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.

• Immediately after implantation, the inner cell mass (embryo) differentiates into an outer layer called ectoderm and an inner layer called endoderm. 

• A mesoderm soon appears between the ectoderm and the endoderm. These three layers give rise to all tissues (organs) in adults.

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 the first week of development, 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 or after one month of pregnancy, the embryo's heart is formed. 

• The first sign of growing foetus may be noticed by listening to the heart sound carefully through the stethoscope 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. 

• By the end of the second month of pregnancy, the foetus develops limbs and digits.

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 from placenta and fully developed foetus , the brain sends a signal to the posterior pituitary to release the oxytocin. This is called foetal ejection reflex.

• Oxytocin causes the strong contraction in the myometrium of the uterus and uterus starts to expel through the birth canal.

• During this time relexin hormone also makes relax the pubic area to lose the baby.

• 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.