Hormones in Early Pregnancy Quiz

Physiology of Pregnancy

• Overview of pregnancy stages: ovulation, fertilization, implantation, embryo, and fetus
• Objectives for the lecture include describing sperm transport, physiological sperm changes before ovum penetration, endocrine changes during pregnancy and placental hormones.

Objectives

• Students will learn the path sperm takes to the mid-oviduct.
• Students will learn about physiological and chemical changes to sperm before penetration of the ovum
• Students will learn about endocrine changes during pregnancy
• Students will learn about placental hormones and their function.

Fertilization

• Sperm chemoattraction to the ovum occurs by signals like oxytocin, prostaglandins and chemotactic factors.
• Sperm adheres to the zona pellucida
• Sperm penetrates the zona pellucida via the acrosome reaction
• Sperm fuses with the egg membrane which leads to the breakdown of the fusion area. Then, the sperm nucleus enters the egg cytoplasm.

Capacitation

• Sperm capacitation occurs in the female genital tract fluids, improving motility and preparing for the acrosome reaction
• Capacitation takes 2-3 hours
• Sperm undergoes physiological and chemical changes.
• Only capacitated sperm can penetrate the zona pellucida

Implantation

• Implantation occurs on the anterior or posterior wall of the uterine body near the fundus, on or about the 6th day (20th of menstrual cycle)
• The endometrium is in the secretory phase.
• Stages of implantation include orientation, apposition, attachment, and invasion
• Blastocyst moves to the uterus, contacts the endometrium and the trophoblast burrows into the uterine wall

Implantation involves

• The blastocyst moves from the fallopian tube to the uterus
• The blastocyst contacts the endometrium
• The trophoblastic layer erodes the endometrium, and the blastocyst burrows into the endometrium.

Placenta

• The placenta forms after implantation
• The trophoblast remains associated with it
• Placental hormones are secreted to maintain pregnancy
• Functions of the placenta include:
  • Transfer of gases
  • Transport of nutrients
  • Excretion of wastes
  • Hormone production (estrogen, progesterone)
  • Formation of a barrier (incomplete and non-selective)

Endocrine Changes During Pregnancy

• After implantation, the syncytiotrophoblast secretes human chorionic gonadotropin (HCG)
• Enlargement of the corpus luteum occurs instead of degeneration
• Corpus luteum secretes progesterone and relaxin to maintain pregnancy, inhibiting uterine contractions
• After the 8th week of pregnancy, HCG levels decrease, but progesterone and estrogen are maintained by the placenta

Hormones

• Estrogen:
  • Produced in the corpus luteum initially, then by the placenta
  • Responsible for uterus and breast growth
• Progesterone:
  • Produced in the corpus luteum and then by the placenta
  • Relaxing smooth muscles
  • Inhibits uterine contractions, preparing the uterus for labor
  • Regulates body fat storage
• Human Chorionic Gonadotropin (HCG):
  • Secreted by the trophoblast of the developing embryo
  • Keeps the corpus luteum healthy, until the placenta takes over

Human Placental Lactogen

• Affects maternal metabolism
• Transfers glucose to the fetus
• Mobilizes fatty acids from maternal stores

Relaxin

• Released by the corpus luteum initially and then by the placenta
• Softens pelvic ligaments
• Reduces myometrial tone

Fetoplacental Unit

• The fetus and placenta work together to produce steroids
• Cholesterol is converted into progesterone, androgens, and estrogens
• These hormones are then transferred across the placenta to the fetus and maternal blood.

Test your Understanding

• The corpus luteum degenerates slower after fertilization/implantation because of HCG.