The document discusses the thyroid and parathyroid glands. It describes the thyroid gland as being butterfly-shaped and located in the neck, regulating metabolism. It produces the hormones T3 and T4. The parathyroid glands are located on the thyroid and secrete parathyroid hormone to regulate calcium levels. The document covers the anatomy, physiology, hormone synthesis and regulation of the thyroid and parathyroid glands.

2. THYROID AND
PARATHYROID GLANDS

3. HYPOTHALAMIC-PITUTARY-THYROID AXIS

4. THYROID

5. THYROID GLAND
The thyroid gland is a butterfly
shaped endocrine organ found in
the neck. It is responsible for
regulating the body’s metabolic
rate via hormones it produces.
 Composed of two lobes, left and
right connected by a narrow
isthmus
 Weighs around 25 grams in
adults
 Each lobe being about 5 cm
long, 3 cm wide and 2 cm thick

6. THYROID GLAND
Location
 The thyroid gland is located immediately below the larynx and anterior to the
upper part of the trachea. It weighs about 25 gms
 Located in the anterior neck, between the C5 and T1 vertebrate
 Just inferior to the Adam’s apple and larynx
Anterolateral Posterolateral Posteromedial
• Sternothyroid
• Sternohyoid
• Common carotid
artery
• Internal jugular vein
• Vagus nerve
• Larynx
• Trachea
• Pharynx
• Oesophagus
• External laryngeal
nerve

7. THYROID GLAND LOCATION

8. THYROID GLAND LOCATION
 The lobes of the thyroid contain many hollow,
spherical structure called follicles, which are the
functional units of the thyroid gland.
 Interspersed between the follicles are C cells, which
secrete calcitonin.
 Each follicle is filled with a thick sticky substance
called colloid
 The major constituent of colloid is a large
glycoprotein called thyroglobulin
 Unlike other endocrine glands, which secretes their
hormones once they are produced, the thyroid gland
stores considerable amount of the thyroid hormones
in the colloid until they are needed by the body

9. VASCULAR SUPPLY
 Blood supply to the thyroid gland is achieved by
 Superior thyroid artery
 Inferior thyroid artery
 These are paired arteries arising on both the left and right
Superior thyroid artery
 It is the first branch of the external carotid artery
 After arising, the artery descends toward the thyroid gland
 It supplies the superior and anterior portions of the gland
Inferior thyroid artery
 It arises from the thyrocervical trunk
 The artery travels superomedially to reach the inferior pole of the thyroid
 It tends to supply the posteroinferior aspect of the gland

10. VASCULAR SUPPLY
Venous drainage
 Venous drainage is carried out by the superior, middle and inferior thyroid veins
which form a venous plexus
 The superior and middle veins drain into the internal jugular veins
 Middle thyroid vein emerges medially and enters the internal jugular vein
 The inferior vein drains into the brachiocephalic vein
Embryonic development
 The thyroid originates form two main structures that are primitive pharynx and
the neural crest
 The lateral thyroid develops from neural crest cells
 The median thyroid, which forms the bulk of the gland, arises from the primitive
pharynx

11. PHYSIOLOGY
 The thyroid gland is the regulator of Metabolism
 T3 and T4 typically act via nuclear receptors in target tissues and initiate a
variety of metabolic pathways
Metabolic processes increased by thyroid hormones include
 Basal metabolic rate
 Gluconeogenesis
 Glycogenolysis
 Protein synthesis
 Lipogenesis
 thermogenesis

12. PHYSIOLOGY
 The thyroid gland is covered by a fibrous
capsule which on microscopic examination is
seen as aggregation of follicles
 Each follicle is lined by follicular cells
 Apart from the gland also contain C-cells
(parafollicular cells) which intervene between
the follicular cells and the basement membrane
 The shape of follicular cells vary on their level
of activity
 Normal – Cells are cuboidal and colloid is
moderate
 Inactive - cells are flat and colloid is abundant
 Highly active – cells are columnar and colloid
is scanty

13. PHYSIOLOGY
Follicular cells
 They secrete 2 hormones T3 (triiodothyronine)
and T4 (tetraiodothyronine) that influence the
rate of metabolism for which iodine is an
essential component
 The activity of follicular cells is influenced by
TSH (thyroid stimulating hormone)
The C-cells (Parafollicular cells)
 Also known as clear cells or light cells
 They secrete hormone thyro-calcitonin which
has as action opposite to that of the parathyroid
hormone on calcium metabolism
 This hormone comes into play when serum
calcium level is high

14. HORMONE SYNTHESIS

15. SYNTHESIS, STORAGE & SECRETION
 Tyrosine and iodine are essential for synthesis of thyroid hormones.
 Both are taken up by the blood
 Tyrosine is synthesised by the body (in the thyroglobulin).
 Iodine is a dietary essential.
 Hormone synthesis occurs on the thyroglobulin
 Following steps are involved synthesis, storage and secretion
 Thyroglobulin production by follicular cell and released into colloid by
exocytosis
 Iodine uptake by follicular cell from the blood and transferred to colloid
 Attachments of iodine to tyrosine on thyroglobulin in colloid
 Coupling processes between the iodinated tyrosine molecules to form T4
and T3
 Secretion (upon stimulation) of T4 and T3 occurs by endocytosis a piece of
colloid, uncouplingof T4 and T3 and diffusion out of the follicular cell into
the blood

16. SYNTHESIS, STORAGE & SECRETION
 Approximately, 90% of the hormones released from the thyroid gland initially
appear in the form of T4
 However, a majority of the T4 that is secreted from the thyroid gland is
subsequently converted to T3.
 T3 is 4times more potent in its biologic form than T4 and is the major hormone
that interacts with the target cells.
 Both the hormones are highly lipophilic and once in the blood, immediately bind
to proteins:
 Thyroid hormone specific protein- thyroxine binding globulin (70-80%)
 Other non-specific proteins
 Less than 0.1% of T4 and 1% of T3 are in unbound form.
 These free T4 and T3 compounds are biologically active, and it is these
components that produce the effects of the thyroid hormones on peripheral
tissues and on the pituitary feedback mechanism.

17. HORMONE REGULATION

18. PHYSIOLOGICAL EFFECTS OF THYROID HORMONES
Metabolic rate and heat production:
 ↑ metabolic activities
 ↑ O₂ consumption to most metabolically active tissues
 BMR can ↑ by 60 – 100%
 Since ↑ metabolism results in ↑ heat production → thyroid hormone effects is
calorigenic
Intermediary metabolism:
 Modulates rates of many specific reactions involved in fuel metabolism
Sympathomimetic effect
 Sympathomimetic: any action similar to one produced by the sympathetic nervous
system
 Thyroid hormone ↑ target cell responsiveness to catecholamines (SNS and adrenal)
 Thyroid hormones are permissive → ↑ production of specific catecholamine target cell
receptors

19. PHYSIOLOGICAL EFFECTS OF THYROID HORMONES
The cardiovascular system:
 ↑ the heart’s responsiveness to circulating catecholamines (permissive action above)
 ↑ heart rate and force of contraction → ↑ CO
 In response to the heat load → peripheral vasodilation to eliminate generation of
extra heat
Growth and the nervous system
 Effect on growth is manifested mainly in growing children
 Thyroid hormone stimulates GH secretion and promotes GH effects
 Lack of thyroid hormone → growth retardation but can be reversed by thyroid
replacement therapy
 Unlike excess GH, excess thyroid hormone does not produce excessive growth
 Important in promoting growth and development of the brain during fetal and
postnatal life

20. PARATHYROID GLANDS
 The parathyroid glands are small endocrine glands
 They are responsible for the production of
parathyroid hormone
 It controls calcium levels in the body
Shape
 They are flattened and oval in shape situated external
to the gland itself, but within its sheath
Anatomical location
 They are located on the posterior, medial aspect of
each lobe of the thyroid gland
Size and weight
 Its size is of grain of rice and is about 30 milligrams
weight and 3-4 cms in diameter

21. PARATHYROID GLANDS
Chief cells
 They are small cells
 They are more abundant
 They secrete parathyroid hormone
Oxyphil cells
 They are much larger
 Less abundant than chief cells
 The number of oxyphil cells increases with age
Vascular supply Blood supply: –
 Through superior and inferior thyroid arteries.
 Venous return: – The parathyroid veins drain into the thyroid plexus of veins.
 Lymphatic drainage: – Into the deep cervical lymph nodes and paratracheal
lymph nodes

22. PARATHYROID GLANDS
Nerve supply
 Nerve supply derived from thyroid branches of the cervical (sympathetic)
ganglia.
 These nerves are vasomotor, not secretomotor – endocrine secretion of
parathyroid hormone is controlled hormonally.
Functions of PTH
 Parathormone is produced by chief cells tends to increase the serum calcium level
 PTH is a peptide hormone, is secreted in response to low blood calcium level
 Its secretion is controlled by negative feedback system
 Suppression of calcium loss in urine.
 Stimulate loss of phosphate ions in urine
 Mobilization of calcium from bone.
 Enhancing absorption of calcium from the small intestine.
 Activation of Vitamin D Activation of Vitamin D

23. PARATHYROID GLANDS

24.  Autoimmune = Graves disease
 Infective = De Quervain’s thyroiditis
 Neoplastic = toxic adenoma
 Iatrogenic = drugs such as amiodarone or lithium. Also from over treating
hypothyroidism
Symptoms
 Increased metabolism
 weight loss and increased appetite
 Heat intolerance
 Sweating
 Diarrhoea
 Tremor
 Irritability/restlessness
 Psychosis
 Oligomenorrhoea
HYPERTHYROIDISM

25.  Increased pulse rate
 Atrial fibrillation
 Palmar erythema
 Hair thinning
 Lid retraction
 Goiter, nodules or bruites
HYPERTHYROIDISM

26.  Eye signs – exomphalos, ophthalmoplegia, lid lag and
lid retraction
 Pretibial myxoedema
 Thyroid acropachy
GRAVES DISEASE

27. Diagnosis
 TSH, T4 and T3
 Thyroid autoantibodies - antithyroid peroxidase and
antithyroglobulin antibodies
 TSH receptor antibodies
 Isotope scan
GRAVES DISEASE

28.  Auto immune
 Hashimoto’s thyroiditis
 Primary myoxedema (or primary atrophic hypothyroidism)
 Dietary – iodine deficiency
 Iatrogenic
 congenital
Symptoms
 Tiredness
 Lethargy
 Depression
 Cold intolerance
 Weight gain
 Constipation
 Menorrhagia
 dementia
HYPOTHYROIDISM