THYROID GLAND PHYSIOLOGY AND
DISORDERS
INTRODUCTION
•
Thyroid
is an endocrine gland situated at root of the neck on either sides of the
trachea.
•
It
has two lobes, which are connected in the middle by an isthmus.
•
It
weighs about 20 to 40 g in adults.
•
Thyroid
is larger in females than in males.
HORMONES OF
THYROID
•
Tetraiodothyronine
or T4 (thyroxine) – 90%
•
Tri-iodothyronine
or T3 – 9-10%
•
Calcitonin
•
T3
acts on the target cells immediately whereas T4 acts slowly
HALFLIFE
•
T4- 7days
•
T3-
10-24 hrs
ACTIONS OF
THYROID HORMONES
1. ACTION ON BASIC METABOLIC RATE (BMR)
PHYSIOLOGY
· Thyroxine increases the metabolic
activities in most of the body tissues, except Brain, retina, spleen, tests and
lungs.
HYPERTHYROIDISM BMR
increased by 60-100% RESULTING
IN · Weight loss · Increased appetite · Increased body temperature HYPOTHYROIDISM BMR
decreased by 20-40% RESULTING
IN · Weight gain · Decreased appetite · Cold intolerance
2. ACTION ON
GROWTH
PHYSILOGY
· Thyroid hormones have general and specific
actions on growth.
· Thyroxin plays important role in
brain development during fetal life and first few years of post natal life.
HYPOTHYROIDISM ·
Lack of thyroxine arrests the growth. ·
Height of the individual may be slightly
less. HYPERTHYROIDISM · Accelerates
the growth.
3. On Heart
Physiology
· Increase beta adrenergic receptors
sensitivity
· Increase Heart rate, cardiac muscle
contractility,
· Maintains vasomotor tone
Hyperthyroidism · Tachycardia · Increased cardiac contractility · Increased CO, HTN Hypothyroidism · Bradycardia · Decreased contractility · Vasoconstriction leads HTN
4. On Skeletal system
PHYSIOLOGY
· Maintains balance between osteobalsts
and osteoclasts.
· Helps for bone growth and maturation.
HYPERTHYROIDISM · Osteoporosis · Increased risk of fracture in
elderly. HYPOTHYROIDISM · Short stature in children
5.On Central
nervous system
PHYSIOLOGY
· Augument sympathetic nervous system
activity
HYPERTHYROIDISM · Anxiety · Insomnia · Lid retraction · Lid lag HYPOTHYROIDISM · Depression · Fatigue · lethargy · memory loss · reduced DTR
6. On Gastro
intenstinal tract
PHYSOILOGY
· Maintains intenstinal motility and GI secretions.
HYPERTHYROIDISM · Diarrhea HYPOTHYRPOIDISM · constipation
PHYSIOLOGY
· Maintains LDL receptors on liver.
HYPERTHYROIDISM · Decreased LDL HYPTHYROIDISM · Increased LDL, Triglycerides
8.On Skin
PHYSIOLOGY
· Maintains blood flow to skin and
sweat glands
· HYPOTHYROIDISM · Hair loss ( outer third of eye
lids) · Brittle, thin nails · Dryness and paleness of skin · Decreased sweat and sebeum HYPERTHYROIDISM · Increased nail growth
(onycholysis) · Increased sweating and sebeum
production
9. Fibroblastic activity
PHYSIOLOGY
· Regulate production and degradation
of glucosamineglycans
HYPERTHYROIDISM · Exopthalmosis · Pretibial myxedema HYPOTHYROIDISM · Pretibial myxedema · Peri orbital edema · Carpel tunnel syndrome
HYPERTHYROIDISM · Oligomennorea · Ammenorrrhea · ED, loss of libido · HYPOTHYROIDISM · Erectile dysfunction · Loss of libido · Gynacomastia · infertility
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