Thyroid hormones & glands

Question 1

Thyroid hormone synthesis

Answer 1

1- Iodine CAPTATION: The iodine from the diet I- is captured by the follicular cells by active transport that diffuses to the colloid through the cell cytoplasm.

2- ORGANIFICATION. The iodine I- is oxidized by peroxidases to reactive forms of I2 which binds to the tyrosine residues of thyroglobulin stored in the colloid. Monoiodotyrosine (MIT) and diiodotyrosine (DIT) are synthesized.

3- COUPLING of iodotyrosines: 2 de DIT give T4 (tyrosine); DIT+MIT give T3. The tyroglobulin + T4 and/or T3 complex is stored in the colloid.

4- HYDROLYSIS. In case of need, through endocytosis, the complex passes back to the follicular cells, where the hydrolysis of thyroglobulin occurs in the lysosomes and T3 and T4 are released.

5- T3 y T4 enter the blood.

Question 2

T4

Answer 2

• =Tetraiodothyronine
• =Thyroxine
• 90%oftotalsecretion.
• Non-active form.

Question 3

T3

Answer 3

• Triiodothyronine
• 10% of total secretion.
• Biologically active form.

Question 4

Thyroid hormones effect

Answer 4

• Increase of metabolic activity. (↑ 𝐺𝐸𝐵)
• Heat generation.
• Stimulation of protein synthesis and lipid and carbohydrate metabolism.
• Increase of neurotransmitters synthesis.
• Synergistic action with catecholamines (sympathetic enhancement).
• Essential in brain development, body growth (in particular: CNS and skeleton).

Question 5

Throid exploration

Answer 5

Physical examination: inspection, palpation, auscultation

Imaging studies: Ultrasound and mammography with radioactive isotopes

Funtional exploration: TSH, T3, T4 and autoantibodies levels

Question 6

3 types of disorders

Answer 6

Hypothyroidsim
Hyperthyroidism
Goiter

Question 7

Primary: Hyperthyroidism

Answer 7

1. Toxic thyroid adenoma

2. Plummer disease

Question 8

Secondary: Hyperthyroidism

Answer 8

1. Tumor = increased TSH
2. Graves disease

• Autoimmune disease (autoantibodies)
• Cause goiter
• Most common type

Question 9

Manifestation: Hyperthyroidism: 1

Answer 9

GENERAL MANIFESTATIONS:
• LOW TOLERANCE TO HEAT → hyperthermia
• WEIGHT LOSS (WITH APPETITE)

SKIN:
• BRIGHT AND FIXED LOOK
• HOT AND MOIST SKIN
• FINE AND BRITTLE HAIR
• UNGUEAL ALTERATIONS

DIGESTIVE SYSTEM:
• DIARRHEA by ↑ peristalsis

RESPIRATORY SYSTEM:
• TACHYPNEA • DYSPNEA

Question 10

Manifestation: Hyperthyroidism: 2

Answer 10

CARDIOVASCULAR SYSTEM:
• INCREASED HEART RATE
• POSITIVE INOTROPIC EFFECT
• INCREASED BLOOD PRESSURE

METABOLISM:
•Hyperglycemia
•Decrease in TG and cholesterol

CNS
• Activation of adrenergic sympathic system

MUSCULOSKELTAL SYSTEM
•Muscular atrophy
• Weakness

Question 11

Graves-basedow disease

Answer 11

• All of the above symptoms
• Exophthalmos (bulging eyes)
• Pretibial edema.

Question 12

Hypothyroidism

Answer 12

Clinical situation associated to a defective function of thyroid hormones on tissues, normally due to a defect of thyroid hormone secretion

Primary: Hashimotos thyroiditis
Secondary
Tertiary

Question 13

Hashimotos thyroiditis

Answer 13

Autoimmune origin

Autoantibodies presence:
• Inhibitors of TSH action
• Antithyroglobulin
• Anti-peroxidase

Question 14

Hypothyroidism in adults

Answer 14

General:

• Low tolerance to cold
• Weight increase

Skin:

• Pale skin
• Hair loss

Digestive:
-Constipation

Cardiovascular

• Decreased cardiac output
• Bradycardia

CNS

• Apathy and sleepiness
• Attention, memory and concentration disorders
• Carpal tunnel syndrome

Question 15

Hypothyroidism in children

Answer 15

Much more serious!

• Growth failure
• Mental retardation

Question 16

Goiter and signs/symptoms

Answer 16

Enlarged thyroid

Cause:

• Goiter due to Increased TSH
  (euthyroid/simple, hypothyroid, hyperthyroid)
• Goiter due to Increased TSI (thyroid stimulating antibodies)