Fetal and Neonatal Physiology: Chapter 84 Summary

Introduction

Lecture by Asif Qureshi, concluding the unit on Endocrine and Reproductive Physiology.
Focus on fetal development, neonatal physiology, and early growth and development.
Important to understand basics of fetal and neonatal physiology as preparation for obstetrics and pediatrics.

Initial rapid development of placenta and fetal membranes before the fetus itself.
Embryo remains microscopic for the first 2-3 weeks after implantation.
Important measurements: 12 weeks (10 cm), 20 weeks (25 cm), 40 weeks (53 cm).
Weight increases proportionally to the cube of the fetus's length (important for calculations in pediatrics).
Rapid weight gain occurs in the last trimester (average weight: 3 lbs in the last 2 months).

Major organ systems begin developing within one month post-fertilization.
By four months, fetal organs are similar in gross structure to those of a neonate, though cellular development continues.
Nervous system and myelination develop gradually, not complete at birth.
Heart begins beating at 4 weeks (initial rate: 65 bpm, increases to 140 bpm).
Red blood cell formation starts in the yolk sac, shifts to liver, spleen, then to bone marrow by the third month.

Fetus cannot breathe air, lungs filled with amniotic fluid; respiratory movements attempt but do not inflate lungs.
Last trimester: respiratory movements inhibited to prevent filling lungs with fluid/debris.

Fetus ingests and absorbs nutrients mid-pregnancy; meconium begins formation.
Kidneys begin urine excretion in the second trimester, contributing to amniotic fluid.
Fetal kidneys not fully functional; renal regulation develops after birth.

Fetus primarily uses glucose for energy; capable of storing fat and protein.
Calcium and phosphate accumulate, particularly in the last month during rapid ossification.
Iron quickly accumulates due to early RBC formation; majority stored in the liver.

Significant changes occur at birth; baby must begin breathing and adjusting circulation.
Factors affecting transition: hypoxia during delivery, temperature changes trigger first breaths.
Delayed breathing can lead to hypoxia; neonates can tolerate 8-10 minutes of hypoxia but risks brain damage.

Fetal circulation bypasses lungs and liver; umbilical vein and ductus venosus facilitate this.
Birth leads to closure of foramen ovale, ductus arteriosus, and ductus venosus, transitioning to adult circulation.

After birth, neonate uses stored glycogen; low glucose levels can occur initially.
Special dietary needs: calcium, vitamin D, iron, and vitamin C are critical for development.

Neonates inherit immunity from mothers, with gamma globulins providing protection for the first 6 months.
Allergies may develop as the infant's immune system matures after a few months.

Neonates have a well-developed endocrine system; however, conditions in the mother can affect the infant.
Issues like maternal diabetes can lead to hypoglycemia in neonates.

Premature infants face exacerbated challenges in organ maturation and homeostasis.
Increased risk of respiratory distress, feeding issues, and temperature regulation problems.
Modern medical care has improved survival rates for premature infants significantly.

The nervous system develops significantly in the first year, affecting behavioral growth and skills.
Brain mass increases rapidly, with significant changes in myelination and functionality.