Types of hormone
• Two hormone categories based on solubility
– Hydrophilic
• Peptide hormones
• Catecholamines
– Lipophilic
• Steroid hormones
• Thyroid hormone
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
1
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Adrenal Glands: anatomy
Embedded above each
kidney in a capsule of fat
•Composed of two
endocrine organs
–Adrenal cortex
•Outer portion
•Secretes steroid
hormones
–Adrenal medulla
•Inner portion
•Secretes
catecholamines
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
2
Adrenal Glands: hormones
Categories of adrenal steroids
• Mineralocorticoids
– Mainly aldosterone
– Influence mineral balance, specifically Na+ and K+
balance
• Glucocorticoids
– Primarily cortisol
– Major role in glucose metabolism as well as in
protein and lipid metabolism
• Sex hormones
– Identical or similar to those produced by gonads
– Most abundant and physiologically important is
dehydroepiandosterone (male “sex” hormone)
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Adrenal Glands: cortisol
• Stimulates hepatic gluconeogenesis
• Inhibits glucose uptake and use by many tissues, but not
the brain
• Stimulates protein degradation in many tissues,
especially muscle
• Facilitates lipolysis
• Plays key role in adaptation to stress
• At pharmacological levels, can have anti-inflammatory
and immunosuppressive effects
• Long-term use can result in unwanted side effects
• Displays a characteristic diurnal rhythm
• Secretion regulated by negative-feedback loop involving
hypothalamic CRH and pituitary ACTH
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
3
Adrenal Glands
• Secrete both male and female sex hormones in both
sexes
– Dehydroepiandrosterone (DHEA)
• Only adrenal sex hormone that has any biological
importance
• Overpowered by testicular testosterone in males
• Physiologically significant in females
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Adrenal Medulla
• Modified part of sympathetic nervous system
• Primary stimulus for increased adrenomedullary secretion:
activation of sympathetic nervous system by stress
• Releases epinephrine and norepinephrine
– Secreted into blood by exocytosis of chromaffin granules
– Vary in affinities for different adrenergic receptor types
• Epinephrine
– Reinforces sympathetic system in mounting general
systemic “fight-or-flight” responses
– Maintenance of arterial blood pressure
– Increases blood glucose and blood fatty acids
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
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Stress Response
• Pattern of reactions to a situation that threatens
homeostasis
• Stress
– Generalized nonspecific response of body to any
factor that overwhelms or threatens to overwhelm
the body’s ability to maintain homeostasis
• Stressor
– Any noxious stimulus that brings about the stress
response
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Stress Response
• All actions coordinated by the hypothalamus
• Generalized stress response
– Activation of sympathetic nervous system
accompanied by epinephrine secretion
• Prepares body for fight-or-flight response
– Activation of CRH-ACTH-cortisol system
• Helps body cope by mobilizing metabolic resources
– Elevation of blood glucose and fatty acids
• Decreased insulin and increased glucagon secretion
– Maintenance of blood volume and blood pressure
• Increased activity of renin-angiotensin-aldosterone
system and increased vasopressin secretion
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
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Pineal Gland
• Tiny, pinecone-shaped structure
• Located in center of brain
• Secretes melatonin
– Hormone of darkness
• Secretion falls to low levels during light of day
– Functions
• Helps keep body’s circadian rhythms in synchrony with
light-dark cycle
• Promotes sleep
• Influences reproductive activity, including onset of
puberty
• Acts as antioxidant to remove free radicals
• Enhances immunity
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Circadian Rhythms
• Suprachiasmatic nucleus (SCN)
– Body’s master biological clock
– Self-induced cyclic variations in clock protein
concentrations within SCN bring about cyclic
changes in neural discharge from SCN
• Cycle takes about a day
• Drives body’s circadian (daily) rhythms
– SCN must be set daily by external cues so body’s
biological rhythms are synchronized with activity
levels driven by surrounding environment
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
6
Circadian Rhythms
• Daily changes in light intensity
– Major environmental cue used to adjust SCN
master clock
– Photoreceptors in retina pick up light signals and
transmit them directly to SCN
– SCN relays message regarding light status to
pineal gland
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
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