Question about epinephrine

Question about epinephrine

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In my class we were told that adrenaline (or epinephrine) causes vasoconstriction. My question was I had always thought that people took this via an EpiPen when they were having an allergic reaction.

So I thought it would make sense, that it would dilate vessels, because this will allow more air through. Or does the constriction help because it tightens the vessels in the throat allowing a reduction of swelling?

An allergic reaction requiring an epipen can be caused by swelling in the throat and/or bronchoconstriction (spasms decreasing the diameter of bronchioles). Bronchoconstriction can occur in the absence of soft tissue swelling in the lips, tongue and throat, and vs. versa.

Epinephrine reduces pharyngeal edema (swelling) because it is a potent vasoconstrictor in small arterioles and precapillary sphincters in most body organ systems. This is effected through alpha-1 adrenergic receptor activation. While the blood pressure and heart rate increase (due to beta-1 adrenergic effects), the permeability at the capillary level is decreased, relieving swelling.

At the same time, epinephrine relaxes bronchial muscle. It has a powerful bronchodilator action when bronchial muscle is contracted because it is a powerful beta2 adrenergic agonist.

Finally, epinephrine inhibits antigen-induced release of inflammatory mediators from mast cells, and to a lesser extent from diminution of bronchial secretions and congestion within the mucosa. Inhibition of mast cell secretion is mediated by beta2 adrenergic receptors.

Adapted from Simons. Kemp et al. World Allergy Organization Journal 2008 1(Suppl 2):S18-S26 doi:10.1186/1939-4551-1-S2-S18

Epinephrine: The Drug of Choice for Anaphylaxis--A Statement of the World Allergy Organization

  • Epinephrine, produced by the adrenal medulla, causes either smooth muscle relaxation in the airways or contraction of the smooth muscle in arterioles, which results in blood vessel constriction in the kidneys, decreasing or inhibiting blood flow to the nephrons.
  • Norepinephrine, produced by the adrenal medulla, is a stress hormone that increases blood pressure, heart rate, and glucose from energy stores in the kidneys, it will cause constriction of the smooth muscles, resulting in decreased or inhibited flow to the nephrons.
  • Together, epinephrine and norepinephrine cause constriction of the blood vessels associated with the kidneys to inhibit flow to the nephrons.
  • epinephrine: (adrenaline) an amino acid-derived hormone secreted by the adrenal gland in response to stress
  • norepinephrine: a neurotransmitter found in the locus coeruleus which is synthesized from dopamine
  • catecholamine: any of a class of aromatic amines derived from pyrocatechol that are hormones produced by the adrenal gland
  • adrenergic: containing or releasing adrenaline

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Biology Question Bank – 41 MCQs on “Endocrine System” – Answered!

41 Questions with Answers and Explanations on “Endocrine System” for Biology Students.

1. MSH of pars intermedia of middle pituitary is responsible for

(a) darkening of skin in lower vertebrates

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(b) light colouration of skin in lower vertebrates

(d) darkening of skin in human beings.

Answer and Explanation:

1. (a): Pars intermedia is the boundary between the anterior and posterior lobes of the pituitary. It contains three types of cells – basophils, chromophobes and colloid- filled cysts. This area produces melanocyte stimulating hormone or MSH. It stimulates the synthesis of black pigment melanin in the skin and also causes dispersion of melanin granules in the pigment cells, thereby darkening the colour in certain animals (fishes amphibians). In man it has no such role.

2. Which hormone possesses anti-insulin effect?

Answer and Explanation:

2. (a): Insulin decreases the level of glucose in the blood while Cortisol (secreted by middle region of adrenal cortex) increases the blood-glucose level by converting proteins and fats into carbohydrates which are, in turn, converted to glucose.

3. Addition of a trace of thyroxine or iodine in water containing tadpoles will

(a) keep them in larval stage

(b) hasten their metamorphosis

(c) slow down their metamorphosis

Answer and Explanation:

3. (b): In 1912, Gudematsch discovered that metamorphosis in frog’s tadpole is increased by the thyroxine hormone which has the iodine as the main constituent. If thyroxine or iodine in added in water having tadpoles in it, then it increases the rate of metamorphosis in tadpole.

Answer and Explanation:

4. (c): Insulin is a hormone secreted by the (3-cells of pancreas on stimulation by a rise in blood-glucose level.

5. Occurrence of Leydig’s cells and their secretion is

(d) testis and testosterone.

Answer and Explanation:

5. (d): A pair of testes is situated in the scrotum of male. The connective tissue present between the seminiferous tubules in a testis contains small clusters of endocrine cells called interstitial cells or Leydig’s cells. These cells secrete various male sex hormones called androgens. The principal androgen is testosterone.

6. ADH or vasopressin is

(a) enzyme that hydrolyses peptides

(b) hormone secreted by pituitary that promotes reabsorption of water from glomerular filtrate

(c) hormone that promotes glycogenolysis

(d) energy rich compound connected with muscle contraction.

Answer and Explanation:

6. (b): Antidiuretic hormone (ADH) or vasopressin is secreted by the posterior lobe of the pituitary gland. It increases the reabsorption of water in the distal convoluted tubule, collecting tubules and collecting ducts of the nephrons of the kidneys. As a result, the reabsorption of water from the glomerular filtrate is increased. Enzyme that hydrolysis peptide is known as peptidase. A hormone that promotes glycogenosis is glucagon and adrenaline. Energy rich compound connected with muscle contraction is ATP.

7. Gastric secretion is stopped by hormone

Answer and Explanation:

7. (a): Enterogastrone is secreted by duodenal epithelium and it slows gastric contractions to delay its emptying and also stops secretion of gastric juice. Gastrin stimulates secretion of gastric juice. Cholecystokinin stimulates release of enzymes in pancreatic juice and release of bile from gall bladder. Cholecystokinin is also known as pancreozymin.

8. Testosterone is produced by

Answer and Explanation:

9. The immediate cause of induction of ovulation in human female is the large plasma surge of

Answer and Explanation:

9. (a): LH (luteinising hormone) is released by anterior lobe of pituitary gland. It causes ovulation, secretion of estrogen from mature ovarian follicle and progesterone from corpus luteum. FSH stimulates sperm formation in the male and growth of ovarian follicles in the female. Progesterone suspends ovulation during pregnancy, fixes the foetus to the uterine wall, forms placenta and controls the development of the foetus in the uterus. Estradiol is the major estrogen in humans.

10. According to the accepted concept of hormone action, if receptor molecules are removed from target organs, then the target organ will

(a) continue to respond to the hormone without any difference

(b) not respond to the hormone

(c) continue to respond to the hormone but will require higher concentration

(d) continue to respond to the hormone but in the opposite way.

Answer and Explanation:

10. (b): The molecules of hormones that are amino acid derivatives, peptides Ci proteins are large and insoluble in lipids, and cannot enter the target cell. Therefore, they act at the cell surface. They bind to specific receptor molecules located on the surface of the cell membrane. Therefore, if receptor molecules are removed from target organs, then the target organ will not respond to the hormone.

11. Which one of the following endocrine glands stores its secretion in the extracellular space before discharging it into the blood?

Answer and Explanation:

11. (b): The thyroid gland secretes three hormones : thyroxine or tetraiodothyronine (T4)’, triiodothyronine (T,) 2 and calcitonin. Thyroxine and Triiodothyronine are iodinated forms of the amino acid tyrosine. They are stored in the colloid that fills the follicles, and are released to the blood when needed. The storage occurs in an unusual place, the extracellular colloid.

12. Which hormone stimulates the secretion of milk from female?

Answer and Explanation:

12. (d): Prolactin hormone stimulates the growth of milk glands during pregnancy and the secretion of milk after delivery. Oxytocin causes release of milk during sucking by the infant. LH causes ovulation and secretion of estrogen and progesterone from ovarian follicle and corpus luteum respectively. Oxytocin, LH and prolactin are released by anterior lobe of pituitary gland. Progesterone is secreted by corpus luteum.

13. Hormones thyroxine, adrenaline and the pigment melanin are formed from

Answer and Explanation:

13. (a): Hormones thyroxine, adrenaline and the pigment melanin are formed from tyrosine. Tyrosine is transformed into dopa through the enzyme tyrosinase. Then through different metabolic pathways it produces thyroxine, adrenaline, melanin etc.

14. The hormone which regulates the basal metabolism in our body is secreted from

Answer and Explanation:

14. (d): The basal metabolism is the minimum amount of energy the body uses in order to maintain vital processes of the body. Generally, this expenditure of energy is expressed in terms of heat production per unit of body surface per day on the basal metabolic rate (BMR). Thyroid is the largest endocrine gland secreting three hormones thyroxine, triiodothyronine and calcitonin.

Thyroxine and triiodothyronine control BMR of the body by regulating the rate of oxidation and production of energy. Calcitonin regulates the concentration of calcium and phosphorus in the blood. Adrenal cortex secretes mineralocorticoids, glucocorticoids and sexcorticoids. Pituitary gland consists of three lobes and all of them secrete separate hormones. Pancreas secretes four hormones – insulin, glucagon, somatostatin and pancreatic polypeptide.

15. The contraction of gall bladder is due to wine System

Answer and Explanation:

15. (a): Cholecystokinin is secreted by duodenal epithelium and it stimulates gall blader to release bile that causes emulsification of fats to increase lipase action on them. Enterogastrone and secretin are also secreted by duodenal epithelium. Enterogastrone slows gastric contractions to delay its emptying and also stops secretion of gastric juice. Secretin causes release of sodium bicarbonate in pancreaticjuice, steps up secretion of bile and inhibits secretion of gastrin. Gastrin stimulates secretion of gastric juice and is secreted by mucosa of pyloric stomach.

The hormone that stimulates the stomach to secrete gastric juice is

Answer and Explanation:

16. (c): Gastrin hormone is secreted by mucosa of stomach and it stimulates secretion of gastric juice. Enterogastrone is secreted by duodenal epithelium. Enterokinase is an enzyme that converts trypsinogen into trypsin. Renin converts caesin of milk into paracaesin and whey protein.

17. Calcitonin is a thyroid hormone which

(a) elevates calcium level in blood

(b) has no effect on calcium

(c) elevates potassium level in blood

(d) lowers calcium level in blood.

Answer and Explanation:

17. (d): Calcitonin is secreted by the C cells. It regulates the concentration of calcium and phosphorus in the blood. It is under the feedback control of plasma calcium concentration, and is secreted when concentration of calcium rises in the blood. It then lowers the concentration of calcium and phosphorus in the plasma by decreasing their release from the bones.

18. Diabetes is due to

Answer and Explanation:

18. (d): Diabetes mellitus is caused by the deficiency of hormone insulin which is secreted by pancreas. Insulin lowers the blood-glucose level. Deficiency of antidiuretic hormone (ADH) leads to diabetes insipidus.

19. The gonadotrophic hormones are secreted by

(a) anterior lobe of pituitary

(b) interstitial cells of testes

(d) posterior part of thyroid.

Answer and Explanation:

19. (a): Gonadotropic hormones are secreted by anterior lobe of pituitary gland. They are as follows:

(a) Follicle-stimulating hormone (FSH) It stimulates growth of ovarian follicles and their secretion of oestrogens in the female, and spermatogenesis (formation of sperms) in the male.

(b) Interstitial-cell stimulating hormone (ICSH). It activates the Leydig’s (interstitial) cells of the test is to secrete androgens. In female, it stimulates the corpus luteum of the ovary to secrete progesterone. In female it is termed luteinizing hormone (LH).

20. Secretion of progesterone by corpus luteum is initiated by

Answer and Explanation:

20. (d): Luteinsing Hormone (LH) in the male, induces the interstitial cells of the testes to produce male sex hormones named androgens such as testosterone. In the female, the luteinising hormone causes ovulation, secretion of female sex hormone, estrogen from the maturing ovarian follicle, and progesterone by the corpus luteum.

Testosterone makes the male genital system to become full grown and functional. Thyroxine promotes growth of body tissues. MSH stimulates synthesis of melanin in the skin.

21. The function of oxytocin is to help in

Answer and Explanation:

21. (d): Oxytocin is secreted by posterior lobe of pituitary gland. It induces contractions of smooth muscles of myoepithelial cells of the mammary glands to cause release of milk during sucking by the infant. Because of its role, oxytocin is called “birth hormone” and “milk ejecting hormone”.

22. Cholecystokinin and duocrinin are secreted by

Answer and Explanation:

22. (c): Cholecystokinin and duocrinin are secreted by intestine. It stimulates pancreas to release enzymes in pancreatic juice and stimulates gall bladder to release bile. Duocrinin causes release of viscous mucus from Brunner’s glands into intestinal juice.

23. MSH is secreted by

(a) anterior lobe of pituitary

(b) middle lobe of pituitary

(c) posterior lobe of pituitary

Answer and Explanation:

23. (b): Middle lobe of pituitary secretes a hormone named melanocyte-stimulating hormone. It stimulates the synthesis of black pigment melanin in the skin, and also causes dispersal of melanin granules in the pigment cells, thereby darkening the colour in certain animals (fishes amphibians). In man it has no such role. Anterior lobe of pituitary secretes FSH, LH, and TSH. ACTH and STH. Posterior lobe of pituitary secretes oxytocin and vasopressin.

24. Which gland secretes odorous secretion in mammals?

Answer and Explanation:

24. (c): The anal glands are small paired sacs located on either side of the anus between the external and internal sphincter muscles. These sebaceous glands within the lining secrete a foul smelling liquid that is used for identification of members within a species. These glands are found in all camivora except bears.

A pair of Bartholin’s glands occurs one on each side of the vaginal opening. They secrete viscid fluid and their ducts pour the fluid into the vestibule to lubricate the vulva during copulation. The prostate gland is present in males surrounding the urethra. It secretes a milky fluid that aids in sperm motility. Liver is the largest gland of the body and performs various functions like deamination, production of bile, glycogenesis, storage etc.

25. Melatonin is secreted by

Answer and Explanation:

25. (a): Pineal gland is a stalked, small rounded organ. It is located on the midline, attached to the posterior end of the roof of the third ventricle in the brain. It secretes two biogenic hormones – melatonin and serotonin. Melatonin causes concentration of pigment granules in the melanocytes.

It also regulates the working of gonads. Pituitary gland secretes a number of hormones, e.g., follicle-stimulating hormone, luteinising hormone, oxytocin etc. Thyroid secretes thyroxine and triiodothyronine. Skin synthesize vitamin D in the presence of sunlight. It exists in two forms: calciferol or D2 and cholecalciferol or Dv D3 circulates in the blood. Calcitriol is active form of D3. It increases absorption of calcium and phosphorus from chyme in the small intestine and accelerate bone formation.

26. Which set is similar

(a) corpus luteum – graafian follicles

(c) bundle of His – pace maker

Answer and Explanation:

26. (a): After ovulation many of the follicular cells remain in the collapsed graafian follicle on the surface of the ovary. The antrum (cavity) of the collapsed follicle fills with a partially clotted fluid.

The follicular cells enlarge and fill with a yellow pigment, lutein. Such a follicle is called a corpus luteum – literally, yellow body. Sebum is secreted by sebaceous glands. SA node is known as pacemaker. Niacin is a vitamin that forms a part of coenzymes (NAD, NADP). Vitamin B7 (Biotin) acts as coenzyme in fatty acid synthesis and in change of pyruvate to oxaloacetate.

27. Mainly which type of hormones control the menstrual cycle in human beings?

Answer and Explanation:

27. (c): Menstrual cycle is controlled by several endocrinal parameters.

In beginning of the cycle FSH (follicle stimulating hormone) of pituitary initiates development of an ovarian follicle. A growing ovarian follicle gradually secretes increasing amount of oestrogen. This in turn leads to sudden surge of LH secretion by the pituitary. As the LH (leutinising hormone) level in blood suddenly increases there is ovulation.

Thus only FSH or LH cannot control all the events of menstrual cycle. Progesteron is released by a corpus luteum after ovulation which actually prepares the uterus for a possible pregnancy.

If there is no fertilisation progesteron level falls and there is beginning of a new cycle.

28. When both ovaries are removed from rat then which hormone is decreased in blood?

(d) gonadotropin releasing factor.

Answer and Explanation:

28. (c): Ovary secretes two hormones. Oestrogen before ovulation and progesteron after ovulation. Oxytocin, prolaction are pituitary hormones and gonadotropin releasing factor is secreted by hypothalamus of brain to stimulate pituitary for the secretion of gonadotropic hormones.

29. Adrenaline directly affects on

(c) dorsal root of spinal nerve

(d) epithelial cells of stomach.

Answer and Explanation:

29. (a): Adrenalin directly affects the SA node to increase rate of heartbeat. Adrenalin prepares the body for emergency reactions like fight & flight. Thus there is increase in heart rate, breathing rate, blood pressure, glucose level in blood, peripheral circulation, etc. (3-cells of islet of Langerhans secrete insulin that lower blood glucose level. Secretion of digestive juice by epithelial cells of stomach is inhibited during this time.

30. Acromegaly is caused by

(c) deficiency of thyroxine

Answer and Explanation:

30. (a): Acromegaly is caused by excess of STH (somatotrophic hormone), relased by anterior lobe of pituitary after adolescence. The bones of the lower jaw and limbs become abnormally enlarge but the body does not attain a giant stature. Excess of thyroxine causes cretinism and myxoedema. Excess of adrenaline causes increased BMR, heartbeat, excitement etc.

31. Which one of the following pairs correctly matches a hormone with a disease resulting from its deficiency?

(c) Parathyroid hormone – Tetany

(d) Insulin – Diabetes insipidus

Answer and Explanation:

31. (c): Parathormone is a hormone secreted by parathyroid glands. Hyposecretion of parathormone lowers concentration of calcium ions in the blood and tissues due to excretion of calcium in urine. This increases the excitability of nerves and muscles, causing cramps and convulsions. Sustained contractions (tetany) of the muscles of larynx, face, hands and feet are produced. This disorder is known as parathyroid tetany. Hypersecretion of parathormone draws more calcium from the bones, resulting in their softening, bending and fracture. This condition is called osteoporosis.

32. Chemically hormones are

(b) proteins, steroids and biogenic amines

Answer and Explanation:

32. (b): Hormones are chemical messengers produced by the ductless glands (sometimes by neurons) and transported in the circulation to target cells. They regulate metabolic processes. Chemically hormones are of different nature like biogenic amines (like thyroxine, adrenaline etc), proteinaceous or polypeptide (like hypothalamic hormones etc.) and steroids (like sex hormones and adrenocorticoids.

33. Which one of the following pairs correctly matches a hormone with a disease resulting from its deficiency?

(a) Luteinizing hormone – Failure of ovulation

(b) Insulin – Diabetes insipidus

(d) Parathyroid hormone – Diabetes mellitus.

Answer and Explanation:

33. (a): Ovulation occurs under the influence of luteinizing hormone and FSH (follicle stimulating hormone) of anterior pituitary gland. Thus, deficiency of lutenaizing hormone results in failure of ovulation. Diabetes mellitus, tetany and diabetes insipidus occur due to deficiency of insulin (secreted from pancreas), parathormone (secreted by parathyroid gland) and vasopressin (ADI I) of posterior pituitary respectively.

34. Which one of the following hormones is modified amino acid?

Answer and Explanation:

34. (a): Epinephrine is synthesized from tyrosine which is a non-essential amino acid possessing cyclic structure with a straight side chain bearing carboxylic and amino group. The conversion of tyrosine to epinephrine involves 4 steps-(a) ring hydroxylation (b) decarboxylation, (c) side-chain hydroxylation (d) N-methylation.

35. Which one of the following statements is correct?

(a) endocrine glands regulate neural activity, but not vice versa

(b) neurons regulate endocrine activity, but not vice versa

(c) endocrine glands regulate neural activity, and nervous system regulates endocrine glands

(d) neither hormones control neural activity nor the neurons control endocrine activity

Answer and Explanation:

35. (c): The endocrine system links the brain to the organs that control body metabolism, growth and development, and reproduction. The endocrine system is regulated by feedback. For example, the hormones that are regulated by the pituitary gland, a signal is sent from the hypothalamus to the pituitary gland in the form of a “releasing hormone,” which stimulates the pituitary to secrete a “stimulating hormone” into the circulation.

The stimulating hormone then signals the target gland to I secrete its hormone. As the level of this hormone rises in the circulation, the hypothalamus and the pituitary gland shut down secretion of the releasing hormone and the stimulating hormone, which in turn slows the secretion by the target gland. This system results in stable blood concentrations of the hormones that are regulated by the pituitary gland.

36. Which one of the following is not a secondary messenger in hormone action?

Answer and Explanation:

36. (d): Secondary messengers are low-weight diffusible molecules that are used to relay signals within a cell. They are synthesized or released by specific enzymatic reactions, usually as a result of an external signal that is received by a transmembrane receptor. cAMP, cGMPand Ca 2 act as secondary messengers and are located within the cytoplasm. Sodium is an essential nutrient which helps to maintain blood volume and keeps nerves functioning.

37. A steroid hormone which regulates glucose metabolism is

37. (b): Glucocorticoids (e.g. Cortisol) are secreted by the middle region of the adrenal cortex. They regulate the metabolism of carbohydrates, proteins and fats. They increase the blood-glucose level by converting proteins and fats into carboy hydrates which are in turn, converted to glucose.

38. Which of the following is an accumulation and release centre of neurohormones?

(a) anterior pituitary lobe

(b) posterior pituitary lobe

(c) intermediate lobe of the pituitary

Answer and Explanation:

38. (d): The neurosecretory cells of the hypothalamus, when stimulated, release hormones, called neurohormones via axons into the capillaries. The neurohormones are carried by the portal blood to the anterior lobe of the pituitary gland and stimulate the latter to release its hormones.

On this account, such hypothalamic hormones are also called releaser hormones. Certain hypothalamic hormones inhibit the secretion of some pituitary hormones. These are termed inhibitory hormones or factors (IH or IF).

39. Which hormone causes dilation of blood vessels, increased oxygen consumption and glucogenesis?

Answer and Explanation:

39. (d): Adrenaline is the hormone secreted by adrenal medulla. It prepares the animal to face special conditions created by physical stress. All these conditions require more energy which is provided by increasing heart beat, blood pressure, respiratory rate, sugar level of blood, blood supply of heart and skeletal muscles and brain through dilation of their small arteries, and oxidative metabolism. It also stimulates the breakdown of liver and muscle glycogen (glucogenesis) to provide glucose for respiration.

40. A person is having problems with calcium and phosphorus metabolism in his body. Which one of the following glands may not be functioning properly?

Answer and Explanation:

40. (d): The parathyroid glands are small endocrine glands in the neck, usually located behind the thyroid gland, which produce parathyroid hormone. Parathyroid hormone (PTH, also known as parathormone) is a small protein that takes part in the control of calcium and phosphorus homeostasis, as well as bone physiology.

When blood calcium level drops below a certain point, calcium-sensing receptors in the parathyroid gland are activated to release hormone into the blood. It then stimulates osteoclasts to break down bone and release calcium into the blood, and increase gastro-intestinal calcium absorption.

The parotid gland, found wrapped around the mandibular ramus, secretes saliva through Stensen’s duct into the oral cavity to facilitate mastication and swallowing. Inflammation of one or both parotid glands is known as parotitis.

The most common cause of parotitis was mumps. Pancreas is a large, elongated gland located behind the lower portion of the stomach that secretes the hormones insulin and glucagon into the blood. These hormones are essential in regulating blood sugar levels.

The pancreas also secretes enzymes into the small intestine that help with digestion and neutralize acid from the stomach. Thyroid gland is bilobed endocrine gland situated in the base of the neck and secretes two iodine-containing thyroid hormones, thyroxine (T4) and triiodothyronine (T3).

They control the rate of all metabolic processes in the body and influence physical development and activity of the nervous system. Disorders associated with thyroid gland are – cretinism, myxoedema, goitre, Hashimoto’s disease due to its hyposecretion and Grave’s disease due to its hypersecretion.

41. Feeling the tremors of an earthquake a scared resident of seventh floor of a multistoryed building starts climbing down the stairs rapidly. Which hormone initiated this action?

Answer and Explanation:

41. (a): Adrenaline (epinephrine), also called emergency hormone, is a hormone, produced by the medulla of the adrenal glands, that increases heart activity, improves the power and prolongs the action of muscles, and increases the rate and depth of breathing to prepare the body for ‘fright, flight, or fight’. At the same time it inhibits digestion and excretion. Similar effects are produced by stimulation of the sympathetic nervous system.

16.4 Endocrine System

The endocrine system produces hormones that function to control and regulate many different body processes. The endocrine system coordinates with the nervous system to control the functions of the other organ systems. Cells of the endocrine system produce molecular signals called hormones. These cells may compose endocrine glands, may be tissues or may be located in organs or tissues that have functions in addition to hormone production. Hormones circulate throughout the body and stimulate a response in cells that have receptors able to bind with them. The changes brought about in the receiving cells affect the functioning of the organ system to which they belong. Many of the hormones are secreted in response to signals from the nervous system, thus the two systems act in concert to effect changes in the body.


Maintaining homeostasis within the body requires the coordination of many different systems and organs. One mechanism of communication between neighboring cells, and between cells and tissues in distant parts of the body, occurs through the release of chemicals called hormones. Hormones are released into body fluids, usually blood, which carries them to their target cells where they elicit a response. The cells that secrete hormones are often located in specific organs, called endocrine glands , and the cells, tissues, and organs that secrete hormones make up the endocrine system. Examples of endocrine organs include the pancreas, which produces the hormones insulin and glucagon to regulate blood-glucose levels, the adrenal glands, which produce hormones such as epinephrine and norepinephrine that regulate responses to stress, and the thyroid gland, which produces thyroid hormones that regulate metabolic rates.

The endocrine glands differ from the exocrine glands. Exocrine glands secrete chemicals through ducts that lead outside the gland (not to the blood). For example, sweat produced by sweat glands is released into ducts that carry sweat to the surface of the skin. The pancreas has both endocrine and exocrine functions because besides releasing hormones into the blood. It also produces digestive juices, which are carried by ducts into the small intestine.

Career Connection


An endocrinologist is a medical doctor who specializes in treating endocrine disorders. An endocrine surgeon specializes in the surgical treatment of endocrine diseases and glands. Some of the diseases that are managed by endocrinologists include disorders of the pancreas (diabetes mellitus), disorders of the pituitary (gigantism, acromegaly, and pituitary dwarfism), disorders of the thyroid gland (goiter and Graves’ disease), and disorders of the adrenal glands (Cushing’s disease and Addison’s disease).

Endocrinologists are required to assess patients and diagnose endocrine disorders through extensive use of laboratory tests. Many endocrine diseases are diagnosed using tests that stimulate or suppress endocrine organ functioning. Blood samples are then drawn to determine the effect of stimulating or suppressing an endocrine organ on the production of hormones. For example, to diagnose diabetes mellitus, patients are required to fast for 12 to 24 hours. They are then given a sugary drink, which stimulates the pancreas to produce insulin to decrease blood-glucose levels. A blood sample is taken one to two hours after the sugar drink is consumed. If the pancreas is functioning properly, the blood-glucose level will be within a normal range. Another example is the A1C test, which can be performed during blood screening. The A1C test measures average blood-glucose levels over the past two to three months. The A1C test is an indicator of how well blood glucose is being managed over a long time.

Once a disease such as diabetes has been diagnosed, endocrinologists can prescribe lifestyle changes and medications to treat the disease. Some cases of diabetes mellitus can be managed by exercise, weight loss, and a healthy diet in other cases, medications may be required to enhance insulin’s production or effect. If the disease cannot be controlled by these means, the endocrinologist may prescribe insulin injections.

In addition to clinical practice, endocrinologists may also be involved in primary research and development activities. For example, ongoing islet transplant research is investigating how healthy pancreas islet cells may be transplanted into diabetic patients. Successful islet transplants may allow patients to stop taking insulin injections.

How Hormones Work

Hormones cause changes in target cells by binding to specific cell-surface or intracellular hormone receptors , molecules embedded in the cell membrane or floating in the cytoplasm with a binding site that matches a binding site on the hormone molecule. In this way, even though hormones circulate throughout the body and come into contact with many different cell types, they only affect cells that possess the necessary receptors. Receptors for a specific hormone may be found on or in many different cells or may be limited to a small number of specialized cells. For example, thyroid hormones act on many different tissue types, stimulating metabolic activity throughout the body. Cells can have many receptors for the same hormone but often also possess receptors for different types of hormones. The number of receptors that respond to a hormone determines the cell’s sensitivity to that hormone, and the resulting cellular response. Additionally, the number of receptors available to respond to a hormone can change over time, resulting in increased or decreased cell sensitivity. In up-regulation , the number of receptors increases in response to rising hormone levels, making the cell more sensitive to the hormone and allowing for more cellular activity. When the number of receptors decreases in response to rising hormone levels, called down-regulation , cellular activity is reduced.

Endocrine Glands

The endocrine glands secrete hormones into the surrounding interstitial fluid those hormones then diffuse into blood and are carried to various organs and tissues within the body. The endocrine glands include the pituitary, thyroid, parathyroid, adrenal glands, gonads, pineal, and pancreas.

The pituitary gland , sometimes called the hypophysis, is located at the base of the brain (Figure 16.13a). It is attached to the hypothalamus. The posterior lobe stores and releases oxytocin and antidiuretic hormone produced by the hypothalamus. The anterior lobe responds to hormones produced by the hypothalamus by producing its own hormones, most of which regulate other hormone-producing glands.

The anterior pituitary produces six hormones: growth hormone, prolactin, thyroid-stimulating hormone, adrenocorticotropic hormone, follicle-stimulating hormone, and luteinizing hormone. Growth hormone stimulates cellular activities like protein synthesis that promote growth. Prolactin stimulates the production of milk by the mammary glands. The other hormones produced by the anterior pituitary regulate the production of hormones by other endocrine tissues (Table 16.1). The posterior pituitary is significantly different in structure from the anterior pituitary. It is a part of the brain, extending down from the hypothalamus, and contains mostly nerve fibers that extend from the hypothalamus to the posterior pituitary.

The thyroid gland is located in the neck, just below the larynx and in front of the trachea (Figure 16.13b). It is a butterfly-shaped gland with two lobes that are connected. The thyroid follicle cells synthesize the hormone thyroxine, which is also known as T4 because it contains four atoms of iodine, and triiodothyronine, also known as T3 because it contains three atoms of iodine. T3 and T4 are released by the thyroid in response to thyroid-stimulating hormone produced by the anterior pituitary, and both T3 and T4 have the effect of stimulating metabolic activity in the body and increasing energy use. A third hormone, calcitonin, is also produced by the thyroid. Calcitonin is released in response to rising calcium ion concentrations in the blood and has the effect of reducing those levels.

Most people have four parathyroid glands however, the number can vary from two to six. These glands are located on the posterior surface of the thyroid gland (Figure 16.13b).

The parathyroid glands produce parathyroid hormone. Parathyroid hormone increases blood calcium concentrations when calcium ion levels fall below normal.

The adrenal glands are located on top of each kidney (Figure 16.13c). The adrenal glands consist of an outer adrenal cortex and an inner adrenal medulla. These regions secrete different hormones.

The adrenal cortex produces mineralocorticoids, glucocorticoids, and androgens. The main mineralocorticoid is aldosterone, which regulates the concentration of ions in urine, sweat, and saliva. Aldosterone release from the adrenal cortex is stimulated by a decrease in blood concentrations of sodium ions, blood volume, or blood pressure, or by an increase in blood potassium levels. The glucocorticoids maintain proper blood-glucose levels between meals. They also control a response to stress by increasing glucose synthesis from fats and proteins and interact with epinephrine to cause vasoconstriction. Androgens are sex hormones that are produced in small amounts by the adrenal cortex. They do not normally affect sexual characteristics and may supplement sex hormones released from the gonads. The adrenal medulla contains two types of secretory cells: one that produces epinephrine (adrenaline) and another that produces norepinephrine (noradrenaline). Epinephrine and norepinephrine cause immediate, short-term changes in response to stressors, inducing the so-called fight-or-flight response. The responses include increased heart rate, breathing rate, cardiac muscle contractions, and blood-glucose levels. They also accelerate the breakdown of glucose in skeletal muscles and stored fats in adipose tissue, and redirect blood flow toward skeletal muscles and away from skin and viscera. The release of epinephrine and norepinephrine is stimulated by neural impulses from the sympathetic nervous system that originate from the hypothalamus.

The pancreas is an elongate organ located between the stomach and the proximal portion of the small intestine (Figure 16.13d). It contains both exocrine cells that excrete digestive enzymes and endocrine cells that release hormones.

The endocrine cells of the pancreas form clusters called pancreatic islets or the islets of Langerhans. Among the cell types in each pancreatic islet are the alpha cells, which produce the hormone glucagon, and the beta cells, which produce the hormone insulin. These hormones regulate blood-glucose levels. Alpha cells release glucagon as blood-glucose levels decline. When blood-glucose levels rise, beta cells release insulin. Glucagon causes the release of glucose to the blood from the liver, and insulin facilitates the uptake of glucose by the body’s cells.

The gonads—the male testes and female ovaries—produce steroid hormones. The testes produce androgens, testosterone being the most prominent, which allow for the development of secondary sex characteristics and the production of sperm cells. The ovaries produce estrogen and progesterone, which cause secondary sex characteristics, regulate production of eggs, control pregnancy, and prepare the body for childbirth.

There are several organs whose primary functions are non-endocrine but that also possess endocrine functions. These include the heart, kidneys, intestines, thymus, and adipose tissue. The heart has endocrine cells in the walls of the atria that release a hormone in response to increased blood volume. It causes a reduction in blood volume and blood pressure, and reduces the concentration of Na + in the blood.

The gastrointestinal tract produces several hormones that aid in digestion. The endocrine cells are located in the mucosa of the GI tract throughout the stomach and small intestine. They trigger the release of gastric juices, which help to break down and digest food in the GI tract.

The kidneys also possess endocrine function. Two of these hormones regulate ion concentrations and blood volume or pressure. Erythropoietin (EPO) is released by kidneys in response to low oxygen levels. EPO triggers the formation of red blood cells in the bone marrow. EPO has been used by athletes to improve performance. But EPO doping has its risks, since it thickens the blood and increases strain on the heart it also increases the risk of blood clots and therefore heart attacks and stroke.

The thymus is found behind the sternum. The thymus produces hormones referred to as thymosins, which contribute to the development of the immune response in infants. Adipose tissue, or fat tissue, produces the hormone leptin in response to food intake. Leptin produces a feeling of satiety after eating, reducing the urge for further eating.

Endocrine Gland Associated Hormones Effect
Pituitary (anterior) growth hormone promotes growth of body tissues
prolactin promotes milk production
thyroid-stimulating hormone stimulates thyroid hormone release
adrenocorticotropic hormone stimulates hormone release by adrenal cortex
follicle-stimulating hormone stimulates gamete production
luteinizing hormone stimulates androgen production by gonads in males stimulates ovulation and production of estrogen and progesterone in females
Pituitary (posterior) antidiuretic hormone stimulates water reabsorption by kidneys
oxytocin stimulates uterine contractions during childbirth
Thyroid thyroxine, triiodothyronine stimulate metabolism
calcitonin reduces blood Ca 2+ levels
Parathyroid parathyroid hormone increases blood Ca 2+ levels
Adrenal (cortex) aldosterone increases blood Na + levels
cortisol, corticosterone, cortisone increase blood-glucose levels
Adrenal (medulla) epinephrine, norepinephrine stimulate fight-or-flight response
Pancreas insulin reduces blood-glucose levels
glucagon increases blood-glucose levels

Regulation of Hormone Production

Hormone production and release are primarily controlled by negative feedback, as described in the discussion on homeostasis. In this way, the concentration of hormones in blood is maintained within a narrow range. For example, the anterior pituitary signals the thyroid to release thyroid hormones. Increasing levels of these hormones in the blood then give feedback to the hypothalamus and anterior pituitary to inhibit further signaling to the thyroid gland (Figure 16.14).

Visual Connection

Goiter, a disease caused by iodine deficiency, results in the inability of the thyroid gland to form T3 and T4. The body typically attempts to compensate by producing greater amounts of TSH. Which of the following symptoms would you expect goiter to cause?

Antidiurectic Hormone

As previously discussed, antidiuretic hormone or ADH (also called vasopressin ), as the name suggests, helps the body conserve water when body fluid volume, especially that of blood, is low. It is formed by the hypothalamus and is stored and released from the posterior pituitary. It acts by inserting aquaporins in the collecting ducts and promotes reabsorption of water. ADH also acts as a vasoconstrictor and increases blood pressure during hemorrhaging.

Regulation of Hormone Production

Hormone production and release are primarily controlled by negative feedback, as described in the discussion on homeostasis. In this way, the concentration of hormones in blood is maintained within a narrow range. For example, the anterior pituitary signals the thyroid to release thyroid hormones. Increasing levels of these hormones in the blood then give feedback to the hypothalamus and anterior pituitary to inhibit further signaling to the thyroid gland (Figure 11.24).

Figure 11.24 The anterior pituitary stimulates the thyroid gland to release thyroid hormones T3 and T4. Increasing levels of these hormones in the blood result in feedback to the hypothalamus and anterior pituitary to inhibit further signaling to the thyroid gland. (credit: modification of work by Mikael Häggström)

Hormones cause cellular changes by binding to receptors on or in target cells. The number of receptors on a target cell can increase or decrease in response to hormone activity.

Hormone levels are primarily controlled through negative feedback, in which rising levels of a hormone inhibit its further release.

The pituitary gland is located at the base of the brain. The anterior pituitary receives signals from the hypothalamus and produces six hormones. The posterior pituitary is an extension of the brain and releases hormones (antidiuretic hormone and oxytocin) produced by the hypothalamus. The thyroid gland is located in the neck and is composed of two lobes. The thyroid produces the hormones thyroxine and triiodothyronine. The thyroid also produces calcitonin. The parathyroid glands lie on the posterior surface of the thyroid gland and produce parathyroid hormone.

The adrenal glands are located on top of the kidneys and consist of the adrenal cortex and adrenal medulla. The adrenal cortex produces the corticosteroids, glucocorticoids and mineralocorticoids. The adrenal medulla is the inner part of the adrenal gland and produces epinephrine and norepinephrine.

The pancreas lies in the abdomen between the stomach and the small intestine. Clusters of endocrine cells in the pancreas form the islets of Langerhans, which contain alpha cells that release glucagon and beta cells that release insulin. Some organs possess endocrine activity as a secondary function but have another primary function. The heart produces the hormone atrial natriuretic peptide, which functions to reduce blood volume, pressure, and Na + concentration. The gastrointestinal tract produces various hormones that aid in digestion. The kidneys produce erythropoietin. The thymus produces hormones that aid in the development of the immune system. The gonads produce steroid hormones, including testosterone in males and estrogen and progesterone in females. Adipose tissue produces leptin, which promotes satiety signals in the brain.

Why Did Mylan Hike EpiPen Prices 400%? Because They Could

UPDATED 08/22/2016, including a statement from Mylan at the end] Mylan pharmaceutical company has a virtual monopoly on EpiPens after a voluntary recall felled their only competitor*, Sanofi’s Auvi-Q, over possible dosage miscalibrations. It’s not the drug being delivered that brings the bucks, though—epinephrine’s a cheap generic. The cost trickery is in the delivery system, the Mylan EpiPen.

The EpiPen’s been around since 1977, but Mylan acquired the autoinjector—which precisely calibrates the epinephrine dosage—in 2007. The patient now pays about 400% more for this advantage to receive a dollar’s worth of the lifesaving drug: EpiPens were about $57 when Mylan acquired it. Today, it can empty pockets of $500 or more in the U.S. (European nations take a different approach to these things).

Gallery: World's 25 Biggest Drugs & Biotech Companies In 2016

It’s what the market will bear, so what’s the problem, right? Only this: Somewhere, right now, a cash-strapped parent or budget-limited patient with a severe allergy will skip acquiring an EpiPen. And someday, they will need it in a life-threatening situation involving exposure to a trigger…and they won’t have it. And they will die. Because they couldn’t afford the delivery mechanism for $1 worth of a drug to keep them alive. Two turning points, a death and one company at the crossroads.

According to NBC, Mylan’s profits from selling EpiPens, which they have aggressively, famously marketed with brilliant success, hit $1.2 billion in 2015. That year, Bloomberg reported that the epinephrine-delivery system represented 40% of Mylan’s operating profits. Bloomberg calls Mylan’s marketing of the EpiPen “a textbook case in savvy branding.”

That savvy comes at steep and increasing individual cost. Even after insurance pays, the customer can be out $400 or more for a pack of two pens, a dollar value that can vary depending on how high the deductible is. And most customers need EpiPens for home and at school for their child (Mylan does have a program that offers free EpiPens to U.S. schools). Indeed, guidelines call for prescribing two doses in case the first one fails, which Mylan used as an opportunity to cease selling single pens and begin selling only two-packs. As one parent wrote in response to this article, which has been updated:

You have left out/misreported one important detail, which is that with a life-threatening allergy, you are supposed to have 2 EpiPens at all times. If you administer one and it is more than 15 minutes before you are in emergency care, you have to administer the second one. So the pack of 2 is not meant to have 1 at school and 1 at home it is because you need both with you at all times. This means that you need a pack of 2 at school and a pack of 2 at home for each person with severe allergies. In our case, with 2 kids, we have to have 8 at all times: 2 for each child at school and 2 for each child at home, and that is if we don’t even use them! If we do have to use one, we have to purchase more.

The coup de grâce that will divide the “have intervention for anaphylaxis” from the “have nots and might die as a result”? The EpiPens have an expiration date of one year. So if you don’t have a life-threatening allergic reaction within that year, that’s obviously a good thing—except that you’re out $400 or more and have to spend $400 more for that special device that delivers $1 worth of drug. One respondent to a Facebook query I made about EpiPens noted:

As a school nurse my mom dealt with families who faced this. Sometimes they'd get the prescription filled and the expiration date would be only a few months away--not even long enough to get through a school year. So families would have to buy multiple per school year. (And the school wanted 2 per kid)

My mom stopped carrying hers because her insurer won't pay for it.

In the US my sister got one. After insurance paid their bit it was $600.

One MD who responded said:

i have a mom who has to pay full price because of a high deductible plan.

Do you have to have the pen to deliver the drug? No. It’s possible to use a syringe, which is exactly what some consumers are doing, along with some emergency medical technicians—the first responders for an anaphylaxis call when the affected person doesn’t, you know, have an EpiPen.

What’s wrong with that? A syringe doesn’t offer the benefit and safety advantage of a well-calibrated dose, and it carries the risk of injection into a vein, instead of muscle, which can be fatal. PBS reported the experience of one mother whose son has an extreme dairy allergy and whose insurance plan is high deductible. The price of two pens--$1,212—was more than her mortgage payment, so she turned to ampules of epinephrine and a syringe as the “rescue” med for her son. Her older son, PBS reports, who also has allergies, just carries around expired EpiPens.

Mylan has tried to save some face—and probably preclude some of the widespread blowback building up with back-to-school stories—by offering a program, the “ co-pay card,” but Marketwatch says that only decreases what the insured consumer spends by $100, so the “ pay” part depends on the insurance plan deductible. See “out-of-pocket costs more than the mortgage,” above.

Uninsured patients can apply to receive EpiPens free of charge through a program that Mylan offers. Of course, people who are insured but who have large deductibles fall between two stools here: They can't afford "white glove" insurance that will provide what can even be full coverage, so they buy high-deductible plans for emergencies and then also have to spend-out-of pocket for EpiPens for. emergencies. In the wake of these stories, the company’s stock, as of this writing, had taken a slide.

Update: Consumers do have access to a generic version of a calibrated delivery device for epinephrine, the Adrenaclick. According to Consumer Reports:

But EpiPen isn't the only epinephrine injector on the market the authorized generic of Adrenaclick (epinephrine auto-injector), is a cheaper option—we found it for $142 at Walmart and Sam’s Club using a coupon from GoodRx. While generic Adrenaclick isn't the same technology and is used differently than EpiPen, both auto-injectors contain the same drug, epinephrine, available in the same dosages, says Barbara Young, Pharm.D., of the American Society of Health-System Pharmacists.

The big caveat with using the non-EpiPen version of the delivery system is that the two devices work differently, in ways that can lead to critical errors if users aren't properly trained. For example, the EpiPen requires removal of a single cap for use whereas the Adrenaclick reportedly requires removal of two caps.

Given the Alice in Wonderland nature of this election season, it’s not that surprising to see distortion of reality and common sense infecting this EpiPen debacle. In this case, we come as close as humans can to a human pot calling a pharma kettle black: Martin Shkreli, poster boy for grasping pharma greed, actually commented to NBC News about Mylan that “these guys are really vultures” and asked, “What drives this company’s moral compass?”

For the uninitiated, Shkreli is the fellow who bested Mylan’s 400% price increase when his company jacked up the price of a anti-malarial/toxplasmosis drug used in HIV-positive patients 5,000%.

Shkreli’s shenanigans earned him the moniker “pharma bro,” but the “bro” in the Mylan case is no bro: She’s "pharma sis" Heather Bresch, now the company’s CEO. The “textbook” marketing plan she hit on expanded the “find” target—one of the three goals of any pharmaceutical company —reaching for parents of children with allergies. The “what-if” fears of parents are a rich vein to tap, one that clearly has proved immensely valuable to Mylan.

The “find” was a huge success. And once those parents were found, hitting the second goal of a pharmaceutical company—“start,” as in “start them on your product”—was almost inevitable. The question now is, in the face of prohibitive pricing, syringe-hacking and all of this negative publicity—in which even Martin “Pharma Bro” Shkreli sees a spot of moral high ground where he can stand—Can Mylan continue to hit that third aim: Keep?

Statement from Mylan:

Mylan has worked tirelessly over the past years advocating for increased anaphylaxis awareness, preparedness and access to treatment for those living with potentially life-threatening (severe) allergies. Ensuring access to epinephrine – the only first-line treatment for anaphylaxis – is a core part of our mission.

We are proud of the programs which we have implemented over the past years to help support access to treatment, including our My EpiPen Savings Card™, a patient assistance program, and theEpiPen4Schools ® program which provides free EpiPen ® (epinephrine injection, USP) Auto-Injectors to U.S. schools.

  • In 2015, nearly 80% of commercially insured patients using the My EpiPen Savings Card™ received EpiPen ® Auto-Injector for .
  • Since the start of the EpiPen4Schools ® initiative in 2013, more than 700,000 free EpiPen ® Auto-Injectors have been distributed, and more than 65,000 schools, approximately half of all U.S. schools, have participated in the program.

With changes in the healthcare insurance landscape, an increasing number of people and families are enrolled in high deductible health plans, and deductible amounts continue to rise. This shift has presented new challenges for consumers, and they are bearing more of the cost. This change to the industry is not an easy challenge to address, but we recognize the need and are committed to working with customers and payors to find solutions to meet the needs of the patients and families we serve.

[This article has been updated to reflect the common practice of carrying two EpiPens at all times in case the first one fails and to add information about Adrenaclick.]

Neurons in the Sympathetic Nervous System

A sympathetic neuron actually consists of two shorter neurons, one leading to the other. The long extension of each neuron is often known as a fiber. A structure called a ganglion is located between the fibers of the two neurons, as shown in the illustration below.

The fiber of the first neuron is called the preganglionic fiber. It releases a neurotransmitter called acetylcholine. This chemical causes the stimulation of the second neuron and its fiber, which is known as the postganglionic fiber. The postganglionic fiber sends the nerve impulse to an effector. The fiber stimulates the effector by releasing noradrenaline as a neurotransmitter.

The preganglionic fibers are colored orange in the above illustration. The postganglionic fibers are colored yellow. The illustration shows that the fiber going to the adrenal medulla is a preganglionic one.

Chapter Review

The pectoral girdle, consisting of the clavicle and the scapula, attaches each upper limb to the axial skeleton. The clavicle is an anterior bone whose sternal end articulates with the manubrium of the sternum at the sternoclavicular joint. The sternal end is also anchored to the first rib by the costoclavicular ligament. The acromial end of the clavicle articulates with the acromion of the scapula at the acromioclavicular joint. This end is also anchored to the coracoid process of the scapula by the coracoclavicular ligament, which provides indirect support for the acromioclavicular joint. The clavicle supports the scapula, transmits the weight and forces from the upper limb to the body trunk, and protects the underlying nerves and blood vessels.

The scapula lies on the posterior aspect of the pectoral girdle. It mediates the attachment of the upper limb to the clavicle, and contributes to the formation of the glenohumeral (shoulder) joint. This triangular bone has three sides called the medial, lateral, and superior borders. The suprascapular notch is located on the superior border. The scapula also has three corners, two of which are the superior and inferior angles. The third corner is occupied by the glenoid cavity. Posteriorly, the spine separates the supraspinous and infraspinous fossae, and then extends laterally as the acromion. The subscapular fossa is located on the anterior surface of the scapula. The coracoid process projects anteriorly, passing inferior to the lateral end of the clavicle.

8.2 Bones of the Upper Limb

Each upper limb is divided into three regions and contains a total of 30 bones. The upper arm is the region located between the shoulder and elbow joints. This area contains the humerus. The proximal humerus consists of the head, which articulates with the scapula at the glenohumeral joint, the greater and lesser tubercles separated by the intertubercular (bicipital) groove, and the anatomical and surgical necks. The humeral shaft has the roughened area of the deltoid tuberosity on its lateral side. The distal humerus is flattened, forming a lateral supracondylar ridge that terminates at the small lateral epicondyle. The medial side of the distal humerus has the large, medial epicondyle. The articulating surfaces of the distal humerus consist of the trochlea medially and the capitulum laterally. Depressions on the humerus that accommodate the forearm bones during bending (flexing) and straightening (extending) of the elbow include the coronoid fossa, the radial fossa, and the olecranon fossa.

The forearm is the region of the upper limb located between the elbow and wrist joints. This region contains two bones, the ulna medially and the radius on the lateral (thumb) side. The elbow joint is formed by the articulation between the trochlea of the humerus and the trochlear notch of the ulna, plus the articulation between the capitulum of the humerus and the head of the radius. The proximal radioulnar joint is the articulation between the head of the radius and the radial notch of the ulna. The proximal ulna also has the olecranon process, forming an expanded posterior region, and the coronoid process and ulnar tuberosity on its anterior aspect. On the proximal radius, the narrowed region below the head is the neck distal to this is the radial tuberosity. The shaft portions of both the ulna and radius have an interosseous border, whereas the distal ends of each bone have a pointed styloid process. The distal radioulnar joint is found between the head of the ulna and the ulnar notch of the radius. The distal end of the radius articulates with the proximal carpal bones, but the ulna does not.

The base of the hand is formed by eight carpal bones. The carpal bones are united into two rows of bones. The proximal row contains (from lateral to medial) the scaphoid, lunate, triquetrum, and pisiform bones. The scaphoid, lunate, and triquetrum bones contribute to the formation of the radiocarpal joint. The distal row of carpal bones contains (from medial to lateral) the hamate, capitate, trapezoid, and trapezium bones (“So Long To Pinky, Here Comes The Thumb”). The anterior hamate has a prominent bony hook. The proximal and distal carpal rows articulate with each other at the midcarpal joint. The carpal bones, together with the flexor retinaculum, also form the carpal tunnel of the wrist.

The five metacarpal bones form the palm of the hand. The metacarpal bones are numbered 1–5, starting with the thumb side. The first metacarpal bone is freely mobile, but the other bones are united as a group. The digits are also numbered 1–5, with the thumb being number 1. The fingers and thumb contain a total of 14 phalanges (phalanx bones). The thumb contains a proximal and a distal phalanx, whereas the remaining digits each contain proximal, middle, and distal phalanges.

8.3 The Pelvic Girdle and Pelvis

The pelvic girdle, consisting of a hip bone, serves to attach a lower limb to the axial skeleton. The hip bone articulates posteriorly at the sacroiliac joint with the sacrum, which is part of the axial skeleton. The right and left hip bones converge anteriorly and articulate with each other at the pubic symphysis. The combination of the hip bone, the sacrum, and the coccyx forms the pelvis. The pelvis has a pronounced anterior tilt. The primary function of the pelvis is to support the upper body and transfer body weight to the lower limbs. It also serves as the site of attachment for multiple muscles.

The hip bone consists of three regions: the ilium, ischium, and pubis. The ilium forms the large, fan-like region of the hip bone. The superior margin of this area is the iliac crest. Located at either end of the iliac crest are the anterior superior and posterior superior iliac spines. Inferior to these are the anterior inferior and posterior inferior iliac spines. The auricular surface of the ilium articulates with the sacrum to form the sacroiliac joint. The medial surface of the upper ilium forms the iliac fossa, with the arcuate line marking the inferior limit of this area. The posterior margin of the ilium has the large greater sciatic notch.

The posterolateral portion of the hip bone is the ischium. It has the expanded ischial tuberosity, which supports body weight when sitting. The ischial ramus projects anteriorly and superiorly. The posterior margin of the ischium has the shallow lesser sciatic notch and the ischial spine, which separates the greater and lesser sciatic notches.

The pubis forms the anterior portion of the hip bone. The body of the pubis articulates with the pubis of the opposite hip bone at the pubic symphysis. The superior margin of the pubic body has the pubic tubercle. The pubis is joined to the ilium by the superior pubic ramus, the superior surface of which forms the pectineal line. The inferior pubic ramus projects inferiorly and laterally. The pubic arch is formed by the pubic symphysis, the bodies of the adjacent pubic bones, and the two inferior pubic rami. The inferior pubic ramus joins the ischial ramus to form the ischiopubic ramus. The subpubic angle is formed by the medial convergence of the right and left ischiopubic rami.

The lateral side of the hip bone has the cup-like acetabulum, which is part of the hip joint. The large anterior opening is the obturator foramen. The sacroiliac joint is supported by the anterior and posterior sacroiliac ligaments. The sacrum is also joined to the hip bone by the sacrospinous ligament, which attaches to the ischial spine, and the sacrotuberous ligament, which attaches to the ischial tuberosity. The sacrospinous and sacrotuberous ligaments contribute to the formation of the greater and lesser sciatic foramina.

The broad space of the upper pelvis is the greater pelvis, and the narrow, inferior space is the lesser pelvis. These areas are separated by the pelvic brim (pelvic inlet). The inferior opening of the pelvis is the pelvic outlet. Compared to the male, the female pelvis is wider to accommodate childbirth, has a larger subpubic angle, and a broader greater sciatic notch.

8.4 Bones of the Lower Limb

The lower limb is divided into three regions. These are the thigh, located between the hip and knee joints the leg, located between the knee and ankle joints and distal to the ankle, the foot. There are 30 bones in each lower limb. These are the femur, patella, tibia, fibula, seven tarsal bones, five metatarsal bones, and 14 phalanges.

The femur is the single bone of the thigh. Its rounded head articulates with the acetabulum of the hip bone to form the hip joint. The head has the fovea capitis for attachment of the ligament of the head of the femur. The narrow neck joins inferiorly with the greater and lesser trochanters. Passing between these bony expansions are the intertrochanteric line on the anterior femur and the larger intertrochanteric crest on the posterior femur. On the posterior shaft of the femur is the gluteal tuberosity proximally and the linea aspera in the mid-shaft region. The expanded distal end consists of three articulating surfaces: the medial and lateral condyles, and the patellar surface. The outside margins of the condyles are the medial and lateral epicondyles. The adductor tubercle is on the superior aspect of the medial epicondyle.

The patella is a sesamoid bone located within a muscle tendon. It articulates with the patellar surface on the anterior side of the distal femur, thereby protecting the muscle tendon from rubbing against the femur.

The leg contains the large tibia on the medial side and the slender fibula on the lateral side. The tibia bears the weight of the body, whereas the fibula does not bear weight. The interosseous border of each bone is the attachment site for the interosseous membrane of the leg, the connective tissue sheet that unites the tibia and fibula.

The proximal tibia consists of the expanded medial and lateral condyles, which articulate with the medial and lateral condyles of the femur to form the knee joint. Between the tibial condyles is the intercondylar eminence. On the anterior side of the proximal tibia is the tibial tuberosity, which is continuous inferiorly with the anterior border of the tibia. On the posterior side, the proximal tibia has the curved soleal line. The bony expansion on the medial side of the distal tibia is the medial malleolus. The groove on the lateral side of the distal tibia is the fibular notch.

The head of the fibula forms the proximal end and articulates with the underside of the lateral condyle of the tibia. The distal fibula articulates with the fibular notch of the tibia. The expanded distal end of the fibula is the lateral malleolus.

The posterior foot is formed by the seven tarsal bones. The talus articulates superiorly with the distal tibia, the medial malleolus of the tibia, and the lateral malleolus of the fibula to form the ankle joint. The talus articulates inferiorly with the calcaneus bone. The sustentaculum tali of the calcaneus helps to support the talus. Anterior to the talus is the navicular bone, and anterior to this are the medial, intermediate, and lateral cuneiform bones. The cuboid bone is anterior to the calcaneus.

The five metatarsal bones form the anterior foot. The base of these bones articulate with the cuboid or cuneiform bones. The metatarsal heads, at their distal ends, articulate with the proximal phalanges of the toes. The big toe (toe number 1) has proximal and distal phalanx bones. The remaining toes have proximal, middle, and distal phalanges.

8.5 Development of the Appendicular Skeleton

The bones of the appendicular skeleton arise from embryonic mesenchyme. Limb buds appear at the end of the fourth week. The apical ectodermal ridge, located at the end of the limb bud, stimulates growth and elongation of the limb. During the sixth week, the distal end of the limb bud becomes paddle-shaped, and selective cell death separates the developing fingers and toes. At the same time, mesenchyme within the limb bud begins to differentiate into hyaline cartilage, forming models for future bones. During the seventh week, the upper limbs rotate laterally and the lower limbs rotate medially, bringing the limbs into their final positions.

Endochondral ossification, the process that converts the hyaline cartilage model into bone, begins in most appendicular bones by the twelfth fetal week. This begins as a primary ossification center in the diaphysis, followed by the later appearance of one or more secondary ossifications centers in the regions of the epiphyses. Each secondary ossification center is separated from the primary ossification center by an epiphyseal plate. Continued growth of the epiphyseal plate cartilage provides for bone lengthening. Disappearance of the epiphyseal plate is followed by fusion of the bony components to form a single, adult bone.

The clavicle develops via intramembranous ossification, in which mesenchyme is converted directly into bone tissue. Ossification within the clavicle begins during the fifth week of development and continues until 25 years of age.

Watch the video: WHAT IS EPINEPHRINE? (July 2022).


  1. Gujind

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  2. Hamilton

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  3. Sinh

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