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  • Hormones are grouped by glands and chemical class in Table 20.1 on page 393.
  • This diagram shows the anatomical location of major endocrine glands in the body. The hypothalamus and pituitary gland are located in the brain, the thyroid and parathyroids are located in the neck, and the adrenal glands and pancreas are located in the pelvic cavity. The gonads include the ovaries in females, located in the pelvic cavity, and the testes in males, located outside this cavity in the scrotum. Also shown are the pineal gland, located in the brain, and the thymus, which lies ventral to the thorax.
  • Growth factors are local hormones (chemical signals) that promote cell division and mitosis.
  • Endocrine hormones and neurosecretions typically are carried in the bloodstream and act at a distance within the body of a single organism. Some chemical signals have local effects only; they pass between cells that are adjacent to one another. Neurotransmitters belong to this category, as do local hormones such as prostaglandins.
  • After passing through the plasma membrane and nuclear envelope, a steroid hormone binds to a receptor protein inside the nucleus. The hormone-receptor complex then binds to DNA, and this leads to activation of certain genes and protein synthesis.
  • The peptide is the first messenger and cAMP (cyclic adenosine monophosphate) is the second messenger.
  • Peptide hormones, called first messengers, bind to a specific receptor protein in the plasma membrane. A protein relay in the membrane ends when an enzyme converts ATP to cAMP, the second messenger, which activates an enzyme cascade.
  • This diagram shows the anatomical location of major endocrine glands in the body. The hypothalamus and pituitary gland are located in the brain, the thyroid and parathyroids are located in the neck, and the adrenal glands and pancreas are located in the pelvic cavity. The gonads include the ovaries in females, located in the pelvic cavity, and the testes in males, located outside this cavity in the scrotum. Also shown are the pineal gland, located in the brain, and the thymus, which lies ventral to the thorax.
  • Inability to produce ADH causes diabetes insipidus, in which a person produces copious amounts of urine with a resultant loss of ions from the blood.
  • The blood level of the last hormone in the sequence exerts negative feedback control over the secretion of the first two hormones.
  • ( Left ) The hypothalamus produces two hormones, ADH and oxytocin, which are stored and secreted by the posterior pituitary. ( Right ) The hypothalamus controls the secretions of the anterior pituitary, and the anterior pituitary controls the secretions of the thyroid, adrenal cortex, and gonads, which are also endocrine glands.
  • In acromegaly, since bone growth is no longer possible in adults, only the feet, hands and face (especially the chin, nose, and eyebrow ridges) can respond.
  • The amount of growth hormone produced by the anterior pituitary during childhood affects the height of an individual. Plentiful growth hormone produces very tall basketball players. Too much growth hormone can lead to giantism, where insufficient amount results in limited stature and even pituitary dwarfism.
  • Acromegaly is caused by overproduction of GH in the adult. It is characterized by the enlargement of bones in the face, the fingers, and the toes as the person ages.
  • Individuals with cretinism are short and stocky, and mental retardation can result unless thyroid hormone therapy is begun early. Hypothyroidism in adults causes myxedema, which is characterized by lethargy, weight gain, loss of hair, slower pulse rate, lowered body temperature, and thickness and puffiness of the skin.
  • An enlarged thyroid gland is often caused by a lack of iodine in the diet. Without iodine, the thyroid is unable to produce thyroxine, and continued anterior pituitary stimulation causes the gland to enlarge.
  • Individuals who have hypothyroidism since infancy or childhood do not grow and develop as others do. Unless medical treatment is begun, the body is short and stocky; mental retardation is also likely.
  • ( Top ) When the blood calcium (Ca 2+ ) level is high, the thyroid gland secretes calcitonin. Calcitonin promotes the uptake of Ca 2+ by the bones, and therefore the blood Ca 2+ level returns to normal. (Bottom) When the blood Ca 2+ level is low, the parathyroid glands release parathyroid hormone (PTH). PTH causes the bones to increase Ca 2+ , the kidneys to reabsorb Ca 2+ and activate vitamin D, and thereafter the intestines absorb Ca 2+ . Therefore, the blood Ca 2+ level returns to normal.
  • Cortisone, the medication that is often administered for inflammation of joints, is a glucocorticoid.
  • Both the adrenal medulla and the adrenal cortex are under the control of the hypothalamus when they help us respond to stress. ( Left ) The adrenal medulla provides a rapid, but short-term, stress response. Effects include increased heartbeat and blood pressure, increased blood glucose, and energized muscles. ( Right ) The adrenal cortex provides a slower, but long-term, stress response. Glucocorticoid effects include protein and fat metabolism instead of glucose breakdown, reduction of inflammation, and a suppression of immune system cells. Mineralocorticoid effects include reabsorption of sodium ions and water by the kidneys, and increases in both blood volume and blood pressure.
  • ( Bottom ) When the blood sodium (Na + ) level is low, a low blood pressure causes the kidneys to secrete renin. Renin leads to the secretion of aldosterone from the adrenal cortex. Aldosterone causes the kdneys to reabsorb Na + , and water follows, so that blood volume and pressure return to normal. (Top) When the blood Na + is high, a high blood volume causes the heart to secrete atrial natriuretic hormone (ANH). ANH causes the kidneys to excrete Na + , and water follows. The blood volume and pressure return to normal.
  • A mild infection can lead to death due to lack of cortisol needed to replenish glucose levels.
  • Addison disease is characterized by a peculiar bronzing of the skin, particularly noticeable in these light-skinned individuals. Note the color of the face (left) and the hands compared to the hand of an individual without the disease.
  • Cushing syndrome results from hypersecretion of hormones due to an adrenal cortex tumor. On the left, the patient as he appeared when first diagnosed with Cushing syndrome. On the right is the same patient, four months after therapy.
  • ( Top ) When the blood glucose level is high, the pancreas secretes insulin. Insulin promotes the storage of glucose as glycogen and the synthesis of proteins and fats (as opposed to their use as energy sources). Therefore, insulin lowers the blood glucose level. ( Bottom ) When the blood glucose level is low, the pancreas secretes glucagon. Glucagon acts opposite to insulin; therefore, glucagon raises the blood glucose level to normal.
  • Following the administration of 100 g of glucose, the blood glucose level rises dramatically in the diabetic but not in the nondiabetic. Glucose appears in the urine when its level exceeds 190 mg/100 ml (called the renal threshold).
  • It is possible that up to 7 million Americans have type II diabetes without being aware of it. Long-term complications of both types of diabetes are blindness, kidney disease, and circulatory disorders, including atherosclerosis, heart disease, stroke, and reduced circulation. The latter can lead to gangrene in the arms and legs. Pregnancy carries an increased risk of diabetic coma, and the child of a diabetic is somewhat more likely to be stillborn or die shortly after birth.
  • Some athletes take anabolic steroids related to testosterone to add muscular strength but this has adverse side effects.
  • Effects of use of anabolic steroids include: balding in men and women; hair on the face and chest in women; deepening of the voice in women; breast enlargement in men and breast reduction in women; kidney disease and retention of fluids, called “steroid bloat”; reduced testicular size, low sperm count, and impotency; “’roid mania” – delusions and hallucinations; depression upon withdrawal; severe acne; high blood cholesterol and atherosclerosis; high blood pressure and damage to the heart; liver dysfunction and cancer; in women, increased size of ovaries, along with cessation of ovulation and menstruation; and stunted growth in youngsters by prematurely halting fusion of the growth plates.
  • Certain prostaglandins reduce gastric secretion and have been used to treat ulcers; others lower blood pressure and have been used to treat hypertension. However, different prostaglandins have contrary effects. Therefore, prostaglandin therapy is still considered experimental.

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  • Endocrine System
  • Endocrine Glands
    • The endocrine system is made of glands and tissues that secrete hormones.
    • Endocrine glands are ductless organs, producing their chemical messengers (hormones) and secreting them directly into the bloodstream, whereas other glands (exocrine glands) produce their chemicals and excrete them into a duct (ex. digestive enzymes, sweat).
    • Hormones are chemicals that influence metabolism of cells, the growth and development of body parts, and homeostasis.
    • Hormones can be classified as protein or steroids .
    • There is a close association between the endocrine and nervous systems.
    • Hormone secretion is usually controlled by either negative feedback or antagonistic hormones that oppose each other’s actions, and results in maintenance of a bodily substance or function within normal limits.
  • The endocrine system
  • Chemical Signals
    • A chemical signal is any substance that affects cell metabolism or behavior of the individual.
    • Chemical signals can be used between body parts, between cells, and between individual organisms ( pheromones ).
    • Underarm secretions may be slightly attractive and may be involved in synchronizing the menstrual cycles of women who live together.
  • Chemical signals
  • Chemical signals
  • The Action of Hormones
    • Steroid hormones enter the nucleus and combine with a receptor protein, and the hormone-receptor complex attaches to DNA and activates certain genes.
    • Transcription and translation lead to protein synthesis.
  • Action of a steroid hormone
  • Hormones trigger changes in their target cells when they bind to receptor proteins on or within the cells. A model of a hormone (A) bound to its protein receptor (B). Each hormone of the endocrine system has a unique molecular shape, which fits into a specific receptor protein on its target cells.
    • Peptide hormones are usually received by a hormone receptor protein located in the plasma membrane.
    • Most often the reception of a peptide hormone leads to activation of an enzyme that changes ATP to cyclic AMP (cAMP).
    • cAMP, as a second messenger , then activates an enzyme cascade.
    • Hormones work in small quantities because their effect is amplified by enzymes.
  • Action of a peptide hormone
    • Hormone production will be regulated in most cases by negative feedback systems. Once the desired outcome is reached, the outcome will inhibit the hormone release.
    • Hormones are also classified as:
      • Tropic: have endocrine glands as their target
      • Non-tropic:don’t have endocrine glands as their target
  • The endocrine system
  • Hypothalamus and Pituitary Gland
    • The hypothalamus regulates the internal environment through the autonomic system and also controls the secretions of the pituitary gland.
    • The pituitary has two portions: the anterior pituitary and the posterior pituitary.
  • Posterior Pituitary
    • The posterior pituitary stores and releases the antidiuretic hormone ( ADH ) and oxytocin produced by the hypothalamus.
    • ADH is secreted during dehydration and causes more water to be reabsorbed by the kidneys; the secretion of ADH is regulated by negative feedback.
    • Oxytocin causes uterine contractions and milk release, and is controlled by positive feedback.
  • Posterior Pituitary ADH is released when the blood plasma concentration is high (and blood pressure is low). ADH stimulates the kidneys to absorb more water, which dilutes the blood plasma (and increases blood pressure).
  • Anterior Pituitary
    • The hypothalamus controls the anterior pituitary by producing hypothalamic-releasing hormones and hypothalamic-inhibiting hormones .
    • The anterior pituitary produces six hormones.
    • Four of these six hormones have an effect on other endocrine glands:
    • Thyroid-stimulating hormone ( TSH ) stimulates the thyroid to produce thyroid hormones;
    • 2) adrenocorticotropic hormone ( ACTH ) stimulates the adrenal cortex to produce cortisol;
    • 3&4) the gonadotropic hormones (FSH and LH) stimulate the gonads to produce sex cells and hormones.
    • In these four instances, the blood level of the last hormone exerts negative feedback control over the secretion of the first two hormones.
  •  
    • The next two anterior pituitary hormones do not effect other endocrine glands.
    • After childbirth, prolactin ( PRL ) causes mammary glands to produce milk.
    • Growth hormone ( GH ) promotes skeletal and muscular growth.
  • Hypothalamus and the pituitary
  • Effects of Growth Hormone
    • The quantity of GH is greatest during childhood and adolescence; GH promotes bone and muscle growth.
    • Pituitary dwarfism results from too little GH during childhood.
    • Giants result from too much growth hormone during childhood.
    • If growth hormone is overproduced in an adult, it causes acromegaly .
  • Effect of growth hormone
  • Acromegaly
  • Thyroid and Parathyroid Glands
    • The thyroid gland is a large gland located in the neck, where it is attached to the trachea just below the larynx.
    • The four parathyroid glands are embedded in the posterior surface of the thyroid gland.
  • Thyroid Gland
    • The thyroid gland requires iodine to produce thyroxine (T 4 ) which contains four iodine atoms, and triiodothyronine (T 3 ) which contains three iodine atoms.
    • Thyroid hormones increase the metabolic rate, and stimulate all body cells to metabolize and use energy at a faster rate.
    • Effects of Thyroid Hormones
    • If too little thyroxine is present  hypothyroidism
      • cold, fatigue, dry skin, hair loss, weight gain, sleep a lot (myxedema in adults)
      • in children, leads to abnormal mental and physical development , growth retardation (cretinism in childhood)
    • If too much thyroxine is present  hyperthyroidism (Grave’s disease)
      • jittery, weight loss, fast heart rate, feel warm, mood swings, hair loss, bulging eyes
      • treated by removing a portion of the thyroid gland (surgically or chemically)
    • If iodine is lacking in the diet, a simple goiter develops.
    • Use of iodized salt helps prevent simple goiters.
    • Iodine is required to synthesize thyroxine
    • swelling is due to the continued stimulation by TSH (no thyroxine made), causes increase in thyroid size in an attempt to make more thyroxine
  • Simple goiter
  • Cretinism
    • Calcitonin
    • The thyroid gland also produces calcitonin , which helps lower the blood calcium level when it is too high.
    • The primary effect of calcitonin is to bring about the deposit of calcium in the bones; it does this by temporarily reducing the activity and number of osteoclasts.
    • When the blood level of calcium is returned to normal, the release of calcitonin is inhibited.
  • Parathyroid Glands
    • Parathyroid glands secrete parathyroid hormone ( PTH ), which raises the blood calcium when it is insufficient, and decreases the blood phosphate level.
    • PTH acts by stimulating the activity of osteoclasts, thus releasing calcium from bone, and stimulates the reabsorption of calcium by the kidneys and intestine.
    • Insufficient parathyroid hormone will cause serious loss of blood calcium and cause tetany .
  • Regulation of blood calcium level
  • Adrenal Glands
    • Adrenal glands sit atop the kidneys and have an inner adrenal medulla and an outer adrenal cortex .
    • The hypothalamus uses ACTH-releasing hormone to control the anterior pituitary’s secretion of ACTH that stimulates the adrenal cortex.
    • The hypothalamus regulates the medulla by direct nerve impulses.
    • The adrenal medulla secretes epinephrine and norepinephrine , which bring about responses we associate with emergency situations.
    • On a long-term basis, the adrenal cortex produces glucocorticoids similar to cortisone and mineralocorticoids to regulate salt and water balance.
    • The adrenal cortex also secretes both male and female sex hormones in both sexes.
  • Adrenal glands
  • Glucocorticoids
    • Cortisol promotes breakdown of muscle proteins to amino acids; the liver then breaks the amino acids into glucose.
    • Cortisol also promotes metabolism of fatty acids rather than carbohydrates, which spares glucose.
    • Both actions raise the blood glucose level.
    • High levels of blood glucocorticoids can suppress immune system function.
  • Mineralocorticoids
    • Aldosterone causes the kidneys to reabsorb sodium ions (Na + ) and excrete potassium ions (K + ).
    • When blood sodium levels and blood pressure are low, the kidneys secrete renin; the effect of the renin-angiotensin-aldosterone system is to raise blood pressure.
  • Regulation of blood pressure and volume
  • Malfunction of the Adrenal Cortex
    • Addison disease develops when the adrenal cortex hyposecretes hormones.
    • A bronzing of the skin follows low levels of cortisol, and mild infection can lead to death; aldosterone is also hyposecreted, and dehydration can result.
    • Cushing syndrome develops when the adrenal cortex hypersecretes cortisol.
    • The trunk and face become round; too much aldosterone results in fluid retention.
  • Addison disease
  • Cushing syndrome
  • Pancreas
    • The pancreas is between the kidneys and the duodenum and provides digestive juices and endocrine functions.
    • Pancreatic Islets of Langerhans secrete:
    • - insulin , from the beta cells, which lowers the blood glucose level
    • - insulin makes cells more permeable to glucose
    • - glucagon , from the alpha cells, which increases the blood glucose level
    • - glucagon causes the conversion of glycogen to glucose
  • Regulation of blood glucose level
  • Diabetes Mellitus
    • The most common illness due to hormonal imbalance is diabetes mellitus .
    • Diabetes is due to the failure of the pancreas to produce insulin or the inability of the body cells to take it up.
    • Hyperglycemia symptoms develop, and glucose appears in the urine.
    • Diabetes is diagnosed using a glucose tolerance test.
  • Glucose tolerance test
    • Type I diabetes mellitus occurs when the pancreas does not produce insulin and the patient requires insulin injections.
    • Most people with diabetes have Type II diabetes mellitus where the pancreas produces insulin but the body cells (insulin receptors) do not respond.
    • Both types lead to long-term serious complications.
    • type I (insulin dependent) caused by lack of insulin production in pancreas, hereditary but may skip generations
    • treated with insulin injections and rigid blood monitoring
    • since insulin is a protein it would be digested if taken orally
    • must monitor both hypoglycemia (need glucagon or glucose) and hyperglycemia (need insulin)
    • in research: islet transplants, gene therapy (thought to have found gene)
    • type II (insulin independent), caused by decreased response to insulin or a decrease in insulin production, (not enough compensation by pancreas), insulin resistance
    • gestational diabetes, during pregnancy, mother develops symptoms – at a greater risk for type II later in life
    • only type I requires daily insulin injections, type II and GDM are treated by exercise, diet & sometimes sulfonamides
    • symptoms of type I and II
      • fatigue (not enough glucose inside cells to provide an energy source – must use fat & protein)
      • excessive thirst & urination (glucose in urine pulls out water by osmosis)
      • increased appetite (& weight loss – type I)
      • increased susceptibility to infection
    • *** in type II, since it onsets slowly, there may be no symptoms initially
    • diabetes causes many complications due to fluctuations in blood sugar and ketoacidosis (products of fat breakdown which are toxic to the body), leads to acetone smell on the breath
    • diabetes insipidous, which has nothing to do with insulin, but ADH production in the pituitary – a tumour or injury causes  ADH or response to ADH, causing frequent urination (up to 30 L per day). Treat with ADH nasal spray
  • Other Endocrine Glands
    • Testes and Ovaries
    • Testes, located in the scrotum, produce the male hormone testosterone .
    • Ovaries in the female produce estrogens and progesterone .
    • Secretions from the gonads are controlled by the anterior pituitary hormones.
    • These sex hormones maintain the sex organs and secondary sex characteristics.
  • The effects of anabolic steroid use
  • Prostaglandins
    • Prostaglandins are produced within cells from arachidonate, a fatty acid.
    • Prostaglandins act close to where they are produced.
    • They cause uterine muscle contraction and are involved in the pain of menstrual cramps; aspirin is effective against the pain by countering prostaglandins.
  • Chapter Summary
    • Hormones are chemical signals that affect the activity of target glands or tissues.
    • Endocrine glands are ductless and distribute hormones by the bloodstream.
    • The hypothalamus is a part of the brain that controls the functioning of the pituitary gland.
    • The anterior pituitary produces several hormones, some of which control other endocrine glands.
    • Growth hormone is produced by the anterior pituitary; giants are due to overproduction of growth hormone during childhood, and pituitary dwarfs are due to underproduction of growth hormone.
    • The thyroid produces two hormones that speed metabolism and another hormone that lowers the blood calcium level.
    • The distinct parathyroid glands produce a hormone that raises blood calcium level.
    • Adrenal glands produce hormones that help us respond to stress.
    • Malfunction of the adrenal cortex leads to the symptoms of Addison disease and Cushing disease.
    • The pancreas secretes hormones that regulate the blood glucose level.
    • Diabetes mellitus occurs when cells are unable to take up glucose and it spills over into the urine.
    • The gonads produce sex hormones that control secondary sex characteristics.
    • Many other tissues, although not traditionally considered endocrine glands, secrete hormones.
    • Hormones influence the metabolism of their target cells.