Female menstrual cycle and ovarian hormone Flashcards
1
Q
What is the most common site of fertilization?
A
The ampulla of the uterine (fallopian) tube
- It transports and houses the ovum
2
Q
What is the function of the ovary?
A
Produces oocytes and female sex hormones
3
Q
What is the function of the fallopian tube?
A
It conveys the secondary oocyte towards the uterus and conveys the developing embryo to the uterus
- It is the primary site of fertilization
4
Q
What is the primary function of the uterus?
A
It orotects and sustains the embryo during pregnancy
5
Q
What is the primary function of the vagina?
A
It receives the sperm and conveys the uterine secretions outside the body
6
Q
What is the primary function of the labia major?
A
It produces the feeling of pleasure during sexual stimulation
7
Q
What is the primary function of the labia majora?
A
It encloses and protects other external reproductive organ
8
Q
What is the function of the labia minora?
A
It protects the opening of the vagina and urethra
9
Q
What are the accessory female sex glands?
A
1) Uterine gland
2) Mammary gland (breasts)
- They support the egg, embryo, and later the newborn
10
Q
Describe the process of Oogenesis
A
- It is the process where a developing egg (oocyte) differentiates into a mature egg (OVUM)
- In one ovarian cycle, one secondary oocyte is released
A) Before birth:
- Primordial germ cells (these cells divide “via mitosis” and migrate into the ovarian cortex
- Once they reach the ovarian cortex, they become an oogonia (oogonium/primordial ovum)
- Each primordial pvum then collects around it a layer of spindle cells from the ovarian stroma (AKA granulosa cells), forming the primordial follicle
- The oogonium completes mitotic replication to form the primary oocyte, and the first stage of meiosis starts by the fifth month of fetal development, but they are arrested in the late stage of PROPHASE-1 until uberty
5) At birth, a female has 1-2 million oocyte
6) After puberty, the first meiotic division of the oocyte is completed, and each oocyte is divided into a large ovum (secondary oocyte) and a small first polar body
7a) The “first polar body” disintigrates
7b) The secondary oocyte gets arrested in Metaphase-2 (if it gets fertilized the final step of meiosis occurs)
11
Q
Summarize the process of oogenesis
A
- Before birth
1) Primordial germ cells
2) Primordial ovum (Oogonium)
3) Primordial follicle
4) Primary oocyte
5a) Secondary oocyte (large ovum)
5b) First polar body (small ovum)
12
Q
What are the granulosa cells?
A
They are the layer of spindle cells from the ovarian stroma that collects around a oogonium, forming a primordial follicle
13
Q
What is a primary oocyte?
A
When the oogonia in the embryonic ovary completes the mitotic replication and starts the first stage of meiosis (5th month of fetal development) and gets arrested at PROPHASE-1 (until puberty)
14
Q
What is the fate of the primary oocyte?
A
After puberty, the primary oocyte completes its first meiosis and forms two oocytes: a large ovum (secondary oocyte) and a small first polar body
- Each contains 23 chromosomes
15
Q
How many chromosomes are found in the large and small oocyte?
A
23 duplicated chromosomes
16
Q
In which stage is the primary oocyte arrested?
A
Prophase-1 (until puberty)
17
Q
What is the fate of the secondary oocyte?
A
It gets released from the ovary to get fertilized each month
18
Q
Describe the follicular development during oogenesis
A
1) Primordial follicle
- Immature and requires two more cell division before fertilization
2) Primary follicle
3) Pre-ovulatory (mature) follicle
4) Corpus luteum (After ovulation, the empty follicle becomes the corpus luteum, which helps maintain pregnancy if fertilization occurs)
19
Q
What is the primary function of the ovaries?
A
Produce and release eggs
20
Q
What is the function of the uterus?
A
It prepares itself to receive and support a potential embryo
21
Q
What is the relationship between the menstrual cycle and the ovarian cycle?
A
The ovarian and menstrual cycle works together in coordination to support reproduction. While the ovarian cycle produces and releases an egg, the menstrual cycle is responsible for preparing the uterus to receive and support a potential embryo
- As the ovarian cycle progresses towards ovulation, the uterine lining thickens in anticipation of implantation
22
Q
What is meant by Anovulatory cycles?
A
It occurs when ovulation does not take place (no egg is released)
23
Q
When does an anovulatory cycle occur?
A
1) Prepuberty
2) Pregnancy
3) Perimenopause and menopause
4) Lactation
24
Q
What are the features of the menstrual cycle?
A
- Each cycle lasts 28 days
- It is a species-dependent feature
- There are considerable variations between females depending on genetics, energy stores, and environment
25
How is leptin associated with the onset of puberty?
- Leptin (an adipocyte-derived protein hormone) plays an important role in the onset of puberty
- Leptin conveys information about the energy stores of the body, which is increased helps in initiating the activation of the hypothalamic-pituitary-gonadal (HPG) axis
- Leptin promotes the production and release of GnRH
- Higher levels of leptin are seen in overweight/obese individuals, which can lead to earlier onset of puberty (precocious puberty)
- Low levels of leptin (low weight individual) can delay puberty or even cause amenorrhea (absence of menstruation) due to insufficient energy signalling
26
What type of information is conveyed to the CNS by leptin?
Energy storage
27
What is meant by precocious puberty?
It is the early onset of puberty due to increased letin stores, which is seen in overweight and obese individuals
28
Summarize the relationship between leptin and the onset of puberty
For puberty to start, the brain needs to sense that the body has enough energy/fat stores to support growth and reproduction
- Low leptin = not enough energy = delays/halt reproductive function "amenorrhea", however, high leptin = ready = support of the reproductive axis
29
What are the main events of the ovarian cycle?
1) Folliculogenesis
2) Ovulation
3) Formation of the corpus luteum
4) Death of the corpus luteum
30
What are the phases of the ovarian cycle?
1) Follicular phase (development of multiple follicles; however, usually only one becomes dominant and reaches full maturity")
- 12-14 days; it starts at the degeneration of the corpus luteum and ends at ovulation
1. Days 1-7: Developing follicle
2. Day 7-14: Mature follicle
3. Day 14: Ovulation (Marked increase in LH and FSH)
2) Luteal phase (formation of the corpus luteum from the ruptures follicle)
- 12-14 days; it starts at ovulation and ends at the degeneration of the corpus luteum
4. Day 14-28: Corpus luteum formation
5. Day 28: regressive corpus luteum
31
What will happen to the corpus luteum if pregnancy occurs?
The corpus luteum won't disintegrate but rather, it will be maintained by hCG
32
What keeps the ovum suspended in the primordial state through childhood?
The granulosa cells, which provide nourishment for the ovum and secrete an oocyte maturation inhibiting factor, which is arrested in the prophase stage of meiosis-1
33
After puberty, what stimulates the growth of the ovary and the follicles?
The FSH and LH from the ant.pit
34
What is meant by folliculogenesis?
It is the first stage of growth, which is the moderate enlargement of the ovum (increasing 2-3 folds) followed by the growth of additional layers of granulosa cells forming a (PRIMARY FOLLICLE)
35
FSH causes an accelerated growth of how many follicles per month?
6-12
36
What is the intial effect of FSH on the PRIMORDIAL FOLLICLE
Rapid proliferation of the granulosa cells, and spindle cells that are derived from the ovarian interstitium collects in several layers outside the granulosa cells, giving rise to a second mass called the theca cells
37
What is the function of the theca cells?
- Theca interna: develops the ability to secrete additional steroid sex hormones (estrogen and progesterone)
- Theca externa: Develops into a highly vascular connective tissue capsule that becomes the capsule of the developing follicle
38
What happens after the primary follicle has formed (Antral stage)?
The mass of the granulosa cells secretes a follicular fluid that contains a high concentration of estrogen, which accumulates, forming an antrum (cavity that appears) within the mass of the granulosa cells, forming the early secondary follicle
- Up to this point, FSH is the main stimulator, accelerated growth then occur
39
What is the mechanism behind the accelerated growth of the secondary follicle?
1) Estrogen is secreted into the follicle and causes the granulosa cells to form an increasing number of FSH receptors
- This occurs just before ovulation (the only time estrogen stimulates the release of FSH and LH rather than inhibiting them
2) Pituitary FSH and estrogen combine to promote LH receptors on the original granulosa cells (allowing LH and FSH stimulation to occur even more rapidly)
- Increased estrogen from the follicle and the LH from the ant.pituitary act together to cause the proliferation of the follicular thecal cells and increase their secretions
- LH peak indicated "OVULATION" (FYI, in cases of infertility LH surges are measured mid-cycle, to determine whether ovulation is occurring or not)
40
What is the importance of LH?
- Indicated ovulation (its surge)
- It is necessary for the final follicular growth and ovulation
- It converts the granulosa and theca cells into progesterone-secreting cells (decreasing the amount of estrogen being secreted and increasing the secretion of progesterone)
41
What is meant by the process of atresia?
It is the involution of the 5-11 follicle, while only one matures, which is said to be due to:
1) The large amount of estrogen from the (1-rapidly growing follicle) acts on the hypothalamus to suppress the secretion of FSH by the ant.pituitary, which leads to lesser growth in the (underdeveloped follicles)
- And thus the largest follicle continues to grow due to the positive feedback effect while all of the other follicles stop growing and involute
42
What is the process of leutinization?
It is the process where the remaining cells of the graffin follicle (remaining granulosa cells and theca interna cells change into lutein cells, they then enlarge and become filled with lipid inclusion, giving them their yellow appearance) forming a mass called the corpus luteum
43
What will happen next with the corpus luteum?
- The corpus luteum will continue to secrete estrogen, progesterone, and inhibin (all during the luteal phase) which will inhibit the release of FSH and LH
- Then estrogen and progesterone secretion by them will cease suddenly, causing the degeneration of the corpus luteum (involution) to become the "corpus albican", increasing the production of FSH and LH and the cycle repeats
44
What will happen if the oocyte gets fertilized?
hCG (which resembles LH) will prevent the involution of the corpus luteum, causing it to secrete larger amounts of estrogen and progesterone, preventing menstruation and causing the endometrium to continue growing and store large amounts of nutrients rather than being shed
45
Summarize the ovulation cycle
- Follicular phase (Days 1-14):
1) Primordial follicle
- Due to the androgens secreted it gets converted to
2) Primary follicle
- Due to the effects of FSH & LH it gets converted to
3) Early secondary follicle
- Continuoued FSH and LH effects convert it to
4) Late secondary follicle
- Further FSH and LH transforms it into
5) Graffin follicle
- Ovulatory stage (LH Surge) leads to the ovulation of a follicle formed of germ cells, theca cells and corona radiate
- Luteal phase (15-28) from the graffin follicle to the corpus luteum
46
What are the hormones of the ovarian cycle?
1) GnRH
2) FSH (causes the maturation of the follicle)
3) Estrogen (produced by the maturating follicle, it slows the FSH and starts the LH)
4) LH (Causes ovulation)
5) Progesterone (Slow LH and prepares the uterus)
- If the corpus is degenerates, Estrogen and progesterone levels falls leading to menstruation
47
Which hormone is responsible for ovulation?
Leutenizing hormone
48
What are the main regulators of the endometrial cycle?
Estrogen and progesterone
49
What are the main events of the endometrial cycle?
1) Menstruation
2) Endometrial growth and proliferation
3) Differentiation of the endometrial epithelium into glandular secretory phenotype
50
What are the phases of the endometrial cycle?
1) proliferative phase
2) Secretory phase
51
What happens in the proliferative phase of the endometrial cycle?
The endometrium undergoes rapid regeneration and growth under the influence of estrogen, which is secreted by the granulosa cells of the developing follicle.
- Estrogen would stimulate the proliferation of both the stromal and epithelial cells, leading to the thickening of the endometrial lining (along with their glands and increased blood vessels)
- This phase concise with the follicular phase of the ovarian cycle
52
What happens in the secretory phase of the endometrial cycle?
- As the cycle progresses towards mid-cycle, the LH surge induces the granulosa cells to secrete progesterone
- Progesterone will initiate the secretory phase, where the endometrial glands begin secreting nutrient-rich fluid to support a potential embryo
- Progesterone causes marked secretory development
- During the secretory phase, the uterus is prepared for implantation of the fertilized ovum by increasing the blood supply, lipid ad glycogen deposits in the stromal cells
53
What will happen to progesterone and estrogen if fertilization does not occur?
The corpus luteum would degenerateleading to a decline in estrogen and progesterone levels, which will lead to the shedding of the endometrial lining (marking the onset of menstruation)
54
What is the hormone responsible for the proliferative stage of the endometrial cycle?
Estrogen secreted by the ovaries
55
56
What is the nutritional source of the ovum once it enters the uterus and until it implants?
Uterine secretions (uterine milk)
56
What will happen in the endometrial cycle if the ovum is not fertilized?
1) The corpus luteum involutes
2) Progesterone and estrogen decreases
- These two factors will lead to menstruation, which is the necrotic endometrium due to the vasospasm of the blood vessels under the effect of the vasoconstrictor, which are expelled by uterine contractions
57
When does estrogen exert a positive feedback to the hypothalamus?
During ovulation
- However, during the follicular and luteal phases, estradiol has a negative feedback on the hypothalamus
58
How is the female monthly rhythm (HPO) Axis regulated?
1- Pulsatile release of GnRH, which stimulates the release of LH and FSH by the anterior pituitary
2- FSH will activate the release of estrogen, inhibin, activin, and progestins from the granulosa cells
3- LH will stimulate the theca cells, producing androgens and progestins. It also stimulates the granulosa cells (same effect as FSH)
4 Estrogen and progestins will then travel to the target tissue, and they could either inhibit or activate both the hypothalamus and the anterior pituitary
59
What is the fate of the androgens produced by the theca cells?
Because the theca cells lack the aromatase, they cannot convert androgens to estrogen
- And thus the andrgens will diffuse out of the theca cells into the adjacent granulosa cells where they will get converted to estrogens via aromatase, which is stimulated by FSH
60
What are the hormones produces by the granulosa cells?
1) Activin (activates the Anterior pituitary)
2) Inhibin (inhibits the anterior pituitary)
3) Estrogen
4) Progestins
61
What are the hormones produced by the theca cells?
1) Androgens
2) Progestins
62
What are the physiological roles of inhibin and activin?
1) FSH stimulates the release of inhibin and activin from the granulosa cells
2) Inhibin will inhibit the release of FSH and LH to a lesser extent by inhibiting the gonadotropes in the anterior pituitary gland
3) Activin will promote the release of FSH by activating the anterior pituitary
63
What structure is responsible for the female sexual sensation?
- Although the vulva vagina dn other perineal regions can create a sexual sensation, the glans of clitoris is especially sensetative
- Sexual sensory signals will be carried by the pudendal nerve and the sacral plexus to the sacral segments of the spinal cord, which will then be transmitted to the cerebrum
- Local reflexes at the sacral and lumbar segments also integrate and play a role
64
Which nerve is responsible for female erection and lubrication?
The parasypathetic nerves which pass through the nervi erigentes from the sacral plexus to the external genitalia, they also supply the bilateral bartholin glands to secrete mucus for lubrication
65
How does orgasm help fertilization?
Orgasm is the maximum intensity of sexual stimulation, and when a female reaches this state it increases the chance of fertilization as orgasm will simulate the spinal cord reflexes which will contract the perineal muscle of the female rhythmically and thus increase the uterine and fallopian tube motility which will help in the transportation of sperm through the uterus towards the oocyte
66
Summarize the menstrual cycle
1) Menstruation
- 1-5 days, where the stratum functionalis sheds (due to the absence of estrogen and progesterone)
2) Proliferation (Estrogen)
- Days 6-14, The regenerative phase, uterine glands, and they also regenerate the coiled arteries of the stratum functionalis (and this occurs under the influence of estrogen)
- Estrogen will also cause thin cervical mucus production for capacitation and so that the sperm can swim more easily, "since it is till day "14" where ovulation takes place"
3) Secretory phase (Progesterone)
- The corpus luteum produces progesterone
- Day 15-28
- It will cause the further growth of blood, gland (and their secretions "rich in glycogen, lipids, and proteins), and the stratum functionalis
- It also forms a thick mucuc plug for the cervix (to protect the potential formed embryo)
