Endocrine System Notes PDF

 RNB 10702 ANATOMY AND PHYSIOLOGY 2 2. THE ENDOCRINE SYSTEM  LEARNING OUTCOMES At the end of the session, the students should be able to: Describe the location, hormones and function each of the following endocrine glands thyroid gland parathyroid glands a...

 RNB 10702 ANATOMY AND PHYSIOLOGY 2 2. THE ENDOCRINE SYSTEM  LEARNING OUTCOMES At the end of the session, the students should be able to: Describe the location, hormones and function each of the following endocrine glands thyroid gland parathyroid glands adrenal glands pancreas gonadal pineal gland thymus gland  THE THYROID GLAND Anatomy The butterfly-shaped thyroid gland is located below the larynx and anterior to the trachea It has two lobes that connected by a bridge-like isthmus Very vascular organ  THE THYROID GLAND (cont..) The thyroid gland consists of thyroid follicles The wall of thyroid follicle consists follicular cells & parafollicular cells Follicular cells produce thyroid hormones Parafollicular cells or C cells produce calcitonin  THYROID HORMONES There are 2 types of thyroid hormones T3 (triiodothyronine ) Constitute only 10% of thyroid output Responsible for most the tissue action of thyroid hormone T4 ( thyrixine or tetraiodothyronine) Constitute 90% of thyroid output  SYNTHESIS, STORAGE & TRANSPORT OF THYROID HORMONES Thyroid hormones are synthesized from iodine and tyrosine Source of iodine – sea fish, bread, vegetables & milk Stored in the lumen of the follicles a colloid & the stored hormones can meet body’s requirements for 1-3 months Transported in the blood by plasma proteins  SECRETION OF THYROID HORMONES 1. Low blood level of thyroid hormones or low metabolic rate stimulate the hypothalamus to secrete thyroid releasing hormone (TRH) 2. TRH is carried to the anterior pituitary, where it stimulates secretion of thyroid-stimulating hormone (TSH) SECRETION OF THYROID HORMONES (cont..) 3. TSH stimulates thyroid follicular cell activity, including thyroid hormone synthesis and secretion, and growth of the follicular cells 4. The thyroid follicular cells release thyroid hormones into the blood until the metabolic rate returns to normal  SECRETION OF THYROID HORMONES (cont..) 5. An elevated level of thyroid hormones inhibits release of TRH and TSH (negative feedback) Conditions that increase ATP (Adenosine Triphosphate) demand - a cold environment, low blood glucose, high altitude, and pregnancy FUNCTION OF THYROID HORMONES  Increase basal metabolic rate (BMR)  Involved in maintenance of body temperature  Stimulate protein synthesis  Increase use of glucose and fatty acids for ATP production  Together with growth hormone & insulin- stimulate body growth for nervous & skeletal systems  CLINICAL APPLICATION (THYROID GLAND) Hyperthyroidism It is an enlarged of thyroid gland & produced excessive of thyroid hormone Lead to toxic goitre & Grave’s disease Characterized by high metabolic rate, hyperactivity, insomnia, nervousness, irritability & chronic fatigue  CLINICAL APPLICATION (THYROID GLAND) cont.. Hypothyroidism It is a deficiency or lack of thyroid hormones In infant may caused cretinism It is a mentally retarded dwarf with abnormal skeletal features In adult may lead to myxedema Symptoms – slow heart rate, low body temp, sensitivity to cold, dry hair & skin, muscular weakness, general lethargy, gain weight  CALCITONIN Secreted by Parafollicular cells or C cells in thyroid gland Calcitonin inhibit osteoclast activity - lowers the blood level of calcium Secretion is controlled by calcium levels in the blood  THE PARATHYROID GLANDS The parathyroid glands are embedded on the posterior surfaces of the lateral lobes of the thyroid There are 2 parathyroid glands attached to each lobe of the thyroid Contain chief cells that produce parathyroid hormone (PTH)  FUNCTION OF PARATHYROID HORMONES Major regulator of the level of calcium (Ca2+ ), magnesium (Mg2+) and phosphate ions in the blood Increases the number and activity of osteoclasts Form reabsorption from urine and inhibits the reabsorption of HPO4-2 (phosphate) so more is secreted in the urine Promotes formation of calcitriol, which increases the absorption of Ca2+ , Mg2+,and HPO4-2 from the GI tract  CLINICAL APPLICATION Hypoparathyroidism It is due to insufficient secretion of PTH Leads to increased nerve excitability Low blood calcium level trigger spontaneous & continuous nerve impulse which stimulate the muscle contraction Hyperparathyroidism Tumor of thyroid gland that may cause excessive secretion of PTH Caused increased osteoclast activity that removes calcium from the bone & increase the level in the blood Excessive calcium may cause kidney stone  ADRENAL GLANDS There are two adrenal glands, one superior to each kidney Consist of an adrenal cortex (outer) and adrenal medulla (inner)  ADRENAL CORTEX HORMONES The cortex is subdivided into three zones, each of which secretes a different group of steroid hormones, all formed from the cholesterol molecule The hormone released via negative feedback mechanism  ADRENAL CORTEX HORMONES (CONT..) Zones of adrenal cortex zona glomerulosa (outer zone) – secrete mineralocorticoid zona fasciculata (middle zone) - secrete glucocorticoid, primarily cortisol zona reticularis (the inner) - Secrete androgens  MINERALOCORTICOIDS Produce by adrenal cortex Major mineralcorticoid - aldosterone Functions Increase reabsorption of sodium & water – in case of dehydration Decrease of potassium reabsorption Adjust blood pressure & blood volume Promotes excretion of H+ (Hydrogen ion) in the urine Secretion is controlled by the renin-angiotensin- aldosterone pathway RENIN-ANGIOTENSIN PATHWAY  GLUCOCORTICOIDS Secreted by middle region of adrenal cortex Major hormone – Cortisol (hydrocortisone) Functions of glucocorticoids & cortisol  Glucose formation – especially in stressful situation  Increase protein breakdown  Stimulate the breakdown of triglycerides in fat  Anti-inflammatory effect – inhibit WBC  Depression immune response PATHWAY OF GLUCOCORTICOIDS HORMONE SECRETION CRH – Corticotropin-releasing hormones ACTH – Adenocorticotropic hormone  ANDROGENS Secreted by the adrenal cortex usually have minimal effects Masculinizing sex hormones Have little effect in men, but play an important role in promoting libido in women  CLINICAL APPLICATION Hypersecretion of hormone from adrenal cortex will cause Cushing’s syndrome Manifest by hyperglycemia, puffiness or edema & loss potassium ion  CLINICAL APPLICATION (cont..) Hyposecretion of hormones from adrenal cortex (glucocorticoids and aldosterone) in adults will caused Addison’s disease Caused body fails to produce enough of certain hormones that help regulate important body functions The physiologic effects include hypoglycemia, Na+ loss, low BP, dehydration, and muscle weakness President John F. Kennedy (1917- 1963) suffered from back pain most of his life & died with Addison's disease  ADRENAL MEDULLA Secrete 2 hormones - epinephrine (adrenalin) and norepinephrine - effects similar to sympathetic responses Hormones secreted in response during stressful situation (fight or flight) EPINEPHRINE – EFFECT AND CONTROL OF SECRETION  THE PANCREAS The pancreas can be classified as both an endocrine and an exocrine gland. It is located posterior & slightly inferior to the stomach  THE PANCREAS (cont..) Consists of Pancreatic islets (islets of Langerhans)  contains hormone-secreting cells - alpha (A) beta (B) Alpha cells () secrete glucagon - increases blood glucose levels Beta cells () secrete insulin - decreases blood glucose levels PANCREATIC HORMONES Insulin - decreases blood glucose levels Glucagon – increase blood glucose level  GONADAL HORMONES Ovaries Produce estrogens, progesterone & inhibin regulate the menstrual cycle maintain pregnancy prepare the mammary glands for lactation Established & maintain the female secondary sex characteristics Testes Produced testosterone, an androgen Function – regulate the production of sperm Develop & maintain the male secondary sex characteristics – beard growth & deepening the voice  THE PINEAL GLAND It is a small endocrine gland attached to the roof of the third ventricle Secretes hormone melatonin - contributes to maintaining the biological clock (seasonal and daily cycles)  THE THYMUS GLAND The thymus gland secretes thymosin, which promotes the proliferation and maturation of T cells T cells are a type of white blood cell (lymphocyte) that destroys microorganisms and foreign substances through direct cellular contact  RECAP/QUIZ What portion of the thyroid gland secretes the hormones that contain iodine? Thyroid follicles What are the hormones that release by the thyroid gland? T3 & T4 What is the causes of a simple goiter? Inadequate intake of dietary iodine  RECAP/QUIZ (cont..) What are the effects of hypersecretion of thyroxine? Toxic goiter & Grave’s disease What are the effects of hyposecretion of thyroxine? Cretinism (child)/myxedema(adult) What is the function of calcitonin? Lowers blood Ca2+ by inhibiting bone resorption Where is the calcitonin produced? Parafollicular cells or C cells produce calcitonin  RECAP/QUIZ (cont..) What is the hormone released by adrenal cortex in the case of dehydration or hemorrhage? Aldosterone What is the major hormone of glucocorticoids? Cortisol What are the effects of hypersecretion of cortisol?  Cushing’s syndrome What are the effects of hyposecretion of glucocorticoids and aldosterone?  Addison’s disease  RECAP/QUIZ (cont..) What hormones have an effect that is similar to that of the sympathetic nervous system? Epinephrine and norepinephrine What is the cells that produce glucagon & Insulin? Alpha cells secrete glucagon Beta cells secrete insulin What is the difference in action between glucagon and insulin? Glucagon - increase blood glucose level Insulin - decreases blood glucose levels  RECAP/QUIZ (cont..) What are the main hormone produced by testes? Testosterone & androgen What are the hormones produced by the ovaries? Estrogens, progesterone, inhibin & relaxin What is the functions of melatonin? Maintaining the biological clock What is the importance of thymus gland? Secrete Thymosin which promotes the proliferation and maturation of T cells