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.