How is hormone production and release primarily controlled?
Hormone production and release are primarily controlled by negative feedback. In negative feedback systems, a stimulus causes the release of a substance whose effects then inhibit further release. In this way, the concentration of hormones in blood is maintained within a narrow range. For example, the anterior pituitary signals the thyroid to release thyroid hormones. Increasing levels of these hormones in the blood then feed back to the hypothalamus and anterior pituitary to inhibit further signaling to the thyroid gland.
Compare and contrast hormonal and humoral stimuli.
The term humoral is derived from the term humor, which refers to bodily fluids such as blood. Humoral stimuli refer to the control of hormone release in response to changes in extracellular fluids such as blood or the ion concentration in the blood. For example, a rise in blood glucose levels triggers the pancreatic release of insulin. Insulin causes blood glucose levels to drop, which signals the pancreas to stop producing insulin in a negative feedback loop.
Hormonal stimuli refer to the release of a hormone in response to another hormone. A number of endocrine glands release hormones when stimulated by hormones released by other endocrine organs. For example, the hypothalamus produces hormones that stimulate the anterior pituitary. The anterior pituitary in turn releases hormones that regulate hormone production by other endocrine glands. For example, the anterior pituitary releases thyroid-stimulating hormone, which stimulates the thyroid gland to produce the hormones T3 and T4. As blood concentrations of T3 and T4 rise they inhibit both the pituitary and the hypothalamus in a negative feedback loop.
Oral contraceptive pills work by delivering synthetic progestins to a woman every day. Describe why this is an effective method of birth control.
Progestins, including progesterone, are hormones that help to control the fertility cycle in women. When progesterone is released, it inhibits the production of GnRH in the hypothalamus. Without GnRH, FSH and LH are not produced in the pituitary gland, so the ovaries are not signaled to mature and release an ovum. If progesterone is delivered to the body every day, it will continuously inhibit this cycle.