HUMAN REPRODUCTION Implantation: From Zygote to Embryo to Fetus

 Implantation
Lesson 5: From Egg and Sperm to Newborn  The zygote attaches into the uterine lining about 6 to 7
days after conception or fertilization in a process known as
implantation. During this time, the zygote takes the form
UNIT 11- HUMAN REPRODUCTION of a blastocyst with an inner cell mass (future embryo) and
• Human reproduction is the biological process by which a man and an outer cell mass (future placenta).
a woman create their children. The sexual nature of human  The Zygote
reproduction (compared with asexual reproduction) results in a  As early as one week after fertilization, the placenta is
genetically unique offspring with a lower chance of inheriting formed from both mother and fetal tissues. The placenta
harmful mutations but with a higher chance of receiving beneficial is a temporary disc-shaped organ that connects the fetus
traits. to the uterine wall. It is the life support system of the
• A person is not obliged to reproduce, but if he/she chooses to do developing fetus that serves as the passageway for the
so, then it must be done with respect to life, person (mother and transfer of nutrients, waste materials, and chemicals
child), family and nature. between the mother and the fetus by osmosis and
• At present, millions die or are disabled because of reproduction- diffusion. It also produces the human chorionic
related causes. It, therefore, becomes incumbent on each one to gonadotropin (HCG). During early pregnancy, HCG
understand how human reproduction occurs in or der to properly stimulates the corpus luteum to enlarge so it can support
care about the offspring and keep it safe. the uterus and the zygote until the placenta takes over.
Detection of HCG is the basis of common pregnancy tests.
The placenta later secretes its own hormones to support
FERTILIZATON: From Egg and Sperm to Zygote the pregnancy and play a role in labor, lactation, and
breastfeeding. The cord is the connecting link between the
Oogenesis and Spermatogenesis fetus and the placenta.
 Oogenesis  In the zygote, the continuous and purposeful cell division
 refers to the production or development of a mature egg and cell differentiation results in the development of the
from one of the hundred thousands of oocytes (immature embryonic membranes and the different germ layers that
eggs) to become a mature egg. As the Graafian follicle give rise to specific organs and body systems at the third
bursts, the ovum is released. This egg is drawn into the week.
fallopian tube. Oogenesis begins before birth but  The Embryo
ovulation occurs once a month on average from puberty  From the fourth to the eighth week of development, the
to menopause. Ova are viable, i.e., can be fertilized, for product of gestation is called an embryo. This is a critical
approximately 24 hours after ovulation time because viruses, drugs and inadequate nutrition can
 Spermatogenesis gravely affect the embryo’s development.
 is the maturation of the immature sperms inside the  The Fetus
testes. As the sperms are released into the male duct  After the eighth week until delivery, the embryo is called a
system, they continue to mature, acquiring motility and fetus. At the end of the third month, the 1-inch Cshaped
optimum fertilizing capacity. The change from immature fetus has already the rudiments of all the organs of a full
to mature sperm takes about 53 days and starts at puberty developed human being. It has a considerably large head
continuing throughout life. Sperms, although viable for 72 and is recognizable as human. The fetus then progressively
hours, are believed to have maximum fertilizing capacity grows and develops to human proportions. Its organ start
for only 24 hours. to function. While in the uterus, the fetus floats in a pale-
Fertilization straw colored liquid called the amniotic fluid.
 This process does not happen by merely swimming in a pool  The Mother
with the opposite sex or using a common or unisex toilet.  In the first few weeks, the mother will not menstruate and
Fertilization starts when millions of sperms are ejaculated into may feel fatigue, light-headedness, dizziness, fainting,
the vagina during intercourse. A few hundred of these sperms abnormal cravings, and nausea and vomiting (morning
survive the acid pH of the vagina, swim upward through the sickness). By the end of the fourth month, (16 weeks) to
movement of their flagella, and ascend to the uterus and into the fifth month (2o weeks), she will “show” and be able to
the fallopian tube to meet the egg. It takes an average of 7 feel the fetus move (quickening). By this time, the mother
hours for the sperm and egg to meet, but can occur within 15 will start to feel better because the morning sickness
minutes to 3 days. After a sperm penetrates the zona pellucida would have improved and she will begin to eat more.
or the thick capsule surrounding one mature egg, changes Towards the latter months, she may experience some
occur in the cell preventing other sperms from entering after heaviness, swollen legs, constipation, pelvic pains,
penetration, the nuclear contents of the sperm and the egg frequent urination, and uterine contractions.
merge in a process called fertilization resulting in a zygote with  The mother must take care of herself to ensure her own
46 chromosomes ( 23 from each parent). The chromosomes health and that of the baby. The maternal in utero
contain the complex genetic blueprint of every detail that environment, made up of nutrition, hormones,
defines a human being and the inherited traits from one’s metabolites, stress, and drugs, is a critical determinant of
parents. The genetic sex is determined at fertilization. As soon fetal growth. It may likewise influence a wide variety of
as the zygote is formed, a series of cell divisions start which disorders in adulthood. The mother should avoid
transforms the single-celled zygote into many cells to give rise infections, smoking and alcohol, psychosocial stress, and
to the future embryo and the placenta. It remains in a mobile medical disorders. Drinking coffee and cola should be
state traveling from the fallopian tube to reach the uterus in discouraged in favor of milk. Pregnant women should have
about 3 to 4 days. egular prenatal consultation. Additional medical
 The fertilization of two different eggs by two different sperms consultations must be done if she experiences severe
results in non-identical twins who may be of different sex and cramps, vaginal discharge or bleeding, headache or visual
are similar as any other siblings. On the other hand, a mitotic disturbances or hand and face edema.
division of a single zygote produces identical twins who are of  The Father
the same sex and are extremely similar in appearance but are  Pregnancy is a cooperative project of both the man and
not entirely alike because of environmental factors. If the the woman from initiation through growth and maturation
mitotic division is incomplete, conjoined twins result. until the delivery of the child. The father plays an
indispensable and essential role as a constant source of
love and support. Some fathers even experience similar
 symptoms as the mothers do in a phenomenon called
sympathetic pregnancy.
 Childbirth
 On average, 280 days from the first day of the mother’s
last menstrual period, the fetus is ready for birth.
Childbirth should be a natural, healthy, participatory, and
joyous experience.
 Labor
 Labor begins with an interplay of factors from the
hormones of the placenta, fetal pituitary and adrenal
glands. It is characterized by regular uterine contractions
of increasing intensity and longer duration, which result in
the expulsion of the mucus plug, opening or dilatation of
the lower portion of uterus (cervix), some bleeding and in
the late stage of labor, rupture of the bag of waters and
the woman’s urge to push. The length of labor from the
time of regular contractions to the delivery of placenta
averages 12 to 15 hours for the first delivery and 5 to 6
hours for the succeeding deliveries.
 Delivery
 With more intense and continuous uterine contractions
and the woman’s pushing efforts, the baby is born.
Afterwards, the placenta (afterbirth) is usually delivered
within 5 minutes. The uterus is then massaged to induce
uterine contractions to minimize or stop bleeding.
 Some women may experience difficulties in the delivery
and the obstetrician may decide to do a Cesarean section
(C section). This process involves cutting through the
abdomen to deliver the baby.
 After Delivery
 After delivery, the newborn is nursed and fed by the
mother. Breast milk is best for the first six months of life. It
is the gold standard for infant feeding. In addition to
providing nutrition, it protects the baby against infections,
and results in less allergy, heavier growth, better
neurodevelopment, and lower rates of chronic disease.
For the mother, breastfeeding is economical and
convenient. It also helps the uterus contract to reduce
bleeding and reconditions the uterine muscles stretched
by pregnancy. Breastfeeding is a natural method of child
spacing and protects the mother from infection, cancer,
diabetes, osteoporosis ad rheumatoid arthritis.
 Republic Act No. 7600 also known as “The Rooming-in and
Breastfeeding Act of 1992,” requires all private and
government health institutions to adopt rooming-in and
breastfeeding practices.