Development
of the human body is the process of growth to maturity. The process begins
with fertilization,
where an egg released from the ovary of
a female is penetrated by a sperm
cell from a male. The resulting zygote develops
through mitosis and cell
differentiation, and the resulting embryo then implants in
the uterus,
where the embryo continues development through a fetal stage until birth.
Germinal Stage
The germinal stage refers to the time from fertilization through the development of the early embryo until implantation is completed in the uterus. The germinal stage takes around 10 days. During this stage, the zygote begins to divide, in a process called cleavage. A blastocyst is then formed and implanted in the uterus. Embryonic development continues with the next stage of gastrulation, when the three germ layers of the embryo form in a process called histogenesis, and the processes of neurulation and organogenesis follow.
Blastocyst Development
Blastocyst development is important stage
for the formation of organs in embryo.
The
blastocyst stays inside a protective cover during maturation called zona
pellucida, which could be described as an egg shell. The outer cells are
located right below this cover, which will create the future placenta and
surrounding tissues to support fetal development in the uterus. The inner cells
of the blastocyst will become the different tissues and organs of the human
body, such as bones, muscles, skin, liver, and heart.
Embryo
Development
As the blastocyst reaches the final steps
in the implantation process into the inner lining of the uterus, it evolves
into a structure called an embryo. This is the time when internal organs and
external structures develop. The mouth, lower jaw, throat are emerging, while
the blood circulation system starts its evolution and a heart tube is created.
The ears arise and arms, legs, fingers, toes, and eyes are being shaped. The
brain and the spinal cord are already formed, while the digestive tract and
sensory organs start their development. The first bones are replacing the
cartilage.
After ten-twelve weeks of pregnancy, the
embryo moves into the final stage of development, a fetus.
Gastrulation
Gastrulation starts in the 3rd week, the inner cell or
embryo starts differentiating into three germinal layers, i.e. ectoderm,
endoderm and mesoderm. These cells transform and get differentiated to all the
tissues and organs, like nerve, blood, muscle, bone, digestive tract, etc.
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
Fetal Development
By the twelfth
week of fertilization the embryo moves into the final stage of development
called the fetal stage. By now, the fetus has formed all of the organs and
structures necessary for a baby, but those organs still need to grow and
develop.
At three months of
pregnancy, the upper and lower extremities of the fetus are completely
developed. Ears and teeth are formed and the reproductive organs have evolved.
At the end of this month, the fetus has completed the expansion of most of the
circulatory and urinary systems and its length is about 5 inches.
At six months, the
fetus can respond to sounds and is around 12 inches long. The fetus continues
to develop and grow changing position and responding to sounds, and stimuli.
The length of the little body can reach 14 inches.
The fetus becomes
a baby at month eight. The brain is evolving quickly so the baby can see and
hear, although the respiratory system requires maturation. The baby can weigh
approximately 5 pounds. Close to the end of the pregnancy at month 9, the baby
responds to stimuli, can move the whole body but space around the new human
being is becoming too tight.
PLACENTA
The interdigitated chronic
villi of trophoblast and uterine cells form the placenta, which is the
connection between the mother and the growing foetus.
The placenta provides
nourishment and oxygen to the embryo and helps in removing carbon dioxide and
waste produced by the embryo. It also acts as an endocrine gland and secretes
various hormones like hCG (Human Chorionic Gonadotropin), estrogen, progestogens,
etc. for maintenance of pregnancy.
Formation of Human Organ
1.The heart is
the first functional organ to develop and starts to beat and pump blood at
around 22 days.
2.The digestive system starts to develop
from the third week and by the twelfth week, the organs have correctly
positioned themselves.
3. The
respiratory system develops from the lung bud, which appears in
the ventral wall of the foregut about four weeks into development.
4. Brain developed around eight week
5. After12 week Male and female external
genital differences observable
Stages of Growth Month-by-Month in Pregnancy
First trimester
The first trimester will span from conception to 12 weeks. This
is generally the first three months of pregnancy. During this trimester, your
baby will change from a small grouping of cells to a fetus that is starting to
have a baby’s features.
Second trimester
This middle section of pregnancy is often thought of as the best
part of the experience. By this time, any morning sickness is probably gone and
the discomfort of early pregnancy has faded. The baby will start to develop
facial features during this month. You may also start to feel movement as your
baby flips and turns in the uterus. During this trimester, many people find out
the sex of the baby. This is typically done during an anatomy scan (an
ultrasound that checks your baby’s physical development) around 20 weeks.
Third trimester
This is the final part of your pregnancy. You may be tempted to
start the countdown till your due date and hope that it would come early, but
each week of this final stage of development helps your baby prepare for
childbirth. Throughout the third trimester, your baby will gain weight quickly,
adding body fat that will help after birth.
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