ANTERIOR PITUITARY HORMONES
In contrast to the posterior pituitary that releases hormones manufactured by the hypothalamus, the anterior pituitary manufactures the hormones it releases into blood.
Different cell types within the anterior pituitary secrete six known peptide hormones.
The table below shows the hormones and the cell types that secrete them
1. Growth hormone (somatotropin)
2. Thyroid stimulating hormone (Thyrotropin)
3. Follicle stimulating hormone (gonadotropin)
4. Luteinizing hormone (gonadotropin, also called interstitial cell stimulating hormone because of its role in males)
5. Adrenocorticotropic hormone (adrenocorticotropin)
|Lactotropes or mammotropes|
GH is the primary hormone responsible for regulating overall body growth.
Growth hormone, an anabolic hormone, promotes the growth of both the long bones and soft tissues of the body.
It enhances growth of soft tissues by
- increasing the number of cell by stimulating cell division and preventing apoptosis
- increasing the size of cells by promoting protein synthesis; proteins are the main structural components of cells
On long bones, GH stimulates the proliferation of epiphyseal cartilage, thus, lengthening the bone. This is the most dramatic effect of growth hormone.
Note that growth hormone can enhance the lengthening of long bones only if the epiphyseal plate is still cartilaginous.
At the end of adolescence, sex hormones cause the fusion of the epiphyseal plate so that bones can lengthen no more despite the continued presence of growth hormone. Accordingly, after the epiphyseal plates fuse, the individual is unable to grow any taller.
Thyroid stimulating hormone
Thyroid stimulating hormone controls the thyroid gland.
- It stimulates secretion of thyroid hormones (T3 and T4)
- It exerts tropic effect on the thyroid gland. It is responsible for maintaining the thyroid gland.
Appropriate amount of TSH is necessary for maintaining the size of the thyroid gland. In pathological conditions when thyroid cells are exposed to sustained higher plasma TSH levels, the gland enlarge enormously to form a huge mass termed goiter.
On the other hand, if the pituitary is removed, thyroid function declines and the gland atrophies. Thus, thyroid-stimulating hormone prevents atrophy of the thyroid gland.
- This hormone is responsible for milk production in lactating (breast-feeding) mothers.
- In addition, it enhances breast development in females.
Its function in males is unclear.
Adrenocorticotropic hormone (ACTH)
- ACTH acts on the adrenal cortex to promote synthesis and release of cortisol. ACTH after release from anterior pituitary circulates to adrenal cortex and stimulates cortisol release.
- It also promotes the growth of the adrenal cortex
ACTH shows increased secretion in response to stress.
Follicle stimulating hormone
FSH has different functions in females and males
In males, FSH is necessary for sperm production (spermatogenesis). Specifically, it maintains the spermatogenic epithelium by stimulating sertoli cells in the testes.
Under the influence of FSH from the anterior pituitary, sertoli cells secrete a host of chemicals that act as paracrine factors to stimulate proliferation and differentiation of the germ cells.
In females, it is responsible for stimulating growth and development of ovarian follicles within which the egg or ova develop.
In females, LH is responsible for the following:
- Final maturation of the ovarian follicles
- Initial formation of the corpus luteum (i.e. luteinization)
- Secretion of progesterone
In males, LH
- Acts on testicular Leydig cells (also called interstitial cells) to stimulate testosterone production and secretion.
Testosterone is responsible for the male secondary characteristics.
2. Is tropic to the Leydig cells
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