Chemical signals in animals

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Chemical signals in animals
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KeywordsReading Ch. 45

• Endocrine system
• Hormone
• Target cell
• Neurosecretory cell
• Steroid
• Amino acid derived hormone
• Surface receptors

• Internal receptors
• Action of steroids
• Glucose homeostasis
• Insulin
• Glucagon
• Epinephrine
• Norepinephrine
• ACTH

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Chemical signals outside of organisms

• Pheromones
• Prey tracking by rattlesnakes

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Pheromone

• A small volatile chemical signal that functions
  in communication between animals
• Often in mate attraction

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Will focus on chemical signals inside organisms

• Two regulatory systems coordinate internal body
  functions
• Nervous system (will deal with in a later
  lecture)
• Endocrine system (focus of todays lecture)

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Endocrine system definition

• The internal chemical communication system
  involving hormones
• Hormone
• Chemical signal secreted into body fluids
  (usually blood)
• Effective in minute amounts

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Hormones act on specific target cells in two ways

• Surface receptors
• Within target cells (internal receptor)

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Surface receptor - often amino acid derived
hormone
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Internal receptor - often steroid hormones
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Action of steroids
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Two specific examples of hormone action

• Glucose homeostasis
• Stress and the adrenal gland

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Glucose homeostasis

• Homeostasis The steady-state physiological
  condition of the body
• Glucose major fuel of cellular respiration
• Normal blood glucose level 900 mg/L
• How is this regulated?
• First look at when glucose levels are too high

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P. 906
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• High blood glucose causes beta cells to release
  insulin

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Summary

• Beta cells release insulin
• Insulin causes body cells and liver to take up
  glucose
• Glucose levels restored

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What happens if you need to increase blood
glucose?
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• Low blood glucose causes alpha cells to release
  the hormone glucagon

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• Glucogon stimulates the liver to break down
  glycogen releasing glucose

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Summary

• Low blood glucose causes alpha cells to release
  the hormone glucagon
• Glucogon stimulates the liver to break down
  glycogen releasing glucose

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Glucose homeostasis

• Example of use of amino-acid derived hormones
  insulin and glucagon are peptides
• Surface receptors on target cells

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Diabetes mellitus

• Greek copious urine, honey
• Type I - autoimmune disorder - cells of pancreas
  are targeted - no ability to produce insulin -
  usually occurs during childhood
• Type II (90) - reduced responsiveness of target
  cells or insulin deficiency-usually occurs after
  age 40

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Stress and the adrenal gland

• Short-term response - Epinephrine (adrenaline)
  and norepinephrine
• Long-term response - ACTH and corticosteroids

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P. 909
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Short-term stress medulla of the adrenal gland
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Some effects of epinephrine and norepinephrine

• Glycogen broken down to glucose
• Increased blood pressure, breathing, metabolic
  rate

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Example of

• Use of neurosecretory cells
• Amino acid-derived hormones

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Long-term stress cortex of the adrenal gland
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Corticosteroids (mineral- and gluco- corticoids)
released by adrenal cortex

• Some effects increased blood volume and blood
  pressure, breakdown of protein and fats

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Example of

• Interaction between nervous and endocrine systems
• Use of steroid hormones