Download 18.Central Endocrine Glands

Chapter 18
The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Endocrine System
• Consists of ductless endocrine glands scattered throughout
body
• Glands secrete hormones which travel through blood to target
cells
– Target cells have receptors for binding with specific
hormone
– Regulates or directs particular function
• 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
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
Tropic Hormones
• Regulates hormone secretion by another endocrine
gland
• Stimulates and maintains their endocrine target
tissues
• Example
– Thyroid-stimulating hormone (TSH) secreted from
anterior pituitary stimulates thyroid hormone
secretion by thyroid gland
• Also maintains structural integrity of thyroid gland
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Hormones
• Plasma concentration of each hormone is normally
controlled by regulated changes in rate of hormone
secretion
• Direct regulatory inputs that 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
Endocrine Dysfunction
• Can arise from a variety of factors
• Most commonly result from abnormal plasma
concentrations of a hormone caused by
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
Chemical or toxic
Immunologic
Other disease processes such as cancer
Iatrogenic
Idiopathic
• 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
Hypersecretion
• Causes
– Tumors 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
• Hormone can influence activity of another hormone
at given target cell in one of three ways
– 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
Pituitary Gland
• Hypophysis
• Small gland located in bony cavity just below
hypothalamus
– Thin stalk connects pituitary gland to
hypothalamus
• Consists of two anatomically and functionally distinct
lobes
– Posterior pituitary (neurohypophysis)
• Composed of nervous tissue
– Anterior pituitary (adenohypophysis)
• Consists of glandular epithelial tissue
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Anatomy of the Pituitary Gland
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Pituitary Gland
• Release of hormones from both anterior and
posterior pituitary is 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
– Conserves water during urine formation
• Oxytocin
– Stimulates uterine contraction during childbirth and milk
ejection during breast-feeding
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Relationship of the Hypothalamus and Posterior Pituitary
1.
2.
3.
The paraventricular and
supraoptic nuclei both contain
neurons that produce
vasopressin and oxytocin. The
hormone, either vasopressin or
oxytocin depending on the
neuron, is synthesized in the
neuronal cell body in the
hypothalamus.
The hormone travels down the
axon to be stored in the neuronal
terminals within the posterior
pituitary.
On excitation of the neuron, the
stored hormone is released from
these terminals into the systemic
blood for distribution throughout
the body.
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Pituitary Gland
• Anterior pituitary
– 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
– 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
– Growth hormone (GH)
» Primary hormone responsible for regulating overall body growth;
important in intermediary metabolism
• Not a 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
Pituitary Gland
• 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
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
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)
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
Vascular Link Between the Hypothalamus and Anterior Pituitary
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Endocrine Control of Growth
• Growth depends on growth hormone but is
influenced by other factors as well
– Genetic determination of an individual’s maximum
growth capacity
– An adequate diet
– Freedom from chronic disease and stressful
environmental conditions
– Normal levels of growth-influencing hormones
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Growth Rate
• Not continuous
• Factors responsible for promoting growth are not the
same throughout growth period
• Fetal growth
– Promoted largely by hormones from placenta
– GH plays no role in fetal development
• Postnatal growth spurt
– Displayed during first two years of life
• Pubertal growth spurt
– Occurs during adolescence
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Normal Growth Curve
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Growth Hormone
• Primarily promotes growth indirectly by stimulating liver’s
production of somatomedins
– Primary somatomedin is insulin-like growth factor (IGF-1)
• Acts directly on bone and soft tissues to bring about most
growth-promoting actions
• Stimulates protein synthesis, cell division, and lengthening
and thickening of bones
• Exerts metabolic effects not related to growth
– Increases fatty acid levels in blood by enhancing
breakdown of triglyceride fat stored in adipose tissue
– Increases blood glucose levels by decreasing glucose
uptake by muscles
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Growth Hormone Abnormalities
• Growth hormone deficiency
– Due to pituitary defect or hypothalamic dysfunction
– Hyposecretion of GH in child is one cause of dwarfism
– Deficiency in adults produces relatively few symptoms
• Growth hormone excess
– Most often caused by tumor of GH-producing cells of
anterior pituitary
– Symptoms depend on age of individual when abnormal
secretion begins
• Gigantism
– Caused by overproduction of GH in childhood before
epiphyseal plates close
• Acromegaly
– Occurs when GH hypersecretion occurs after adolescence
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
Growth
• Other hormones besides growth hormone are essential for
normal growth
– Thyroid hormone
• Growth severely stunted in hypothyroid children
• Hypersecretion does not cause excessive growth
– Insulin
• Deficiency often blocks growth
• Hyperinsulinism often spurs excessive growth
– Androgens
• Play role in pubertal growth spurt, stimulate protein synthesis
in many organs
• Effects depend on presence of GH
– Estrogens
• Effects of estrogen on growth prior to bone maturation are
not well understood poorly
Chapter 18 The Central Endocrine Glands
Human Physiology by Lauralee Sherwood ©2007 Brooks/Cole-Thomson Learning
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
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