The endocrine system - Summer 2024.pdf

Chapter 13 The Endocrine System 1 1 13.1 The endocrine system produces hormones The endocrine system produces hormones  Endocrine system: is a collection of specialized cells, and tissues that secrete hormones. ...

Chapter 13 The Endocrine System 1 1 13.1 The endocrine system produces hormones The endocrine system produces hormones  Endocrine system: is a collection of specialized cells, and tissues that secrete hormones.  Endocrine glands: ductless organs that secrete hormones into blood, interstitial fluid and lymph, and located thorough the body.  Hormones:  Chemical messengers secreted by endocrine glands  Circulate in the bloodstream  Play a critical role in the regulation of physiological processes because they regulate the target cell responses such as;  reproduction, growth and development, metabolism, fluid, and electrolyte balance, sleep, and many other body functions. Human Biology (BIOL 108) Health Track 2 Figure 13.1 13.2. Types of hormones Types of Hormones  The hormones of the human body can be divided into two major groups on the basis of their chemical structure.  Group 1: Hormones derived from amino acids include amines, peptides, and proteins; called non-steroid hormones  Amine hormones - synthesized from the amino acids tryptophan or tyrosine. Example; melatonin is derived from tryptophan, and thyroid hormones are derived from tyrosine.  Peptide hormones - consist of short chains of amino acids; example, antidiuretic hormone (ADH).  protein hormones - are longer polypeptides; examples, growth hormones, follicle stimulating hormone (FSH).  Group 2: Those derived from lipids include steroids; called steroid hormones.  Example, the reproductive hormones testosterone and the estrogens. 4 13.5 The hypothalamus-pituitary complex Hypothalamus  Homeostatic control center of the brain  Links nervous system and endocrine system  Produces oxytocin, antidiuretic hormone (ADH), directly affecting the tissues  Produces releasing and inhibiting hormones to regulate secretion of other glands. Pituitary gland  “Master” gland  Secretes hormones that regulate other endocrine organs  Two lobes: posterior and anterior  Hypothalamus-pituitary complex is considered as the command center of Endocrine system. Human Biology (BIOL 108) Health Track 5 13.5 The hypothalamus-pituitary complex The posterior pituitary stores ADH and oxytocin Antidiuretic hormone (ADH)  Target: kidneys (collecting ducts)  Action: reduces amount of water in urine Oxytocin  Target: uterus, mammary gland  Action: Induces uterine contractions during labor (birth). Induces milk ejection through neuroendocrine reflex Human Biology (BIOL 108) Health Track 6 13.5 The hypothalamus-pituitary complex Growth hormone (somatotropin)  Target: most cells especially bone, muscle  Action: promotes growth during childhood and adolescence, cell division, protein synthesis and metabolism.  GH levels are controlled by the release of GHRH and GHIH (also known as somatostatin) from the hypothalamus. TSH (thyroid-stimulating hormone)  Target: thyroid gland  Action: stimulates synthesis and secretion of thyroid hormones  TSH is released from the anterior pituitary in response to thyrotropin-releasing hormone (TRH) from the hypothalamus Human Biology (BIOL 108) Health Track 7  13.5 The hypothalamus-pituitary complex ACTH (adrenocorticotropic hormone)  Target: adrenal cortex  Action: releases glucocorticoids (cortisol)  The release of ACTH is regulated by the corticotropin-releasing hormone (CRH) from the hypothalamus in response to normal physiologic rhythms.  A variety of stressors can also influence its release. FSH and LH (Follicle stimulating hormone and luteitizing hormones)  called gonadotropins; produced at puberty (age 10–13)  FSH  Target: gonads (testes and ovaries).  Action: stimulate gametes (male and female) production, and secretion of estrogen from ovaries. Human Biology (BIOL 108) Health Track 8 13.5 The hypothalamus-pituitary complex  LH  Target: gonads (testes and ovaries).  Action: triggers ovulation, production of estrogens and progesterone by the ovaries, and production of testosterone by the male testes. Prolactin  Target: mammary glands  Action: Stimulates development of mammary glands and milk production Human Biology (BIOL 108) Health Track 9 13.5 The hypothalamus-pituitary complex Pituitary Disorders: Hypersecretion and Hyposecretion  Diabetes insipidus  Hyposecretion of ADH results in inability to conserve water appropriately  Causes excessive urination, dehydration, thirst  Gigantism  Hypersecretion of growth hormone during childhood  Acromegaly  Excessive growth of bones in the face, hands, and feet due to excessive levels of GH in adults who have stopped growing.  Pituitary dwarfism  Hyposecretion of growth hormone during childhood Human Biology (BIOL 108) Health Track 10 13.6 Thyroid Gland Thyroid Gland  A butterfly shaped thyroid gland is located just below larynx in neck.  Parathyroid glands embedded in back of thyroid  Thyroid is involved in regulating metabolism  Both thyroid and parathyroid are involved in calcium balance Human Biology (BIOL 108) Health Track 11 13.6 Thyroid Gland The thyroid gland: thyroxine speeds cellular metabolism Thyroxine (T4) and Triiodothyronine (T3)  Secretion: mediated through hypothalamus-pituitary secretions  Target: all cells  Action: regulate the cellular metabolism; production of ATP from glucose and affect growth and development Calcitonin  Target: bones  Action: Lowers blood calcium levels - Decreases rate of bone resorption by inhibiting osteoclasts - Stimulates uptake of calcium by bones - Important for bone growth and development in children Human Biology (BIOL 108) Health Track 12 13.7 The Parathyroid Gland Parathyroid hormone (PTH)  Secreted in response to lower blood calcium levels  Target: bone, intestine, kidney  Action: increase blood calcium levels - Removes calcium and phosphate from bone - Increases absorption of calcium by the digestive tract - Causes kidneys to retain calcium and excrete phosphate Human Biology (BIOL 108) Health Track 13 13.8 The Endocrine pancreas The pancreas secretes glucagon, insulin, and somatostatin  The pancreas has both exocrine and endocrine functions  Pancreatic hormones are involved in regulating blood glucose levels  Its pancreatic islets—clusters of cells formerly known as the islets of Langerhans—secrete the hormones glucagon (by Alpha cells), insulin (by beta cells), somatostatin (by delta cells), and pancreatic polypeptide (by PP cells). Human Biology (BIOL 108) Health Track Figure 13.15 Pancreas 14 13.8 The Endocrine pancreas The pancreas secretes glucagon, insulin, and somatostatin  Pancreatic hormones are involved in regulating blood glucose levels Insulin  Target: liver, muscle, and adipose tissue  Action: Lowers blood glucose level - Promotes uptake of sugar by cells in liver, muscle, and adipose tissue. - Promotes conversion of glucose into glycogen in liver, and also proteins and fat. Glucagon  Target: liver, muscle, and adipose tissue  Action: Raises blood sugar - Causes breakdown of glycogen to glucose in liver Human Biology (BIOL 108) Health Track 15 13.8 The Endocrine pancreas Disorders of the endocrine system  Diabetes mellitus  Disorder of blood sugar regulation  Inability to get glucose into cells where it can be used, results in high blood sugar levels  Glucose and excess water appear in the urine  Symptoms: dehydration, thirst, fatigue, frequent infections, blurred vision, tingling of hands/feet  Two types: type 1 and type 2 Human Biology (BIOL 108) Health Track 16 13.8 The Endocrine pancreas Disorders of the endocrine system  Type 1 diabetes (insulin-dependent)  Pancreas does not produce enough insulin  Treated with insulin injections  Results from autoimmune destruction of beta cells of pancreatic islets  There may be a genetic component and/or environmental trigger  Typical onset is during childhood or adolescence  5–10% of all cases of diabetes Human Biology (BIOL 108) Health Track 17 13.8 The Endocrine pancreas Disorders of the endocrine system  Type 2 diabetes (Non-insulin-dependent)  Characterized by insulin resistance: cells fail to respond appropriately to insulin  Most often seen in adults over 40  Lifestyle factors (diet, exercise) play a role in onset  Treatment: lifestyle changes, variety of medications  90–95% of all cases of diabetes Human Biology (BIOL 108) Health Track 18 13.9 The adrenal glands The adrenal glands comprise of cortex and medulla  The adrenal gland consists of an outer cortex of glandular tissue and an inner medulla of nervous tissue  Adrenal cortex: is divided into three zones: Each region secretes its own set of hormones.  zona glomerulosa- Mineralocorticoids, such as aldosterone  zona fasciculata- Glucocorticoids, such as cortisol  zona reticularis- Androgens Figure 13.17 Adrenal glands Human Biology (BIOL 108) Health Track 19 13.9 The adrenal glands Glucocorticoids (Cortisol)  Target: most cells  Action: Maintain blood glucose levels during prolonged fasting - Suppress inflammatory responses Mineralocorticoids (Aldosterone)  Target: kidneys (distal tubule and collecting duct)  Action: promotes sodium reabsorption and potassium excretion. So, it regulates sodium, potassium, water balance Human Biology (BIOL 108) Health Track 20 13.9 The adrenal glands The adrenal glands comprise the cortex and medulla  Adrenal medulla:  Neuroendocrine organ  Secretion stimulated by nervous system  Hormones: Epinephrine (adrenaline) and norepinephrine (noradrenaline) are synthesized and stored in specialized cells called chromaffin cells in the adrenal (innervated by sympathetic nerves) Epinephrine and norepinephrine  Target: Liver, muscle, adipose tissue  Action: rises blood glucose level, increases heart rate, dilates or constrict blood vessels, increases respiration - participate in fight-or-flight response of the nervous system Human Biology (BIOL 108) Health Track 21 13.10 Gonadal hormones Testes and ovaries produce sex hormones  The human gonads (testes and the ovaries) are responsible for the production of gametes (sperm and eggs) and also produce the steroid sex hormones. Testes  Testes produce testosterone  Target: most cells  Actions: - Before birth, responsible for development of external male genitalia - At onset of puberty - Regulates development and normal functioning of sperm and male reproductive organs - Regulates development of male secondary sex characteristics Human Biology (BIOL 108) Health Track 22 13.10 Gonadal hormones Ovaries  Produce Estrogen and Progesterone  Target: most cells  Action: Estrogen Initiates development of secondary sex characteristics - Estrogen and progesterone regulates menstrual cycle Human Biology (BIOL 108) Health Track 23 13.11 The Pineal glands  Pineal gland secretes melatonin  Located deep within the brain inferior but somewhat posterior to the thalamus but receives input from optic nerve  The pinealocyte cells that make up the pineal gland secretes melatonin Melatonin  Target: many cells  Action: may be important in synchronizing the body’s circadian cycle and may be important in the onset of puberty. Human Biology (BIOL 108) Health Track 24 13.12 Thymus gland  Thymus gland aid the immune system  Located in the upper chest, over the heart  Most active during early development and childhood  Secretes thymosin and thymopoietin Thymosin and thymopoietin  Target: T lymphocytes  Action: Assist maturation of T lymphocytes Human Biology (BIOL 108) Health Track 25