Endocrine System

1
Endocrine System

• Chapter 45

2
Hormones

• a hormone is a chemical signal that is released
  in one part of the body travels to another part
  of the body (through the circulatory system)
  where it elicits a particular response in the
  target cells
• 3 major classes of hormones
• proteins peptides
• amines
• steroids lipid-soluble tend to bind
  to cytoplasmic receptors inside target cells

water-soluble tend to bind to receptor proteins
on cell surface of target cells
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Simple Endocrine Pathway

• a signal molecule (stimulus) binds to a receptor
  protein on an endocrine cell which triggers the
  release of hormones
• hormones travel through blood stream to effector
  cells, eliciting a response

4
Simple Neurohormonal Pathway

• endocrine gland receives a stimulus from a
  sensory neuron which triggers the release of
  hormones
• hormones travel through blood stream to effector
  cells, eliciting a response

5
Simple Neuroendocrine Pathway

• endocrine gland receives a stimulus from a
  sensory neuron which triggers the release of
  hormones
• hormones travel through blood stream bind to
  receptor proteins on endocrine cells of another
  endocrine gland which triggers the release of a
  second hormone
• this hormone travels through the blood stream to
  effector cells, eliciting a response

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Feedback Loops

• Negative Feedback Loops
• effector response reduces the initial stimulus
  thereby preventing overreaction
• Positive Feedback Loops
• effector response reinforces the initial stimulus
  thereby leading to an even greater response

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Events of Hormonal Signaling

• reception the binding of a signal molecule to a
  receptor protein on/in a target cell
• signal transduction the series of events in the
  cell triggered by the binding a signal molecule
  to a receptor protein
• response the change in cell behavior as a
  result of the signal transduction pathway
• gene transcription, enzyme activation, change in
  uptake/secretion of specific molecules,
  rearrangement of the cytoskeleton

Review Chapter 11
8
Human Endocrine Glands

• hypothalamus
• pineal gland
• anterior posterior pituitary glands
• thyroid gland
• parathyroid glands
• adrenal glands (cortex medulla)
• pancreas
• gonads (ovaries, testes)

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Hypothalamus

• bridge between the endocrine nervous systems
• acts as part of the nervous system when it sends
  electrical signals to the adrenal gland to
  release adrenaline during times of stress
• acts like a nerve when it secretes
  gonadotropic-releasing hormone which stimulates
  the anterior pituitary to release FSH LH
• acts as an endocrine gland when it produces
  oxytocin ADH that it stores in the posterior
  pituitary
• contains the bodys thermostat
• contains centers for regulating hunger thirst

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hypothalamus
posterior pituitary
anterior pituitary
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Pituitary Gland

• anterior pituitary synthesizes secretes
  several hormones
• FSH LH stimulate activities ovaries testes
• TSH promotes normal thyroid development
• ACTH stimulates adrenal cortex to produce
  secrete steroid hormones
• GH stimulates bone growth
• posterior pituitary stores secretes 2
  hormones made in hypothalamus
• oxytocin stimulates uterine contractions
  mammary glands
• ADH promotes water-retention by kidneys

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Pineal Gland

• located near the center of the brain
• releases melatonin which is involved in
  biological rhythms regulated by light dark
  cycles

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Thyroid Gland

• located on trachea
• produces
• thyroxine controls metabolic rate
• calcitonin lowers blood calcium levels

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Parathyroid Glands

• located on the surface of the thyroid gland
• releases parathyroid hormone (PTH)
• raises blood calcium levels
• counteracts effect of calcitonin

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Adrenal Glands

• located above the kidneys
• adrenal medulla releases epinephrine (adrenaline)
  norepinephrine (noradrenaline)
• involved in the fight-or-flight response
  (short-term stress response)
• raises blood sugar level by increasing rate of
  glycogen breakdown by the liver
• adrenal cortex releases glucocorticoids
• involved in long-term stress response
• raises blood sugar level

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Pancreas

• releases
• insulin lowers blood glucose levels
• glucagon raises blood glucose levels

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Gonads

• ovaries (females)
• estrogens maintenance of the female reproductive
  system development of secondary sex
  characteristics stimulate uterine lining growth
• progesterone promote uterine lining growth
• testes (males)
• androgens (ex testosterone) maintenance of the
  male reproductive system development of
  secondary sex characteristics aid in sperm
  formation