Endocrine System

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Endocrine System

• Modified from
• http//www2.kumc.edu/instruction/nursing/nrsg812/e
  ndocrine/
• Images from
• http//www.endocrineweb.com/
• gened.emc.maricopa.edu/bio/bio181/BIOBK/BioBookEND
  OCR.html

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Mechanisms of Hormone Action

• Certain secretory cells release chemical agents
  (hormones) for the purpose of mediating biologic
  responses in distant Target Cells.
• Hormones sources
• Single amino acid (catecholamines)
• Chains amino acids (peptide hormones of
  hypothalamus)
• Cholesterol (steroids)

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Mechanisms of Hormone Action

• Hormones control and integrate many body
  functions with this system.
• In general, hormonal control regulates the
  metabolic functions of the body, the types of
  effects that occur inside the cell and determined
  the character of the cell itself.
• The endocrine system works with the nervous
  system to regulate metabolism, water and salt
  balance, blood pressure, response to stress, and
  sexual reproduction.

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3 Forms of Hormonal Communication

• 1. Endocrine hormones are secreted into blood
  to regulate the function of distant target cell
• 2. Paracrine endocrine cells secrete into
  surrounding extracellular space. Target cells are
  neighbors
• 3. Neuroendocrine Directly into blood
  (norepin), into brain interstitial space
  (Vasopressin)

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Endocrine System

• Endocrine System Hormones/Glands whose functions
  are solely endocrine include
• pituitary (hypophysis)
• pineal
• thyroid
• parathyroids
• adrenals
• pancreas

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Hypothalamus and Pituitary

• Pituitary has direct neural and blood connection
  to the hypothalamus
• Hypothalamus sends releasing factors to anterior
  pituitary
• Hypothalamus stimulates posterior pituitary via
  neural pathway

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Hypothalamus

• Hypothalamus can synthesize and release hormones
  from its axon terminals into the blood
  circulation.
• controls pituitary function and thus has an
  important, indirect influence on the other glands
  of the endocrine system.
• exerts direct control over both the anterior and
  posterior portions of the pituitary gland.
• regulates pituitary activity through two
  pathways a neural pathway and a portal venous
  pathway.

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Hypothalamus

• Neural pathways extend from the hypothalamus to
  the posterior pituitary lobe, where the hormones
  are stored and secreted.
• Portal venous pathways connect the hypothalamus
  to the anterior pituitary lobe, carry releasing
  and inhibiting hormones

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Pituitary Gland

• Pituitary Gland is located at the base of the
  skull in an indentation of the sphenoid bone.
• Is joined to the hypothalamus by the pituitary
  stalk (neurohypophyseal tract) and consists of
  the anterior pituitary and the posterior pituitary

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Anterior pituitary gland (adenohypophysis)

• Called the master gland, because its anterior
  lobe has direct control over the secretion of
• ADH - antidiuretic hormone (vasopressin)
• ACTH - adrenocorticotrophic hormone
• TTH - thyrotrophic hormone
• GH - growth hormone
• FSH - follicle stimulating hormone
• LH - leutinizing hormone

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Posterior pituitary

• Stores and secretes hormones made in the
  hypothalamus and contains many nerve fibers.
• ADH (Antidiuretic Hormone/Vasopressin), which
  controls the rate of water excretion into the
  urine
• Regulates Na K reabsorption in the kidneys
  this influences blood volume blood pressure
• Oxytocin, which, among other functions, helps
  deliver milk from the glands of the breast.

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Adrenal Glands

• Adrenal Glands have an outer cortex and an inner
  medulla.
• The adrenal cortex and medulla are major factors
  in the body's response to stress.

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KidneysRenal Hormones

• Renin is an hormone/enzyme (released from
  juxtaglomerular cells)

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Thyroid Gland

• Thyroid function is regulated by the
  hypothalamus and pituitary, feedback controls
  an intrinsic regulator mechanism

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Thyroid Problems

• Thyroid gland enlargement may or may not be
  associated with abnormal hormone secretion.
• An enlarged thyroid gland can be the result of
• iodine deficiency (Goiter)
• inflammation, or
• benign or malignant tumors

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Parathyroid Glands

• There are 4 parathyroid glands located behind the
  thyroid.
• Parathyroid Glands are important in calcium
  metabolism phosphorus metabolism

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Pancreas

• endocrine gland, secreting the hormones insulin
  and glucagon, exocrine gland, producing digestive
  enzymes.
• Secretes insulin, glucagon (regulate blood sugar)
  

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Cellular Mechanisms of Hormone Action

• Hormonal interaction with target cells begin
  withreversible binding to specific receptors

1. Interactions with membrane receptor
(protein) 2. Interactions with nuclear receptors
(steroid)
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Amino Acid Based Hormones

• Bind to receptor sites on cell membranes
• Amino acid hormone binding causes changes to
  occur receptor can activate carrier molecules
  which transport substances across the membrane
• receptor can activate second messengers

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Second Messengers

• Second Messengers set a series of reactions in
  motion
• Activate adenylate cyclase, generates cAMP from
  ATP
• cAMP activates other proteins within the cell
  increases glycogenolysis lipolysis
• Open Ca2 ion channels, activates calmodulin
• Hydrolyzes phospholipase C into inositol
  triphosphate diacylglycerol

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Steroid Hormones

• Steroid hormones are produced by chemical
  modification of cholesterol

• Major classes steroid hormones
• glucocorticoids (cortisol)
• mineralocorticoids (aldosterone)
• androgens (testosterone)
• estrogens (estradiol)
• Vitamin D metabolites

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Steroid Hormones

• Diffuse into cell and influence DNA
• Bind to a protein associated with DNA
• Cause DNA to increase synthesis of specific amino
  acids

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Feedback Loops

• The release of a hormone is often triggered by a
  change in the concentration of some substance in
  the body fluids.
• Each hormone has a corrective effect, eliminating
  the stimulus, which then leads to a reduction in
  hormone secretion.
• This process is called a negative feedback
  homeostatic control system to keep hormones at
  normal levels. (if levels increased it would be
  called positive feedback)

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Blood Sugar Control

• Insulin and glucagon are produced by small groups
  of cells in the pancreas (islets of Langerhans).
  
• Beta cell make insulin (beta cells) and Alpha
  cells that make glucagon
• Insulin is released when the blood sugar rises
  too high. Insulin tells the cells to use sugar.
• Glucagon is produced when the blood sugar is
  falling too low. Glucagon tells the liver to
  release sugar that was stored there when the
  blood sugar was higher.