Endocrine System Tortora Chapter 18, edition 13 Ebaa M Alzayadneh, DDS, PhD Integrative Physiology and Pharmacology

Endocrine System Overview Regulated by Signals from nervous system Chemical changes in the blood Other hormones Most hormonal regulation by negative feedback Few examples of positive feedback University of Jordan 3

Hypothalamus and Pituitary Gland Hypothalamus is a major link between nervous and endocrine system Pituitary is attached to hypothalamus by infundibulum and divided in to: Anterior pituitary or adenohypophysis Posterior pituitary or neurohypophysis The anterior pituitary receives signalling molecules from the hypothalamus, and in response, synthesizes and secretes seven important hormones. The posterior pituitary does not produce any hormones of its own,but, it stores and secretes two hormones made in the hypothalamus. University of Jordan 4

Hypothalamus and Pituitary Gland

Anterior pituitary Release of hormones is stimulated by hypothalamus releasing hormones (factors). Regulated by negative feedback Hypothalamic hormones made by neurosecretory cells transported by hypophyseal portal system to ant. pituitary. Anterior pituitary hormones that act on other endocrine systems called tropic hormones, synthesizing cells are called trophs cells. University of Jordan 6

Anterior pituitary To memorize ant. Pituitary hormones " FLAGTOP " F: Follicle Stimulating Hormone L: Luteinizing Hormone A: ACTH : Adrenocorticotropic hormone G: Growth Hormone T: Thyroid Stimulating Hormone O: MSH - melanOcyte stimulating hormone P: Prolactin University of Jordan 7

Hormones of the Anterior Pituitary (FLAG TOP) Follicle-stimulating hormone (FSH) by gonadotrophs cells Ovaries initiates development of oocytes, testes stimulates testosterone production Luteinizing hormone (LH) by gonadotrophs cells Ovaries stimulates ovulation, testes stimulates testosterone production Adrenocorticotropic hormone (ACTH) or corticotropin Released by corticotrophs cells Stimulates glucocorticoid secretion by adrenal cortex Thyroid-stimulating hormone (TSH) or thyrotropin by thyrotrophs Stimulates synthesis and secretion of thyroid hormones by thyroid University of Jordan 8

Hormones of the Anterior Pituitary Prolactin (PRL):released by lactotrophs Promotes milk secretion by mammary glands Melanocyte-stimulating Hormone (MSH) Unknown role in humans Human growth hormone (hGH) or somatotropin released by somatotrophs Stimulates secretion of insulin-like growth factors (IGFs) that promote growth, protein synthesis University of Jordan 9

10 ANTERIOR PITUITARY HORMONES Hypothalamus Hormone that stimulate Hormone released from Adenohypophysis (ant. Pituitary) Major Function/ Target Growth hormone releasing and inhibiting hormones (GHRH, GHIH) Human Growth Hormone (hGH) Also called somatotropin, stimulates secretion of insulin-like growth factors (IGFs) that promote growth Thyrotropin releasing hormone (TRH) Thyroid Stimulating Hormone (TSH) Stimulates synthesis and secretion of thyroid hormones by the thyroid gland Prolactin inhibiting hormone (PIH- dopamin) Prolactin (PRL) Stimulates breast growth, and development of the mammary glands

University of Jordan 11 ANTERIOR PITUITARY HORMONES Hypothalamus Hormone Hormone released from Adenohypophysis Major Function/ Target Gonadotropic releasing hormone (GnRH) Follicle Stimulating hormone (FSH) Ovaries initiate development of oocytes; testes initiate development of spermatozoa Gonadotropic releasing hormone (GnRH) Luteinizing hormone (LH) Ovaries stimulate ovulation; testes stimulate testosterone production

University of Jordan 12 ANTERIOR PITUITARY HORMONES Hypothalamus Hormone Hormone released from Adenohypophysis Major Function/ Target Corticotropin releasing hormone (CRH) Adrenocorticotropic Hormone (ACTH) Stimulates release of mineralocorticoid, glucocorticoid, and androgen hormones from the adrenal cortex Corticotropin releasing hormone (CRH) Melanocyte Stimulating hormone (MSH) Stimulate the production and release of melanin by melanocytes in skin and hair. MSH signals to the brain have effects on appetite and sexual arousal

Negative Feedback Regulation University of Jordan 13

Pituitary Hormones Anterior Pituitary: Trophic effects: High blood [hormone] causes target organ to hypertrophy. Low blood [hormone] causes target organ to atrophy. University of Jordan 14

University of Jordan 15 Low blood glucose (hypoglycemia) stimulates release of GHRH 1 Low blood glucose (hypoglycemia) stimulates release of hGH GHRH stimulates secretion of hGH by somatotrophs GHRH 1 2 Low blood glucose (hypoglycemia) stimulates release of hGH GHRH stimulates secretion of hGH by somatotrophs GHRH hGH and IGFs speed up breakdown of liver glycogen into glucose, which enters the blood more rapidly Low blood glucose (hypoglycemia) stimulates release of hGH GHRH stimulates secretion of hGH by somatotrophs GHRH hGH and IGFs speed up breakdown of liver glycogen into glucose, which enters the blood more rapidly Blood glucose level rises to normal (about 90 mg/100 mL) Low blood glucose (hypoglycemia) stimulates release of hGH GHRH stimulates secretion of hGH by somatotrophs GHRH hGH and IGFs speed up breakdown of liver glycogen into glucose, which enters the blood more rapidly Blood glucose level rises to normal (about 90 mg/100 mL) If blood glucose continues to increase, hyperglycemia inhibits release of GHRH Anterior pituitary Low blood glucose (hypoglycemia) stimulates release of High blood glucose (hyperglycemia) stimulates release of hGH GHRH stimulates secretion of hGH by somatotrophs GHIHGHRH hGH and IGFs speed up breakdown of liver glycogen into glucose, which enters the blood more rapidly Blood glucose level rises to normal (about 90 mg/100 mL) If blood glucose continues to increase, hyperglycemia inhibits release of GHRH Anterior pituitary GHIH inhibits secretion of hGH by somatotrophs Low blood glucose (hypoglycemia) stimulates release of High blood glucose (hyperglycemia) stimulates release of hGH GHRH stimulates secretion of hGH by somatotrophs GHIHGHRH hGH and IGFs speed up breakdown of liver glycogen into glucose, which enters the blood more rapidly Blood glucose level rises to normal (about 90 mg/100 mL) If blood glucose continues to increase, hyperglycemia inhibits release of GHRH GHIH inhibits secretion of hGH by somatotrophs Low blood glucose (hypoglycemia) stimulates release of High blood glucose (hyperglycemia) stimulates release of Anterior pituitary hGH GHRH stimulates secretion of hGH by somatotrophs GHIHGHRH A low level of hGH and IGFs decreases the rate of glycogen breakdown in the liver and glucose enters the blood more slowly hGH and IGFs speed up breakdown of liver glycogen into glucose, which enters the blood more rapidly Blood glucose level rises to normal (about 90 mg/100 mL) If blood glucose continues to increase, hyperglycemia inhibits release of GHRH GHIH inhibits secretion of hGH by somatotrophs Low blood glucose (hypoglycemia) stimulates release of High blood glucose (hyperglycemia) stimulates release of Anterior pituitary hGH GHRH stimulates secretion of hGH by somatotrophs GHIHGHRH A low level of hGH and IGFs decreases the rate of glycogen breakdown in the liver and glucose enters the blood more slowly Blood glucose level falls to normal (about 90 mg/100 mL) hGH and IGFs speed up breakdown of liver glycogen into glucose, which enters the blood more rapidly Blood glucose level rises to normal (about 90 mg/100 mL) If blood glucose continues to increase, hyperglycemia inhibits release of GHRH GHIH inhibits secretion of hGH by somatotrophs Low blood glucose (hypoglycemia) stimulates release of High blood glucose (hyperglycemia) stimulates release of Anterior pituitary hGH GHRH stimulates secretion of hGH by somatotrophs GHIHGHRH A low level of hGH and IGFs decreases the rate of glycogen breakdown in the liver and glucose enters the blood more slowly Blood glucose level falls to normal (about 90 mg/100 mL) hGH and IGFs speed up breakdown of liver glycogen into glucose, which enters the blood more rapidly Blood glucose level rises to normal (about 90 mg/100 mL) If blood glucose continues to increase, hyperglycemia inhibits release of GHRH If blood glucose continues to decrease, hypoglycemia inhibits release of GHIH Effects of hGH and IGFs High levels of GH before puberty causes Gigantism, after puberty causes Acromegaly. Low levels of GH before puberty causes Dwarfism, after puberty leads to some Metabolic effects