Hormones and the Endocrine System

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Hormones and the Endocrine System
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Hormones

• Chemical signals that are secreted into
  extracellular fluid, carried by the circulatory
  system, and communicate regulatory messages
  within the body.

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Hormones

• Hormones may reach all cells, but only some will
  respond (have the correct receptors)

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Regulation

• Hormones are needed for homeostasis
• Communication is needed to coordinate metabolic
  rate, growth, development, etc.

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Homeostasis

• Remember- The body relies on control pathways and
  feedback to generate the appropriate response

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Homeostasis

• Reception of stimuli ?
• Info. sent to control center ?
• Comparison to desired value ?
• Signal sent to effector ?
• Response

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Feedback

• Negative Feedback- the response reduces the
  initial stimulus
• Positive Feedback- response enhances initial
  stimulus

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Communication

• Requires Two Systems
• Nervous
• Uses electrical signals to respond quickly to
  sudden changes

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Communication

• Endocrine
• Coordinates slower, long acting responses to
  stimuli
• Regulates growth and developmental processes

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Overlap between systems

• Neurosecretory cells are specialized nerve cells
  that release hormones into the blood

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Example

• Adrenal glands (medulla) releases epinephrine
  (adrenaline)
• Stimulated by neurons and secreted by
  neurosecretory cells

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Hypothalamus

• Hypothalamus receives information from neurons
  and stimulates secretion of hormones

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In other words.

• Hypothalamus
• master control center
• Nervous system
• Receives info regulates pituitary
• Pituitary
• Master gland
• Endocrine gland
• Releases hormones that regulate other glands
  (tropic hormones)

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How Hormones Work

• Hormones do not affect every cell, just the cells
  they need to.

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How Hormones Work

• Three classes
• Proteins and peptides
• Amines (from amino acids)
• Steroids

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How Hormones Work

• All Involve three events
• Reception ? signal transduction ? Response
• Binding of signal molecule to receptor triggers
  signal transduciton

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Water Soluble Hormones

• Proteins and Amines
• Communicate from the outside

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Water Soluble Hormones

• Receptors for these are in the cell membrane
• Binding to receptor activates proteins in the
  cytoplasm.
• These proteins may move into nucleus and affect
  gene transcription

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How do we know?

• Frogs skin color
• Direct injection of hormone into cell produced no
  effect

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Diverse Responses

• Different receptors OR different intracellular
  proteins lead to different responses

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Epinephrine (Adrenaline)

• Intestinal Blood vessels shrink
• Skeletal blood vessels dilate
• Liver cells break down glycogen

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Lipid Soluble Hormones

• Steroids
• Communicate from the inside
• Enter cell
• Bind to receptors within the cytoplasm or nucleus

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Lipid Soluble Hormones

• This receptor is usually a transcription factor,
  and therefore controls gene expression.

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How do we know?

• Nuclei of reproductive cells in rats contain
  estrogen and progesterone while other cells did
  not.

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Again

• Different intracellular receptors will lead to
  different responses.