Unit B: Reproduction and Development Chapter 16 Section 16.2-2 Hormonal Control of the Female Reproductive System

Primary Sex Characteristics Primary sexual characteristics – physical characteristics of an organism that are directly involved in reproduction. Includes all the structures of the female reproductive system. Examples for females: ovaries uterus Fallopian tubes etc. Primary Sex Characteristics

Secondary Sex Characteristics Secondary sexual characteristics – external features of an organism that are indicative of its gender, but are not reproductive organs themselves. Examples for females: enlarged breasts less facial hair more body fat wider hips Secondary Sex Characteristics

Female Reproductive Hormones 1. Estrogen produced and secreted by the follicle cells in the ovaries inhibits growth of facial hair initiates secondary sexual characteristics causes thickening of the endometrium Female Reproductive Hormones

3. Follicle Stimulating Hormone (FSH) 2. Progesterone produced and secreted by the corpus luteum inhibits ovulation during pregnancy firms the cervix to prevent expulsion of the fetus continues stimulation of the endometrium 3. Follicle Stimulating Hormone (FSH) gonadotropic hormone – hormone produced by the pituitary that regulates the function of the ovaries in females and the testes in males produced and secreted by the pituitary gland stimulates the development of the follicle cells in the ovary

4. Luteinizing Hormone (LH) gonadotropic hormone produced and secreted by the pituitary gland stimulates ovulation and the formation and maintenance of the corpus luteum 5. Gonadotropin Releasing Hormone (GnRH) produced by the hypothalamus stimulates FSH and LH

Menstrual cycle – an almost monthly cycle in which the endometrial lining of the uterus prepares for pregnancy; if pregnancy does not occur the lining is shed at menstruation. The menstrual cycle is divided into 4 phases. Flow Phase (menstruation) Follicular Phase Ovulatory Phase Luteal Phase Menstrual Cycle

Flow Phase: Days 1-5 AKA menstruation. The shedding of the endometrium. It is the only phase in the menstrual cycle that can be determined externally; therefore this phase is used to mark the beginning of the cycle. Approximately 5 days is required to clean the uterus. Flow Phase: Days 1-5

Follicular Phase: Days 6-13 Is the development of the follicle cells in the ovaries. As the follicles develop, estrogen is produced and secreted, increasing the estrogen concentration in the blood. Endometrium is produced. Follicular Phase: Days 6-13

Ovulatory Phase: Day 14 Secondary oocyte bursts from the ovary. Estrogen levels fall. Follicle cells begin to change into the corpus luteum. Ovulatory Phase: Day 14

The full development of the corpus luteum marks the beginning of the luteal phase. Corpus luteum secretes both estrogen and progesterone. Estrogen and progesterone levels rise in the blood. Estrogen and progesterone cause thickening of the endometrium in preparation of pregnancy. Luteal Phase: Days 15-28

Inhibits further ovulation. Firms the cervix to prevent expulsion of the fetus. When fertilization does not occur, estrogen and progesterone levels drop causing uterine contractions. These contractions cause the endometrium to pull away from the uterine wall. Shedding of the endometrium marks the beginning of the flow phase once again.

Phase Description of Events Hormone Produced Days Flow menstruation 1-5 Follicular follicles develop endometrium is formed estrogen produced by follicle cells 6-13 Ovulation s. oocyte bursts from ovary 14 Luteal corpus luteum forms and endometrium thickens estrogen and progesterone produced by the corpus luteum 15-28

Negative Feedback Systems for FSH and LH Beginning at puberty when estrogen is low, the hypothalamus secretes GnRH. GnRH activates the pituitary gland to secrete FSH. During the follicular phase of the menstrual cycle, the blood carries FSH to the ovary, which stimulates the development of the follicle cells. The follicle cells secrete estrogen, which initiates the development of the endometrium. Negative Feedback Systems for FSH and LH

As estrogen levels rise, a negative feedback message is sent to the pituitary gland to turn off secretions of FSH. The follicular phase has ended. Simultaneously, the rise in estrogen stimulates the release of LH. LH acts on the follicles stimulating the release of the secondary oocyte. Ovulation occurs. After ovulation LH acts on the remaining follicle cells turning them into corpus luteum.

The luteal phase has now begun. The corpus luteum secretes both estrogen and progesterone, this increases further development of the endometrium. As these two hormones build up, a second negative feedback system is activated. It tells the pituitary to stop releasing LH and the hypothalamus to stop releasing GnRH. Estrogen and progesterone levels drop, signaling the beginning of menstruation.