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Endocrine System
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Endocrine System
• Overall functions
– Regulate organic metabolism and H2O and
electrolyte balance
– Induce adaptive changes to help body cope with
stressful situations
– Promote smooth, sequential growth and
development
– Control reproduction
– Regulate red blood cell production
– Along with autonomic nervous system, control
and integrate both circulation and the digestion
and absorption of food
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
1
Tropic Hormones
• Regulates hormone secretion by another endocrine
gland
• Stimulates and maintains endocrine target tissues
• Example
– Thyroid-stimulating hormone (TSH)
– secreted from anterior pituitary
– stimulates thyroid hormone secretion by thyroid gland
– maintains structural integrity of thyroid gland
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Negative Feedback
Gland 1
Hormone 1
Gland 1
↑ Hormone X
Gland 2
Hormone 2
Positive Feedback
Hormone 1
Gland 2
↓ Hormone X
-
↑ Hormone X
-
Hormone 2
Gland 3
Gland 3
Hormone 3
Hormone 3
↑ Hormone X
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
2
Hormones
• Plasma concentration of each hormone controlled
by regulated changes in rate of secretion
• Direct inputs influence secretory output of endocrine
cells
– Neural input
– Input from another hormone
• Effective plasma concentration also influenced by
– Rate of removal from blood by metabolic
inactivation and excretion
– Rate of activation or its extent of binding to
plasma proteins
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
3
Endocrine Dysfunction
• Arises from a variety of factors
• Most commonly result from inappropriate rates of
secretion
– Hyposecretion
• Too little hormone is secreted
– Hypersecretion
• Too much hormone is secreted
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Hyposecretion
• Primary hyposecretion
– Too little hormone is secreted due to abnormality within
gland
– Causes
•
•
•
•
•
•
•
Genetic
Dietary (eg lack of iodine)
Chemical or toxic
Immunologic (autoimmune diseases)
Other disease processes such as cancer
Iatrogenic (eg surgical removal)
Idiopathic (unknown)
• Secondary hyposecretion
– Gland is normal but too little hormone is secreted due to
deficiency of its tropic hormone
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
4
Hypersecretion
• Causes
– Tumours that ignore normal regulatory input and
continuously secrete excess hormone
– Immunologic factors
• Primary hypersecretion
– Too much hormone is secreted due to
abnormality within gland
• Secondary hypersecretion
– Excessive stimulation from outside the gland
causes oversecretion
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Hormone Influence at Target Cell
• Target cell may be unresponsive to hormone due to
lack of receptors.
• Can be pathological or physiological
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
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Hormone Influence at Target Cell
• Hormone can influence activity of another hormone at target cell
in one of three ways, generally via altering receptor expression.
– Permissiveness
• One hormone must be present in adequate amounts for full
exertion of another hormone’s effect
– Synergism
• Occurs when actions of several hormones are complimentary
• Combined effect is greater than the sum of their separate effects
– Antagonism
• Occurs when one hormone causes loss of another hormone’s
receptors
• Reduces effectiveness of second hormone
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Hypothalamus and Pituitary Gland
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
6
Pituitary Gland
• Release of hormones controlled
by hypothalamus
• Posterior pituitary
– Along with hypothalamus
forms neuroendocrine system
– Does not actually produce any
hormones
– Stores and releases two small
peptide hormones
• Vasopressin (ADH)
• Oxytocin
Relationship between Hypothalamus and
Posterior Pituitary
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Anterior Pituitary Gland
Secretes six different peptide hormones that it produces itself
• Tropic hormones
– Thyroid-stimulating hormone (TSH)
» Stimulates secretion of thyroid hormone
– Adrenocorticotropic hormone (ACTH)
» Stimulates secretion of cortisol by adrenal cortex
– Growth hormone (GH)
» Primary hormone responsible for regulating overall body growth;
important in intermediary metabolism
– Follicle-stimulating hormone (FSH)
» In females, stimulates growth and development of ovarian follicles;
promotes secretion of estrogen by ovaries
» In males, required for sperm production
– Luteinizing hormone (LH)
» In females, responsible for ovulation and luteinization; regulates ovarian
secretion of female sex hormones
» In males, stimulates testosterone secretion
• Non-tropic hormone
– Prolactin (PRL)
» Enhances breast development and milk production in females
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
7
Hypothalamic regulation of Anterior Pituitary
•
•
Hypothalamic releasing and inhibiting hormones help regulate anterior pituitary hormone
secretion
Two most important factors that regulate anterior pituitary hormone secretion
– Hypothalamic hormones
– Feedback by target-gland hormones
Vascular Link between Hypothalamus
and Anterior Pituitary
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Hypothalamus and Pituitary
synthesis
TRH
CRH
GnRH
PRH PIH GHRH SS
+
Blood
oxytocin
ADH
TSH
ACTH
FSH
-
+
-
vessels
LH prolactin
GH
storage and secretion
breast
kidney
adrenal
thyroid
uterus blood vessels
cortex
gonads
breast
many
tissues
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
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Hypothalamic Releasing and Inhibiting Hormones
• Secretion of each anterior
pituitary hormone is
stimulated or inhibited by
one or more hypothalamic
hypophysiotropic hormones
Hormone
Effect on Anterior
Pituitary
Thyrotropin-Releasing
hormone (TRH)
Stimulates release
of TSH
Corticotropin-Releasing
hormone (CRH)
Stimulates release
of ACTH
Gonadotropin-releasing
hormone (GnRH)
Stimulates release
of FSH and LH
Growth-hormone releasing
hormone (GHRH)
Stimulates release
of growth hormone
Growth-hormone inhibiting
hormone (GHIH). Also
known as somatostatin.
Inhibits release of
growth hormone
and TSH
Prolactin-releasing
hormone (PRH)
Stimulates release
of prolactin
Prolactin-inhibiting
hormone (PIH)
Inhibits release of
prolactin
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Negative Feedback
Gland 1
Hormone 1
Gland 1
↑ Hormone X
Gland 2
Hormone 2
Positive Feedback
Hormone 1
Gland 2
↓ Hormone X
-
↑ Hormone X
-
Hormone 2
Gland 3
Gland 3
Hormone 3
Hormone 3
↑ Hormone X
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
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