AVS 271 Anatomy and Physiology

1
AVS 271 Anatomy and Physiology

• Handout 14
• October 13, 2008
• Endocrinology
• Chapter 12

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Endocrine System

• Consists of the ductless glands that
  secrete hormones (classical type)

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Hormone Structure and Synthesis

• Three main chemical classes of hormones
  (classical)
• Amines
• Peptides and proteins (glycoproteins)
• Steroids

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Amine Hormones

• They are all derivatives of the amino acid
  tyrosine
• Thyroid hormones
• Thyroxine (T4)
• Triiodothyronine (T3)
• Biogenic amines (Catecholamines)
• Epinephrine and norepinephrine
• Adrenal medulla and synapses of sympathetic
  neurons
• Dopamine
• Hypothalamus

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Peptide and Protein Hormones

• Range in size from lt 10 amino acids to gt
  200 amino acids
• Many are glycoproteins (usually large
  proteins)
• Synthesis
• Preprohormone synthesized in the rough ER
• Cleaved to create a prohormone in the ER
• Prohormone packaged into secretory vesicles
  by the Golgi apparatus
• Cleaved to create the active hormone at
  this time

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Peptide / Protein Hormone Synthesis
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Steroid Hormones

• Cholesterol is the precursor of all steroid
  hormones
• Adrenal cortex
• Aldosterone
• Cortisol
• Corticosterone
• Gonadal steroids
• Estradiol
• Progesterone
• Testosterone

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Hormone Transport in the Blood

• Protein (peptide) and catecholamine hormones
  are water soluble and are transported
  dissolved in the blood plasma
• Steroid and thyroid hormones are transported
  bound to plasma proteins
• The total hormone concentration in the
  plasma is the sum of the free and bound
  hormone
• Only the free hormone is able to diffuse
  out of the plasma and interact with its
  target tissue

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Hormone Metabolism and Excretion
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Control of Hormone Secretion

• Most hormones are released only in short
  bursts, with little or no secretion
  occurring between bursts
• Secretion is controlled by
• Changes in plasma concentrations of mineral
  ions (eg., sodium) or organic nutrients
  (eg., glucose)
• Neurotransmitters released from neurons
  impinging upon endocrine cells
• Another hormone acting upon endocrine cells

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