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Transcript
Chapter 9: Endocrine System The #1 Function of the Endocrine System is: - The communication and control of the body but providing a slower & longer lasting signal using hormones (chemicals secreted into & circulated by the blood) Endocrine Vs Nervous Hormones travel to every point in the body – neurotransmitters travel short distances over synapse Endocrine can regulate most body cells – nervous system can only control organs innervated w/ efferent fibers Hormones appear slowly & last longer – neurotransmitters are rapid & short-lived Organs of the Endocrine System are all glands – but not all glands are in the Endocrine System (ex. lacrimal glands, sebaceous glands, sudoriferous glands) - endocrine glands can be made of glandular epithelium or neurosecretory tissue (modified neurons) Review! - Endocrine gland – ductless gland that secretes in - Exocrine gland – secretes out to the surface – ex.) sweat gland Some Hormone Classifications: - tropic hormones – those that target other endocrine glands & stimulate their growth & secretion - sex hormones – those that target reproductive tissues - anabolic hormones – those that stimulate anabolism in their target cells 2 Chemical Structures of Hormones 1.) Nonsteroid Hormones – a.) Proteins – consists of: insulin growth hormone calcitonin prolactin adrenocorticotropic hormone parathyroid hormone glucagon b.) c.) d.) Glycoproteins – consists of: follicle-stimulating hormone luteinizing hormone, thyroidstimulating hormone chorionic gonadotropin Peptides – consists of : antidiuretic hormone oxytocin melanocyte-stimulating hormone somatostatin thyrotropin-releasing hormone atrial natriuretic hormone gonadotropin-releasing hormone Amino acid derivatives – consists of: 1.) Amines – norepinephrine, epinephrine, melatonin 2.) Iodinated amino acids – thyroxine, triiodothyronine 2.) Steroid Hormones – made from cholesterol (4 interconnected rings) - they are lipid soluble & can pass directly through the cell membrane of a target organs cell - ex.) cortisol, aldosterone, estrogen, progesterone, testosterone How Do Hormones Work? - hormones bind to specific receptors on or in a cell (target cell) - cells usually have many different receptors types so they can be acted upon by different hormones - hormones are the main regulators of metabolism, growth & development, reproduction, etc. - they also maintain homeostasis - if hormones work together – synergism if small amount of 1 hormone allows a 2nd to have full effect – permissiveness when 1 hormone produces the opposite effect of another - antagonism Steroid Hormone Action – Mobile-Receptor Hypothesis - lipid so they are not very soluble in blood plasma – attach to soluble plasma proteins - can pass into cells so most have receptors on the cell’s inside - once inside they combine with specific receptors & enter the nucleus to influence cell activity by acting on specific genes Nonsteroid Hormone Action – 2nd Messenger Hypothesis or Fixed-Membrane-Receptor Hypothesis - in this hypothesis: a.) protein hormones serve as 1st messengers providing communication between endocrine glands & target organs b.) another molecule acts as a 2nd messenger providing communication within a hormone’s target cell Regulation of Hormone Secretion - regulation of the secretion of hormones depends on negative feedback – secretion continues until a point is reached & the system is shut off - positive feedback is a mechanism that amplifies the change from the hormone instead of reversing the change - positive feedback is most of the time very harmful leading to death, however, it can be helpful especially in labor contractions The Major Endocrine Organs: 1.) Pituitary Gland – about the size of a grape & lies deep in the cranial cavity surrounded by the sphenoid bone – is really 2 endocrine glands A.) anterior pituitary gland – or adenohypophysis – has the structure of endocrine glands B.) posterior pituitary gland – or neurohypophysis – has the structure of nervous tissue Hormones of the Anterior Pituitary Gland 1.) thyroid stimulating hormone (TSH) 2.) adrenocorticotrophic hormone – (ACTH) 3.) follicle stimulating hormone – (FSH) 4.) lutenizing hormones – (LH) – in males –also referred to as interstitial cell-stimulating hormone (ICSH) - hyposecretion of FSH & LH leads to sterility in both males & females 5.) melanocyte stimulating hormone – (MSH) 6.) growth hormone – (GH) - increase blood glucose levels – this increase is called hyperglycemia - hypersecretion during childhood results in gigantism (body proportions are fairly normal), if during adulthood results in acromegaly (change in facial features, hands & feet) – most hypersecretion cases are due to pituitary gland tumors - hyposecretion during childhood results in pituitary dwarfism (body proportions are fairly normal just miniaturized) 7.) prolactin (lactogenic) hormone – function in males is not known Hormones of the Posterior Pituitary Gland 1.) antidiuretic hormone – (ADH) 2.) oxytocin ***Amazing fact of the Posterior Pituitary Gland (PPG) is that the 2 hormones released are produced in the hypothalamus – so technically the PPG is not an endocrine gland because it does not produce the hormones - release of hormones is controlled by nervous stimulation Major Endocrine Organs cont.. 2.) Pineal Gland – small, cone-shaped gland found in the roof of the 3rd ventricle of the brain – secretes a number of hormones in small quantities – only one to show a significant amount is Melatonin – its levels rise & fall over the course of the day – believed to establish our internal clock & inhibit ovarian activity during childhood - abnormal secretion causes winter depression – exposure to sunlight is low & melatonin levels are high 3.) Thyroid Gland – lies in the neck just below the larynx (voice box) – consists of 2 lobes – secretes: A.) Thyroid Hormone – is actually 2 active hormones: 1.) Thyroxine – (T4) – contains 4 iodine atoms – more important & more abundant 2.) Triiodothyronine – (T3) – contains 3 iodine atoms - Problems that can occur: a.) Simple Goiter – painless enlargement of the thyroid gland as a result of low intake of iodine causing a hyposecretion of thyroxine b.) Cretinism – hyposecretion of thyroxine in the formative years – results in dwarfism where the adult body parts remain childlike – if untreated will result in mental retardation c.) Myxedema – hyposecretion of thyroxine in the adult years – have mental & physical sluggishness, puffiness in the face, fatigue, poor muscle tone, low body temperature, obesity & dry skin d.) Hyperthyroidism – generally results from a tumor in the thyroid gland – there is an oversecretion of thyroid hormone that will increase the metabolic rate so food is burned at an excessive rate – symptoms include a loss of weight, increased appetite, nervous irritability, protruding eyes (condition called exophthalmos) – one form of hyperthyroidism is Graves’ Disease e.) Hashimoto disease – autoimmune damage to thyroid causing hyperthyroidism B.) Calcitonin –or thyrocalcitonin – acts as an antagonists to the parathyroid gland to maintain homeostasis - few problems are known but calcitonin production does cease in the elderly 4.) Parathyroid Gland – small gland, usually 4 of them found on the back of the thyroid gland - secrete parathyroid gland hormone (or parahormone) – (PTH) - problems that occur result in a life & death situation – too little causes uncontrollable spasms that lead to death – too much cause fragile bones 5.) Hypothalamus - adjusts the secretions of the anterior pit. Gland through (-) feedback – secretes: A.) Growth hormone-releasing hormone - GRH B.) Growth hormone-inhibiting hormone – GIH – somatostatin C.) Corticotropin- releasing hormone – CRH D.) Thyrotopin- releasing hormone – TRH E.) Gonadotropin- releasing hormone – GNRH F.) Prolactin- releasing hormone – PRH G.) Prolactin-inhibiting hormone – PIH 6.) Adrenal Gland – curves over the top of each kidney – is 2 organs that function as one – they are: A.) Adrenal Cortex – outer part of gland – its secreted hormones are called corticoids & the adrenal cortex has 3 layers: 1.) Zona glomerulosa – outer zone - secretes mineralocorticoids (MCs) - the main hormone of this group is aldosterone B.) 2.) Zona fasciculata – middle zone – secretes glucocorticoids (GCs) - main hormone of this group is cortisol or cortisone 3.) Zona reticularis – inner zone – secretes sex hormones – in males androgens are produced that are weak because of the testosterone produced by the testes - in females some estrogens are produced & this helps stimulate the sex drive Adrenal Medulla – inner part of the adrenal glands - secretes epinephrine (adrenaline) & norepinephrine (noradrenaline) – they belong to a group called catecholamines because the nervous system also releases norepinephrines as a neurotransmitter - these are fast acting stress responses - these hormones are essential for maintaining life - in a threatening situation – the nervous system brings about the “fight or flight” response – the adrenal medulla is stimulated & adrenaline is secreted – the heart will beat faster, increase in blood pressure, more blood to muscle, more glucose from the GCs for more energy - prolonged stress causes the GCs to “burn out” - death Problems with the Adrenal Glands: usually caused by tumors 1.) Addison’s Disease – hyposecretion of the zona reticularis – symptoms are: bronze tone of the skin, electrolyte & H2O balance is off, muscle become weak, hypoglycemia, burnout, susceptible to infections 2.) Aldosteronism – hypersecretion of aldosterone – Na+ retention & K+ loss 3.) Hypersecretion of sex hormones – leads to male secondary sex characteristics – apparent in females, hidden in males 4.) Cushing’s Syndrome: hypersecretion of the zona fasciculata – symptoms are: “moon face”, “buffalo hump” of fat on upper back, high blood pressure, hyperglycemia, diabetes, weak bones, immune system suppression Major Endocrine Organs cont… 7.) Pancreatic Islets – located within the pancreas (found close to the stomach in the abdominal cavity) – also known as the islets of Langerhans – the hormone-producing tissue is scattered among the pancreatic cells they secrete pancreatic digestive juices (exocrine system) - produces 2 important hormones: a.) Glucagon – secreted by the alpha cells of the islets – it is stimulated by low blood levels of glucose – will target the liver to breakdown stored glycogen to glucose (glycogenesis) which increases blood glucose concentration – no known disorders from hypo- or hypersecretion b.) Insulin – secreted by the beta cells if the islets – acts on almost all body cells & helps the transport of glucose across their cell membranes – is stimulated by high blood levels of glucose - is the only hormone that decreases blood glucose levels - disorders: 1.) without it glucose could not be used by cells 2.) diabetes mellitus – too much glucose in the blood spills into the urine causing dehydration – weight loss, infections, excessive urination, excessive thirst, & hunger – without treatment leads to a coma & then death c.) d.) Somatostatin – produced by the delta cells of the islets Pancreatic polypeptide - produced by the pancreatic polypeptide cells or F cells – influences digestion 8.) Thymus – located in the upper thorax, posterior to the sternum – composed mostly of connective tissue & fat – large in infants & children, size decreases in adulthood – produces: a.) Thymosine b.) Thymopoietin ***Both play a role in the dvlpt & function of the body’s immune system 9.) Gonads – produce sex hormones that are identical to those produced by the adrenal cortex – difference is the source & amounts – don’t function until puberty - 2 types: a.) female gonads – ovaries – stimulated by the anterior pituitary gland - 2 groups of steroid hormones: 1.) Estrogens – mainly Estrone & Estradiol – produced by the ovarian (Graafian) follicles 2.) Progesterone – produced by the corpus luteum (which also secretes a small amount of estrogen) - disorders – from hyposecretion – infertility - decrease in later years - menopause b.) male gonads – testes – also stimulated by the APG – hormone is Androgens – mainly Testosterone – produced by the interstitial cells of testes - disorders – from hyposecretion – sterility 10.) Placenta – temporary Endocrine Gland – produces hormones that maintain pregnancy – secretes: a.) Estrogen ovaries become inactive during b.) Progesterone pregnancy c.) Human Chorionic Gonadotropins (hCG) – what a pregnancy test picks up d.) Human Placenta Lactogen – prepares breast for lactation e.) Relaxin – relaxes pelvic ligaments for birth 11.) Stomach & Intestinal Mucosa – produces: a.) Gastrin b.) Secretin c.) Cholecystokinin d.) Ghrelin 12.) Kidneys – erythropoietin, active vitamin D3 13.) Heart – atrial wall secretes atrial natriuretic hormone (ANH) that stimulates Na+ loss from kidneys