The key difference between parafollicular and follicular cells is the type of secretion each type of cell makes. Parafollicular cells secrete calcitonin, whereas follicular cells secrete thyroxin and triiodothyronine.
The thyroid gland is a main endocrine gland. Thyroid hormones perform a varying array of functions, from maintaining homeostasis in the body to regulating metabolism. Parafollicular and follicular cells reside next to each other in the thyroid gland. This article discusses the difference between parafollicular and follicular cells.
CONTENTS
1. Overview and Key Difference
2. What are Parafollicular Cells
3. What are Follicular Cells
4. Similarities Between Parafollicular and Follicular Cells
5. Side by Side Comparison – Parafollicular vs Follicular Cells in Tabular Form
6. Summary
What are Parafollicular Cells?
Parafollicular cells or C cells secrete calcitonin from the thyroid glands. They belong to the class of neuroendocrine cells. They are present in the connective tissues beside the follicular cells in the thyroid gland. Moreover, they are large and pale in comparison to follicular cells. Parafollicular cells can be seen attached to the basal membrane. Development of the parafollicular cells takes place through the pharyngeal endoderm from the fourth pharyngeal pouch.
Figure 01: Parafollicular Cells
The main function of parafollicular cells is to secrete calcitonin. Calcitonin is the hormone required for calcium homeostasis in humans. When blood calcium levels increase, the parafollicular cells secrete calcitonin to lower the blood calcium level. Furthermore, calcitonin also inhibits bone resorption. In addition to the secretion of calcitonin, they also secrete small amounts of serotonin, somatostatin and CGRP.
What are Follicular Cells?
Follicular cells (thyroid epithelial cells or thyrocytes) are present in the thyroid gland. They produce and secrete thyroid hormones. There are two main thyroid hormones as thyroxin and triiodothyronine.
Figure 02: Follicular Cells
Follicular cells are simple cuboidal epithelial cells. They are arranged as spherical follicles. Also, they embed themselves in the fluid-filled space known as colloids. Moreover, they form a follicular lumen in the inner side. The basal membrane of the follicular epithelial cells contain receptors for thyroid stimulating hormone.
The development of the follicular cells takes place in the endodermal mass in the region of the tongue known as foramen cecum. The main function of follicular cells is the release of thyroid hormones. Moreover, they take up iodide and amino acids in the circulation and result in the release of the thyroid hormones with the help of proteases.
What are the Similarities Between Parafollicular and Follicular Cells?
- Both types of cells are present in the thyroid gland.
- Moreover, rest on a basal membrane.
- They secrete substances that are important for the functioning of our body.
What is the Difference Between Parafollicular and Follicular Cells?
Parafollicular cells and follicular cells are present in the thyroid gland. However, there is a difference between parafollicular and follicular cells based on their function, structure and development. The main function of parafollicular cells is to secrete calcitonin; therefore, it regulates calcium homeostasis. In contrast, the main function of follicular cells is to secrete thyroxin and triiodothyronine. So, this is the key difference between parafollicular and follicular cells. Moreover, they vary in size as well. Parafollicular cells are larger in contrast to the follicular cells.
The below infographic presents more information regarding the difference between parafollicular and follicular cells.
Summary – Parafollicular vs Follicular Cells
In brief, parafollicular and follicular cells present in the thyroid gland secrete varying endocrine hormones. However, there is a difference between parafollicular and follicular cells based on their function, structure and development. Parafollicular cells secrete calcitonin while follicular cells secrete thyroxin and triiodothyronine. They are present besides each other, but they vary in their development. The cell size also varies as parafollicular cells are larger than the follicular cells. Moreover, parafollicular cells have a more definite round shape, unlike follicular cells. Thus, this is a summary of the difference between parafollicular and follicular cells.
Reference:
1. Kališnik, M., et al. “The Interdependence of the Follicular, Parafollicular, and Mast Cells in the Mammalian Thyroid Gland: A Review and a Synthesis – Kališnik – 1988 – American Journal of Anatomy – Wiley Online Library.” American Journal of Anatomy, John Wiley & Sons, Ltd, 3 Feb. 2005, Available here.
Image Courtesy:
1. “Tiroides 03 100X” By Andrea Mazza – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Thyroid follicle cells” By CFCF – Own work (CC BY-SA 3.0) via Commons Wikimedia