Glands and Hormones of the Endocrine System
From MyMCAT
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[edit] Introduction
A properly functioning endocrine system is vital to the normal development and health of the body. Diabetes, gigantism, and dwarfism are just a few of the limitless list of disorders that can accompany an endocrine disorder. While the MCAT does not expect you to know the exhaustive list of all hormones and their related disorders, you are required to know the major players and be able to reason how changes to their function might effect the body.
[edit] Glands
Glands can exist as endocrine or exocrine. In the latter, exocrine glands discharge chemicals into ducts which then allows them to flow to their target. Endocrine glands, on the other hand, release their contents directly into the blood stream. These secreted chemicals, known as hormones, can then flow throughout the entire body until they reach their target. It is these ductless glands that we will discuss below.
[edit] The Pituitary Gland
The pituitary gland, residing at the center of one's brain, is no larger than a pea but capable of producing a powerful array of hormones. The pituitary is made up of two separate halves, the anterior and posterior pituitary respectively, each with its own set of activities.
[edit] The Anterior Pituitary
The anterior pituitary is often considered a "master control" in that four of the six hormones it secretes do not have a direct effect on the body, instead these hormones act on OTHER endocrine glands to stimulate them and in turn to release their own hormones. These hormones that act to stimulate other endocrine glands are called tropic hormones.
Tropic Hormones:
TSH (Thyriod Stimulating Hormone)
TSH acts on the Thyriod, triggering it to release its own hormone (Thyriod Hormone).
ACTH (Adrenocorticotropic Hormone)
ACTH acts on the adrenal cortex triggering it to increase in size and to secrete large amounts of its hormones (numerous corticosteroid hormones).
FSH (Follicle Stimulating Hormone)
FSH acts on ovarian follicles in the ovaries to grow and mature to the point of ovulation, these follicles in tern release estrogens. In males, FSH stimulates the seminiferous tubules to grown and form sperm.
LH (Luteinizing Hormone)
In males, LH is known as Interstitial Cell Stimulating Hormone (ICSH), and triggers the testis to produce testosterone and other male specific hormones.
Direct Hormones:
Prolactin
Prolactin stimulates mammary gland development for eventual lactation (milk secretion). After birth, prolactin acts to stimulate the breasts to secrete milk.
Endorphins
Endrophins are used as an analgesic in the body to numb or dull pain.
GH (Growth Hormone)
Growth hormone, also known as somatotropin, is a peptide hormone which stimulates growth and cell reproduction in cells. As one would expect from a hormone which stimulates anabolic activities (building up), GH also acts to promote protein synthesis and energy usage by breaking down lipid (lipolysis) and glyconeogenesis in the liver as well as increasing calcium retention (in bones) and muscle sarcomere size.