Chapter 13 Endocrine System

1. Chapter 13Endocrine System • Endocrine glands are ductless • Exocrine glands have ducts

2. Major Endocrine Glands

3. General Characteristics • Includes the cells, tissues, and organs that secrete hormones into body fluids • The exocrine system secretes into tubes or ducts which lead to internal or external body surfaces Ex: sweat and sebaceous glands

4. Endocrine glands and their hormones help regulate metabolic processes: control the rates of some chemical reactions, aid in transporting substances through cell membranes, and help regulate water balance, electrolyte balance, and blood pressure. • Play vital roles in reproduction, development, and growth

5. Comparison of Nervous System and Endocrine System • Neurons release neurotransmitters into a synapse, affecting postsynaptic cells • Glands release hormones into the bloodstream • Only target cells of hormone responds

6. Comparison of Nervous System and Endocrine System

7. Hormone Types • A hormone is a biochemical secreted by a cell that affects the function of another cell. • Five general types: steroids, amines, peptides, protein hormones, glycoproteins (last four are also called nonsteroidal)

8. Steroids • lipids that include complex rings of carbon and hydrogen atoms • derived from cholesterol • ex: estrogen and testosterone

9. Amines • Derived from amino acids • Produced by neurons • Ex: epinephrine and norepinephrine • Also synthesized from the adrenal medulla from tyrosine

10. Peptides • Short chains of amino acids • Ex: oxytocin and antidiuretic hormone

11. Protein hormones • Long chains of amino acids • Ex: growth hormone and parathyroid homone

12. Glycoprotiens • A protein joined to a carbohydrate • Ex: follicle-stimulating hormone

13. Types of Hormones

14. Prostoglandins • Paracrine substances that regulate only neighboring cells (local action) • Lipids that are made from a type of fatty acid • Found in the liver, kidneys, heart, lungs, thymus, pancreas, brain, and reproductive organs • Regulates the formation of cAMP (2nd messenger)

15. Actions of hormones • Hormones bind to specific receptors on target cells • Each hormone receptor is a protein or glycoprotein that has a binding site for a specific hormone • The more receptors a hormone binds, the greater the cellular response

16. Steroid hormones • Soluble in cell membranes • Can diffuse easily into target cells • Once inside they bind to receptors (usually in the nucleus)

17. Specific genes are activated which are transcribed into mRNA • mRNA goes to the cytoplasm and directs the synthesis of specific proteins • Proteins then cause the cellular changes associated with the hormone

18. Actions of Steroid Hormones • hormone crosses membranes • hormone combines with receptor in nucleus • synthesis of mRNA activated • mRNA enters cytoplasm to direct synthesis of protein

19. Nonsteroid hormones • Combines with specific receptors on the target cell membrane • Receptor binding alters the function of enzymes or membrane transport mechanisms which changes the concentration of other cellular components • The first messenger is the hormone that triggers the activity

20. Second messengers are the biochemicals that cause the changes in response to the hormones • Many hormones use cyclic AMP as a second messenger • Many second messenger molecules can be activated in response to just a few hormone-receptor complexes • Cells are highly sensitive to changes in the concentration of nonsteroid hormones

21. Actions of Nonsteroid Hormones • hormone binds to receptor on cell membrane • ATP converted to cAMP • cAMP acts as a 2nd messenger • cAMP promotes a series of reactions leading to cellular changes • Takes place in cytoplasm

22. Actions of Nonsteroid Hormones

23. Control of Hormonal Secretions • primarily controlled by negative feedback mechanism

24. Negative Feedback

25. Major Endocrine Glands

26. Pituitary Gland • About 1 cm in diameter • Attached to the hypothalmus by the pituitary stalk (infundibulum) and lies in the stella turcica of the sphenoid bone • Consists of an anterior lobe (adenohypophysis) and a posterior lobe (neurohypophysis) • Anterior lobe secretes GH, TSH, ACTH, FSH LH, and PRL

27. Posterior lobe cells (pituicytes) do not synthesize any hormones • ADH and OT are secreted by the nerve endings of special neurons into the bloodstream in posterior lobe • Cell bodies of neurosecretory cells are in the hypothalmus

28. Substances secreted by the hypothalmus are carried directly to the anterior lobe • hypothalmus is an endocrine gland and it also controls other endocrine glands • Anterior pituitary also controls other endocrine glands

29. Most hypothalmic releasing hormones act on specific cells of the anterior pituitary(AP) • some actions are inhibitory • most stimulate the AP to release hormones that then stimulate other endocrine gland secretions • negative feedback regulates hormone levels in the bloodstream – fig 13.8 page 496

30. Pituitary Gland • Two distinct portions • anterior pituitary (adenohypophysis) • posterior pituitary (neurohypophysis)

31. Pituitary Gland Control • Hypothalamic releasing hormones stimulate cells of anterior pituitary to release hormones • Nerve impulses from hypothalamus stimulate nerve endings in the posterior pituitary gland to release hormones

32. Anterior Pituitary Hormones • AP lobe is enclosed in a dense capsule of connective tissue and consists of epithelial tissue arranged around • thin blood vessels • Five types of secretory cells within the epithelial tissue • Table 13.6 page 503

33. Posterior Pituitary Hormones • Posterior lobe consists mainly of nerve fibers and neuroglial cells (pituicytes) • Pituicytes support nerve fibers that originate in the hypothalmus • Table 13.6 page 503

34. Hormones of the Pituitary Gland

35. Hypothalamic Hormones

36. Thyroid Gland • Very vascular • Made of 2 large lateral lobes connected by a broad isthmus • Located just below the larynx on either side and anterior to the trachea • Removes iodine from the blood

37. Structure of the thyroid gland • It is covered by connective tissue made of follicles (secretory parts) • Follicles produce and secrete hormones • Extrafollicular cells(C cells) lie outside the follicles • Center filled with a clear viscous glycoprotein called colloid

38. Thyroid Gland

39. Thyroid Hormones • Follicular cells synthesize thyroxine (T4)and triiodothyronine (T3) which affect the metabolic rates of cells • Follicular cells need iodine salts to produce T3 and T4 • thyroid enlarges (goiter) if not enough iodine • C cells produce calcitonin

40. Thyroid Gland Hormones

41. Disorders of the Thyroid Gland

42. Disorders of the Thyroid Gland • Graves Disease • Hyperthyroidism • Cretinism • Infantile hypothyroidism

43. Parathyroid Gland • Located on the posterior surface of the thyroid gland • Usually 4 of them • Each gland is a small, yellowish brown structure covered by a thin capsule of connective tissue • Body consists of many tightly packed secretory cells associated with capillary networks

44. Parathyroid Glands

45. Parathyroid Hormone • PTH increases blood calcium ion concentration and decreases blood phosphate ion concentration through actions in the bones, kidneys, and intestines • PTH stimulates bone resorption by osteocytes and osteoclasts • Ca and PO4 ions are released into blood

46. PTH causes kidneys to conserve blood Ca ions and excrete more PO4 ions in the urine • PTH helps kidneys convert Vitamin D into an active form which controls the absorption of Ca ions from the intestines

47. Parathyroid Hormone

48. Parathyroid Hormone Mechanism by which PTH promotes calcium absorption in the intestine

49. Disorders of the Parathyroid Glands

50. Adrenal Glands • Sits atop each kidney • Embedded in adipose tissue that encloses each kidney