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Embryo Development – Development Process of Fetus

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Birth gives process to a child is known as reproduction. A species’ survival depends on its ability to reproduce. There are two different ways to reproduce: Sexual reproduction is asexual reproduction. Asexual reproduction is a type of reproduction that occurs without the involvement of 2 parents.

Asexual reproduction refers to the process of reproduction in which only one parent is involved. There is no cross-pollination of genetic data. Example- Hydra blossoms. Sexual reproduction is a type of reproduction in which two parents work together to produce a child. Males and females have reproductive organs that are distinct. The male and female gametes are produced in these organs, and they combine to make the progeny. Both parents’ genetic information is inherited. Example– Mammals, Humans

Embryo Development


When male and female gamete fused together then a diploid cell is formed called a zygote (2n). Then the zygote starts diving, at this phase only mitotic division occurred in the cell no reductional division at this particular phase. Hormones helped in the development of the embryo, once the zygote is implanted in the inner endometrium of the uterus then the placenta formation starts from which the fetus gets all the essential requirements for growth and development. The various stages of embryo development are referred to as embryo development. Plants and mammals have different embryonic development. Even in mammals, various stages of embryonic development occur in different species. The zygote is generated after fertilization. The zygote divides into two, four, eight, or sixteen cell stages during mitosis. Blastomeres are the name for these cells.  An embryo with eight to sixteen blastomeres is known as a morula. The morula continues to divide mitotically and develops into a blastocyst. The trophoblast is the blastocyst’s outer layer, and it attaches to the endometrium, which is the uterine wall. The gastrulation process starts within the 3 weeks. The formation of germinal layers is known as Gastrulation. Later, these cells (ectoderm, mesoderm, and endoderm) differentiated into different types of cells with specific functions.

  • Ectoderm– nervous system, brain, spinal cord, epidermis, hair, nails, etc.
  • Mesoderm– connective tissue, muscles, circulatory system, notochord, bone, kidney, gonads
  • Endoderm– internal organs, stomach, liver, pancreas, bladder, lung, gut lining

Embryonic Development

Second Week-The implantation process begins in the first week and is completed by the second week. The blastocyst’s inner cell mass creates the embryo.  tissues of the blastocyst differentiate further. At the end of the second week, the implantation is complete. The placenta, which connects the mother and the growing fetus, is made up of uterine cells and the trophoblast. The placenta supplies the embryo with nutrients and oxygen while also assisting in the removal of waste that would be created by the embryo. It also functions as an endocrine gland, secreting hormones such as hCG, estrogen, progestogens, and others to keep the pregnancy going.

Third Week-The inner cell or embryo begins to differentiate into three germinal layers, namely ectoderm, endoderm, and mesoderm, in the third week. These cells change and differentiate into many tissues and organs So in week three notochord would be formed, gastrulation takes place and neurulation takes place.

In week four we would see the beats of the heart.

On week five-size approx 4 mm of the fetus, gall bladder, ears, spleen, pharyngeal arches, and pancreas would form.

On week six-size-approx 8 mm of the fetus’s, eyes, nose, stomach, and kidney precursors would be developed.

On week seven-size approx 13 mm of the fetus’s, primary sex organs, lungs, and lymphatic system would develop.

On week eight-size approx 20 mm of the fetus, follicles of hair, and ear start developing.

By the month of nine fetuses would be grown fully.

Pregnancy Marker

  • The heart is the first organ to start working, developed in 1 month of pregnancy.
  • In the second Month, Limbs, and digits are  formed
  • Up to 1 Trimester- all the major organs developed, and sex organs are visible.
  • After 4 months-fetus starts moving, and hair starts growing.
  • After the 2nd trimester- eyelashes formed, and eyelids separate.
  • Until near the time of parturition, the lungs continue to mature. Throughout pregnancy, the brain accumulates new cells.

Conceptual Questions

Question 1: What would happen in the fourth week? 


In the fourth week, we can appreciate the heartbeat.

Question 2: By which month foetus would be grown mostly?


By the ninth month, the fetus would be grown fully.

Question 3: What is morula?


The embryo would be having sixteen blastomeres is called a morula.

Question 4: In which week we would appreciate the eyes forming?


During the week of six, we would appreciate the forming of eyes.

Question 5: In which week we would appreciate the forming of the ear?


In the eighth week, we would appreciate the formation of the ear.

Question 6: What would the placenta do?


The placenta would supply the nutrients and the oxygen for the fetus.

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Last Updated : 02 Jul, 2022
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