Module 2 Section 3

Question 1

explain female reproductive physiology

Answer 1

• females undergo complex monthly cycling in which an egg, or ova, matures and is released
• this is accompanied by a cyclical secretion of the female sex hormones, estrogen and progesterone

Question 2

explain the purpose of cycling in female reproduction

Answer 2

• the entire purpose of cycling is to prepare the female body for a potential pregnancy
• each month hormones influence an ova to mature and be released
• at the same time, hormones also influence the uterine lining in preparation for the implantation of. fertilized egg
• if the released ova is not fertilized, the ova decays and the uterine lining is shed during the menstrual phase

Question 3

explain the first step of oogenesis

Answer 3

• the undifferentiated primordial cells in the ovaries undergo mitotic division during fetal life
• by around the fifth month of gestation, the oogonia have divided to give ride to 6-7 million primary oocytes
• this process ceases with the primary oocytes arrested just prior to their meiotic division
• each of these primary oocytes is surrounded by a single layer of granulosa cells and this structure is called a primordial follicle
• immediately, the number of primary oocytes starts to decay such that by birth, only 2 million primordial follicles remain
• this represents the entire complement of potential ova a woman will have through her life

Question 4

explain the second step of oogenesis

Answer 4

• the primordial follicles give rise to an ongoing trickle of developing follicles
• once the follicles begin development, the entire structure is called a primary follicle
• the developing primary follicle either results in the release of an ova, or it will undergo atresia and decay
• prior to puberty, all primary follicles that develop undergo atresia
• after puberty, only about 400 primary follicles will mature and release ova
• by menopause, the pool of primary follicles is exhausted and a woman’s reproductive capacity ceases

Question 5

explain the third step of oogenesis

Answer 5

• from puberty until menopause, a small fraction of the primary follicles will develop into secondary follicles on a cyclic basis
• primary follicles get larger, over 1000-fold, due to buildup of cytoplasmic materials that would be necessary for early embryonic development
• just prior to ovulation, the primary oocyte undergoes its first meiotic division to produce two daughter cells, each with 23 pairs of chromosomes
• during this division the majority of the cytoplasm goes to one of these daughter cells, which is called the secondary oocyte
• the other daughter cell forms the first polar body, which will eventually degenerate

Question 6

explain the fourth step of oogenesis

Answer 6

• the secondary oocyte is released during ovulation
• if it is fertilized by a sperm, it will undergo the second meiotic division in which 23 single stranded chromosomes form the second polar body, while the remaining 23 single stranded chromosomes combine with the 23 single stranded chromosomes from the sperm

Question 7

explain the ovarian cycle

Answer 7

• at the onset of puberty the ovarian cycle alternates between two phases, the follicular phase, which prepares a mature egg, and the luteal phase, which prepares the reproductive tract for potential implantation
• this cycle on average lasts 28 days

Question 8

what is the first stage of the follicular phase

Answer 8

• the follicular phase begins with the proliferation of granulosa cells in a primary follicle
• the granulosa cells divide to form several layers around the oocyte

Question 9

what is the second stage of the follicular phase

Answer 9

• the granulosa cells secret glyciproteins that form a thick extracellular matrix that surrounds the oocyte and separates it from the granulosa cells
• this membrane is known as the zona pellucida
• while the granulosa cells are proliferating, specialized ovarian connective tissue cells differentiate and surround the granulosa cells with a layer of thecal cells
• together, the thecal and granulosa cells are known as follicular cells
• the development of this primary follicle is due to the influence of FSH and estrogen

Question 10

explain the third stage of the follicular phase

Answer 10

• as the follicle enlarges, it becomes a secondary follicle, which is now capable of secreting estrogens, primarily estradiol
• the formation of the secondary follicle is mainly due to FSH and estrogen

Question 11

explain the fourth stage of the follicular phase

Answer 11

• also during this stage, a fluid filled cavity known as an antrum is formed within the granulosa cells
• expansion of the antrum increases the size of the follicle as it matures
• estrogen secretion also increases

Question 12

explain the fifth stage of the follicular phase

Answer 12

• each cycle, one of the follicles develops faster than the others to develop into a mature follicle by around 14 days of the follicular cycle
• in the mature follicle, the oocyte has undergone its first meiotic division to become a secondary oocyte
• also at this time, the location of the oocyte is not central in the follicle, but rather to the side of the growing follicle

Question 13

explain the sixth stage of the follicular phase

Answer 13

• under the influence of LH and FSH, ovulation occurs around day 14
• the ovarian follicle ruptures to release the ovum into the abdominal cavity
• the leaking antral fluid helps push the ovum into the oviduct
• the release of the ovum represents the end of the follicular phase

Question 14

explain the first stage of the luteal phase

Answer 14

• once the ovum has been released, the remaining follicular cells undergo a process called luteinisation to form the corpus luteum
• the corpus luteum becomes highly vascularized and it becomes very active in secreting hormones, mainly progesterone with some estrogens

Question 15

explain the second stage of the luteal phase

Answer 15

• if within around 14 days the ovum is not fertilized and implanted, the corpus luteum rapidly degenerates to form the corpus albicans, which is essentially a fibrous scar tissue
• this signifies the end of one ovarian cycle and the follicular phase begins again

Question 16

explain the LH surge

Answer 16

• ovarian cycle is under control of FSH, LH, and estrogen
• FSH and estrogen are important for stimulating early follicular development and formation of the secondary follicle
• LH is also important in the production of estrogen, which is secreted in increasing quantities by the secondary follicle
• during the follicular phase, the anterior pituitary preferentially releases LH as the circulating estrogen inhibits the actions of GnRH on FSH-secreting cells of the anterior pituitary
• as estrogen levels continue to rise, estrogen then exerts a positive feedback action on the anterior pituitary to cause a surge in LH secretion
• the LH surge has several actions

Question 17

what are the actions of the LH surge

Answer 17

• it stops estrogen synthesis by follicular cells
• it reinitiates meiosis in the oocyte
• it triggers release of local factors that increase the swelling of the follicle and weaken the wall
• it differentiates the follicular cells into luteal cells

Question 18

explain the hormonal control of the luteal phase

Answer 18

• during luteal phase, LH continues to maintain the corpus luteum
• it begins secreted large amounts of progesterone in preparation of a potential pregnancy
• progesterone causes changes in the uterine lining to prepare for potential implantation of an embryo to establish a pregnancy
• if no implantation occurs, the rapid degradation of the corpus luteum results in a rapid drop in circulating progesterone

Question 19

explain the uterine cycle

Answer 19

• like the ovarian cycle, the uterine or menstural cycle also lasts around 28 days
• during this cycle, the uterus is prepared for the possible implantation of fertilized ovum
• if this does not occur, the uterus is stripped clean to prepare for the next cycle
  these changes within the uterus are under hormonal control

Question 20

what are the 2 layers of the uterus

Answer 20

1. the myometrium: an outer layer comprised of smooth muscle
2. the endometrium: the inner lining that is highly vascularized and also has many glands

Question 21

what are the 3 phases of the uterine cycle

Answer 21

1. menstural phase
2. proliferation phase
3. secretory phase

Question 22

explain the first phase of the uterine cycle - menstural phase

Answer 22

• with decreased estrogen at the end of the luteal phase, the endometrial growth ceases
• the decrease in estrogen and progesterone results in the local release of prostaglandins
• these protaglandins constrict the blood supply to the endometrium, and cause the myometrium to rhythmically contract
• the endometrial lining then sloughs off and is expelled out through the vagina

Question 23

how long does menstruation usually last

Answer 23

• usually lasts from 5-7 days
• during this time, the newly developing follicles are secretin enough estrogen to begin repair of the endometrium

Question 24

explain the second phase of the uterine cycle - proliferation phase

Answer 24

• this phase begins when the menstrual flow ceases and it coincides with the later stages of the ovarian follicular phase
• at the end of the menstrual phase, the endometrium consists only of a few layers of cells less than 1 mm in thickness
• under the influence of estrogen, these cells proliferate and there is an ingrowth of glands and blood vessels until the lining is 3-5mm in thickness
• ovulation occurs during this phase, in which the ovum leaves the ovary and begins traveling through the oviduct towards the uterus

Question 25

explain the third phase of the uterine cycle - secretory phase

Answer 25

- with the formation of the corpus luteum and the beginning of th eovarian luteal phase, the secretory phase begins - the large amounts of progesterone and estrogen convert the endometrium into a richly vascularized and glycogen-filled tissue necessary to support an early embryo - by this phase, the ovum has made its way to the uterus - without implantation, the corpus luteum degrades and triggers the next menstrual phase

Question 26

what is endometriosis

Answer 26

- a disorder in which the endometrium grows outside the uterus - the endometrial tissue commonly grows on the ovaries, fallopian tubes, connective tissues such as the ligaments stabilizing the uterus and ovaries, and other tissues lining the pelvis - less commonly it can spread to tissues beyond the pelvic region, such as to the large and small bowel or abdomen

Question 27

explain menopause

Answer 27

- a significant event in the female reproductive system as it represents the end of reproductive capacity - women, at birth, have around 2 million primary follicles in their ovaries - prior to puberty, there is a continual decay or atresia of these follicles - following puberty, each month several of these primary follicles begin to develop yet only one typically will release an ovum - this monthly cycle continues until, sometime between the age of 45 and 55, there are no more viable primary follicles in the ovaries and follicular growth stops and the ovarian and uterine cycles cease

Question 28

what is a consequence of menopause

Answer 28

- without monthly follicular development, there is a dramatic decrease in estrogen secretion - this decrease affects other body systems such as the skeletal and cardiovascular systems - estrogen helps to promote strong bones by inhibiting osteoclast activity (can result in osteoporosis)