Jan 22 - Female Reproductive Physiology Flashcards
What are the ovaries?
They are the primary female reproductive organs. They produce ova (via oogenesis) and secrete female sex hormones
What are the two female sex hormones?
Estrogen
Progesterone
What is the role of estrogen?
It is essential for ova maturation and release, the establishment of female secondary sexual characteristics. It is essential for the transport of sperm from the vagina to the fertilization site in the oviduct. It contributes to breast development in anticipation of lactation
What is the role of progesterone?
It is important in preparing suitable environment for nourishing a development embryo/fetus. It contributes to breasts’ ability to produce milk
What is gametogenesis?
The production of haploid gametes from diploid or haploid precursor cells. In males it’s called spermatogenesis, in females, it’s called oogenesis. There are identical steps of chromosome replication and division during gamete production in both sexes
Describe a primary oocyte?
It is surrounded by a single layer of granulosa cells. It contains diploid number of 46 replicated chromosomes and it remains in meitoic arrest for years until they are prepared for ovulation
What is a primary follicle?
An oocyte + a granulosa cell
What is the fate of a primary follicle?
After development starts, there are two possible fates: reach maturity and ovulate or degenerate to form scar tissue (atresia)
What happens between puberty and menopause?
The follicle develop into secondary (antral) follicles on cyclic basis
What are oogonia?
Undifferentiated primordial germ cells in fetal ovaries. They divide mitotically to give rise to 6 million to 7 million oogonia by fifth month of gestation. During the last part of fetal life, the early steps of first meiotic division, but do not complete it
What happens just before ovulation?
A primary oocyte completes it first meiotic division yielding the first polar body and a secondary oocyte
What happens to the second oocyte?
It is ovulated. Sperm entry into the vagina triggers second meiotic division which produces a secondary polar body and a mature haploid ovum which unites with haploid sperm cell during fertilization
What is the ovarian cycle?
Aka the menstrual cycle
It is normally interrupted only by pregnancy
It is finally terminated by menopause
What are the two alternating phases of the ovarian cycle?
The follicular phase
The luteal phase (after the egg has been release)
What dominates the follicular phase?
It is dominated by the presence of maturing follicles
What dominates the luteal phase?
It is characterized by the presence of the corpus luteum
Describe the follicular phase
It operates the first half of the cycle. Granulosa cells of some primary follicles proliferate. The oocyte inside each follicle enlarges. Theca cells (comprise a layer of the ovarian follicles) in the follicle secrete increased amounts of estrogen. Rapid follicular growth continues during the follicular phase
How does ovulation occur?
One follicle usually grows more rapidly and matures about 14 days after the onset of follicular development. The follicle ruptures to release the oocyte from the ovary (ovulation). The released oocyte enters the oviduct where it may or may not be fertilized
What happens to the old follicular cells after ovulation?
During the last 14 days of the ovarian cycle (luteal phase) the old follicular cells undergo structural transformation to form the corpus luteum. It become highly vascularized and becomes fully functional within four days after ovulation. It continues to increase in size for another four or five days
What happens to the corpus luteum if the ovum is not fertilized and implants?
It degenerates within about 14 days after its transformation
Explain the hormonal interactions during the follicular phase
During the follicular phase, the rise in FSH signals the ovarian follicle to secrete more estrogen. The rise in estrogen feed back to inhibit FSH secretion which declines as follicular phase proceeds. LH rises in the follicular phase; as it peaks in mid-cycle, it triggers ovulation. The estrogen output decreases and the mature follicle is converted to a corpus luteum
Explain the hormonal interactions during the luteal phase
The corpus luteum secretes progesterone and estrogen. Progesterone output inhibits the release of FSH and LH. The low LH levels cause the corpus luteum to degenerate and progesterone levels decline. Now FSH can start to rise again, initiating a new cycle
How does LH affect the thecal cells?
LH stimulates the thecal cells in the ovarian follicle. On stimulation, the thecal cells convert cholesterol into androgen. Androgen diffuses from the thecal cells into the adjacent granulosa cells.
How does FSH affect the granulosa cells?
FSH stimulates the granulosa cells in the ovarian follicle. On stimulation, the granulosa cells convert androgen into estrogen. Part of the estrogen is secreted into the blood, where it exerts systemic effects. Part of the estrogen remains within the follicle and contributes to antral formation. Local estrogen, along with FSH, stimulates proliferation of the granulosa cells
What is inhibin?
Hormone secreted by developing follicle that inhibits the secretion of GnRH from the hypothalamus and LH and FSH from the anterior pituitary
What causes ovulation?
Ovulation and subsequent luteinization of the ruptured follicle are triggered by an abrupt, massive increase in LH secretion
What is the result of the abrupt, massive increase in LH secretion?
It halts estrogen synthesis
It reinitiates meiosis in the oocyte of the developing follicle
It triggers production of the locally acting prostaglandins
It causes differentiation of the follicular cells into the luteal cells
What causes the massive increase in LH secretion?
High levels of estrogen
How is the corpus luteum controlled?
LH “maintains” the corpus luteum; this is, after triggering development of the corpus luteum, LH stimulates ongoing steroid hormone secretion by this ovarian structure. Under the influence of LH, the corpus luteum secretes both progesterone and estrogen, with progesterone being its most abundant hormonal product
What do high levels of progesterone result in?
They inhibit the release of GnRH and LH from the hypothalamus and the anterior pituitary, respectively
What are the three phases of the cyclic uterine changes?
Menstrual phase
Proliferative phase
Secretory or progestational phase
Describe the menstrual phase
It’s characterized by the discharge of blood and endometrial debris from the vagina. The first day of menstruation is considered the start of a new cycle. It coincides with the end of the ovarian luteal phase and onset of the follicular phase. There is also release of uterine prostaglandin
What does the release of prostaglandin during the menstrual phase do?
It causes the vasoconstriction of the endometrial vessels. This distrupts blood supply and cause death of the endometrium. Prostaglandin secretion also stimulates mild rhythmic contractions of the uterine myometrium. This helps expel blood and endometrial debris from uterine cavity out through the vagina (menstrual flow)
Describe the proliferative phase
It begins concurrent with the last portion of the ovarian follicular phase. The endometrium starts to repair itself and proliferative under the influence of estrogen from newly growing follicles.
Estrogen-dominant proliferative phase last from the end of menstruation to ovulation
The peak of estrogen levels trigger LH surge responsible for ovulation
Describe the secretory phase
The uterus enters this phase after ovulation when the new corpus luteum is formed. The corpus luteum secretes large amounts of progesterone and estrogen (the progesterone converts the endometrium to a highly vascularized, glycogen-filled tissue). The endometrial glands actively secrete glycogen. If fertilization and implantation do not occur, the corpus luteum degenerates and the new follicular phase and menstrual phase begin once again
What is menopause?
The cessation of a woman’s menstrual cycle
It usually occurs between the ages of 45 and 55
The midlife hypothalamic change may trigger the onset of menopause.
What precedes menopause?
A period of progressive ovarian failure characterized increasingly inregular cycles and dwindling estrogen levels. The loss of estrogen primarily affects skeleton and cardiovascular system
What is the period of transition during menopause called?
Climacteric
Where does fertilization take place?
In the oviduct; normally occurs in the upper third of the oviduct (in the ampulla)
When does fertilization occur?
It must occur within 24 hours after ovulation
How long do sperm survive?
Sperm usually survive about 48 hours but can survive up to five days in female reproductive tract
Describe the migration of sperm within the female reproductive tract
Sperm deposited in the vagina travel through the cervical canal, uterus and to the upper third of the oviduct.
How does the female reproductive tract aid in sperm migration?
Via contractions of the myometrium, upward contractions of the oviduct smooth muscle and allurin released by mature eggs
Describe how fertilization occurs
The first sperm to reach the ovum fuses with the plasma membrane of the ovum. This triggers a chemical change in the ovum’s surrounding membrane that makes the outer layer impermeable to entry of any more sperm. The head of the fused sperm is gradually pulled into the ovum’s cytoplasm. Within an hour, the sperm and the egg nuclei fuse and the fertilized ovum is now called a zygote
What happens after fertilization?
The fertilized ovum divides mitotically and within a week, it grows and differentiates into a blastocyst capable of implantation
How does implantation occur?
Blastocyst implants in the endometrial lining by means of enzymes released by trophoblasts. Enzymes digest the endometrial tissue and carve a hole in the endometrium for implantation of the blastocyst. Endometrial cells release nutrients for use by the developing embryo
What is the role of the trophoblast?
It accomplishes implantation and develops into fetal portions of placenta
What is the destiny of inner cell mass?
They are destined to become the fetus
What happens after implantation?
The placenta develops
What is the placenta?
It is the organ of exchange between maternal and fetal blood and acts as a transient, complex endocrine organ that secretes essential pregnancy hormones
What hormones does the placenta secrete?
Human chorionic gonadotropin, estrogen, progesterone, human chorionic somatomammotropin, relaxin and placental PTHrp (parathyroid hormone-related peptide)
What is the role is the of human chorionic gonadotropin?
It maintains the corpus luteum until the placenta takes over that function in the last two trimesters.
It stimulates the secretion of testosterone by the developing testes in XY embryos
How is pregnancy determined (what is a pregnancy test looking for)?
It tests for the presence of human chorionic gondatropin
How are the placenta and amniotic sac formed?
Finger-like projections of chorionic tissue extend into the pools of maternal blood. Soon the developing embryo sends out capillaries into these chorionic projections to form placental villi. Inner cell mass forms a fluid-filled amniotic cavity called the amniotic sac or amnion and filled with amniotic fluid
What is the role of the placenta?
The placenta performs the functions of the digestive system, the respiratory system and the kidneys for the “parasitic” fetus. Nutrient and oxygen diffuse from the maternal blood across the thin placental barrier into the fetal blood, whereas carbon dioxide and other metabolic wastes simultaneously diffuse from the fetal blood into the maternal blood
What is the role of estrogen in pregnancy?
It stimulates growth of the myometrium, increasing uterine strength for parturition
It helps prepare the myometrium, increasing uterine strength for partruition
What is the role of progesterone in pregnancy?
It suppresses uterine contractions to provide a quiet environment for the fetus
It promotes formation of a cervical mucus plug to prevent uterine contamination
It helps prepare the mammary glands for lactation
What is the role of human chorionic somatomammotropin in pregnancy?
It is believed to reduce maternal use of glucose and to promote the breakdown of stored fat (similar to growth hormone) so that greater quantities of glucose and free fatty acids may be shunted to the fetus
It helps prepare the mammary glands for lactation (similar to prolactin)
What is the role of relaxin in pregnancy?
It softens the cervix in preparation for cervical dilation at partruition
It loosens the connective tissue between the pelvic bones in preparation for partruition
What is the role of placental PTHrp in pregnancy?
It increases maternal plasma calcium ion levels for the use in calcifying fetal bones; if necessary, promotes localized dissolution of maternal bones, mobilizing their calcium ion stores for use by the developing fetus
What is afterbirth?
The loss of the placenta; it causes a dramatic drop in progesterone and estrogen levels (breastfeeding can now start)
How long does gestation last?
About 38 weeks from conception
What are the physical changes made within the mother that meet the demands of pregnancy?
Uterine enlargement
Breasts enlarge and develop the ability to produce milk
The volume of blood increase by 30 percent
Weight gain
Respiratory activity increase by about 20 percent
Urinary output increases
Kidneys excrete additional wastes from the fetus
Nutritional requirements increase
What is parturition?
Labour, delivery, birth
What are the requirements of parturition?
Dilation of the cervical canal to accommodate the passage of the fetus from the uterus through the vagina the outside
It also requires contraction of the uterine myometrium that are sufficiently strong to expel the fetus
What happens once contractions start?
Once contractions begin at the labour onset, positive-feedback cycle progressively increases force
Pressure of the fetus against the cervix reflexively increases oxytocin secretion
What is the role of oxytocin in parturition?
It causes stronger contractions
A positive-feedback cycle progressively increases until cervical dilation and delivery are complete
What are the stages of labour?
Cervical dilation
Delivery of the baby
Delivery of the placenta
After delivery, the uterus shrinks to pregestational size (involution)
Describe the cervical dilation stage of labour
It’s the longest stage
It lasts from several hours to as long as 24 hours in a first pregnancy
Describe the delivery of the baby stage of labour
It begins when cervical dilation is complete
It usually last 30 to 90 minutes
Describe the delivery of the placenta stage of labour
It’s a second series of uterine contractions separates placenta from the uterus
It’s the shortest stage - usually completed within 15 to 30 minutes after the baby is born
How does is the breast prepared for lactation?
Elevated placental estrogen and progesterone promote development of ducts and alveoli in mammary glands
What does prolactin do?
It stimulates synthesis of enzymes essential for milk production by alveolar epithelial cells
Withdrawal of placental steroids at parturition initiates lactation
How is lactation sustained?
It is sustained by suckling, which triggers the release of oxytocin and prolactin
What is the role of oxytocin in sustaining lactation?
It causes milk ejection by stimulating cells surrounding alveoli to squeeze secreted milk out through ducts
What is the role of prolactin in sustaining lactation?
It stimulates secretion of more milk to replace the milk ejected as the baby nurses
