BS2001 Lecture 2 Notes: Endocrine System I
BS2001 Lecture 2 Notes: Endocrine System I BS2001
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This 4 page Class Notes was uploaded by Loges Gobi on Wednesday October 7, 2015. The Class Notes belongs to BS2001 at Nanyang Technological University taught by Valerie Lin in Summer 2015. Since its upload, it has received 72 views. For similar materials see Physiology in Biological Sciences at Nanyang Technological University.
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Date Created: 10/07/15
BSZOOl LECTURE 2 NOTES ENDOCRINE SYSTEM I Endocrine system consists of ductless endocrine glands that secrete hormones Specialized glands thyroid gland adrenal glands etc Endocrine cells in tissue hypothalamus adipose tissue leptin Hormones Peptides gt TRH vasopressin insulin growth hormone glycoproteins FSH and LH Amines gt derived from tyrosine Steroids gt hydrophobic hormones derived from cholesterol Effects of hormones mediated by specific hormone receptors in cell Location of hormone receptor depends on chemical nature of hormone gt Receptors for hydrophilic hormones are on cell surface membrane gt Gprotein linked activates second messenger pathway or ion channels Ionchannel linked mostly for neuropeptide hormones and Enzymelinked most are protein kinases gt Receptors for hydrophobic hormones are intacellular gt mainly mediated by nuclear receptors except for glucocorticoid receptor Regulation of endocrine function 1 Hormone secretion Respond to changes in internal and external envt Negative and positive feedback and feedfoward Neuroendocrine re exes secretion of epinephrine by adrenal medulla is under control of sympathetic nervous system Diurnal rhythms gt pertaining to daylight hours cortisol secretion 2 Tissue sensitivity Tissue receptors Transcription cofactors 3 Hormone binding to plasma proteins metabolism and excretion Endocrine disorders mostly result from hyposecretion or hypersecretion of a hormone Hyposecretion heredity dietary deficiency immunologic factors causes can be primary or secondary due to deficiency of another hormone can be treated by Hormone Replacement Therapy Hypersecretion due to tumors of the endocrine gland immunologic factors cause can be primary or secondary Lack of tissue response endocrine dysfunction arise from unresponsiveness of a target cells to a hormone type II diabetes Central endocrine glands 1 Hypothalamus and the anterior pituitary gland Hypothalamus forms lower lateral walls and oor of the third ventricle Pituitary gland attaches to hypothalamus via infundibulum gt structurally and functionally divided into anterior and posterior lobe gt anterior lobe adenohypophysis consists of glandular tissue whilst posterior lobe neurohypophysis consists of neural tissue Anterior pituitary hormones TROPHIC HORMONES target other endocrine glands gt Adrenocorticotropic hormone ACTH stimulate adrenal cortex to produce corticosteroids Thyroidstimulating hormone TSH stimulates thyroid to produce thyroxine Luteinizing hormone LH needed for ovulation formation of corpus luteum stimulates testes to produce testosterone Folliclestimulating hormone FSH required for development of ovarian follicles and for sperm development Prolactin induces lobuloalveolar growth of mammary gland and stimulates lactogenesis Growth hormone promote growth of tissues and essential for metabolic regulation Hypothalamus neurons secrete releasing and inhibiting hormones that regulate secretions of anterior pituitary hormones gt hypothalamic hormones transported to AP via hypothalamichypophyseal portal system blood vessels connecting capillaries in the hypothalamus with capillaries in the AP Thyrotropinreleasing hormone TRH stimulate TSH release Corticotropinreleasing hormone CRH stimulate ACTH release Gonadotropinreleasing hormone GRH stimulate FSH and LH Growth hormonereleasing hormone GHRH stimulate GH release Growth hormoneinhibiting hormone GHIHsomatostatin inhibit GH release Prolactinreleasing hormone PRH stimulates prolactin release Prolactininhibiting hormone PIH dopamine Hypothalamuspituitaryadrenalgonadalthyroid axis gt negative feedback through which the hormone from target gland can act on the hypothalamus and the AP to inhibit the secretion of releasing and stimulating hormoes Growth hormone AP gt growth effects indirectly via insulinlike growth factor 1 IGF 1 gt stimulates liver and other tissues to secrete IGF1 gt IGF1 stimulates growth of soft tissues and lengthening and thickening of bones gt metabolic effects increases protein synthesis maintains blood glucose level by decreasing uptake of glucose in peripheral tissues and enhance glucose synthesis in liver mobilizes fat store as energy by stimulating triglyceride breakdown and oxidation in adipocytes VVV VV VV V VVVV Growth hormone is critical for bone growth V VVVV Control of GH secretion Osteoblasts bone formation Osteoclasts bone remodeling Chondrocytes cartilage cells Matrix consists of collagen fibers calcium phosphate crystals and nerves and blood vessels Growth in length GH stimulates osteoblast activity and proliferation of chondrocytes resulting in lengthening of epiphyseal plates osteoblast deposit collagen gt attracts calcium phosphate crystals gt calcification gt hard bone Growth in width coordinated activity of osteoblast and osteoclast stimulated by GH gt deposition on outer resoprtion on inner surfaces Secretion of GH is highest during sleep and decrease during wakefulness Exercise high amino acids low fatty acids and low glucose increase GH secretion GH deficiency dwarfism GH excess gigantism and acromegaly Other hormones besides GH essential for growth gt gt Thyroid hormonepermissive role effect of GH manifest only when sufficient thyroid hormone is present Insulin structurally related to IGF and also promote protein synthesis gt Androgen play important role in prepubertal growth spurt and stimulate protein synthesis gt role depends on presence of GH responsible for men s musculature development and promotes ossification of epiphyseal plate Estrogen prepubertal growth spurt adult level stimulates ossification of epiphyseal plate so as to stop bone lengthening 2 Posterior pituitary gland Anatomical and functional extension of hypothalamus Stores and release vasopressin and oxytocin that are produced by hypothalamus both hormones remarkably similar in sequence Antidiuretic hormone ADHVasopressin gt V VV V Promotes water retention by stimulating insertion of aquaporins into membranes of kidney tubules High concentrations causes contraction of arteriolar smooth muscle vasoconstriction Mission is to maintain blood osmolarity and volume Major stimulus is increase in plasma osmolarity detected by osmoreceptors in hypothalamus Decrease in blood volume and pressure detected by left atrial volume receptor Oxytocin gt Stimulates contractions of uterus during labour gt labour initiated when oxytocin receptor concentration reaches a critical threshold gt Stimulates contractions of the myoepithelial cells surrounding mammary alveoli to facilitate milkejection gt Oxytocin receptor is G proteinlinked receptor 3 Pineal gland Tiny pine cone shaped structure in centre of brain Secretes melatonin derived from tryptophan which increases with darkness and peaks after middle night Secretion controlled by the suprachiasmatic nucleus SCN of hypothalamus master pacemaker of circadian rhythym gt special type of retinal ganglion cells RGC detect light gt melanopsin in RGCs believed to be circadian photopigment gt when melanopsin activated in response to light it triggers action potential that is transmitted as nerve impulse to SCN which regulates melatonin secretion