The Endocrine System PDF

The Endocrine System Dr. Atiq Hassan College of Applied Medical Sciences King Khalid University  Endocrine Glands 2 kinds of glands Exocrine – ducted Endocrine – ductless Secrete products into interstitial fluid, diffuse into blood Endocrine glands...

The Endocrine System Dr. Atiq Hassan College of Applied Medical Sciences King Khalid University  Endocrine Glands 2 kinds of glands Exocrine – ducted Endocrine – ductless Secrete products into interstitial fluid, diffuse into blood Endocrine glands include Pituitary, thyroid, parathyroid, adrenal and pineal glands Hypothalamus, thymus, pancreas, ovaries, testes, kidneys, stomach, liver, small intestine, skin, heart, adipose tissue, and placenta, also work as endocrine glands Copyright 2009, John Wiley & Sons, Inc.  Hypothalamus and Pituitary Gland Hypothalamus is a major link between nervous and endocrine system Pituitary attached to hypothalamus by infundibulum Anterior pituitary or adenohypophysis Posterior pituitary or neurohypophysis Copyright 2009, John Wiley & Sons, Inc. Hypothalamus and Pituitary Gland Copyright 2009, John Wiley & Sons, Inc.  Anterior pituitary Release of hormones stimulated by releasing and inhibiting hormones from the hypothalamus Also regulated by negative feedback Hypothalamic hormones made by neurosecretory cells transported by hypophyseal portal system Anterior pituitary hormones that act on other endocrine systems called tropic hormones Copyright 2009, John Wiley & Sons, Inc.  Hormones of the Anterior Pituitary Growth hormone (GH) or somatostatin Stimulates secretion of insulin-like growth factors (IGFs) that promote growth, protein synthesis Thyroid-stimulating hormone (TSH) or thyrotropin Stimulates synthesis and secretion of thyroid hormones by thyroid Follicle-stimulating hormone (FSH) Ovaries initiates development of oocytes, testes stimulates testosterone production Luteinizing hormone (LH) Ovaries stimulates ovulation, testes stimulates testosterone production Copyright 2009, John Wiley & Sons, Inc.  Hormones of the Anterior Pituitary Prolactin (PRL) Promotes milk secretion by mammary glands Adrenocorticotropic hormone (ACTH) or corticotropin Stimulates glucocorticoid secretion by adrenal cortex Copyright 2009, John Wiley & Sons, Inc.  Acromegaly and Gigantism Excess GH leads to development of gigantism if hypersecretion is present during early life– a rare condition Symmetrical enlargement of body resulting in true giant with overgrowth of long bones, connective tissue and visceral organs. Excess GH leads to acromegaly if hypersecretion occurs after body growth has stopped. Elongation of long bones not possible so there is over growth of cancellous or spongy bones– protruding jaw, thickening of phalanges, and over growth of visceral organs Gigantism Identical twins, 22 years old, excess GH secretion 0  Posterior pituitary Does not synthesize hormones Stores and releases hormones made by the hypothalamus Transported along hypothalamohypophyseal tract Oxytocin (OT) Antidiuretic hormone (ADH) or vasopressin Copyright 2009, John Wiley & Sons, Inc.  1 High blood osmotic 5 Low blood pressure stimulates osmotic hypothalamic stimulates pressure inhibits osmoreceptors hypothalamic hypothalamic osmoreceptors osmoreceptors Osmoreceptors Osmoreceptor 2 Osmoreceptors activate the s neurosecretory cells 6 Inhibition of osmo- receptors reduces that synthesize and cells or release that synthesize ADH and stops ADH secretion release ADH Hypothalamu s 3 Nerve impulses liberate ADH from axon terminals in the posterior pituitary into the bloodstream AD ADH H Target tissues 4 Kidneys retain Sudoriferous Arterioles more water, (sweat) glands constrict, which decrease water which increases decreases loss by blood pressure urine output perspiration from the skin  Thyroid Gland Located inferior to larynx 2 lobes connected by isthmus Thyroid follicles produce thyroid hormones Thyroxine or tetraiodothyronine (T4) Triiodothyronine (T3) Both increase BMR, stimulate protein synthesis, increase use of glucose and fatty acids for ATP production Parafollicular cells or C cells produce calcitonin Lowers blood Ca2+ by inhibiting bone resorption Copyright 2009, John Wiley & Sons, Inc. Thyroid Gland  Control of thyroid hormone secretion Thyrotropin-releasing hormone (TRH) from hypothalamus Thyroid-stimulating hormone (TSH) from anterior pituitary Situations that increase ATP demand also increase secretion of thyroid hormones Copyright 2009, John Wiley & Sons, Inc.  1 Low blood levels of T3 and T4 T3 or low metabolic rate stimulate release of of Hypothalamus Hypothalamu TR s H 2TRH, carried by hypophyseal portal veins to anterior pituitary, 5Elevated stimulates T3inhibit release of TSH s by thyrotrophs release TS TSH of H TRH and TSH Anterior 3 TSH released into pituitar (negative blood stimulates feedback thyroid follicular y ) cells T3 and T4 4 Thyroi released into blood by d follicle follicular cells Actions of Thyroid Hormones: Increase basal metabolic rate Stimulate synthesis of Na+/K+ ATPase Increase body temperature (calorigenic effect) Stimulate protein synthesis Increase the use of glucose and fatty acids for ATP production Stimulate lipolysis Enhance some actions of catecholamines Regulate development and growth of nervous tissue and bones bones  Grave’s disease Hyperthyroidism caused by circulating antibodies to the TSH receptor. Associated with diffuse goiter. Autoantibodies bind to TSH receptor and mimic the action of TSH itself leads to persistent stimulation of thyroid and elevated levels of thyroid hormones.  Parathyroid Glands Embedded in lobes of thyroid gland Usually 4 Parathyroid hormone (PTH) or parathormone Major regulator of calcium, magnesium, and phosphate ions in the blood Increases number and activity of osteoclasts Elevates bone resorption Blood calcium level directly controls secretion of both calcitonin and PTH via negative feedback Copyright 2009, John Wiley & Sons, Inc. Parathyroid Glands Roles of Calcitonin, Parathyroid hormone, Calcitrol in Calcium Homeostasis Copyright 2009, John Wiley & Sons, Inc.  1High level of Ca2+ in 3 Low level of Ca2+ in blood blood stimulates parathyroid stimulates thyroid gland gland chief cells to release parafollicular cells to more PTH. release more CT. 6 CALCITRIOL stimulates increased absorption of Ca2+ from foods, which increases blood Ca2+ level. 5 PTH also stimulates the kidneys to 4 PARATHYROID HORMONE (PTH) 2 CALCITONIN inhibits release promotes release of Ca2+ from osteoclasts, thus CALCITRIOL. bone extracellular matrix into decreasing blood and slows loss of Ca2+ blood Ca2+ level. in urine, thus increasing blood Ca2+ level. Osteoclasts: Bone cell which absorbs bone tissue during growth and healing.  Adrenal Glands 2 structurally and functionally distinct regions. Adrenal cortex Mineralocorticoids (aldosterone) It is involved in maintaining water and electrolyte balance. it stimulates the reabsorption of sodium (Na+) by the renal tubules and excretion of potassium (K+) in the urine. It involved in the regulation of blood volume and blood pressure. Glucocorticoids- affect glucose homeostasis It include Cortisol (hydrocortisone), cortisone, collectively known as ‘steroids. Sex hormones- Sex hormones secreted by the adrenal cortex are mainly androgens (male sex hormones). Copyright 2009, John Wiley & Sons, Inc.  Adrenal Glands Adrenal medulla Modified sympathetic ganglion of autonomic nervous system Intensifies sympathetic responses Epinephrine (Adrenaline) Norepinephrine (noradrenaline)-postganglionic neurotransmitter of the sympathetic division of the autonomic nervous system Copyright 2009, John Wiley & Sons, Inc. Adrenal Glands Copyright 2009, John Wiley & Sons, Inc.  Pancreatic Islets Both exocrine and endocrine gland Roughly 99% of cells produce digestive enzymes Pancreatic islets or islets of Langerhans Alpha or A cells secrete glucagon – raises blood sugar Beta or B cells secrete insulin – lowers blood sugar Delta or D cells secrete somatostatin – inhibits both insulin and glucagon F cells secrete pancreatic polypeptide – inhibits somatostatin, gallbladder contraction, and secretion of pancreatic digestive enzymes. Normal Blood Glucose level is about 100 mg/100 ml Copyright 2009, John Wiley & Sons, Inc. 1 Low blood glucose 5 High blood glucose (hypoglycemia) glucose (hyperglycemia) stimulates alpha (hypoglycemia) stimulates beta cells cells to secrete stimulates alpha to secrete cells cells to secrete to secrete Normal Blood Glucose level is about 100 mg/100 mL Negative Feedback Regulation of Glucagon and Insulin GLUCAGO INSULIN N 2 Glucagon acts on 6Insulin acts on various hepatocytes on body cells to: various (liver cells) to: hepatocytes body cells to: accelerate facilitated (liver cells) convert to: glycogen diffusion of glucose into glucose into cells (glycogenolysis) speed conversion of form glucose from glucose into glycogen lactic acid and (glycogenesis) certain amino acids increase uptake of (gluconeogenesis) amino acids and increase protein synthesis speed synthesis of fatty 3 Glucose released acids (lipogenesis) by hepatocytes blood slow glycogenolysis raises glucose level blood glucose rises to normal slow gluconeogenesis level glucose to normal (about 100 mg/100 level to normal mL 7Blood glucose level falls 4 If blood glucose 8If blood glucose continues to rise, continues hyperglycemia inhibits to fall, hypoglycemia release of glucagon inhibits inhibits release of release of glucagon insulin  Ovaries and Testes Gonads – produce gametes and hormones Ovaries produce 2 hormones estrogens and progesterone With FSH and LH regulate menstrual cycle, maintain pregnancy, prepare mammary glands for lactation, maintain female secondary sex characteristics Relaxin produced during pregnancy Testes produce testosterone – regulates sperm production and maintains male secondary sex characteristics Inhibin inhibits FSH Copyright 2009, John Wiley & Sons, Inc.  Pineal Gland Attached to roof of 3rd ventricle of brain at midline Masses of neuroglia and pinealocytes Melatonin – amine hormone derived from serotonin Appears to contribute to setting biological clock More melatonin liberated during darkness than light Copyright 2009, John Wiley & Sons, Inc.  Disorders of endocrine glands Gigantism Acromegaly Dwarfism- abnormally low stature or small size. Goitre- enlarged thyroid gland that causes the neck to swell. Galactorrhoea- is the spontaneous flow of milk from the breast, Amenorrhoea- is the absence of a menstrual period in a woman of reproductive age. Sterility in women- female infertility. Impotence in men- male infertility Simmond disease- is caused by destruction of the anterior lobe of the pituitary gland Diabetes insipidus- condition where the body loses too much fluid through urination Graves disease- an autoimmune disease that affects the thyroid. Cushing syndrome- A primary adrenal gland disease  ATTENTION! For more details and Preparation for Quizzes and all exams Please read from the reference book Ross and Wilson's Anatomy and Physiology in Health and Illness 12th Edition; ISBN: 13978-0-443-10101-4. (Pages 215-229)