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Endocrine System ( Hormones )

Endocrine System ( Hormones ). Prof. Dr. Suat Erdoğan EBN School of Medicine Medical Biochemistry Department November 2013. Outline. Introduction to endocrine system Hormone-receptor interaction Peptide and steroid hormones Endocrine organs

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Endocrine System ( Hormones )

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  1. Endocrine System(Hormones) Prof. Dr. Suat Erdoğan EBN School of Medicine Medical Biochemistry Department November 2013

  2. Outline • Introduction to endocrine system • Hormone-receptor interaction • Peptide and steroid hormones • Endocrine organs • Diseases related with endocrine system disorders

  3. Introduction • Hormones arechemicalsubstances produced by a cell, a gland, or an organ in one part of the body that affects cells in nearby or other parts of the organism. • Generally, only a small amount (picomol to nmol) of hormone is required to alter cell metabolism. • In essence, it is a chemical messengerthat transports a signal from one cell to another. • Hormone action at the cellular level begins with the association of the hormone and its specific receptor.

  4. Hormone is a chemical messenger that transports a signal from one cell to another

  5. Endocrine and nervoussystems worktogether • Hormones (endocrine) and neurotransmitters (nervous) are integrated and the coordinate cellular functions in the body. • The nervousand endocrine systems function in a coordinated manner to promotegrowth, homeostasis and reproductive competence. • Therefore, endocrine and neuronal systemsare the main control systems (chief) of the body.

  6. Target cell and receptor • Most hormones circulate in blood, coming into contact with essentially all cells. However, a given hormone usually affects only a limited number of cells, which are called target cells. A target cell responds to a hormone because it bears receptorsfor the hormone. • Hormone receptors are found either exposed on the surface of the cell or within the cell, depending on the type of hormone.

  7. Hormone-receptor interaction

  8. Endocrine Organs • Hypothalamus • Pituitary gland (=hypophysis) • Pineal gland • Thyroid gland • Parathyroid glands • Thymus • Adrenal: 2 glands • Cortex • Medulla • Pancreas • Gonads • Ovaries • Testes

  9. Endocrine organs located throughout body. Actions mediate all tissues. Control of endocrinesystem through feedback mechanisms.

  10. Chemicalstructure of hormones Chemically, therearethreetypes of hormones: • Hormonal amine (amino acid) • Peptide, protein orglycoprotein • Steroid

  11. Aminehormones • Synthesized from a single amino acid • Melatonin from tryptophan. • Thyroid hormone from tyrosine. • Catecholamines (epinephrine, norepinephrine) from tyrosine.

  12. Protein/Peptide Hormones • Hydrophilic • Large • Can't fit through membrane • Second messenger mechanism of action • Most hormones • Example: Insulin

  13. Steroid Hormones • Small • Lipophilic (orhydrophobic) • Travel in blood withcarrier. • Change protein synthesis. • Cytoplasmic or nuclear receptors. • Synthesized fromcholesterol. • Example: testosterone

  14. Hormoneactions: Hormone + Receptorcomplex

  15. Hypothalamusand Pituitary (hyophysis) • Hypothalamus__ • Anterior pituitary__ • (adenohypophysis) • _____________Posterior pituitary • (neurohypophysis) • Hypothalamus___________ • Pituitary__________ • (hypophysis)

  16. Why is the Hypothalamus so Important? • Secretes regulatory homones • RH (releasinghormones) • RIH (inhibitoryhormones) • "Directs" pituitary

  17. Hypothalamus Connection to pituitary Neuronal to POSTERIOR PITUITARY Endocrine to ANTERIOR PITUITARY RH = Pituitary releasing hormones RIH = Pituitary release inhibiting hormones

  18. Hypothalamus controls anterior pituitary hormone release • Releasing hormones (releasing factors) of hypothalamus Secreted like neurotransmitters from neuronal axons into capillaries and veins to anterior pituitary (adenohypophysis) TRH (thyroid releasing hormone) -----turns on* TSH CRH (corticotropin releasing hormone) -----turns on ACTH GnRH (gonadotropin releasing hormone) ---turns on FSH and LH PRF (prolactin releasing hormone) -----turns on PRL GHRH (growth hormone releasing hormone) ----turns on GH • Inhibiting hormones of hypothalmus PIF (prolactin inhibiting factor) -----turns off PRL GH (growth hormone) inhibiting hormone ---turns off GH The hypothalamus controls secretion of hormones which in their turn control the secretion of hormones by the thyroid gland, the adrenal cortex and gonads: in this way the brain controls these endocrine glands *Note: “turns on” means causes to be released

  19. Neurosecretory cells in Hypothalamus • Nuclei synthesize and secrete hormones • Neuronal connection to POSTERIOR pituitary • Antidiuretic Hormone (ADH), Oxytocin

  20. STIMULUS • Hypothalamus • Releasing Hormone • (Release-Inhibiting Hormone) • Pituitary • Stimulating Hormone • Gland • Hormone • Target

  21. The Pituitary (hypophysis) Sits in hypophyseal fossa: depression in sellaturcica of sphenoid bone. Pituitary secretes 9 hormones • 1. TSH • 2. ACTH • 3. FSH • 4. LH • 5. GH • 6. PRL • 7. MSH Two divisions: • Anterior pituitary (adenohypophysis) • Posterior pituitary (neurohypophysis) The first four are “tropic” hormones, they regulate the function of other hormones • ________ • _________________________________________________________________ • 8. ADH (antidiuretic hormone), or vasopressin • 9. Oxytocin

  22. What the letters stand for… • TSH: thyroid-stimulating hormone • ACTH: adrenocorticotropic hormone • FSH: follicle-stimulating hormone • LH: luteinizing hormone • GH: growth hormone • PRL: prolactin • MSH: melanocyte-stimulating hormone • ADH: antidiuretic hormone • Oxytocin

  23. What do the hypophysis hormones do? • The four tropic ones regulate the function of other hormones: • TSH stimulates the thyroid to produce thyroid hormone • ACTH stimulates the adrenal cortex to produce corticosteroids: aldosterone and cortisol • FSH stimulates folliclegrowth and ovarian estrogen production; stimulates sperm production and androgen-binding protein • LH has a role in ovulation and the growth of the corpus luteum; stimulates androgensecretion by interstitial cells in testes

  24. The others from the anterior pituitary… • GH (= somatrotropic hormone) stimulates growth of skeletal epiphyseal plates and body to synthesize protein • PRL stimulates mammary glands in breast to make milk • MSH stimulates melanocytes; may increase mental alertness

  25. Hypophysis (pituitary) hormones

  26. Target organs of hypophysis

  27. From the posterior pituitary (neurohypophysis) • ADH (antidiuretic hormone = vasopressin) stimulates the kidneys to reclaim more water from the urine, raises blood pressure. • Oxytocin stimulatescontractionof smooth muscle in reproductive tracts, in females initiating labor and ejection of milk from breasts.

  28. Anterior hypophysis hormones

  29. Control of Endocrine Function • Positive • or Negative Feedback mechanisms • Self-regulating system

  30. Positive Feedback • Baby pushes on cervix • Nervous signal to Hypothalamus • Hypothalamus manufactures oxytosin • Oxytosin transported to POSTERIOR PITUITARY & released • oxytosin stimulates uterine contraction • Loop stops when baby leaves birth canal

  31. Negative Feedback • Most common control mechanism • Level of hormone in blood or body’s return to homeostasis shuts off loop at hypothalamus and pituitary

  32. Negative Feedback: Thyroid

  33. The Thyroid Gland • Anterior neck on trachea just inferior to larynx • Two lateral lobes and an isthmus • Produces hormones • Thyroid hormone: tyrosine based with 3 or 4 iodine molecules • T4 (thyroxine) and T3

  34. Some Effects of Thyroid Hormone (Thyroxine) • Increases the basal metabolic rate • The rate at which the body uses oxygen to transform nutrients (carbohydrates, fats and proteins) into energy • Affects many target cells throughout the body; some effects are • Protein synthesis • Bone growth • Neuronal maturation • Cell differentiation

  35. The Parathyroid Glands • Most people have four • On posterior surface of thyroid gland (sometimes embedded)

  36. Parathyroids(two types of cells) • Chief cells produce PTH • Parathyroid hormone (PTH) or parathormone • A small protein hormone

  37. Function of PTH • Increases blood Ca++(calcium)concentration when it gets too low • Mechanism of raising blood calcium • Stimulates osteoclasts to release more Ca++ from bone • Decreases secretion of Ca++ by kidney • Activates vitamin D, which stimulates the uptake of Ca++ from the intestine • Unwitting removal during thyroidectomy was lethal • Has opposite effect on calcium as calcitonin (which lowers Ca++ levels)

  38. The Effects of Calcitonin • Secreted from thyroid parafollicular (C) cells when blood calcium levels are high • Calcitonin lowers Ca++ by slowing the calcium-releasing activity of osteoclasts in bone and increasing calcium secretion by the kidney • Acts mostly during childhood

  39. The Pancreas Exocrine and endocrine cells • Acinar cells (forming most of the pancreas) • Exocrine function • Secrete digestive enzymes • Islet cells (of Langerhans) • Endocrine function Thepancreassecretestwohormones: • Insulin • Glucagon

  40. Insulin • Insulinis a small protein consisting of 51 amino acids. • Beta cells secrete insulin in response to a rising level of circulating glucose ("blood sugar"). • Insulin affects many organs. It stimulates skeletal muscle fibers to • take up glucose and convert it into glycogen; • take up amino acids from the blood and convert them into protein. • acts on liver cells • stimulating them to take up glucose from the blood and convert it into glycogen while • inhibiting "gluconeogenesis"; that is, the conversion of fats and proteins into glucose. • Dropsin the level of blood sugar

  41. Glucagon • Glucagon raises blood glucose levels by • stimulating the liver to metabolize glycogen into glucose molecules and • to release glucose into the blood. • stimulates adipose tissue to metabolize triglycerides into glucose and to release glucose into the blood.

  42. Diabetesmellitusanditscomplications Two types of diabetes mellitus: • Type 1 (Insulin-Dependent Diabetes Mellitus or IDDM). It is characterized by little (hypo) or no circulating insulin. • Type 2: (Non Insulin-Dependent Diabetes Mellitus (NIDDM) and adult-onset diabetes). The problem appears to be a failure to express a sufficient number of glucose transporters in the plasma membrane of their skeletal muscles.

  43. InsulinvsGlucagon

  44. Histo-anatomy of Adrenal glands • Each is really two endocrine glands • Adrenal cortex (outer) • Adrenal medulla (inner) • Unrelated chemicals but all help with extreme situations

  45. Main hormones of Adrenal Gland • Adrenal medulla • Secretes epinephrine and norepinephrine • Adrenal cortex • Secretes lipid-based steroid hormones, called “corticosteroids” – “cortico” as in “cortex” • MINERALOCORTICOIDS • Aldosterone is the main one • GLUCOCORTICOIDS • Cortisol (hydrocortisone) is the main one

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