The key difference between oocyte and follicle is that oocyte is an immature egg which undergoes meiosis in order to produce a mature egg cell while follicle is a fluid-filled sac that contains an immature egg or oocyte.
Oogenesis is a complicated process that produces female gametes or egg cells. It begins even before the birth of the female baby. Oocytes are the female gametocytes which undergo meiosis to form the ova. They are immature diploid cells found inside the follicles. Follicles are small sacs filled with fluid. Each follicle has the potential to release a mature egg cell for fertilization. Oocytes divide by two meiotic cell divisions in order to form mature egg cells or ova.
CONTENTS
1. Overview and Key Difference
2. What is an Oocyte
3. What is a Follicle
4. Similarities Between Oocyte and Follicle
5. Side by Side Comparison – Oocyte vs Follicle in Tabular Form
6. Summary
What is an Oocyte?
An oocyte is an immature egg found inside a follicle. It is formed during female gametogenesis. Oocyte undergoes meiosis to produce a mature ovum or egg cell. When an oocyte begins maturation and division, it is known as a primary oocyte. The primary oocyte is then subject to the first meiotic division and produces the secondary oocyte. The secondary oocyte is an immature female gamete produced after the completion of meiosis I. Second phase of meiosis is arrested till secondary oocyte is fertilized with a sperm. Soon after fertilization, secondary oocyte undergoes meiosis II and produces a mature egg cell called the ovum. The ovum nucleus fuses with the sperm nucleus and produces the zygote, which can develop into an individual.
Figure 01: Oocyte
What is a Follicle?
A follicle is a fluid-filled small sac found in female ovaries. They are roughly spheroid cellular aggregations. Normally, an ovary contains 8 to 10 follicles. They can be 2 mm to 28 mm in size. Follicles contain immature eggs known as oocytes. Follicle nourishes and protects the oocyte. Each follicle has the potential to release a mature egg cell or ovum for fertilization. In a normal menstrual cycle, one follicle will grow bigger until it ruptures at ovulation to release the egg. This takes place on the 14th day after the beginning of the menstrual cycle. Moreover, follicles secrete hormones which influence stages of the menstrual cycle and release essential reproductive hormones.
Figure 02: Follicle
Follicle size and status are vital information during fertility assessments and treatments. A pelvic ultrasound scan can assess the size and number of follicles present in the ovaries. Egg quality and follicle count are two important factors that affect successful pregnancy. The number of follicles within the ovaries indicates the state of fertility. The egg quality depends on age and lifestyle.
What are the Similarities Between Oocyte and Follicle?
- Follicle and oocyte are two structures found inside a woman’s ovary.
- Follicles contain oocytes.
- One follicle has the potential to release a mature egg or ovum.
What is the Difference Between Oocyte and Follicle?
An oocyte is an immature egg while a follicle is a small fluid-filled sac. So, this is the key difference between oocyte and follicle. Structurally, an oocyte is a diploid cell while a follicle is a cellular aggregation. Thus, it is another difference between oocyte and follicle.
Moreover, a further difference between oocyte and follicle is that the oocyte divides by meiosis to produce egg cells for fertilization while the follicles nourish and protect oocytes, release essential reproductive hormones and transform into the corpus luteum after ovulation.
Summary – Oocyte vs Follicle
The oocyte is an immature egg. It is a diploid cell which undergoes meiosis to produce mature eggs. The ovarian follicle is the basic unit of female reproductive biology. It is a fluid-filled sac that contains an oocyte. Follicle grows and gets bigger in order to rupture and release an egg. Thus, this is the summary of the difference between oocyte and follicle.
Reference:
1. “What Are Follicles And Why Are They Important For My Fertility?” London Women’s Clinic, Available here.
2. “Oocyte.” Wikipedia, Wikimedia Foundation, 12 Apr. 2020, Available here.
Image Courtesy:
1. “Oocyte with Zona pellucida (27771482282)” By ZEISS Microscopy from Germany – Oocyte with Zona pellucida, (CC BY-SA 2.0) via Commons Wikimedia
2. “Graafian Follicle, Human Ovary (3595817584)” By Ed Uthman from Houston, TX, USA – Graafian Follicle, Human OvaryUploaded by CFCF (CC BY 2.0) via Commons Wikimedia