Chapter 16, Reproductive System, Part C

Chapter 16: Reproductive System & Development
Part C: Menstrual cycle, Pregnancy
1. Menstrual (uterine) cycle
a. Overview
i. Cyclic changes of the endometrium
ii. Regulated by cyclic production of estrogens and progesterone
iii. FSH and LH regulate the production of estrogens and progesterone
iv. Both female cycles are about 28 days in length
v. Ovulation typically occurs about midway through cycle on day 14
1. However, variations occur
b. Stages
i. Menstrual phase
1. Days 1-5
2. Functional layer of the endometrium is sloughed
3. Bleeding occurs for 3-5 days
4. By day 5, growing ovarian follicles are producing more estrogen
ii. Proliferative stage
1. Days 6-14
2. Regulation of functional layer of the endometrium
3. Estrogen levels rise
4. Ovulation occurs in the ovary at the end of this stage
iii. Secretory stage
1. Days 15-28
2. Progesterone levels rise and increase the blood supply to the endometrium
3. Endometrium increases in size and readies for implantation
4. If fertilization does occur
a. Embryo produces a hormone a hormone (HCG) that causes the corpus luteum to continue producing its hormones
5. If fertilization does not occur
a. Corpus luteum degenerates as LH blood levels decline
c. Hormones produced by ovaries
i. Estrogen
1. Produced by follicle cells
2. Cause secondary sex characteristics:
a. Enlargement of accessory organs
b. Development of breasts
c. Appearance of axillary and pubic hair
d. Increase in fat beneath the skin, particularly in hips and breasts
e. Widening and lightening of the pelvis
f. Onset of menses (menstrual cycle)
ii. Progesterone = the hormone of pregnancy
1. Produced by the corpus luteum
2. Production continues until LH diminishes in the blood
3. Does not contribute to the appearance of secondary sex characteristics
4. Helps maintain pregnancy
5. Prepares breasts for milk productions
6. Feedback
d. Mammary glands
i. Present in
1. Modified
ii. Function is
iii. Stimulated by