Development of Human embryo followed by parturition and lactation

Human embryonic development , Parturition and lactation

After the fertilization and implantation , embryo undergoes the further development and attain complete body structure with in gestation period.

First and second week of embryo development.

Cells of blastocyst start to differentiate and form extra embryonic membranes named Amion, Chorion, Allantois, and yolk sac for protection, respiration, excretion and nourishment respectively. The cells of the inner cell mass also create a space with the amnion  known as amniotic cavity. This cavity is filled with amniotic fluid.

The sample of amniotic fluid is used to detect the genetic disorder of the foetus by the technique of Amniocentesis.

This blastocyst with amniotic fluid contains stem cells that have capability to make any body organ. The embryo is freely moved in this amniotic fluid.

Third week of embryo development 

During this week, gastrulation starts and gastrulation results in the formation of three germinal  layers from the cells of blastocyst. The embryo looks like an oval shape. During the third week, the umbilical cord was also developed by the  joint effort of yolk sac and allantois.These three germinal layers are ectoderm, mesoderm and endoderm. The cells of ectoderm and endoderm are tightly arranged but cells of mesoderm are loosely packed.

The ectoderm is differentiated and forms  the central and peripheral nervous systems, sensory organs, epidermis, hair, and nails. Mesoderms form the skeleton, muscles, connective tissue, heart, blood vessels, and kidneys. The endoderm gives rise to  gastrointestinal tract, liver, and pancreas, as well as the lungs.

Fourth  week of embryo development

The cells of endometrium start to withdraw its function and all function is taken over by the placenta.The placenta connects to the foetus by  the umbilical cord.   Placenta removed deoxygenated blood and wastes from the fetus through the umbilical cord. Nutrients and oxygen are carried from the mother to the foetus  by the placenta through the  umbilical cord. 

During the fourth week ,the heart  also starts to beat but it can not pump the blood. The sound of heart beating may be heard clearly by using a stethoscope. During this time the liver starts to produce Red blood cells until bone marrow is not developed This is a temporary responsibility of the embryonic liver. 

Fifth and Six week of embryo development

During the fifth week, the eye pits are developed, limb buds are clearly visible and  the rudiments  pulmonary system can be seen.

During the sixth week, movement of  foetal limb occurs. The gastrointestinal system develops too rapidly. Fingers are developed in  hands and feet. 

Seventh and Eight week of embryo development

In the seventh week, the facial structure including nostrils, outer ears, and lenses are developed. By the eighth week, the head  becomes large and all major brain structures are developed.  The external genitalia are well demarcated therefore  male and female embryos are easily distinguished. Bone begins to replace cartilage in the embryonic skeleton through the process of ossification. 

Parturition and lactation

After attaining the full gestation period, the foetus is fully developed in the uterus. As the foetus is developed completely. The signal is sent by the uterus to the brain for its expulsion. 

Parturition is a neuro endocrine mechanism. After receiving the signal , the brain sends a signal to the posterior pituitary to release the oxytocin. Oxytocin causes the strong contraction in the perimetrium of the uterus and fortune starts to expel through the birth canal. During this time relexin hormone also makes the pubic area lose the baby. This is called foetal ejection reflex.

At the end of pregnancy, the mammary gland produces milk for nourishment of the newborn baby. This period is known as lactation period. During the initial day of lactation, the milk is called colostrum. It is yellowish in colour.

👌👌Remember- Colostrum is rich in immunoglobulin A that provides resistance to babies against various infections.

That is the reason doctors recommend the first day of breast feeding for a new born baby.