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The Endocrine S ystem . Contributes to: control of growth, development, reproduction, behaviour , energy metabolism, and water balance By: Secreting hormones To control Organ and tissue functions. Endocrine System.
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The Endocrine System • Contributes to: • control of growth, development, reproduction, behaviour, energy metabolism, and water balance • By: • Secreting hormones • To control • Organ and tissue functions
Endocrine System • A system of ductless secretory organs (glands) located in various parts of the body • Include • Pineal • Anterior/posterior pituitary • Thyroid • Parathyroid • Thymus • Adrenal • Islets of Langerhans, • Ovaries • Testes • Main function • Secrete hormones directly into the blood or extracellular fluid
Hypothalamus • Is not a gland but a region of the brain • Part of the nervous system • Very important for function of endocrine system • Produce neurohormones that stimulate or inhibit production of other hormones in the pituitary gland
Hormones of The Hypothalamus • Thyrotropin-releasing hormone (TRH) • Stimulates release of thyroid-stimulating hormone (TSH) • Gonadotropin-releasing hormone (GnRH) • Stimulates release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) • Growth hormone-releasing hormone (GHRH) • Stimulates release of growth hormone (GH) • Corticotropin-releasing hormone (CRH) • Release of adrenocorticotropic hormone (ACTH) • Somatosin • Inhibits the release of growth hormone (GH) • Dopamine • Inhibits the release of thyroid-stimulating hormone (TSH)
Hormones: Maintaining Homeostasis • Chemical management system for the body • Chemicals produced by cells in one part of the body that regulate the processes of cells in another part of the body • Chemical messengers • act on cells from another part of the body • Local regulators (paracrine) • act on nearby cells • Self regulators (autocrine) • cells that produce chemicals to stimulate their own cellular processes
Tropic vs Non-Tropic Hormones • Tropic Hormones • Target endocrine glands • Nontropic Hormones • Target cells, tissues, and organs
Hormones • Produced and secreted by cells, tissues and organs that compose the endocrine system (glands) directly into the blood or extracellular fluid • Hormones are circulated throughout the body • Only target cells will respond to specific hormones • Hormones are broken down by enzymes in target cell, liver or kidneys where they are reused or excreted
Hormones • Secreted in an inactive form –prohormones • Prohormones are converted by target cells or by enzymes in the blood to an active form • Angiotensinogen → angiotensin
Hormones • Protein hormones • Consist of AA (3 to 200 in length) • Usually hydrophilic (water soluble) • Diffuse well through blood • Cannot pass through lipid bilayer • Steroid hormones • Derived from cholesterol • Not water soluble • Usually encased with protein (protein carrier) to travel through blood • Pass easily through lipid bilayer
Hormone Mechanisms • Water-Soluble • Cannot pass membrane • Bind to receptor molecules in the cell membrane • Signal is activated • Secondary messenger is activated (cAMP – cyclic adenosine monophosphate) • Change is caused inside cell • Acts in the cytosol or the nucleus • Regulate protein production, ion channels • Activation of protein kinases • Glucagon • Breakdown of glycogen into glucose
Hormone Mechanisms • Lipid-Soluble • Can pass membrane (lipid) • Bind to receptors inside a cell (cytosol or nucleus) • Turn on or off an action of a specific gene • Changes amount of protein that is synthesized by cell • Aldosterone • Increase sodium absorption → increases water retention → increase blood pressure
Major Features of Hormone Mechanisms • Only the cells that contain surface or internal receptors for the hormones respond to the hormones • Once bound to their receptors, hormones produce a response by turning cellular processes on or off. They do this by altering the proteins that are functioning in or produced by the cell • Hormones are effective in very small concentrations because of the amplification that occurs in both the surface and internal receptor mechanisms • The response to a hormone differs among target organs and among species
Hormones: Negative Feedback Mechanisms • Secretion of hormones are regulated by negative feedback mechanisms • Hormones inhibit other hormones • Multiple hormones can be secreted at a time
The Pituitary Gland • The Master Gland • Produces hormones that control most of the other glands in the endocrine system • Made up of anterior lobe and posterior lobe • Links endocrine system to nervous system via portal vein (hypothalamus) • Influenced by hypothalamus • Releasing hormones/inhibiting hormones
2. portal vein • 4. anterior pituitary gland • 5. hypophyseal vein • 6. posterior pituitary gland • 8. pituitary stalk • 9. capillary network • 10. neurons • 11. neurosecretory cells • 12. hypothalamus
Anterior Pituitary Gland • Major hormones secreted into the bloodstream • Tropic • Growth hormone (both) • thyroid-stimulating hormone • adrenocorticotropic hormone • follicle-stimulating hormone • luteinizing hormone • Nontropic • Prolactin • Melanocyte-stimulating hormone
Prolactin • Promote milk production in mammary glands • Suckling on nipple causes stimulus • Regulated by dopamine • Too much • Hyperprolactinaemia • Too little • Hypoprolactinaemia
Growth hormone • Cell division, protein synthesis, bone growth • Release of growth hormone stimulates release of IGF in liver (insulin growth factor) that stimulates these functions • Conversion of glycogen to glucose, fats to fatty acids – regulates levels in blood • Stimulates cells to take up FA, AA and limits muscle cells to take up glucose
Growth hormone • Underproduction • Dwarfism • Heart disease, increased fat • Cause • Genetic, benign tumour on pituitary gland • Overproduction • Acromegaly – body tissues get larger over time • Gigantism – excessive production of growth hormone • Cause • Benign tumour on pituitary gland
Thyroid-stimulating hormone • Controls production of the thyroid hormones • Underproduction • Hyperthyroidism • Cause • Thyroid is producing too much thyroid hormone • Overproduction • Hypothyroidism • Cause • Thyroid if producing too much thyroid hormone
Adrenocorticotropic hormone • Controls production of cortisol, adrenaline, noradrenaline • Underproduction • Cushing’s syndrome • Cause • Steroid medication, tumour of pituitary gland • Overproduction • Cushing’s disease • Addison’s disease (loss of function of cortex of adrenal gland) • Cause • Adenoma (non-cancerous tumour) in the pituitary gland • Autoimmunity
Follicle-stimulating hormone/luteinising hormone • Puberty development/function of the gonads (testes/ovaries) • Sex steroid production • Germ cell production (sperm/eggs) • Underproduction • Incomplete development at puberty • Infertility • Overproduction • Turner syndrome (female is missing entire/parts of x chromosome) • Kallmann’s syndrome (failure to start/complete puberty) • Cause • Testicular/ovarian failure,
Melanocyte-stimulating hormone • Causes darkening in humans by releasing melanin in the skin and hair and eyes • Specialized cells called melanocytes release melanin • Protects from UV rays • Overproduction • Increase production of melanin • Cause • Prolonged exposure to sun or skin tanning • Underproduction • Lack of skin pigmentation • Loss of natural protection from UV rays and sun • Cause • Damage to pituitary glands
Posterior pituitary gland • Stores and releases 2 major hormones into the bloodstream • Antidiuretic hormone (vasopressin) • oxytocin • These hormones are produced by the hypothalamus and stored here
Antidiuretic Hormone (vasopressin) • Causes distal convoluted tubule to become permeable to water • Helps maintain water balance • Overproduction • Kidneys retain too much water • Underproduction • Kidneys excrete too much water
Oxytocin • Contraction of the womb • Lactation • Overproduction • Not clear • Underproduction • Linked to autism
Thyroid gland • Located in the front of the throat and shaped like a bow tie • Secretes • Thyroxine (T₄) • calcitonin
Thyroxine (T₄) • Prohormone (inactive) • Active form is triiodothyronine • Contains 4 iodine atoms • Regulates body’s metabolic rate, heart and digestive function, muscle control, brain development, maintenance of bones • Overproduction • Thyrotoxicosis – too much thyroxine in bloodstream recognized by goitre • Causes • Hyperthyroidism • Graves Disease • Underproduction • Hypothyroidism • Causes • Autoimmune diseases, poor iodine diet
Calcitonin • Reduces levels of Calcium (Ca²⁺) in the blood stream • Opposes the action of parathyroid hormone • Overproduction • No apparent effect on body • Underproduction • No apparent effect on body
Parathyroid gland • 4 spherical glands (size of a pea) located on each side of the posterior surface of the thyroid gland • Secretes • Parathyroid hormone
Parathyroid hormone • Stimulates enzymes in kidneys to convert vitamin D into calcitrol increasing absorption of Ca²⁺ and phosphates from food • Underproduction • Muscle cramps • Osteoporosis • Overproduction • Kidney stones
Pineal gland • Located near the centre of the brain • Secretes • melatonin • Secretion of melatonin is controlled by circadian rhythm (biological processes that fluctuate on a 24 hour timetable) • Helps to synchronize biological clock (jet lag, sleep disorders) • Melatonin also produced in retina of the eye • Overproduction • Reduced core body temperature • Underproduction • No apparent effect on the body
Adrenal glands • Consist of two regions • Adrenal medulla • contains highly modified neuro-secretory neurons 2. Adrenal cortex • contains non-neural endocrine cells
Adrenal medulla • Secretes • Epinephrine, nor-epinephrine • These chemicals can act as hormones or neurotransmitters (transmit nerve signals to brain) • Part of the “fight or flight” response
Epinephrine • Released when body encounters stresses • Increase heart rate • glycogen and fat breakdown • Major blood vessels dilate (increase blood flow) • Blood vessels in skin constrict (chills and sweating) • Increase in blood pressure • Reduces water loss • Digestive system slows • Used to counter anaphylaxis
Adrenal cortex • Secretes • Aldosterone, cortisol
Glucocorticoids • Cortisol – Helps raise blood glucose levels using three mechanisms • Stimulate synthesis of glucosefrom fats and proteins • Reduce glucose uptake by the body cells except in the central nervous system • Promote breakdown of fats and proteins into fatty acids and amino acids as alternative fuels
Mineralocorticoids • Aldosterone • Increase amount of sodium /water reabsorption in bloodstream • Increase amount of potassium removal in urine • Increase blood pressure • Overproduction • High blood pressure, low potassium, alkaline blood • Causes • Adrenal tumour • Underproduction • Addison’s disease, low blood pressure
Regulating blood sugar • Occurs automatically in our body • Pancreas – contain both exocrine and endocrine glands • Exocrine • secretes digestive enzymes into the small intestine • Endocrine • Islets of Langerhans - Secretes insulin (beta cells) and glucagon (alpha cells)
Insulin/Glucagon • Regulate the ability of most tissues in the body to metabolize fuel substances (glucose, fats, proteins)
Insulin • Secreted by beta cells • Lower blood glucose levels by • Acts on skeletal muscles, liver cells, adipose tissue (fat) to uptake glucose • In the Liver • Lowers fatty acid levels • promotes fatty acid uptake and storage in adipose tissue • Inhibits breakdown of fats into fatty acids • Lowers amino acid levels • Promotes protein synthesis • Inhibits breakdown of proteins
Glucagon • Secreted by alpha cells • Increase blood glucose levels by • Stimulating breakdown of glycogen into glucose • Stimulates breakdown of fats into fatty acids • Stimulates breakdown of proteins into amino acids • Stimulate cells to use amino acids and non-carbohydrates to synthesize glucose
Unstable levels of glucose • Hyperglycemia (above 200mg/dL of blood) • Blood glucose levels are too high • (norm 115-200mg/dL) • Symptoms • Frequent urination, sugar in the urine, vision problems, fatigue, weight loss • Hypoglycemia (below 70mg/dL of blood) • Blood glucose levels are too low • (norm 70-115mg/dL) • Symptoms • Nervousness, cold sweats, hunger, headaches, weakness
Diabetes • High glucose levels in the blood caused by problems with insulin production • Symptoms • Frequent urination, increased thirst/appetite • Classified into 3 different types • Type 1 • Type 2 • Gestational