THYROID GLAND PHYSIOLOGY AND DISORDERS

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

 

 

 7.On Liver

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

Increase sebaum and sweat production

 

 

 

 

9. Fibroblastic activity

PHYSIOLOGY

·     Regulate production and degradation of glucosamineglycans

HYPERTHYROIDISM ·       Exopthalmosis ·       Pretibial myxedema

HYPOTHYROIDISM ·       Pretibial myxedema ·       Peri orbital edema ·       Carpel tunnel syndrome

 

 

 

 

 

 

 

 10.On  Reproductive system

HYPERTHYROIDISM ·       Oligomennorea ·       Ammenorrrhea ·       ED, loss of libido ·

HYPOTHYROIDISM ·       Erectile dysfunction ·       Loss of libido ·       Gynacomastia ·       infertility