CC2 LEC - 9: THYROID GLAND

Isthmus

Thyroid gland is made up of two lobes resting on each side of the trachea and are bridged together with _____

Isthmus

Tied the two lobes with the thyroid tissue running anterior to the trachea

Parathyroid gland

posterior surface of the thyroid gland

4th to 8th week of gestation

Thyroid glands in humans start to develop in the fetus at about. _____

Reaching 11th week

Time when thyroid gland is capable of secreting thyroid hormones

Lower anterior neck

Thyroid gland is located in front of the _____

Bow tie or butterfly like

Structure of thyroid gland

Structural units of Thyroid

Follicles

Colloid

Each follicle has a core which is made up of ____

Colloid

consist of homogenous viscous fluid consisting mainly of a glycoprotein iodine complex called thyroglobin

Thyroglobulin

A glycoprotein iodine complex

1. T3

2. T4

3. Calcitonin

Thyroi gland secretes (3):

1. Follicular cells

2. Parafollicular cells

2 types of cells:

1. T3 (triiodothyronine)

2. T4 (thyroxine)

2 types of Follicular cells (produced by):

Calcitonin

A type of parafollicular cell:

1. Globulin

2. Albumin

T3 is bound to (2):

1. Globulin

2. Albumin

3. Pre-albumin

T4 is bound to (3):

1. Tissue growth

2. Development of CNS

3. Elevated heat production

4. Control of oxygen

5. Influence carbohydrate and protein metabolism

6. Energy conservation

Thyroid hormones function (6):

3,5,5' triiodothyronine

T3 is also known as:

T3

Has the most active thyroid hormonal activity

75-80%

Almost ____ is produced from the tissue deiodination of T4

T3 Thyrotoxicosis

Principal application of T3 is in diagnosing ______

Hyperthyroidism

T3 is better indicator of recovery and recurrence from ____

1. 80-200 ng/dl or 1.2-3.1 nmol/L in adult

2. 105-245 ng/dl or 1.8-3.8 nmol/L in children

Reference values of T3 in adult and children:

3,5,3'5' tetraiodothyronine

T4 is also known as:

T4

Principal secretory product

T4

Major fraction of organic iodine in the circulation

T4

Prehormone for T3 production

Thyroid gland

All circulating T4 originates in the +++++

1. Inhibition of TSH secretion

2. Vice versa

Elevated levels of T4 causes (2):

1. 5.5-12.5 ug/dl or 71-161 nmol/L (adult)

2. 11.8-22.6 ug/dl or 152-292 nmol/L (neonate)

Reference value of T4:

Iodine

Most important element in the biosynthesis of thyroid hormones

Below 50ug/day

Iodine intake that can cause deficiency:

1. Monoiodotyrosine (MIT)

2. Diiodotyrosine (DIT)

Iodintion of tyrosine residues in the thyroglobulin results in the formation of (2):

Many tissues

Conversion of T4 and T3 takes place in _______

Metabolically inactive

Protein bound hormones are _______

Inner ring of T4

Reverse T3 is produced by removal of one iodine from ______

Around 12 hrs

Latent period of T3

Around 72 hrs

Latent period of T4

Around 2 days

Half-life of T3

Around 7-9 days

Half-life of T4

1. Increase BMR

2. Increase protein, carbohydrate, fat metabolism

3. Potentiate actions of cathecholamines

4. Interaction with other endocrine system

5. Effect on the CNS

6. Increase Vit. A and retinal synthesis

Main action of T3 and T4 (6):

Agenesis

complete absence of organ

Incomplete descent

From base of tounge to trachea

Lingual thyroid

Complete failure to descent from base of tounge

Thyroglossal cyst

Segment of duct persists and presents as lump years later

Hyperthyroidism

Refers to an excess of circulating thyroid hormone

Hyperthyroidism

1. Patients are slim & thin

2. Increase appetite

3. Decrease weight

4. Exophthalmia

5. Heat intolerance

7. Increace activitty

Hypothyroidism

Insufficient amounts of thyroid hormne are available to tissues

Hypothyroidism

1. Patients are obese

2. Decrease appetite

3. Increase body weight

4. Edematous

5. Increase chloresterol level

6. Cold intolerance

7. Decrease activity

1. Thyrotoxicosis

2. Grave's disease

3. Reidel's thyroiditis (Reidel's Struma)

4. Subclinical hyperthyroidism

5. Subacute granulomatous/subacute nonsuppurative thyroiditis (De Quervain's thyroiditis)

Disorders of Hyperthyroidism (5):

Thyrotoxicosis (Plummer's disease)

Overactive thyroid gland maes too much thyroxine

1. TSH is low

2. FT4 is normal

3. T3 increase

Findings in Thyroxoticosis (3):

1. Mood swings

2. Restless

3. Sleep difficulties

4. Tremor of hands

5. Palpitations

6. Sore eyes

7. Goiter

Features of Thyrotoxicosis (7):

Grave's disease

Hyperthyroidism with peculiar edema behind the eyes

Grave's disease

Hypersecretion of thyroid stimulating immunoglobulins (TSIs)

Grave's disease

Whole gland is smoothly enlarged and the whole gland is overactive

6x more commonly in women

Grave's disease occurs _____ more commonly

1. Exophthalmos

2. Pritibial myxedema

2 features of Grave's disease:

Reidel's thyroiditis (Reidel's Struma)

Thyroid turns into a woody or stony-hard mass

Subclinical hyperthyroidism

Shows no clinical symptoms

-TSH level is low

-FT3 and FT4 normal

Subacute granulomatous/subacute nonsuppurative thyroiditis (De Quervain's Thyroiditis)

Associated with

-neck pain

-low grade fever

-swing in thyroid function tests

1. Thyroid peroxidase antibodies are ABSENT

2. ESR and thyroglobulin are ELEVATED

2 clinical findings of Subacute granulomatous/subacute nonsuppurative thyroiditis (De Quervain's Thyroiditis)

1. Myxedema

2. Hashimoto's disease (chronic autoimmune)

3. Cretinism

4. Secondary hypothyroidism

5. Goiter

Disorders of Hypothyroidism (5):

Myxedema

Caused by autoimmune damage to the thyroid or surgical removal

Myxedema

Underactive thyroid gland

Myxedema

Describes the peculiar nonpitting swelling of the skin

Myxedema

The skin becomes infiltrated by mucopolysaccharides

Myxedema

Hypothyroidism during the adult years

Hashimoto's disease

The most common cause of primary hypothyroidism

1912

Hashimoto was described in the year ____

Hashimoto's disease

An autoimmune disease in which thyroid land is attacked by variety of antibody mediated immune response

Hashimoto's disease

The thyroid is replaced by a nest of lymphoid tissue

Enlargement of thyroid gland

Hashimoto's disease is associated with:

Hashimoto's disease

Acquired hypothyroidism in later childhood due to development of autoantibodies to thyroid tissue components

Cretinism

severely stunted physical and mental growth due to untreated congenital hypothyroidism due to maternal nutritional deficiency of Iodine

Decreased T4

Screening test of Cretinism

Increased TSH

Confirmatory test of Cretinism

1. Babies at 5-10 days have heel prick blood test

2. Thyroid function

3. Guthrie test

Cretinism prevention (3):

Guthrie test

Test for phenylketonuria

Thyroid function

Measures TSH, if high - thyroxine is given immediately

Cretinism

Hyposecretion of thyroid hormones during fetal life or infancy

Cretinism

Iodine deficiency during fetal/neonates

Secondary hypothyroidism

Caused by TSH (thyrotrophin) deficiency

1. Surgery

2. Autoimmune disease

3. Resistance to TSH

4. Iodine deficiency

Causes of Hypothyroidism (4):

Goiter

Enlarged thyroid gland which is a symptom of many thyroid disorders

1. Hypo

2. Hyper

3. Euthyroid state

Goiter is a symptom of (3):

Calcitonin

Produced by parafollicular cells

Calcitonin

Involve in calcium deposition

1. Inhibition of osteoclast activity

2. Decrease plasma concentration

Calcitonin action on bone (2):

1. Increased urinary excretion of Ca2+

2. Decrease plasma concentration

Calcitonin action on kidneys (2):

Calcitonin

Marker for medullary thyroid cancer

Parathyroid gland

four tiny glands, located in the neck, that control the body's calcium levels and phosphate metabolism

1. Bone

2. Kidney

3. Intestine

Parathyroid gland body targets (3):

Prevent hypocalcemia

Primary role of PTH:

1. Chief cells

2. Oxyphil cells

PTH type of cells (2):

Chief cells

Type of cell that synthesize and secrete hormone PTH

Oxyphil cells

Non secretory cell and Seen only after puberty

1. Primary hyperparathyroidism

2. Secondary hyperparathyroidism

Disease associated with hyperparathyroidism (2):

Primary hyperparathyroidism

Most common cause of hypercalcemia