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Menstrual Cycle, Pregnancy, & Birth

Anatomy & Physiology Mrs. Halkuff. Menstrual Cycle, Pregnancy, & Birth. Menstrual Cycle. A series of hormonal changes that help to prepare a woman’s body for pregnancy. Menarche : First female period that usually occurs around age 12.

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Menstrual Cycle, Pregnancy, & Birth

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  1. Anatomy & Physiology Mrs. Halkuff Menstrual Cycle, Pregnancy, & Birth

  2. Menstrual Cycle • A series of hormonal changes that help to prepare a woman’s body for pregnancy. • Menarche: First female period that usually occurs around age 12. • A cycle can range from 21-45 days, with 28-32 days being the average. • Consists of 2 cycles: • Ovarian Cycle • Uterine Cycle

  3. Ovarian Cycle • Involves changes in the ovaries • Can be divided into 2 phases: • Follicular Phase (Days 1-13) • First day of menstruation until ovulation. • Egg growth/maturation is occurring in the ovaries. • Luteal Phase (Days 14-28) • From ovulation until menstruation begins.

  4. Uterine Cycle • Involves changes in the uterus. • Occurs together with the Ovarian Cycle. • Can be divided into 2 phases: • Proliferative Phase (Days 5-14) • Occurs after menstruation but before ovulation • Endometrium rapidly grows in thickness • Secretory Phase (Days 14-28) • Occurs at ovulation if fertilization does not occur. • Egg & endometrium begin to break down.

  5. Ovulation • During the first half of the menstrual cycle, as many as 20 egg follicles begin to grow in the ovaries due to Follicle Stimulating Hormone (FSH). • Half way through the cycle, there is a spike in the Luteinizing Hormone (LH) which signals the release of the most mature egg from the ovary. This is referred to as ovulation. • The remaining egg follicles undergo atresia, or cell degeneration. • If more than one egg follicle grows to maturity, they can also be released from ovary increasing the chance of fraternal twins or triplets.

  6. How Conception Occurs • Fertilization occurs when a sperm and egg unite in the fallopian tube, creating new life. • The female egg can only be fertilized for 12-24 hours after being released. • An average 300 million sperm are released in one ejaculation, however only 10,000 will reach the uterus due to the harsh acidic environment of the vagina. • Most sperm only survive for 12-24 in the vagina with a maximum of about 72 hours. • This environment is necessary to deplete a fatty covering on the sperm that will then allow the sperm to fuse with the egg.

  7. Sperm Anatomy

  8. Sperm Physiology • To fertilize an egg, sperm must undergo a 3-step modification process. • Capacitation: Secretions in the female reproductive tract modify the sperm’s membrane to allow it to fertilize the egg. • Hyperactivation: They become better, more efficient swimmers. • Acrosome Reaction: The acrosome creates an enzyme reaction with the egg’s zonapellucida, weakening it and allowing entry.

  9. Fertilization • Once a sperm(X or Y) has penetrated the egg (X), a chemical reaction takes place within the egg making it impossible for another sperm to enter. • Almost immediately the nuclei of the sperm and egg fuse to produce a diploid zygote containing genetic material from both mother and father. • The sex of the fetus is determined at this point. • If an X sperm meets the X egg = girl (XX) • If a Y sperm meets the X egg = boy (XY)

  10. Implantation • The fertilized egg will make its way to the uterus where it will implant. • It takes roughly 7 days for the fertilized egg (blastocyst) to travel and implant. • Occasionally a fertilized, dividing egg will attach to the lining of the fallopian tube. This is called an ectopic pregnancy. • This type of pregnancy must be terminated for the safety of the mother. The fallopian tube is not elastic and the growing blastocyst will rupture the tube.

  11. Pregnancy • A typical pregnancy lasts approximately 40 weeks (280 days) • These 40 weeks are broken up into trimesters: • 1st Trimester: Weeks 1-14 • 2nd Trimester: Weeks 14-27 • 3rd Trimester: Weeks 27-40

  12. Embryonic Development • Fertilized egg is called an embryo until 8 weeks after fertilization.

  13. Fetal Development • From weeks 10-40, the baby is termed a fetus.

  14. Birth (Parturition) • 3 Stages 1. Shortening/dilation of cervix 2. Descent/birth of infant 3. Delivery of placenta

  15. Labor Stage 1: Effacement & Dilation • As baby moves down, cervix thins (effaces). • Given as a percentage (75% effaced). • Cervix begins to open (dilates). • Assigned a number 1-10

  16. Labor Stage 2: Fetal Expulsion • Cervix must be fully dilated to 10 cm. • Mother is pushing • Baby’s head is crowning • Baby has large head and shoulders and must maneuver out in a specific pattern of rotation:

  17. Labor Stage 3: Umbilical Cord Clamped & Placenta Expulsion • Typically the umbilical cord is clamped & cut in the first 3 minutes of birth. • The placenta is delivered 15-30 minutes after birth.

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