Human Reproduction and Embryonic Development

Spermatogenesis vs. Oogenesis

• Nutritive material accumulates more during oogenesis than in spermatogenesis.
• Cells resulting from oogenesis vary in size because the nutritive material is not distributed equitably.
• The formation of sperm requires a differentiation process to obtain functional gametes, which does not occur in oogenesis.

Differences Between Embryo and Fetus

Organogenesis, the formation of organs, occurs in the first trimester of pregnancy; at this stage, the developing organism is considered an embryo. From the second trimester onwards, it is classified as a fetus.

The Zygote

In biology, a zygote (also known as a fertilized egg) is the cell resulting from the union of male and female gametes during sexual reproduction in organisms such as animals, plants, fungi, and some unicellular eukaryotes. Its cytoplasm and organelles are always of maternal origin, as they come from the egg.

Sexual Reproduction

Sexual reproduction is the primary method of reproduction for humans and most multicellular organisms. Many species do not use it as an exclusive mode of reproduction but alternate it with asexual models. It also occurs in single-celled organisms, especially protozoa and algae.

Asexual Reproduction

Asexual reproduction, also called vegetative reproduction, occurs when a single cell or part of a developed organism's body is capable of forming a complete individual genetically identical to the parent through mitotic processes.

Fertilization

Fertilization is the contact between male and female gametes. This contact does not necessarily imply that the fertilization of an egg is immediate.

Embryology and Developmental Biology

Embryology, or more modernly, developmental biology, is a branch of biology responsible for studying morphogenesis and embryonic development—from gametogenesis through the formation of the nervous system until the adult form is reached. The formation and development of an embryo is called embryogenesis. It is a discipline closely linked to anatomy and histology.

The Fetus

A fetus is a developing viviparous vertebrate, a stage that begins once the embryonic stage is complete and lasts until birth. During fetal life, no new organs or tissues are formed; instead, the maturation of existing ones occurs.