Download Tropic Hormones

Chapter Outline
The Endocrine System:
Endocrine Glands and
Hormone Actions
I.
II.
III.
IV.
V.
Primary Endocrine Organs
Secondary Endocrine Organs
Hormone Actions at the Target Cell
Abnormal Secretion of Hormones
Hormone Interactions
Endocrine Glands
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Derived from epithelial tissue
Primary endocrine organs
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The primary function is the secretion of hormones
Hormones are chemicals messengers that
secreted by specialized cells
Secondary endocrine organs
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The secretion of hormones is secondary to other
functions
Endocrine
Organs
Figure 6.1
I. Primary Endocrine Organs
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Hypothalamus and
pituitary gland are
connected via
infundibulum
Hypothalamus
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Part of brain
Synthesize ADH and
oxytocin
Produce releasing
and inhibiting topic
hormones that
regulate the secretion
of anterior pituitary
gland hormones
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Pituitary gland
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Figure 6.2
Anterior lobe is a
“typical” endocrine
gland that synthesizes
and secrets hormones
Figure 6.2b
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Pituitary gland
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Posterior lobe
contains neural
endinds that
originated from the
hypothalamus.
These neural
endings stores and
releases two
hypothalamic
neurohormones
Neurohormones stored by posterior pituitary
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Antidiuretic hormone (ADH or vasopressin)
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Is made in paraventricular nucleus of hypothalamus
Functions in water balance and osmolarity
Oxytocin
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Is synthesized by supraoptic nucleus of hypothalamus
Functions in milk ejection
Figure 6.3 Neural Connection to Posterior Pituitary
Hypothalamic-Pituitary Portal
System
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Tropic Hormones
Portal system
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Links two capillary
beds
Exchange between
blood and tissue
occurs in capillaries
Affect release of another hormone
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Releasing hormones
Inhibiting hormones
Figure 6.4
Common Tropic Hormone
Pathway
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Hypothalamus secretes releasing or inhibiting
hormone into capillary bed
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Tropic Hormones of Hypothalamus
and Anterior Pituitary
Blood with tropic hormones enters portal vein
Hypothalamic tropic hormones access anterior
pituitary secretory cells through capillary beds alter
release of anterior pituitary tropic hormones
Anterior pituitary tropic hormones enter
bloodstream in same capillary bed and travel
to distant endocrine gland to trigger release
of hormone
Target
Figure 6.5
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Control of Hypothalamic
Tropic Hormone Release
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Hypothalamus
Tropic hormone 1
secretion
Neural input
Hormonal
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Negative Feedback Loops
Short loop
negative
feedback
Long loop
negative
feedback
Negative feedback
Circadian rhythm
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Anterior pituitary
Tropic hormone 2
secretion
Suprachiasmatic nucleus of hypothalamus
Endocrine gland
Hormone 3 secretion
Target cell response
Figure 6.6
Pineal Gland
Feedback Control: Thyroid
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Hypothalamus
Thyrotropin releasing
hormone (TRH) secretion
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Glandular tissue in
brain
Secretes melatonin
Anterior pituitary
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Thyroid stimulating
hormone (TSH) secretion
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Long loop
negative
feedback
Function unknown
May be involved in
circadian rhythms
Thyroid gland
Thyroid hormone
secretion
Target cell response
Figure 6.7
Thyroid and Parathyroid
Glands
Figure 6.2a
Hormones of the Thyroid
Gland
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Two thyroid hormones
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T4, tetraiodothyronine (thyroxin)
T3, triiodothyronine
Regulate metabolism rate
Critical for normal growth and
development
Calcitonin
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Lowers calcium levels in blood
Figure 6.8
3
Parathyroid Hormone (PTH)
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Thymus
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Raises calcium levels in blood
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Promote the release of calcium from bone
Stimulate
z Calcium absorption by intestine
z Calcium reabsorption by kidney
z Vitamin D3 synthesis
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Adrenal Glands
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Locates close to the heart
Secretes thymosin
Regulates T cell function
Critical for immune function
Adrenal Glands
Located
above kidney
also called
suprarenal
glands
Figure 6.9a
Hormones of the Adrenal
Gland: Adrenocorticoids
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Mineralocorticoids (aldosterone)
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Adrenal Medulla
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Secreted from zonae glomerulosa
Regulates sodium and potassium levels
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Secreted from zonae fasciculata and reticularis
Regulates body’s response to stress
Regulates metabolism
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Sex hormones (androgens)
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Secreted from zonae fasciculata and reticularis
Regulate reproductive function
Secretory cells = chromaffin cells
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Glucocorticoids (cortisol)
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Figure 6.9b
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80% epinephrine (adrenaline)
20% norepinephrine
<1% dopamine (prolactin secretion, a
neurotransmitter that involved in pleasure and
awards)
Epinephrine and norepinephrine are involved in
metabolism, cardiac function and fight or flight
Under neural control
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Anatomy of the Pancreas
Endocrine Pancreas
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Islets of Langerhans
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Alpha cells: glucagon
Beta cells: insulin
Delta cells: somatostatin (inhibit secretion of
pancreatic hormones; regulate the function of
digestive function)
F cells: pancreatic polypeptide
Figure 6.10
Exocrine Pancreas
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Acinar and duct cells secrete fluid
and enzymes into digestive tract
Gonads
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Male—testes
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Testosterone
Androstenedione
Female—ovaries
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Estradiol
Progesterone
Placenta of pregnant female
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II. Secondary Endocrine
Organs
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Heart: atrial natriuretic peptide (ANP)
Kidneys: erythropoietin
GI tract: several
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Cholecystokinin
Secretin
Gastrin
Estrogens and progesterone
III. Hormone Actions at the
Target Cell
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Control of hormone levels in blood
Transport of hormones
Hormone interactions
Liver: insulin-like growth factors
(somatomedins)
Skin and kidneys: calcitriol
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Control of Hormone Levels in
Blood
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Neural Control of Hormone
Release
Rate of hormone secretion
Amount of hormone bound to plasma
proteins
Rate of hormone metabolism
Figure 6.11
Hormonal Control by a
Circadian Rhythm
Humoral Control of Hormone
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Neural control of circadian rhythm
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Hormonal control of circadian rhythm
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Suprachiasmatic nucleus of the hypothalamus
Melatonin
Resets daily cycle based on light stimulus
All tropic hormones of hypothalamus affected
by circadian rhythm from suprachiasmatic
nucleus
Figure 6.12
Transport of Hormones
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Hydrophilic hormones
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Peptides, catecholamines
Dissolved in plasma
Rate of Hormone Metabolism
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Hydrophobic hormones
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Steroids, thyroid hormones
Bound to carrier proteins
Only free hormone can bind to receptor
Only free hormone can be metabolized
Longer half-life
Sites of hormone metabolism
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Target cell by lysosome
Blood by proteolytic enzymes
Liver
Steroids and thyroid hormones are
metabolized more slowly than peptide
enzymes
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They are bound to carriers in blood
Lipophilic hormones can be stored in
adipose tissue
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IV. Abnormal Secretion of
Hormones
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Hormone levels must be kept in balance
Pathologies
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Hyposecretion: too little
Hypersecretion: too much
Abnormal Tissue Responsiveness
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The effects of combined actions
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Primary
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Abnormality in endocrine organ secreting
hormone
Secondary
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Normal hormone levels
Tissue responds inappropriately
V. Hormone Interactions
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Primary versus Secondary
Secretion Disorders
Abnormality in tropic hormone
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Antagonism
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Antagonism
Synergistic or additive
Permissiveness
The effects of hormones oppose each other.
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Blood calcium level
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Effects of two hormones favor each
other but the net effect exceeds the
sum of individual effects
Example: Glucagon, cortisol, and
epinephrine on blood glucose
Parathyroid hormone ↑ calcium level
Calcitonin ↓
Blood glucose level
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Synergism
Hypothalamic tropic hormone
Anterior pituitary tropic hormone
Glucagon ↑glucose level
Insulin↓
Permissiveness
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One hormone needed for another to exert its
effects
Examples:
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Thyroid hormones cause expression of adrenergic
receptors in bronchiolar smooth muscle
Estrogen causes expression of progesterone
receptors in uterus
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