Brief Endocrinology 2015. The Endocrine System Exocrine glands - transport their hormones to target tissues via ducts. Endocrine Are ductless & secrete.

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  • Brief Endocrinology2015

  • The Endocrine SystemExocrine glands - transport their hormones to target tissues via ducts.

    EndocrineAre ductless & secrete hormones into bloodstream

  • Endocrine glands: are those glands that has no ducts so called (ductless) and secret its products (Hormones) directly to the blood as the thyroid and pituitary glandsThe functions of the body are regulated by the nervous and the endocrine system. A hormone :- A hormone is a chemical messenger, secreted from endocrine glands, released directly into the blood transported by the circulation to the tissues upon which they exert their effects and exerts a regulatory effect on the body cells

  • *HormonesHormones are made by the glands cells, possibly stored, then releasedCirculate throughout the body vasculature, fluidsInfluences only specific tissues:

    target cells that have a receptor for that particular hormoneA hormone can have different effects on different target cells: depends on the receptor

  • Target CellA target cell is only a target cell if it is has a functional receptor (a protein) for the hormone. *

  • *What is a receptor?It is a protein made by the target cell (protein synthesis after gene expression)The protein is made, then inserted into plasma membrane, or found in cytoplasm or nucleoplasmThe active site on the protein fits the hormone Acts to convert the signal into a response

  • Chemical characteristics of hormones1-Proteins and Polypeptides, including hormones secreted by the anterior and posterior pituitary gland, the pancreas (insulin and glucagon), the parathyroid gland (parathyroid hormone), and many others.

    2- . Steroids hormones:-are derived mainly from cholesterol secreted by the adrenal cortex (cortisol and aldosterone), the ovaries (estrogen and progesterone), the testes (testosterone), and the placenta (estrogen and progesterone

    3-. Derivatives of the amino acid Tyrosine, secreted by the thyroid (thyroxine and triiodothyronine) and the adrenal medullae (epinephrine and norepinephrine)

  • Regulation of hormone secretion

  • *Regulation & CommunicationNervous system System of neurons transmits electrical signal to target tissue release neurotransmitters into a synapse, affecting postsynaptic cells

    Endocrine systemThe collection of endocrine glands makes up the endocrine system.Glands release hormones into the blood stream to target cells

  • Comparison between endocrine and nervous systemsNervous system wiredChemical signal at target cellRapidBrief durationEndocrine systemWirelessChemical signal at target cellSlowLong duration

  • Functional Classification of hormonesTrophic hormone: Acts on another endocrine gland to stimulate secretion of its hormone. Called trophic hormones; trophic means feed.

    For example, thyrotropin, or thyroid-stimulating hormone (TSH), stimulates the secretion of thyroid hormones. Adrenocorticotropin, or adrenocorticotropic hormone (ACTH), stimulates the adrenal cortex to secrete the hormone cortisol. Both trophic hormones are produced by the pituitary gland; in fact, many trophic hormones are secreted by the pituitary. The pituitary gland is sometimes referred to as the Master gland because its hormones regulate the activity of other endocrine glands.Nontrophic hormone: Acts on nonendocrine target tissues. For example, parathormone released from the parathyroid glands acts on bone tissue to stimulate the release of calcium into the blood. Aldosterone released from the cortical region of the adrenal glands acts on the kidney to stimulate the reabsorption of sodium into the blood.

  • Major Endocrine GlandsHypothalamusPituitary GlandThyroid GlandParathyroid GlandsThymus GlandAdrenal Glands PancreasOvariesTestesPineal Gland*

  • Major endocrine glands in the body

  • Hypothalamus is located at the base of the brain. It controls the autonomic nervous system and the endocrine systems. The hypothalamus controls the endocrine system by controlling the pituitary gland. Secretes releasing hormones to cause the pituitary to release its hormones andSecretes inhibiting hormones to turn off secretion of pituitary hormones *

  • Hypothalamus HormonesGrowth Hormone Releasing Hormone (GH-RH) stimulate GH secretionProlactin Releasing Hormone (PRL-RH) stimulate PRL secretionThyroid Stimulating Hormone Releasing Hormone (TSH-RH) stimulate TSH secretionAdrenocorticotropic Hormone Releasing Hormone (ACTH-RH) stimulate ACTH secretionMelanocyte Stimulating Hormone Releasing Hormone (MSH-RH) stimulate MSH secretionFollicle Stimulating Hormone Releasing Hormone (FSH-RH) stimulate FSH secretionLuteinizing Hormone Releasing Hormone (LH-RH) stimulate LH secretion

  • The AdenhypophysisGrowth hormone (GH) Causes the body to growProlactin (PRL): Stimulates lactation (milk production) in femalesStimulated lacrimation (desire to cry) , Decreased in adolescent males so it decreases desire to cryThyroid Stimulating Hormone (TSH): Causes the thyroid gland to release thyroid hormoneAdrenocorticotropic hormone (ACTH) :Acts on adrenal cortex to stimulate the release of cortisol ,Helps people cope with stressMelanocyte-stimulating hormone (MSH):Darkens skin pigmentationIncreases during pregnancy: Also has effects on appetite and sexual arousalFollicle-stimulating hormone (FSH) :Present in males and females, affects both, Stimulates maturation of sex cellsLuteinizing hormone (LH) :Induces ovulation in femalesInduces testosterone in males


  • *Two divisions:

    Anterior pituitary(adenohypophysis)

    Posterior pituitary(neurohypophysis)

    Sits in hypophyseal fossa: depression in sella turcica of sphenoid bone

    Pituitary secretes 9 hormonesThe Pituitary

    1. TSH2. ACTH3. FSH4. LH5. GH6. PRL7. MSH

    8. ADH (antidiuretic hormone), or vasopressin9. Oxytocin_________________________________________________________________The first four are tropic hormones, they regulate the function of other hormones________

  • Hormones secreted by the pituitary gland

  • Anterior pituitary hormonesFSH & LHGHAnterior PituitaryGonadsThyroid glandMammary glandsAdrenal cortexTSHProlactinACTH++++Most tissues+ protein synthesis; Lipolysis; & blood glucose+ T4; + T3 + thyroid growth+ milk; + breast dvlp. regulate reproductive system glucocorticoids estrogen; progeterone; + testosterone+ gametes; + ovulation; + corpus Lut.

  • The NeurohypophysisThis is a continuation of the brain; cell bodies of special neurons in the hypothalamus have axons which go to the neurohypophysis and synapse on capillaries there. Instead of releasing neurotransmitter, they release hormones. Oxytocin: Childbirth contractions, milk letdown Antidiuretic hormone (ADH)Signals kidneys to increase water reabsorption

  • Humoral StimulationSomething in the blood is being monitored. When the level of that substance is too high or low, it stimulates the release of the hormone.Examples are insulin, glucagon, parathyroid hormone, and aldosterone. When you eat, glucose gets high, releases insulin, which tells cells to take in the sugar. Excess sugar is then converted to glycogen, which is the storage form.When glucose is low, glucagon is released, glycogen is broken back down to glucose and released into the blood.When blood calcium is low, parathyroid gland hormone tells the intestinal cells to absorb more calcium, and kidneys to reabsorb more Ca++, and stimulates osteoclasts to degrade bone matrix so calcium goes into blood.


  • Neuronal StimulationExamples are oxytocin, ADH (neurohypophysis hormones) and Epinephrine (adrenal medulla hormone)*Hormonal Stimulation This is when one endocrine gland releases a hormone that stimulates another endocrine gland to release its hormone.Examples are any of the hypothalamus or anterior pituitary hormones, and also the adrenal cortex (steroid) hormones (except aldosterone) and thyroid hormone.

  • Hormonal regulation of hormone secretion

  • Short feedback loop:Retrograde transport of blood from anterior pituitary to the hypothalamus.Hormone released by gonads (estrogen) inhibits anterior pituitary hormone FSH.

    Long feedback loopHormone released by gonads (Testosteronee) inhibits anterior hypothalamic hormone as GnRHNegative feed back: a hormone from a peripheral gland, for example, testosterone binds to its receptor on cells in the hypothalamus and pituitary gland, and inhibit the secretion of the tropic hormones: FSH

  • Positive feed back: a hormone from a peripheral gland, for example, estrogen, binds to its receptor on cells in the hypothalamus and adenohypophysis, and has the effect of increasing secretion of tropic hormones LH



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