Hormone Regulation: Calcitonin and Thyroid Hormone

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Questions and Answers

In the thyroid gland, which hormone is involved in regulating calcium levels?

Tri-iodothyronine (T3)

Somatostatin

Calcitonin (correct)

Thyroxine (T4)

Where does the thyroid gland originate from in embryonic development?

Foregut endoderm (correct)

Neural crest

Notochord

Mesoderm

What is the primary function of the thyroid gland?

Regulating blood sugar levels

Producing digestive enzymes

Storing pancreatic hormones

Synthesizing thyroid hormones (correct)

Which of the following is NOT a thyroid hormone?

Insulin Signup and view all the answers

What is the location of the thyroid gland in the body?

Anterior and inferior to the larynx Signup and view all the answers

What is the connection between the two lobes of the thyroid gland?

Isthmus Signup and view all the answers

What is the trigger for calcitonin secretion?

Elevated blood Ca2+ levels Signup and view all the answers

Which of the following is a symptom of hyperthyroidism?

Nervousness Signup and view all the answers

What is the primary cause of goiter?

Chronic dietary iodine deficiencies Signup and view all the answers

What is the function of parathyroid hormone (PTH)?

Regulation of blood calcium levels Signup and view all the answers

What is the characteristics of the cytoplasm of principal cells in the parathyroid glands?

Pale-staining and slightly acidophilic Signup and view all the answers

What is the result of inadequate secretion of TSH by the anterior pituitary gland?

Hypothyroidism Signup and view all the answers

What is the location of the parathyroid glands?

On the back of the thyroid gland Signup and view all the answers

What is the characteristic of the granules in parafollicular cells?

Irregularly shaped and small Signup and view all the answers

What is the unique characteristic of the thyroid gland among endocrine glands?

It stores secretory product outside the cells Signup and view all the answers

What is the function of the septa in the thyroid gland?

To divide the gland into lobules Signup and view all the answers

What is the precursor for the active thyroid hormones in the thyroid colloid?

Thyroglobulin Signup and view all the answers

What type of cells are found in the basal lamina of the follicular epithelium or as isolated clusters between follicles?

Parafollicular cells (C cells) Signup and view all the answers

What is the role of thyroid-stimulating hormone (TSH) in the thyroid gland?

To control the activity of follicular cells Signup and view all the answers

What is the characteristic of the follicular cells in active thyroid glands?

They have a more low columnar shape Signup and view all the answers

How long can the thyroid gland supply the body with hormone without additional synthesis?

Up to 3 months Signup and view all the answers

What type of capillaries are found in the stroma of the thyroid gland?

Fenestrated capillaries Signup and view all the answers

Study Notes

Thyroid Gland

The thyroid gland is located anterior and inferior to the larynx and consists of two lobes united by an isthmus.
It synthesizes thyroid hormones, including thyroxine (T4), tri-iodothyronine (T3), and calcitonin.
The gland originates from the foregut endoderm near the base of the developing tongue during early embryonic life.

Thyroid Follicles

The thyroid gland is composed of millions of rounded epithelial thyroid follicles of variable diameter.
Each follicle has a simple epithelium and a central lumen densely filled with gelatinous acidophilic colloid.
The thyroid is the only endocrine gland that stores a large quantity of secretory product outside the cells, in the colloid.
Thyroid colloid contains the large glycoprotein thyroglobulin, the precursor for active thyroid hormones.
There is sufficient hormone in follicles to supply the body for up to 3 months without additional synthesis.

Thyroid Cells

Follicular cells (thyrocytes) have a shape that varies from squamous to low columnar, depending on their activity.
Their size and features vary with their activity, which is controlled by thyroid-stimulating hormone (TSH) from the anterior pituitary.
Active glands have more follicles of low columnar epithelium, while glands with mostly squamous follicular cells are hypoactive.

Parafollicular Cells (C Cells)

Parafollicular cells are an endocrine cell type found inside the basal lamina of the follicular epithelium or as isolated clusters between follicles.
They are derived from the neural crest and are larger than follicular cells, staining less intensely.
They have ultrastructural features of active polypeptide-secreting cells, with secretory granules that vary in size, morphology, and electron density.

Calcitonin

Calcitonin is secreted by parafollicular cells (C cells) and is triggered by elevated blood Ca2+ levels.
It inhibits osteoclast activity.

Parathyroid Glands

The parathyroid glands are four small ovoid masses, each 3 × 6 mm in size, with a total weight of about 0.4 g.
They are located on the back of the thyroid gland, usually embedded in the gland's capsule.
Each gland is contained within a thin capsule, with septa extending into the gland and supporting dense elongated clusters of secretory cells.

Principal (Chief) Cells

Principal cells are the endocrine cells of the parathyroid glands, with small polygonal cells and round nuclei.
They have pale-staining, slightly acidophilic cytoplasm with irregularly shaped cytoplasmic granules containing parathyroid hormone (PTH).

Goiter

Goiter is a condition caused by chronic dietary iodine deficiencies, which inhibit thyroid hormone production.
This leads to excessive growth of thyroid follicles and enlargement of the thyroid gland.

Graves' Disease

Graves' disease is an autoimmune disorder characterized by antibodies that produce chronic stimulation of the follicular cells and release of thyroid hormones (hyperthyroidism).
This causes a hypermetabolic state marked by weight loss, nervousness, sweating, heat intolerance, and other features.

Hypothyroidism

Hypothyroidism is a condition characterized by reduced thyroid hormone levels, which can be caused by local inflammation (thyroiditis) or inadequate secretion of TSH by the anterior pituitary gland.
It is often manifested by tiredness, weight gain, intolerance of cold, and decreased ability to concentrate.

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Description

This quiz covers the secretion of calcitonin, its role in inhibiting osteoclast activity, and the effects of dietary iodine deficiencies on thyroid hormone production.