Embryology is the study of the origin and prenatal development of an organism which comprises the germinal, embryonic, and fetal periods. The germinal period consists of the first two weeks from conception, the embryonic period includes the third to eighth week from conception, and the fetal period consists of the ninth week from conception to birth. Gestation in embryology refers to the period from conception to birth. The gestation period is different from gestational age which is measured in weeks starting from the first day of the mother’s last menstrual period.

What is Embryology?

Embryology is the study of the formation of the embryo and fetus. The formation of a single-celled embryo takes place by fusion of gametes: Sperm is the male gamete, and the egg is the female gamete. This single-celled embryo develops into a Zygote which further undergoes a series of cell divisions known as cleavage to form blastocyst. A blastocyst is a hollow ball of cells that adheres to the uterus and uptake nutrients and oxygen from the mother. This process is known as implantation. Germinal (0-2 weeks), embryonic (3-8 weeks), and fetal periods (9 weeks – birth) are various developmental stages of prenatal development of an organism.

Also Read: Fertilization and Implantation

The period from conception to birth is known as the gestation period. The formation of primordial cells occurs during the embryonic stage. These primordial cells move towards gonads followed by the maturation of fertile oocytes and spermatozoa by meiosis. The process by which the human embryo develops and takes shape is known as human embryonic development or human embryogenesis.

The early phases of development are marked by the processes of cell division and cellular differentiation of the embryo. From weeks three through eight, a developing human is called an embryo, and from the ninth week of gestation until birth, it is called a fetus. The study of embryogenesis, including the transformation of a single-cell embryo into a baby, is known as embryology. Embryogenesis is a process in which the development of an embryo occurs into to fetus.

What is Embryogenesis?

The process of embryonic development that takes place in the first eight weeks following fertilization is known as embryogenesis. The embryo is made up of the trophoblast and the embryoblast when the blastocyst is implanted in the endometrium. The trophoblast primarily contributes to the placenta’s development, whereas the embryoblast goes on to develop into other bodily components.

During the second week of development, the chorionic cavity, yolk sac, extraembryonic mesoderm, and amniotic cavity develop. Through the process of gastrulation, the bilaminar disc differentiates into a trilaminar embryonic disc in weeks three and four. The three germ layers give rise to various structures. During weeks three and four, the process of neurulation contributes to the development of the nervous system. The primary characteristics of weeks five through eight are organogenesis and ongoing differentiation of embryonic tissue.

Stages of Embryology

The process by which the sperm and egg fuse to form the zygote is known as fertilization.

• Blastocyst development: Development of the blastocyst involves the division of the zygote into a small group of cells inside a structure known as the blastocyst, which has a trophoblast and an inner cell mass.
• Blastocyst implantation: When a blastocyst attaches itself to the uterine wall, the trophoblast divides into the placenta and the inner cell mass forms the embryonic disc. This process is known as blastocyst implantation.
• Embryo development: The three germ layers (ectoderm, mesoderm, and endoderm) as well as the main organs and systems that emerge from the embryonic disc are formed during the process of embryonic development.
• Fetal development: It is the growth and maturation of fetus until birth.

Human Development

The process by which a single cell differentiates and grows into a multicellular human being is extremely exact and intricate. When a sperm fertilizes an oocyte (ovum), a continuous process starts. The zygote then develops into a definite organ system and eventually reaches its early functioning stage. Cell division, migration, proliferation, differentiation, death, and rearrangement is some of the mechanisms of transformation. A deeper comprehension of embryology aids in the development of healthcare plans:

• Treatment methods for infertility
• Diagnosis and surgical interventions during pregnancy
• methods for preventing congenital abnormalities.

Duration and Stages of Pregnancy

Pregnancy in humans is an amazing physiological process that lasts an average of 266 days, or around 38 weeks or 9 months. This gestational time is carefully divided into three separate periods, or trimesters, that last around three months each. These trimesters mark particular developmental turning points and physiological shifts for the developing fetus as well as the mother.

1. First trimester (0-12 weeks): The duration of this period is first three months. Pre-embryonic and embryonic development stress, nutritional deficiencies are the common problems during this period. Foods such as raw cabbage, potatoes, coffee should be avoided during this time as these have harmful effects on embryo. During this time, “morning sickness,” a condition marked by nausea and vomiting, is common. It is thought that this state serves as a defense mechanism, maybe guarding against ingesting chemicals that could harm the developing fetus.
2. Second trimester (13-24 weeks): The duration of this period is from fourth to sixth months. This period is characterized by development of fetus in which most of the organs are developed. In this stage, most organs go through their formation and maturation. The fetus starts to show physical characteristics and its physiological systems begin to work. This stage is marked by the fetus’s apparent growth and development and is frequently linked to a decrease in the mother’s pregnancy-related discomforts.
3. Third trimester (25 weeks-birth): It includes seventh to nine months. The baby continues to grow and develop during the last trimester. The developing fetus starts to move more and more, kicking and straining. Important developmental milestones are reached by the thirtieth week: the sense organs are fully formed, fingernails appear, bones ossify, and the bone marrow begins to produce red blood cells. In addition, the foetus loses its covering of lanugo, a tissue that resembles hair and acts as protection.In this stage growth of baby occurs. Various body movements including kicking, stretching starts in baby. The development of red blood cells (RBC) in bone marrow, fingernails, sense organs take place.

Also Read:

• Human Pregnancy
• Spermatogenesis
• Oogenesis
• Human Reproduction
• Diploblastic And Triploblastic Organization
• Anatomy – Overview, Types and Application

FAQ’s – Embryology

What are the 4 stages of embryology?

There are 4 stages of embryonic development including:

• Morula
• Blastula
• Gastrula
• Organogenesis

What is Embryology Period?

After fertilization, the embryo remains in the embryonic stage until the eighth week, after which it becomes a fetus. The embryo undergoes significant changes throughout the brief embryonic stage, which lasts just roughly seven weeks. These developments occur during this time.

What are the Types of Embryology?

The scientific study of or embryology, is made up of a number of specialised sub-disciplines, each of which provides a different perspective on the complex mechanisms guiding the creation and development of organisms.

1. Descriptive Embryology
2. Comparative Embryology
3. Experimental Embryology
4. Chemical Embryology
5. Teratology

What is Scope of Embryology?

A scientist who studies embryology is known as an embryologist. Most frequently, embryologists collaborate with doctors to help patients with clinical research and reproductive health concerns.

Who is the Father of Embryology?

Karl Ernst von Baer is the father of embryology.