ENDOCRINE SYSTEM

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ENDOCRINE SYSTEM
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TYPES OF GLANDS

• Endocrine
• Exocrine

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Endocrine glands Endocrine tissue

• Pineal gland
• Pituitary gland
• Thyroid gland
• Parathyroid glands
• Thymus
• Adrenal gland
• Pancreas
• Ovaries / Testes

• Stomach
• Duodenum
• Kidney

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Chemistry of Hormones

• Amines - simple hormones synthesized from
  tyrosine
• Proteins and Peptides - chains of amino acids
  hooked together
• Steroids - lipid soluble hormones derived from
  cholesterol
• Eicosanoids - hormones derived from arachidonic
  acid (from lipids)

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Mechanisms of Hormone Action

• Alters plasma membran permeability
• Stimulates synthesis of protein
• Activates or deactivates enzymes
• Induces secretory activity
• Stimulates mitosis

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Lipid Soluble Hormones

• Thyroid and steroid hormones cross the cell
  membrane and bind to INTRACELLULAR receptors in
  the cytoplasm or nucleus
• The hormone- receptor complex triggers activation
  or inactivation of specific genes
• Synthesis of new protein alters cellular activity
  causing a physiological response

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Water Soluble Hormones

• Protein and catecholamine hormones act by binding
  to receptors located on the cell membranes of
  target cells
• Hormones act as the 1st messenger which in turn
  activates a series of events involving cAMP as
  the 2nd messenger
• cAMP activates protein kinases
• G-proteins link the first messenger and the
  second messenger

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Hormone Release

• Humoral - hormones released in response to
  changing blood levels
• Neural - nerve fibers stimulate release
• Hormonal - one hormone stimulates the release of
  another

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Endocrine Glands
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Pituitary Gland

• Master gland
• Located within the sella turcica of the sphenoid
  bone
• Associated closely with the hypothalamus
• Differentiated into the anterior pituitary, or
  glandular portion, the posterior pituitary, or
  nervous portion and the avascular pars intermedia
  located in between

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Posterior lobe - Neurohypophysis

• Connected with the hypothalamus via the
  supraopticohypophyseal tract
• Oxtocin (OT)
• Antidiuretic hormone (ADH)
• diabetes insipidus

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Anterior lobe (Adenohypophysis)

• Controlled by releasing and inhibiting hormones
  produced by the hypothalamus
• Growth hormone (GH)
• somatotropin
• dwarfism, giantism, acromegaly
• Thyroid - stimulating hormone (TSH)
• Adrenocorticotropic hormone (ACTH)

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Acromegaly
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Anterior lobe of the Pituitary

• Follicle - stimulating hormone (FSH)
• Luteinizing hormone (LH)
• Prolactin (PRL)
• Melanocyte - stimulating hormone (MSH)

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Thyroid Gland

• Located below the larynx, two lobes connected by
  an isthmus
• Hormones synthesized from iodine and tyrosine
• Follicle cells manufacture thyroglobin and store
  it as colloid
• Triiodothyronine (T3) / Thyroxine (T4)
• Goiter, Graves Disease, Cretinism, Myxedema
• Calcitonin (CT) - lowers calcium levels

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Parathyroid gland

• Four tiny glands located on posterior thyroid
• Parathyroid hormone (PTH)
• Raises blood calcium

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Adrenal Glands

• Located retroperitoneally and superior to the
  kidney
• Can be subdivided into outer cortex and inner
  medulla

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Adrenal Medulla

• Consists of hormone-producing cells called
  chromaffin cells
• Epinephrine / Norepinephrine (NE)
• Sympathomimetic hormones
• Released under stress by direct innervation from
  the autonomic nervous system

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Adrenal Cortex

• Manufactures steroid hormones called
  corticosteroids
• Divided into three regions zona glomerulosa,
  zona fasciculata, zona reticularis
• Zona glomerulosa (outer) - releases
  mineralocorticoids, principally aldosterone which
  controls electrolyte balance in the kidneys

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Adrenal Cortex

• Zona fasciculata (middle) - produces
  glucocorticoids such as cortisol and cortisone
  controlled by ACTH
• Addisons Disease, Cushings Disease
• Zona reticularis (inner) - produces adrenal sex
  hormones such as estrogens and androgens
• virilism, gynecomastia

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Cushings Disease
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Thymus Pineal Gland

• Located posterior to the sternum and between the
  lungs
• Thymosin

• Located in the roof of the 3rd ventricle of the
  brain
• Melatonin

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Pancreas

• Located posterior and inferior to the stomach
• Both exocrine and endocrine
• Islets of Langerhans
• Alpha cells - glucagon
• Beta cells - insulin
• Delta cells - somatostatin
• Diabetes mellitus - Type I, TypeII

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Ovaries

• Located in the pelvic cavity
• Estrogens
• Estradiol, estriol, estrone
• Progesterone
• Inhibin
• Relaxin

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Testes

• Located in the scrotum
• Testosterone
• Inhibin

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