Endocrine System: Parafollicular Cells and Parathyroid Glands

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Questions and Answers

Where is the thyroid gland located?

Lateral to the larynx and trachea

Posterior to the larynx and trachea

Medial to the larynx and trachea

Anterior to the larynx and trachea (correct)

What is the function of thyroid hormone?

To regulate metabolism, growth, and development (correct)

To increase calcium levels in the blood

To decrease bone resorption

To lower blood pressure

What is the function of calcitonin hormone?

To increase calcium levels in the blood

To decrease bone resorption (correct)

To regulate metabolism, growth, and development

To lower blood pressure

What is the stroma of the thyroid gland composed of?

A double capsule, CT septa, and reticular fibers Signup and view all the answers

What is the composition of the thyroid parenchyma?

Millions of rounded epithelial structures called follicles Signup and view all the answers

What is the function of follicular cells?

To store thyroid hormone in follicles Signup and view all the answers

What type of cells are found inside the basal lamina of the follicular epithelium?

Parafollicular cells Signup and view all the answers

What is the approximate duration that the thyroid gland can supply the body with hormone without additional synthesis?

Up to three months Signup and view all the answers

What is the shape of Chief cells in the Parathyroid gland?

Small polygonal cells Signup and view all the answers

What is the function of Oxyphil cells in the Parathyroid gland?

Unknown Signup and view all the answers

What is the characteristic of the cytoplasm of Oxyphil cells?

Deep eosinophilic and contain many mitochondria Signup and view all the answers

What happens to Chief cells with increasing age?

They are replaced by fat cells Signup and view all the answers

What is the major function of Parathyroid hormone (PTH)?

Raises blood Ca2+ levels Signup and view all the answers

What is the primary function of the parathyroid glands?

To regulate calcium levels in the blood Signup and view all the answers

What is the characteristic of the nucleus of Chief cells?

Large nuclei Signup and view all the answers

What triggers the secretion of calcitonin from parafollicular cells?

Elevated blood Ca2+ levels Signup and view all the answers

What is the main difference between the cytoplasm of Chief cells and Oxyphil cells?

Color of the cytoplasm Signup and view all the answers

Which gland is responsible for secreting thyroid hormones?

Thyroid gland Signup and view all the answers

What is the function of parathyroid hormone (PTH) on bones?

To release calcium stored in bone tissue Signup and view all the answers

What is the role of PTH in kidney function?

To increase calcium reabsorption from the urine Signup and view all the answers

What is the result of PTH on phosphorus levels in the blood?

Increased phosphorus levels Signup and view all the answers

What is the structural component of the parathyroid gland that surrounds each gland?

Signup and view all the answers

What is the function of calcitonin?

To suppress bone resorption by osteoclasts Signup and view all the answers

What is the location of the parathyroid glands?

Behind the thyroid gland Signup and view all the answers

Study Notes

The Thyroid Gland

Located in the front of the neck, anterior to the larynx and trachea
Releases two hormones:
- Thyroid hormone (Thyroxin): regulates metabolism, growth, and development
- Calcitonin hormone: lowers calcium levels in the blood by decreasing bone resorption
Histology:
- Stroma: double capsule, CT septa, and reticular fibers that form a network supporting the thyroid parenchyma
- Parenchyma: composed of millions of rounded epithelial structures called follicles
- Follicles: each consists of a simple epithelium and a central lumen filled with a gelatinous substance called colloid
- Colloid contains thyroglobulin, the precursor for active thyroid hormones
- Follicular cells (Principal cells): range in shape from squamous to low columnar
- Parafollicular cells (C cells): synthesize and secrete calcitonin, which suppresses bone resorption by osteoclasts

Feedback Mechanism

Not explicitly mentioned in the text, but implied through the regulation of calcium levels

The Parathyroid Glands

4 small glands located behind the thyroid gland
Regulate the body's calcium and phosphorus levels through the secretion of parathyroid hormone (PTH)
Functions:
- Calcium regulation: releases PTH into the bloodstream when blood calcium levels drop below normal
- Bone maintenance: PTH acts on the bones to release calcium stored in bone tissue
- Kidney function: PTH acts on the kidneys to increase calcium reabsorption and convert vitamin D into Calcitriol
- Phosphorus regulation: PTH decreases phosphorus reabsorption in the kidneys, leading to increased excretion in the urine
Histology:
- Stroma: thin capsule, CT septa, and network of reticular fibers that support the parenchyma cells
- Parenchyma: consists of cords of polygonal cells surrounded by a rich network of fenestrated blood capillaries
- Chief cells: secrete parathyroid hormone, have large nuclei, and pale cytoplasm with glycogen granules and lipid droplets
- Oxyphil cells: unknown function, few in number, with large polygonal shape, small and dense nucleus, and deep eosinophilic cytoplasm with many mitochondria

Comparison of Glands

Thyroid gland: follicular cells secrete thyroid hormones, C cells secrete calcitonin
Parathyroid glands: chief cells secrete parathyroid hormone
Functions: thyroid hormones increase metabolic rate, calcitonin lowers blood Ca2+ levels, parathyroid hormone raises blood Ca2+ levels

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Description

This quiz covers the structure and function of parafollicular cells and parathyroid glands in the endocrine system, including their role in regulating calcium levels.