Endocrine System

1. Endocrine System Textbook Chapter 11

2. Learning Objectives • Describe the secretions of the endocrine system • Distinguish between endocrine, autocrine, and paracrine secretions • Distinguish between endocrine and exocrine glands • Explain how the nervous and endocrine systems are alike and different • Name some of the functions of hormones • Explain how steroid and nonsteroid hormones affect target cells • Discuss how negative feedback mechanisms regulate hormonal secretions • Explain how the nervous system controls secretion of hormones • Describe the functions of the hormones that the pituitary gland secretes • Describe the location of the thyroid gland, and list the hormones it secretes • Describe the functions of the hormone that the parathyroid glands secrete • Describe the location of the adrenal glands, and list the hormones they secrete • Describe the location of the pancreas, and list the hormones it secretes • Describe how the body responds to stress

3. Introduction to the Endocrine System • The endocrine system works with the nervous system to regulate the functions of the body • This is done by cells, tissues, and organs (called endocrine glands) that secrete hormones • Hormones diffuse directly into the bloodstream and act on cells called target cells that are in different parts of the body

4. Paracrine vs Autocrine vs Endocrine • Some secretions are rapidly broken down and do not reach the bloodstream, but still act as messenger molecules • Referred to as “local hormones” • Paracrine secretions affect only neighboring cells • Autocrine secretions affect only the cell secreting the substance • Endocrine secretions secrete outside the internal environment

5. The Endocrine System • The endocrine system includes: • Brain • Hypothalamus • Pituitary gland • Pineal gland • Thyroid gland • Parathyroid gland • Thymus gland • Adrenal gland • Pancreas • Ovaries (female) • Testes (male)

6. Endocrine System & Nervous Systems • Both the endocrine and nervous systems oversee cell-to-cell communications using chemical signals • The nervous system uses neurotransmitters • The endocrine system uses hormones • Endocrine glands and their hormones help regulate metabolic processes • Control the rates of certain internal reactions, aid in the transport of substances across cell membranes, and help regulate water and electrolyte balances

7. Endocrine System vs. Nervous System

8. Hormone Action • 2 general types of hormones: • Steroids (or steroid-like substances) • Nonsteroids • Steroids are made from cholesterol • Nonsteroids are made from amino acids • Steroid hormones activate cells in a different manner than nonsteroid hormones

9. Steroid Hormones • Pass through a cell membrane and bind with receptor molecules in the cytoplasm • The receptor molecules then move to the nucleus, where they can activate certain genes to synthesize the needed proteins

10. Nonsteroid Hormones • Must join with a receptor on the target cell’s membrane • Then the hormone is taken into the cell via active transport • Once the hormone is inside the cell, the production of a compound called cyclic AMP is signaled • This causes the target cell to produce the necessary enzymes

11. Types of Hormones

12. The Glands of the Body: Exo vs Endo • The glands in the body can be grouped into 2 categories: • Exocrine glands produce substances, not hormones, that have an effect in the same tissues where they’re produced • Ex. Sebaceous glands • Endocrine glands produce hormones that are secreted into the bloodstream and travel to the place where they exert their effect

13. Control of Hormonal Secretions • Because hormones are constantly being excreted in urine and broken down in the liver, the secretion of hormones must be ongoing. • Hormone secretion is controlled in 3 ways, all of which use negative feedback • In each case, a gland or the system detects the concentration of a hormone in the blood, a process the hormone controls, or an action the hormone has on the internal environment

14. Control of Hormone Secretion • 1. They hypothalamus, which constantly receives information about the internal environment, regulates the anterior pituitary gland’s release of hormones • Many anterior pituitary hormones affect the activity of other endocrine glands

15. Control of Hormone Secretions • 2. The nervous system stimulates some glands directly • Ex. The adrenal gland secretes its hormones in response to impulses from the nervous system

16. Control of Hormone Secretions • 3. Another group of glands responds directly to changes in the composition of the internal environment • Ex. When blood glucose levels rise, the pancreas secretes insulin, and when blood glucose level falls, it secretes glucagon

17. Pituitary Gland & Hypothalamus • Located at the base of the brain, where a pituitary stalk attaches to the hypothalamus • The hypothalamus is what connects the nervous system to the endocrine system • 1 cm in diameter • Anterior pituitary (lobe) • Posterior pituitary (lobe) • The brain controls most of the pituitary gland’s activity

18. Anterior Pituitary & Hypothalamus • Small blood vessels connect the anterior portion of the pituitary to the hypothalamus • The hypothalamus releases releasing hormones • When the anterior pituitary receives these releasing hormones, it is stimulated to secrete one of its hormones

19. Anterior Pituitary Hormones • The anterior pituitary is an enclosed capsule of dense connective tissue • Consists largely of epithelial tissue organized into blocks around blood vessels • So far, there are 5 types of secretory cells identified in the anterior pituitary • 4 of these cell types secrete a different hormone: • Growth Hormone (GH) • Prolactin (PRL) • Thyroid-stimulating Hormone (TSH) • Adrenocorticotropic hormone (ACTH) • The 5th type of cell secretes both follicle-stimulating hormone (FSH) and luteinizing hormone (LH)

20. Anterior Pituitary Hormones • Growth Hormone (GH) • Stimulates cells to enlarge and divide more frequently • Speeds the rate at which cells utilize carbohydrates and fats • Nutritional state also influences control of GH • More GH is released in response to an abnormally low blood glucose level (and vice versa)

21. Anterior Pituitary Hormones • Prolactin (PRL) • Stimulates and sustains a woman’s milk production following birth • Controlled by a combination of stimulating and inhibiting hormones • No normal role in males has been established yet • Abnormally elevated levels of PRL can disrupt sexual function in both sexes • Thyroid-Stimulating Hormone (TSH) • Regulates thyroid hormone production and secretion by the thyroid gland

22. Anterior Pituitary Hormones • Adrenocoritcotropic Hormone (ACTH) • Controls the manufacture and secretion of certain hormones in the adrenal gland • Stimulated by the release of hormones in the hypothalamus and stress • Follicle-stimulating Hormone (FSH) and Luteinizing Hormone (LH) • Exert their actions on the reproductive organs (testes and ovaries)

23. Posterior Pituitary & Hypothalamus • The posterior pituitary is actually part of the nervous system • The hormones that are produced in the posterior pituitary are made in the nerve cell bodies of the hypothalamus • They travel down the nerve cells that end at the posterior pituitary

24. Posterior Pituitary & Hypothalamus

25. Posterior Pituitary Hormones • Composed mostly of axons and neuroglia (nerve cells) • Hormones associated with the posterior pituitary: • Antidiuretic hormone (ADH) • Oxytocin (OT) • Transported down the nerve cells from the hypothalamus to the posterior pituitary, where they are held in vesicles • Impulses from the hypothalamus release the hormones into the bloodstream

26. Posterior Pituitary Hormones • Antidiuretic Hormone (ADH) • A diuretic is a chemical that increases urine production, an antidiuretic decreases urine formation • ADH reduces the volume of water the kidneys excrete (an antidiuretic effect) • Helps to regulate the water concentration of body fluids • Secretion controlled by the hypothalamus • Dehydration due to water loss results in the release of ADH, which acts on target cells in the kidneys • The kidneys produce less urine, which conserves water • Drinking excess water will inhibit the release of ADH, so the kidneys will excrete a larger volume of dilute urine until water levels in the body return to normal • ADH is also known as vasopressin, because at high levels it causes constriction of the blood vessels (vasoconstriction)

27. Posterior Pituitary Hormones • Oxytocin (OT) • In females, OT contracts muscle in the uterine wall and stimulates uterine contractions in the later stages of childbirth • OT also stimulates contraction of cells associated with milk-producing glands • Plays a role in bonding mother and child and sexual partners • In males, OT may play a role in sexual response • OT is also an antidiuretic, but much weaker than ADH

28. In Class Assignment • Read and outline Section 11.6 (Thyroid Gland) • Answer questions 23-25

29. Parathyroid Glands • The parathyroid glands are on the posterior surface of the thyroid glands • Most people have 4 parathyroid glands

30. Structure of Parathyroid Glands • A thin capsule of connective tissue covers each parathyroid gland • The body of the gland contains many, tightly packed secretory cells

31. Parathyroid Hormone • Parathyroid hormone increases the blood calcium ion concentration and decreases the blood phosphate ion concentration • PTH affects the bones, kidneys, and intestines • Increases the activity of osteoclasts (cells that absorb bone) and release calcium and phosphate in the blood • Causes the kidneys to conserve blood calcium and excrete more phosphate in the blood • Secretion of PTH is regulated by the negative feedback between the parathyroid gland and the blood calcium concentration

32. Adrenal Glands • The adrenal glands are closely associated with the kidneys and sit on top of each kidney • Adrenal hormones play roles in maintaining blood sodium levels and responding to stress

33. Structure of Adrenal Glands • Each adrenal gland is very vascular (a lot of blood flow) and consists of 2 parts: • Adrenal medulla • Adrenal cortex

34. Structure of Adrenal Gland • Adrenal Medulla • Consists of irregularly shaped cells organized into groups around blood vessels • Adrenal Cortex • Composed of closely packed masses of epithelial cells, organized in layers

35. Hormones of the Adrenal Medulla • The cells of the medulla secrete epinephrine and norepinephrine • The effects of these hormones are similar to a nervous system response, but the hormonal effects last up to 10 times longer • Increase heart rate, the force of cardiac muscle contraction, and blood glucose level • Dilate airways, which makes breathing easier, elevate blood pressure, and decrease digestive activity • Secretion of these hormones prepares the body for “fight or flight” responses

36. Hormones of the Adrenal Cortex • The cells in the cortex produce more than 30 different steroids • Unlike the medullary hormones (a person can live without them), hormones produced by the cortex are vital • A person who lacks these hormones will likely die within a week • The most important cortical hormones are aldosterone, cortisol, and certain sex hormones

37. Hormones of the Adrenal Cortex • Aldosterone • Steroid Hormone • Helps regulate the concentration of mineral electrolytes • Causes the kidney to conserve sodium ions and excrete potassium ions • Secretion stimulated by an increase in the blood concentration of potassium ions • Secretion indirectly stimulated by the kidneys if blood pressure falls

38. Hormones of the Adrenal Cortex • Cortisol • Affects glucose, fat, and protein metabolism • Steroid hormone • Inhibits protein synthesis in tissues • Promotes the release of fatty acids from adipose tissue • Stimulates the liver to synthesize glucose from noncarbohydrates • Cortisol helps to keep blood glucose levels within the normal range between meals • Negative feedback controls the release of cortisol

39. Hormones of the Adrenal Cortex • Adrenal Sex Hormones • The hormones produced are male types, but some are converted to female hormones in the skin, liver, and adipose tissue • Contribute to the early development of reproductive organs

40. Pancreas • The pancreas consists of 2 types of tissue • Functions as an exocrine gland (secretes digestive juices) and endocrine gland (releases hormones)

41. Structure of the Pancreas • The pancreas is an elongated, somewhat flattened organ • Posterior to the stomach • A duct joins the pancreas to the small intestine • The endocrine part of the pancreas consists of 2 types of cells: • Alpha cells (secrete glucagon) • Beta cells (secrete insulin)

42. Hormones of the Pancreas • Glucagon • Raises the blood sugar concentration • Stimulates the liver to break down glycogen and convert noncarbohydrates into glucose • Glucagon more effectively elevates blood glucose than epinephrine • Negative feedback regulates the secretion of glucagon • Low blood glucose stimulates alpha cells to release glucagon • This control prevents hypoglycemia when blood glucose is low (between meals)

43. Hormones of the Pancreas • Insulin • Lower blood glucose level (opposite of glucagon) • Promoting diffusion of glucose into cells that have insulin receptors (adipose tissue, liver, and skeletal muscle) • Stimulates the liver to form glycogen from glucose • Negative feedback sensitive to blood glucose concentration regulates insulin secretion • When blood glucose levels are high (after eating), beta cells release insulin • Prevents too high blood glucose levels

44. Diabetes Mellitus • Metabolic disease that arises from deficiency of insulin or inability of cells to recognize insulin • Persistent elevated blood glucose affects the eyes, heart, kidneys, and peripheral nerves • According to the CDC: • 30.1 million people in the US have diabetes (1 in every 10 people) • 84.1 million people have prediabetes (1 in every 3 people and 9 in 10 people don’t know)

45. Diabetes Mellitus • Insulin deficiency disturbs metabolism of carbohydrates, proteins, and fats • Diabetes impairs movement of glucose into adipose and skeletal muscle cells • At the same time, formation of glycogen decreases • As a result, blood sugar rises (hyperglycemia) • When blood sugar levels reach a certain point, excess glucose gets excreted in the urine  which causes too much water to be excreted  dehydration and extreme thirst

46. Type 1 Diabetes • Usually appears before age 20 • Autoimmune disease in which the immune system destroys the beta cells in the pancreas • People with Type 1 must carefully monitor their blood glucose levels • Lab test every 3 months • Self-monitoring • People with Type 1 must administer insulin to mimic regular pancreatic functions • Self injection once or several times a day • Insulin pump

47. Type 1 Diabetes

48. Type 2 Diabetes • About 85-90% of people with diabetes have Type 2 • Beta cells produce insulin, but body cells lose the ability to recognize it • Most affected individuals are overweight when symptoms begin • Treatment includes diet, exercise, and maintaining a desirable body weight • There are oral drugs to help control glucose levels and weight loss surgery can stabilize blood sugar

49. Other Endocrine Glands • Pineal Gland • Small structure between the cerebral hemispheres • Secretes melatonin in response to changing light conditions outside the body • Secretion is suppressed during the day and increased at night • May help regulate circadian rhythms (patterns of repeated activity associated with day and night)

50. Other Endocrine Glands • Thymus • Lies posterior to the sternum and between the lungs • Large in children but shrinks over time • Secretes thymosins • Affect the production and differentiation of certain white blood cells • Plays an important role in immunity