The Endocrine System & Homeostasis PDF

1ST YEAR FUNDAMENTALS OF BIOMEDICAL SCIENCE The Endocrine System with Dr. Nikki Jordan-Mahy  Lecture Plan The Endocrine System Hormones & receptors Where are the Endocrine Glands? Hormonal Secretion: Systemic, Paracrine or Autocrine...

1ST YEAR FUNDAMENTALS OF BIOMEDICAL SCIENCE The Endocrine System with Dr. Nikki Jordan-Mahy  Lecture Plan The Endocrine System Hormones & receptors Where are the Endocrine Glands? Hormonal Secretion: Systemic, Paracrine or Autocrine Types of hormones Lipid Soluble Hormones Water Soluble Hormones The Mechanism of Action of Lipid & Water Soluble Hormones Homeostasis Negative Feedback Positive Feedback Aims & Objectives:  Gain a knowledge of the endocrine system, hormones & their action  Understand the mechanisms which are used to control the secretion of hormones Help  Dr. Nikki Jordan-Mahy - [email protected]  Introduction to the Human Body: Essentials of Anatomy & Physiology - By Tortora & Grabowski  Anatomy and Physiology - By Martini  Hormones & Receptors Hormones - regulatory chemicals Secreted into blood & passed to a specific target organ where they cause a physiological change Hormones are produced by endocrine glands Different from exocrine glands Exocrine Glands include sweat glands, salivary glands & mucus glands & their secretions are passed through a channels or ducts Endocrine Glands different as they secrete directly into the blood stream & are called ductless glands e.g pituitary, thyroid, parathyroid, adrenal, pineal glands Other organs secrete hormones as a 2nd function - hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart & placenta Where are the Endocrine Glands? Within the Cranium These endocrine glands are located at the base of the brain - the brain can stimulate or inhibit hormones release They are: 1. Hypothalamus 2. Pituitary & 3. Pineal glands The CNS & endocrine system work closely together each capable of modulating the activity other each other e.g. Lions & PMT Where are the Endocrine Glands? Within the Abdomen These are: 1. Thyroid gland & parathyroid gland – in the neck 2. Adrenal gland & Pancreas – in the abdomen 3. Gonads (ovaries & testis) in the pelvic cavity Other regions: Other organs produce hormones include: thymus, stomach, mucosal cells of the duodenum, placenta, heart, kidney & liver  Endocrinology The endocrine system & nervous system function closely & together regulate the body processes – they can stimulate or inhibit each other They maintain the steady state or Homeostasis of the body e.g. just like a central heating system The nervous system regulates the body with nervous impulses, which are fast & short lived While the endocrine system regulates with hormones which are slower but more prolonged effect Nerves Hormones  How Hormones Work Hormones are very powerful – a little goes a long way Most hormones affect a few cell types Cells will only respond to a hormone if they have the specific hormone receptors E.g. Thyroid-stimulating hormone (TSH) only binds to the TSH-receptor on the thyroid gland The number of receptors can vary – there may be down regulation of receptors when the hormone is present in abundance Similarly there may be an up-regualtion of receptor numbers if hormone production is reduced E.g. At birth ↑fetal cortisol ↑maternal oestrogen ↑ receptors for oxytocin on the uterus, now oxytocin can now trigger labour Hormones Hormonal Secretion: Systemic, Paracrine or Autocrine A systemic effect = circulating hormones A local effect can be Paracrine (beside) or Autocrine (self) The paracrine & autocrine hormones provoke a faster response & the circulating systemic hormones have a slower response FSH from the anterior pituitary to the ovaries & stimulates oocyte development Gastrin produced by gastric G- cells stimulate parietal cells to produce HCl Testosterone from the testis acts on the testis to increase spermatogenesis  Types of Hormone Hormones are specific organic substances that act like chemical messagers just like neurotransmitters There are 4 basic types: Steroids, Proteins, Amines (or Catecholamines), & Eicosanoids They are divided into water or lipid soluble hormones: Lipid - Soluble Hormones 1. Steroids - synthesized from cholesterol & all have 4 carbohydrate rings Each hormone has a unique functional group attached on a rings 20 steroid hormones e.g. cortisol, cortisone, oestrogen, progesterone, testosterone & aldosterone 22-9 Lipid Soluble 2. Thyroid Hormones (T3 & T4) - synthesized by the addition of iodide to 2 coupled molecules of tyrosine The tyrosine makes this hormone lipid soluble 3. Nitric oxide (NO) – synthesis is catalyzed by nitric oxide synthase Acts as a neurotransmitter (↓gut motility) & hormone (causes vasodilation) N=O Water - Soluble Hormones 1. Amines – Produced from amino acids, but has no peptides bonds Contains atoms of carbon, hydrogen & nitrogen & always has an amine group (-NH2) – e.g. Adrenaline & Nor-adrenaline Nor-adrenaline or Nor- epinephrine 2. Peptide & proteins - consist of chain of 3 to 200 amino acids bound together in chains. E.g. insulin, anti-diuretic hormones (ADH) & oxytocin There is a sub-group of protein hormone that have carbohydrate side chains = Glycoproteins E.g. Thyroid stimulating hormone (TSH) & parathyroid hormone (PTH) 3. Eicosanoids - derived from arachidonic acid (fatty acid) E.g. prostaglandins or leukotrienes Mechanism of Action Fat Soluble Hormone: Use transport /carrier proteins  Are produced in the liver  Make their hormones temperately water soluble  Slows the rate of filtration in the kidney & loss in urine  Act are a hormone reserve (1) 0.1-10% of the fat soluble hormones are free in bl. & can diffuse across capillaries to target tissues (2) It can then diffuse across the phospholipids cell membrane & bind to a receptor – cytosol or nucleus (3) It can now cause a tissue specific effect e.g. (or ) gene expression → DNA transcription to mRNA translation → (4) protein synthesis → changes cell activity Mechanism of Action 1. Water Soluble Hormone: bind to the hormone receptor on the cell membrane (first messenger) & activate a G-protein 2. This causes release of a secondary messenger cyclic AMP (cAMP) ATP + adenylate cyclase = cAMP Adenylate cyclase is found in the cell membrane 3. & 4. cAMP activates 1 or several protein kinases which adds a phosphate group to enzymes, making them active (or not) 5. New proteins / enzymes are produced that charge the cell activity This process is stopped by phosphodiesterase, which makes the cAMP inactive Other secondary messengers: Ca 2+, cGMP (guanosine monophosphate), IP3 (inositol triphosphate) Homeostasis  Claude Bernard (1813-1878) suggested that the internal environment of the body must be kept constant in a 'steady state'  Walter B. Cannon (1971-1945) coined the term Homeostasis Homeo = sameness Stasis = state  Our cellular environment constantly changing  There is a limited range of internal conditions in which cells can operate  Homeostasis:- it required for the maintenance of relatively stable conditions in the body's internal environment  E.g. Blood glucose is kept at 90mg/100ml of bl  E.g. Body temperature is kept at 37˚C  Disruptions to Homeostasis External Environmental Changes – e.g. extreme temperature or changes in oxygen levels Internal Environmental Changes – e.g. ↓blood glucose due to lack of food Physiological Stress - Demands from physical activity e.g. loss of a metabolic stores Disruptions are: Mild and temporary & balance is quickly restored or Intense and prolonged (poisoning or severe infections) were there is no restoration of homeostasis & death occurs  Disruptions to Homeostasis Homeostasis – is maintained by feedback systems or loops: These feedback system have:  A Receptor to monitor & re-monitor changes  A Control center to determine if action is needed – is the change big enough  An Effector to make a change  There are 2 types of feedback systems:  Negative feedback - were there is a corrective  or  blood levels of a hormone or compound to maintain a constant level  Positive feedback - were a change in one hormone causes more hormone to be released, which continues until this cycle is interrupted Negative Feedback Regulation of Thyroxine & the Basal Metabolic Rate (BMR) BMR  Hypothalamus detects ↑ 1 Hypothalamus detects 5 ↓blood glucose blood glucose (hyperglycemia) (hypoglycemia) stimulates beta cells Negative Feedback stimulates alpha cells Regulation of Glucose Blood glucose need to be at 90mg/100ml GLUCAGON INSULIN plasma 2 6 Insulin acts on: Glucagon acts on ↑Glucose facilitated liver hepatocytes to: diffusion into cells Convert glycogen to glucose Speed conversion of (glycogenolysis) glucose into glycogen ↑ Glucose from lactic acid & (glycogenesis) certain amino acids ↑ Amino acids uptake & ↑ (gluconeogenesis) protein synthesis ↑ Synthesis of fatty acids (lipogenesis) ↓ Glycogenolysis 3 Glucose released ↓ Gluconeogenesis & ↑blood glucose to normal levels 7 Blood glucose level falls 4 If blood glucose If blood glucose continues 8 continues to rise there is an to fall, hypoglycemia inhibits glucagon inhibits release of insulin Negative Feedback of Stress Regulation of Stress ACTH = Cope with stress Adrenocorticotrophin hormone 1 High blood osmolarity 5 Low blood stimulates osmolarity hypothalamic osmoreceptors inhibits hypothalamic osmoreceptors & Negative Feedback of 2 Osmoreceptors Osmoreceptors ADH production Regulation Blood activate the neurosecretory cells that synthesize and Osmolarity & Pressure release ADH Hypothalamus 3 Nerve impulses liberate ADH from axon terminals in the posterior pituitary into the bloodstream ADH Target tissues 4 Kidneys retain vasoconstrict, ADH = Antidiuretic hormone water & ↓ urine ↓Sweating ↑blood pressure output 22-21 Positive Feedback of Parturition OT = Oxytocin  The Master Endocrine Gland - Pituitary The pituitary & hypothalamus are believed to be the master endocrine glands as their hormones control other endocrine glands Hypothalamus is a section of brain above the pituitary glands Hypothalamus receives input from the brain, blood system & major organs Hypothalamus controls the production of the 9 pituitary gland hormones using different releasing & inhibiting hormones e.g. GHRH & GHIH  The Pituitary Gland GH TSH FSH LH MSH PROLATIN OXYTOCIN ACTH ADH  Pituitary Hormones Hormones Target Tissue Role Levels Levels Growth hormones (GH) Body tissues ILGF production & growth & GHRH GHIH [glucose] Thyroid stimulating Thyroid gland Thyroxine & metabolism TRH Thyroxine & GHIH hormones (TSH) Anterior Pituitary Follicle stimulating Ovaries & testis Oestrogen & oocyte GnRH Inhibin, & oestrogen Hormones (FSH) development (♀) & sperm (♀) & testosterone (♂) production (♂) Luteining Hormone (LH) Ovaries & testis Ovulation &  oestrogen & GnRH Oestrogen & progesterone (♀) &  progesterone (♀) & testosterone (♂) testosterone (♂) Prolatin Breast Milk production PRH PIH (Dopamine) Adrenocorticotrophic Adrenal cortex Glucocorticoids (cope with CRH Glucocorticoids hormones (ACTH) stress) (corticotrophic releasing hormone) Posterior Pituitary Melanocyte stimulating Skin Pigment & brain activity Sun PIH (Dopamine) hormone (MSH) CRH Antidiuretic hormone Kidney, skin & ↓Water loss Hypothalamic Normal osmotic (ADH) arteries Osmotic pressure stimuli pressure Oxytocin Uterus Parturition & milk let down Nervous No stmuli impulses 22-25