Female Reproductive Physiology Flashcards

Fertilization

• Before fertilization, sperm must be introduced into the female reproductive tract.
• Most ejaculated sperm fail to reach the oocyte due to:
  • Leakage from the vagina.
  • Destruction by the acidic vaginal environment.
  • Destruction by immune cells.
• Approximately 1000 surviving sperm use chemoreceptors to locate the oocyte in the fallopian tube.

Oocyte Viability

• The oocyte must be ovulated to allow fertilization.
• The potential for fertilization is highest during the first few days post-ovulation.
• Oocyte viability: 12-24 hours.
• Sperm survival: up to 5 days in the female reproductive tract.

Contraceptive Methods

• Methods to prevent sperm from reaching beyond the vagina:
  • Condoms
  • Diaphragms
  • Cervical caps and sponges
• Rhythm method (timing of ovulation):
  • Not very effective.
  • Sex before ovulation: higher probability of pregnancy (sperm can survive).
  • Sex after ovulation: slightly lower chance of pregnancy.

Fertilization Process

• Sperm release acrosomal enzymes to digest the zona pellucida.
• After penetration, meiosis II continues, forming a polar body and mature ovum.
• The zona pellucida hardens.
  • This is to prevent polyspermy (fertilization by multiple sperm).
• Maternal and paternal chromosomes combine, forming the zygote (fertilized egg).

Chromosomes

• Oocytes have an X chromosome.
• Sperm have either an X or Y chromosome.
• X-chromosome sperm are generally more robust and survive longer than Y-chromosome sperm.
• Intercourse before ovulation increases the chance of conceiving a female child because the more robust X-chromosome sperm can outlast the Y-chromosome sperm while waiting for ovulation.

Zygote Development

• Within 24 hours of fertilization, the zygote undergoes mitotic divisions.
• Morula: solid mass of approximately 32 cells.
• The developing embryo travels down the fallopian tube for 4-5 days.
• Blastocyst: a more complex hollow structure.
• During this time, the uterus is preparing for implantation and hormones are fluctuating.

Blastocyst Differentiation

• The blastocyst differentiates into:
  • Trophoblast: the outer cell layer.
    • Invades the endometrium, forming parts of the placenta and chorion.
  • Inner cell mass: a cluster of cells that will form the embryo.

Implantation

• Implantation completes about 12 days after ovulation.
• The trophoblast and chorion secrete human chorionic gonadotropin (hCG).
  • hCG prevents the corpus luteum from degenerating during the first trimester, maintaining high progesterone and estrogen levels.
• After the first trimester, the placenta secretes progesterone and estrogen.
  • This is because the placenta takes over the role of maintaining the pregnancy from the corpus luteum.

Placenta and Chorion Development

• hCG promotes placenta formation.
• Extra-embryonic mesoderm forms the chorion, delivering embryonic blood.
• Chorionic villi form the umbilical artery and veins.
• The endometrium forms sinuses that fill with maternal blood.
• Fetal and maternal blood do not mix but allow diffusion of substances.

First Trimester

• The embryo develops and obtains nutrients from the placenta by the end of the third month.
• Maternal and embryonic circulatory systems exchange materials (oxygen, water, nutrients, waste).
• The first trimester is the primary period for organ development.
• At 8 weeks, all major adult structures are present in the fetus, and a heartbeat can be detected.

Fetal Circulation - Umbilical Cord

• One umbilical vein carries oxygen and nutrients to the fetal heart (partially oxygenated).
  • One of the two degenerates, leaving only the left.
• Two umbilical arteries carry carbon dioxide and waste from the fetal heart to the placenta (deoxygenated).
  • Come off the distal end of the internal iliac arteries.

Fetal Circulation

• The umbilical vein picks up O_2 and nutrients and enters the inferior vena cava (IVC) near the liver.
• Oxygen saturation is approximately 80%.
• The ductus venosus directs blood from the umbilical vein, superior to the liver, into the IVC (bypasses the liver).
• Bypassing the liver is crucial as the liver isn't fully developed and functional yet.

Fetal Circulation - Bypassing the Pulmonary Circuit

• Before birth, blood leaving the right side of the heart mostly bypasses the pulmonary circuit.

  • Lungs are not fully functional in utero because the fetus obtains oxygen from the placenta.

• Two ways this occurs:

  1. Foramen ovale moves most of the oxygenated blood in the IVC directly to the left atrium.
     • This is due to the position of the IVC, foramen ovale, and back pressure in the pulmonary circuit.
  2. The ductus arteriosus moves blood from the pulmonary artery to the aortic arch.

• Blood in the descending aorta is only partially oxygenated and goes to the lower body.

• Blood sent to the head, neck, and upper limbs has a higher oxygen concentration.

  • Ensuring that the brain receives the most oxygenated blood.

Fetal Circulation

• Deoxygenated blood from the upper body enters the superior vena cava (SVC) and then the right atrium.
• Partially oxygenated blood from the inferior vena cava enters the right atrium.
• This blood mixes in the right atrium before being sent to the pulmonary circuit.
• Blood is still sent to the lungs to nourish the developing lung tissue, even though they aren't being used for oxygen exchange.

Fetal Circulation

• The two umbilical arteries carry carbon dioxide and waste to the placenta.
  • Carry about 58% oxygen.
  • Come off the distal end of the internal iliac arteries.

Second and Third Trimesters

• The uterus grows enough to become visible.
• The fetus continues to grow.
• Fetal activity increases and may be visible through the abdominal wall.
• Childbirth begins with labor and strong, rhythmic uterine contractions.

Anatomical Changes During Pregnancy

• The uterus pushes into the abdominal and pelvic cavities.
  • Presses against the diaphragm, urinary bladder, and pelvic blood vessels.
  • Increases pressure in the abdominopelvic cavity, affecting organs and leg drainage.
• Relaxin causes pelvic ligaments and the pubic symphysis to relax, widen, and become flexible.
• Lumbar curvature becomes accentuated (lordosis).

Labor and Delivery

• Labor is the expulsion of the fetus from the uterus through the vagina.
• During the last few weeks of pregnancy, fetal cortisol increases, causing the placenta to release more estrogen.
  • This increases oxytocin receptors in the uterus.

Labor and Delivery - Hormonal Changes

• Mother and fetus secrete oxytocin.
• The placenta releases prostaglandins.
  • These cause the cervix to soften.
  • Uterine contractions increase, causing the release of more oxytocin (positive feedback loop).

Labor and Delivery - Dilation

• True labor begins with dilation and regular uterine contractions (usually painful).
• Contractions move from the upper uterus toward the vagina, becoming more vigorous and rapid, and the cervix softens.
• The amniotic sac ruptures, releasing fluid.
• The cervix fully dilates at 10 cm.

Labor and Delivery - Expulsion and Placental Stage

• Expulsion begins from full dilation to complete delivery of the infant (2hr to 20 min).
• "Crowning" occurs when the largest dimension of the baby’s head distends the vulva.
• The placental phase involves strong uterine contractions compressing blood vessels, limiting bleeding, and shearing off the uterine wall.
  • This is important to prevent excessive postpartum hemorrhage.

Changes After Birth

• The circulatory pattern must change to deliver deoxygenated blood to the lungs and oxygenated blood to body systems.
• The umbilical cord is cut.
• The baby takes its first breath, causing the following changes:
  • Umbilical vessels are occluded

Circulatory Changes After Birth

• Umbilical vessels, the liver, and lung bypasses are occluded.
• Foramen ovale = Fossa ovalis
• Ductus venosus = Ligamentum venosum
• Umbilical vein = Ligamentum teres
• Umbilical arteries = Median umbilical ligaments
• Ductus arteriosus = Ligamentum arteriosum

Check your understanding

• Explain the progesterone and estrogen production changes that occur when fertilization does occur and when fertilization does not occur.

• What are the different ways to prevent pregnancy? Discuss how the method prevents pregnancy.

• What are the three phases of labor?

• Explain the hormonal changes that occur for labor to start.

• Describe the anatomical changes to a woman’s body as her pregnancy develops.

• For pregnancy to continue, what hormones are secreted? Where are these hormones secreted from?

• You want to have a son. When would be the best time for intercourse to increase the likelihood of conceiving a male? Explain why? What if you want a daughter?

• What is the function of hCG and why is it not important after the first trimester of pregnancy?

• The life span of the ovarian corpus luteum is extended for nearly three (3) months after implantation, but otherwise it deteriorates. Explain why this is so. Explain why it is important that the corpus luteum remains functional following implantation.

• Why is it only one sperm out of the thousands (or millions) available enters the oocyte?

• Jenna, a freshman in your dormitory, tells you she just discovered that she is three (3) months pregnant. Since she came to college she has been drinking alcohol heavily and experimenting with various recreational drugs. Given what you know about the first trimester of pregnancy what would you tell her and why?

• The placenta is a marvelous, but temporary, organ. Starting with a description of its formation, show how it is in an intimate part of both fetal and maternal anatomy and physiology during the gestation period.

• In substantial pain, Laticia called her doctor and explained (between sobs) that she was about to have her baby “right here.” The doctor calmed her and asked how she had come to that conclusion. She said that her water had broken and that her husband could see the baby’s head. Was she right? If so, what stage of labor was she in? Do you think that she had time to make it to the hospital 60 miles away? Why or why not?

• Describe what is housed within the umbilical cord.

• Discuss the function of ductus venosus in a fetus.

• Discuss the function of the ductus arteriosus in the fetus.

• Describe how fetal blood circulation differs from adult blood circulation.

  • What are the special structures found in the fetus?
  • What does each of these structures become after birth?
  • Why does the fetus need these special features in its circulatory pathway?

• Where are all the places that oxygenated and deoxygenated blood mix in the fetus?

• What does each fetal circulatory structure become after birth?

Clinical Case Study

• Ms. Johansen, 38, is 26 weeks pregnant with her first child and has preeclampsia.

1. How does increased blood volume affect cardiac output (CO), and what factor(s) must change so that blood pressure decreases?
2. One of your fellow nurses says preeclampsia is characterized by vasoconstriction. Does this make senses? Why or why not?
3. Her doctor wants to put delivery off as long as possible because premature babies have multiple problems. One possible problem is that the ductus arteriosus does not close. Why would this be a problem?

• Ms. Johansen’s tests indicate liver and kidney damage. Her doctor schedules delivery for tomorrow morning and orders an injection of cortisol.

1. What role does cortisol play in a developing fetus and how would an injection of cortisol help a premature infant?
2. Cortisol prompts the fetal lungs to begin synthesizing surfactant. Why is this important?