What is a Graafian Follicle?

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Ovarian follicles are the essential units of female reproductive biology, each of which is packed with roughly spherical aggregations of cells found in the ovary. A Graafian follicle, or ovarian follicle, is present inside an ovary and is a minute cyst within which an egg, or ovum, develops. A Graafian follicle is a follicle that ruptures and releases its ovum when stimulated. Generally, women are born with many undeveloped follicles, each containing an immature ovum. As soon as puberty is attained and menstruation commences, one ovum matures each month inside its containing follicle. The follicle grows bigger and breaks at around day 14 of the cycle, discharging the ovum in a process known as ovulation.

What is the developmental cycle of a follicle?

The developmental cycle of a follicle goes through a range of follicle stages:

• Primordial follicle: During birth, each and every one of the existing primary oocyte is surrounded by thin, single layers of so-called follicular epithelial cells. These are bordered from the rest of the ovarian stroma by a thin basal lamina. An oocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. In humans, oocytes are established in the ovary before birth and may remain latent awaiting initiation for up to 50 years. Follicular epithelial cells are former coelomic epithelial cells. The primordial follicles always form the greater part of the follicles in the ovary. Primordial follicles are indiscernible to the naked eye. However, these eventually develop into primary, secondary and tertiary vesicular follicles.
• Primary follicle: When the primordial follicles are tranformed into primary follicles, the follicular epithelium that surrounds the oocyte becomes iso- to highly prismatic.
• Secondary follicle: If primary follicles stay alive, secondary follicles with follicular epitheliums including multiple rows are produced. This is now called the ‘stratum granulosum’. In the secondary follicles, a glycoprotein layer, the pellucid zone, between the oocyte and follicular epithelium becomes noticeable. Cytoplasmic processes of the granulosa cells that lie upon it reach the oocyte through the pellucid zone and hence promise their maintenance function. Outside the basal lamina the stroma ovarii organizes itself to become theca folliculi You do not have access to view this node.
• Tertiary follicle or Graafian follicle: If the secondary follicles stay alive, tertiary follicles are produced. Their distinguishing feature is a fluid-filled cavity, the antral follicle. The oocyte lies at the edge in a heap made of granulosa epithelial cells, the cumulus oophorus. For the time being, it has developed so large that its cellular nucleus has reached the size of a whole primordial follicle. The connective tissue around the follicle has already differentiated itself obviously into a theca interna, well supplied with capillaries, out of large, lipid-rich cells (hormone production) and a theca externa, which forms a transition to the stroma ovarii and contains larger vessels. What is crucial for a flourishing follicle growth is a well-developed net of capillaries in the ‘theca interna’. The exact navigating method that leads to the selection of a follicle and its following maturation to become a ‘Graafian follicle’ is still mysterious. Prior to ovulation a growth spurt of the tertiary follicles occur. Graafian follicle corresponds to a especially large tertiary follicle that can be expected to be sufficient for ovulation. Tertiary vesicular follicles are occasionally called ‘Graafian follicles’.

How to understand the structure of ovary?

An ovary is subdivided into:

• Cortical (ovarian cortex)
• Medullary compartments (ovarian medulla).

Mutually, blood and lymph vessels are found in the loose connective tissue of the ovarian medulla. In the cortical compartment, the oocytes are found within a variety of follicle stages. The sex hormones manipulate the primordial follicles to grow and a restructuring to happen. Consecutively, from the primordial follicles the primary follicles, secondary follicles, and tertiary follicles develop. Only a small percentage of the primordial follicles reach the tertiary follicle stage - the great majority meets their end in advance in the various maturation stages. Large follicles leave scars behind in the cortical compartment and the small ones vanish without a trace. The tertiary follicles get to be the largest and, shortly before ovulation, can reach a diameter up to 2.5 mm through a special spurt of growth. They are then termed ‘Graafian follicles’. Occasionally, a Graafian follicle is unsuccessful to shrink after the ovum is discharged, or may not release it in any way. This makes the follicle to stay full of fluid and to persist to grow into a follicular ovarian cyst. Usually, these cysts vanish after a number of weeks without any required You do not have access to view this node.

What is Corpus luteum?

Graafian follicles are fluid-filled shell that surrounds and protects the developing egg cell inside the ovary during the menstrual cycle. Once the Graafian follicle has ruptured, it fills with blood, at times causing slight abdominal uneasiness. This blood is rapidly substituted by cells which are prosperous in fat, called luteal cells, and the follicle becomes the "corpus luteum." The luteal cells manufacture estrogen and progesterone and this is known as the luteal phase of the menstrual cycle. If pregnancy follows, the corpus luteum remains, but if there is no pregnancy, it starts to break down a few days before the start of the next menstrual bleed, ending up as scar tissue. Rarely, the corpus luteum may not break but becomes a blood-filled cyst, called a luteal cyst or corpus luteum cyst. These cysts are noramlly noticed in women experiencing fertility You do not have access to view this node. 

What happens to the lining of the uterus when a graafian follicle develops in the ovary?

When the follicle grows. it produces some hormones which reacts with the uterine wall to become thickened and to be filled with enormous blood. This change is a kind of preparation of the uterus to obtain the fertilized egg and to provide for the development of the future embryo.

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