IM

Reproduction and Contraception

Maintaining the Endometrium

  • Hormonal Changes:
    • If pregnancy doesn't occur, the corpus luteum degenerates.
    • Progesterone levels decrease, leading to the closing off of the spiral arteries.
    • This results in the death and shedding of cells, causing the menstrual period.

Pregnancy and Human Chorionic Gonadotropin (hCG)

  • hCG Production:

    • If pregnancy occurs, the cells that will form the placenta start producing hCG within a few days.

  • Pregnancy Tests:

    • Home pregnancy tests detect the presence of hCG in urine.
    • The appearance of lines (pink or blue) indicates a positive result.

  • Specificity of hCG:

    • hCG is only produced when a placenta is present.
    • Its presence confirms pregnancy.

  • Role of hCG as a Rescue Hormone:

    • hCG rescues the corpus luteum, extending its lifespan.
    • Normally, the corpus luteum lasts for about ten days before degenerating.
    • hCG prolongs its function for three weeks or more.

  • Continued Progesterone Production:

    • The corpus luteum continues to produce progesterone under the influence of hCG.
    • Progesterone maintains the spiral arteries and the endometrium.

  • Importance of Endometrium:

    • Maintaining the endometrium is crucial for the growth of the cell ball (early embryo).
    • Shedding the endometrium would result in the loss of the developing embryo.

Contraceptive Methods and Effectiveness

  • Pregnancy Rate Without Contraception:

    • A regular couple having regular intercourse for a year has an 85% chance of pregnancy without contraception.
    • This means that 15% of such couples will not get pregnant in a year.

  • Effectiveness Table:

    • The table presents pregnancy rates with typical use of various contraceptive methods over a year.

Vasectomy

  • Procedure:

    • A minor surgical procedure where the vas deferens is cut and sealed.
    • The vas deferens is easily palpable in the scrotum.

  • Steps:

    • A small incision is made.
    • The vas deferens is brought to the surface.
    • A section is cut out and the ends are sutured and cauterized to create scar tissue.

  • Tension:

    • The tube is under tension, causing it to retract when cut.
    • A section is removed to prevent the ends from reconnecting.

  • Bilateral Procedure:

    • Both vas deferens must be cut as there are two testes and two vas deferens.

  • Anesthesia:

    • Local anesthetic is used, and the injection can be painful due to the sensitivity of the area.

  • Post-operative Care:

    • Sitting on frozen peas or vegetables is recommended to reduce swelling and discomfort.
    • A sperm test is performed after a couple of months to confirm the absence of sperm.

Tubal Ligation

  • Female Equivalent:

    • Equivalent to a vasectomy in males, but performed on the uterine tubes.

  • Procedure:

    • The uterine tubes are cut to block the passage of the gamete to the uterus.

  • Anatomical Difficulty:

    • More complex than vasectomy due to the location of the tubes and the proximity of the ovarian ligament.
    • It is crucial to cut the tube and not the ovarian ligament.

  • Method:

    • Typically performed laparoscopically with minimally invasive techniques.
    • The abdomen is inflated with gas to improve visibility.
    • Usually done through the umbilicus to avoid scars.

Fertilization

  • Acrosomal Reaction:

    • Sperm release digestive enzymes (acrosomes) from their heads to digest the zona pellucida, a glycoprotein layer surrounding the oocyte.
    • Sperm must swim through cells and digest their way to reach the cell membrane.

  • Sperm Journey:

    • Sperm are deposited in the vagina and must swim up through the uterus to the correct uterine tube.
    • They may follow a chemical gradient, but it could also be a random process.

  • Role of Multiple Sperm:

    • Multiple acrosomal reactions are needed to digest the zona pellucida.
    • It is beneficial for some sperm to go ahead and make progress before others finish the job.

  • Oocyte Stage:

    • The oocyte is still in metaphase II of meiosis and is a secondary oocyte, not yet a mature ovum.

  • Sperm Entry:

    • Only the sperm nucleus enters the oocyte; no organelles from the sperm, including mitochondria, enter.
    • All mitochondria in an individual come from their mother (maternal inheritance).

  • Completion of Meiosis:

    • Penetration by the sperm triggers the completion of meiosis in the oocyte.
    • The oocyte enters anaphase II, and non-equal cytokinesis occurs, forming a second polar body.

Zygote Formation

  • Conception:

    • The fusion of the sperm and egg pronuclei.
    • Creates a zygote, which is the first diploid cell.

  • Chromosome Number:

    • 23 chromosomes from the sperm combine with 23 chromosomes from the ovum.

  • Location:

    • Occurs in the lateral portion of the uterine tube.

Cleavage and Blastocyst Formation

  • Cell Division:

    • The zygote undergoes cell division, forming two cells, then four, eight, sixteen, and so on.
    • This process takes about four to six days to reach the uterus.

  • Cleavage:

    • A special type of cell division where the number of cells increases, but the size of the cells decreases.
    • Mitosis occurs during cleavage.

  • Blastocyst:

    • By day four or five, a hollow structure called the blastocyst forms.
    • It consists of a fluid-filled cavity, an inner cell mass, and surrounding cells (trophoblasts).

Differentiation

  • Cell Fate:
    • Differentiation occurs early.
    • The inner cell mass will form the embryo.
    • The trophoblast cells will form membranes and contribute to the placenta.

Implantation

  • Mechanism:

    • The blastocyst attaches to the uterine wall and embeds within it around day six or seven.

  • Orientation:

    • The inner cell mass must be against the uterine wall for implantation to occur.
    • Incorrect orientation prevents implantation.

  • Trophoblast Function:

    • Trophoblast cells produce digestive enzymes that erode the endometrium.
    • The blastocyst burrows into the endometrium, and the epithelial tissue repairs itself over the top.

  • Success Rate:
    * High percentage of blastocysts don't implant.

Placenta Formation

  • Structure:

    • Develops by day 11 and is derived from both maternal and fetal tissues.

  • Function:

    • Serves as the organ for gas exchange, nutrient exchange, and waste exchange between the mother and fetus.

  • Separation of Circulations:

    • Maternal and fetal blood do not mix, but are brought into close proximity for exchange.

  • Chorionic Villi:

    • Fetal structures that protrude into the endometrium, increasing surface area for exchange.
    • Villi are surrounded by maternal blood in spaces created by digestive enzymes.

Uterine Wall and Placental Location

  • Location of Development:

    • The baby grows within the wall of the uterus, not in the cavity.
    • The uterine cavity becomes smaller as the baby grows.

  • Trophoblast Derivatives:

    • The villi, amnion, and yolk sac are formed from trophoblast cells.

Physiological Changes During Pregnancy

  • Maternal Stress:

    • Pregnancy places significant stress on the female body.
    • Increased caloric needs, respiratory effort, and kidney workload.

  • Fetal Manipulation:

    • The fetus produces hormones to manipulate the mother for its own benefit.
    • Examples include gestational diabetes (increased sugar demand) and increased blood pressure.

Labor and Delivery

  • Positive Feedback Loop:

    • Cervical stretch leads to oxytocin release, causing more contractions and further stretch.
    • Cervical \ Stretch \rightarrow Oxytocin \ Release \rightarrow Contractions

  • Stages of Labor:
    * Early dilation (first stage): Cervix is stretched and dilated via intermittent contractions.
    * Expulsion: Baby is delivered head first, allowing the shoulders to twist through.
    * Placental Stage: Expulsion of the placenta.

  • Fetal Skull:

    • Baby's skull bones are flexible with fontanels to allow for passage through the birth canal.

  • Maternal Adaptations:

    • The pubic symphysis loosens due to hormones, increasing the pelvic outlet.

  • Placental Delivery:

    • Detachment of the placenta leaves a bleeding wound in the uterine wall, potentially causing blood loss.

  • Cord Cutting:

    • The umbilical cord is cut after delivery.
    • Cord blood can be banked for its stem cells.

  • Placental Disposal:

    • Cultural decisions vary: in some cultures its consumed for nutrients, in the past it was sold to cosmetic companies in the UK.

Lactation

  • Mammary Glands:

    • Mammals lactate to provide nutrients and immunoglobulins (IgAs) in breast milk.

  • Colostrum:

    • The first milk is rich in immunoglobulins and beneficial for the baby's immune system development.

  • Hormonal Control:

    • Prolactin and oxytocin, controlled by the anterior pituitary, are required for lactation.

  • Tactile Stimulation:

    • Nursing/breastfeeding stimulates the nipple area, maintaining hormone production and milk supply.

  • Extended Breastfeeding:

    • Can continue for an extended period of time as long as stimulation around the nipple continues.

Menopause and Andropause

  • Menopause:

    • In females, estrogen levels decline around 45-50 years old.
    • Ovulation becomes intermittent and eventually ceases, leading to infertility.

  • Andropause:

    • In males, sperm production and testosterone levels decrease with age, but not as drastically as estrogen in females.
    • There is no complete cessation of sperm production equivalent to menopause.