Endrocrine System Basic Medical Science I

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ENDOCRINE SYSTEM Part I Prepared and Presented by: Marc Imhotep Cray, M.D.:

ENDOCRINE SYSTEM Part I Prepared and Presented by: Marc Imhotep Cray, M.D. Reference Resource: Textbook in Medical Physiology and Pathophysiology Essentials and Clinical Problems Endrocrine Glands in Humans Drag/Drop Hormone Match ZeroBio 1

Target Cell Receptors at Three Locations :

Target Cell Receptors at Three Locations 2

SIGNAL TRANSDUCTION See: G-protein Signal Transduction Video:

SIGNAL TRANSDUCTION See: G-protein Signal Transduction Video 3

EXAMPLE: subdivisions of the adrenal gland:

EXAMPLE: subdivisions of the adrenal gland 4

Endocrine System:

Endocrine System Communication system Allows for cells in distant parts of body to communicate Communication generally slower in onset, but longer in duration, compared to nervous system communication Consists of all the organs that secrete hormones (endocrine organs) 5


Hormones Chemical Messengers Produced by an endocrine gland Released into and carried via bloodstream to target tissues Target tissues = tissue bearing receptors that can bind and physiologically respond to the chemical messenger in question Amount of chemical messenger produced and released into circulation is generally very small 6

Peptide Hormones:

Peptide Hormones Majority of hormones are proteins/peptides Preprohormones prohormones active form Bind to receptors located on the plasma membrane ( surface receptors ) Responses generally occur very rapidly and are short-lived, compared to steroid hormone responses 7

PowerPoint Presentation:

Cell Surface Receptors G-protein coupled receptors Enzyme receptors Receptors associated with ion channels 8

PowerPoint Presentation:

G-Protein Coupled Receptors Animation: G-protein Signal Transduction Hormone binds to extracellular site on receptor On cytoplasmic side, receptor is associated with inhibitory or stimulatory G-Proteins (guanine-binding) Hormone binding on extracellular side activates intracellular G-proteins Activated G-Proteins interacts with effector proteins (ion channels and enzymes) to elicit physiological response 9

G-Protein Coupled Receptors:

G-Protein Coupled Receptors 10

PowerPoint Presentation:

Enzyme Receptors Hormone binds to extracellular portion of receptor Site on cytoplasmic portion of receptor has enzymatic activity that is activated by hormone binding on the extracellular side Altered enzyme activity leads to chain of reactions that produce physiological response 11

Enzyme Receptors (animation):

Enzyme Receptors (animation) 12

PowerPoint Presentation:

Receptors Possessing Ion Channels Hormone binds to site on extracellular part of receptor Receptor itself also functions as ion channel Binding of hormone to extracellular portion of the receptor causes change in shape of receptor that alters open/closed ion channel status 13

Receptors Possessing Ion Channels:

Receptors Possessing Ion Channels 14

Steroid Hormones:

Steroid Hormones Modified Cholesterol Derivatives Cholesterol = precursor for their production Have fused ring structures Are lipid soluble Readily dissolve in and pass through plasma membrane Bind to cytoplasmic or nuclear receptors Alter gene transcription/protein production Physiologic effects occur more slowly but last longer than peptide hormone responses 15

Steroid Hormone Production:

Adrenal glands: aldosterone, cortisol, and androgens Kidneys: 1,25-dihydroxyvitamin D 3 Gonads Ovaries: progesterone and estrogens Testes: androgens (testosterone) See Animation: Biochemistry of Cholesterol by Rodney F. Boyer Steroid Hormone Production 16

Amine Hormones:

Amine Hormones Amino acid (tyrosine) derivatives Includes: T3 (triiodothyronine)and T4 (thyroxine) = thyroid hormones Catecholamines Epinephrine & norepinephrine = adrenal (medulla) hormones important in stress response Dopamine (hypothalamic hormone) Animation: Adrenaline Action University of Washington 17

Neurons vs Endocrine Cells:

Neurons vs Endocrine Cells Neurons Respond to environ- mental changes by production and transmission of electrical signals stimulate effector cells via NT release into the synapse Endocrine Cells Respond to environ- mental changes by production of hormones Stimulate effector cells via hormone release into the bloodstream 18

Neuroendocrine Cells:

Neuroendocrine Cells Cells with properties of both neurons and endocrine cells Specialized neurons that, when stimulated, produce chemical messengers (hormones) that are released into the circulatory system Represent the site of functional overlap of the neural and endocrine system 19

Coitus-Induced Ovulation:

Coitus-Induced Ovulation Neuroendocrine Reflex Occurs in rabbits, cats, ferrets, camel, llama Ovulation is triggered by mating - does not occur in the absence of mating Neural signals initiated by mating alter reproductive hormones to trigger ovulation 20

Prolactin and Oxytocin:

Prolactin and Oxytocin Prolactin = hormone from the anterior pituitary that plays a role in milk formation Oxytocin = hormone from the posterior pituitary that plays a role in milk release and uterine contraction 21

Milk Let-Down Reflex:

Milk Let-Down Reflex Suckling of newborn produces neural signals that stimulate neurons in hypothalamus to secrete oxytocin Oxytocin produces contraction of smooth muscle in the mammary glands the moves milk through ducts and expels it from the nipple, thus promotes milk release Mental stimuli can also produce neural signals that cause same response Lactating women can experience milk let-down in response to crying baby 22

Hypothalamic-Pituitary Axis:

Hypothalamic-Pituitary Axis Hypothalamus Region of brain (diencephalon) Lies below third ventricle at base of brain Important regulator of endocrine action Pituitary Gland (hypophysis) Endocrine gland connected to hypothalamus by infundibulum (stalk containing nerves and small blood vessels) 23

Link to next lecture ENDOCRINE SYSTEM Part II:

Link to next lecture ENDOCRINE SYSTEM Part II 24

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