Chapter 18: The Endocrine System

Chapter 18: The Endocrine System PRINCIPLES OF ANATOMY AND PHYSIOLOGY The Nervous and Endocrine Systems... Act together to coordinate functions of all body systems Nervous system Nerve impulses / Neurotransmitters Faster responses, briefer effects, acts on specific target Endocrine system Hormone - a mediator molecule is released in 1 part of the body; but regulates activity of cells in other parts Slower responses, effects last longer, broader influence Endocrine Glands Two kinds of glands Exocrine - ducted (sudoriferous, sebaceous, mucous, digestive) Endocrine - ductless Secrete products into interstitial fluid, diffuse into blood Endocrine glands include Pituitary, thyroid, parathyroid, adrenal and pineal glands Hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart, adipose tissue, and placenta - not exclusively endocrine glands PINEAL GLAND HYPOTHALAMUS PITUITARY GLAND Thyroid gland PARATHYROID GLANDS Trachea PARATHYROID GLANDS (behind thyroid glands) SKIN THYROID GLAND Lung LIVER ADRENAL GLANDS PANCREAS SMALL INTESTINE Trachea THYMUS HEART STOMACH KIDNEY Uterus OVARY Scrotum Female TESTES Male Hormone Activity Hormones (H') affect only specific target tissues with specific receptors Receptors constantly synthesized and broken down Down-regulation = large amounts of H' leads to a decrease in target-cell receptors Up-regulation = low amounts of H' leads to increase in target-cell receptors Endocrine cell Circulating hormone Blood capillary Hormone types Circulating - circulate in blood throughout body Hormone receptor Distant target cells Local hormones - act locally (a) Circulating hormones Paracrine - act on neighboring cells Autocrine - act on the same cell that secreted them Paracrine cell Paracrine receptor- Paracrine Nearby target cell Autocrine receptor Autocrine cell Autocrine (b) Local hormones (paracrines and autocrines) Chemical classes of hormones Lipid-soluble - use transport proteins produced by 'liver' Steroid H' - (large diversity) Thyroid H' - (iodine added to aa tyrosine) Nitric oxide - (NO), is both H' and N' Water-soluble - circulate in "free" form Amine H' - removal of CO2 (-NH3+) Peptide H' (antidiuretic, oxytocin)/ Protein H' (hGH, insulin) Eicosanoid H' (prostaglandins, leukotrienes) Mechanisms of Hormone Action Response depends on both hormone and target cell Lipid-soluble hormones bind to receptors inside target cells Water-soluble hormones bind to receptors on the plasma membrane Activates second messenger system Amplification of original small signal Responsiveness of target cell depends on Hormone's concentration Abundance of target cell receptors Influence exerted by other hormones Permissive (1st activated by another H'), synergistic and antagonistic effects Lipid-soluble and Water-soluble Hormones Free hormone Blood capillary Transport protein 1 Lipid-soluble hormone diffuses into cell 2 Activated receptor-hormone complex alters gene expression Nucleus Receptor Cytosol DNA 3 Newly formed mRNA directs synthesis of specific proteins on ribosomes mRNA Ribosome New protein 4 New proteins alter cell's activity Target cell 000 Blood capillary 000 Water-soluble hormone Receptor 1 Binding of hormone (first messenger) to its receptor activates G protein, which activates adenylate cyclase Adenylate cyclase G protein ATP CAMP Second messenger 2 Activated adenylate cyclase converts ATP to cAMP Protein kinases 6 Phosphodiesterase inactivates cAMP 3 CAMP serves as a second messenger to activate protein kinases Activated protein kinases Protein ATP 4 Activated protein kinases phosphorylate cellular proteins ADP Protein-p 5 Millions of phosphorylated proteins cause reactions that produce physiological responses Target cell Control of Hormone Secretion Regulated by Free hormone Blood capillary 1. Signals from nervous system Transport protein 1 Lipid-soluble hormone diffuses into cell 2. Chemical changes in the blood 2 Activated receptor-hormone complex alters gene expression Nucleus 3. Other hormones Receptor Most hormonal regulation by negative feedback Cytosol 3 Newly formed mRNA directs synthesis of specific proteins on ribosomes DNA mRNA Ribosome Few examples of positive feedback New protein 4 New proteins alter cell's activity Target cell Hypothalamus and Pituitary Gland Hypothalamus is a major link between nervous and endocrine system Pituitary attached to hypothalamus by infundibulum Anterior pituitary or adenohypophysis Posterior pituitary or neurohypophysis Hypothalamus and Pituitary Gland Hypothalamus Pituitary gland Posterior pituitary Anterior pituitary Sagittal section of pituitary gland HYPOTHALAMUS Primary plexus of the hypophyseal portal system Posterior hypophyseal veins POSTERIOR PITUITARY Infundibulum Pars nervosa Infundibulum Capillary plexus of the infundibular process Hypophyseal fossa POSTERIOR Inferior hypophyseal artery Hypothalamic neurosecretory cell Hypophyseal portal veins (b) Path of releasing and inhibiting hormones Median eminence Superior hypophyseal artery Pars tuberalis ANTERIOR PITUITARY Pars distalis Sphenoid bone Hypophyseal portal veins Secondary plexus of the hypophyseal portal system Anterior hypophyseal veins ANTERIOR Anterior pituitary Release of hormones stimulated by releasing and inhibiting-hormones from the hypothalamus Also regulated by negative feedback Hypothalamic hormones made by neurosecretory cells transported by hypophyseal portal system Anterior pituitary hormones that act on other endocrine systems called tropic hormones Hormones of the Anterior Pituitary Somatotrophs secrete Human growth hormone (hGH) or somatostatin Stimulates secretion of insulin-like growth factors (IGFs) that promote growth, protein synthesis Thyrotrophs secrete Thyroid-stimulating hormone (TSH) or thyrotropin Stimulates synthesis and secretion of thyroid hormones by thyroid 1. Gonadotrophs secrete Follicle-stimulating hormone (FSH) Ovaries initiates development of oocytes, testes stimulates testosterone and sperm production 2. Gonadotrophs secrete Luteinizing hormone (LH) Ovaries stimulates ovulation, testes stimulates testosterone production Hormones of the Anterior Pituitary Lactotrophs secrete Prolactin (PRL) Promotes milk secretion by mammary glands Corticotrophs secrete Adrenocorticotropic hormone (ACTH) or corticotropin Stimulates glucocorticoid (i.e., cortisol) secretion by adrenal cortex Corticotrophs secrete Melanocyte-stimulating Hormone (MSH) Unknown role in humans Negative Feedback Regulation Corticotropin releasing hormone (CRH) Hypothalamus CRH stimulates release of corticotropin (ACTH) Anterior pituitary Corticotropin (ACTH) Elevated cortisol inhibits release of CRH by hypothalamic neurosecretory cells Elevated cortisol inhibits release of corticotropin by anterior pituitary corticotrophs Corticotropin stimulates secretion of cortisol by adrenal cortex Adrenal cortex 1 Low blood glucose (hypoglycemia) stimulates release of 6 High blood glucose (hyperglycemia) stimulates release of GHRH GHIH 2 GHRH stimulates secretion of hGH by somatotrophs hGH 7 GHIH inhibits secretion of hGH by somatotrophs Anterior pituitary 3 hGH and IGFs speed up breakdown of liver glycogen into glucose, which enters the blood more rapidly 8 A low level of hGH and IGFs decreases the rate of glycogen breakdown in the liver and glucose enters the blood more slowly 4 Blood glucose level rises to normal (about 90 mg/100 mL) 9 Blood glucose level falls to normal (about 90 mg/100 mL) 5 If blood glucose continues to increase, hyperglycemia inhibits release of GHRH 10 If blood glucose continues to decrease, hypoglycemia inhibits release of GHIH