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The Endocrine System/Part II Joe Pistack MS/ED Thyroid Gland • Largest of the endocrine glands. • Situated on the front sides of the trachea. • Butterfly-shaped, has two lobes connected by a tissue band called the isthmus. Thyroid Gland • Thyroid gland contains two types of cells: • Follicular cells-located within the thyroid follicle. Secrete T3 and T4 (discussed later) • Parafollicular cells-located between the follicles. • Each type of cells secrete a particular hormone. Thyroid Gland • Composed of secretory units called follicles. • Each follicle is filled with a clear, viscous substance called colloid. • Follicular cells secrete two thyroid hormones: • (1) triiodothyronine (T3) • (2) tetraiodothyronine (T4 or thyroxine) Thyroid Gland • Functions of T3 and T4: • Regulate all phases of metabolism and are necessary for the proper functioning of all other hormones. • Thyroid hormones are necessary for the normal maturation of the nervous system and for normal growth and development. Hypothyroidism • Adult-results in a condition called Myxedema. • Myxedema-slowed metabolic state. • Skin becomes thick and puffy due to accumulation of a thick fluid under the skin. Hypothyroidism • • • • • • • • Signs/Symptoms: Slow heart rate Sluggish peristalsis Constipation Low body temperature Low energy Loss of hair Weight gain Hypothyroidism • Cretinism-infant born with no thyroid gland. • Fails to develop both physically and mentally. • Child will be short and stocky with abnormal skeletal development and severe mental retardation. Hyperthyroidism • Hyperthyroidism-caused by an excess of thyroid hormone. • Metabolic state is “sped-up”. • At risk for developing fast rhythm disorders of the heart. Hyperthyroidism • Grave’s disease-common type of hyperthyroidism. • Signs/Symptoms: • Increased heart rate • Increased peristalsis/diarrhea • Elevation in body temperature • Hyperactivity • Weight loss • Emotional swings Hyperthyroidism • Grave’s disease is also characterized by bulging eyes (exophthalmia). • Bulging of eyes is caused by fat pads behind the eyeballs pushing the eyeballs forward in the eye socket. Iodine • Synthesis of T3 and T4 requires iodine. • Iodine in the body comes from dietary sources. • Most of the iodine in the blood is pumped into the follicular cells of the thyroid hormones where it is used in the synthesis of thyroid hormones. Iodine Deficiency • Iodine deficient state –T3 and T4 production decreases because iodine is necessary for the synthesis of the thyroid hormones. • With insufficient iodine, negative feedback is not possible. • Persistent stimulation of the thyroid gland by TSH causes thyroid to enlarge. Iodine Deficiency • Enlarged Thyroid gland is called a goiter. Diagnosis is usually made by ultrasound. Calcitonin • Calcitonin-secreted by the parafollicular cells of the thyroid gland. • Calcitonin helps regulate blood levels of calcium. Parathyroid Glands • Four tiny glands that lie along the posterior surface of the thyroid gland. • Secretes parathyroid hormone (PTH). Parathyroid Glands • Low blood level of calcium stimulates the release of PTH. • PTH has three target organs: – Bone – Digestive tract – Kidneys • Overall effect of PTH is to increase calcium levels. Parathyroid Gland • Hypocalcemia-low calcium levels. • Calcium deficiency results in continuous muscle contraction known as tetany. • Contorts the wrist , can cause sustained contraction of the muscles of the larynx (laryngospasm). Hypercalcemia • Increased calcium level. • PTH stimulates osteoclastic activity in the bones, moves calcium out of the bone causing hypocalcemia. • Hypercalcemia depresses the nervous, cardiac and GI systems causing fatigue, bradycardia, anorexia and constipation. Adrenal Glands • small glands located above the kidneys. • Consists of two regions: • Inner medulla • Outer cortex Adrenal Medulla • Inner region of the adrenal gland, considered an extension of the sympathetic nervous system “fight or flight”. • Catecholamines- Hormones that are secreted in emergency situations. They are: – Epinephrin (adrenaline) – Norepinephrine Adrenal Medulla • Catecholamines help the body respond to stress by: • Elevating blood pressure. • Increasing heart rate. • Convert glycogen to glucose in the liver, more glucose available to the cells. • Increases metabolic rate, making more energy. • Opens up the bronchial passages. Adrenal Cortex • Outer region of the adrenal gland. • Secretes hormones called steroids. • • • • Three steroidsGlucocorticoids Mineralcorticoids Sex hormones Adrenal Cortex • Adrenal cortical hormones are essential for life. • • • • Adrenal cortical hormones regulate: Glucocorticoids sugar Mineralcorticoids salt Sex hormones sex Adrenal Cortex • Glucocorticoids-convert amino acids into glucose (gluconeogenesis). • Maintain blood glucose levels between meals. • Ensures steady supply of glucose for the brain and other cells. • Chief glucocorticoid is cortisol. Adrenal Cortex • Cortisol is secreted in greater amounts during stress. (physiological stress, disease, physical injury, emotional stress). • Has an anti-inflammatory effect. • Ex. Cortisol-like drug-prednisone, used in treatment of arthritis or severe allergic response. Adrenal Cortex • Mineralocorticoids: • Aldosterone-chief mineralocorticoid. • Plays a role in the regulation of blood volume and blood pressure and in the concentration of electrolytes. • Called salt retaining hormone. Adrenal Cortex • Sex hormones: • Secreted in small amounts. • Female hormones-estrogens. • Male hormones-androgens. Adrenal Gland • Adrenal insufficiency is life threatening and must be treated with steroids and replacement of fluids and electrolytes. • Hypersecretion-excess of adrenal cortical hormones. • Cushing’s syndrome-elevated blood levels of steroids, such as prednisone. Adrenal Cortex • • • • • • • • Cushing’s syndrome s/s: Truncal obesity. Rounded facial appearance (moon face). Excess fat deposition between the shoulders (buffalo hump). Facial hair (hirsutism). Thin skin that bruises easily. Bone loss . Muscle weakness. Cushing’s Syndrome Adrenal Gland • Hyposecretion-adrenal gland fails to secrete adequate amounts of adrenal cortical hormones. • Addison’s disease-adrenal insufficiency. • s/s-generalized weakness, muscle atrophy, bronzing of the skin, severe loss of fluids and electrolytes. Addison’s Disease The Pancreas • Long slender organ that lies transversely across the upper abdomen. • Functions as an endocrine and exocrine gland. • Secretes two hormones: insulin and glucagon. • Islets of Langerhans-hormone-secreting cells of the pancreas. The Pancreas Pancreas • Islets of Langerhans contain two types of cells: • Alpha cells-secrete glucagon. • Beta cells-secrete insulin. • Both regulate blood sugar. Pancreas • Insulin is released in response to increased blood levels of glucose as occurs following a meal. • Secretion of insulin decreases as blood levels of glucose decrease. • Insulin has many target tissues, exerts widespread effects. Insulin and Blood Glucose • Insulin decreases blood glucose levels for two reasons: – Increases transport of glucose from the blood into the cells. – Stimulates the cells to burn glucose as fuel. • Insulin is the only hormone that lowers blood glucose. Pancreas • • • • • • • Hyperglycemia-excess glucose in the blood. Signs/symptoms: Glucosuria-glucose in the urine. Polyuria-excretion of large volumes of urine. Polydipsia-excessive thirst. Polyphagia-excessive eating. Acidosis-due to the rapid breakdown of fatty acids. Pancreas • • • • • • • • Hypoglycemia-low blood sugar. Signs/symptoms: Cool, clammy skin Weakness Pale Lethargy Headache Shakiness Gonads • Sex glands: • Ovaries in female. • Testes in male. • Ovaries secrete : estrogen and progesterone. – Females appear female because of estrogen • Testes secrete : testosterone – Males appear male because of testosterone. Thymus Gland • Thymus gland-lies in the thoracic cavity behind the sternum. • Larger in child than in an adult, becomes smaller as child hits puberty. • Secretes the hormones called thymosins, play a role in immunity. Thymus Gland Pineal Gland • Cone-shaped gland, located close to the thalamus in the brain. • Called the body’s “biological clock” controlling many biorhythms. • Secretes a hormone called melatonin. Pineal Gland • Plays a role in sexual maturation and the sleep-wake cycle. • Melatonin secretion is lowest during the daylight hours and highest at night. Pineal Gland Prostaglandins • Hormones derived from a fatty acid called arachidonic acid- a fatty acid found in the membranes of body cells • Produced by many tissues. • Chemical mediators of pain and inflammation, increase sensitivity of nerve endings to pain • Aspirin and ibuprofin block synthesis of prostaglandins-useful in pain control. As we Age • Alteration in the secretion of hormones. • Decrease in the levels of secretion of the glands. • Decrease in the level of thyroid hormones and decreased metabolic rate. • Decrease in the amount of growth hormone, decrease in muscle mass and increase in storage of fat. • Diminished circadian control.