Female reproductive system Flashcards
- Structure and function of the ovaries and ovarian follicles
The ovaries are made up of two main types of tissue: the outer cortex and the inner medulla. The cortex contains follicles, which are the structures that contain the eggs. The medulla contains blood vessels, lymphatic vessels, and nerves.
Ovarian follicles are tiny fluid-filled sacs located in the ovarian cortex. Each follicle contains an immature egg, also known as an oocyte. Follicles are categorized based on their size and stage of development.
During each menstrual cycle, several follicles begin to grow and develop under the influence of follicle-stimulating hormone (FSH) from the pituitary gland. Eventually, one follicle becomes dominant and continues to mature, while the others regress. The mature follicle releases the egg during ovulation, which occurs around day 14 of a typical 28-day menstrual cycle.
After ovulation, the empty follicle transforms into a structure called the corpus luteum, which produces hormones such as progesterone. If the egg is fertilized and implants in the uterus, the corpus luteum continues to produce hormones to support the pregnancy. If the egg is not fertilized, the corpus luteum degenerates, hormone levels drop, and the menstrual cycle begins again.
Stages of the menstrual cycle
Menstruation: This is the first stage of the menstrual cycle and lasts for about 3-7 days. During this stage, the uterus sheds its lining, which results in vaginal bleeding.
Follicular phase: This stage begins on the first day of menstruation and lasts for about 10-14 days. During this stage, the pituitary gland in the brain releases follicle-stimulating hormone (FSH), which stimulates the ovaries to produce follicles. One follicle will mature and become dominant, and the estrogen levels will increase.
Ovulation: This is the midpoint of the menstrual cycle and occurs around day 14 (in a 28-day cycle). During ovulation, the dominant follicle releases a mature egg into the fallopian tube. This is the time when fertilization can occur if sperm are present.
Luteal phase: This stage begins after ovulation and lasts for about 14 days. During this stage, the empty follicle that released the egg becomes the corpus luteum, which produces progesterone. The progesterone prepares the uterus for a possible pregnancy by thickening the uterine lining. If the egg is not fertilized, the corpus luteum will eventually break down, and the menstrual cycle will begin again.
How the menstrual cycle is regulated by circulating hormones
The menstrual cycle is regulated by a complex interplay of hormones that are produced and released by different glands in the body. The main hormones involved in regulating the menstrual cycle are:
Gonadotropin-releasing hormone (GnRH): This hormone is produced in the hypothalamus, a small region of the brain, and it stimulates the pituitary gland to release follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
Follicle-stimulating hormone (FSH): This hormone is released by the pituitary gland in response to GnRH, and it stimulates the growth of follicles in the ovaries. Follicles are small sacs that contain immature eggs.
Estrogen: As the follicles grow, they produce estrogen, which helps to thicken the uterine lining and prepare the body for possible pregnancy.
Luteinizing hormone (LH): When estrogen levels reach a certain threshold, the pituitary gland releases a surge of LH, which triggers ovulation - the release of a mature egg from the ovary.
Progesterone: After ovulation, the empty follicle that released the egg becomes the corpus luteum, which produces progesterone. Progesterone helps to maintain the thickened uterine lining and prepare the body for possible pregnancy.
