L9 Endocrine System PDF

The Endocrine system BIOL2012SEF Dr Emily Wong 1 Introduction The endocrine system is a system of glands, each of which secretes a type of hormone directly into the bloodstream to regulate the body Hormones have definite effects on skin and health Their functions are directly related to many body co...

The Endocrine system BIOL2012SEF Dr Emily Wong 1 Introduction The endocrine system is a system of glands, each of which secretes a type of hormone directly into the bloodstream to regulate the body Hormones have definite effects on skin and health Their functions are directly related to many body conditions – Skin problems, e.g. acne – Health conditions, e.g. menopause Hormones are basically chemical messengers that are secreted by glands within our body 2 Nervous system & Endocrine system They work together to coordinate our body functions. Nervous system – – – – – Made of neurons Instant response Effects are rather short-lived Stimulated by nerve impulse Conduct along the axons of neurons – At synapse, nerve impulse triggers the release of mediator, neurotransmitter Endocrine system – – – – Made of secretory cells Slower response Effects are rather long lasting Release of mediator, hormone – Secreted into interstitial fluid – Transport throughout the body by blood 3 Control by Neurons 4 Glands Exocrine glands – Have ducts through which chemicals travel – E.g. oil glands and sweat glands Endocrine glands – Are ductless, and they secrete hormones directly into bloodstream – E.g. the release of epinephrine by adrenal gland 5 Types of Hormones Steroid hormones and nonsteroid hormones Steroid hormones – Lipid loving (hydrophobic) – Not highly soluble in blood – Have to bind with carrier protein to form lipoprotein for transportation in blood – e.g. Estrogen and progesterone produced by ovary Testosterone released by testes 6 Steroid Hormones 7 Types of Hormones Nonsteroid hormones – Water loving (hydrophilic) – Dissolved in blood stream and easily be transported – 1. Amine hormones, e.g. triiodothyronine (T3) and thyroxine (T4) released by thyroid gland Epinephrine and norepinephrine secreted by adrenal medulla Dopamine produced by hypothalamus – 2. Peptide and Protein hormones, e.g. Insulin released by pancreas Growth hormone secreted by anterior pituitary gland 8 Amine Hormones 9 Peptide and Protein Hormones 10 How does it works Each cell contains receptor proteins. The hormone would specifically binds to the receptor. Just like the “keys” and “locks” Since the cell membrane is hydrophobic, receptors for steroid homones are located inside the cell while receptors for nonsteroid homones are located on the cell surface 11 Hormonal signaling involves the following: 1. 2. 3. 4. Biosynthesis of a particular hormone in a particular tissue Storage and secretion of the hormone Transport of the hormone to the target cell(s) Recognition of the hormone by an associated cell membrane or intracellular receptor protein 5. Relay and amplification of the received hormonal signal via a signal transduction process: This then leads to a cellular response. The reaction of the target cells may then be recognized by the original hormone-producing cells, leading to a down-regulation in hormone production. This is an example of a homeostatic negative feedback loop. 6. Degradation of the hormone. 12 Signal transduction is the process by which an extracellular signaling molecule activates a membrane receptor, that in turn alters intracellular molecules creating a response. There are two stages in this process: – 1) a signaling molecule activates a certain receptor on the cell membrane – 2) causing a second messenger to continue the signal into the cell and elicit a physiological response. the signal can be amplified [Optional: https://www.youtube.com/watch?v=ic8Z4ajCzio ] 13 14 The endocrine glands 15 16 17 Hypothalamus (下丘腦) The most important function of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland Is the “interpreter” between the brain and the pituitary gland Able to detect needs of various parts of the body by chemically monitoring the blood It synthesizes and secretes certain neurohormones, (hypothalamic-releasing hormones) and these in turn stimulate or inhibit the secretion of pituitary hormones 18 Pituitary gland (腦下垂體) Pituitary gland (hypophysis) size of a pea and weighing 0.5 g Is found in the center of the head Serves as the “brain” of the endocrine system functionally connected to the hypothalamus 19 Anterior & Posterior pituitary pituitary gland consists of two components: the anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis) Secretes many hormones called “trophic hormones” – Which are chemicals “signal hormone” that cause other glands to make other hormones – E.g. Follicle-stimulating hormone (FSH), causes the production of sex hormones in the glands present in the sex organ 20 Others Growth hormone (GH) – stimulates growth, cell reproduction and regeneration Melanocyte-stimulating hormones (MSH or intermedins) – produced by cells in the intermediate lobe of the pituitary gland – stimulate the production and release of melanin by melanocytes in skin and hair – increases in humans during pregnancy. This, along with increased estrogens, causes increased pigmentation in pregnant women 21 The Hypothalamus and Pituitary Gland 22 Pineal gland Located in the brain Very small, funnel shaped Function: not well understood Produce melatonin, a hormone that affects the modulation of wake/sleep patterns 23 Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in presentation mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Slide Show mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Control by Neurons 25 Control Systems Involving the Hypothalamus and Pituitary 26 Control by Other Hormones A hormone that controls the secretion of another hormone is called a tropic hormone. 27 Types of Endocrine Disorders Hyposecretion: the secretion of too little hormone Hypersecretion: the secretion of too much hormone Hyporesponsiveness and Hyperresponsiveness occurs when the target cells do not respond properly to a hormone. 28 Thyroid gland is found in the neck Regulates both cellular and body metabolism and produces hormones that stimulate growth Thyroxine (T4) and Triiodothyronine (T3): growth and development, rate of metabolism Calcitonin: regulation of normal calcium homeostasis 29 Hyperthyroidism & hypothyroidism Hyperthyroidism: – Thyroid gland secretes too much thyroid hormone – Physical symptoms – heart palpitations, weight loss, and fatigue – Skin symptoms – thinning of skin, hair loss and rapidly growing nails Hypothyroidism: – Thyroid gland secretes not enough thyroid hormone – Physical symptoms – weight gain, poor balance and hearing problems – Skin symptoms – puffy eyelids, facial swelling, dry and dehydrated skin 30 Control of Thyroid Function 31 Goiter is a swelling in the thyroid gland over 90% cases of goiter are caused by iodine deficiency Thyroid gland uses a lot of iodine in the production of hormones This is why it is important to have some iodine in the diet 32 Parathyroid gland are small endocrine glands in the neck that produce parathyroid hormone (PH) usually located on the rear surface of the thyroid gland control the amount of calcium in the blood and within the bones 33 When blood calcium levels drop below a certain point calcium-sensing receptors in the parathyroid gland are activated Produce and release Parathyroid hormone (PTH) into the blood (decrease in calcitonin production) stimulating osteoclasts to break down bone and release calcium increases gastrointestinal calcium absorption blood calcium levels increases *Parathyroid hormone has effects antagonistic to those of calcitonin. 34 Adrenal glands Also named suprarenal glands Located above the kidneys has two distinct structures, the adrenal cortex and the medulla weight of the adrenal glands in an adult human ranges from 7 to 10 grams 35 Adrenal Cortex – Outer core – Synthesis of corticosteroid hormones – including cortisol, corticosterone, androgens Adrenal Medulla – Inner part – Produces adrenaline (epinephrine) and noradrenaline (norepinephrine). – Epinephrine secreted when body is under stress 36 The Endocrine Response to Stress The endocrine system responds to stresses on the body such as trauma, infection, pain, sleep deprivation, fright, and other emotional stresses by increasing the release of cortisol from the adrenal cortex and epinephrine from the adrenal medulla. 37 Physiological Functions of Cortisol Permits action of epinephrine and norepinephrine on muscles and blood vessels Maintains cellular concentrations of metabolic enzymes required to produce glucose between meals As a glucocorticoid, it maintains plasma glucose concentration Decreases events associated with the inflammatory response such as capillary permeability and production of prostaglandins Important for fetal development 38 Effects of Cortisol Release During Stress 39 Other Hormones Released During Stress Aldosterone, vasopressin, growth hormone, glucagon, beta-endorphin (endogenous morphine) Fight-or-flight response: epinephrine and norepinephrine 40 Adrenal gland disorder and skin Produce too much adrenal hormones (hydrocortisone) – Cushing’s syndrome Thinning of skin, bruises Produce not enough adrenal hormones Severe hyperpigmentation, dark freckles 41 Pancreas Digestive organ Endocrine gland producing several important hormones, including insulin & glucagon Insulin: – Secreted by beta cells – causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen Glucagon: – Secreted by alpha cells – causes the liver to convert stored glycogen into glucose, which is released into the bloodstream 42 Blood glucose levels Cells take up glucose molecules Stored in liver/muscle in “glycogen” Blood glucose levels are maintained by insulin and glucagon Produced by Islets of Langerhans Alpha cells  produce glucagon  more glycogen break down into glucose raise blood glucose Beta cells  produced insulin  more glucose build into glycogen lower blood glucose 43 Thymus gland Located in the chest Secretes thymosin – promote production and maturation of white blood cells 44