Biology II FBI102 PDF

Assoc. Prof. Dr. Melis SÜMENGEN ÖZDENEFE 1 2  Animal hormones are chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body  Hormones reach all parts of the body, but only ta...

Assoc. Prof. Dr. Melis SÜMENGEN ÖZDENEFE 1 2  Animal hormones are chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body  Hormones reach all parts of the body, but only target cells have receptors for that hormone 3  Chemical signaling by hormones is the function of the endocrine system  The nervous system is a network of specialized cells—neurons—that transmit signals along dedicated pathways  The nervous and endocrine systems often overlap in function 4  Animals use chemical signals to communicate in diverse ways 5  The ways that signals are transmitted between animal cells are classified by two criteria ◦ The type of secreting cell ◦ The route taken by the signal in reaching its target 6  Hormones secreted into extracellular fluids by endocrine cells reach their targets via the bloodstream  Endocrine signaling maintains homeostasis, mediates responses to stimuli, regulates growth and development 7  Blood vessel RESPONSE (a) Endocrine signaling Synapse Neuron RESPONSE RESPONSE (d) Synaptic signaling (b) Paracrine signaling Neurosecretory cell Blood RESPONSE vessel RESPONSE (c) Autocrine signaling (e) Neuroendocrine signaling 8  Local regulators are molecules that act over short distances, reaching target cells solely by diffusion  In paracrine signaling, the target cells lie near the secreting cells  In autocrine signaling, the target cell is also the secreting cell 9  Paracrine and autocrine signaling play roles in processes such as blood pressure regulation, nervous system function, and reproduction  Local regulators that mediate such signaling include the prostaglandins  Prostaglandins function in reproduction, the immune system, and blood clotting 10  Blood vessel RESPONSE (a) Endocrine signaling Synapse Neuron RESPONSE RESPONSE (d) Synaptic signaling (b) Paracrine signaling Neurosecretory cell Blood RESPONSE vessel RESPONSE (c) Autocrine signaling (e) Neuroendocrine signaling 11  In synaptic signaling, neurons form specialized junctions with target cells, called synapses  At synapses, neurons secrete molecules called neurotransmitters that diffuse short distances and bind to receptors on target cells 12  In neuroendocrine signaling, specialized neurosecretory cells secrete molecules called neurohormones that travel to target cells via the bloodstream 13  Blood vessel RESPONSE (a) Endocrine signaling Synapse Neuron RESPONSE RESPONSE (d) Synaptic signaling (b) Paracrine signaling Neurosecretory cell Blood RESPONSE vessel RESPONSE (c) Autocrine signaling (e) Neuroendocrine signaling 14  Members of an animal species sometimes communicate with pheromones, chemicals that are released into the environment  Pheromones serve many functions, including marking trails leading to food, defining territories, warning of predators, and attracting potential mates 15  Molecules used in intercellular signaling vary substantially in size and chemical properties 16  Local regulators such as the prostaglandins are modified fatty acids  Others are polypeptides and some are gases  Nitric oxide (NO) is a gas that functions in the body as both a local regulator and a neurotransmitter  When the level of oxygen in blood falls, NO activates an enzyme that results in vasodilation (expansion of vessel), increasing blood flow to tissues 17  Hormones fall into three major classes: polypeptides, steroids, and amines  Polypeptides and amines are water-soluble whereas steroid hormones and other largely nonpolar hormones are lipid-soluble 18 Water-soluble (hydrophilic) Lipid-soluble (hydrophobic) Polypeptides Steroids 0.8 nm Insulin Cortisol Amines Epinephrine Thyroxine 19  Water-soluble hormones (polypeptides and amines) are secreted by exocytosis, travel freely in the bloodstream, and bind to cell-surface receptors  Lipid-soluble hormones (steroids) diffuse across cell membranes, travel in the bloodstream bound to transport proteins, and diffuse through the membrane of target cells  They bind to receptors in the cytoplasm or nucleus of the target cells 20 (a) Water-soluble hormone; (b) Lipid-soluble hormone; receptor in plasma receptor in nucleus or membrane cytoplasm SECRETORY SECRETORY CELL CELL Water- Lipid- soluble soluble hormone hormone Blood Blood vessel vessel Transport Receptor protein protein TARGET CELL TARGET OR Receptor CELL protein Cytoplasmic Gene response regulation Cytoplasmic response Gene regulation NUCLEUS NUCLEUS 21  Binding of a hormone to its receptor initiates a signal transduction pathway leading to responses in the cytoskeleton, enzyme activation, or a change in gene expression 22  The hormone epinephrine has multiple effects in mediating the body’s response to short-term stress  Epinephrine binds to receptors on the plasma membrane of liver cells  This triggers the release of messenger molecules that activate enzymes and result in the release of glucose into the bloodstream 23  EXTRACELLULAR FLUID Hormone (epinephrine) Adenylyl G protein cyclase GTP G protein-coupled ATP receptor cAMP Second messenger Inhibition of glycogen synthesis Protein kinase A Promotion of glycogen breakdown CYTOPLASM 24  The response to a lipid-soluble hormone is usually a change in gene expression  When a steroid hormone binds to its cytosolic receptor, a hormone-receptor complex forms that moves into the nucleus  There, the receptor part of the complex acts as a transcriptional regulator of specific target genes 26  Hormone EXTRACELLULAR (estradiol) FLUID Estradiol receptor Plasma membrane Hormone-receptor complex NUCLEUS CYTOPLASM DNA Vitellogenin mRNA for vitellogenin 27  The same hormone may have different effects on target cells that have ◦ Different receptors for the hormone ◦ Different signal transduction pathways  For example, the hormone epinephrine can increase blood flow to major skeletal muscles, but decrease blood flow to the digestive tract 29  Same receptors but different intracellular proteins (not shown) Different receptors (a) Liver cell (b) Smooth muscle cell (c) Smooth muscle cell in wall of blood in wall of blood vessel that supplies vessel that supplies skeletal muscle intestines Epinephrine Epinephrine Epinephrine β receptor β receptor α receptor Glycogen deposits Glucose Glycogen breaks down Cell relaxes. Cell contracts. and glucose is released from cell. Blood vessel dilates, Blood vessel Blood glucose level increasing flow to constricts, decreasing increases. skeletal muscle. flow to intestines. 30  Endocrine cells are often grouped in ductless organs called endocrine glands, such as the thyroid and parathyroid glands, testes, and ovaries  In contrast, exocrine glands, such as salivary glands have ducts to carry secreted substances onto body surfaces or into body cavities 31 32 33  Hormones are assembled into regulatory pathways 34  Hormones are released from an endocrine cell, travel through the bloodstream, and interact with specific receptors within a target cell to cause a physiological response 35  For example, the release of acidic contents of the stomach into the duodenum stimulates endocrine cells there to secrete secretin  This causes target cells in the pancreas, a gland behind the stomach, to raise the pH in the duodenum 36  Simple endocrine pathway Example: secretin signaling STIMULUS Low pH in duodenum Endocrine S cells of duodenum cell Negative feedback Hormone Secretin ( ) Target Pancreatic cells cells RESPONSE Bicarbonate release 37  In a simple neuroendocrine pathway, the stimulus is received by a sensory neuron, which stimulates a neurosecretory cell  The neurosecretory cell secretes a neurohormone, which enters the bloodstream and travels to target cells 39  For example the suckling of an infant stimulates signals in the nervous systems that reach the hypothalamus  Nerve impulses from the hypothalamus trigger the release of oxytocin, from the posterior pituitary  This causes the mammary glands to secrete milk 40 Simple neuroendocrine pathway Example: oxytocin signaling STIMULUS Suckling Sensory neuron Hypothalamus/ posterior pituitary Positive feedback Neurosecretory cell Oxytocin (▪) Neurohormone Target Smooth muscle in cells mammary glands RESPONSE Milk release 41  A negative feedback loop inhibits a response by reducing the initial stimulus, thus preventing excessive pathway activity  Positive feedback reinforces a stimulus to produce an even greater response  For example, in mammals oxytocin causes the release of milk, causing greater suckling by offspring, which stimulates the release of more oxytocin 42  In a wide range of animals, endocrine organs in the brain integrate function of the endocrine system with that of the nervous system 43  The endocrine pathway that controls the molting of larva originates in the larval brain where neurosecretory cells produce PTTH (Prothoracicotropic hormone)  In the prothoracic gland, PTTH directs the release of ecdysteroid 44  Bursts of ecdysteroid trigger each successive molt as well as metamorphosis  Metamorphosis is not triggered until the level of another hormone, JH (juvenile hormone), drops 45  Brain Neurosecretory cells Corpora cardiaca Corpora allata Prothoracic PTTH gland High JH Low Ecdysteroid JH EARLY LARVA PUPA ADULT LATER LARVA 46  The hypothalamus receives information from the nervous system and initiates responses through the endocrine system  Attached to the hypothalamus is the pituitary gland, composed of the posterior pituitary and anterior pituitary 47  The posterior pituitary stores and secretes hormones that are made in the hypothalamus  The anterior pituitary makes and releases hormones under regulation of the hypothalamus 48  Cerebrum Pineal gland Thalamus Hypothalamus Cerebellum Pituitary Spinal cord gland Hypothalamus Posterior pituitary Anterior pituitary 49  Neurosecretory cells of the hypothalamus synthesize the two posterior pituitary hormones ◦ Antidiuretic hormone (ADH) regulates physiology and behavior ◦ Oxytocin regulates milk secretion by the mammary glands 50  Hypothalamus Neurosecretory cells of the hypothalamus Neurohormone Axons Posterior pituitary Anterior pituitary HORMONE ADH Oxytocin TARGET Kidney tubules Mammary glands, uterine muscles 51  Hormone production in the anterior pituitary is controlled by releasing hormones and inhibiting hormones secreted by the hypothalamus  For example, prolactin-releasing hormone from the hypothalamus stimulates the anterior pituitary to secrete prolactin (PRL), which has a role in milk production 52  Neurosecretory cells of the hypothalamus Hypothalamic Portal vessels releasing and inhibiting hormones HORMONE Endocrine cells of Posterior the anterior pituitary pituitary Anterior pituitary TARGET hormones FSH and LH TSH ACTH Prolactin MSH GH Testes or Thyroid Adrenal Mammary Melanocytes Liver, bones, ovaries cortex glands other tissues Tropic effects only Nontropic effects only Tropic and nontropic effects 53  Sets of hormones from the hypothalamus, anterior pituitary, and a target endocrine gland are often organized into a hormone cascade pathway  The anterior pituitary hormones in these pathways are called tropic hormones 54  In humans and other mammals, thyroid hormone regulates many functions  If thyroid hormone level drops in the blood, the hypothalamus secretes thyrotropin- releasing hormone (TRH) causing the anterior pituitary to secrete thyroid-stimulating hormone (TSH)  TSH stimulates release of thyroid hormone by the thyroid gland 55  STIMULUS 1 Thyroid hormone levels drop. Sensory neuron 2 The hypothalamus secretes Hypothalamus TRH into the blood. Portal vessels carry TRH to anterior Negative feedback Neuro- pituitary. secretory cell TRH 3 TRH causes anterior pituitary to secrete TSH▲. Anterior TSH pituitary Circulation throughout body via blood Thyroid gland 4 TSH stimulates endocrine cells in thyroid gland to secrete T3 and T4. Thyroid hormone 6 Thyroid hormone blocks TRH release and TSH release Circulation preventing overproduction throughout of thyroid hormone. body via blood 5 Thyroid hormone levels RESPONSE return to normal range. 56  Hypothyroidism, too little thyroid function, can produce symptoms such as ◦ Weight gain, lethargy, cold intolerance  Hyperthyroidism, excessive production of thyroid hormone, can lead to ◦ High temperature, sweating, weight loss, irritability, and high blood pressure  Malnutrition can alter thyroid function 57  Graves’ disease, a form of hyperthyroidism caused by autoimmunity, is typified by protruding eyes  Thyroid hormone refers to a pair of hormones ◦ Triiodothyronin (T3), with three iodine atoms ◦ Thyroxine (T4), with four iodine atoms  Insufficient dietary iodine leads to an enlarged thyroid gland, called a goiter 58 Low level of High level of iodine uptake iodine uptake 59  Growth hormone (GH) is secreted by the anterior pituitary gland and has tropic and nontropic effects  It promotes growth directly and has diverse metabolic effects  It stimulates production of growth factors  An excess of GH can cause gigantism, while a lack of GH can cause dwarfism 60 61  Endocrine signaling regulates homeostasis, development, and behavior 62  Two antagonistic hormones regulate the homeostasis of calcium (Ca2+) in the blood of mammals ◦ Parathyroid hormone (PTH) is released by the parathyroid glands ◦ Calcitonin is released by the thyroid gland 63  PTH increases the level of blood Ca2+ ◦ It releases Ca2+ from bone and stimulates reabsorption of Ca2+ in the kidneys ◦ It also has an indirect effect, stimulating the kidneys to activate vitamin D, which promotes intestinal uptake of Ca2+ from food  Calcitonin decreases the level of blood Ca2+ ◦ It stimulates Ca2+ deposition in bones and secretion by kidneys 64  NORMAL BLOOD Ca2+ LEVEL (about 10 mg/100 mL) Blood Ca2+ level rises. Blood Ca2+ level falls. Active vitamin D increases Ca2+. PTH stimulates Ca2+ uptake and promotes activation of vitamin D. Parathyroid glands PTH release PTH. PTH stimulates Ca2+ release. 65  The adrenal glands are associated with the kidneys  Each adrenal gland actually consists of two glands: the adrenal medulla (inner portion) and adrenal cortex (outer portion) 66  The adrenal medulla secretes epinephrine (adrenaline) and norepinephrine (noradrenaline)  These hormones are members of a class of compounds called catecholamines  They are secreted in response to stress- activated impulses from the nervous system  They mediate various fight-or-flight responses 67  Epinephrine and norepinephrine ◦ Trigger the release of glucose and fatty acids into the blood ◦ Increase oxygen delivery to body cells ◦ Direct blood toward heart, brain, and skeletal muscles and away from skin, digestive system, and kidneys 68  The adrenal cortex reacts to endocrine signals  It releases a family of steroids called corticosteroids in response to stress  These hormones are triggered by a hormone cascade pathway via the hypothalamus and anterior pituitary  Humans produce two types of corticosteroids: glucocorticoids and mineralocorticoids 69  Glucocorticoids, such as cortisol, influence glucose metabolism and the immune system  Mineralocorticoids, such as aldosterone, affect salt and water balance 70 (a) Short-term stress response and the adrenal medulla (b) Long-term stress response and the adrenal cortex Stress Hypothalamus Nerve Spinal cord impulses Releasing (cross section) hormone Neuron Anterior pituitary Blood vessel Adrenal Neuron ACTH medulla Adrenal Adrenal gland cortex Kidney Effects of epinephrine and norepinephrine: Effects of Effects of mineralocorticoids: glucocorticoids: Glycogen broken down to glucose; increased blood glucose Retention of sodium Proteins and fats broken Increased blood pressure ions and water by down and converted to Increased breathing rate kidneys glucose, leading to Increased metabolic rate increased blood glucose Change in blood flow patterns, leading to Increased blood Partial suppression of increased alertness and decreased digestive, volume and blood immune system excretory, and reproductive system activity pressure 71  The gonads, testes and ovaries, produce most of the sex hormones: androgens, estrogens, and progestins  All three sex hormones are found in both males and females, but in significantly different proportions 72  The testes primarily synthesize androgens, mainly testosterone, which stimulate development and maintenance of the male reproductive system  Testosterone causes an increase in muscle and bone mass and is often taken as a supplement to cause muscle growth, which carries health risks 73 Bipotential gonad Male duct Female duct (Wolffian) (Müllerian) Embryo (XY or XX) Testosterone Absence of male hormones AMH Testis Ovary Uterus Vas Oviduct deferens Bladder Bladder Seminal vesicle Male (XY) fetus Female (XX) fetus 74  Estrogens, most importantly estradiol, are responsible for maintenance of the female reproductive system and the development of female secondary sex characteristics  In mammals, progestins, which include progesterone, are primarily involved in preparing and maintaining the uterus  Synthesis of the sex hormones is controlled by follicle-stimulating hormone and luteinizing hormone from the anterior pituitary 75  Between 1938 and 1971 some pregnant women at risk for complications were prescribed a synthetic estrogen called diethylstilbestrol (DES)  Daughters of women treated with DES are at higher risk for reproductive abnormalities, including miscarriage, structural changes, and cervical and vaginal cancers 76  DES is an endocrine disruptor, a molecule that interrupts the normal function of a hormone pathway, in this case, that of estrogen 77  The pineal gland, located in the brain, secretes melatonin  Primary functions of melatonin appear to relate to biological rhythms associated with reproduction and with daily activity levels  The release of melatonin by the pineal gland is controlled by a group of neurons in the hypothalamus called the suprachiasmatic nucleus (SCN) 78  Over the course of evolution the functions of particular hormones have diverged  For example, thyroid hormone plays a role in metabolism across many lineages, but in frogs has taken on a unique function: stimulating the resorption of the tadpole tail during metamorphosis  Prolactin also has a broad range of activities in vertebrates 79  Adult frog Tadpole 80  Melanocyte-stimulating hormone (MSH) regulates skin color in amphibians, fish, and reptiles by controlling pigment distribution in melanocytes  In mammals, MSH plays roles in hunger and metabolism in addition to coloration 81