Introduction To The Endocrine System

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Introduction To The Endocrine System

• Chemical Messengers

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Hormones

• 1. Control rates of enzymatic reactions
• 2. Control transport of molecules across cell
  membranes
• 3. Control gene expression and the synthesis of
  proteins

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Hormones

• Exerts effect at a very low concentration

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Classification

• 1. Peptide hormones

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Ca-dependent Exocytosis
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Peptide Hormone

• Water soluble Dissolve in the ECF
• Relatively short half-life regulated by rate of
  secretion
• Lipophobic work through hormone-receptor
  complexes via signal transduction and cAMP second
  messengers
• Open/close channels, modulating metabolic
  enzymes, transport proteins

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Classification

• 2. Steroid hormones

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Steroid Hormones

• All have similar structures because they are all
  derived from cholesterol
• Organs that synthesize steroid hormones
• Adrenal cortex
• Gonads
• Placenta

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Steroid Hormones

• Synthesized in smooth ER
• Diffuse easily through membranes, into and out of
  cells
• Found bound to protein carrier molecules in the
  blood
• Steroid-secreting cells cannot store hormones in
  secretory vesicles, therefore, regulation is at
  the level of synthesis

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Classification

• 3. Amine
• 3 Groups of amine hormones
• Created from a single amino acid

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Amine

• 1.)Melatonin derived from tryptophan
• 2.)Catecholamines derived from tyrosine
• Neurohormones Epinephrine, norepinephrine,
  dopamine
• Membrane receptors like peptide hormones
• 3.)Thyroid derived from tyrosine
• Intracellular receptors that activate genes

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Definition -trophic

• Any hormone that controls the secretion of
  another hormone is known as a trophic hormone
• -tropin

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Definition Synergism

• Two hormones act at their target so that the
  combination is more than additive

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Definition Permissiveness

• One hormone cannot fully exert its effects unless
  a second hormone is present

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Definition Antagonism

• Two molecules work against each other, one
  diminishing the effectiveness of the other
• Tendency of one substance to oppose the action of
  the other

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Endocrine Antagonists

• Opposing physiological actions
• Dont necessarily have to work through the same
  receptor via competitive inhibition
• May act through opposing metabolic pathways

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Examples

• Parathyroid hormone increases blood calcium
  levels, whereas calcitonin decreases blood
  calcium levels
• Glucagon increases blood glucose levels, whereas
  insulin decreases blood glucose levels

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HypothalamusPituitary Gland

• Animations
• 10.16
• 10.17
• 10.18

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Hypothalamic-Hypophyseal Portal System

• Hypothalamic neurohormones act on the anterior
  pituitary gland to stimulate or inhibit the
  synthesis and release of hormones produced in the
  endocrine cells of the anterior pituitary
• Hypothalamic Trophic hormones

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Hypothalamic pituitary portal system

• Hormone secreting cells in the anterior pituitary
  are the target cells for tropic hormones from the
  hypothalamus
• Hypothalamus releases a tropic hormone that
  effects the release of another tropic hormone
  from the anterior pituitary
• This tropic hormone effect the release of a third
  hormone from another endocrine gland, and this
  hormone exerts effects on target cells of the body

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Anterior PituitaryAdenohypophysis

• Prolactin Milk Production and immune system
  (non-endocrine target)
• Somatotropin (growth hormone) metabolism
• Gonadotropins
• Follicle-stimulating hormone (FSH)
• Luteinizing hormone (LH)
• Thyroid-stimulating hormone (TSH thyrotropin)
• Adrenocorticotrophic hormone (ACTH
  corticotropin) Adrenal cortex-cortisol

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Posterior PituitaryNeurohypophysis

• Storage and release for 2 neurohormones
  synthesized in neurons in the hypothalamus
• 1. Vasopressin (antidiuretic hormone ADH)
  Water balance
• 2. Oxytocin milk ejection during breastfeeding
  and uterine contraction

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Overview

• Hypothalamus and Pituitary Function
• Animation 10.25

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Thyroid Glands

• Tetraiodothyronine (T4)
• Triiodothyronine (T3)
• T3 and T4 regulate the bodys metabolic rate and
  are necessary for normal growth and development
• Calcitonin Regulates calcium levels in the blood

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Parathyroid Glands

• Four
• Posterior surface of the thyroid
• Secrete Parathyroid hormone (PTH), an important
  regulator of calcium levels in the blood

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Thymus

• Lies close to the heart
• Secretes thymosin
• Critical for T-cell maturation and function

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Adrenal Glands

• Animations
• 10.37
• 10.38
• 10.39

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Adrenal Glands

• Adrenal cortex 80 of the glands total mass
• Secretes adrenocorticoids
• Mineralocorticoids Aldosteroneregulates sodium
  reabsorption and potassium excretion by the
  kidneys
• Glucocorticoids Cortisolregulates the bodys
  response to stress protein, carbohydrate and
  lipid metabolism blood glucose
• Sex hormones Androgensregulate reproductive
  function

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Adrenal Glands

• Adrenal Medulla 20 total mass
• Contains chromaffin cells and secretes
  catecholamines
• 80 of the secreted hormones is epinephrine
• 20 is norepinephrine
• lt1 is dopamine

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Pancreas

• Endocrine and Exocrine functions
• Exocrine pancreas acinar cells and duct cells
  that secrete enzymes and fluid into the digestive
  tract
• Endocrine pancreas islets of Langerhans
• b cells secrete insulin
• cells secrete glucagon
• d cells secrete somatostatin
• F cells secrete pancreatic polypeptide

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Secondary Endocrine Organs

• Heart Atrial natriuretic peptide (ANP) which
  regulates sodium reabsorption
• Kidneys Erythropoietin which stimulates RBC
  production
• Digestive organs Secrete several hormones
  important in digestive and absorptive processes
• Liver insulin-like growth factors which promote
  tissue growth
• Skin calcitrol (vitamin D3) which regulates
  blood calcium levels

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REVIEW

• Figure 7-2
• Table 7-1
• INTERACTIVE PHYSIOLOGY ENDOCRINE SYSTEM