FunctionsThe endocrine system influences almost every cell,organ, and function of our bodies. The endocrinesystem is instrumental in regulating mood, growth anddevelopment, tissue function, metabolism, and sexualfunction and reproductive processes.In general, the endocrine system is in charge of bodyprocesses that happen slowly, such as cell growth.Faster processes like breathing and body movementare controlled by the nervous system. But even thoughthe nervous system and endocrine system are separatesystems, they often work together to help the bodyfunction properly.
Hormones• The foundations of the endocrine system are the hormones and glands. As the bodys chemical messengers, hormones transfer information and instructions from one set of cells to another. Many different hormones move through the bloodstream, but each type of hormone is designed to affect only certain cells.There are three general classes (groups) of hormones. These are classified into three groups by chemical structure, not function.
-1) Steroid hormones including prostaglandins which function especially in a variety of female functions (aspirin inhibits synthesis of prostaglandins, some of which cause “cramps”) and the sex hormones all of which are lipids made from cholesterol,2) Amino acid derivatives (like epinephrine) which are derived from amino acids, especially tyrosine, and
-3) Peptide hormones (like insulin) which is the most numerous/diverse group of hormones. A gland is a group of cells that produces and secretes, or gives off, chemicals. A gland selects and removes materials from the blood, processes them, and secretes the finished chemical product for use somewhere in the body.
Exocrine GlandsSome types of glands release their secretions inspecific areas. For instance, exocrine glands, suchas the sweat and salivary glands, releasesecretions in the skin or inside the mouth.Mammary glands, lacrimal glands, gastric glands,sebaceous glands, mucous glands are alsoexocrine glands. Endocrine glands, on the otherhand, release more than 20 major hormonesdirectly into the bloodstream where they can betransported to cells in other parts of the body.
Endocrine GlandsThe major glands that make up the human endocrine system include the: 1. Hypothalamus 2. Pituitary gland (hypophysis) 3. Thyroid gland 4. Parathyroid glands 5. Thymus 6. Adrenal glands 7. Pancreas 8. Pineal gland (epiphysis) 9. Reproductive glands (which include the ovaries and testes)
HypothalamusThe hypothalamus, a collection of specializedcells that is located in the lower central part ofthe brain, is the main link between theendocrine and nervous systems. Nerve cells inthe hypothalamus control the pituitary glandby producing chemicals that either stimulateor suppress hormone secretions from thepituitary.
The Pituitary GlandThe pituitary gland is located at the base of the humanbrain. It is suspended from the hypothalamus, to whichit is connected by a short stem. The gland consists oftwo parts: the anterior lobe (adenohypophysis) and theposterior lobe (neurohypophysis).The anterior lobe secretes at least seven hormones.One hormone, the human growth hormone (HGH),promotes body growth by accelerating proteinsynthesis. This hormone is also knownas somatotropin. A deficiency of the hormone resultsin dwarfism; an oversecretion results in gigantism.
Another hormone of the anterior pituitary isprolactin, also called lactogenic hormone (LH).This hormone promotes breast development andmilk secretion in females. A third hormone isthyroid-stimulating hormone (TSH). The functionof TSH is to control secretions of hormones fromthe thyroid gland. A fourth hormone isadrenocorticotropic hormone (ACTH). Thishormone controls the secretion of hormonesfrom the adrenal glands.
-There are three more hormones produced in the anteriorlobe of the pituitary gland. The first is follicle-stimulatinghormone (FSH). In females, FSH stimulates thedevelopment of a follicle, which contains the egg cell; inmales, the hormone stimulates sperm production. The nexthormone is luteinizing hormone (LH). In females, LHcompletes the maturation of the follicle and stimulates theformation of the corpus luteum, which temporarily secretesfemale hormones. In males, LH is interstitial cell-stimulatinghormone (ICSH), which stimulates the production of malehormones in the testes. The final hormone is melanocyte-stimulating hormone (MSH), which stimulates productionof the pigment melanin.
-The posterior pituitary gland manufactures twohormones that are produced in theneurosecretory cells in the hypothalamus, andpass into the neurohypophysis through the axonsof these cells. When they are needed they arereleased. The first hormone is antidiuretichormone (ADH). This hormone stimulates waterreabsorption in the kidneys. It is alsocalled vasopressin. The second hormone isoxytocin, which stimulates contractions in themuscles of the uterus during birth.
The Thyroid GlandThe thyroid, located in the front part of the lowerneck, is shaped like a bow tie or butterfly andproduces the thyroid hormones thyroxine andtriiodothyronine. These hormones control therate at which cells burn fuels from food toproduce energy. Thyroid hormones affect threefundamental physiologic processes: cellulardifferentiation, growth, and metabolism.Thyroxine production depends on the availabilityof iodine.
-The production and release of thyroid hormones is controlled by thyrotropin, which is secreted by the pituitary gland. The more thyroid hormone there is in a persons bloodstream, the faster chemical reactions occur in the body.The thyroid gland also produces another hormone called calcitonin, and the parathyroid glands secrete parathyroid hormone. Parathyroid hormone and calcitonin participate in control of calcium and phosphorus homeostasis and have significant effects on bone physiology.
The Parathyroid GlandsThe parathyroid glands are located on theposterior surfaces of the thyroid gland. Theyare tiny masses of glandular tissue thatproduce parathyroid hormone, alsocalled parathormone. Parathyroid hormoneregulates calcium metabolism in the body byincreasing calcium reabsorption in thekidneys, and by increasing the uptake ofcalcium from the digestive system.
The Thymus GlandThe thymus is a gland that forms part of the immune system. It is situated in the upper part of the chest, behind the breastbone, and is made up of two lobes that join in front of the trachea. Each lobe is made of lymphoid tissue, consisting of tightly packed white blood cells and fat. The thymus enlarges from about the 12th week of gestation until puberty, when it begins to shrink. It secretes thymosins, which influence the development of the T- lymphocytes of the immune system. Its function is to transform lymphocytes (white blood cells developed in the bone marrow) into T-cells (cells developed in the thymus). These cells are then transported to various lymph glands, where they play an important part in fighting infections and disease. Swelling of lymph glands and fever are a signal that immune cells are multiplying to fight off invaders of the body: bacteria, fungi, viruses or parasites.
The Adrenal (Suprarenal) Glands• The adrenal glands are two pyramid-shaped glands lying atop the kidneys. The adrenal glands consist of an outer portion, the cortex, and an inner portion, the medulla.• The adrenal cortex secretes a family of steroids called corticosteroids. The two main types of steroid hormones are mineralocorticoids and glucocorticoids. Mineralocorticoids, such as aldosterone, control mineral metabolism in the body. They accelerate mineral reabsorption in the kidney. Mineralocorticoid secretion is regulated by ACTH from the pituitary gland. Glucocorticoids, such as cortisol and cortisone, control glucose metabolism and protein synthesis in the body. Glucocorticoids are also anti-inflammatory agents.
Adrenal MedullaThe adrenal medulla produces twohormones: epinephrine (adrenaline) andnorepinephrine (noradrenaline). Epinephrineincreases heart rate, blood pressure, and theblood supply to skeletal muscle. Epinephrinefunctions in stressful situations to promote thefight–flight response. Norepinephrine intensifiesthe effects of epinephrine. Both hormonesprolong and intensify the effects of thesympathetic nervous system.
PancreasThe pancreas is located just behind the stomach. Its endocrine portion consists of cell clusters called the islets of Langerhans.The pancreas produces two hormones: insulin and glucagon. Insulin is a protein that promotes the passage of glucose molecules into the body cells and regulates glucose metabolism. In the absence of insulin, glucose is removed from the blood and excreted in the kidney, a condition called diabetes mellitus. Diabetes mellitus is characterized by glucose in the urine, heavy urination, excessive thirst, and a generally sluggish body metabolism.
-The second pancreatic hormone, glucagon,stimulates the breakdown of glycogen toglucose in the liver. It also releases fat fromthe adipose tissue so the fat can be used forthe production of carbohydrates.The pancreas is also associated with thedigestive system because it produces andsecretes digestive enzymes (Acinar cells).
Pineal Gland (epiphysis)The pineal gland is a tiny gland in themidbrain. Its functions are largely unknown,but it seems to regulate mating behaviors andday–night cycles.
The Reproductive GlandsThe gonads are the main source of sexhormones. Both men and women have gonads. Inmen the male gonads, or testes, are located inthe scrotum. They secrete hormones calledandrogens, the most important of which istestosterone. These hormones tell a boys bodywhen its time to make the changes associatedwith puberty, like penis and height growth,deepening voice, and growth in facial and pubichair. Working with hormones from the pituitarygland, testosterone also tells a guys body whenits time to produce sperm in the testes.
-A girls gonads, the ovaries, are located in her pelvis.They produce eggs and secrete the female hormonesestrogen and progesterone. Estrogen is involved whena girl begins to go through puberty. During puberty, agirl will experience breast growth, will begin toaccumulate body fat around the hips and thighs, andwill have a growth spurt. Estrogen and progesteroneare also involved in the regulation of a girls menstrualcycle. These hormones also play a role in pregnancy.