from UV
radiation.
D. Pars distalis (and tuberalis). [Hadley, pp. 95-107]
1. Produces six hormones.
a. All are peptides.
b. All are synthesized in anterior pituitary.
c. Four of them stimulate other endocrine glands.
2. Glycoprotein family.
a. Thyroid-stimulating hormone (TSH) stimulates the thyroid
gland.
b. Luteinizing hormone (LH) and follicle-stimulating hormone
(FSH) stimulate the gonads (gonadotropins).
c. Produced by basophils.
d. Greater than 200 a.a.
e. Two peptide subunits.
1. Alpha subunit is identical in all three hormones.
2. Beta subunits are structurally distinct.
3. Subunits must be combined for biological activity (fig. 5.7).
3. Adrenocorticotropic hormone (ACTH).
a. Stimulates the adrenal cortex.
b. Produced by basophils.
c. 39 a.a.
d. Large precursor protein cleaves into several different hormones.
4. Growth hormone family.
a. Growth hormone stimulates growth and affects metabolism.
1. Growth hormone is the most abundant hormone of the
anterior pituitary.
b. Prolactin stimulates milk production.
c. Produced by acidophils.
d. Large proteins (almost 200 a.a.).
e. Similar in sequence and tertiary structure.
Hormone
Structure
Source
Target Organ
Thyrotropin (TSH)
Glycoprotein
(>200 a.a.)Thyrotrophsb
Thyroid gland
Gonadotropins
(FSH & LH)Glycoprotein
(> 200 a.a.)Gonadotrophsb
Gonads
Corticotropin
(ACTH)39 a.a.
Corticotrophsb
Adrenal cortex
(growth hormone)
191 a.a.
Somatotrophsa
Bone, cartilage,
muscle, liverProlactin
199 a.a.
Lactotrophsa
Mammary glands
a Acidophils
b Basophils
