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HORMONES
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How Steroid Hormones Work:
Source: BIOU301: Genetics and Molecular Biology at Northeastern University. Introduction to Signaling Lecture. Oct. 23, 2007.
Please note that other hormones that are hydrophilic work by binding to a receptor on a cell membrane. The hormone-receptor binding signals a series of reactions inside the cell. In other words, the hormone can cause a series of intracellular reactions without ever entering the cell (Saladin, Kenneth S. Anatomy and Physiology : The Unity of Form and Function. 4th ed. New York: McGraw-Hill Education, 2006).
Class Names of sex steroid hormones:
Estrogens-Maintain size and function of female sex organs. Promotes adolescent skeletal growth and helps to sustain adult bone mass.
Androgens-Maintain size and function of male sex organs. Stimulates development of public and axillary hair and apocrine scent glands (armpit, pubic region, around nipples, and bearded regions) at puberty. They also sustain the sex drive. Promotes adolescent skeletal growth and helps to sustain adult bone mass.
Source: Brown, G. A. (2006). Testosterone Prohormone Supplements. Medicine & Science in Sports and Exercise, 38, 1451-1461.
Source: Saladin, Kenneth S. Anatomy and Physiology : The Unity of Form and Function. 4th ed. New York: McGraw-Hill Education, 2006
Selected Hormones:
Dehydroepiandrosterone (DHEA) – Released from the adrenal cortex. It is an androgen hormone that can be converted into testosterone. It is an important source of androgen for women.
Cortisol — Falls under a group of hormones called glucocorticoids that are secreted by the adrenal cortex. It is a catabolic hormone that breaks down proteins, releases fatty acids by breaking down fat, inhibits protein synthesis, synthesizes glucose from noncarbohydrate sources (gluconeogenesis) to increase blood sugar levels, decreases glucose utilization by cells, and has an ant-inflammatory effect (Saladin, Kenneth S. Anatomy and Physiology : The Unity of Form and Function. 4th ed. New York: McGraw-Hill Education, 2006). It is increased during intense exercise and stress.
Glucagon — A hormone that is released by the pancreas to elevate blood sugar levels by gluconeogenesis (proteins and fats are broken down and converted into glucose), lipolysis (breakdown of fat), and by signaling the liver to breakdown glycogen to glucose (glycogenolysis) (Saladin, Kenneth S. Anatomy and Physiology : The Unity of Form and Function. 4th ed. New York: McGraw-Hill Education, 2006). Usually elevated during exercise when blood sugar levels are low.
Growth Hormone — An anabolic hormone secreted by the anterior lobe of the pituitary gland that stimulates bone and muscle growth through protein synthesis and mitosis of chondrocytes in cartilage. It also breaks down stored fat in a process known as lipolysis, which has a protein-sparing effect. It also plays a role in electrolyte balance by promoting sodium, potassium, and chloride retention and enhancing calcium absorption (Saladin, Kenneth S. Anatomy and Physiology : The Unity of Form and Function. 4th ed. New York: McGraw-Hill Education, 2006). Lastly, it inhibits the uptake of glucose in certain cells (anti-insulin effect).
Insulin —A hormone that is secreted by the pancreas in order to lower the blood glucose levels in the body. Stimulates the uptake of glucose from muscle and fat cells and stimulates the storage of glucose as glycogen in the muscle and liver cells. Inhibits the synthesis of glucose (gluconeogenesis), stores excess glucose at fat, and promotes protein synthesis (Saladin, Kenneth S. Anatomy and Physiology : The Unity of Form and Function. 4th ed. New York: McGraw-Hill Education, 2006).
Insulin-like growth factor— It is produced in the liver. Growth hormone must act through insulin-like growth factors to increase cartilage formation, skeletal growth, increase protein synthesis, increase cell growth, and increase cell differentiation (Saladin, Kenneth S. Anatomy and Physiology : The Unity of Form and Function. 4th ed. New York: McGraw-Hill Education, 2006). In other words, growth hormone indirectly causes these effects to occur, whereas insulin-like growth factors directly cause them.
Testosterone —A hormone that is responsible for many secondary male sexual characteristics, number of red blood cells, decreased body fat, and muscle growth produced by the testes. Free Testosterone can be used by your muscles; however, if the testosterone levels are too high, hormones such as SHBG can bind to it thus making the hormone useless. It can also be converted into estrogen or DHT causing baldness and increased water weight. There have been studies that have shown a relationship between the amount of testosterone in the body and prostate cancer.
Vascular Endothelial Growth Factor (VEGF) —A hormone that stimulates muscle growth by increasing the number of capillaries in your body and increasing muscle oxygenation.
Source: Ivy, PhD, John , and Robert Portman, PhD. Nutrient Timing. North Bergen: Basic Health Publications Inc., 2004. 165-173.
Leptin—A protein hormone that is released in response to the amount of fat in the body. Controls appetite by signaling the brain that it is full (Insel, P., Turner, Rd, R. E., & Ross, D. (2004). Proteins and Amino Acids. Nutrition (pp. 204-243). Sudbury, MA: Jones and Bartlett.). Obesity is associated with defective leptin receptors. This means that it is possible to have a normal amount of leptin but the hormone will not be able to attach to the appropriate cell. As a result, the brain can't receive the signal because leptin can't attach correctly (Saladin, Kenneth S. Anatomy and Physiology : The Unity of Form and Function. 4th ed. New York: McGraw-Hill Education, 2006). Taking leptin as a pill will not work because leptin is a protein and proteins are digested in the stomach.
Last Updated:
March 22, 2009
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