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Endocrine System Glands and Hormones Definitions • Hormones are chemicals regulators, secreted into the blood, that affect the functioning of other cells • These “other cells” are called target cells • Hormones are specific for certain targets because hormones bind to specific receptors of target cells Hormones Regulate • • • • • • Growth Metabolism Fluid and electrolyte Acid-base balance Reproduction Blood pressure Endocrine Glands and Tissues • Secrete hormones Examples – Pituitary gland (hypophysis) – Thyroid gland – Parathyroid glands – Adrenal glands – Pancreas – Gonads – Endocrine tissues within other organs Chemistry of hormones • Compounds that act as hormones are: – – – – – Steroids (derived from cholesterol) Amines (derived from a single amino acid) Peptides (smaller chains of amino acids) Proteins (polypeptide chains of amino acids) Glycoproteins (protein/carbohydrate complex) Hormone Secretion Stimulus Gland ----------------Hormone Hormone secretion Blood Receptor-----------Target cell Action Control of Secretion • Negative feed back – Stimulus is decreased or inhibited by some factor such as concentration of hormone – Attempts to maintain normal levels of secretion • Positive feed back – Stimulus for secretion is increased or exaggerated Specific Glands Pituitary Gland (Hypophysis) • Small gland connected to hypothalamus • Two parts – Anterior pituitary (adenohypophysis) – Posterior pituitary (neurohypophysis) hypothalamus ---------infundibulum posterior pituitary--------- -------anterior pituitary Pituitary Gland • Posterior pituitary derived from neural brain tissue and connects to hypothalamus by the stalk-like hypothalamic hypophyseal tract • Anterior pituitary from ectodermal tissue in the roof of embryonic mouth. -----------------------infundibulum Pituitary Gland • Posterior pituitary secretes two hormones – Hormones produced by hypothalamus and placed in posterior pituitary for secretion • Anterior pituitary largest part – Produces and secretes most of the hormones – Under direct control of hypothalamus • Hypothalamus secretes releasing and inhibiting hormones that reach anterior pituitary through hypophyseal portal circulation. Hormones of the Posterior Pituitary • Oxytocin (OT) – Target tissues are smooth muscles of reproductive system of both sexes – Actions in female • Labor (uterine) contractions • Release of milk from mammary glands (milk letdown) – Actions in male • Contraction of smooth muscle in reproductive tissue Hormones of Posterior Pituitary • Antidiuretic Hormone (ADH) (vasopressin) – Target tissues are kidneys, sweat glands and arterioles – Actions • Causes kidneys and sweat glands to conserve water • Causes vasoconstriction of arterioles Hormones of Anterior Pituitary • Human Growth Hormone (hGH) – Targets all cells especially skeletal and muscle tissue – Actions • Promotes secretion of insulin-like growth factors (IGFs) within target tissues • IGFs increase: -rate of cell division for growth -protein synthesis needed for growth -use of fat for energy • Results in growth to adulthood and maintenance of skeleton and muscles in adults Hormones of the Anterior Pituitary Human Growth Hormone Imbalances • Pituitary dwarfism caused by hyposecretion in children and adolescents resulting in small body • Giantism caused by hypersecretion in infants and children resulting in height of over 8 feet • Acromegaly caused by hypersecretion in adults resulting in distorted facial features Giantism Acromegaly Hormones of Anterior Pituitary • Thyroid stimulating hormone (TSH) – Targets thyroid gland – Stimulates secretion of the thyroid hormones • Adrenocorticotropic Hormone (ACTH) – Targets Adrenal cortex – Stimulates secretion of glucocorticoids from adrenal glands Hormones of Anterior Pituitary • Prolactin (PRL) – Targets mammary glands – Stimulates milk production in mammary glands in concert with other hormones • Gonadotropins – – – – Follicle Stimulating Hormone (FSH) and Luteinizing Hormone (LH) Target the ovaries and testes (gonads) Control female and male reproductive physiology Control of Secretion of Anterior Pituitary Hormones • Secretion Stimulated by releasing hormones (RH’s) from hypothalamus through hypophyseal portal system • Secretion suppressed by inhibiting hormones (IH’s) from hypothalamus through hypophyseal portal system • All controlled by negative feedback Thyroid Gland • Large butterflyshaped gland in neck below voice box (larynx) • Has Two lobes connected by an isthmus right lobe----- --------left lobe ------------isthmus thyroid follicle----- Histology of Thyroid • Composed of many follicles filled with jellylike (colloidal) thyroglobulin protein • Thyroid hormones T3 and T4 synthesized by follicle cells and stored in combination with thyroglobulin Thyroglobulin with T3 and T4 Thyroid Hormones • T3 short for triiodothyronine • T4 short for tetraiodothyronine (thyroxine) Thyroid Hormones • Formed by addition of iodine to the thryroglobulin • 3 & 4 stands for number of iodines Secretion of T3 & T4 • Synthesis and secretion stimulated by anterior pituitary hormone TSH • Portion of stored thyroglobulin taken in from colloid by follicles cells • Colloid digested by lysosomes releasing T3 & T4 • T3 & T4 enter blood, combine with transport proteins and are transported to target cells Synthesis and Secretion of T3 & T4 Figure 18.11 in text Target Cells and Actions of T3 & T4 • Actions – ATP production by mitochondria (aerobic cell respiration) – Normal growth • Control by negative feedback Thyroid and Negative Feedback • Increase in blood levels of T3 & T4 etc. • Release of thyrotropin releasing hormone (TRH) inhibited • Release of thyroid stimulating hormone (TSH) inhibited • Secretion of T3 & T4 decreases Imbalances of T3 & T4 • Thyroid dwarfism (Cretinism) – Too little secretion of thyroid hormones during fetal development and infancy. – Severe forms of mental and physical retardation in the newborn. – Retardation is reversible if hormonal replacement therapy is started during the first four months of life. Imbalances of T3 & T4 • Hypothyroidism (in adults) – Too little T3 & T4 – Symptoms • • • • • • • • MR bradycardia BT lethargy goiter weight gain cold intolerance myxedema Imbalances of T3 & T4 • Hyperthyroidism (in adults) – Too much T3 & T4 – Grave’s disease most common form – Symptoms • • • • • • • • MR tachycardia BT anxiety & irritability goiter Exophthalmia (exophthalmos) heat intolerance weight loss Imbalances of T3 & T4 • Endemic goiter and iodine deficiency – Insufficient dietary iodine to make T3 & T4 – Endemic means localized or regional – Lack of negative feedback from T3 & T4 causes over stimulation and overgrowth of the thyroid gland. – Goiter results (enlarged thyroid gland) Thyroid Disorders Endemic Goiter Exophthalmia Control of Blood Calcium • Calcitonin (CT) from thyroid lowers blood calcium by adding it to bones • Parathyroid hormone from parathyroid glands (small pea-shaped gland embedded in back of thyroid) increases blood calcium by removing it from bones Adrenal Glands • Located on top of kidneys • Gross Anatomy – Enclosed by capsule – Outer cortex – Inner medulla Structure of Adrenal Gland Histology of Adrenal Glands • Cortex with three zones – Secrete steroid hormones called corticoids – Outer (glomerular) zone • Cells in globular clusters • Secretes mineralocorticoids – Middle (fascicular) zone • Cells form vertical elongated bundles • Secrete glucocorticoids Histology of Adrenal Glands – Inner (reticular) zone • Cells form irregular, net-like pattern • Secrete some sex steroids in both sexes • More important in females – Affects female sex drive – Produces some estrogens • Secretion stimulated by ACTH Corticoids • Mineralocorticoids: glomerular zone – Aldosterone most important – Regulates blood sodium, potassium and acid – Regulation affects fluid & electrolyte homeostasis Corticoids • Glucocorticoids from fascicular zone • Principle one is cortisol • Actions include – Response to stress by • Glucose formation from fats and protein • Conversion of excess glucose to glycogen for storage in liver • use of fat for energy assures glucose availability for brain Corticoids • Glucocorticoid actions • Reduce inflammation • Various steroids including cortisol, cortisone, and synthetic steroids used medically to reduce inflammation • Control is by negative feedback Imbalances of Glucocorticoids • Addison’s disease – Insufficient glucocorticoids – Lack of energy – Weight loss – Inability to resist stress – John F. Kennedy had it Imbalances of Glucocorticoids • Cushing’s Disease – – – – – – – Excessive glucocorticoids Muscle wasting Fat redistribution Spindly arms & legs Large abdomen with stretch marks Rounded face Fatty hump between shoulders Addison’s Disease – President Kennedy Before Steroid Treatment During Steroid Treatment Cushing’s Syndrome Before After Adrenal Medulla • Develop from same tissue as the sympathetic nervous system • Chromaffin cells receive direct innervation from sympathetic nervous system • Sympathetic stimulation increases hormone secretion by adrenal medulla • Hormones are sympathomimetic – effects mimic those of sympathetic NS – cause fight-flight behavior Hormones of Adrenal Medulla • Catecholamines • epinephrine and norepinephrine • (adrenaline & noradrenaline) – Targets – most cells – React quickly to stress by: • heart rate and strength • blood flow to skeletal muscles, heart and brain • Dilation of airways • fuel for energy • blood pressure Pancreas • Large leaf-shaped gland • Located in the curve of small intestine and extend to the spleen • Both endocrine and exocrine – Endocrine part secretes hormones – Exocrine part secretes digestive enzymes Anatomy of Pancreas • Five inches long, consists of head, body & tail • Most cells produce digestive enzymes • Endocrine cells in pancreatic islets produce hormones Cell Organization in Pancreas • Exocrine acinar cells surround a small duct • Endocrine cells secrete near a capillary Histology of the Pancreas • 1 to 2 million pancreatic islets • Contains 4 types of endocrine cells Cell Types in the Pancreatic Islets • • • • Alpha cells (20%) produce glucagon Beta cells (70%) produce insulin Delta cells (5%) produce somatostatin PP cells (5%) produce pancreatic polypeptide Actions of Insulin • Insulin decreases blood glucose by: – uptake of glucose into cells – synthesis of liver glycogen for storage • Insulin also protein & fat synthesis Actions of Glucagon • Glucagon increases blood glucose by: – Synthesis of glucose from amino acids in the liver – breakdown of liver glycogen into glucose – release of glucose from liver into blood Regulation of Glucagon & Insulin Secretion • High blood glucose after a meal stimulates secretion of insulin and inhibits secretion of glucagon • Low blood glucose when fasting stimulates release of glucagon and inhibits secretion of insulin FED STATE FASTING STATE Diabetes Mellitus • Insulin is unavailable for uptake of glucose into the cells • Or the cells are not responding to insulin • Blood glucose levels becomes elevated – hyperglycemia Diabetes Mellitus • Two Types: – Type I (IDDM) or juvenile DM • Beta cells destroyed by own immune system • Insulin levels low or absent. • Insulin injections required. • Usually develops in people younger than 20 Diabetes Mellitus – Type II (NIDDM) or maturity onset DM • Most common type (90%) • Insulin may still be secreted but cells may be less sensitive to its actions • Insulin injections may not be required • Mostly in people over 35 who are obese • May be controlled by diet Three Signs (P’s) of DM • Polyuria - Excessive urination • Polydypsia - Excessive water drinking • Polyphagia - Excessive eating Complications of DM • Cardivascular disease • Loss of vision • Kidney disease - Most complications linked to high glucose and acidosis - Acidosis caused by excessive use of fat for energy instead of glucose