Endocrine System Endocrine System Documentation 0 Revised: August 23, 2005
ENDOCRINE SYSTEM The endocrine system is closely related to the nervous system in its functioning. This system, like the nervous, helps to coordinate and regulate the activities of cells, tissues and organs of the body and maintain homeostasis. While the nervous system is general, has a rapid effect, the actions of the endocrine system are generally slow and go on for long periods of time. In contrast to exocrine glands whose secretions are transported through ducts to their respective destinations, endocrine glands are ductless. The endocrine glands secrete biologically active chemicals called hormones directly into the blood. Many endocrine glands are discrete organs whose primary functions are the production and secretion of hormones. The pancreas functions as both an exocrine and an endocrine gland; the endocrine portion of the pancreas is composed of microscopic structures called the pancreatic islets, or islets of Langerhans. The concept of the endocrine system, however, must be extended beyond these organs. In recent years, it has been discovered that many other organs in the body secrete hormones. When these hormones can be demonstrated to have significant physiological functions, the organs that produce them may be categorized as endocrine glands, although they serve other functions as well. A partial list of the endocrine glands should include the heart, liver, hypothalamus, and kidneys. Hormones affect the metabolism of their target organs and help regulate total body metabolism, growth and reproduction. As the body begins to experience the changes of puberty, the nervous and endocrine systems begin to impact bodily functions. Changes in the brain and pituitary gland help us evolve from adolescents to teens and then to adults. The word endocrine describes the cells, tissues, and organs that secrete hormones into the body. Both the nervous and endocrine systems work together to control homeostasis by way of electrical impulses and chemical messengers. Neurons tend to act over short distances within a few milliseconds while hormones can take up to several hours or more to bring about their responses. These two systems coordinate their activities like an interlocking supersystem. Certain portions of the nervous system stimulate or inhibit the release of hormones; meanwhile hormones are very capable of stimulating or inhibiting the transmission of nerve impulses. In this partnership the endocrine system is primarily involved with physiologic function. We ll come back to this later in this document. The product of endocrine glands is hormones. Hormones are chemical messengers of the body: made primarily from proteins and steroids. They have an effect on target organs and cells. Endocrine System Documentation 1 Revised: August 23, 2005
Primary Mechanisms of Endocrine Disease The endocrine system can be affected by numerous diseases. They usually will present themselves as tumors or other abnormalities due to glands secreting too much or too little of their hormones. Production/secretion of too little hormone is called hyposecretion, and production/secretion of too much is called hypersecretion. It could be any number of mechanisms in place to cause either of these conditions to exist. Hypersecretion tumors could cause an abnormal increase in numbers of endocrine tissue cells which causes an increase in hormone secretions. Another cause could be autoimmunity caused by the immune system ill-functioning. Another could be the failure of the feedback mechanisms that regulate secretion. Hyposecretion this could be because of tissue death caused by a blockage or failure of blood supply, or because of abnormal operation of regulatory feedback loops. Possibly abnormalities of immune function could cause this as well. The Major Glands of the Endocrine System Hypothalamus this is the link between the body/mind and nerve/endocrine function. It resides in the brain. Its main purpose is homeostasis. Example: it affects blood pressure, body temperature, and fluid and electrolyte balance The hypothalamus has a primary influence over the pituitary gland, which in turn, controls other endocrine glands by way of hormones. It does this by secreting hormones with either a releasing or inhibiting affect on the pituitary hormones. Pathologic Conditions of the Hypothalamus: Psychosocial dwarfism, failure-to-thrive syndrome and delayed tissue healing (all of which result from stress, emotional disorders and deprivation) can result from suppression of hypothalamic release of growth hormone. Pituitary this is the so called master gland. It is situated beneath the hypothalamus in the brain and is made up of two lobes, the anterior and posterior. This is at about eye level. Many people believe that this is actually the third eye. Others believe it is actually a different gland that deserves this title of the third eye, the pineal gland. The pituitary secretes hormones that regulate growth, fluid balance and lactation. It is a source of what is known as tropic hormones which are hormones that have a stimulating effect on other endocrine glands. There is a difference between the two lobes of the pituitary. The posterior lobe is not considered a true endocrine gland as it only stores and releases hormones. It does not synthesize them as well. It secretes two major hormones. The larger anterior lobe secretes six major hormones. Endocrine System Documentation 2 Revised: August 23, 2005
Anterior Lobe Hormones: Growth hormone (GH) stimulates and controls growth of bone and soft tissue, and increases glycogen synthesis and fat metabolism. Thyroid-stimulating hormone (TSH) stimulates the thyroid gland to produce thyroid hormones for metabolism regulation. Adrenocorticotropic hormone (ACTH) stimulates the growth and development of the adrenal cortex; stimulates the adrenal cortex to produce cortisol. Prolactin (PRL) stimulates the production of milk in the mammary glands of the breast; promotes breast development during pregnancy. Interestingly enough, this is found in both men and women. Follicle stimulating hormone (FSH) stimulates development of the follicle which is a structure in the ovaries that produces eggs. It also stimulates production of sperm. Luteinizing hormone (LH) this acts with FSH to develop the follicle and promotes ovulation. It also stimulates the secretion of testosterone from the testes. Posterior Lobe Hormones: Antidiuretic hormone (ADH) this is also referred to as vasopressin. It increases water reabsorption in the kidney to decrease urine formation. Oxytocin stimulates contraction of the uterus in childbirth and the milk letdown response causing milk ducts to release milk. Pathologic Conditions of the Pituitary: Because growth hormones are released during sleep, a disrupted sleep pattern could be the cause of fibromyalgia and other pain and fatigue syndromes, and the body could have problems with cellular repair consequently. Therapeutic massage has been shown to have the beneficial influence of bringing about more restful sleep patterns. Stress over a long period of time will generate large amounts of glucocorticoids which are known to suppress the immune system. The use of any form of body work that reduces stress will also help to reduce the effects of stress in the body. Pineal - this is a small, cone-shaped gland that is attached to the upper portion of the thalamus and encapsulated by the meninges covering the brain. It weighs only about 1/5 of a gram in a child and begins to regress in size at about age 7. In an adult it appears to be a thickened strand of fibrous tissue. While there is no direct nervous system connection, it is none the less able to be innervated by sympathetic nerve fibers. All functions of this gland have not yet been identified. This is truly the third eye spoken about in many Eastern philosophies. These theories show it to be the gland of inner sight or awareness. Its major function is to secrete its principal hormone known as melatonin. During the daytime, neural pathways from the retinas in the eyes depress the secretion of melatonin. Its secretion occurs at night only. The pineal is involved in the regulation of circadian rhythms, including the reproductive cycle. Endocrine System Documentation 3 Revised: August 23, 2005
As this gland is the body s clock, gonadal maturation begins when there is a decrease in melatonin secretions. Excessive secretion is associated with a delay in the onset of puberty. Secretion is highest in children of age s one through five. This makes sense when you remember that growth hormone is also secreted at night and also mainly active in children. Melatonin is responsible for us being able to fall asleep, stay asleep, and sleep soundly. By the time we reach age 50, the pineal all but stops production of melatonin. This could explain why as we grow older we seem to sleep less. Older adults often complain that while they fall asleep early (maybe by nine or ten PM) they are often wide awake again by three or four AM. Pathological Conditions of the Pineal Gland: Not being able to fall asleep Not being able to stay asleep for more than a few hours Not sleeping soundly waking up several times through the night Various styles of therapeutic massage will help promote and support effective sleep patterns. Parathyroid this is composed of four to five tiny glands embedded in the posterior side of the thyroid gland. It functions to secrete parathyroid hormone. This promotes calcium movement from bone tissue and absorption from the intestines. Pathologic Conditions of the Parathyroid Gland: An excess of parathyroid hormone causes too much calcium to be removed from bone giving us weak bones. A deficiency of parathyroid hormone can cause hypocalcemic tetany. Symptoms include loss of sensation, muscle twitches, uncontrolled spasm and convulsion. In hyperparathyroidism there will be mild to severe skeletal pain and possibly osteoporosis. Be sure to provide appropriate referral if there has been no attempt from the individual to discover the underlying cause of the condition. Thyroid this is on the trachea below the thyroid cartilage. With a right and a left lobe, it is shaped like a bowtie. This gland is heavier in women than in men. Thyroxine (T4) this increases metabolic rate by way of catabolism of carbohydrates. Triiodonthyronine (T3) together with Thyroxine, they regulate the rate of growth of an individual. Calcitonin this lowers blood calcium levels by inhibiting the release of calcium from bone tissue. Endocrine System Documentation 4 Revised: August 23, 2005
Pathologic Conditions of the Thyroid Gland: Hyperthyroidism is the second most common endocrine disorder after diabetes and it most often affects women. Mostly caused by autoimmune dysfunction, the symptoms would include increased metabolic rate, excessive sweating, weight loss, fatigue, nervousness, loose stools, tachycardia (an unusually rapid heart rate of over 100 beats per minute), warm moist skin, hand tremor and hyperactivity. This can mimic manicdepression and usually there is a goiter (an enlarged thyroid gland). Grave s Disease is another form of hyperthyroidism and will include a goiter along with abnormal eyeball protrusion resulting from excess fluid behind the eye. This runs in families, is associated with autoimmune problems, and is most common in women between 20 and 40 years of age. Hypothyroidism can actually result from treatment of hyperthyroidism by radioactive iodine, overdosing of antithyroid medication, or partial or complete thyroidectomy. Symptoms would include weakness, fatigue, lower metabolic rate, constipation, hoarseness, bradycardia (abnormally slow heart rate), skin dryness, weight gain to the point of obesity, sluggishness and slowed mental function with psychotic behavior. If thyroid hormones are absent in a fetus or during infancy, it can result in cretinism (dwarfism with mental retardation). Thymus this is located deep to the sternum, between the lungs at the level of T-4 & T-5. This produces T-cells (thymus-dependant cells) which are specialized lymphocytes used in body immunity. This gland is large in children, providing some evidence that its production of hormones may slow down with age. Hormones Secreted: Thymosin this stimulates the t-cells in the body that have already been produced. Adrenal this is a pair of pyramid shaped glands, each on top of a kidney. Sometimes referred to as the suprarenal glands. Each consists of an inner portion called the medulla, and an outer layer called the cortex. Adrenal Cortex this secretes three major glucose producing hormones derived from cholesterol. ACTH from the pituitary gland, which receives its messages from the hypothalamus, stimulates the release of these three hormones. Cortisol this is released in response to stress. It increases blood sugar levels, fatty acid immobilization and immunosupression. Aldosterone this helps regulate blood pressure by promoting sodium uptake and potassium secretion by the kidneys. Sex hormones these regulate sexual development and sex drive. They are as follows: Testosterone causes masculinization. Estrogens causes feminization. Progesterone another feminization hormone Endocrine System Documentation 5 Revised: August 23, 2005
Adrenal Medulla the tissue structure in this portion is similar to nerve tissue and functions as part of the sympathetic nervous system. Epinephrine sometimes called adrenaline, produces a sympathetic response of fight or flight, or an alarm response to stress. This can cause an increase in heart rate. Norepinephrine sometimes called noradrenalin, produces a sympathetic response slightly less intense than that produced by epinephrine. Affects peripheral vasoconstriction, raising blood pressure. Studies have shown that various methods of therapeutic massage can help dissipate the concentration of adrenal medulla hormones while reducing cortisol levels. This promotes improved sleep, better digestion, increased immune function and improved tissue repair. This all supports the body to return to a state of homeostasis. Ovaries these are the female gonads located in the pelvic cavity that produce sex hormones identical to those of the adrenal cortex. Because this is their primary function, they secrete larger amounts than the adrenal cortex and secrete them in a cyclical way to regulate the menstrual cycle, support pregnancy, and prepare for lactation. Estrogen this regulates menstrual changes and sex drive. It is responsible for the development of secondary sexual organs (mammary glands, vagina and the uterine tubes), and the distribution of fat. Progesterone this prepares the uterus for implantation of a fertilized egg and prevents spontaneous abortion by preserving the lining of the uterus. Testes these are the male gonads located in the pelvic cavity that produce sex hormones identical to those of the adrenal cortex. Again, like in the ovaries, they secrete larger amounts. Testosterone this is the main male hormone. This regulates the production of sperm cells in the testes and the development of the penis and accessory glands. It also causes development of body and facial hair, a deeper voice and larger muscles and bones than in females. Pancreas this is a long, slender gland located deep to the stomach. It is a dual gland in that it is both exocrine and endocrine. While its enzymes aid in digestion, it also produces hormones. There are islands of cells called the islets of Langerhans interspersed within the exocrine gland tissues. It is these islets that produce the hormones. Insulin this hormone is produced by the beta cells of the islets. It lowers the blood sugar levels by promoting glucose uptake by the cells. Glucagon this hormone is produced by the alpha cells of the islets. It increases blood sugar levels by releasing glucose from glycogen stored in the liver. Endocrine System Documentation 6 Revised: August 23, 2005
Pathological conditions of the pancreas: Benign tumors will occasionally cause high insulin levels. More often though, high insulin levels occur in diabetic people who take insulin without eating properly. This result is called insulin reaction (too much insulin). If more glucose enters the blood, glucose levels fall causing hypoglycemia (low blood sugar). Symptoms will be confusion and weakness. True hypoglycemia is rare, usually this is caused by improper diet. A hypofunction disorder would be diabetes. This is caused by the pancreas not producing enough insulin or stopping insulin production. Now cells will not absorb glucose causing incr3eased amount to remain in the blood stream hyperglycemia. Huge amounts of water will accompany the glucose through the kidneys as it is a diuretic. This is how the excess is released in the urine. Symptoms are dehydration, high blood sugar, and coma induced by acidosis depressing the cerebral cortex. At this point the breathing rate will increase. Differences between endocrine and exocrine glands: The endocrine glands are ductless and secrete hormones directly into the blood stream or diffuse them into nearby tissues. The exocrine glands have ducts and secrete their products directly into ducts that open to specific areas. General characteristics and function of endocrine glands: Helps regulate metabolic processes Regulates chemical make-up of extracellular fluid Helps transport substances through membranes Helps regulate water and electrolyte balances homeostasis Plays a role in the integration of growth and development Plays a role in the reproductive process Hormones: Definition an organic substance secreted by a cell that effects the function of another cell Are released into extracellular spaces The physiological action is restricted to the target cell Target cells or receptor cells are specific only to the hormone meant for it Controls of hormonal secretions: Negative feedback system this is thy typical regulatory system. It works like all other negative feedback systems in the body. An example would be a thermostat in the room. If you set the temperature at 65 with the heat on, when the thermostat reads a temperature of below 65, it will start the furnace. If the air conditioning is on and the thermostat reads a temperature of above 65, it starts the air conditioning unit. Nerve control if you remember, a chemical found in a synapse is called a neurotransmitter. When this same chemical is found in the bloodstream or a tissue, it is called a hormone. Neurotransmitters act on adjacent cells, where hormones may travel long distances in the body before they reach their target cells. The main differences Endocrine System Documentation 7 Revised: August 23, 2005
between the endocrine system and the nervous system control are speed and duration of effect. The nervous system is fast acting with a short duration of effect, where the endocrine system is slow acting with a long duration of effect. This gives us a balance of control, with the nervous system responding quickly and the endocrine system taking over to sustain a response. Stress because the major repair and energy restoring mechanisms of the body are supported most effectively in the parasympathetic pattern and because most energy is expended and tissue damage created during fight-or-flight activity, we can begin to see the importance of supporting parasympathetic function to allow sufficient time for restoration and repair of the body. A general rule of thumb is that for every 15 minutes of stressful activity, the body requires about 45 minutes of parasympathetic balancing time. Actually in a healthy person, 25% of the day involves stressful activity with parasympathetic restoration processes making up another 25%. The other 50% of the time is taken up with both actions taking place at the same time. Dysfunction will result when stress dominates a demanding lifestyle will create dysfunction. The endocrine system secretes hormones that regulate body functions. Stress will affect this system in a number of ways: Stress causes the hypothalamus to release hormones to activate the fight-or-flight response of the sympathetic division of the autonomic nervous system. This causes increased levels of glucose in the bloodstream, increased heart and breathing rate, higher blood pressure and more blood to flow to the muscles and nervous systems. Prolonged stress may cause constant secretion of fight-or-flight inducing hormones which, in turn, will decrease immunity, cause gastrointestinal ulcers, and increase blood pressure. Endocrine System Documentation 8 Revised: August 23, 2005