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The Endocrine System and Its Disorders Comprehensive Study Notes
What Is the Endocrine System? In general, the endocrine system is in charge of body processes that happen slowly, such as cell growth. Faster processes like breathing and body movement are controlled by the nervous system. But even though the nervous system and endocrine system are separate systems, they often work together to help the body function properly. The foundations of the endocrine system are the hormones and glands. As the body's 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. Which of these glands has the best name? Hypothalamus Pituitary Parathyroid Adrenal VoteView Results 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. Some types of glands release their secretions in specific areas. For instance, exocrine (pronounced: EK-suh-krin) glands , such as the sweat and salivary glands, release secretions in the skin or inside the mouth. Endocrine glands , on the other hand, release more than 20 major hormones directly into the bloodstream where they can be transported to cells in other parts of the body. The major glands that make up the human endocrine system include the:
- hypothalamus
- pituitary gland
- thyroid
- parathyroids
- adrenal glands
- pineal body
- reproductive glands (which include the ovaries and testes)
Hypothalamus
The hypothalamus (pronounced: hi-po-THAL-uh-mus), a collection of specialized cells that is located in the lower central part of the brain, is the main link between the endocrine and nervous systems. Nerve cells in the hypothalamus control the pituitary gland by producing chemicals that either stimulate or suppress hormone secretions from the pituitary.
Pituitary
Although it is no bigger than a pea, the pituitary (pronounced: puh-TOO-uh-ter-ee) gland , located at the base of the brain just beneath the hypothalamus, is considered the most important part of the endocrine system. It's often called the "master gland" because it makes hormones that control several other endocrine glands. The production and secretion of pituitary hormones can be influenced by factors such as emotions and changes in the seasons. To accomplish this, the hypothalamus provides information sensed by the brain (such as environmental temperature, light exposure patterns, and feelings) to the pituitary. The tiny pituitary is divided into two parts: the anterior lobe and the posterior lobe. The anterior lobe regulates the activity of the thyroid, adrenals, and reproductive glands. The anterior lobe produces hormones such as:
- growth hormone , which stimulates the growth of bone and other body tissues and plays a role in the body's handling of nutrients and minerals
- prolactin (pronounced: pro-LAK-tin), which activates milk production in women who are breastfeeding
- thyrotropin (pronounced: thy-ruh-TRO-pin), which stimulates the thyroid gland to produce thyroid hormones
- corticotropin (pronounced: kor-tih-ko-TRO-pin), which stimulates the adrenal gland to produce certain hormones The pituitary also secretes endorphins (pronounced: en-DOR-fins), chemicals that act on the nervous system and reduce feelings of pain. In addition, the pituitary secretes hormones that signal the reproductive organs to make sex hormones. The pituitary gland also controls ovulation and the menstrual cycle in women. The posterior lobe of the pituitary releases antidiuretic (pronounced: an-ty-dy-uh-REH-tik) hormone , which helps control the balance of water in the body. The posterior lobe also produces oxytocin (pronounced: ahk-see-TOE-sin), which triggers the contractions of the uterus in a woman having a baby. Thyroid The thyroid (pronounced: THY-royd), located in the front part of the lower neck, is shaped like a bow tie or butterfly and produces the thyroid hormones thyroxine (pronounced: thy-RAHK- sin) and triiodothyronine (pronounced: try-eye-oh-doe-THY-ruh-neen). These hormones control the rate at which cells burn fuels from food to produce energy. The production and release of thyroid hormones is controlled by thyrotropin (pronounced: thy-ruh-TRO-pin), which is secreted by the pituitary gland. The more thyroid hormone there is in a person's bloodstream, the faster chemical reactions occur in the body. Why are thyroid hormones so important? There are several reasons — for example, they help kids' and teens' bones grow and develop, and they also play a role in the development of the brain and nervous system in kids. Parathyroids Attached to the thyroid are four tiny glands that function together called the parathyroids (pronounced: par-uh-THY-roydz). They release parathyroid hormone , which regulates the level of calcium in the blood with the help of calcitonin (pronounced: kal- suh-TOE-nin), which is produced in the thyroid.
little, a teen may be unusually short. Doctors can often treat problems with the endocrine system by controlling the production of hormones or replacing certain hormones with medication. Endocrine problems that can affect teens include: Adrenal insufficiency. This condition occurs when the adrenal glands don't produce enough corticosteroids. The symptoms of adrenal insufficiency may include weakness, fatigue, abdominal pain, nausea, dehydration, and skin changes. Doctors treat adrenal insufficiency with medications to replace corticosteroid hormones. Type 1 diabetes. When the pancreas fails to produce enough insulin, type 1 diabetes (previously known as juvenile diabetes) occurs. In kids and teens, type 1 diabetes is usually an autoimmune disorder, which means that some parts of the body's immune system attack and destroy the cells of the pancreas that produce insulin. To control their blood sugar levels and reduce the risk of developing diabetes problems, kids and teens with this condition need regular injections of insulin. Type 2 diabetes. Unlike type 1 diabetes, in which the body can't produce normal amounts of insulin, in type 2 diabetes the body can't respond to insulin normally. Kids and teens with the condition tend to be overweight. Some kids and teens can control their blood sugar level with dietary changes, exercise, and oral medications, but many will need to take insulin injections like people with type 1 diabetes. Growth hormone problems. Too much growth hormone in kids and teens who are still growing will make their bones and other body parts grow excessively. This rare condition (sometimes called gigantism) is usually caused by a pituitary tumor and can be treated by removing the tumor. The opposite can happen when a kid or teen has a pituitary glad that doesn't produce enough growth hormone. Doctors may treat these growth problems with medication. Hyperthyroidism. Hyperthyroidism is a condition in which the levels of thyroid hormones in the blood are very high. In kids and teens, the condition is usually caused by Graves' disease, an immune system problem that causes the thyroid gland to become very active. Doctors may treat hyperthyroidism with medications, surgery, or radiation treatments. Hypothyroidism. Hypothyroidism is a condition in which the levels of thyroid hormones in the blood are very low. Thyroid hormone deficiency slows body processes and may lead to fatigue, a slow heart rate, dry skin, weight gain, and constipation. Kids and teens with this condition may also grow more slowly and reach puberty at a later age. Hashimoto's thyroiditis is an immune system problem that often causes problems with the thyroid and blocks the production of thyroid hormone. Doctors often treat this problem with medication. Precocious puberty. If the pituitary glands release hormones that stimulate the gonads to produce sex hormones too early, some kids may begin to go through puberty at a very young age. This condition is called precocious puberty. Kids and teens who are affected by precocious puberty can be treated with medication that will help them develop at a normal rate.
The endocrine system is the collection of glands that produce hormones that regulate metabolism, growth and development, tissue function, sexual function, reproduction, sleep, and mood, among other things.The endocrine system is made up of the pituitary gland, thyroid gland, parathyroid glands, adrenal glands, pancreas, ovaries (in females) and testicles (in males). The word endocrine derives from the Greek words "endo," meaning within, and "crinis," meaning to secrete, according to Health Mentor Online. In general, a gland selects and removes materials from the blood, processes them and secretes the finished chemical product for use somewhere in the body. The endocrine system affects almost every organ and cell in the body, according to the Merck Manual. Although the hormones circulate throughout the body, each type of hormone is targeted toward certain organs and tissues, the Merck Manual notes. The endocrine system gets some help from organs such as the kidney, liver, heart and gonads, which have secondary endocrine functions. The kidney, for example, secretes hormones such as erythropoietin and renin. Hormone levels that are too high or too low indicate a problem with the endocrine system. Hormone diseases also occur if your body does not respond to hormones in the appropriate ways. Stress, infection, and changes in the blood's fluid and electrolyte balance can also influence hormone levels. The most common endocrine disease in the United States is diabetes, a condition in which the body does not properly process glucose, a simple sugar. This is due to the lack of insulin or, if the body is producing insulin, because the body is not working effectively, Hormone imbalances can have a significant impact on the reproductive system, particularly in women, Loh explained. Another disorder, hypothyroidism, occurs when the thyroid gland does not produce enough thyroid hormone to meet the body’s needs. Loh noted that insufficient thyroid hormone can cause many of the body's functions to slow or shut down completely. Thyroid cancer begins in the thyroid gland and starts when the cells in the thyroid begin to change, grow uncontrollably and eventually form a tumor, according to Loh. Hypoglycemia, also called low blood glucose or low blood sugar, occurs when blood glucose drops below normal levels. This typically happens as a result of treatment for diabetes when too
Pituitary Gland The pituitary gland , also known as the hypophysis, is a small pea-sized lump of tissue connected to the inferior portion of the hypothalamus of the brain. Many blood vessels surround the pituitary gland to carry the hormones it releases throughout the body. Situated in a small depression in the sphenoid bone called the sella turcica, the pituitary gland is actually made of 2 completely separate structures: the posterior and anterior pituitary glands.
- Posterior Pituitary : The posterior pituitary gland is actually not glandular tissue at all, but nervous tissue instead. The posterior pituitary is a small extension of the hypothalamus through which the axons of some of the neurosecretory cells of the hypothalamus extend. These neurosecretory cells create 2 hormones in the hypothalamus that are stored and released by the posterior pituitary: - Oxytocin triggers uterine contractions during childbirth and the release of milk during breastfeeding. - Antidiuretic hormone (ADH) prevents water loss in the body by increasing the re-uptake of water in the kidneys and reducing blood flow to sweat glands.
- Anterior Pituitary : The anterior pituitary gland is the true glandular part of the pituitary gland. The function of the anterior pituitary gland is controlled by the releasing and inhibiting hormones of the hypothalamus. The anterior pituitary produces 6 important hormones:
- Thyroid stimulating hormone (TSH), as its name suggests, is a tropic hormone responsible for the stimulation of the thyroid gland.
- Adrenocorticotropic hormone (ACTH) stimulates the adrenal cortex, the outer part of the adrenal gland, to produce its hormones.
- Follicle stimulating hormone (FSH) stimulates the follicle cells of the gonads to produce gametes—ova in females and sperm in males.
- Luteinizing hormone (LH) stimulates the gonads to produce the sex hormones —estrogens in females and testosterone in males.
- Human growth hormone (HGH) affects many target cells throughout the body by stimulating their growth, repair, and reproduction.
- Prolactin (PRL) has many effects on the body, chief of which is that it stimulates the mammary glands of the breast to produce milk. Pineal Gland The pineal gland is a small pinecone-shaped mass of glandular tissue found just posterior to the thalamus of the brain. The pineal gland produces the hormone melatonin that helps to regulate the human sleep-wake cycle known as the circadian rhythm. The activity of the pineal gland is inhibited by stimulation from the photoreceptors of the retina. This light sensitivity causes melatonin to be produced only in low light or darkness. Increased melatonin production causes humans to feel drowsy at nighttime when the pineal gland is active.
Adrenal Glands The adrenal glands are a pair of roughly triangular glands found immediately superior to the kidneys. The adrenal glands are each made of 2 distinct layers, each with their own unique functions: the outer adrenal cortex and inner adrenal medulla.
- Adrenal cortex : The adrenal cortex produces many cortical hormones in 3 classes: glucocorticoids, mineralocorticoids, and androgens. 1. Glucocorticoids have many diverse functions, including the breakdown of proteins and lipids to produce glucose. Glucocorticoids also function to reduce inflammation and immune response. 2. Mineralocorticoids, as their name suggests, are a group of hormones that help to regulate the concentration of mineral ions in the body. 3. Androgens, such as testosterone, are produced at low levels in the adrenal cortex to regulate the growth and activity of cells that are receptive to male hormones. In adult males, the amount of androgens produced by the testes is many times greater than the amount produced by the adrenal cortex, leading to the appearance of male secondary sex characteristics.
- Adrenal medulla : The adrenal medulla produces the hormones epinephrine and norepinephrine under stimulation by the sympathetic division of the autonomic nervous system. Both of these hormones help to increase the flow of blood to the brain and muscles to improve the “fight-or-flight” response to stress. These hormones also work to
increase heart rate, breathing rate, and blood pressure while decreasing the flow of blood to and function of organs that are not involved in responding to emergencies. Pancreas The pancreas is a large gland located in the abdominal cavity just inferior and posterior to the stomach. The pancreas is considered to be a heterocrine gland as it contains both endocrine and exocrine tissue. The endocrine cells of the pancreas make up just about 1% of the total mass of the pancreas and are found in small groups throughout the pancreas called islets of Langerhans. Within these islets are 2 types of cells—alpha and beta cells. The alpha cells produce the hormone glucagon, which is responsible for raising blood glucose levels. Glucagon triggers muscle and liver cells to break down the polysaccharide glycogen to release glucose into the bloodstream. The beta cells produce the hormone insulin, which is responsible for lowering blood glucose levels after a meal. Insulin triggers the absorption of glucose from the blood into cells, where it is added to glycogen molecules for storage. Gonads The gonads—ovaries in females and testes in males—are responsible for producing the sex hormones of the body. These sex hormones determine the secondary sex characteristics of adult females and adult males.
- Testes : The testes are a pair of ellipsoid organs found in the scrotum of males that produce the androgen testosterone in males after the start of puberty. Testosterone has effects on many parts of the body, including the muscles, bones, sex organs, and hair follicles. This hormone causes growth and increases in strength of the bones and muscles, including the accelerated growth of long bones during adolescence. During puberty,
- Heart : The cardiac muscle tissue of the heart is capable of producing the hormone atrial natriuretic peptide (ANP) in response to high blood pressure levels. ANP works to reduce blood pressure by triggering vasodilation to provide more space for the blood to travel through. ANP also reduces blood volume and pressure by causing water and salt to be excreted out of the blood by the kidneys.
- Kidneys : The kidneys produce the hormone erythropoietin (EPO) in response to low levels of oxygen in the blood. EPO released by the kidneys travels to the red bone marrow where it stimulates an increased production of red blood cells. The number of red blood cells increases the oxygen carrying capacity of the blood, eventually ending the production of EPO.
- Digestive System : The hormones cholecystokinin (CCK), secretin, and gastrin are all produced by the organs of the gastrointestinal tract. CCK, secretin, and gastrin all help to regulate the secretion of pancreatic juice, bile, and gastric juice in response to the presence of food in the stomach. CCK is also instrumental in the sensation of satiety or “fullness” after eating a meal.
- Adipose : Adipose tissue produces the hormone leptin that is involved in the management of appetite and energy usage by the body. Leptin is produced at levels relative to the amount of adipose tissue in the body, allowing the brain to monitor the body’s energy storage condition. When the body contains a sufficient level of adipose for energy storage, the level of leptin in the blood tells the brain that the body is not starving and may work normally. If the level of adipose or leptin decreases below a certain threshold, the body enters starvation mode and attempts to conserve energy through increased hunger and food intake and decreased energy usage. Adipose tissue also produces very
low levels of estrogens in both men and women. In obese people the large volume of adipose tissue may lead to abnormal estrogen levels.
- Placenta : In pregnant women, the placenta produces several hormones that help to maintain pregnancy. Progesterone is produced to relax the uterus, protect the fetus from the mother’s immune system , and prevent premature delivery of the fetus. Human chorionic gonadotropin (HCG) assists progesterone by signaling the ovaries to maintain the production of estrogen and progesterone throughout pregnancy.
- Local Hormones : Prostaglandins and leukotrienes are produced by every tissue in the body (except for blood tissue) in response to damaging stimuli. These two hormones mainly affect the cells that are local to the source of damage, leaving the rest of the body free to function normally. 1. Prostaglandins cause swelling, inflammation, increased pain sensitivity, and increased local body temperature to help block damaged regions of the body from infection or further damage. They act as the body’s natural bandages to keep pathogens out and swell around damaged joints like a natural cast to limit movement. 2. Leukotrienes help the body heal after prostaglandins have taken effect by reducing inflammation while helping white blood cells to move into the region to clean up pathogens and damaged tissues. What is the Endocrine System?
- Growth hormone: Stimulates growth of bone and tissue (Growth hormone deficiency results in growth failure. Growth hormone deficiency in adults results in problems in maintaining proper amounts of body fat and muscle and bone mass. It is also involved in emotional well-being.)
- Thyroid-stimulating hormone (TSH): Stimulates the thyroid gland to produce thyroid hormones (A lack of thyroid hormones either because of a defect in the pituitary or the thyroid itself is called hypothyroidism.)
- Adrenocorticotropin hormone (ACTH): Stimulates the adrenal gland to produce several related steroid hormones
- Luteinizing hormone (LH) and follicle-stimulating hormone (FSH): Hormones that control sexual function and production of the sex steroids, estrogen and progesterone in females or testosterone in males
- Prolactin: Hormone that stimulates milk production in females The posterior lobe produces the following hormones, which are not regulated by the hypothalamus:
- Antidiuretic hormone (vasopressin): Controls water loss by the kidneys
- Oxytocin : Contracts the uterus during childbirth and stimulates milk production The hormones secreted by the posterior pituitary are actually produced in the brain and carried to the pituitary gland through nerves. They are stored in the pituitary gland. Thyroid Gland
The thyroid gland is located in the lower front part of the neck. It produces thyroid hormones that regulate the body's metabolism. It also plays a role in bone growth and development of the brain and nervous system in children. The pituitary gland controls the release of thyroid hormones. Thyroid hormones also help maintain normal blood pressure, heart rate, digestion, muscle tone, and reproductive functions. Parathyroid Glands The parathyroid glands are two pairs of small glands embedded in the surface of the thyroid gland, one pair on each side. They release parathyroid hormone, which plays a role in regulating calcium levels in the blood and bone metabolism. Adrenal Glands The two adrenal glands are triangular-shaped glands located on top of each kidney. The adrenal glands are made up of two parts. The outer part is called the adrenal cortex, and the inner part is called the adrenal medulla. The outer part produces hormones called corticosteroids, which regulate the body's metabolism, the balance of salt and water in the body, the immune system, and sexual function. The inner part, or adrenal medulla, produces hormones called catecholamines (for example, adrenaline). These hormones help the body cope with physical and emotional stress by increasing the heart rate and blood pressure. Pineal Body
carbohydrates, and fats. They reduce the immune system's inflammatory responses and help to maintain blood pressure and heart function. A vital function of corticosteroids is to help the body respond to stress. Corticosteroid production by the adrenal glands follows a sequence of events. The hypothalamus (see Anatomy of the Endocrine System) releases corticotropin- releasing hormone (CRH), which causes the pituitary gland to secrete adrenocorticotropic hormone (ACTH), which in turn stimulates the adrenal glands to produce corticosteroid. When the corticosteroid level is low, more CRH and ACTH are produced; when the corticosteroid level is high, less CRH and ACTH are produced. Under normal conditions, the corticosteroid level and CRH/ACTH levels are in dynamic balance; Cushing's disease occurs when that balance is disturbed. Excess corticosteroids have detrimental effects on many of the tissues and organs of the body. All of these effects together are called Cushing's syndrome. Overproduction of corticosteroids can be caused by a tumor in the pituitary gland, which produces excess ACTH, thereby stimulating the adrenal gland to produce excess corticosteroids. This condition is called Cushing's disease because the origin is in the hypothalamic pituitary system. Cushing's syndrome is a qcollection of symptoms which look and act like Cushing's disease but is not the result of pituitary ACTH overproduction. Endogenous Cushing's syndrome is the result of autonomous, unregulated production of corticosteroids by a tumor within one or both of the adrenal glands
themselves. The most common cause of Cushing's syndrome, however, is exogenous Cushing's syndrome, which results from taking excessive amounts of corticosteroid drugs. The majority of cases of Cushing's syndrome are caused by administration of corticosteroids (exogenous) for the treatment of long-term diseases such as asthma, arthritis, and lupus. Cushing's Syndrome Causes
- Exogenous administration of corticosteroids
- Endogenous (produced by the body) corticosteroid overproduction
- Adrenal gland tumors: Overproduction of corticosteroid may be due to an adrenal tumor, which could be cancerous or noncancerous.
- ACTH-producing pituitary tumors: Pituitary tumors produce excess ACTH, which acts on the adrenal gland to produce excess corticosteroid.
- Some lung tumors or other tumors outside the pituitary gland may produce ACTH, which in turn stimulate the adrenal glands to produce excess corticosteroid Cushing's Syndrome Symptoms Patient CommentsShare Your Story
- Weight gain, especially in the face, neck region, upper back, and torso (see Images 1-2)
- Changes in skin, including purple stretch marks, easy bruising, and other signs of skin thinning
- Proximal muscle weakness causing difficulty in climbing stairs, getting out of a low chair, and raising arms
