The Endocrine System Nervous system short term/ fast Endocrine - PDF document

HIHIM 409 Interrelationship between nervous and endocrine system The Endocrine System • Nervous system – short term/ fast • Endocrine system – long term/slow l / l http://www.youtube.com/watch?v=Ry5fTZfZHIs&feature=related http://www.youtube.com/watch?v=uj_KIhkOcGY&NR=1 HIHIM 409 Interrelationship between nervous and Differences between systems endocrine system • Endocrine system good for gradual changes • Nervous system – Embryological changes – short term/ fast – Puberty – Menstrual cycle • Endocrine system – Water balance – long term/slow l / l • Nervous system good for split second decisions – Interpreting sight and sound – Muscles to move you out of danger – memory Hormone effects • Hormone 1. Stimulate synthesis of enzymes or structural – Chemical messenger made in one place, proteins transported by blood, to have action in another 2. Increase or decrease rate of synthesis place 3. Turn existing enzyme or membrane channel 3 i i b h l • Target cell “ on ” or “ off ” – Cell where hormone has effect must have receptor for the hormone – Only cells with appropriate receptor responds to hormone 1

HIHIM 409 Similarities Endocrine vs. Exocrine Cells • Are similarly organized: • Endocrine – rely on release of chemicals – Glandular secretory cells that release their secretions into extracellular fluid – share many chemical messengers – ductless ductless – are regulated primarily by negative feedback are regulated primarily by negative feedback • Exocrine – share a common goal: to preserve homeostasis – Secrete their products onto epithelial surfaces – ducted Hormones • Can be divided into 3 groups: 1. amino acid derivatives 2. peptide hormones 3 3. lipid derivatives (steroid hormones) lipid derivatives (steroid hormones) Figure 18– 1 Figure 18– 2 2

HIHIM 409 Amino Acid Derivatives Tyrosine Derivatives • Small molecules structurally related to amino • Thyroid hormones acids • Compounds: • Synthesized from the amino acids tyrosine and tryptophan tryptophan – epinephrine (E) epinephrine (E) – norepinephrine (NE) – dopamine, also called catecholamines Do not memorize Tryptophan Derivative Peptide Hormones • Melatonin: • Chains of amino acids – produced by pineal gland • Synthesized as prohormones: – inactive molecules converted to active hormones before or after secretion before or after secretion Do not memorize 3

HIHIM 409 2 Classes of Lipid Derivatives Eicosanoids • Eicosanoids: • Are small molecules with five ‐ carbon ring at one end – derived from arachidonic acid • Steroid hormones: • Are important paracrine factors – derived from cholesterol d i d f h l l • Coordinate cellular activities di ll l i i i • Affect enzymatic processes in extracellular fluids Do not memorize Do not memorize Leukotrienes Prostaglandins • Are eicosanoids released by activated white • A second group of eicosanoids produced in blood cells, or leukocytes most tissues of body • Important in coordinating tissue responses to • Are involved in coordinating local cellular g injury or disease injury or disease activities • SINGULAIR is a different way to treat seasonal allergies because it blocks leukotrienes instead of blocking histamine Do not memorize Do not memorize Steroid Hormones Steroid Hormones • Are lipids structurally similar to cholesterol • Remain in circulation longer than peptide • Hormones differ in side chains hormones • Released by: • Are absorbed gradually by liver – reproductive organs (androgens by testes, reproductive organs (androgens by testes • Are converted to soluble form d l bl f estrogens, and progestins by ovaries) • Are excreted in bile or urine – adrenal glands (corticosteroids) – kidneys (calcitriol) 4

HIHIM 409 Free Hormones Secretion and Distribution of Hormones • Typically released into capillary bed for fast • Remain functional for less than 1 hour: uptake and distribution – diffuse out of bloodstream: • bind to receptors on target cells • Circulate freely or bound to transport proteins – are absorbed: are absorbed: • broken down by cells of liver or kidney – are broken down by enzymes: • in plasma or interstitial fluids Thyroid and Steroid Hormones Mechanisms of Hormone Action • Remain in circulation much longer • Hormone Receptor • Enter bloodstream: – Is a protein molecule to which a particular molecule binds strongly – more than 99% become attached to special – Each cell has receptors to respond to several transport proteins p p different hormones • Free and bound hormone state – Different tissues have different combinations of – As free removed, bound is released receptors – Blood contains substantial reserve of bound – Presence or absence of specific receptor hormones determines hormonal sensitivity Location of Receptor • Depends on type of hormone • Cell membrane receptors – Generally water soluble hormones • Intracellular receptors – Generally lipid soluble hormones Figure 18– 4a 5

HIHIM 409 Endocrine Reflexes Endocrine Reflex Triggers 1. Humoral stimuli: • Functional counterparts of neural reflexes – changes in composition of extracellular fluid • In most cases, controlled by negative feedback 2. Hormonal stimuli: mechanisms – arrival or removal of specific hormone arrival or removal of specific hormone 3. Neural stimuli: – arrival of neurotransmitters at neuroglandular junctions Negative feedback Simple Endocrine Reflex • Involves only 1 hormone • Endocrine cells respond directly to changes in extracellular fluid • Secreted hormone adjusts activities of target cell to restore homeostasis restore homeostasis • For example: – heart – pancreas – parathyroid gland – digestive tract Complex Endocrine Reflex Pulses • Involves: • Hypothalamic and pituitary hormones released in sudden bursts – 1 or more intermediary steps – 2 or more hormones • Frequency varies response of target cells 6

HIHIM 409 Hypothalamus and Pituitary Gland • Pituitary gland (or hypophysis) was thought to be “ master gland ” • Now we know it is controlled by N k it i t ll d b hypothalamus Figure 18– 1 Hypothalamus Hypothalamus and Pituitary Gland • http://www.youtube.com/watch?v=Vae5CcaPN_8&feature=related • Integrates activities of nervous and endocrine systems in 3 ways: 1. Secretes regulatory hormones: – special hormones control endocrine cells in i l h t l d i ll i anterior pituitary gland – Hormones of anterior pituitary control endocrine cells in thyroid, adrenal cortex and reproductive organs Hypothalamus Hypothalamus 2. Acts as an endocrine organ Hormones of posterior pituitary made by • hypothalamus 3 3. Contains autonomic centers: Contains autonomic centers: – exert direct neural control over endocrine cells of adrenal medullae Figure 18– 5 7

HIHIM 409 Pituitary Gland Figure 18– 6 Pituitary Gland Pituitary Gland • Also called hypophysis • Releases 9 important peptide hormones • Lies within sella turcica • Hormones bind to membrane receptors • Hangs inferior to hypothalamus: – connected by infundibulum • Divided into anterior and posterior lobe based on function and developmental anatomy Anterior Lobe Anterior Lobe • Also called adenohypophysis • Hypophyseal portal system – Usual circulatory arrangement is heart, artery, capillary bed, vein and back to heart p y , – Portal system has 2 capillary beds heart, artery, capillary bed, portal veins, 2 nd – capillary bed , vein and back to heart Figure 18– 6 8

HIHIM 409 2 Classes of Hypothalamic Regulatory Hormones 1. Releasing hormones Stimulates synthesis and secretion of hormone • from anterior lobe 2 2 2. Inhibiting hormones Inhibiting hormones Inhibits synthesis and secretion of hormone • from anterior lobe Figure 18– 7 Hormones of the Anterior Lobe of the Pituitary • 7 hormones • Endocrine cell in anterior pituitary may be – TSH –Thyroid Releasing Hormon controlled by one or the other or both – ACTH – Adreoncorticotrophic Hormone • Releasing and inhibiting hormones – FSH – Follicle Stimulating Hormone transported directly to anterior pituitary by p y p y y – LH – Lutienizing Hormone g hypophyseal portal system – PRL – Prolactin Releasing Hormone – GH – Growth Hormone • Rate of secretion is controlled by negative – MSH – Melanocyte Stimulating Hormone feedback • Aka tropic or trophic hormones because they turn on or support other endocrine glands Thyroid ‐ Stimulating Hormone (TSH) • Also called thyrotropin • Triggers release of thyroid hormones • Released in response to Thyrotropin ‐ releasing hormone from hypothalamus h f h h l • Negative feedback – As thyroid hormone rises, TSH and TRH decline Figure 18– 8a 9