THE HUMAN ENDOCRINE SYSTEM Biology 12 E. McIntyre

1. THE HUMAN ENDOCRINE SYSTEM Biology 12 E. McIntyre

2. Introduction to The Human Endocrine System • The purpose of the Endocrine system is to aid in maintaining homeostasis. • The endocrine system produces hormones.Hormones are chemical regulators produced by cells in one part of the body that affect cells in another part of the body. • The endocrine system consists of a series of glands having no direct connection to other parts of the body, i.e.. they are ductless. • Note: Exocrine Glands have a duct to connect them directly to a specific site in the body, e.g.. the salivary glands.

3. Endocrine Glands Cross section of a brain!

4. Hormones • Hormones are produced and secreted into the blood stream bythe endocrine glands. The circulatory system carries hormones to other parts of the body via the blood. • Hormones are chemical messengers responsible for co-ordinating certain body functions. In general they are stimulatory. • The word hormone comes from the Greek hormon, meaning “to excite or set into motion”.

5. ...Hormones Function of Hormones • Hormones exert their effects on specific locations in the body called target tissues (this could be a whole organ or just a few cells). Their effects are long term, controlling functions such as growth, metabolism, maturity and the balance of chemicals in the body.

6. ...Hormones The Mode of Action of Hormones • Hormones act at the molecular level by causing changes in cell metabolism, for example: • protein synthesis • enzyme activity • permeability of cell membranes • DNA translation • there are two basic ways in which hormones do this, based on the type of hormone:

7. (What’s Metabolism?) • The sum of the chemical reactions occurring within a cell or a whole organism; includes the energy-releasing breakdown of molecules (catabolism) and the synthesis of new molecules (anabolism).

9. ...Hormones mcgraw-hill animation steroid hormones steroid_hormone animation Steroid Hormones • The hormone diffuses directly into the cell. • Here it fuses with a receptor molecule. • This receptor molecule is only present in the target cells for that particular hormone. • The hormone/receptor combination effects the translation of DNA in the nucleus.

10. Clip

11. ...Hormones Protein Hormones: • The hormone binds to a receptor molecule located on the surface of the cells of the target tissue. • This causes the production of a secondary messenger molecule within the cell, e.g.. cyclic AMP. • The secondary messenger molecule causes a change in cell metabolism, e.g.. activates an enzyme.

12. Negative Feedback • In a negative feedback system some factor, such as blood pressure, changes. The change is detected by a sensor. The sensor sends a message to an integrating center which in turn stimulates an effector. The effector will do something to alter the factor that changed. • In the example to the right blood pressure has increased. Receptors in the carotid arteries detect the change in blood pressure and send a message to the brain. The brain will cause the heart to beat slower and thus decrease the blood pressure. Decreasing heart rate has a negative effect on blood pressure.

13. The Pituitary Gland: The Master Gland • An outgrowth from the base of the fore-brain and in direct nervous contact with it. • This gland secretes a range of hormones; • Some of these hormones have a direct effect on their target organs... • while others have an indirect effect by causing other glands to secrete further hormones. • It is for this reason that the pituitary gland is often called the master gland, as it regulates the secretions of a number of other endocrine glands.

14. ... The Pituitary Gland Structure • The pituitary gland consists of two lobes, the anterior and the posterior lobes. Each releases specific hormones under the direction of the hypothalamus.

15. The POSTERIOR Pituitary • The posterior lobe of the pituitary stores and releases hormones which have been produced by the hypothalamus. The hormones travel by way of specialized nerve cells from the hypothalamus to the pituitary.

16. The Hormones of the POSTERIOR Pituitary Antidiuretic Hormone (ADH) • regulates water balance in the body by increasing water absorption by the kidneys • Oxytocin: • stimulates uterine contractions during birth • also stimulates milk production

17. The ANTERIOR Pituitary • The anterior lobe of the pituitary, unlike the posterior lobe, produces its own hormones. • Like the posterior lobe, the anterior lobe is richly supplied with nerves from the hypothalamus. • The hypothalamus regulates the release of hormones from the anterior pituitary. Hormones are secreted from the nerve ends of the cells of the hypothalamus and transported in the blood to the pituitary gland. Most of these hormones activate specific cells in the pituitary, causing the release ofpituitary hormones, which are then carried by the blood to target tissues.

18. The Hormones of the ANTERIOR Pituitary • Somatotropin (STH) or Growth Hormone (GH) • has a direct effect on the growth of tissues • is produced in greater quantities during childhood • Thyroid Stimulating Hormone (TSH) • has an indirect effect on metabolic rate, by affecting the thyroid gland • stimulates the thyroid gland, causing it to produce the hormone thyroxin

19. ...The Hormones of the ANTERIOR Pituitary • Adrenocorticotropic Hormone (ACTH) • stimulates the adrenal cortex to produce a range of hormones responsible for stress relief • Gonadotropic Hormones: • Follicle Stimulating Hormone (FSH) • Females: stimulates the development and production of ova, causes the release of estrogens • Males: stimulates the production of sperm cells • Lutinizing Hormone (LH) • Females: causes the development of the corpus luteum. (A structure that develops in the ovary and secretes progesterone ) • Males: (called interstitial cell stimulating hormone - ICSH) stimulates the production of testosterone from the interstitial cells of the testes

20. ...The Hormones of the ANTERIOR Pituitary • Prolactin • stimulates milk production after birth • Melanocyte Stimulating Hormone (MSH) • stimulates melanin (a brown pigment) production in the skin • responsible for changing the skin colour of certain reptiles and amphibians

24. Control of Pituitary Hormone Secretions: • Brought about by the hypothalamus, which monitors the levels of hormones and other chemicals in the blood and forms a connection between the nervous and endocrine systems.

25. Control of Secretions from the Anterior Pituitary • The hypothalamus contains neurosecretory cells which produce and release pituitary hormone releasing factors into the capillaries in the upper part of the anterior pituitary • these releasing factors stimulate specific cells in the anterior pituitary to produce and release the various tropins and other hormones of the anterior pituitary into the blood leaving the pituitary gland, to be carried to their target organs. • Certain releasing factors inhibit the release of hormones from the anterior pituitary e.g.. dopamine inhibits the secretion of prolactin

26. Control of the secretions from the posterior pituitary • Unlike the anterior pituitary, the posterior pituitary does not actually produce its own hormones. • The hormones released from the posterior pituitary are produced in the hypothalamus and pass down neurosecretory cells into the cells of the posterior pituitary. They are stored here and released into the blood leaving the pituitary gland when needed.

27. The Thyroid Gland: Producesthree hormones; Thyroxine which controls the basic metabolic rate and also influences growth rate by controlling the growth and differentiation of cells. Triiodothyroxine, which appears to have the same functions as thyroxine. Calcitonin which effects bone development and muscle contraction (both need calcium)

28. Thyroid disorders • Thyroid absorbs iodine from blood. • Iodine is assimilated into thyroglobin. • When stimulated, thyroglobin becomes thyroxine. • Goiter is when there is no iodine, therefore the precursor to thyroglobin builds up in the thyroid gland. • Iodine is added to table salt, i.e.. iodized salt, to overcome the problem of dietary deficiency of iodine.

29. Over secretion of thyroxine: • Referred to as hyperthyroidism. • In adults this condition causes over-activity, decreased body weight, increased heart rate and blood pressure, which can lead to heart failure - called thyrotoxicosis.

30. Under secretion of thyroxine: • Referred to as hypothyroidism • In infants: results in retarded mental and physical development called cretinism. This can be easily treated by early administration of thyroid extract. • In adults: causes sluggishness and over-weight. This condition is called myxoedema.

31. Control of Thyroxine Production • This provides an example of negative feedback control of the endocrine system: Clip 1

32. The Parathyroid Glands: • These are located as two pairs of small glands on either side of the thyroid gland • They secrete parathormone which increases plasma calcium concentrations (opposite effect to calcitonin) • Parathormone stimulates the breakdown of calcium in the bones and causes it to be released into the blood.

33. Over secretion of parathormone: • Hyperparathyroidism causes the bones to soften due to excess calcium released from the bone.

34. Under secretion of parathormone: • Hypoparathyroidism causes muscle cramps due to lack of calcium for muscle contraction, it is all absorbed into bone.

35. The Adrenal Glands: • These are located just above each kidney • They consist of two layers, an outer cortex and an inner medulla. • Each layer secretes specific hormones. Adrenal gland clip Adrenal cortex clip

36. Secretions from the adrenal cortex: • Glucocorticoids - the most important being cortisol (a steroid hormone). This hormone stimulates the conversion of proteins and fats to glucose for use in cellular respiration and makes available amino acids for protein synthesis necessary for the repair of cells. This is important in the recovery of the body from stress.

37. Clip 1

38. Cortisol also reduces the allergic and inflammatory responses caused in damaged tissues, by inhibiting the immune system. (Cortisone is a drug given in many instances to reduce inflammation or allergic response)

39. Mineralocorticoids - the most important being aldosterone. This hormone stimulates the absorption of sodium ions by the kidneys to maintain salt and water balance in the blood.

40. HORMONES THAT AFFECT BLOOD SUGAR

41. Abnormalities Associated with the Pituitary • Abnormalities Related to the Secretion of Growth Hormone: • Dwarfism • Caused by under secretion of GH during childhood resulting in reduced over all growth. • Under secretion in adults has been linked to early senility.

42. Gigantism • caused by over secretion of GHduring childhood.

43. Acromegaly • caused by over secretion of GHduring adulthood, leading to excessive growth of facial bones and those of the hands and feet. Andre the Giant 7’ 4” 500 lbs

45. Gonadocorticoids (Sex hormones) - in fact these are hormones very similar to the sex hormones and have similar effects, to maintain the viability of the gonads and cause the developmentof secondary sex characteristics. Clip 1

46. Control of the secretions from the Adrenal Cortex: • Secretions from the adrenal cortex are stimulated by ACTH from the anterior pituitary. • The control of these secretions demonstrates the feedback mechanism:

47. Secretions from the Adrenal Medulla: • Unlike the adrenal cortex, which is under hormonal control, the release of hormones from the adrenal medulla is controlled by the nervous system, another illustration of the connections between the nervous and endocrine systems.

48. In stressful situations the sympathetic nervous system stimulates the release of two hormones from the adrenal medulla: adrenaline and noradrenaline (also called epinephrine and norepinephrine) • These two hormones essentially have the same functions, to prepare the body for stressful or exciting situations when vigorous activity may be required. Clip 1

49. Epinephrine & Norepinephrine serve to prolong and maintain the body in a state of preparation for activity longer than could be maintained by the nervous system alone. • They cause the following effects: • heart rate increases • breathing rate increases • pupils dilate • blood is diverted from non-essential tasks, such as digestion, to the muscles for activity • anal and bladder sphincters relax. • face becomes pale (blood diverted from here) • hair stands on end, sweating increases. Clip 1

50. The Pancreas: • The pancreas has both endocrine and exocrine functions; • Glucose control • Digestive enzyme production • It also has patches of specialized cells which produce two hormones, insulin and glucagon, that are secreted into the blood stream. • These patches of cells are referred to as the islets of Langerhans