The document summarizes the structure, location, and functions of the thyroid gland. It notes that the thyroid gland has a butterfly shape with two lobes connected by an isthmus. It regulates metabolism and other bodily functions through hormones like thyroxine and triiodothyronine. When overactive, it can cause hyperthyroidism and goiter; when underactive, it can cause hypothyroidism, cretinism, or myxedema. The parathyroid glands help regulate blood calcium levels through parathyroid hormone and calcitonin.

1. THYROID GLAND
By,
Ramya V,
1st M.SC. ZOOLOGY,
BHARATHIAR
UNIVERSITY,
COIMBATORE.

2. STRUCTURE

3. SHAPE OF THYROID
GLAND
• Thyroid consist of two lobes connected by a
narrow isthmus.
• Each lobe is pyramidal in shape, with its apex
directed upward and its base directed
downward.
• A butterfly-shaped organ.
• A small pyramidal lobe projecting upward
from the isthumus is often present to the left of
the midline.

4. SIZE OF THYROID GLAND
• The thyroid gland weighs 10 to 20 gms in
normal adults.
• Thyroid volume measured by ultrasonography
(US) is slightly greater in men than women.
• It increases with age and body weight.
• It decreases with increasing iodine intake.
• The thyroid is one of the most vascular organs
in the body.

5. LOCATION
• The normal thyroid gland is immediately
caudal to the larynx and the anterolateral
portion of the trachea.
• The thyroid is bordered by the trachea and
esophagus medially and the carotid sheath
laterally.

6. ANATOMY OF THYROID
GLAND
• The tissue of the thyroid gland is composed
mostly of thyroid follicles.
• The follicles are made up of a central cavity
filled with a sticky fluid called colloid.
• Surrounded by a wall of epithelial follicle
cells.
• Follicle consist of 2 types of cells, namely
principle cells and parafollicullar cells or c-
cells.

9. FUNCTIONS OF THYROID
• Increase pulmonary ventilationand thecellular uptake and
utilizationof oxygen.
• Regulatethe functioning ofnervous system.
• Promote theintestinalabsorption and also thesynthesis of
glucose.
• Maintainor improve milk production in lactating females.

10. • The hormone reduces cholestrol level.
• Influence the rate at which food moves
through the digestive tract.
• Control the rate at which dying cells are
replaced.
• Promote
» Growth,
» Differentiation,
» Development.

11. BIOSYNTHESIS OF TH
• Thyroid hormone produces three types of hormones
• They are
» Thyroxine (T4) ortetraiodothyroxine,
» Thyroxine (T3) or triiodothyroxine,
» Calcitonin.

12. COMPARISION
T4
• Major hormone secreted by
the thyroid follicles.
• 4 bound iodine atoms.
• Constructed from the
linkage of 2 tyrosine amino
acid.
T3
• Most is formed at the target
tissues by conversion of T4
to T3.
• 3 bound iodine atoms.
• Constructed from the
linkage of 2 tyrosine amino
acid.

13. CALCITONIN
• Calcitonin secreted by thyroid gland.
Associated hormones Chemical class Chemical class
Thyroxine (T4),
triiodothyronine (T3)
Amine Stimulate basal
metabolic rate.
Calcitonin Peptide Reduces blood Ca2+
levels.

14. SYNTHESIS OF THYROSIN

15. BIOSYNTHESIS
• Active uptake of iodide into follicular cell.
• Iodide iodine - H2O 2 (catalysed by TPO).
• Active uptake of iodine at follicular/ colloid
interface.
• Incorporation of iodine onto tyrosine residues
of thyroglobulin.
• Coupling of iodinated tyrosine.
• Storage of T3 and T4.

16. PROCESS
1. Iodine formation,
2. Thyroglobulin formation,
3. Iodination,
4. Coupling,
5. Sceretion of thyroid hormone.

18. 1. Iodine formation
• Iodine- raw material
• Iodine actively transported into the follicle cells by the action of sodium- iodide
symporter.
• One iodide ion along with 2 Na ions across plasma membrane.
• Energy gets from Na- K pump.
• Process of concentrating iodide in the cell- iodide trapping.
• Iodide secreted into the colloid.

19. 2.Thyroglobulin formation
• It is a glycoprotein – 2 sub units.
• Synthesized in thyroid cells.
• Following the entry of amino acids from extra
cellular fluid.
• Secreted into colloid – exocytosis.
• Granules contains thyroid peroxidase.

20. 3. Iodination
• Iodine binds with thyroglobulin –
organification.
• Thyrosine iodized to monoiodothyrosin and
then to diiodothyrosine.
• Iodinase-enzyme.
• 1 Iodine + 1 Thyrosine = MIT
• 2 Iodine+ 1 Thyrosine = DIT

21. 4. Coupling of iodotyrosyls
• 2 DIT = T4
• 1 MIT + 1 DIT = T3
• Drugs that inhibit oxidation also inhibits
coupling
• The thyroid hormones formed (T3/T4) remain
as integral parts of thyroglobulin
– Still attached to thyroglobulin, stored in lumen of
follicles until degraded later

22. 5. Secretion of thyroid hormone
• Thyroxin bound to thyroglobulin into follicular
cells.
• TSH stimulates pinocytosis of thyroglobulin
into follicular cell.
• Lysozyme enzyme hydrolyze peptide bonds
• Release T4 from thyroglobulin.
• T3 & T4 discharge freely into capillaries.

23. DISORDERS

24. THYROID DISORDERS
• Thyroid storm
• Goiter
Hyperthyroidisim
• Cretinism
• Myxoema
• Sick euthyroiditis
• Subacute thyroiditis
Hypothyroidisim

25. HYPERTHYROIDISIM
• Hyperthyroidism is a condition in which an
overactive thyroid gland is producing an excessive
amount of thyroid hormones that circulate in the
blood.
• Thyroid hormones include thyroxine (T4) and
triiodothyronine (T3), representing 99.9% and
0.1% of thyroid hormones, respectively.
• T3 is actually the most active thyroid hormone.
• Much of the T4 is converted to T3 in the
bloodstream.

26. GOITER
• A goiter is an enlarged thyroid gland that
causes the neck to swell.
• The degree of swelling and the severity of
symptoms produced by the goiter depends on
the individual.
• Some cases involve a small amount of
swelling, whereas others can involve
considerable swelling that actually constricts
the trachea and causes breathing problems.

27. causes of goiter
• Nodules - benign lumps.
• Smoking - thiocyanate in tobacco smoke interferes
with iodine absorption.
• Hormonal changes - pregnancy, puberty, and
menopause can affect thyroid function.
• Thyroiditis - inflammation caused by infection.
• Lithium - a psychiatric drug that can interfere with
thyroid function.
• Overconsumption of iodine - too much iodine can
cause a goiter.
• Radiation therapy - particularly to the neck.

28. SYMPTOMS
• A visible swelling at the base of your neck that
may be particularly obvious when you shave
or put on makeup.
• A tight feeling in your throat.
• Coughing.
• Hoarseness.
• Difficulty swallowing .
• Difficulty breathing.

29. HYPOTHYROIDISIM
• Hypothyroidism, or underactive thyroid, develops
when the thyroid gland fails to produce or secrete as
much thyroxine (T4) as the body needs.
• Thyroid gland doesn't produce enough of certain
important hormones.
• Hypothyroidism upsets the normal balance of chemical
reactions in body.
• abnormally low activity of the thyroid gland, resulting
in retardation of growth and mental development in
children and adults.

30. IN CHILD IN ADULT
HYPOTHYROIDISM
CRETINISM MYXODEMA

31. CRETINISIM MYXOEDEMA
Definition It is a condition arising from
a deficiency of thyroid
hormone, which is
characterized by dwarfism
and mental retardation.
It is a disease resulting from
the under-activity of the
thyroid gland, which is
characterized by puffy eyes,
face, hands and mental
sluggishness.
Cause It is caused due to low
levels of iodine in the body.
It is caused due to low
levels of thyroid hormone
in the blood.
Symptoms Fatigue
Lethargy
Mental impairment
Depression
Cold intolerance
Hoarseness
Dry skin
Weight gain
Swelling of skin
Hair loss
Mental impairment
Bone maturity delay
Slow thoughts and
reflexes.
Thickened skin
Protruding stomach
Treatment An increase in an iodine
filled diet helps preventing
cretinism.
It can be managed by
treating the underlying
cause of the disease.
Hypothyroidism Neonatal hypothyroidism. Adult hypothyroidism

32. PARATHYROID

33. PHARATHYROID GLAND
• Parathyroid glands are small endocrine glands.
• Humans usually have four parathyroid glands,
variably located on the back of the thyroid gland.
SIZE
• Normal parathyroid glands are approximately the
size of a grain of rice or a lentil.
• Normal glands are usually about 5 by 4 by 2 mm
in size and weight 35 to 50 milligrams.

35. HISTOLOGY
Two unique types of cells are present in the
parathyroid gland
• Chief cells, which synthesize and release
parathyroid hormone. These cells are small, and
appear dark when loaded with parathyroid
hormone, and clear when the hormone has been
secreted, or in their resting state.
• Oxyphil cells, which are lighter in appearance and
increase in number with age, have an unknown
function.

36. PARATHYROID HORMONE
(PTH)
• Parathyroid hormone (PTH), also called
parathormone or parathyrin.
• It is secreted by parathyroid gland

37. FUNCTIONS
• Increase blood calcium concentration when it
gets too low.
• Increase renal tubular reabsorption of
calcium.
• Mechanism of raising blood calcium
• Stimulate osteoglast to release more calcium from
bone.
• Decreases secretions of calcium by kidney.
• Activates vitamin-D, with stimulates the uptake of
calcium from the intestine.

38. CALCITONIN
• Calcitonin is a hormone secreted by the thyroid
gland that reduces the concentration of blood
calcium level when it has risen to an above
normal level.
• This polypeptide hormone is made up of 32
amino acids and is produced mainly by the
parafollicular cells (also known as C cells) of the
thyroid gland.
• In fish, birds and other non-mammalian animals,
calcitonin is produced by cells of the
ultimobranchial body.

39. CALCIUM
• the recommended daily
intake
• the plasma
concentration
• calcium excreted
• 1000mg
• 2.22.22.6mmol/L
• Kidneys 2.5 10mmol/24
hrs - 2.5-

41. THANK YOU