The key difference primary secondary and tertiary follicle is their growth and nature; Primary follicle develops from the stimulation of primordial follicle, and it has a single layer of follicular cells whereas, the secondary follicle develops from the primary follicle, and it is a preantral follicle having multiple layers of granulosa cells. Meanwhile, the tertiary follicle develops from the secondary follicle and has a fluid-filled cavity and diverse layers of cuboidal granulosa cells.
Folliculogenesis is a critical process of female reproductive health and propagation of species. It is the developmental process of ovarian follicles starting from primordial follicles set up in early life and culminating with either ovulation or follicular death. Follicle formation is tightly regulated and controlled by hormonal and molecular mechanisms. Moreover, folliculogenesis is essential since it allows the synthesis of vital sex steroid hormones. There are five different development stages of ovarian follicles. They are primordial, primary, secondary, tertiary and graffian follicles. Based on the presence or absence of a fluid-filled cavity (antrum) in the granulosa compartment, these follicles are further divided into preantral follicles and antral follicles. Primordial, primary and secondary follicles are preantral follicles while tertiary or ovulatory or Graffian follicles are antral follicles.
CONTENTS
1. Overview and Key Difference
2. What is Primary Follicle
3. What is Secondary Follicle
4. What is Tertiary Follicle
5. Similarities Between Primary Secondary and Tertiary Follicle
6. Side by Side Comparison – Primary vs Secondary vs Tertiary Follicle in Tabular Form
7. Summary
What is Primary Follicle?
A primary follicle is a follicle that develops as a result of the stimulation of primordial follicle. It is a preantral follicle which does not have a fluid-filled cavity. The primary follicle has a single layer of follicular cells, and it is a small follicle. Moreover, it is an immature ovarian follicle comprising an immature ovum and few specialized epithelial cells surrounding it.
Figure 01: Folliculogenesis
Oocytes in the primary follicle are surrounded by a single layer of cuboidal granulosa cells. Primary follicle grows, and it is recognized by an increase in oocyte diameter and an increase in granulose cell number.
What is Secondary Follicle?
A secondary follicle is the third stage of follicle development. It is formed from the primary follicle. Similar to the primary follicle, secondary follicle also lacks a fluid-filled cavity. Hence it is a preantral follicle. Structurally, secondary follicles are larger than primary follicles. The primary oocyte within the secondary follicle is surrounded by several layers of granulosa cells, abasal lamina and a theca layer.
What is Tertiary Follicle?
A tertiary follicle is the fourth stage of follicle development. It is formed from the secondary follicle. The tertiary follicle has a fluid-filled cavity or antrum, which is absent in the primary and secondary follicles. Hence, it is an antral follicle. The appearance of antrum shows the formation of a tertiary follicle. In comparison to primary and secondary follicles, the tertiary follicle is larger in size. But the mitotic rate of the granulosa and theca cells begins to decline in tertiary follicles unlike in the other two types of follicles. In the tertiary follicle, the oocyte is surrounded by a diverse layer of cuboidal granulosa cells with antral space
What are the Similarities Between Primary Secondary and Tertiary Follicle?
- Primary, secondary and tertiary follicles are three types of follicles develop during the folliculogenesis.
- All three types contain oocytes within them.
- They develop at puberty.
- Their primary role is to support oocyte.
What is the Difference Between Primary Secondary and Tertiary Follicle?
The primary follicle is an immature follicle formed from the stimulation of primordial follicle. The secondary follicle, on the other hand, is the follicle which develops from the primary follicle and has multiple layers of granulosa cells. Meanwhile, the tertiary follicle develops from the secondary follicle, and it has multiple layers of granulosa cells and an antrum. Thus, this is the key difference between primary secondary and tertiary follicle. Moreover, the primary follicles are small. But, the secondary follicles are larger than the primary follicles, and the tertiary follicles are larger than the secondary follicles.
Below infographic tabulates more differences between primary secondary and tertiary follicle.
Summary – Primary vs Secondary vs Tertiary Follicle
Primary, secondary and tertiary follicles are three development stages of ovarian follicles. Primary follicles are formed from primordial follicles while secondary follicles are formed from primary follicles. Subsequently, the tertiary follicles are formed from secondary follicles. Both primary and secondary follicles lack a fluid-filled cavity called antrum while tertiary follicle has an antrum. Furthermore, the primary follicle has a single layer of granulosa cells, while both secondary and tertiary follicles have multiple layers of granulosa cells. Thus, this summarizes the difference between primary secondary and tertiary follicle.
Reference:
1. “Folliculogenesis.” Wikipedia, Wikimedia Foundation, 11 Nov. 2020, Available here.
2. “Follicle Growth and Development.” GLOWM, Available here.
Image Courtesy:
1. “Follicle development stages” By Tnhath – Own work (CC BY-SA 4.0) via Commons Wikimedia