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Chapter 7 - The Endocrine System

75 c1 steroid hormones c2 only made in a few organs

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cholesterol) (Fig. 7.5) C.1) Steroid Hormones C.2) Only made in a few organs (C.2.a) Adrenal cortex Aldosterone, cortisol, androgens (C.2.b) Gonads Estrogen, androgens, progesterone C.3) Synthesized in the smooth endoplasmic reticulum C.4) Steroids are lipophilic , so they diffuse out of the gland and into target cell very easily (C.4.a) Not stored, rather produced and secreted very quickly C.5) Not water soluble, so they are carried in the blood bound to protein carriers (e.g. albumin) (C.5.a) This protects it from enzymatic degradation and so increases the half-life of steroid hormones C.6) Carrier proteins inhibit cellular uptake (C.6.a) only unbound steroid hormone can diffuse into the target cell (C.6.b) Protein carriers obey the law of mass action (C.6.c) Only a small amount of “free” hormone is needed for physiological response C.7) Generally act on cytoplasmic or nuclear receptors (C.7.a) Genomic vs. Nongenomic effects C.8) Action of Steroid Hormones D) Amine Hormones (Fig. 7.6) D.1) Derived from one of two amino acids: (D.1.a) Tryptophan (melatonin) (D.1.b) Tyrosine (catecholamines and thryroid hormones) III) Control of Hormone Release A) Hormones can be classified by their reflex pathways A.1) In a simple reflex pathway, the response usually serves as a negative feedback signal to turn off/down the reflex A.2) Often the integrating center (i.e. endocrine cell) receives multiple input signals. B) Endocrine Cell as a Sensor B.1) In the simplest of endocrine reflexes, the endocrine cell acts as the receptor and integrating center
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(B.1.a) Parathyroid endocrine cells (Fig. 7.7) Parathryroid hormone (PTH) acts on target tissues to increase plasma Ca 2+ Monitor plasma Ca 2+ using GPCR With Ca 2+ bound, parathyroid hormone (PTH) release is inhibited Plasma Ca 2+ decreases (B.1.b) Pancreatic beta cells (Fig. 7.7) insulin C) Many Endocrine Reflexes Involve the Nervous System C.1) Stimuli integrated in the CNS influence the release of several hormones. C.2) There are two endocrine structures incorporated in the brain that release (neuro)hormones: the hypothalamus and the pituitary D) Neurohormones D.1) The nervous system produces 3 major types of neurohormones: (D.1.a) Catecholamines Produced by specialized neurons in the adrenal medulla (D.1.b)
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