Human Development Stages

Human Development and Aging

• Puberty in females occurs from 11 to 13 years, while in males, it occurs from 12 to 14 years.
• During puberty, there is a period of rapid growth followed by a period of slower growth.
• Adult stature is reached in females by 17 to 18 years and in males by 19 to 20 years.

Fertilization and Prenatal Development

• Prenatal development begins at fertilization, where a sperm attaches to a secondary oocyte, and their contents combine.
• The secondary oocyte is surrounded by the corona radiata and zona pellucida.
• The sperm's acrosome binds to a receptor on the zona pellucida, initiating the acrosomal reaction.
• The first sperm cell to penetrate the zona pellucida binds to a receptor on the oocyte, causing depolarization, which prevents additional sperm from attaching.
• The zona pellucida degenerates, preventing further sperm from attaching.

Implantation and Formation of the Placenta

• The syncytiotrophoblast surrounds maternal blood vessels, forming cavities called lacunae that contain maternal blood.
• Cords of cytotrophoblast surround the syncytiotrophoblast and lacunae, and embryonic mesoderm and blood vessels grow into these cords.

Mature Placenta and Fetus

• Branches from the cords of cytotrophoblasts sprout into chorionic villi that protrude into the lacunae.
• The entire embryonic structure facing the maternal tissues is called the chorion.
• As the placenta matures, the cytotrophoblast disappears, and the embryonic blood supply is separated from the maternal blood supply by only the embryonic capillary wall, a basement membrane, and a thin layer of syncytiotrophoblast.

Newborn

• The respiratory system and cardiovascular system undergo changes, including the closure of the foramen ovale and ductus arteriosus.
• The umbilical vein and arteries degenerate, and the digestive system begins to function.
• The liver does not produce adult bilirubin for the first two weeks, and lactose can be digested, but other food must be gradually introduced.
• Oxytocin stimulates milk letdown in the breast.

Aging and Death

• Atherosclerosis is the deposit and hardening of materials in lesions in large and medium-sized arteries, leading to arteriosclerosis, thrombus, and/or embolus.
• Progressive aging of cells occurs due to exposure to toxic substances, such as free radicals, which can react with and alter cells.
• Poor diet may lead to vitamin deficiency, and a decrease in ATP production may occur due to mitochondrial DNA mutations.
• The immune system becomes less responsive to outside antigens but more responsive to self-antigens.
• A genetic component contributes to longevity, and progeria is a genetic trait causing premature aging.

Genetics

• Genetics is the study of heredity, and Mendelian genetics is the study of how genetic traits are passed on to offspring.
• Genotype refers to the genes an organism has for a given trait, while phenotype refers to the expression of those genes as a trait.
• Dominant and recessive alleles are alternate forms of genes, and dominant alleles mask the effects of recessive alleles.
• Homozygous refers to having two of the same alleles for a trait, while heterozygous refers to having one dominant and one recessive allele for a trait.

Chromosomes

• Chromosomes contain thousands of genes and are found in discrete sections of DNA.
• Autosomal and sex chromosomes are the two types of chromosomes, and diploid refers to having two copies of chromosomes, while haploid refers to having one copy, only in gametes.
• Karyotype is a map of chromosomes.
• Homologous pairs of chromosomes are pairs where one is from the father and the other is from the mother, and locus refers to the location of a gene on a chromosome.