Development, Growth, Aging, and Genetics

Chapter 29: Development, Growth, Aging, and Genetics

Key Concepts

• Fertilization: The sperm attaches to a secondary oocyte, and the contents of the sperm enter the oocyte, leading to the formation of a zygote.

• Germinal Period: This stage includes cell divisions, implantation of the blastocyst into the uterine wall, and formation of the placenta.

• Embryonic Development: During this stage, three germ layers develop: ectoderm, mesoderm, and endoderm, each contributing to the formation of various organs and systems.

• Pregnancy: Divided into three trimesters:

  • First Trimester (week 1-12): Significant changes as the fertilized egg develops into a fetus.
  • Second Trimester (week 13-28): Considered the most comfortable for the mother; fetal movement becomes noticeable.
  • Third Trimester (week 29-40): Increased discomfort for the mother as the fetus gains weight and prepares for birth.

• Fetal Monitoring: Techniques such as amniocentesis, chorionic villus sampling, and ultrasound to check fetal health and development.

• Birth: The process, also known as parturition, includes three stages:

  1. Dilation: Onset of contractions until full dilation of cervix.
  2. Expulsion: From dilation until the baby is born.
  3. Placental Stage: Afterbirth; expulsion of the placenta.

Postnatal Life Stages

• Neonatal: Birth to 1 month postpartum.
• Infancy: 1 month to 1-2 years old, characterized by rapid physical growth and development.
• Childhood: 1-2 years to puberty, critical for emotional and social development.
• Adolescence: Puberty (around 11-14 years) to 20 years, marked by significant physical and emotional changes.
• Adulthood: 20 years to death.
  • Young Adult: 20-40 years.
  • Middle Age: 40-65 years.
  • Older Adult: 65 years to death.

Fertilization Process

1. Sperm Entry: The sperm penetrates the outer layers of the oocyte, activating an acrosomal reaction.
2. Polyspermy Prevention: Fast and slow blocks to polyspermy occur to prevent multiple sperm from fertilizing one oocyte.
3. Meiotic Division: The oocyte completes its second meiotic division upon fertilization, leading to the formation of the female pronucleus.
4. Zygote Formation: The fusion of the female and male pronuclei results in the diploid zygote.

Germinal Period Stages

• Initial Cell Division: The zygote divides into two cells and continues to divide into a morula (solid ball of cells), and then into a blastocyst.
• Blastocyst Development: The inner cell mass forms the embryo while the trophoblast develops into the placenta.
• Implantation: The blastocyst embeds itself into the uterine wall, initiating interaction with maternal tissues.

Germ Layer Derivatives

• Ectoderm: Forms skin, nervous system.
• Mesoderm: Forms muscles, bones, and cardiovascular system.
• Endoderm: Forms the lining of the digestive and respiratory systems.

Complications during Pregnancy

• Placenta Previa: Placenta develops near or over the cervix, risking bleeding.
• Abruptio Placentae: Premature separation of the placenta from the uterus, leading to serious risks for mother and baby.

Congenital Disorders

• Congenital disorders may arise from genetic factors, environmental factors, or a combination of both. Teratogens like alcohol can cause significant developmental issues.

Modern Monitoring Techniques

• Amniocentesis: Used for genetic testing around 15 weeks of gestation to detect chromosomal abnormalities.
• Chorionic Villous Sampling (CVS): Performed earlier than amniocentesis during the first trimester for quicker results.
• Ultrasound: Non-invasive method to monitor fetal health, using sound waves to visualize the fetus.

Apgar Score

• Evaluates newborn's physical condition at 1 and 5 minutes after birth based on:
  1. Appearance
  2. Pulse
  3. Grimace
  4. Activity
  5. Respiratory effort
• Scores range from 0 to 10; higher scores indicate better health.

Lactation Symptoms

• The process of producing milk involves hormonal changes triggered by suckling; colostrum is produced in the early days postpartum, rich in antibodies.