The thyroid gland is located in the neck region and controls metabolism. It secretes the hormones thyroxine and triiodothyronine, which regulate basal metabolic rate, protein synthesis, and the body's sensitivity to other hormones. Hypersecretion of thyroid hormones increases metabolic rate and causes weight loss, while hyposecretion decreases metabolic rate and causes weight gain. Conditions that result from thyroid hormone imbalance include hypothyroidism, which causes slowed metabolism, and hyperthyroidism, which increases metabolism.

1. THYROID
GLAND
RAMYA.H.
1st year M.Sc. Food & Nutrition

2. INDEX
 Introduction
 Location
 Structure
 Hormones
Hormonal functions
Hypersecretion and hyposecretion
Hypothyroidism & Hyperthyroidism

3. INTRODUCTION
• The thyroid gland is one of the largest endocrine glands in the
body.
• Consists of two connected lobes.
• Controls the metabolic rate, protein synthesis, and controls the
body's sensitivity to other hormones.

4. LOCATION
• Situated in the neck region in front of the larynx and trachea.
• The gland is made up of two lobes of thick red glandular tissue
joined together by a narrow strip or bridge called isthmus.
• Two lobes are connected by a narrow isthmus in front of the
trachea.

5. STRUCTURE
• The thyroid gland is a butterfly-shaped organ with two
lobes, one on the right and the left as the wings.
• Each lobe is about 5 cm long, 3 cm wide and 2 cm thick,
with the isthmus about 1.25 cm in length.
• The lobes are asymmetrical with the right lobe usually
larger.
• The gland is usually larger in women.

6. • The thyroid gland is covered by a thin fibrous sheath,
the capsule of the thyroid.
• The capsule enters into the gland and forms the
septum that divides the thyroid tissue into microscopic
lobules.

7. HORMONES
• The thyroid gland secretes two main hormones,
• Thyroxine also called T4.
• Triiodothyronine or T3.
• Thyroxine contains four atoms of Iodine.
• Triiodothyronine contains three atoms of Iodine.
• Thyroxine is secreted in more amounts compared to
triiodothyronine.
• Triiodothyronine is more efficient than thyroxine.

8. HORMONAL FUNCTIONS
1. Regulation of Basal Metabolic Rate and intake of oxygen.
2. Regulation of cellular metabolism.
I. It stimulates synthesis of protein
II. It increases the breakdown of lipids
III. Lowers cholesterol level
3. Regulation of growth and development.
I. Helps in the normal development of the nervous system,
brain & reproductive organs

9. HYPERSECRETION &
HYPOSECRETION
Sl.
no
Effects of
thyroid
hormones
Hypersecretion Hyposecretion
1. Basal metabolic
rate
BMR can be increased to about
60-100% above normal. The
person is hyperactive.
BMR decreases to about half the
normal rate. The person becomes
sluggish.
2. Carbohydrate
metabolism
Increased uptake of glucose by
cells. Increased gluconeogenesis.
Increased breakdown of glucose.
Decrease in uptake of glucose by
cells. Decreased gluconeogenesis.
Decreased breakdown of glucose.
3. Fat metabolism Fat reserves are depleted,
increased oxidation of the free
fatty acids. Increases the
excretion of cholesterol in the
Fat metabolism is slowed down.

10. Sl.no
.
Effects of
thyroid
hormones
Hypersecretion Hyposecretion
4. Requirements of
vitamins
Increased requirement of vitamins as
many function as co-enzymes.
Vitamins are easily depleted.
There is a decrease in vitamin
requirement.
5. Body weight Normally decreases the body weight,
but as there is an increase in appetite
with a consequent increase in weight
may occur.
Body weight increases.
6. Cardiovascular
system
Increased blood flow and cardiac
output. Increase in heart rate. Pulse
pressure is increased.
Decreased blood flow and cardiac
output. Decrease in heart rate. Pulse
pressure is decreased.
7. Respiration As there is an increase in oxygen
uptake, there is an increase in the
rate of respiration.
There is decrease in the rate of
respiration.
8. Muscles Slight increase in secretion increases
muscle vigour. Excessive secretion
Muscles become sluggish, and after a
contraction there is delayed relaxation.

11. Sl.n
o
Effects of
thyroid
hormones
Hypersecretion Hyposecretion
9. Gastrointestinal
tract
Increases the secretion of digestive juices.
There is increased motility of GI tract. The
person suffers from diarrhea.
Decreased secretion and decreased
motility. The person suffers from
constipation.
10. CNS Increase in cerebral activity. The person
suffers from nervousness, anxiety.
Decrease in cerebral activity. He becomes
less alert.
11. Endocrine glands Thyroid hormones stimulate the secretion
of other endocrine glands because they
create a need for their hormones such as
insulin, parathyroid hormone &
glucocorticoids.
No stimulation of other endocrine glands
&there is decrease in secretion of their
hormones.
12. Sexual function In men, there is increase in libido but
excess can lead into impotence. In women,
there is oligomennorrhea or reduced
bleeding.
In men, there is a loss of libido. In women,
loss of libido, excessive bleeding &
frequent menstrual bleeding.
13. Sleep Though a person feels tired he is not able
to sleep.
The person feels drowsy and can sleep for
12 to 14 hours a day.

12. HYPOTHYROIDISM
• Hypothyroidism in early childhood and in the foetal stage
results in Cretinism.
• The children become dwarf and are mentally retarded.
• Hypothyroidism in adults results in Myxedema. There is edema
and puffiness in the face.
• Goitre or enlargement of the thyroid gland can occur due to
deficiency of iodine in the diet.

13. HYPERTHYROIDISM
•Hyperthyroidism results in Grave’s disease. There
is enlargement of the gland and edema behind
the eyes and the eyes protrude. This is
Exophthalmic goitre.

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