The Endocrine System Major Glands and What They Do: Hypothalamus- controls release and inhibition of hormones via the pituitary gland. It releases hormones in capillaries in a region at the base of the hypothalamus which then drain into port vessels(short blood vessels) that subdivide into the anterior pituitary. This is the direct route for the hormones to get to the hypothalamus’ errand boy, the pituitary gland. Pituitary Gland- located at the base of human brain and has two parts. Anterior lobe produces HGH and promotes body growth by speeding up protein synthesis. It also produces LH, which promotes breast development and milk secretion in females. Posterior lobe stores and then releases two hormones that are produced in hypothalamus. The first, ADH, stimulates water reabsorption in the kidneys. The second, oxytocin, stimulates contractions in the uterus during birth. Pineal Gland- small mass of tissue in the center of the brain. Secretes melatonin, which regulates the functions related to light and to seasons marked by changes in day length. Most of the functions are related to biological rhythms associated with reproduction. Thyroid Gland- consists of two lobes located on the ventral surface of the trachea and produces T3 and thyroxine (T4), which regulates metabolism. Also produces calcitonin, which regulates the level of calcium in the blood. The thyroid plays a major role in maintaining homeostasis in the body. Parathyroid Glands- Four tiny masses of glandular tissue embedded in the thyroid that produce parathyroid hormone, which regulate calcium metabolism by increasing calcium reabsorption in kidneys and the conversion of vitamin D into its active form. Adrenal Glands- Two pyramid shaped glands adjacent to the kidneys, which consist of an outer cortex, and an inner medulla. Cortex secretes steroids called corticosteroids. Two main types of steroid hormones (mineralocorticoids and glucocorticoids) control mineral metabolism in the body and accelerate mineral reabsorption in the kidneys and control glucose metabolism and protein synthesis in the body. It responds to endocrine signals, not nervous input.

(Cortex cont’d) Stress can cause the hypothalamus to secrete a hormone that stimulates the release of ACTH, which stimulates cells of the adrenal cortex to synthesize and secrete the corticosteroids. A third group of corticosteroids are sex hormones. Medulla has close functional ties with the nervous system and secretory cells are derived from cells of the neural crest. produces epinephrine (adrenaline) and norepinephrine (noradrenaline). Epinephrine increases heart rate, blood pressure, and the blood supply to the skeletal muscle. Norepinephrine intensifies the effects of epinephrine. Both intensify the effects of the sympathetic nervous system and are responses to positive or negative stress. The medulla is under control of the nerve cells from sympathetic nervous system and when excited, they release acetylcholine which stimulates the release of epinephrine. Pancreas- the exocrine portion has endocrine cell clusters called the islets of Langerhans scattered throughout. Produces insulin and glucagon and secretes them directly into the circulatory system. Alpha cells produce insulin, which promotes the passage of glucose molecules into body cells and regulates glucose metabolism. Beta cells produce glucagon, which stimulates breakdown of glycogen to glucose in the liver and releases fat so it can be used as carbs. By negative feedback, the blood glucose concentration determines the relative amount of either hormone to by secreted by the islet cells. Type I diabetes- insulin dependent. An autoimmune disorder in which the immune system attacks pancreas cells. Type II diabetes- insulin independent. Characterized by either a deficiency of insulin or by reduced responsiveness in target cells due to some change in insulin receptors. Ovaries- secretes estrogen and encourages development of secondary female characteristics. Testes- secrete androgens, which promote secondary male characteristics. (Testosterone is androgen).

Major Hormones: Antidiuretic hormone (ADH)- part of a complex feedback system that helps regulate the osmolarity in the blood. (Posterior Pituitary) Growth hormone (GH)- a protein that promotes growth directly as well as stimulates the production of growth factors. (Anterior Pituitary) Insulinlike growth factors- produced by the liver and circulate in blood plasma and directly stimulate bone and cartilage growth. (Anterior Pituitary/ Liver) Prolactin (PRL)- a protein very similar to GH. Produces a variety of effects on different species, but in mammals it stimulates the mammary gland’s growth and milk synthesis. Follicle-stimulating hormone (FSH) and Luteinizing hormone (LH)- also called gonadotropins, are both similar glycoproteins. They stimulate the activities of the male and female gonads. (Anterior Pituitary) Thyroid-stimulating hormone (TSH)- also a similar glycoprotein, and it stimulates the production of hormones by the thyroid gland. (Anterior Pituitary) ACTH- stimulates the production and secretion of steroid hormones by the adrenal cortex. (Anterior Pituitary) MSH (Melatonin)- regulates the activity of pigment containing cells in the skin of some vertebrates. Secreted at night, and the amount that is secreted determines how long your night is. Triiodothyronine (T3)- contains three iodine atoms and Thyroxine (T4) contains four hydrogen atoms. (Thyroid Gland) Parathyroid Hormone (PTH)- raises blood levels of calcium and has an effect opposite of the effect of calcitonin. (Parathyroid Glands) Glucagon and Insulin- antagonistic hormones that regulate the concentration of glucose in the blood. When blood glucose level exceeds the normal level, insulin is released. When the blood glucose levels drops below the set point, glucagon is released. Epinephrine and Norepinephrine- adrenaline and norepinephrine (Adrenal Glands) Estrogen- female sex hormone (ovaries) Progesterone- works with estrogen to bring about the menstrual cycle. Testosterone- male sex hormone (testes)

Summary and Vocabulary The endocrine system is made up of hormone secreting glands and affects the communication within the body. Together with the nervous system and immune system, together the three help the body respond and cope with different types of stress. Hormones are chemicals that assist in regulating body functions. The glands that produce them release them into the blood stream and are then taken to various places throughout the body. The pituitary gland is sometimes known as the “master gland” because when stimulated by the hypothalamus, it releases various hormones that control other glands in the body. HormoneProduced by Involved in regulating ThyroxineThyroid glandMetabolic rate InsulinPancreasLevel of blood sugar MelatoninPineal gland Biological rhythms, sleep Cortisol, Norepinephrine, Epinephrine, Adrenaline Adrenal glands Bodily functions during stressful and emotional states Androgens Testes (and ovaries and adrenal glands to a lesser extent) Male secondary sex characteristics, sexual arousal in males and females Estrogens Ovaries (and testes and adrenal glands to a lesser extent) Breast development and menarche in females Progesterone Ovaries (and testes and adrenal glands to a lesser extent) Preparation of uterus for implantation of fertilized egg

Summary and Vocabulary (Cont’d) Endocrine Functions: Growth Repair Sexual reproduction Digestion Maintaining homeostasis How Hormones Work: A hormone will only act on a part of the body if it fits, hence there are specific target sites for specific hormones. These target sites (such as an organ), has specially shaped receptors and if the hormone fits, it will go to work. Feedback loops allow the body to maintain its delicate balance of hormone levels. Once the hormone has been released, its effects on other organs are sent as signals to the pituitary gland who responds to what the body needs. Glands: A gland is a group of cells that produces a secretes chemicals. It selects and removes materials from the blood, processes them, and secretes the finished chemical product for use somewhere in the body. Vocab: Positive feedback- process that amplifies a small change (reinforcement change) Negative feedback- a response that opposes the original stimulus