Download 1 High level of Ca 2+ in blood stimulates thyroid gland parafollicular

Thyroid Gland
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On each side of trachea is lobe of thyroid
Weighs 1 oz & has rich blood supply
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Photomicrograph of Thyroid Gland
18-2
Copyright 2009, John Wiley & Sons, Inc.
Thyroid Gland
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Located inferior to larynx
2 lobes connected by isthmus
Thyroid follicles produce thyroid hormones
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Thyroxine or tetraiodothyronine (T4)
Triiodothyronine (T3)
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Both increase BMR, stimulate protein synthesis, increase use
of glucose and fatty acids for ATP production ,and growth
increases sympathetic activity
Parafollicular cells or C cells produce calcitonin
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Lowers blood Ca2+ by inhibiting bone resorption
Copyright 2009, John Wiley & Sons, Inc.
Actions of Thyroid
Hormones
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T3 & T4 = thyroid
hormones responsible for
our metabolic rate,
synthesis of protein,
breakdown of fats, use of
glucose for ATP production
18-5
Control of thyroid hormone secretion
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Thyrotropin-releasing hormone (TRH) from
hypothalamus
Thyroid-stimulating hormone (TSH) from
anterior pituitary
Situations that increase ATP demand also
increase secretion of thyroid hormones
Copyright 2009, John Wiley & Sons, Inc.
1 Low blood levels of T3
and T3 or low metabolic
rate stimulate release of
Hypothalamus
TRH
2 TRH, carried
by hypophyseal
portal veins to
anterior pituitary,
stimulates
release of TSH
by thyrotrophs
5 Elevated
T3inhibits
release of
TRH and
TSH
(negative
feedback)
TSH
3 TSH released into
blood stimulates
thyroid follicular cells
Anterior
pituitary
4 T3 and T4
Thyroid
follicle
released into
blood by
follicular cells
Actions of Thyroid Hormones:
Increase basal metabolic rate
Stimulate synthesis of Na+/K+ ATPase
Increase body temperature (calorigenic effect)
Stimulate protein synthesis
Increase the use of glucose and fatty acids for ATP production
Stimulate lipolysis
Enhance some actions of catecholamines
Regulate development and growth of nervous tissue and bones
Thyroid Gland



Located inferior to larynx
2 lobes connected by isthmus
Thyroid follicles produce thyroid hormones


Thyroxine or tetraiodothyronine (T4)
Triiodothyronine (T3)



Both increase BMR, stimulate protein synthesis, increase use
of glucose and fatty acids for ATP production
increases sympathetic activity
Parafollicular cells or C cells produce calcitonin

Lowers blood Ca2+ by inhibiting bone resorption
Copyright 2009, John Wiley & Sons, Inc.
Actions of Thyroid
Hormones


T3 & T4 = thyroid
hormones responsible for
our metabolic rate,
synthesis of protein,
breakdown of fats, use of
glucose for ATP production
Calcitonin = responsible for
building of bone & stops
reabsorption of bone (lower
blood levels of Calcium)
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Parathyroid Glands
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4 pea-sized glands found on back of thyroid gland
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Parathyroid Glands
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Embedded in lobes of thyroid gland
Usually 4
Parathyroid hormone (PTH) or parathormone
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Major regulator of calcium, magnesium, and
phosphate ions in the blood
Increases number and activity of osteoclasts
Elevates bone resorption
Blood calcium level directly controls secretion
of both calcitonin and PTH via negative
feedback
Copyright 2009, John Wiley & Sons, Inc.
Parathyroid Hormone
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Raise blood calcium and Mg levels (decrease
HPO4) -2 )
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increase activity of osteoclasts
increases reabsorption of Ca+2 by kidney
increase loss of phosphate (HPO4) -2 in urine
promote formation of calcitriol (vitamin D3) by
kidney which increases absorption of Ca+2,
HPO4 and Mg+2 by intestinal tract
Opposite function of calcitonin
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1 High level of Ca2+ in blood
stimulates thyroid gland
parafollicular cells to
release more CT.
3 Low level of Ca2+ in blood
stimulates parathyroid
gland chief cells to release
more PTH.
6 CALCITRIOL stimulates
increased absorption of
Ca2+ from foods, which
increases blood Ca2+ level.
5 PTH also stimulates
the kidneys to release
CALCITRIOL.
4 PARATHYROID HORMONE (PTH)
promotes release of Ca2+ from
bone extracellular matrix into
blood and slows loss of Ca2+
in urine, thus increasing blood
Ca2+ level.
2 CALCITONIN inhibits
osteoclasts, thus decreasing
blood Ca2+ level.
Adrenal Glands
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One on top of each kidney
3 x 3 x 1 cm in size and weighs 5 grams
Cortex produces 3 different types of hormones
from 3 zones of cortex
Medulla produces epinephrine & norepinephrine
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Structure of Adrenal Gland
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Cortex derived from mesoderm
Medulla derived from ectoderm
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Adrenal Glands
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2 structurally and functionally distinct regions
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Adrenal cortex
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Mineralocorticoids affect mineral homeostasis
Glucocorticoids affect glucose homeostasis
 Cortisol “hydrocortisone”, corticosterone and cortisone
Androgens have masculinzing effects
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Dehydroepiandrosterone (DHEA) only important in females
Adrenal medulla
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Modified sympathetic ganglion of autonomic
nervous system
Intensifies sympathetic responses
Epinephrine and norepinephrine
Copyright 2009, John Wiley & Sons, Inc.
Mineralocorticoids
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95% of hormonal activity due to aldosterone
Functions
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increase reabsorption of Na+ with Cl- , bicarbonate
and water following it
promotes excretion of K+ and H+
Hypersecretion = tumor producing
aldosteronism
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high blood pressure caused by retention of Na+ and
water in blood
18-17
Regulation of Aldosterone
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Glucocorticoids
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95% of hormonal activity is due to cortisol
Functions = help regulate metabolism
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increase rate of protein catabolism & lipolysis
conversion of amino acids to glucose
stimulate lipolysis
provide resistance to stress by making
nutrients available for ATP production
raise BP by vasoconstriction
anti-inflammatory effects reduced
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reduce release of histamine from mast cells
decrease capillary permeability
depress phagocytosis
Decrease tissue repair
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Adrenal Medulla
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Chromaffin cells receive direct innervation
from sympathetic nervous system
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Produce epinephrine & norepinephrine
Hormones are sympathomimetic
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develop from same tissue as postganglionic
neurons
effects mimic those of sympathetic NS
cause fight-flight behavior
Acetylcholine increase hormone secretion
by adrenal medulla
18-20