Thyroid gland&parathyroid gland - Secretion, Function and Regulation

1. THYROID GLAND &
PARATHYROID GLAND
SECRETIONS, FUNCTIONS AND
REGULATION
SELINA SRAVANTHI
SAROJINI NAIDU VANITA PHARMACY MAHA VIDYALAYA,
TARNAKA, HYDERABAD, TELANAGANA

2. THYROID GLAND
 Butterfly-shaped
 located just inferior to the
larynx (voice box).
 It is composed of right and
left lateral lobes, one on
either side of the trachea,
that are connected by an
Isthmus anterior to the
trachea
 It is highly vascularized and
receives 80–120 mL of
blood per minute.
RIGHT
LATER
AL
LOBE
LEFT
LATER
AL
LOBE
ISTHMU
S

3. THYROID GLAND
 Microscopic spherical sacs called thyroid follicles
make up most of the thyroid gland.
 The wall of each follicle consists of cells called
follicular cells – secrete THYROID HORMONES(T3
AND T4)
 A few cells called parafollicular cells or C cells lie
between follicles.
 They produce the hormone CALCITONIN- which helps
regulate calcium homeostasis.
 The thyroid gland is the only endocrine gland that
stores its secretory product in large quantities—
normally about a 100-day supply.
 T4 normally is secreted in greater quantity than T3, but
T3 is several times more potent.
 Moreover, after T4 enters a body cell, most of it is
converted to T3 by removal of one iodine.

4. FORMATION, STORAGE, AND RELEASE
OF THYROID HORMONES
IODIDE
TRAPPING
Follicular cells trap
iodide by transport from
blood to cytosol
SYNTHESIS FROM
THYROGLOBULIN
Follicular cells synthesize
Thyroglobulin in RER-packed
in secretory vesicles-released
in Lumen after exocytosis
OXIDATION OF IODIDE
Amino Acids- Tyrosine in
Thyroglobulin has to become
iodinated.
Cannot bind until they undergo
oxdn
2I - I2
IODINATION OF
TYROSINE
I2 formed reacts with
tyrosine to form
monoiodotyrosine (T1)
and diiodotyrosine (T2)
Sticky material formed is
COLLOID
COUPLING OF T1 AND
T2
2T2 T4
T1+ T2 T3
PINOCYTOSIS AND
DIGESTION OF COLLOID
Droplets of colloid reenter
follicular cells by pinocytosis and
merge with lysosomes.
Digestive enzymes of lysosomes
break down TGB, cleaving T3
and T4.
TRANSPORT IN
BLOOD
T3 and the T4
combine with
transport proteins in
the blood, mainly
thyroxine-binding
globulin (TBG).
SECRETION OF
THYROID
HORMONES
T3 and T4 are lipid
soluble, diffuse
through the plasma
membrane into
interstitial fluid and
then into the blood.

6. FUNCTIONS OF THYROID HORMONES
 Thyroid hormones increase basal metabolic rate (BMR)-
stimulating the use of cellular oxygen to produce ATP-
metabolism of carbohydrates, lipids, and proteins increases.
 Stimulate synthesis of additional sodium-potassium
pumps (Na/K ATPase)- use large amounts of ATP to eject
sodium ions (Na) from the cytosol into the extracellular fluid
and potassium ions (K) from the extracellular fluid into the
cytosol. As cells produce and use more ATP, more heat is
given off, and body temperature rises. This phenomenon is
called the calorigenic effect. In this way, thyroid hormones
play an important role in the maintenance of normal body
temperature.

7. FUNCTIONS OF THYROID HORMONES
 In the regulation of metabolism, the thyroid hormones
stimulate protein synthesis and increase the use of
glucose and fatty acids for ATP production. They also
increase lipolysis and enhance cholesterol excretion, thus
reducing blood cholesterol level.
 The thyroid hormones enhance some actions of the
catecholamines (norepinephrine and epinephrine)
because they up-regulate beta (β) receptors. For this reason,
symptoms of hyperthyroidism include increased heart rate,
more forceful heartbeats, and increased blood pressure.
 Together with human growth hormone and insulin,
thyroid hormones accelerate body growth, particularly
the growth of the nervous and skeletal systems.
Deficiency of thyroid hormones during fetal development,
infancy, or childhood causes severe mental retardation and

8. CONTROL OF THYROID HORMONE

9. CALCITONIN
 Parafollicular cells of the thyroid glands
produce CALCITONIN (CT)
 Decrease the level of calcium in the blood
by inhibiting the action of osteoclasts, the
cells that break down bone extracellular
matrix.
 The secretion of ct is controlled by a negative
feedback system

11. PARATHYROID GLAND
 Several round masses
of tissue partially
embedded in the
posterior surface of
the lateral lobes of the
thyroid
 One superior and one
inferior parathyroid
gland are attached to
each lateral thyroid
lobe.- Total four
glands

12. FUNCTIONS OF PARATHYROID GLANDS
 Regulates of the levels of calcium (Ca2+), magnesium (Mg2+), and
phosphate (HPO42-)ions in the blood.
 The specific action of PTH is to increase the number and activity
of osteoclasts.
 The result is elevated bone resorption, which releases ionic
calcium (Ca2+) and phosphates (HPO42-) into the blood.
 PTH also acts on the kidneys.
 First, it slows the rate at which Ca2+ and Mg2+ are lost from
blood into the urine.
 Second, it increases loss of HPO42- from blood into the urine
thereby decreases blood HPO42- level and increases blood Ca2+
and Mg2+ levels.
 A third effect of PTH on the kidney is to promote formation of the
hormone calcitriol, the active form of vitamin D. Calcitriol, or
vitamin D3, increases the rate of Ca2+, HPO4 2-, and Mg2+
absorption from the gastrointestinal tract into the blood.