chart of the endocrine system
The endocrine system is a system of ductless glands that produce hormones. The system helps to regulate all of the body’s functions. It controls our feelings of hunger, how fast we grow, our body temperature, water balance, salt balance, how awake we feel, how happy we feel, how we grow into men and women and more. Unlike the nervous systems, whose signals are electrochemical and have immediate impact and effect, the endocrine system sends signals that are chemical and longer lasting. They precondition the behavior of systems, making them chemically possible or through the activation or deactivation of genes. The endocrine glands are not be confused with the exocrine glands, which include the tear glands, sweat glands, mammary glands, oil glands, some glands in digestive system, (for example the salivary glands) which have ducts. Definition of a hormone: an informational molecule synthesized by endocrine cells that have specific effects in very low concentrations and are delivered through various modes of secretion to target cells called receptor cells found in cell membranes. There are over 100 known hormones used by the human body.
The study of the endocrine system is called endocrinology. o The field was first started about 150 years ago when a scientist named Berthold started experimenting with castrated chickens, a practice that produced capons, which are good to eat but not very aggressive. He then transplanted testes from other males to capons and they became aggressive and grew wattle and combs.
In 1889, a pair of anatomists called Von Mering and Menkowski discovered Diabetes Mellitus (which means ‘sweet water’). They did a biopsy of a dog and found an organ they didn’t know (the pancreas), removed it, and sewed the dog back up. The dog got sick and died, but before dying it urinated a lot and ants were very attracted to it urine. One of the anatomists tasted the urine and found it very sweet. They concluded that the pancreas had something to do with carbohydrate metabolism. Later scientists would eventually isolate the hormone called insulin from the pancreas.
Hormonal control of body function is through negative feedback control systems that are like a thermostat on a heating system. A drop in temperature causes the thermostat to switch on the furnace. When the thermostat detects that the temperature has reached a defined level it turns off the furnace. o Some Biological Examples:
1. A person eats a lot fish and the rise in calcium levels in the blood causes the secretion of the thyroid hormone called calcitonin, which predisposes bone cells to absorb calcium from the blood, when that happens calcium level drops and the thyroid stops secreting calcitonin. The illustration below depicts the negative feedback loop controlling the release of calcitonin.
2. Males must have constant levels of both testosterone and lutenizing hormone (LH) for the testes to produce sperm and function properly. LH stimulates testosterone production, but testosterone inhibits LH production. Thus if testosterone in the blood rises it inhibits LH and then less testosterone is produced until the testosterone level falls below a level that it inhibit LH production which starts up again and promotes more testosterone production. In this way a constant level of testosterone is maintained.
3. When one eats foods high in carbohydrates, they are broken down by the digestive system into simpler sugars and carried by the blood. This causes the pancreas to produce the hormone, insulin, that stimulates cells to absorb sugar from the blood and the liver to convert blood sugar into glycogen. This lowers blood sugar levels thus causing a cutoff of the production of insulin, when
blood sugar is low enough, the pancreas secretes another hormone glucagon that stimulates the liver and muscles to convert glycogen into glucose raising blood sugar, which, turn inhibits glucagon production.
4. When one is startled or senses danger the adrenal glands are called into action by the hypothalamus (the nexus between the nervous system and the endocrine system), which releases norepinephrine and epinephrine (adrenaline) into the blood stream effecting a change of up to 100% increase in the body's metabolic rate. The following chart depicts what is called the fight of flight mechanism.
The major endocrine glands and their functions : Hormone(s) Secreted § For each of the six hormones secreted by the anterior Pituitary gland, the hypothalamus secretes two hormones: one that stimulates release and one that inhibits release. Oxytocin Antidiuretic Hormone (Vasopressin) Corticotropin Primary Action Control the function of the anterior pituitary gland
Endocrine Gland Hypothalamus
§ § Pituitary Gland §
Released from the posterior pituitary gland Stimulates release of adrenal hormones involved in stress
(Anterior) § § Thyrotropin Follicle Stimulating Hormone
reactions Stimulates the release of thyroid hormones In females stimulates follicle growth and estrogen secretion in the ovaries, In Males promotes spermatogenesis in the testes . In females stimulates ovulation, corpus luteum formation; In males, promotes testosterone secretion. Stimulates and sustains milk production. Generalized growth promoting effects in juveniles and plays role in glucose and protein metabolism in adults. Causes uterine contractions leading to birth. Controls water balance in the body. Regulates carbohydrate and lipid metabolism. Lowers calcium levels in the blood. Elevates calcium levels in the blood. Raises blood sugar level, helps control lipid and protein metabolism. Promotes sodium reabsorbtion in the kidney – salt and water balance Influences sexual maturity, general growth, onset of puberty. Raises blood sugar level, increase heart rate and force of heart contractions Promotes constriction and dilation of blood vessels Key role in spermatogenesis, development of genitals and maintenance of accessory and secondary sex traits. Key role in egg production, stimulates thickening of uterine lining for pregnancy, development of genitals and maintenance of accessory and secondary sex traits. Prepares and maintains uterine lining, stimulates breast
Prolactin Growth Hormone
Pituitary Gland (Posterior) Thyroid
§ § § § § §
Oxytocin (manufactured in Hypothalamus) Antidiuretic Hormone (Vasopressin) Triiodothyronine, Thyroxine Calcitonin Parathyroid Hormone Glucocorticoids
Parathyroid Adrenal (cortex)
§ Adrenal (medulla) §
Sex Hormones (Androgens, Estrogen, Progestrogen) Epinephrine (adrenaline)
§ Testes §
development. Lowers blood sugar by stimulating glucose uptake by cells and liver conversion of glucose into glycogen. Raises blood sugar by stimulating liver to convert glycogen and fat into glucose. Promote development of infectionfighting abilities and lymphocyte function in immune system. Influences daily biorhythums, sexual activity and sexual development.
§ Thymus Pineal § §
Glucagon Thymosin Melatonin