The Endocrine System

1. The Endocrine System Anatomy Ch. 9

2. Hormones • Hormones are chemical substances that are secreted by endocrine cells into the extracellular fluids and regulate the metabolic activity of other cells in the body. • Nearly all hormones can be classified as either amino acid based molecules (proteins, peptides, and amines) or steroids. • All hormones are amino acid based except for sex hormones and the hormones of the adrenal cortex.

3. A hormone affects only certain tissue cells or organs which are called target cells or organs. • For a target cell to respond to a hormone the target cell must have specific protein receptors on the plasma membrane that the hormone can attach to.

4. The term hormone comes from the Greek word meaning “to arouse”. • Hormones bring about their effects on the body’s cells by altering the cells activity. • These alterations may include increasing or decreasing the rate of a normal metabolic process

5. Changes that occur due to hormone binding: • Permeability of the plasma membrane • Formation of proteins or enzymes in the cell • Activation or deactivation of enzymes • Stimulation of mitosis (cell division) • Increasing secretion

6. Mechanisms of hormone changes in the cell • Direct Gene Activation • Used by steroids • The steroids diffuse through the plasma membrane of the target cell • The steroid enters the nucleus • The steroid binds to a specific receptor in the nucleus • The new combination of the hormone and receptor binds to a specific site on the DNA • The binding with the DNA causes certain genes to form mRNA. • The mRNA sends information out of the nucleus and new proteins are made.

8. Second Messenger System • Used by acid based molecules • These hormones are not able to enter the target cell so they bind to hormone receptors on the target cells plasma membrane. • The hormone which is the first messenger binds to a membrane receptor. • This binding sets off a series of reactions that activates an enzyme. • The enzyme causes a reaction that will produce the second messenger in the cell. • The role of the second messenger is to oversee any changes in the cell and promote the response of the target cell to the hormone. • There are many different second messengers.

10. Control of hormone release • Negative feedback mechanisms are the primary means of regulating blood levels of nearly all hormones. • There are 3 categories of stimuli that activate endocrine organs: • Hormonal stimuli • The most common type of stimuli in which endocrine organs are prodded into action by other hormones • Humoral stimuli • Changing blood levels of certain ions and nutrients stimulate hormone release • Neural stimuli • Nerve fibers stimulate hormone release

11. The major endocrine organs • The major endocrine organs of the body include the: • Pituitary gland • Thyroid gland • Parathyroid gland • Adrenal gland • Pineal gland • Thymus • Pancreas • Gonads (testes and ovaries)

13. The hypothalamus is part of the nervous system but is also recognized as a major endocrine organ. • The function of some gland is purely endocrine (pituitary, thyroid, adrenals, and parathyroid). • Other glands, such as the pancreas and gonads, have both endocrine and exocrine functions. • Endocrine glands are ductless glands which means that hormones that are produced are released into blood or lymph. • Exocrine glands release products at the body’s surface or into body cavities through ducts.

14. Pituitary-hypothalamus relationship • The anterior pituitary gland controls the activities of so many other glands that it is sometimes called the master gland. • The release of each hormone from the pituitary gland is controlled by hormones produced by the hypothalamus. • The pituitary gland is connected to the hypothalamus. • The hypothalamus produces 2 hormones, oxytocin and antidiuretic, which are stored and released by the posterior pituitary gland.

15. Anterior Pituitary hormones • Growth Hormone (GH) • Growth of skeletal muscles and long bones • Prolactin (PRL) • Stimulates and maintains milk production in the mother’s breasts. • Adrenocorticotropic Hormone (ACTH) • Regulates the endocrine activity of the cortex portion of the adrenal gland • Thyroid-stimulating Hormone (TSH) • Influences the growth and activity of the thyroid gland • Follicle-stimulating Hormone (FSH) • Stimulates development of sperm and egg cells • Lutenizing Hormone (LH) • Triggers ovulation of the egg and produces progesterone and estrogen in females • Stimulates testosterone production in males

16. Posterior pituitary hormones • Oxytocin • Released in significant amounts only during childbirth and in nursing women. • Stimulates powerful contractions of the uterus during childbirth • Causes milk ejection in a nursing woman • Antidiuretic Hormone (ADH) • Causes the kidneys to reabsorb more water from forming urine. As a result urine volume decreases and blood volume increases. • Increases blood pressure by causing constriction of arterioles. Because of this function it is sometimes called vasopressin.

17. Thyroid hormones • Thyroxine (T4) & Triiodothyronine (T3) • Both control the rate at which glucose is burned and converted into body heat and energy. • Every tissue in the body is a target • Important for normal tissue growth and development • The major metabolic hormones • Difference is in the number of bound iodine atoms. • Calcitonin • Decreases blood calcium levels by causing calcium to be deposited in the bones

18. Parathyroid hormones • Parathyroid Hormone (PTH) • The most important regulator of calcium levels in blood. • Stimulates the breakdown of bone matrix to release calcium into the blood and increase blood calcium levels.

19. Adrenal Cortex Hormones • Aldosterone (outer most of the cortex) • Regulates mineral content of the blood, particularly sodium and potassium. • The target is the tubules of the kidneys that either reabsorb minerals or allow them to be flushed out of the body as urine. • When aldosterone levels rise the kidneys reabsorb more sodium and secrete more potassium. • When more sodium is reabsorbed then more water is absorbed. • Aldosterone regulates both water and electrolyte balance.

20. Aldosterone also assists in the regulation of blood pressure. • Renin is an enzyme produced in the kidneys when blood pressure drops and causes the release of aldosterone. Blood pressure increases. • A hormone released by the heart called atrial natriuretic peptide (ANP) prevents aldosterone release and therefore reduces blood pressure.

21. Cortisone and Cortisol (middle layer of the cortex) • Increase blood glucose levels (hyperglycemic) • Decrease inflammation and reduce pain by inhibiting pain causing molecules called prostaglandins • Often prescribed as drugs to suppress inflammation.

22. Androgens and Estrogens (inner most cortex) • Sex hormones • Androgens (males) • Estrogens (females)

23. Adrenal medulla hormones • Epinephrine (adrenaline) • Norepinephrine (noradrenaline) • Both are released as part of the sympathetic division of the ANS (fight or flight) • Both are pumped into the blood stream in enhance and prolong the effects of the sympathetic division. • Increase heart rate, blood pressure, and blood glucose levels, and dilate the small passageways of the lungs • The result is more oxygen and glucose in the blood. • Both hormones help the body to deal with short term stressful situations.

24. The hormones of the medulla help the body to cope with brief short term stressors. • The hormones of the cortex help the body to deal with prolonged stressors.

25. Pancreas hormones • Insulin • High levels of glucose in the blood cause the release of insulin into the blood • Insulin is responsible for the storage of glucose as glycogen when blood levels are too high • Insulin is hypoglycemic because it decrease the levels of glucose in blood. • Glucagon • Low levels of glucose in the blood cause the release of glucagon into the blood • Glucagon causes the breakdown of glycogen • Glucagon is hyperglycemic because it increases glucose levels. • Target organ is the liver

26. Pineal hormone • Melatonin • Levels rise and fall during the night and day • Peak levels occur at night making us drowsy and sleepy. • The lowest levels occur during the daylight hours peaking around noon. • Sleep trigger that plays a role in establishing the body’s day and night cycle. • Helps to coordinate the hormones of fertility. • Inhibits the reproductive system until adult body size has been reached.

27. Thymus hormone • The thymus is largest in infants and children and decreases in size as you reach adulthood. • Thymosin • Are essential for normal development of T- lymphocytes (white blood cells). • Important in the immune response of children.

28. gonads • Ovaries • Estrogen • Development of sex characteristics in women (primarily growth and maturation of reproductive organs). • Responsible for appearance of secondary sex characteristics. • Development of breasts • Pubic hair • Widening of the hips • Increased body fat

29. Progesterone • Acts with estrogen to bring about the menstrual cycle and breast development. • Quiets the muscles of the uterus so that an implanted embryo will not be aborted. • Helps prepare breast tissue for lactation.

30. Testes • Androgens: male sex hormones • Testosterone • Promotes the growth and maturation of the reproductive organs • Causes secondary sex characteristics • Facial hair • Development of bones and muscles • Lowering voice • Continuous production of sperm

31. Other hormones produced • Prostaglandins (All body cells) • Increase blood pressure • Constrict respiratory pathways • Stimulate muscles of the uterus promoting labor • Enhancing blood clotting • Promoting inflammation and pain • Increasing output of digestive secretions by stomach • Causes fever

32. Gastrin (Stomach) • Stimulates the release of HCl • Intestinal Gastrin (Duodenum of small intestine) • Stimulates gastric glands and motility of the stomach • Secretin (Duodenum) • Stimulates the release of pancreatic juice and bile. • Reduces secretions and motility of the stomach

33. Cholecystokinin (CCK) (Duodenum) • Stimulates the release of pancreatic juice • Stimulates the release of stored bile from the gall bladder • Allows bile and pancreatic juice to enter the duodenum • Erythropoietin (Kidneys) • Stimulates the production of red blood cells in bone marrow • Active Vitamin D3 • Stimulates the transport of calcium across the intestinal walls

34. Atrial Natriuretic Peptide (ANP) (Heart) • Inhibits sodium ion reabsorption and renin release • Inhibits the secretion of aldosterone which decreases blood volume and pressure • Leptin (Adipose tissue) • Suppresses appetite in the brain and increases energy expenditure • Resistin (Adipose tissue) • Blocks insulin’s action on liver cells

35. Placenta Hormones • Human chorionic gonadotropin (hCG) • Stimulates the ovaries to continue producing estrogen and progesterone which helps maintain the lining of the uterus • Human placental lactogen (hPL) • Works with estrogen and progesterone in preparing the breasts for lactation. • Relaxin • Causes the mother’s pelvic ligaments and pubic symphysis to relax and become more flexible.

36. Developmental aspects of the endocrine system • The pituitary gland is derived from epithelium of the oral cavity and neural tissue from the hypothalamus • The pineal gland comes from neural tissue • Most epithelial glands develop as little saclike outpockets of the mucosa of the digestive tract. • Thyroid, thymus, pancreas

37. Most endocrine organs operate smoothly until old age. • During late middle age, the efficiency of the ovaries begins to decline causing menopause • Reproductive organs atrophy and ability to bear children ends • Problems associated with estrogen deficiency begin to occur such as arteriosclerosis and osteoporosis.

38. The efficiency of the endocrine system gradually declines in old age. • There are striking changes in aging women. • Growth hormone levels decline. • Elderly people are less resistant to infection possibly due to underproduction of defensive hormones. • Exposure to chemicals throughout life decreases endocrine function. • This may explain higher cancer rates among older adults.

39. Older people are often hypothyroid. • All older people have some decline in insulin production. • Type 2 diabetes is most common in this age group.

40. Homeostatic imbalances of the endocrine system • Pituitary dwarfism • Hyposecretion of GH during childhood • Proportions are normal • Gigantism • Hypersecretion of GH • Person becomes extremely tall • Proportions are normal • Acromegaly • Facial bones enlarge as do the feet and hands • Occurs when hypersecretion continues after long bone growth has ended. • Most cases of hypersecretion result from tumors of the affected gland.

41. Sterility • Hyposecretion of FSH or LH • Diabetes Insipidus • Hyposecretion of ADH • Excessive urine output • People are continually thirsty and drink huge amounts of water

42. Goiters • Enlargement of the thyroid gland • Results when the diet is deficient of iodine • The source of iodine is our diet • The foods richest in iodine is seafood • Cretinism • Occurs when there is a lack of secretion of thyroxine due to lack of stimulation by TSH • Results in dwarfism if it occurs in childhood • Untreated individuals are usually mentally retarded.

43. Myxedema • Occurs due to hypothyroidism in adults • Physical and mental sluggishness • Other signs: • Puffiness of the face • Fatigue • Poor muscle tone • Low body temperature • Obesity • Dry skin

44. Grave’s disease • Occurs due to hyperthyroidism which is usually caused by a tumor on the thyroid. • Symptoms of hyperthyroidism: • High BMR • Intolerance of heat • Rapid heart beat • Weight loss • Nervous and agitated behavior • Inability to relax • In addition to these symptoms, a person with graves disease has an enlarged thyroid gland and a bulging of the eyes

45. Tetany • Occurs when blood calcium levels fall too low. • Neurons become extremely irritable and overactive • Impulses are delivered so rapidly that the muscles go into uncontrollable spasms

46. Addison’s Disease • Hyposecretion of the adrenal cortex of cortisol and aldosterone. • Characterized by a peculiar bronze tone of the skin • Sodium and water are lost from the body due to low aldosterone levels • This leads to water and electrolyte balance problems • This usually leads to a weakening of the muscles • Other signs and symptoms: • Hypoglycemia • Lessened ability to cope with stress • Suppression of the immune system

47. Hyperaldosteronism • Hyperactivity of the cortical area • Excessive water and sodium are retained • High blood pressure and edema result • Potassium is lost which results in disruption of the activities of the heart and nervous system

48. Cushing’s syndrome • Hypersecretion of cortisol from the middle cortical area • Swelling of the face and increase amount of fat in the upper back. • Other effects: • High blood pressure • Hyperglycemia • Weakening of the bones • Severe depression of the immune system

49. Masculinization • Hypersecretion of sex hormones • Occurs regardless of gender • Often masked in males but results are dramatic in females.

50. Diabetes mellitus • Without insulin blood glucose levels rise dramatically • Normal range is 80 to 120 • When this occurs, glucose begins to spill into the urine. • As glucose flushes from the body, water follows which leads to dehydration. • Because glucose is not available, fats and proteins are broken down to meet energy requirements.