Biology 12 Unit 2: Reproduction and Development Female System

Female Structures

Female Reproductive SystemSystem

The Menstrual Cycle: onset of the first menstrual cycle is called menarche (approx. age 12) at the start of puberty each cycle lasts about 28 days & continue until menopause (approx. age 40-50) there are three phases:

Menstrual phase the beginning of the cycle is marked by the shedding of the endometrium lasts approx. 5 days. Called menstruation.

Follicular phase after menstruation, a follicle in the ovary develops as the follicle develops it secretes estrogen, which causes the endometrium to thicken again continues to approx. day 14

Ovulation (day 14) the follicle bursts open and an ovum is released into the fallopian tube, called ovulation the follicle cells differentiate into the corpus luteum this signals the end of the Follicular phase and the start of the Luteal phase

Luteal phase the cells of the corpus luteum secrete progesterone, which continues to cause the endometrium to thicken ready for the implantation of a fertilized ovum continues up to day 28 if the ovum is not fertilized in the fallopian tube, the level of progesterone falls and the endometrium breaks down, signaling the start of the next cycle

Hormonal Control of the Female Reproductive System: five hormones are involved; a releasing hormone (GnRH), two from the anterior pituitary (the gonadotropins, FSH and LH) and two from the ovaries (estrogen and progesterone) at the onset of puberty the hypothalamus releases gonadotropin-releasing hormone and begins the release of gonadotropins, which regulate the menstrual cycle and indirectly cause the development of female secondary sex characteristics

FSH stimulates follicle development the follicle cells secrete estrogen which has four effects: 1. it causes the development and maintenance of female secondary sex characteristics 2. it causes the repair of the endometrium 3. it has a negative feedback effect on the pituitary to switch off production of FSH 4. it has a positive (stimulatory) feedback effect on the pituitary to cause the secretion of LH

LH has two effects: 1. it causes ovulation 2. it causes the follicle cells to differentiate and form the corpus luteum, which secretes both estrogen and progesterone (most importantly, progesterone)

Progesterone and Estrogen progesterone (and estrogen) further increase the development of the endometrium and have a negative feedback effect on the pituitary to inhibit the secretion of both FSH and LH

Corpus Luteum without any gonadotropins, the corpus luteum degenerates and the levels of estrogen and progesterone fall, the endometrium breaks down so that menstruation begins and FSH is produced again beginning the next cycle

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