Essay about Endocrine System

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MLT 116
Mader Chapter 10: The Endocrine System

I. Introduction Endocrine system = endocrine glands & their hormones Hormones = chemical messengers; released directly into bloodstream (or extracellular fluid) ( target tissue ( effect Response is slower & longer lasting than nervous system Endocrinology = study of endocrine glands & their hormones

A. Hormone action Two basic types hormones: 1. peptides: amino acids, polypeptides, proteins Ex: T4, FSH, LH peptide hormones involve 2-messenger system hormone binds to plasma membrane receptor ( activates cAMP (uses ATP) ( activates enzymes within cell ( effect

2. steroids: lipid soluble Ex: estrogen, testosterone steroid hormones pass thru plasma membrane ( affects protein synthesis at DNA level in nucleus built from cholesterol backbone

B. Endocrine glands = ductless glands; secrete product (hormone) directly into bloodstream ( specific target tissue

Effects of hormones: Fluid, electrolyte, acid-base balance Metabolic rate Sex characteristics Growth & development Stimulate/inhibit other hormones

Many hormones regulated by negative feedback: high amount hormone turns off release Involves hypothalamus ( anterior pituitary ( specific endocrine gland

II. Hypothalamus & pituitary

A. Hypothalamus (within brain): produces “releasing hormones” ( tell anterior pituitary to release stimulating (tropic) hormones Hypothal also releases inhibitory hormones

Generic feedback loop:

RH SH effector hormone Hypothal --------( AP ----------( specific gland -------------------( target tissue

Neg feedback

AP = anterior pituitary RH = releasing hormone SH = stimulating (tropic) hormone

In words: The hypothalamus produces a releasing hormone, which tells the anterior pituitary to release a stimulating (tropic) hormone. The stimulating hormone goes to a specific endocrine gland and tells the gland to produce its “effector” hormone. The effector hormone goes to its target tissue and has the desired effect. When there is plenty of effector hormone, it turns off the production of SH from the AP, thus regulating the entire pathway like a thermostat. (We will look at specific examples later)

B. Pituitary gland: divided into anterior & posterior; located below hypothalamus Hypothalamus & pituitary connected by pituitary stalk = infundibulum

1. Posterior pituitary: releases hormones made in hypothalamus( stored in/released from post pit a. antidiuretic hormone (ADH, vasopressin): controls/promotes water reabsorption in kidney

body dehydrated ( signals ADH release ( tells kidney to keep water in body/excrete small amount concentrated urine

body well-hydrated ( suppresses ADH ( excrete large amount dilute urine beer & caffeine suppress ADH!

Diabetes insipidus = decreased ADH ( patient excretes large amounts of very dilute urine (Note: this “diabetes” is not related to diabetes mellitus/has nothing to do with glucose)

b. oxytocin ( uterine contractions during labor & milk release (with prolactin from AP) also affects prostate gland/plays role in ejaculation

2. Anterior pituitary (AP) = “master control gland” Produces stimulating (tropic) hormones ( tells specific endocrine gland to produce effector hormone

a. Tropic(stimulating) hormones from AP Hormone Target gland Effect 1. TSH thyroid T4/T3 release 2. ACTH adrenal cortex cortisol release 3. FSH ovaries follicle growth/estrogen release testes sperm production 4. LH ovaries
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