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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Classification

• 1. Peptide hormones

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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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Figure 7-3 - Overview
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Figure 7-5
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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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Figure 7-6
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Figure 7-7 - Overview
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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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Figure 7-8
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Figure 7-22 Overview (1 of 4)
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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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Figure 23-7a
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Figure 23-7b
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Thyroid Glands

• Thyroid hormones
• Derived from tyrosine, contain iodine
• Tetraiodothyronine (T4)
• Triiodothyronine (T3)
• C cells of thyroid gland secrete Calcitonin

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Figure 23-8
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Figure 23-9 Overview
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Table 23-2
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Thyroid Disorders

• Hyperthyroidism
• Increases oxygen consumption and metabolic heat
  production. Patients have warm, sweaty skin, and
  complain of heat intolerance.
• Excess TH increases protein catabolism and may
  cause muscle weakness. Patients report weight
  loss.
• Nervous system effects hyperexcitable reflexes
  and psychological disturbances ranging from
  irritability and insomnia to psychosis.
• Affect beta adrenergic receptors causing rapid
  HR, increased force of contraction due to
  upregulation of beta 1 adrenergic receptors on
  myocardium.

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Thyroid Disorders

• Hypothyroidism
• Slows metabolic rate and oxygen consumption.
  Patients are intolerant of cold because they are
  generating less heat.
• Decreases protein synthesis. In adults, it
  causes brittle nails, thinning hair, dry and thin
  skin. Causes accumulation of mucopolysaccharides
  under the skin, which attract water and cause a
  puffy appearance of myxedema. Children have slow
  bone and tissue growth and are short for their
  age.
• Nervous system slowed reflexes, slow speech and
  thought processes, feeling of fatigue.
• Bradycardia

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Table 23-7
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Parathyroid Glands

• Four
• Secrete Parathyroid hormone (PTH parathormone)

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Figure 23-22
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Table 23-5
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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
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Adrenal Cortex

• Adrenal cortex 80 of the glands total mass
• Secretes adrenocorticoids
• 1.) Mineralocorticoids Aldosteroneregulates
  sodium reabsorption and potassium excretion by
  the kidneys

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Adrenal Cortex (cont.)

• 2.) Glucocorticoids Cortisol
• Promotes gluconeogenesis in the liverincreases
  blood glucose concentrations
• Skeletal muscle protein catabolism to provide a
  substrate for gluconeogenesis
• Enhances lipolysis so that fatty acids are
  available to peripheral tissues for energy use.
  Glycerol from fatty acids can be used for
  gluconeogenesis
• Suppresses the immune system
• Causes negative calcium balance decreases
  intestinal calcium absorption and increases renal
  calcium excretion, resulting in net loss of
  calcium from the body. Catabolic in bone tissue,
  causes breakdown of calcified bone matrix.
• States of cortisol excess or deficiency cause
  mood changese and memory and learning
  alterations.
• Used as an immunosuppressant poison ivy, bee
  stings, pollen allergies, transplantation
  rejection

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Cortisol Pathologies

• Hypocortisolism Addisons disease
• Hyposecretion of adrenal steroid hormones,
  usually following autoimmune destruction of the
  adrenal cortex.
• Hypercortisolism Cushings syndrome
• Hyperglycemia
• Muscle protein breakdown and lipolysis, cause
  tissue wasting

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Adrenal Cortex (cont.)

• 3.) 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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Figure 11-10 - Overview
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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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Table 22-3
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Figure 22-11 - Overview
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Table 22-5
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Diabetes Review Article

• Posted online

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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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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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Figure 7-18
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Definition Permissiveness

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

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Example

• Thyroid hormone alone No development of
  reproductive system.
• Reproductive hormones alone Delayed development
  of reproductive system
• Reproductive hormones with adequate thyroid
  hormone Normal development of reproductive
  system

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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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Figure 22-14
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Figure 22-15
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REVIEW

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