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Figure 2. Follicular phase diagram of hormones and their origins. Follicle-stimulating hormone (FSH) is secreted by the anterior pituitary gland (Figure 2). FSH secretion begins to rise in the last few days of the previous menstrual cycle, [3] and is the highest and most important during the first week of the follicular phase [4] (Figure 1).
Menstrual cycle The menstrual cycle is a series of natural changes in hormone production and the structures of the uterus and ovaries of the female reproductive system that makes pregnancy possible. The ovarian cycle controls the production and release of eggs and the cyclic release of estrogen and progesterone. The uterine cycle governs the preparation and maintenance of the lining of the ...
At menopause, only 1,000 follicles remain. It seems likely that early menopause occurs for women with low populations at birth, and late menopause occurs for women with high populations at birth, but there is as yet no clinical evidence for this. [4] The process by which primordial cells 'wake up' is known as initial recruitment.
[2] [3] [4] Recently, this hypothesis has been challenged with some thorough histology. Sawyer et al. hypothesized that in sheep most of the granulosa cells develop from cells of the mesothelium (i.e., epithelial cells from the presumptive surface epithelium of the ovary). [5]
Ovulation is an important part of the menstrual cycle in female vertebrates where the egg cells are released from the ovaries as part of the ovarian cycle. In female humans ovulation typically occurs near the midpoint in the menstrual cycle and after the follicular phase. Ovulation is stimulated by an increase in luteinizing hormone (LH).
[10] [2] At the physiological level, menopause happens because of a decrease in the ovaries' production of the hormones estrogen and progesterone. [1] While typically not needed, measuring hormone levels in the blood or urine can confirm a diagnosis. [11] Menopause is the opposite of menarche, the time when periods start. [12]
As follicles grow, they acquire receptors for luteinizing hormone, a pituitary hormone that reinitiates meiosis in the oocyte and causes ovulation of a fertilizable egg. Luteinizing hormone acts on receptors in the outer layers of granulosa cells of the follicle, causing a decrease in cyclic GMP in the granulosa cells. [ 4 ]
This area is about 4 cm x 3 cm x 2 cm in size. [3] [4] The ovaries are surrounded by a capsule, and have an outer cortex and an inner medulla. [4] The capsule is of dense connective tissue and is known as the tunica albuginea. [5] Usually, ovulation occurs in one of the two ovaries releasing an egg each menstrual cycle.