Ch 8 Endocrine system

Communication of the nervous and endocrine systems

(a) A neuron communicates by using action potentials to deliver neurotransmitters to the specific target tissue. (b) Endocrine cells secrete a hormone that is taken up into the bloodstream through capillaries and delivered to a general target tissue, where the hormone leaves the capillaries to fit into receptors.

Hypothalamus-pituitary relationship:

(a) location of the hypothalamus and pituitary gland; (b) the hypothalamus-anterior pituitary relationship, in which releasing hormones from the endocrine cells in the hypothalamus enter capillaries and travel through the blood in a portal vessel to capillary beds in the anterior pituitary; (c) ADH and oxytocin are produced by neuron cell bodies in the hypothalamus, travel through axons, and are released and stored in the posterior pituitary until they are needed, at which time they are released from there into the blood. The connection between the hypothalamus and the posterior pituitary is very different from that of the hypothalamus and the anterior pituitary. Groups of neuron cell bodies (nuclei) in the hypothalamus produce antidiuretic hormone (ADH) and oxytocin. These two hormones are delivered by axonal transport through the infundibulum to the posterior pituitary, where they are stored. Nerve signals from the hypothalamus travel through the infundibulum and trigger the release of ADH and oxytocin from the posterior pituitary when they are needed. Although these two hormones are technically made in the hypothalamus, they are referred to as posterior pituitary hormones because they are released from there.

Place the following steps of thyroid hormone secretion in the order they would be used if there is a need to increase metabolism.

1) The hypothalamus releases TRH which targets the anterior pituitary. 2) The anterior pituitary is stimulated to release TSH which targets the thyroid gland. 3) The thyroid is stimulated to release thyroid hormone, which travels to several target tissues. 4) Thyroid hormone stimulates cells to increase metabolism. 5) Thyroid hormone travels to the anterior pituitary to inhibit further secretion of TSH and to the hypothalamus to inhibits further secretion of TRH.

Cushing's syndrome

A collection of health problems related to excess cortisol in the blood as a result of hypersecretion of ACTH from the pituitary gland.

Myxedema

A complication of hypothyroidism, usually triggered by infection or trauma, that can result in shock, coma, or death if not treated.

Diabetes insipidus

A disorder in which the posterior pituitary does not release sufficient ADH to cause water reabsorption in the kidney.

Diabetes mellitus

A disorder that results from insufficient insulin produced by the pancreas or an insufficient response to the insulin that is produced. There are two forms of this disease, based on the cause: type 1 diabetes mellitus and type 2 diabetes mellitus.

The secretion of a hormone can be initiated in three ways:

A neuron stimulating a gland. An example of neural stimulation of a gland occurs when sympathetic neurons stimulate the adrenal medulla to secrete epinephrine in times of pain, fear, and/or stress. A Hormone stimulating a gland. An example of this can be seen when the hormones released by the hypothalamus stimulate the secretion of hormones from the anterior pituitary. For example, GnRH from the hypothalamus results in the secretion of FSH and LH from the anterior pituitary. A substance other than a hormone stimulating a gland. An example of this can be seen with the pancreas, which monitors blood glucose levels. Glucose is not a hormone, but if glucose levels are high, the pancreas responds to that stimulation by secreting insulin.

Location of receptors—protein hormones.

A protein hormone (1) fits into a receptor on the cell membrane (2), causing a chemical reaction that forms a molecule called cAMP—a second messenger (3). The second messenger stimulates changes inside the cell (4) as the function of the hormone. In this case, molecule A changes to B, which causes molecule C to change to D (5).

Location of receptors—steroid hormones.

A steroid hormone (1) passes through the cell membrane and fits into a receptor inside the nucleus (2) to stimulate protein synthesis (3 to 5). Steroid hormones and thyroid hormone can directly cross the membrane and fit into receptors inside the cell where the function will be carried out. This may be in the cytoplasm or in the nucleus. They do not need a second messenger.

Adrenal Cortex Degeneration

Addison's disease is the result of adrenal cortex degeneration. His adrenal cortex no longer functions to produce hormones. What are the consequences of this disease? Aldosterone is a major mineralocorticoid hormone that helps maintain homeostasis by controlling fluid and electrolyte balance. It targets the kidney to promote Na+ and water reabsorption and K+ excretion. The amount of water reabsorbed affects blood volume and therefore blood pressure. Without production of aldosterone, will have decreased ability to regulate blood pressure and blood volume. will also lose more Na+ in the urine and keep more K+ in his blood, disrupting his electrolyte balance. Another hormone important in maintaining homeostasis is cortisol. Cortisol is a major glucocorticoid that is used to promote the breakdown of fat and protein to make glucose, thus raising blood glucose levels. It also raises the amount of amino acids in the blood. Cortisol is a major hormone for dealing with stress. It provides the means to acquire the necessary glucose and amino acids in the blood to respond to stress. It also suppresses the immune system and reduces inflammation. Without cortisol, the ability to use fat and protein as fuel is reduced, as is the body's ability to deal with stress and inflammation. Dehydroepiandrosterone (DHEA) is an androgen produced by the adrenal cortex. It is a precursor to testosterone. The effects of decreased DHEA are minimal because the adrenal cortex is not his main source of testosterone. The majority of his testosterone comes from his testes. The body has lost some of its ability to maintain homeostasis if the adrenal cortex is not producing its hormones. That in itself is a move from homeostasis. How does the body try to fix this? The hypothalamus will recognize the need for cortisol, especially in times of stress The hypothalamus responds to the need for cortisol by producing corticotropin-releasing hormone (CRH). The CRH goes to the anterior pituitary, telling it to produce ACTH. The ACTH travels to the adrenal cortex to stimulate its production of glucocorticoids only not mineralocorticoids or androgens. This negative feedback response is intended to correct only the low cortisol levels and restore homeostasis. If the adrenal cortex has degenerated, it will not be able to respond to the ACTH. The hypothalamus will continue to see the need, so it will continue to produce more CRH, which will cause the anterior pituitary to produce more ACTH. The high ACTH levels in the blood, along with low cortisol levels, are one means of diagnosis for Addison's disease.

Hormones of the Adrenal Cortex

Adrenal cortex Gland: Hormone: Mineralocorticoids (aldosterone), Target tissue: Kidneys, Function: Promote sodium (Na+) and water reabsorption; promote potassium (K+) excretion; maintain blood volume and pressure Hormone: Glucocorticoids (cortisol), Target Tissue: Most tissues, Function: Stimulate the breakdown of protein and fat to make glucose; suppress the immune system; reduce inflammation. Hormone: Androgens (dehydroepiandrosterone [DHEA]) Target tissue: Most tissues, Function: Precursor to testosterone, responsible for male secondary sex characteristics and for sex drive in both sexes.

how does the body maintain normal, homeostatic blood glucose levels?

After the meal, the pancreas recognizes the increased blood glucose levels, and it releases the hormone insulin, which travels through the bloodstream to any cell that has an insulin receptor. Once insulin fits into the receptor, that cell takes in glucose from the blood, lowering blood glucose levels. Most cells have an insulin receptor, including the liver. The liver will convert the glucose it takes in to glycogen, a starch that is used as a storage molecule for glucose. Through the secretion of insulin, the cells have taken in the glucose they need, and blood sugar levels are brought back to homeostasis. No snack before going to bed. By 6 a.m., it has been 12 hours since last ate. Cells have used the available glucose, but they still need more glucose to carry out cellular respiration. Blood glucose levels have fallen below homeostasis. The pancreas recognizes that blood glucose levels are below normal. His pancreas responds by releasing glucagon. Glucagon travels everywhere through the bloodstream, but it affects cells of the liver because they have receptors for glucagon. Glucagon in the liver's receptors causes the liver cells to convert stored glycogen back to glucose for release back into the blood. Homeostatic blood glucose levels are restored.

What are the categories of hormones based on chemical structure?

Amino acid derivatives, proteins, steriods

Graves' disease

An autoimmune disorder characterized by hypersecretion of thyroid hormone from the thyroid gland.

Hashimoto's disease

An autoimmune disorder characterized by hyposecretion of thyroid hormone from the thyroid gland.

In Addison's disease, the adrenal cortex degenerates. This results in an inability to produce which hormones?

Androgens, Cortisol, and Aldosterone.

Goiters

Another endocrine system disorder involves the presence of goiters. A goiter is an enlargement of the thyroid gland. Iodine is necessary in the diet for the production of thyroid hormone. Normally, the anterior pituitary produces TSH to stimulate the thyroid when metabolism is low. If iodine is not available in the diet, hyposecretion of thyroid hormone results. This sets up a positive feedback loop of continued stimulation of the thyroid gland by TSH from the anterior pituitary. Even though the thyroid gland continues to enlarge with all the stimulation, functional thyroid hormone is not produced. Other than the goiter, the effects of hyposecretion of thyroid hormone include weight gain, reduced appetite, constipation, dry skin, and lethargy. Hypersecretion of thyroid hormone can also result in an enlarged thyroid gland, called a toxic goiter. The most common cause of this condition is Graves' disease. Graves' disease is a type of hyperthyroidism caused by an autoimmune disorder. In Graves' disease, an antibody made by white blood cells to fight a foreign invader mistakenly fits into TSH receptors of the thyroid gland and acts like TSH. The antibody is made for life and has no regard for metabolism levels, so the thyroid gland is constantly stimulated to produce more and more thyroid hormone no matter what the metabolism or anterior pituitary gland would indicate. Other than the goiter, the effects of hypersecretion of thyroid hormone can include weight loss, increased appetite, bouts of diarrhea, soft skin, exophthalmos (bulging eyes), and hyperactivity. Graves' disease is diagnosed by testing the blood for TSH levels, T4 levels, TSH-receptor antibody levels, and radioactive iodine uptake. Treatment can include iodine and other drugs that inhibit the release of thyroid hormone or interrupt thyroid hormone production. Surgery may also be used to decrease the size of the goiter. It is important to note that radiation treatment or removal of part of the thyroid can cause hypothyroidism

The hypothalamus regulates the activities of the _____ pituitary gland by ______

Anterior; secreting hormones that inhibit or stimulate production of hormones

clinical point

As women age, their ovaries stop releasing eggs and their menstrual periods eventually stop. This is called menopause. To assess whether a woman is in menopause, blood tests can be used to determine the level of FSH and estrogen. Women in menopause will have increased levels of FSH and decreased levels of estrogen. During the onset of menopause, periods may be irregular. Clinicians may also test thyroid hormone levels to ensure that the irregular periods are caused by menopause and not caused by a problem with the thyroid gland.

The hormone made by the heart that targets the kidney to regulate urine production is

Atrial natriuretic hormone (ANH)

Common Diagnostic Tests for Endocrine System Disorders

Blood Test: A procedure that involves obtaining a sample of blood and analyzing its contents. Blood tests can reveal whether the appropriate amount of hormone is present. Computed tomography (CT): An imaging technique used to visualize internal structures. The scan produces images in "slices" of areas throughout the body. A CT scan can be used to determine whether a tumor is present. DEXA (dual-energy X-ray absorptiometry) scan: A test that uses low-dose radiation to measure bone density in the hip and vertebrae. DEXA scans can be used to determine changes in bone as bones age. Magnetic resonance imaging (MRI) or nuclear magnetic resonance imaging (NMRI): An imaging technique used to visualize internal structures. This test provides great contrast between various soft tissues in the body. MRI can be used to detect a tumor or changes in soft tissue. Urinalysis: A test that involves a physical, chemical, and microscopic examination of urine. Results that do not fall within normal limits may indicate a condition or disease. A urinalysis may reveal inappropriate levels of certain chemicals in the urine. X-ray: Electromagnetic radiation that sends photons through the body, allowing the visualization of dense structures such as bone. X-rays can be used to determine changes in bone growth.

Cushing's Syndrome

Cushing's syndrome is a collection of disorders that results from the excess production of ACTH from the pituitary gland. The hypersecretion of ACTH is usually caused by a pituitary tumor. The excess ACTH causes high levels of cortisol in the blood. Individuals with Cushing's syndrome have a variety of symptoms, such as a moon face, obesity in the trunk of the body, collection of fat on the lower neck and shoulders, muscle weakness, thin skin, compromised immunity, poor wound healing, hypertension, kidney stones, osteoporosis, glucose intolerance, and mental disturbances. See Figure 8.20. Blood tests, urinalysis, and MRI can be used to diagnose Cushing's syndrome. Cushing's syndrome is treated with drugs that block corticosteroid secretion or with surgery or radiation to remove tumors.

Addison's disease

Degeneration of the adrenal cortex, which results in the inability to produce adequate amounts of glucocorticoid hormones, mineralocorticoid hormones, and androgens.

Diabetes Insipidus

Diabetes insipidus is a totally different disease than diabetes mellitus. It has nothing to do with glucose, insulin, or the pancreas. Diabetes insipidus is a problem with the posterior pituitary. In this disease, the posterior pituitary does not release sufficient ADH to cause water reabsorption in the kidneys. Therefore, too much water goes out in urine (polyuria), and the water for the extra urine is taken from the blood, reducing blood volume. The hypothalamus recognizes this and sends the signal for thirst, so the individual drinks to replace the lost water (polydipsia). Even though diabetes mellitus and diabetes insipidus are totally different diseases that have totally different causes, two symptoms—polyuria and polydipsia—are common to both disorders.

Diabetes Mellitus

Diabetes mellitus is a problem with the use of insulin in blood glucose regulation. Either insufficient insulin is produced, or the response to the insulin that is produced is insufficient. There are two forms of this disease, distinguished by the cause.

An ______ goiter is an enlargement of the thyroid gland resulting from an iodine deficiency. An _______ goiter is an enlargement of the thyroid gland resulting from hypersecretion of thyroid hormone.

Endemic; Toxic

Which two of the following organ systems function in communication?

Endocrine and Nervous

Hormones may be eliminated from the body in four ways:

Excretion. The kidneys can remove a hormone from the blood and excrete it in urine, or the liver can remove a hormone from the blood and excrete it in bile. Metabolism. Enzymes in the blood, liver, kidneys, or other target tissues can break down the hormone and excrete it or use it for cellular processes. For example, the breakdown of protein hormones results in amino acids that can be used for protein synthesis. Active transport. A hormone such as epinephrine can be taken back up by a cell through active transport so that it can be recycled and released at another time. Conjugation. The liver can bind water-soluble molecules to a hormone so that it will be excreted at a faster rate.

Effects of Melatonin

Gland: Pineal Gland; Hormone: Melatonin, Target tissue Brain and hypothalamus, Function: Helps regulate daily biological rhythms; inhibits GnRH production Hypothalamus gland; Hormone: GnRH (gonadotropin-releasing hormone) Target tissue: Anterior pituitary, Function Releases FSH and LH Anterior pituitary: Hormone: FSH (follicle-stimulating hormone), Target tissue Ovaries, Function: Stimulates secretion of estrogen Hormone: LH (luteinizing hormone), Target tissue: ovaries, Function: Stimulates ovulation Ovaries: Hormone: Estrogen, Target tissue: Most tissues, Function: Stimulates female secondary sex characteristics; regulates menstrual cycle and pregnancy

Insulin and Glucagon

Gland: Pancreas Hormone: Insulin-Target tissue: most tissues, liver, Function: Stimulates cells to take in glucose to lower blood glucose levels; tells liver to store glucose as glycogen Glucagon: Target tissue: Liver Function: Stimulates glycogen conversion to glucose and then its secretion to raise blood glucose levels

Which accurately describe growth hormone?

Growth hormone is released by the anterior pituitary. Growth hormone stimulates tissue growth. Growth hormone stimulates calcium absorption.

Autocrine, paracrine, endocrine and pheromone are hormone categories based on the location of the

Hormone receptor

Posterior pituitary

Hormone: ADH (Antidiuretic hormone): Target tissue: Kidneys Function: Increases water retention Oxytocin: Target tissue: 1) Uterus Function: 1. Stimulates uterine contractions 2) Lactating breasts Function: 2. Stimulates release of milk

Adrenal medulla

Hormone: Epinephrine, Target tissue: Most tissues, Function: Raises metabolic rate; increases heart and respiration rates; increases blood glucose levels (complements sympathetic nervous system) The adrenal medulla is the middle of the adrenal gland. It is often stimulated by the sympathetic nervous system in situations of fear, pain, and stress.

Ovaries

Hormone: Estrogen, Target tissue: most tissues, Function: Stimulates female secondary sex characteristics;* regulates menstrual cycle and pregnancy The ovaries begin to produce their hormones at puberty and continue producing them until menopause. A major hormone produced in the ovaries is estrogen, which is responsible for the development of secondary sex characteristics in the female.

Pancreas

Hormone: Insulin: Target tissue: Most tissues, liver, Function: Stimulates cells to take in glucose to lower blood glucose levels; tells liver to store glucose as glycogen Glucagon: Target tissue: Liver Funtion: Stimulates glycogen conversion to glucose and then its secretion to raise blood glucose levels The pancreas is part of the endocrine and digestive systems. The pancreas is an elongated gland and has a pebbly appearance. It is inferior and posterior to the stomach. Only about 2% of the gland produces hormones for the endocrine system. The endocrine cells are grouped to form 1 to 2 million pancreatic islets (islets of Langerhans). The two hormones produced by the islets—insulin and glucagon—are important in the regulation of blood glucose levels.

Adrenal cortex

Hormone: Mineralocorticoids (aldosterone), Target tissue: Kidneys, Function: Promote sodium (Na+) and water reabsorption; promote potassium (K+) excretion; maintain blood volume and pressure Glucocorticoids (cortisol), Target tissue: Most tissues, Function: Stimulate the breakdown of protein and fat to make glucose; suppress the immune system; reduce inflammation Androgens (dehydroepiandrosterone [DHEA]) Target tissue: Most tissues, Function: Precursors to testosterone, responsible for male secondary sex characteristics and for sex drive in both sexes The adrenal cortex is the outer layer of the adrenal gland. It produces over 25 different hormones classified in three major categories: mineralocorticoids, glucocorticoids, and androgens.

Parathyroids

Hormone: PTH (parathyroid hormone) Target tissue: 1. Osteoclasts Function: 1. Stimulates bone reabsorption to increase blood calcium levels 2. Kidneys Function: 2. Stimulates reabsorption of calcium by the kidneys to maintain blood calcium levels 3. Small intestine Function: 3. Stimulates calcium absorption There are usually four parathyroid glands in the body. They are typically embedded in the posterior surface of the thyroid gland, with two on each side of the trachea. They release parathyroid hormone (PTH), which stimulates both the reabsorption of calcium from the bone and the absorption of calcium in the small intestine and prevents the loss of calcium to urine in the kidney.

Other tissues

Hormone: Prostaglandins, Target tissue: Many tissues, Function: Have a variety of functions, such as relaxing smooth muscle in respiratory airways and blood vessels and causing contraction of smooth muscle in the uterus

Thyroid

Hormone: T3 and T4 (thyroid hormone), Target tissue: Most tissues, Function: Elevates metabolic rate; increases heart and respiration rates; stimulates appetite Calcitonin Target tissue: Osteoblasts Function: stimulates bone deposition Resembles a bow tie, is anterior and lateral to the trachea and just inferior to the larynx. T3 and T4 are two forms of the principal hormone produced by the thyroid, which is called thyroid hormone. Their function is to increase metabolism in most tissues. Calcitonin is also produced in the thyroid gland. It functions to stimulate the deposition of calcium in the bone, making it more relevant for children than adults. Thyroid hormone is vital to metabolism regulation in the body. The production of this hormone requires the mineral iodine. The natural nutritional sources of iodine are ocean fish, shellfish, and seaweed. Because these foods are not common in everyone's diet on a regular basis, iodine is added to table salt, which is common in almost everyone's diet. Iodine is listed on the packaging as iodized salt. It is necessary to consume an adequate amount of iodine to maintain homeostasis.

Testes

Hormone: Testosterone, Target tissue: most tissues Function: Stimulates male secondary sex characteristics,† sex drive, and sperm production The testes produce the hormone testosterone in the fetus for the development of male anatomy. Testosterone production is dormant from birth to puberty, and then it begins again at puberty to promote the development of male secondary sex characteristics. Production of testosterone continues after puberty throughout life but significantly decreases after midlife.

Hypothalamus gland

Hormone: GnRH (gonadotropin-releasing hormone) Target tissue Anterior pituitary, Function: Stimulates secretion of FSH and LH CRH (corticotropin-releasing hormone) Target tissue Anterior pituitary, Function: Stimulates secretion of ACTH TRH (thyrotropin-releasing hormone) Target tissue Anterior pituitary, Function: Stimulates secretion of TSH GHRH (growth hormone-releasing hormone) Target tissue Anterior pituitary, Function: Stimulates secretion of GH Plays a major role as a gateway for the brain to control the endocrine system. Connected to the pituitary gland's two parts by a stalk called the infundibulum, which serves as a passageway. Hormones produced by endocrine cells in the hypothalamus enter the blood through the capillary beds in the hypothalamus. The blood and hormones are carried through the infundibulum in a portal vessel (blood vessel directly connecting two capillary beds) to capillary beds in the anterior pituitary. Hormones can then leave the bloodstream to bind to their receptors in the anterior pituitary. This system of blood vessels allows for the direct distribution of hormones through the blood from the hypothalamus to the anterior pituitary without traveling to the rest of the body. Hormones from the hypothalamus directly affect the release of hormones from the anterior pituitary.

Anterior pituitary

Hormone: TSH (thyroid-stimulating hormone) Target Tissue: Thyroid, Function: Stimulates secretion of thyroid hormone and growth of the thyroid ACTH (adrenocorticotropic hormone), Target Tissue: Adrenal cortex, Function: Stimulates secretion of glucocorticoids and growth of the adrenal cortex FSH (follicle-stimulating hormone), Target tissue: 1. Ovaries Function: 1. Stimulates secretion of estrogen 2. Testes Function: 2. Stimulates sperm production LH (luteinizing hormone) Target tissue: 1) Ovaries Function: 1. Stimulates ovulation 2. Testes Function: 2. Stimulates secretion of testosterone GH (growth hormone) Target tissue: Liver, bone, cartilage, muscle, adipose tissue, Function: Stimulates widespread tissue growth

Pineal gland

Hormone: Melatonin Target Tissue: Brain, Hypothalamus Function: Helps regulate daily biological rhythms; Inhibits GnRH production It resembles a pine cone. It is located beneath the posterior end of the corpus callosum in the brain. The complete function is not known, although it may have a function in establishing sleep-wake cycles of daily biological rhythms. What is known is that the pineal gland reaches its maximum size between the ages of 1 and 5 and usually shrinks to one-fourth that size by the end of puberty. The hormone melatonin produced by the pineal gland is believed to suppress gonadotropin-releasing hormone (GnRH) from the hypothalamus

Hypothalamus-anterior pituitary target-tissue relationship.

Hormones from the hypothalamus enter the bloodstream and target the anterior pituitary, stimulating the release of hormones from the anterior pituitary into the bloodstream to travel to their target tissues.

acromegaly

Hypersecretion of GH from the anterior pituitary gland, which happens during adulthood, resulting in bones becoming excessively massive.

Gigantism

Hypersecretion of GH from the anterior pituitary gland, which happens during childhood, before the epiphyseal plates close, resulting in excessive growth of bones.

Pituitary dwarfism

Hyposecretion of GH from the anterior pituitary gland, which happens during childhood, resulting in unusually short stature.

Hypothalaumus respons to decreased cortisol

Hypothalamus gland: Hormone: CRH (corticotropin-releasing hormone). Target tissue: Anterior pituitary Function: Releases ACTH Anterior Pituitary gland; Hormone: ACTH (adrenocorticotropic hormone), Target tissue: Adrenal cortex, Function: Stimulates secretion of glucocorticoids and growth of the adrenal cortex

Hypothyroidism

Hypothyroidism is characterized by a hyposecretion of thyroid hormone. There are two main causes of hypothyroidism, Hashimoto's disease and hypothyroidism that results from the treatment of hyperthyroidism: Hashimoto's disease is an autoimmune disorder that results in the chronic inflammation of the thyroid gland. The inflammation of the gland does not allow it to function properly and results in hyposecretion of thyroid hormone. As mentioned previously, the treatment of hyperthyroidism can involve radiation of the thyroid gland or surgical removal of part of the thyroid gland. Either of these treatments can result in hyposecretion of thyroid hormone. Symptoms of hypothyroidism include fatigue, weight gain, an enlarged thyroid gland, intolerance of cold temperatures, joint and muscle pain, constipation, impaired fertility, depression, and a slow heart rate. Hypothyroidism is more likely to affect women between the ages of 40 and 60. Blood tests can be used to diagnose hypothyroidism. These tests would detect TSH levels, T4 levels, and the presence of thyroid autoantibodies, which are antibodies formed against one's own tissues. Physical examination can be used to determine whether the thyroid is enlarged. Treatment of hypothyroidism involves methods to reduce the size of the thyroid gland and the use of synthetic thyroid hormone to increase thyroid hormone levels.

bOTH TYPES OF DIABETES

If cells cannot use the glucose in the blood, they must turn to other sources of energy in the body, such as fat and protein. Therefore, diabetes mellitus, left untreated, is a wasting disease characterized by visible weight loss and loss of muscle mass, even though the individual may be eating a high-caloric diet. Normally, the kidney filters out the glucose in the blood while removing wastes. It then reabsorbs all of the glucose so that none is lost in urine. However, in either type of diabetes mellitus, there is too much glucose in the blood. The kidney filters out the glucose but does not have time to completely reabsorb all of it. As a result, some of the glucose is lost in urine (glucosuria). Water follows the glucose, so urine output is increased (polyuria). The water for the extra urine is taken from the blood, reducing blood volume. The hypothalamus recognizes this and sends the signal for thirst, so the individual drinks to replace the lost water (polydipsia, excessive thirst). The glucose lost in urine is unable to enter the cells where it should be converted into ATP to be used for energy. This causes a lack of energy and results in excessive hunger and increased appetite (polyphagia). Both types of diabetes mellitus have possible life-threatening complications. Therefore, blood glucose levels need to be monitored closely. Hyperglycemia (too much sugar in the blood) has a devastating effect on the walls of blood vessels. Even blindness and kidney failure can be the direct result of the deterioration of vessels of the retina and kidney. Uncontrolled diabetes mellitus also leads to other degenerative cardiovascular disease complications and neurological diseases. Circulation to the tissues and nerves of the extremities may be compromised, leading to neuropathy (diseases involving the nervous system) and tissue death.

Gigantism

If hypersecretion of GH happens during childhood, before the epiphyseal plates close, gigantism results. Individuals with gigantism have accelerated bone growth, resulting in a larger than usual stature due to excessive endochondral growth. They can also suffer from swelling of soft tissues, peripheral nerve damage, and delayed onset of puberty.

Pituitary Dwarfism

If there is hyposecretion of GH during childhood, pituitary dwarfism results. The individual is abnormally short in stature. See Figure 8.18. Growth during childhood Page 331 may be less than 2 inches per year, and puberty may be delayed or not come at all. There is no main cause of hyposecretion of GH in children. A deficiency in GH secretion can result from a congenital defect or from a brain injury, a tumor, or other health conditions that occurred after the child was born. Diagnosis of hyposecretion growth disorders involves blood tests to measure hormone levels. Repeat physical examinations and growth charting will show whether growth has slowed down or whether it is on track. MRI can be used to examine the pituitary gland. X-rays and DEXA scans can be used to examine bone size and age.

Acromegaly

If there is normal secretion of GH in childhood but hypersecretion of GH in adulthood, acromegaly results. In acromegaly, the epiphyseal plates have closed normally, preventing any further elongation of long bones, but all of the bones become more massive through excessive appositional bone growth (covered in the skeletal system chapter) in adulthood. This can be especially seen in the bones of the face. Adults suffering from acromegaly may also have thickened skin, a deeper voice, degenerative arthritis, peripheral nerve damage, headaches, and organ enlargement. Hypersecretion of GH throughout life can occur and would result in a giant with acromegaly. Diagnosis of hypersecretion growth disorders involves blood tests to measure hormone levels. In addition, CT, MRI, or X-rays can be used to locate the presence of a pituitary tumor and determine any changes in tissues and bone that might indicate gigantism or acromegaly.

Growth Disorders

In addition to diabetes, other disorders of the endocrine system include growth disorders. Growth disorders can be the result of improper secretion of GH from the anterior pituitary. GH is secreted during childhood to promote the growth of most tissues. Levels of GH normally decrease in adulthood. Growth disorders that result in a hypersecretion of GH are usually caused by a pituitary tumor. Hypersecretion of GH will result in either gigantism or acromegaly.

Endocrine system

It is all about communication. It involves one part of the body communicating with another part of the body to maintain homeostasis. Uses chemicals called hormones to carry messages. Responds to a stimulus by producing a chemical hormone and secreting it outside the gland that produced it. The blood carries this hormone throughout the body. The hormone will work not just on a few cells but on all of the cells that have a receptor for it. The effects of the hormone will continue until it has been cleared from the target tissue. Communication through the endocrine system is much slower to start, is less specific as to its target, and takes longer to end than communication by the nervous system.

Gland

May be a separate structure, or it may be made up of groups of cells within an organ that function together to produce hormones. The hormones produced by the gland are secreted outside the cells that produce them. There are no special ducts to carry the hormones to their destinations. Instead, the bloodstream is the transportation system. Once secreted by the gland, the hormones are picked up by the blood and travel everywhere the blood travels—to the liver, the eye, even the big toe. Although a hormone travels everywhere, it has an effect only on its target tissue because the cells of the target tissue have receptors for that specific hormone.

Type 2 Diabetes Mellitus

Most diabetics have type 2 diabetes mellitus. This form of the disease is characterized by the inability to respond to the insulin produced by the pancreas. The number of receptors is insufficient to adequately respond to the insulin produced in the regulation of blood glucose levels. In the beginning of the disease, insulin levels may be high, but the cells have down-regulated their receptors, so they are not responsive to the insulin produced. As a result, blood glucose levels stay chronically high. The pancreas responds accordingly with more and more insulin that has less and less of an effect. Eventually, the pancreas stops responding to the high blood glucose levels, and insulin levels fall. If the disease is diagnosed early in its progression, type 2 diabetics can be treated with medications that increase cells' sensitivity to insulin, dietary changes that moderate blood glucose levels, and exercise, which encourages up-regulation of receptors. If not treated early, however, the type 2 diabetic may have to be treated with insulin as well.

Regulation of Hormone Secretion and Distribution

Most hormones are not secreted at a constant rate. In order to maintain homeostasis, they are secreted when there is a need; their secretion is usually regulated by negative feedback mechanisms.

Consequences of Reduced Melatonin Production at Puberty

Normally, the pineal gland's production of melatonin is reduced at puberty. This creates a chain of events that involves many hormones. The function of a hormone involves another hormone, you should continue charting. Melatonin normally inhibits the production of GnRH by the hypothalamus. When the melatonin is reduced, so is the inhibitory effect on the hypothalamus. The hypothalamus is free to produce GnRH, which then goes to the anterior pituitary, telling it to produce FSH and LH. FSH targets the ovaries to stimulate the production of estrogen, which will promote the development of secondary sex characteristics. LH targets the ovaries to stimulate ovulation.

What is the name of the hormone that causes contraction of muscles in the uterine wall during childbirth and also ejection of milk from mammary glands in lactating breasts?

Oxytocin

Proteins in the blood that bind to a hormones to "time-release" its effects are?

Plasma proteins

Proteins

Protein hormones are made of chains of amino acids. Examples of protein hormones include insulin, thyroid-stimulating hormone (TSH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), growth hormone (GH), parathyroid hormone (PTH), antidiuretic hormone (ADH), adrenocorticotropic hormone (ACTH), glucagon, calcitonin, oxytocin, and hormones from the hypothalamus. Proteins are too large to pass through cell membranes.

Target tissues have cells with _______ for specific hormones

Receptors

Steroids

Steroid hormones are derived from a cholesterol molecule. Examples of steroid hormones include estrogen, testosterone, progesterone, mineralocorticoids, and glucocorticoids. As lipids, they can pass through cell membranes to reach receptors anywhere in the cell. Cholesterol is needed to help maintain homeostasis by synthesizing steroid hormones and other digestive salts. Cholesterol can be acquired through the diet and can be produced by the liver. It is a steroid found in high concentration in liver and egg yolks. It is also found in whole milk, butter, cheese, and meats; but cholesterol is not found in plants.

Receptor Regulation

Target tissues can regulate their sensitivity to a hormone by adjusting the number of receptors for that hormone. Up-regulation is an increase in the number of receptors for a given hormone. In this case, the cell has more receptors for the hormone to bind, so it has become more sensitive to the hormone and the effects of the hormone are increased. Down-regulation occurs when a cell decreases the number of receptors for a hormone. Here, there are fewer opportunities to bind a hormone to a receptor, so the cell is less sensitive to the hormone and the effects of the hormone are reduced. Down-regulation is often a response to chronically high levels of a hormone. (a) up-regulation, (b) down-regulation.

Adrenal glands

The adrenal glands appear to sit as a cap, superior and medial to the kidneys. The two parts of the adrenal gland—the adrenal cortex and the adrenal medulla—function to produce different hormones.

Transport and action of protein and steroid hormones.

The chemical composition affects how the hormone is distributed in the blood. Thyroid hormone, in the last example, can easily pass through cell membranes. If it were allowed to do that, much of the thyroid hormone would immediately go into the cells, causing a huge spike in metabolism and then a dramatic fall when the hormone was used up. The body has a way to time-release thyroid hormone and steroid hormones that can easily pass through cell membranes. Transport proteins, called plasma proteins, made by the liver are used to bind to some of the hormone in the blood. The bond is a reversible one, meaning that at any one time, some of the hormone will be free to enter the cell and some of the hormone will be bound to plasma proteins, making it too large to enter the cell. As time goes by, more of the hormone is freed from the plasma proteins so that it can enter the cell.

Hormone Elimination

The effects of a hormone will continue until the hormone is eliminated from the system. Therefore, the method of hormone elimination is important in regulating the duration of the hormone's effects.

Negative feedback inhibition of the hypothalamus and pituitary gland by the thyroid gland.

The hypothalamus releases thyrotropin-releasing hormone (TRH), which goes to its target tissue, the anterior pituitary, and fits into receptors. The anterior pituitary is then stimulated to release TSH, which goes to its target tissue, the thyroid gland, and fits into receptors. The thyroid is then stimulated to release thyroid hormone, which travels to several target tissues. Thyroid hormone travels to most cells, stimulating them to increase metabolism (heat is given off as a by-product). Thyroid hormone also travels to the anterior pituitary, where it inhibits the further secretion of TSH. Thyroid hormone also travels to the hypothalamus, where it inhibits the further secretion of TRH. This negative feedback mechanism is an example of homeostasis and is the thyroid's method of saying to the anterior pituitary and hypothalamus that it has received the message to secrete thyroid hormone and is following through on the message. It keeps the secretion rate from going too high.

Location of the Target Tissue

The location of the target tissue is also relevant to the eventual delivery method of the hormone, as outlined in the list that follows. Hormone function can be categorized by the location of the cells producing the hormone relative to the location of their target tissues: Autocrine refers to the secretion of a hormone by cells of the same tissue type that the hormone targets. An example of this is the production of prostaglandins by the smooth muscle of the uterus, which causes the smooth muscle of the uterus to contract during birth. Paracrine refers to hormones that work on neighboring cells without having to go through the blood to get to the target tissue. An example of this can be seen with endocrine cells in the stomach, which cause neighboring cells to produce hydrochloric acid. Endocrine refers to hormones that travel through the blood to get to their target tissue. Pheromone refers to chemicals that cause a response outside the body, in another individual.

Location of Hormone receptors

The two basic classes of receptors for hormones are based on their location—either on the cell membrane or somewhere inside the cell. Protein hormones must bind to receptors on the cell membrane because they cannot enter the cell. They fit into the receptors on the basis of their specific shape—like a key fits into a lock. The hormones may initiate a response directly on the membrane, such as opening a channel; or they may initiate a response inside the cell, such as initiating protein synthesis. If the response is to occur inside the cell, a second-messenger system must be used. In this system, the binding of a hormone in the receptor on the cell membrane causes a chemical reaction inside the membrane. This reaction creates a second messenger, which then carries the information to where it is needed in the cell to initiate the function of the hormone.

Target tissues

There are many target tissues for the various hormones of the body. What makes a tissue a target tissue is the presence of specific receptors for specific hormones based on the hormone's chemical makeup and shape.

Amino Acid Derivatives

These hormones are derived from amino acids. Thyroid hormone, epinephrine , and melatonin are examples of amino acid derivatives. This type of hormone may or may not be able to cross cell membranes. For example, thyroid hormone can easily pass across a cell membrane to reach a receptor inside the cell, while epinephrine cannot.

Insulin and Glucagon Secretion

This scenario analyzes the role of insulin and glucagon over a 12-hour period. Paul has a dinner at 6 p.m. He eats pasta and garlic bread with chocolate cake for dessert, a meal rich in carbohydrates. His digestive system will work to break down the carbohydrates into their building blocks, monosaccharides (simple sugars), so that they can be absorbed into the bloodstream. Soon after his meal, his blood sugar level rises above homeostasis. Cells need glucose (blood sugar), but too much sugar in the blood is harmful to the body. Over time, it can lead to coronary artery disease, peripheral nerve damage, and damage to small blood vessels in the kidney and retina.

What is the disorder cause by the pancreatic cells inability to secrete insulin? It usually appears before age thirty and treatment requires insulin injections.

Type 1

Type 1 Diabetes Mellitus (Insulin Dependent)

Type 1 diabetes mellitus is usually diagnosed before age 30. The exact cause of this disease is unknown, but many think that it occurs because the body is challenged with a viral infection. The immune system responds by making antibodies to fight the pathogen, but the antibodies also attack the cells of the pancreatic islets that produce insulin. Once most of the islets have been destroyed, the ability to regulate glucose levels in the blood is lost. Type 1 diabetics need to monitor their blood glucose levels closely and inject insulin to maintain homeostasis of blood glucose levels.

The treatment for growth disorders involves

adjusting the hormone levels back to normal. For individuals suffering from a hypersecretion of GH, adjustment of the GH levels might result from removing the tumor that is responsible for the hypersecretion. This may be done by surgery or radiation therapy. For individuals who suffer from hyposecretion of GH, treatment involves GH injections to increase the levels of GH in the body.

adren/o

adrenal glands

adrenal/o

adrenal glands

Gonads

are also endocrine glands. Gonads are the ovaries in a female and the testes in a male, and they function in both the endocrine and reproductive systems.

Anatomy of the Endocrine System

composed of glands that make chemicals called hormones that travel to target tissues to tell them to do something.

Prediabetes

condition in which the blood glucose levels and results of the hemoglobin A1c test, a measurement of the average glucose concentration in plasma over a 2- to 3-month period, are higher than normal but not high enough to be classified as diabetes mellitus. The statistic of 79 million Americans over 20 years of age having prediabetes gives insight on how many new cases of diabetes can potentially exist. The screening for prediabetes is helpful in that it allows health care providers to work with patients on measures that might decrease their blood glucose and hemoglobin A1c levels and potentially avoid the onset of the disease. Diabetes mellitus not only affects blood glucose levels but can cause many other health complications, such as heart disease and stroke, hypertension, eye disorders, kidney disease, nervous system disorders, amputations, weakened immune system, dental disease, and depression. Weight loss and increased physical activity have been shown to prevent or delay the onset of type 2 diabetes mellitus.1

cortic/o

cortex

Aden/o

gland

hormon/o

hormone

The excessive production of a hormone is called ________, while the deficient production of a hormone is __________

hypersecretion; hyposecretion

Four scenarios can help you understand the interaction of the glands and hormones of this system:

insulin and glucagon secretion, consequences of reduced melatonin production at puberty, adrenal cortex degeneration, and hormonal regulation of childbirth. It is always helpful to create a chart of the relevant gland, hormone, target tissue, and function when working with endocrine questions. Always remember that if the function of a hormone involves another hormone, you must chart that hormone too.

Myxedema

is a serious complication that occurs in people suffering from hypothyroidism. It usually occurs in the elderly population and can be triggered by infection, trauma, surgery, certain medications, and other health conditions such as hypoglycemia and stroke. Symptoms of myxedema include an altered mental state, hypothermia, cardiovascular and gastrointestinal problems, and a myxedematous face (characterized by puffiness, drooping eyelids, swelling around the eyes, and hair loss). Myxedema is diagnosed by testing the blood for thyroid hormone levels and also testing electrolyte levels. It is very important for people suffering from myxedema to get treatment immediately as the condition can quickly become lethal. Patients are usually placed in intensive care and treated for shock, electrolyte imbalances, and infection. They are monitored closely for heart attacks, and they receive synthetic thyroid hormone to increase thyroid hormone levels.

Half-life

is the length of time it takes for one-half of a substance to be eliminated from the circulatory system. Steroid hormones and thyroid hormone have their half-lives extended by binding to plasma proteins. Their levels tend to be more constant. Protein hormones and epinephrine have relatively short half-lives because they are quickly degraded, recycled, or excreted.

Effects of Aging on the Endocrine System

levels of hormones decline with age. This can be seen most dramatically with the hormones estrogen and testosterone. The production of both hormones is dramatically reduced during midlife. Estrogen production by the ovaries ceases with menopause. Testosterone production continues after midlife, but it gradually declines and at age 80 is about 20% of what its peak was at age 20. Both estrogen and testosterone serve as a lock on calcium in the bone. Therefore, the effects of osteoporosis may be seen as the production of these hormones decreases with age. Even if the levels of some other hormones remain high with age, the sensitivity of their target tissues often decreases with down-regulation of receptors. This is often seen in the development of diabetes mellitus in elderly people.

andr/o

male

pancreat/o

pancreas

Hormonal Regulation of Childbirth

pregnancy at full term the fetal head is pushing on the neck of the uterus (called the cervix), which causes the cervix to send nerve impulses to the brain. The hypothalamus in the brain responds by stimulating the posterior pituitary to release oxytocin. Oxytocin goes to its target tissue, the uterus, and causes it to contract. The uterine contractions push on the fetus, causing more pressure on the cervix. The whole cycle keeps repeating itself until the baby is born.

crin/o

secrete

gonad/o

sex glands

ster/o

steroid

gluc/o

sucar

glyc/o

sugar

dips/o

thirst

thyr/o

thyroid gland