Endocrine System Year 1 2024 PDF

The endocrine System Year 1 Chapter 15 Academic year 2023/2024 Dr. Tarik AlShaibani What is the endocrine system? Introduction and some definitions The endocrine system is the hormonal system which boasts several glands that secret or release their hormones directly into the blood (i.e., the circula...

The endocrine System Year 1 Chapter 15 Academic year 2023/2024 Dr. Tarik AlShaibani What is the endocrine system? Introduction and some definitions The endocrine system is the hormonal system which boasts several glands that secret or release their hormones directly into the blood (i.e., the circulatory system), to regulate distant target organs. In other words, the endocrine system is the glands and organs that make hormones and release them directly into the blood so they can travel to tissues and organs all over the body. The hormones released by the endocrine system control many important functions in the body, including growth and development, metabolism, sleep, blood pressure, and reproduction. It performs its function by a feedback loops, most likely by a negative feedback mechanisms. Endocrine glands produce hormones that are secreted into the bloodstream and distributed to target cells where they alter cellular metabolism. Hypothalamus and pituitary glands: the hypothalamus controls the secretions of the pituitary gland, which, in turn, controls the secretion of certain other glands like the thyroid glands, the ovaries, the testes, and the adrenal gland cortex. The endocrine system and the nervous systems work together to control the other organ systems and maintain homeostasis throughout the body. brain b Q ② Loading… memorizing Loading… What is a target cell? Are the cells that have the receptor for the specific hormone Exocrine vs. endocrine glands ducts Exocrine glands secrete their products into ducts that carry these products to other organs or outside the body directly Endocrine glands secrete their products directly into the bloodstream Action of peptide hormones peptide normone Example: The hormone Epinephrine ( as a first messenger) and the activation of a Y 2nd messenger system (cAMP) Provides glucose from breaking down Glycogen by activation of cAMP Because the hormone does not enter the cell it is called FIRST messenger, and the cAMP is called the SECOND messenger. Action of steroid hormones Steroid hormones enter the cell (they are lipids) and bind to their receptors (usually in nucleus but also sometimes in cytoplasm) All derived from Cholesterol and contain 4 carbon rings. (Adrenal cortex, ovary, testis). Slow action (because they synthesize new proteins rather than activation of already existing enzymes as in peptide hormones) but their action lasts longer. The hormone attaches to DNA and activates certain genes. Important Note : The thyroid hormones act in a similar way to steroids (even they are not steroids) hormones) endocrine - boast system glands that -make hormone and releases it -controls important by - Secrete hormones into the bloodstream functions : into the growth , -> to endocrine target hypothalamus & Pituitary Hypothalamus cells where they alter pituitary : , blood pressures cellular metabolism work glands thyroid , ovaries like travels causes of walls anteriole to Cardiovascular system from in und (first pancreas to liver messenger) messenger (Camp) provides messenger Steroid hormone - - derived and hormone glucose hormone doesn't enter the cell (lipid) to receptor cytoplasm from cholestrol Slow action thyroid because the cell and bind nucleus - cortex contract b - gland together to control homeostasis hormone epinephrine normone ; enter testes , adrenal hormone between neurotransmitter and hormone : - , releasing : Neurotransmitter : called first reproduction Stimulating difference peptide sleep controls pituitary endocrine Hypothalamus , the body gland Pituitary controls Secretion of other & metabolism throughout feedback negative nervous travel blood to and contain (synthesize attaches to and steroid new u carbon ring protein) DNA and activates certain hormone act the same genes even though - causes liver cell to store glucose Major glands of the endocrine system 1. 2. 3. 4. 5. 6. 7. 8. 9. Hypothalamus brain Posterior and Anterior pituitary glands brain Thyroid gland throat Parathyroid glands throat Adrenal glands Kidney Pancreas Pancreas Gonads (Testes and Ovaries) Thymus gland chest Pineal gland brain The hypothalamus and pituitary 1. Hypothalamus Acts as the link between the nervous system and endocrine system. Regulates internal environment through communications with the autonomic nervous system. For examples, Helps control heartbeat Helps control body temperature Helps control water-salt balance Controls glandular secretions Loading… The hypothalamus also control the secretion of the pituitary hormones. 2. The Posterior Pituitary Gland – – Stores antidiuretic hormone (ADH) and oxytocin that are produced by the hypothalamus. ADH: regulates water balance by reabsorbing water into the bloodstream (deficiency of this hormone causes Diabetes Insipidus, loss of too much water in urine, i.e., urine becomes very diluted). The hypothalamus has receptors measuring the concentration of the blood. When the blood is concentrated, as in dehydration, the Hypothalamus secretes ADH which goes to the kidney leading into reabsorption of water. And if the blood is hypotonic, less ADH is secreted. Oxytocin: causes uterine contractions during childbirth and allow milk to be released during breast feeding. Stimulation of cervix during late pregnancy will cause stimulation of hypothalamus to release Oxytocin and childbirth starts. Suckling of the breast by the baby stimulates the hypothalamus to release Oxytocin leading into milk ejection or letdown. 3. The Anterior Pituitary Gland Controlled by hypothalamic-releasing and hypothalamic-inhibiting hormones, examples, thyroid –releasing hormone (TRH) and thyroidinhibitory hormone (TIH). 1. Hormones produced by the anterior pituitary: Thyroid-stimulating hormone (TSH): stimulates the thyroid to produce thyroid hormones Adrenocorticotropic hormone (ACTH): stimulates the adrenal cortex to produce cortisol Gonadotropic hormones: stimulate gonads to produce sex cells and hormones Prolactin (PRL): stimulates mammary glands to develop and produce milk only after childbirth Melanocyte-stimulating hormone (MSH): causes skin cells to produce melanin Growth hormone (GH) or somatotropic hormone promotes growth and stimulate liver to produce IGF-1 (Insulin-like growth factor) which stimulates growth of skeletal and muscular tissues. Growth hormone stimulates protein synthesis. Its secretion is mainly during the night, and after exercise. 2. 3. 4. 5. 6. Growth Hormone (GH) anterior pituitary Pituitary dwarfism – too little GH is produced during childhood that results in small stature Gigantism – too much GH is produced during childhood that results in overgrowth in all parts and poor health Acromegaly – overproduction of GH in adult that results in larger than normal feet, hands, and face (bones not get longer but thicker or wider) 4. The Thyroid gland – – – A large gland located below the larynx. Composed of follicles filled with T3 and T4. Thyroid hormones have no target organ, they stimulate the metabolism of all the cells of the body. Thyroid hormone (TH, as T3 and T4): regulates metabolism of all the body tissues Iodine is needed in the diet to allow the thyroid gland to produce its hormones. Iodine deficiency causes Simple Goiter. Also, C cells in thyroid gland secrete the hormone calcitonin which helps lowering blood Ca2+ levels by 1- stimulating the deposition of calcium in the bones by osteoblasts 2- reducing the activity of the osteoclast cells Thyroid abnormalities in hypo large thyroid Buyper A. B. C. D. Iodine , TSH Simple goiter – thyroid enlarges due to lack of iodine in the diet. Low Thyroid hormone causes increase in TSH which will stimulate the Thyroid to increase its size (increases its ability to absorb more Iodine from the blood). low due to lack of hormones thyroid Hypothyroidism – low blood levels of thyroid hormones Congenital hypothyroidism: thyroid does not develop properly and is characterized in a short, confused person that may be mentally retarded (Critinism) I. > - retarded Myxedema: hypothyroidism in adults characterized by lethargy (lack of energy), weight gain, loss of hair, cold intolerant and thick, puffy skin. 2 Hyperthyroidism (Grave’s Disease) – excess thyroid hormones in the blood due to overactive thyroid gland which causes enlargement of the gland (Goiter) Exophthalmic goiter is characterized by enlargement of the thyroid gland, protrusion of the eyes, hyperactive, nervous and suffers from insomnia. This can be treated by Radioactive iodine (kills the thyroid cells). Thyroid tumor: can also cause hyperthyroidism (treated by radioactive iodine or surgery). A symptom of hyperthyroidism Hyperthyroidism is characterized by an increased metabolic rate, weight loss, and nervousness, insomnia. The eyes may also protrude (exophthalmos), as in this photograph. 5. Parathyroid glands Small glands embedded in the surface of the thyroid gland Produces parathyroid hormone (PTH): causes blood Ca2+ level to increase blood by: PTH increases calcium in - promoting osteoclast activity. -Activation of Vitamine D (Calcitriol) in the kidneys resulting into: 1- Calcium reabsorption in the kidney. 2- Calcium absorption from the GI tract – – Vitamin D helps calcium to be absorbed Hypoparathyroidism- Low Ca++ levels and Tetany (involuntary muscle contraction). Hyperparathyroidism: Release of Ca++ from bones osteoporosis (weak bones and easy fracture) also, kidney stones. low calcium levels = tetany hyper-too much Osteoporosis calcium Kidney stones 6. The Adrenal glands Adrenal glands Glands that sit on top of the kidneys 2 parts of each gland Adrenal medulla: controlled by the nervous system Adrenal cortex: portions are controlled by ACTH from the anterior pituitary – – cortisol I insulin Y Adrenal medulla stress normone Is the inner portion of the adrenal glands Hypothalamus initiates stimulation of hormone secretion in the adrenal medulla Produces: hormones that allow a short-term response to stress (“fight or flight” response) Epinephrine (adrenaline) Norepinephrine – – Adrenal cortex Outer portion of the adrenal glands Produces hormones that provide a long-term response to stress – 2 major types of hormones: Mineralocorticoids : Aldosterone hormone : regulates salt and water balance, targets the kidney. Causes sodium reabsorption and potassium secretion. (Role in Blood Pressure Regulation) Glucocorticoids: cortisol : 1) regulates carbohydrate, protein and fat metabolism 2) Suppresses the body’s inflammatory response Cortisone is the artificial hormone (man-made) – Other types of hormones secreted by the adrenal cortex are the sex hormones (small amounts, of both sexes hormones) GCs increase blood glucose by 1- Increase protein breakdown, making aminoacids which are converted into glucose by the liver. 2- promote the metabolism of fatty acids rather than glucose Cushing syndrome – hypersecretion of glucocorticoids by the adrenal cortex characterized by weight gain in the trunk of the body but not arms and legs. Tendency to Diabetes Meletus. Sometimes *Masculinization*, High BP. Fat mobilization from periphery into midline sections. Y male traits Same boy after hypersecretion of glucocorticoids cortison increases = Cushing syndrome Opposite Adrenal glands malfunction deficiency Addison’s disease – hyposecretion of glucocorticoids by the adrenal cortex characterized by bronzing of the skin, unable to cope with stress. Hyposecretion of Aldosterone leads into dehydration, Na+ loss. Bronzing of the skin is due to elevated levels of ACTH (loss of negative feedback). ACTH has similar structure to MSH which stimulates the release of melanin. Endocrine diseases: Growth Hormone (GH): Dwarfism (low GH in childhood) ,Giantism (High GH since childhood, Acromegaly (High GH in adulthood) Thyroid: Cretinism (congenital hypothyroidism), Myxedema (adult hypothyroidism) Hyperthyroidism (Grave’s disease/ exophthalmic hyperthyroidism) Adrenal gland: Addison’s disease (Hyposecretion of glucocorticoid/ aldosterone) Cushing syndrome: (Hypersecretion) 7. Pancreas - insulin -glucagon Fish-shaped organ behind the stomach Composed of 2 tissues: Exocrine: produces and secretes digestive juices Endocrine (islets of Langerhans): produces and secretes hormones 1. Insulin – secreted when blood glucose is high and stimulates uptake of glucose by cells (muscle and liver) 2. Glucagon – secreted when blood glucose is low and stimulates the breakdown of glycogen in the liver 8. Thymus gland Lies beneath the sternumChest This gland is largest and most active during childhood T lymphocytes mature here Secretes hormones called thymosin that aid in differentiation of lymphocytes 9. Pineal gland - - Located in the brain Secretes melatonin that regulates the sleep/wake cycle (circadian rhythm) May also regulate sexual development Melatonin Sexual development Hormones from other tissues Erythropoietin: secreted by the kidney to increase red blood cell production ↑ feeling of fullness -> by fat cells Leptin: produced by fat cells and acts on the hypothalamus to give a feeling of being satiated ( Full, not hungry) – Prostaglandins: A groups of potent chemicals that are not carried in the bloodstream but work locally on neighboring cells Some cause smooth muscle contraction Major impact on reproductive organs Many other roles in the body Aspirin and ibuprofen block the synthesis of these – – – – Loading… Principal Endocrine Glands and Hormones Endocrine gland Hormone Released Chemical Class Target Tissues/Organs Chief Function(s) of Hormones Hypothalamus Hypothalamic-releasing and releaseinhibiting hormones Peptide Anterior pituitary Regulate anterior pituitary hormones Posterior pituitary Antidiuretic (ADH) Peptide Kidneys Stimulates water reabsorption by kidneys Oxytocin Peptide Uterus, mammary glands Stimulates uterine muscle contraction release of milk by mammary glands Thyroid –stimulating (TSH) Glycoprotein Thyroid Stimulates thyroid Adrenocorticotropic (ACTH) Peptide Adrenal cortex Stimulates adrenal cortex Gonadotropic [follicle-stimulating (FSH), luteinzing (LH)] Glycoprotein Gondas Egg and sperm production, and sex hormone production Prolactin (PRL) Protein Mammary glands Milk production Growth (GH) Protein Soft tissues, bones Cell division, protein synthesis, and bone growth Melanocyte-stimulating (MSH) Peptide Melanocytes in skin Unknown function in humans; regulates skin color in lower vertebrates Thyroxine (T4) and triiodothyronine (T3) Iodinated amino acid All tissues Increases metabolic rate; regulates growth and development Calcitonin Peptide Bones, kidneys, intestine Lowers blood calcium level Anterior pituitary Thyroid Principal Endocrine Glands and Hormones (CONT..) Endocrine gland Hormone Released Chemical Class Target Tissues/Organs Chief Function(s) of Hormones Parathyroids Parathyroid (PTH) Peptide Bones, kidneys, intestine Raises blood calcium level Adrenal cortex Glucocorticoids (cortisol) Steroid All tissues Raise blood glucose level, prot. breakdown Mineralocorticoids (aldosterone) Steroid Kidneys Reabsorb sodium and excrete potassium Sex hormones Steroid Gonads, skin, muscles, bones Stimulate reproductive organs and bring about sex characteristics Adrenal medulla Epinephrine and norepinephrine Modified amino acid Cardiac and other muscles Emergency situations; raise blood glucose level Pancreas Insulin Protein Liver, muscles, adipose tissue Lowers blood glucose level; promotes formation of glycogen Glucagon Protein Liver, muscles, adipose tissue Raises blood glucose level Androgens (testosterone) Steroid Gonads, skin, muscles, bones Stimulate secondary male sex characteristics Ovaries Estrogens and progesterone Steroid Gonads, skin, muscles, bones Stimulate female sex characteristics Thymus Thymosins Peptide T lymphocytes Production and maturation of T lymphocytes Pineal gland Melatonin Modified amino acid Brain Circadian and circannual rythms; possibly involved in maturation of sex organs Gonads Testes