Within the biology and biochemistry topics, the MCAT will test you on the endocrine system, so it’s a good idea to start brushing up on the basics as soon as you can.
Check out our video lesson on MCAT endocrine system basics, and keep reading for a quick endocrine system review.
MCAT Endocrine System Review
The endocrine system is the collection of glands that produce hormones that regulate metabolism, growth and development, tissue function, sexual function, reproduction, sleep, and mood, among other things.
The endocrine system is made up of many organs and glands throughout the body. In the brain, endocrine activity is focuses primarily in the thalamus, the hypothalamus, and the pituitary gland.
Types of Endocrine Hormones
Let’s start with the basic categories of hormone:
- Steroid hormones are non-polar, which means they can cross the plasma membrane. This gives them the opportunity to bind to nuclear receptors inside the cell.
- Peptoid hormones are large polymers of amino acids, and not necessarily non-polar. These hormones typically bind to receptors on the cytoplasm.
- Tropic hormones stimulate glands to produce other hormones.
Hormones of the Anterior Pituitary
Now let’s review the hormones of the anterior pituitary. You need to know them all, and know what they do.
Follicle-Stimulating Hormone (FSH): In women, FSH stimulates the ovarian follicle, causing an egg to grow. It also triggers the production of estrogen in the follicle. The rise in estrogen tells your pituitary gland to stop producing FSH and to start making more LH. In men, FSH stimulates testicular growth and enhances the production of an androgen-binding protein by the Sertoli cells, which are a component of the testicular tubule necessary for sustaining the maturing sperm cell.
Luteinizing Hormone (LH): In women, LH causes the egg to be released from the ovary, a process called ovulation. In men, LH stimulates testosterone production from the interstitial cells of the testes (Leydig cells).
Adrenocorticotropic hormone (ACTH): ACTH stimulates the adrenal cortex to release a hormone called cortisol. Cortisol is a stress hormone, which increases blood sugars (amongst other things).
Thyroid-Stimulating Hormone (TSH): Thyroid stimulating hormone causes the thyroid gland to release thyroid hormone.
Thyroid hormone increases metabolism. So, someone with increased thyroid hormone (hyperthyroidism), is going to be hot, experience weight loss and difficulty sleeping, and have a lot of energy.
Some with hypothyroidism is going to have weight gain, be lethargic and cold, and have difficulty thinking clearly.
Basically, things slow down with low thyroid hormone, and speed up with high thyroid hormone.
Prolactin: So far these hormones have all been tropic hormones (because they act on a gland, in this gland here to cause release of another hormone). Prolactin is not tropic. It directly causes breast development and milk production from the mammary glands.
Growth Hormone (GH): Growth hormone is also not tropic, because it has a direct effect. It causes growth and development: muscle growth, bone growth, and protein synthesis. It also increases blood sugar.
Hormones of the Hypothalamus
These hormones stimulate the anterior pituitary to release the hormones we’ve just discussed.
Gonadotropin-Releasing hormone (GNRH): released from the hypothalamus, and causes anterior pituitary to release FSH and LH. So obviously, this is a tropic hormone.
Corticotropin-Releasing Hormone (CRH): stimulates ACTH.
Thyroid Hormone-Releasing Hormone (TRH): stimulates TSH.
Growth Hormone-Releasing Hormone (GHRH): stimulates GH.
You should also, with relation to growth hormone, be familiar with the terms gigantism and acromegaly.
- Gigantism is an excess of growth hormone, while the growth plates were still open. So, gigantism makes people be very tall.
- Acromegaly is an excess of growth hormone when the growth plates have already closed. And what this results in is instead of people being very tall, things grow longitudinally. So, very big boned people, and people who have later onset growth hormone, basically so they have acromegaly growth hormone, after the growth plates have closed, their face changes, the bones develop and they kind of have a characteristic face.
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