Amniotic membrane ruptures to release amniotic fluid (

Uterine Cycle

  • Days 1-5: Low estrogen and progesterone levels cause the thickened uterine lining to degenerate and shed during menstruation.

  • Days 6-13 (Proliferative Phase):

    • Estrogen (from the follicle) increases, leading to the thickening of the endometrium.

    • Increased vascularization and development of mucus glands occur in the lining.

  • Day 14: Ovulation occurs; the follicle transforms into the Corpus Luteum.

  • Days 15-28 (Secretory Phase):

    • Progesterone levels increase, causing the endometrium to double in thickness.

    • Mucus glands secrete a thick mucus material.

    • The endometrium is prepared to receive a fertilized egg (zygote).

  • Ovarian Hormone Levels: Estrogen and progesterone levels fluctuate throughout the cycle.

  • Estrogen: Peaks during the proliferative phase, promoting endometrium repair and regeneration.

  • Progesterone: Dominates the secretory phase, supporting secretion by endometrial glands.

  • If No Fertilization Occurs:

    • The corpus luteum degenerates due to absence of fertilization.

    • Estrogen and progesterone levels decline, causing the endometrium to shed.

Hormonal Regulation of the Menstrual Cycle

  • Hypothalamus: Secretes Gonadotropin-Releasing Hormone (GnRH).

  • Anterior Pituitary: GnRH stimulates the anterior pituitary to release Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH).

  • FSH: Promotes follicle growth in the ovary.

  • LH: Triggers ovulation, with a mid-cycle LH peak.

  • Ovary: Follicle produces estrogen.

  • Corpus Luteum: Produces progesterone and estrogen.

  • Hormone Levels and Phases:

    • Follicular Phase: FSH promotes follicle growth, leading to increased estrogen levels.

    • Ovulation: LH surge triggers ovulation.

    • Luteal Phase: Corpus luteum secretes progesterone and estrogen.

    • If fertilization does not occur: corpus luteum turns into corpus albicans

    • Menstruation: Occurs when estrogen and progesterone levels are low.

The Menstrual Cycle

  • Ovarian Cycle:

    • Follicular Phase: Estrogen rises.

    • Luteal Phase: Progesterone and estrogen are secreted by the corpus luteum.

    • If no implantation occurs, the corpus luteum turns into the corpus albicans.

  • Uterine Cycle:

    • Menses: Triggered by low estrogen.

    • Proliferative Phase: Influenced by estrogen, the endometrium thickens.

    • Secretory Phase: Influenced by progesterone, the endometrium becomes highly vascular and edematous.

    • The cycle restarts with menses.

Fertilization and Implantation

  • Fertilization:

    • Sperm Count: Hundreds of sperm may reach the egg, but only one fertilizes it.

    • Acrosome Reaction: Sperm releases enzymes to penetrate the egg's outer layer.

    • Fusion: Plasma membranes of the egg and sperm fuse, and the sperm nucleus enters the egg.

    • Zygote Formation: Sperm nucleus fuses with the egg nucleus, forming a zygote.

  • Implantation:

    • Zygote Development: The fertilized egg develops as it travels down the oviduct to the uterus.

    • Attachment: The fertilized egg attaches to the endometrium (implantation) several days after fertilization.

    • Interruption of Menstrual Cycle: The menstrual cycle must be interrupted for nine months to allow the developing offspring to grow.

    • HCG Production: The zygote produces Human Chorionic Gonadotropin (HCG) to prevent menstruation.

Role of HCG and Corpus Luteum

  • HCG Function: Maintains the corpus luteum, which continues to produce progesterone to prevent the endometrium from shedding.

  • Pregnancy Test: Monoclonal antibodies are used to detect HCG in pregnancy tests.

  • Corpus Luteum Persistence: The corpus luteum persists for 3-6 months.

  • Hormonal Maintenance:

    • HCG maintains the corpus luteum.

    • The corpus luteum maintains the endometrium.

    • Progesterone thickens the cervix.

Placenta Formation and Function

  • Placenta Formation: The placenta forms from both maternal and fetal tissues.

  • Functions:

    • Provides exchange of molecules between fetal and maternal blood.

    • Continues production of HCG and also produces progesterone and estrogen.

  • Hormonal Control: Higher levels of progesterone and estrogen shut off the release of FSH and LH from the anterior pituitary, preventing ovulation and maintaining the endometrium.

  • Placental Structure: Contains umbilical cord, villi, placental membrane, and intervillous space for exchange between maternal and fetal blood.

Fetal Development and Positioning

  • Fetal Position: The fetus rotates with its head pointed toward the cervix.

  • Breech Position: If the fetus is not in the head-down position (breech), a Cesarean section may be required.

  • End of Pregnancy: At the end of nine months, the fetus averages a length of 525 mm525 \, \text{mm} (20 inches) and a weight of 3380 g3380 \, \text{g} (7.5 pounds).

Labour and Childbirth

  • Labour: Involves contractions lasting over 40 seconds occurring every 15-20 minutes.

  • Trigger of Childbirth: Involves prostaglandins and oxytocin from the mother's pituitary gland.

Oxytocin

  • Production and Storage: Oxytocin is a hormone made in the hypothalamus and stored in the posterior pituitary gland.

  • Functions:

    • Causes the uterus to contract.

    • Used to artificially induce labor.

    • Stimulates the release of milk from the mammary glands for nursing.

Positive Feedback System of Oxytocin

  • Mechanism: The level of oxytocin in the blood feeds back to the posterior pituitary, increasing its release.

  • Process:

    • The growing baby's head exerts pressure against the cervix.

    • Sensory nerves in the cervix send a nerve signal to the posterior pituitary to release oxytocin.

    • Oxytocin is released into the blood.

    • It causes stronger uterine contractions, which further stimulate sensory nerves, leading to more oxytocin release.

    • The cycle ends when the baby is pushed out of the uterus, stopping the stimulation of sensory nerves.

  • Instability: A positive feedback system is unstable and does not lead to homeostasis.

Stages of Childbirth (Parturition)

  • Three Stages

    • Includes labor and expulsion of the fetus.

Stage 1

  • Cervix Dialation

  • Mucus Plug
    : The mucus plug from the cervical canal is expelled.

  • Amniotic membrane
    : Amniotic membrane ruptures to release amniotic fluid

  • Stage 2

  • Expulsion of the Fetus
    : The baby is delivered during this stage.

  • Umbilical Cord Clamping
    : The umbilical cord is clamped and cut.

  • Stage 3

  • Expulsion of the Placenta
    : The placenta is expelled from the uterus.

  • Postpartum Bleeding
    : Bleeding occurs as the uterus contracts to its normal size.

  • Mammary Glands and Lactation

  • Prolactin
    : Causes the mammary glands to make milk after childbirth.

  • Suckling
    : Causes the release of prolactin and oxytocin.

  • Milk Production

  • Colostrum
    : Produced by the mammary glands for the first few days after birth.

Rich in protein and antibodies (IgA).

  • Breast Milk

  • Composition
    : Contains lactose, lipids, amino acids, vitamins, minerals, and water.

  • Antibodies
    : Provides antibodies, especially IgA, for passive immunity.

  • Passive Immunity
    : The process of receiving antibodies from an outside source.