1 Key concepts: Hormones and other signaling molecules bind to target receptors, triggering specific response pathways. Negative feedback and antagonistic hormone pairs are common features of the endocrine system. The endocrine and nervous systems act individually and together in regulating animal physiology. Endocrine glands respond to diverse stimuli in regulating metabolism, homeostasis, development and behavior. Chapter 45 Hormones And Endocrine System

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H ORMONES AND OTHER SIGNALING MOLECULES BIND TO TARGET RECEPTORS, TRIGGERING SPECIFIC RESPONSE PATHWAYS ( PP ). Types of secreted signaling molecules: Hormones are secreted into extracellular fluids by endocrine cells or ductless glands and reach target cells via blood. Local regulators act on neighboring cells in paracrine signaling and on the secreting cell itself in autocrine signaling. Neurotransmitters also act locally, but some secrete neurohormones that act throughout the body. 3

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H ORMONES AND OTHER SIGNALING MOLECULES BIND TO TARGET RECEPTORS, TRIGGERING SPECIFIC RESPONSE PATHWAYS. Chemical classes of hormones: Hormones can be polypeptides, amines or steroids and can be water soluble or lipid soluble. Hormone receptor location: Protein hormones bind to receptors embedded in the plasma membrane, steroid hormones and thyroid hormones enter target cells and bind to receptors in the cytoplasm or nucleus. 5

H ORMONES AND OTHER SIGNALING MOLECULES BIND TO TARGET RECEPTORS, TRIGGERING SPECIFIC RESPONSE PATHWAYS. Cellular response pathways: Binding of water soluble hormones to cell surface receptors triggers intracellular signal transduction leading to specific responses in the cytoplasm but lipid soluble hormones and its receptors act in the nucleus to regulate transcription specific genes. Multiple effects of the same hormone: The same hormone may have different effects on the target cells. 6

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S IGNALING BY LOCAL REGULATORS Several types of chemical compounds function as local regulators: Neurotransmitters: are local regulators in the synapses of the nervous system. Growth factors: are peptides and proteins that stimulate cell proliferation. Prostaglandins (PGs): are modified fatty acids, released from most types of cells into the interstitial fluid, affecting nearby cells. Nitric oxide (NO): it is a gas with many types of cells can produce and it has multiple function. Highly reactive and potentially toxic, NO usually trigger changes in a target cell within a few seconds of contact and then breaks down. When NO secreted by neurons, function as neurotransmitter; secreted by white blood cells, it kills certain bacteria and cancer cells. 8

9 Negative feedback and antagonistic hormone pairs are common features of the endocrine system (pp ). Simple endocrine pathway Negative feedback is a loop in which the response reduces the initial stimulus

N EGATIVE FEEDBACK AND ANTAGONISTIC HORMONE PAIRS ARE COMMON FEATURES OF THE ENDOCRINE SYSTEM. To see how such control systems operate, we’ll consider the regulation of blood glucose levels. Two antagonistic hormones, insulin and glucagon regulate the concentration of glucose in the blood. Insulin from beta cells of pancreas reduce blood glucose level by promoting cellular uptake of glucose, glycogen formation in the liver, protein synthesis and fat storage. Glucagon from alpha cells increase blood glucose level by stimulating conversion of fat and glycogen to glucose in the liver and breakdown of the fat and protein to glucose. Diabetes mellitus which is marked by elevated blood glucose levels result from inadequate production of insulin (type 1) or loss of responsiveness of target cells to insulin (type 2) 10

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T HE ENDOCRINE AND NERVOUS SYSTEMS ACT INDIVIDUALLY AND TOGETHER IN REGULATING ANIMAL PHYSIOLOGY ( PP ) Coordination of endocrine and nervous systems in vertebrates: The hypothalamus, contain sets of neurosecretory cells. Some produce direct acting hormones that are stored and released from the posterior pituitary. Other hypothalamic cells produce hormones that are transported by portal blood to the anterior pituitary. Two kinds of hormones secreted into the blood: Releasing hormones make the anterior pituitary secrete its hormones. Inhibiting hormones make the anterior pituitary stop secreting hormone. 12

P OSTERIOR PITUITARY HORMONE  The pituitary gland has two lobes: anterior and posterior lobes: The posterior pituitary or neurohypophysis, that stores and releases two hormones: oxytocin and antidiuretic hormone, ADH. They function in simple neurohormone pathways. Oxytocin induces uterine contractions during childbirth and milk ejection ADH enhances water re -absorption in the kidneys. 13

14 Simple neurohormone pathway

Some hormones called tropic hormones, have other endocrine glands as their targets in a hormone cascade pathways. 15 A hormone cascade pathway

A NTERIOR PITUITARY HORMONES The anterior pituitary produces: Tropic hormones: 1. Thyroid stimulating hormone (TSH), regulate the thyroid gland secretions 2. Follicle stimulating hormone (FSH) and (LH), they also called gonadotropins because they stimulate the activities of the male and female gonads. 3. Adrenocorticotropic hormones (ACTH), control the production and secretion of steroid hormones by the adrenal cortex. Nontropic hormones: 1. Prolactin (PRL) stimulate mammary glands growth and milk synthesis 2. Melanocyte – stimulating hormone (MSH), it stimulate skin pigmentation. 3. Endorphins, the brain’s natural opiates, inhibit perception of pain. Growth hormone (GH): has both tropic and nontropic actions. It promotes growth directly and stimulate the production of growth factors. 16

E NDOCRINE GLANDS RESPOND TO DIVERSE STIMULI IN REGULATING METABOLISM, HOMEOSTASIS, DEVELOPMENT AND BEHAVIOR ( PP ).  Thyroid hormones: The thyroid gland consists of two lobes located on the ventral surface of the trachea. The thyroid gland produces iodine containing hormones triiodothyronine (T3) and thyroxine (T4) that stimulate metabolism and influence development and maturation. The thyroid gland also secrete calcitonin which lowers calcium levels in the blood. The hypothalamus and anterior pituitary control the secretion of thyroid hormones. 17

P ARATHYROID HORMONE AND VITAMIN D: CONTROL OF BLOOD CALCIUM  The four parathyroid glands embedded in the surface of the thyroid gland The parathyroid glands raise plasma calcium levels by secreting parathyroid hormone (PTH) PTH stimulate the kidneys to activate vitamin D, which in turn stimulates the intestines to increase uptake of calcium from food. In bone, PTH induces specialized cells called osteoclasts to decompose the mineralized matrix of bone and realse Ca +2 into the blood. Calcitonin and (PTH) maintain calcium homeostasis by acting on kidneys and bone. 18

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A DRENAL HORMONES : RESPONSE TO STRESS Neurosecretory cells in the adrenal medulla release epinephrine and norepinephrine in response to stress. These hormones mediate various fight or flight responses.  The adrenal cortex releases three functional classes of steroid hormones: Corticosteroids (Including sex hormones), Glucocorticoids, such as cortisol, influence glucose metabolism and the immune system; Mineralocorticoids, primarily aldosterone, affect salt and water balance. 20

M ELATONIN AND B IORHYTHMS  The pineal gland is a small mass of tissue near the center of the brain The pineal gland secretes melatonin which is secreted at the night, which influences skin pigmentation, biological rhythms and reproduction in various vertebrates. 21