Endocrine System

1. Endocrine System

2. Endocrine System Overview • Endocrine system • Consists of ductless glands • Secrete hormones directly into bloodstream • Affect the function of specific body organs • Regulates many intricate body functions

4. Messenger Molecules • Cells must communicate with one another to coordinate cell processes within tissues and to maintain homeostasis. • Cell-to-cell communication is carried out via messenger molecules.

5. Three types of chemical signals are used for cell-to-cell communication.

6. Four methods of cell-to-cell communication are found in the human body, ranging from direct to remote communication.

7. Endocrine hormones • Produced by endocrine (“ductless”) glands and secreted into the bloodstream. • Endocrine hormones may affect a wide array of target cells to produce multiple effects. • Two types: peptides (small proteins) and steroids (lipids).

8. Hormones and Receptors

9. Peptide Hormones • Peptide hormones do not enter the cell directly. These hormones bind to receptor proteins in the cell membrane. • When the hormone binds with the receptor protein, a secondary messenger molecule initiates the cell response. • Because peptide hormones are water soluble, they often produce fast responses.

10. peptide or amino acid-derived hormone (first messenger) 2 Hormone–receptor binding activates an enzyme that catalyzes the synthesis of a second messenger, such as cyclic AMP 1 The hormone binds to a receptor on the plasma membrane of a target cell cyclic AMP- synthesizing enzyme (cytoplasm) (extracellular fluid) ATP active enzyme receptor product cyclic AMP (second messenger) 4 The activated enzymes catalyze specific reactions plasma membrane inactive enzyme reactant 3 The second messenger activates other enzymes nuclear envelope (nucleus)

11. Steroid Hormones • Steroid hormones enter through the cell membrane and bind to receptors inside of the target cell. • These hormones may directly stimulate transcription of genes to make certain proteins. • Because steroids work by triggering gene activity, the response is slower than peptide hormones.

12. steroid hormone (extracellular fluid) The hormone binds to a receptor in the nucleus or to a receptor in the cytoplasm that carries it into the nucleus 2 The hormone–receptor complex binds to DNA and causes RNA polymerase to bind to a nearby promoter site for a specific gene 3 1 A steroid hormone diffuses through the plasma membrane DNA plasma membrane hormone receptor ribosome RNA polymerase 5 The mRNA leaves the nucleus, then attaches to a ribosome and directs the synthesis of a specific protein product 4 RNA polymerase catalyzes the transcription of DNA into messenger RNA (mRNA) mRNA gene new protein nuclear envelope (cytoplasm) (nucleus)

13. Hormones Everywhere! • Many other organs besides the endocrine glands produce hormones. • Kidneys produce several hormones that regulate blood pressure, which is essential for kidney function. • The digestive system produces several hormones that regulate appetite.

15. Role of the Hypothalamus • The thalamus receives sensory information, relays some to the hypothalamus. • Hypothalamus monitors the body for temperature, pH, other conditions. • Hypothalamus signals pituitary gland if conditions need to be corrected.

16. Pituitary Gland • Referred to as “master gland” • Secretes hormones that control functions of other glands • Known as hypophysis • Has two distinct lobes with specific functions

17. Role of the Pituitary • The pituitary is the “master gland” that signals other glands to produce their hormones when needed. • The anterior lobe of the pituitary receives signals from the hypothalamus, and responds by sending out the appropriate hormone to other endocrine glands. • The posterior pituitary receives oxytocin or antidiuretic hormone (ADH) from the hypothalamus, relays them to the body as necessary.

18. Pituitary Gland • Anterior Pituitary Gland = Adenohypophysis • Secretes Growth Hormone (GH) • Also called Somatotropic Hormone (STH) • Regulates growth of bone, muscle, and other body tissues • Secretes Adrenocorticotropic Hormone (ACTH) • Stimulates normal growth and development of adrenal cortex and secretion of corticosteroids

19. Pituitary Gland • Anterior Pituitary Gland • Secretes Thyroid-Stimulating Hormone (TSH) • Promotes and maintains normal growth and development of the thyroid gland • Stimulates secretions of the thyroid hormones • Secretes Lactogenic Hormone (LTH) • Also called Prolactin • Promotes development of breasts during pregnancy • Stimulates secretion of milk from breasts after delivery of baby

20. Pituitary Gland • Anterior Pituitary Gland • Secretes Follicle-Stimulating Hormone (FSH) • Stimulates secretion of estrogen and production of eggs in the female ovaries • Stimulates production of sperm in the male testes • Secretes Luteinizing Hormone (LH) • Stimulates female ovulation and the secretion of testosterone in the male • Melanocyte-Stimulating Hormone (MSH) • Controls intensity of pigmentation in pigmented cells of the skin

21. Pituitary Gland • Posterior Pituitary Gland = Neurohypophysis • Secretes Antidiuretic Hormone (ADH) • Decreases excretion of large amounts of urine • Increases reabsorption of water by the renal tubules • Secretes Oxytocin (OT) • Stimulates contraction of the uterus during childbirth • Stimulates release of milk from the breasts of lactating women in response to the suckling reflex of the infant

22. Located below the thalamus and above the pituitary gland (=epiphysis) Regulates the pituitary gland secretions through two different mechanisms Hypothalamus

23. 1- Neurons, receiving information from receptors, fire APs which travel down to the post pituitary gland and stimulate the release of stored neurohormones – Oxytocin (OT) and anti-diuretic hormone (ADH) Hypothalamus - neurohypophysis

24. Hormones of the posterior pituitary

25. 2- Upon stimulation, secretory cells located in the hypothalamus secrete “releasing” hormones which travel down a capillary bed toward the anterior pituitary gland (adenopituitary). Each type of releasing hormones will stimulate the secretion and release of a pituitary hormone. Hormones which control the secretion of other hormones are tropic hormones (found in hypothalamus and pituitary gland) Hypothalamus – adenohypophysis

26. Anterior pituitary Figure 6.8

27. Pituitary Hormones

28. Mechanism of control Figure 6.6

29. Hormones of the hypothalamus and anterior pituitary gland Figure 6.5

30. Pineal Gland • Tiny, pinecone-shaped gland • Located behind dorsal aspect of midbrain region • Plays a part in supporting body’s biological clock • Regulation of patterns of eating, sleeping, and reproduction • Secretes melatonin • Induces sleep

31. Thyroid Gland • Located in front of the neck just below the larynx, on either side of the trachea • Consists of a right and left lobe

32. Thyroid Gland • Secretes Triiodothyronine (T3) • Helps regulate growth and development of body • Helps control metabolism and temperature • Secretes Thyroxine (T4) • Helps maintain normal body metabolism • Secretes Calcitonin • Helps regulate the level of calcium in the blood

33. Located in the neck, just below the larynx Secrete 2 types of hormone: - thyroid hormones  stimulate cell metabolism, triiodothyronine (T3) and thyroxine (T4) – iodine is needed to synthesize these hormones - calcitonin  decrease blood calcium The thyroid gland Figure 6.8a

34. T3 and T4 secreted by the follicular cells Stored as colloid Parafollicular cells (C cells) secrete calcitonin Thyroid hormones

35. Thyroid Hormones T3 and T4 • Target organs: all cells • Role: Increase cell metabolism, oxygen consumption • Permissive role for some other hormones (growth hormone)

36. Thyroid hormone regulation Figure 6.7

37. Parathyroid Glands • Four tiny rounded bodies located on dorsal aspect of thyroid gland • Secrete Parathyroid Hormone (PTH) • Also known as parathormone • Regulates level of calcium in blood

38. Four nodules located in the back of the thyroid gland Secreted parathyroid hormone or parathormone or PTH Action of PTH opposes action of calcitonin Both hormones play a role in calcium metabolism, regulating the level of calcium in blood. Parathyroid glands

39. Roles of calcium • Most calcium ions are stored in the bones • Calcium is an important cofactor for enzymatic activity, plays a role in blood coagulation and action potentials. • Calcitonin and PTH participate in calcium regulation • Vitamin D helps PTH activity

40. Calcitonin promotes blood calcium decrease, by: 1. calcium deposition on bone 2. calcium dumping by the kidney PTH promotes blood calcium increase by: 1. bone resorption 2. calcium reabsorption by kidney 3. increase calcium absorption by intestine Calcium regulation:

41. Calcium Metabolism: Figure 23-20: Calcium balance in the body

42. Figure 19.20

43. Thymus • Single gland located in mediastinum near the middle of the chest, just beneath sternum • Large in fetus and infants, shrinks with age • Secretes thymosin and thymopoietin • Stimulates production of T cells that are involved in the immune response

44. Adrenal Glands • Two small glands, one positioned atop each kidney • Also known as suprarenal glands • Consists of an adrenal cortex and an adrenal medulla • Each has independent functions

45. Adrenal Glands • Adrenal cortex secretes corticosteroids • Mineralocorticoids • Regulate how mineral salts (electrolytes) are processed in the body • Glucocorticoids • Influence metabolism of carbohydrates, fats, and proteins in the body • Necessary for maintaining normal blood pressure • Have an anti-inflammatory effect on the body • Increase glucose available during “fight-or-flight” responses by the body

47. Adrenal Glands • Adrenal cortex secretes • Gonadocorticoids • Sex hormones secreted in small amounts • Contribute to secondary sex characteristics in males and females

48. Adrenal Glands • Adrenal medulla secretes catecholamines • Epinephrine = adrenaline • Sympathiomimetic agent • Increases heart rate and force of heart muscle contraction • Dilates bronchioles in the lungs • Decreases peristalsis in the intestines • Raises blood glucose levels by causing the liver to convert glycogen into glucose

49. Adrenal Glands • Adrenal medulla secretes • Norepinephrine = noradrenaline • Known as a sympathomimetic agent • Produces a vasoconstrictor effect on the blood vessels, thereby raising blood pressure

50. Adrenal gland hormones