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Endocrine System

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

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Endocrine System

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  1. Endocrine System Glands and Hormones

  2. 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

  3. Hormones Regulate • Growth • Metabolism • Fluid and electrolyte • Acid-base balance • Reproduction • Blood pressure

  4. Endocrine Glands and Tissues • Secrete hormones Examples • Pituitary gland (hypophysis) • Thyroid gland • Parathyroid glands • Adrenal glands • Pancreas • Gonads • Endocrine tissues within other organs

  5. 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)

  6. Hormone Secretion Stimulus Gland ----------------Hormone Hormone secretion Blood Receptor------------ Action Target cell

  7. 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

  8. Specific Glands

  9. Pituitary Gland (Hypophysis) • Small gland connected to hypothalamus • Two parts • Anterior pituitary (adenohypophysis) • Posterior pituitary (neurohypophysis) hypothalamus ---------infundibulum posterior pituitary--------- -------anterior pituitary

  10. 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

  11. 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.

  12. 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

  13. 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

  14. 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

  15. 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

  16. Giantism

  17. Acromegaly

  18. 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

  19. 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

  20. 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

  21. Thyroid Gland • Large butterfly-shaped gland in neck below voice box (larynx) • Has Two lobes connected by an isthmus --------left lobe right lobe----- ------------isthmus thyroid follicle-----

  22. Histology of Thyroid • Composed of many follicles filled with jelly-like (colloidal) thyroglobulin protein • Thyroid hormones T3 and T4 synthesized by follicle cells and stored in combination with thyroglobulin Thyroglobulin with T3 and T4

  23. Thyroid Hormones • T3 short for triiodothyronine • T4 short for tetraiodothyronine (thyroxine)

  24. Thyroid Hormones • Formed by addition of iodine to the thryroglobulin • 3 & 4 stands for number of iodines

  25. 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

  26. Synthesis and Secretion of T3 & T4 Figure 18.11 in text

  27. Target Cells and Actions of T3 & T4 • Actions • ATP production by mitochondria (aerobic cell respiration) • Normal growth • Control by negative feedback

  28. 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

  29. 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.

  30. Imbalances of T3 & T4 • Hypothyroidism (in adults) • Too little T3 & T4 • Symptoms • MR • bradycardia • BT • lethargy • goiter • weight gain • cold intolerance • myxedema

  31. 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

  32. 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)

  33. Thyroid Disorders Exophthalmia Endemic Goiter

  34. 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

  35. Adrenal Glands • Located on top of kidneys • Gross Anatomy • Enclosed by capsule • Outer cortex • Inner medulla

  36. Structure of Adrenal Gland

  37. 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

  38. 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

  39. Corticoids • Mineralocorticoids: glomerular zone • Aldosterone most important • Regulates blood sodium, potassium and acid • Regulation affects fluid & electrolyte homeostasis

  40. 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

  41. Corticoids • Glucocorticoid actions • Reduce inflammation • Various steroids including cortisol, cortisone, and synthetic steroids used medically to reduce inflammation • Control is by negative feedback

  42. Imbalances of Glucocorticoids • Addison’s disease • Insufficient glucocorticoids • Lack of energy • Weight loss • Inability to resist stress • John F. Kennedy had it

  43. 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

  44. Addison’s Disease – President Kennedy Before SteroidTreatment During SteroidTreatment

  45. Cushing’s Syndrome After Before

  46. 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

  47. 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

  48. 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

  49. Anatomy of Pancreas • Five inches long, consists of head, body & tail • Most cells produce digestive enzymes • Endocrine cells in pancreatic islets produce hormones

  50. Cell Organization in Pancreas • Exocrine acinar cells surround a small duct • Endocrine cells secrete near a capillary

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