3. FUNCTIONAL ANATOMY.
GROSS ANATOMY
Largest endocrine
gland
15-25 gm
Consists of 2 lobes
joined by narrow
Isthmus.
High blood supply –
400-600ml/100g/min.
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4. HISTOLOGICAL STRUCTURE
Each lobe divide3d
into lobules by fibrous
septa.
Each lobules made up
of several follicles.
Each follicle lined by
Follicular cells.
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5. HISTOLOGICAL STRUCTURE
Follicular cells.
Cuboidal & contains colloid.
Secrete Thyroid Hormones.
Parafollicular cells (C cells).
Between follicular cells
Secrete Calcitonin.
Colloid.
Homogenous material in each
follicle
Contains Thyroglobulin.
Tuesday, February 20, 2018
6. THYROID HORMONES
2 Principal Hormones
Tri-iodothyronine T3
Thyroxine T4
T3 – 10% , Responsible for
most of tissue actions.
T4 – 90%
Calcitonin – hormone
secreted by Parafollicular
cells, concerned with Calcium
Homeostasis.
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8. THYROID HORMONES
BIOSYNTHESIS & STORAGE
Iodine trapping
Synthesis &
secretion of
thyroglobulin
Oxidation of iodides.
Organification of
thyroglobulins.
Coupling reaction.
Storage.
Tuesday, February 20, 2018
9. IODINE TRAPPING
Uptake of iodide by thyroid
gland.
By Iodine pump or Na/I –
symporter.
Thyroid stimulating
hormone – controls iodide
uptake.
Anti-thyroid agents –
Thiocynate & Perchlorate
inhibit Iodide transport.
Tuesday, February 20, 2018
10. SYNTHESIS & SECRETION OF
THYROGLOBULIN
Thyroglobulin – large Glycoprotein synthesized in
rough endoplasmic reticulum of thyroid epithelial
cells & then released into lumen.
1 molecule of Thyroglobulin contains – 140
thyrosine residue which is a substrate for iodine for
thyroid hormone synthesis.
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12. OXIDATION OF IODIDES.
Once inside gland iodide is taken into lumen by
transporter – Pendrin.
Then iodide is oxidised to Iodine by enzyme
Peroxidase.
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13. ORGANIFICATION OF
THYROGLOBULINS.
Iodination of tyrosine
residue in thyroglobulin
molecule.
Tyrosine is 1st
iodinated
at position 3 to form
Mono-iodotyrosine
(MIT) & then at position
5 to form Di-
iodotyrosine (DIT)
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14. COUPLING REACTION.
One molecule of MIT &
DIT coupled to form
Tri-iodothyronine
(T3)
2 molecules of DIT
coupled to form
Thyroxine (T4)
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15. STORAGE.
Once Thyroglobulin is
iodinated is stored in
lumen.
Stored thyroid
hormones can meet
body requirements for
1-3 months.
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16. SECRETION
Endocytosis – colloid
containing iodinated
Thyroglobulin is secreted by
Endocytosis.
Colloid enters the cytoplasm
as colloid droplets.
Proteolysis – colloid droplets
fuses lysosome vesicles
containing proteolytic
enzymes & releases T3,T4,
MIT & DIT.
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17. TRANSPORT
Bound form – most of
T3 & T4 are bound to
specific proteins.
Thyroxine binding
Globulins – bind 70%
of T3 & T4.
Free form – 0.5% of
T3 & 0.05% of T4.
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18. METABOLISM
Deiodination – about 40%
T4 deiodinated into T3 by
enzyme 5’-deiodinase.
Decarboxylation – very
few decarboxylated to form
tetraiodothyroacetic acid &
tri-iodothyroacetic acid.
Conjugation – 15% T3 & T4
are conjugated in liver to
form glucoronides &
sulphates.
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19. REGULATION OF THYROID
HORMONE SECRETION.
Through Negative
Feedback
Auto Regulation of
thyroid gland.
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23. ACTIONS OF THYROID
HORMONE
Effect on growth & tissue
development.
Effect on metabolic rate in general.
Effects on metabolism.
Carbohydrate
Fats
Proteins
Vitamins
Respiratory effects.
Cardiovascular effects.
Effects on nervous system
Development
Functioning of nervous tissue
Effects on GIT.
Effects on reproductive system
Effects on other endocrine
glands.
Effects on kidney.
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24. EFFECT ON GROWTH & TISSUE
DEVELOPMENT.
Role in normal body
growth & skeletal
maturation.
Bone development
Teeth development.
Role in tissue
differentiation &
maturation.
Role in development of
nervous tissue.
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25. EFFECT ON METABOLIC RATE
IN GENERAL.
Stimulate metabolic
activities
Increases basal rate of
oxygen consumption
and heat production.
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26. EFFECTS ON METABOLISM.
Carbohydrate – increase glucose absorption & metabolism.
Fats – Mobilization of fats from adipose tissue 7 decreases
plasma cholesterol levels.
Proteins – Physiologically anabolic effect & in high conc
catabolic effect.
Vitamins – increases quantity of enzymes so causes vitamin
deficiency.
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27. RESPIRATORY EFFECTS.
Increase in resting
respiratory rate, minute
ventilation &
ventilatory response to
hypercapnia & hypoxia.
Increase in oxygen
carrying capacity of
blood.
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28. CARDIOVASCULAR EFFECTS.
Tachycardia.
Increase force of cardiac
contraction.
Increase cardiac output.
Blood pressure – systolic
increases & diastolic
decreases.
Vasodilatation & increased
blood flow to tissue.
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29. EFFECTS ON NERVOUS SYSTEM
Development
Functioning of
nervous tissue.
Effect on functioning
of nervous tissue.
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30. EFFECTS ON GIT.
Increase in appetite &
food intake.
Increase in rate of
secretion of digestive
juices.
Increase in motility of
GIT.
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31. EFFECTS ON REPRODUCTIVE
SYSTEM
In Males – lack of
hormones causes loss
of libido & excess
causes Impotence.
In Females –
menorrhagia &
Polymenorrhagia.
Irregular periods &
Amenorrhoea.
Tuesday, February 20, 2018
32. EFFECTS ON OTHER
ENDOCRINE GLANDS.
Pituitary,
adrenocortical
secretion & oestrogen :
androgen ratio
increased.
Parathyroid & 1,25-
(OH)2 – Vit D decreased.
Tuesday, February 20, 2018
33. EFFECTS ON KIDNEY.
Renal plasma flow
GFR
Tubular transport
maximum.
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42. INFANTILE HYPOTHYROIDISM
( CRETINISM) –
Hypothyroidism in 1st
yr
of life.
Mental retardation,
marked retardation of
growth, delayed
milestone development,
pot belly, protruding
tongue, flat nose, dry
skin & sparse hairs.
Tuesday, February 20, 2018
43. ADULT HYPOTHYROIDISM
(MYXODEMA)
Due to infiltration of skin
by Myxodematous
tissue.
Clinical features –
General – Tiredness,
weight gain, cold
intolerance, decreased
sweating.
CVS – Bradycardia,
Anaemia.
Tuesday, February 20, 2018