Pregnancy and Childbirth 2

The Reproductive System

Pregnancy and Childbirth Overview

• The reproductive system plays a critical role in human development, focusing on pregnancy and childbirth processes.

Implantation

• Definition: The process where the embryo adheres to the endometrium of the uterus.
• Nutritional Support: Endometrial cells provide essential nutrients, serving as the only nutritional source for the first week post-implantation.
• Placenta Formation: The endometrium grows over the embryo, and the placenta begins to form.
• Hormonal Activity: The embryo secretes human chorionic gonadotropin (HCG), which stimulates the corpus luteum to secrete estrogen and progesterone for maintaining the pregnancy.

Ectopic Pregnancy

• Definition: Occurs when the embryo implants outside the uterus, commonly in the fallopian tubes.
• Signs and Symptoms: This includes vaginal bleeding, pelvic pain, and low HCG levels.
• Risks: Possible risk of tubal rupture leading to severe abdominal pain, fainting, and shock.
• Treatment Options: Can involve medication or surgical intervention.

The Placenta

• Structure: A temporary organ formed from both maternal (endometrium) and fetal (outer layer of embryo) tissues.
• Function: Provides fetal nutrition from week 9 until birth.
• Connection: The placenta is connected to the fetus through the umbilical cord, containing two umbilical arteries carrying deoxygenated blood and one umbilical vein carrying oxygenated blood.

Placental Physiology

• Chorionic Villi: Contain fetal capillaries and are surrounded by maternal blood for nutrient exchange.
• Placental Barrier: A semipermeable membrane separating maternal and fetal blood, facilitating diffusion of oxygen, nutrients, and waste products.
• Delivery Impact: Rupture of chorionic villi during delivery can allow fetal blood to cross into maternal circulation.

Multiple Births

• Monozygotic: Single fertilized egg divides, usually sharing one placenta and being genetically identical.
• Multizygotic: Two or more eggs fertilized separately, each developing its own placenta, resulting in non-identical siblings.

Development by Week 8

• Major Developments: All body systems and major brain regions are present, and the heart is fully functional.
• Hemopoiesis Starts: Blood cell formation begins, with the development of limbs, fingers, and toes.

Fetal Circulation

• Pathway: The umbilical vein passes through the liver as the ductus venosus and drains into the inferior vena cava (IVC).
• Blood Bypass: Cardiac blood bypasses the lungs via the foramen ovale and ductus arteriosus.
• Artery Function: Umbilical arteries branch from the internal iliac arteries returning to the placenta.

Development from Weeks 9 - Birth

Weeks 9 - 12

• Brain Development: The brain enlarges; retina forms; nervous control develops.

Weeks 13 - 16

• Sensory Reception: General sensory systems begin establishing; digestive glands develop.

Weeks 17 - 20

• Physical Developments: The fetus assumes a position due to spatial constraints; lanugo covers the body.

Weeks 21 - 30

• CNS Changes: Myelination of the central nervous system begins; lungs prepare producing surfactant.

Weeks 30 - Birth

• Final Developments: The skin thickens and subcutaneous fat accumulates; most babies born at 35-40 weeks.

Circulatory Adaptations at Birth

• Closure of Bypass Structures: Foramen ovale becomes fossa ovalis; ductus arteriosus becomes ligamentum arteriosum.
• Arteries & Veins: Umbilical arteries/vein undergo fibrosis, becoming ligaments and aiding in postnatal adaptations.

Immune System Adjustments

• Adaptive Immunity: Development of the adaptive immune system; newborns receive IgG from the mother, which declines as their own levels rise.
• IgA: Present in breast milk, providing critical immune support until weaning.

Lactation Process

• Hormonal Control: Estrogen and progesterone levels stimulate mammary gland growth; prolactin promotes milk production.
• Neuroendocrine Reflex: Suckling triggers oxytocin release for milk ejection, simultaneously contracting the uterus.

Colostrum and Breast Milk

• Colostrum: Initial milk high in protein and antibodies, produced in small amounts for the first few days.
• Breast Milk: Transition to mature milk occurs postpartum; it is primarily water, higher in fat and lactose than colostrum, providing critical immunity.

Milk Production and Ejection

• Milk Ejection Mechanism: Involves positive feedback from mechanoreceptors in the nipples, stimulating both prolactin for production and oxytocin for ejection during nursing.

Summary of Infant Stomach Capacity

• Day 1: Size of a cherry; capacity 5-7 ml (1-1.4 teaspoons).
• Day 3: Size of a walnut; capacity 22-27 ml (0.75-1 oz).
• One Week: Size of an apricot; capacity 45-60 ml (1.5-2 oz).
• One Month: Size of a large egg; capacity 80-150 ml (2.5-5 oz).

Conclusion

• Understanding the anatomy and physiology of the reproductive system provides insights into the stages of pregnancy, childbirth, and early infant development.