021 prenatal development notes

Course Name: Cognitive Sciences, Psychology and Other Related Sciences in Edcucation [PPB2014] Topic 3: Child Development: Prenatal Development

of 16

PRENATAL DEVELOPMENT 1.1 Conception and Heredity

There are several processes in conception and heredity. Those processes are:

i. Fertilization ii. Genes and Chromosomes iii. Genetic Transmission iv. Abnormalities

Fertilization Fertilization is the process where the sperm and ovum combine to create one cell called zygote (cell formed by the union of two gametes i.e. sperm and zygote). Ova always carry the x chromosome sperm, either x or y. You can see the union of sperm and ovum in the graphic shown.

Figure 1: The Process of Fertilization When a girl is born, there are 400,000 ova and these immature ova are contained in her two ovaries. Within the ovaries each of the ova has its own small sac called follicle. During ovulation, which happens approximately every 28 days, the ovum is released by the follicle and swept along through the fallopian tube towards uterus by tiny hair cells called cilia. This is the time when fertilization normally occurs.


of 16

Figure 2: Ovary In general, sperm are produced by a mature male in the testicles or testes, at the rate of several hundred millions a day. The sperm will be released into a woman's vagina when a man achieves a sexual climax. From here, the sperm will swim through the fallopian tube in search of the ova. They will use a sensory mechanism like the human nose to find their target.

Figure 3: How The Sperm and Ovum Meet Fertilization is most likely to occur on the day of ovulation through the sexual intercourse between a man and a woman. This is when the ovum and any sperm cells in the woman's body will die if fertilization does not occur. The sperm cells then will be absorbed by the woman's white blood cells while the ovum passes through the uterus and exits through the vagina. In summary, fertilization is the process of combining male's sperm and female's ovum to form a cell called zygote.


of 16

Genes and Chromosomes When you look at yourself in a mirror and you must be wondering how on earth you have the same straight hair like your mother while your sister has curly hair like your father. This is due to the genes that contain all the hereditary material of parents that will be passed on to their children. Genes determine the characteristics in a human being. Each cell in the human body consists of approximately 100,000 genes, which are made of deoxyribonucleic acid (DNA). Each gene has a different function. Therefore, it is located according to its function in a position on a rod-like structure called chromosomes. DNA contains the data needed to construct the proteins required to carry out each of the body functions. There are 23 pairs (46 in total) of chromosomes in each cell, except for the gametes, which are the sperm and ovum (the sex cells). The gametes have only 23 chromosomes and receive only one chromosome from each pair through a complex process called meiosis. Meiosis is a process where cells divide themselves. The meiotic division is random except for monozygotic twins where each child receives a different combination of genes.

Figure 4: The Meiosis Process Zygote is a single-cell formed after a successful conception, which can then develop into a human body. The process undergoes mitosis where the cells divide themselves into half, and the halves divide into another halves, and the process continues. Even though the division can be countless, the original heredity information remains the same. A normal development will have each cell containing the 46 identical chromosomes from the original zygote.


of 16

Figure 5: The Zygote Process During conception, the 23 chromosomes from the sperm and the ovum will combine. The pairs are called autosomes. However, these autosomes are not sex related. Only the 23rd pair that is the sex chromosome determines the baby's sex. Let us move to the process of determining the sex of the baby. As we know, females carry two X chromosomes and males carry an X and Y chromosomes. Therefore, all babies will automatically receive X chromosomes from their mothers and either X or Y chromosomes from their fathers. The sex of the babies is determined after the process of receiving both chromosomes from the parents.

Figure 6: The Process of Determining the Sex of the Baby


of 16

Genetic Transmission The default sex chromosome in a woman is known as the X chromosome. On the other hand, the male sperm carries either an X chromosome or Y chromosome. When the sperm and ovum combine, a baby's sex depends on the chromosome received from the sperm. For example, the resident chromosome in a female is X. If a combining sperm also carries the X chromosome; the result would be a female child (XX). Otherwise, if a Y chromosome is carried to the ovum, most likely a male child (XY) will be produced. However, to produce a male child a number of activities must happen in six to eight weeks after the transmission of the genes. The new XY embryo must produce ongoing high level of testosterone, the male hormone. If this does not happen, the XY embryo will retain female characteristics to produce a female child. In genetic transmission, a characteristic that can be expressed and physically observed is referred to as an individual's phenotype, while the characteristic that cannot be observed is the genotype. An individual has both of these. However, experience can change the characteristics in an individual. For example, a child who could not curl his/her tongue could now do so from his/her experience.

Figure 7: Genetic Transmission Meanwhile, the genes that can produce alternative forms of a characteristic (such as an ability or inability to curl the tongue) are called alleles. Every child receives one allele from each parent. If both the parents' alleles are the same, a child is considered homozygous for the characteristic he/she inherited. If one parent transmits an allele that has the ability to curl the tongue to the child while the other parent contributes an allele that lacks that ability, the child is considered heterozygous. Moreover, in dominant inheritance, a child can express an ability that one or both parents can express.


of 16

Abnormalities Abnormality is a phenomenon of uncommon happenings. Genetic defects and diseases happen because there is an abnormality in the transmission and construction of genes and chromosomes in an individual. Defected but dominant genes and chromosomes may cause a child to inherit the defect. However, inheritance of abnormal genes and chromosomes in an individual can still be either dominant (producing the same phenotype in the organism through the same allele or different) or recessive (capable of producing its characteristic phenotype in the organism only when its allele is identical) inheritance (something that may be transmitted). Below are the common genetic autosomal chromosomal abnormalities, or birth defects:

i. Down Syndrome It is a minor-to-severe mental retardation caused by an extra twenty-first chromosome i.e. the most common chromosomal defect. There is no treatment for this, but programs that stimulate the intellect can be effective. Mothers over 40 have higher likelihood of producing children with Down Syndrome.

ii. Hemophilia It is characterized by excessive bleeding, which usually affects males. In severe cases, this can cause arthritis in adulthood. Frequent transfusion of blood with clotting factors is one way to cope with this abnormality.

iii. Phenylketonuria It is a metabolic disorder that can cause mental retardation. However, preparing a special diet starting from the few weeks of life can prevent it.

iv. Tay-Sachs Disease

Tay-Sachs disease is a degenerative disease of the brain and nerve cells that can cause death before the age of 5. Unfortunately, there is no treatment for this disease.

v. Sickle-Cell Anemia The sickle-cell anemia is caused by the deformed fragile red blood cells that can clog the blood vessels, depriving the body of oxygen. The symptoms are severe pain, stunted growth, frequent infections, leg ulcers, gallstones and susceptibility to pneumonia and stroke. Painkillers and antibiotics would be a good treatment for anemia and infections respectively.

On the other hand, the sex chromosomes abnormalities are as shown in the table below:

Pattern / Name Characteristic Treatment XYY Male, tall stature, tendency to low IQ

especially verbal.

No special treatment

XXX (Triple X) Female, normal appearance, menstrual irregularities, learning disorders, mental retardation.

Special education

XXY (Kleinfelter) Male, sterility, underdeveloped secondary sex characteristics, small testes, learning disorders.

Hormone therapy, special education

XO (Turner) Female, short stature, impaired spatial Hormone therapy, special


of 16

abilities, no menstruation, sterility, webbed neck, underdeveloped sex organs, incomplete development of secondary sex characteristics.

education

Fragile x Minor-to-severe mental retardation symptoms, which are more severe in males, include delayed speech and motor development, speech impairments and hyperactivity, the most common inherited form of mental retardation.

Educational and behavioral therapies when needed

Figure 8: Sex Chromosomes Abnormalities

1.2 Prenatal Development

There are several concepts and factors involved during the prenatal development, which are:

i. Stages of Prenatal Development ii. Maternal Factors in Prenatal Development iii. Prenatal Care

Stages of Prenatal Development The nine months of prenatal period can be divided into three trimesters, each being three months long. The development of an unborn child occurs in three stages, which are:

i. Germinal Stage This stage occurs approximately from fertilization to two weeks after. In this stage, the fertilized ovum divides itself and becomes more complex. The resulting organism is then implanted in the wall of the uterus. Within 36 hours after fertilization the zygote will divide itself into two cells that will determine the human body parts. On reaching the uterus through the fallopian tube, the fertilized ovum will have changed into a fluid-filled sphere called a blastocyst, floating freely in the uterus for one to two days.


of 16

Figure 9: The Germinal Stage

In addition, at this stage, some parts of the blastocyst will then develop into organs that will nurture and protect the unborn baby. The parts are the placenta, the umbilical cord and the amniotic sac. The placenta will provide oxygen and nourishment to the developing baby through the umbilical cord. The placenta will also help combat internal infections and diseases. The placenta is connected to the embryo by the umbilical cord, which is a life support system, containing two arteries and one vein. The amniotic sac is a fluid-filled membrane that protects the baby and provides some room for the baby to move around.

Figure 10: The Blastocyst Parts in Germinal Stage


of 16

ii. Embryonic Stage

This stage occurs from week two of conception for a period of eight to twelve weeks, in which the organs and major body systems (respiratory, digestive and nervous) develop at a fast rate. During this period, the major organs take shape in at least a primitive form. The head develops first before the other parts of the body. By the fourth week after conception, a tiny heart has formed and has begun to beat. The backbone and vertebral canal will have also been formed. The eyes, ears, nose, and mouth rapidly take shape and buds that will become legs and arms appear.

Figure 11: Four Week After Conception

At the eighth week, the embryo is a little over an inch long and has a distinct human appearance. This is a critical period in the unborn development, a period when the embryo is most vulnerable to the influences of the prenatal environment. Almost all-developmental birth defects happen during the first three months of pregnancy, after which the defects that occur will be less serious. Moreover, in the seventh and eighth prenatal weeks, the process of sexual differentiation begins. If the embryo inherited a Y chromosome at conception, testes will develop. If it inherited an X chromosome, ovaries will develop.

iii. Fetal Stage This is the stage during which the first bone cells make an appearance and the embryo slowly evolves into a fetus after about eight weeks. By the twelfth week, the unborn would have fully developed into a fetus. Here, the fetus grows about 20 times in length, and organs and body systems become more complex. All aspects of the unborn child such as fingernails, toenails and eyelids will develop rapidly in this stage and the fetus starts to move.


of 16

At the end of sixth month, the fetus can hear sounds and the eyes become sensitive to light. Moreover, in the middle of the ninth month, the fetus is so large that its most comfortable position is a head down posture.

Figure 12: The Baby at the End of 6 Months

Maternal Factors in Prenatal Development There are factors that have the tendency to affect prenatal development. When a woman is pregnant she is directly responsible in influencing her unborn child. In addition, paternal factors and unavoidable environmental hazards can also influence the development of the prenatal. The factors that influence prenatal development are the mother's age, nutrition, emotion, physical activity, drugs, maternal illnesses, radiation, etc. If the mother is an adolescent, the possible rate of death among newborn is high because these babies are usually premature. The mother's immature reproductive system, poor nutrition, and lack of prenatal care and low socioeconomic status can cause the premature babies. However, paternal factors and unavoidable environmental hazards can also cause premature babies. The ideal age for women to get pregnant would be in the 20s. In fact, when women reach the age of 30 and above, the chances of giving birth to a baby with Down Syndrome will increase as their age increases. Nutrition is another factor that influences the unborn child. The unborn child depends totally on the mother for nutrition, which is carried by the mother's blood. This is the reason why malnourished mothers would often produce malformed babies. However, mothers would help improve the performance of their babies in the first three years of life if a special diet supplement is given to the mothers during pregnancy. When the pregnant mother experiences stress or fear, or any other forms of intense emotions, physiological changes such as change in respiration can occur in the mother. If the mother produces adrenaline in response to fear for example, the blood flows to the uterine area. This restricts and hampers the reception of adequate oxygen by the fetus. On the other hand, moderate physical activities like jogging and cycling do not endanger the unborn child. In fact, these exercises do help to improve respiration, circulation, muscle tone and skin elasticity that will contribute to healthier pregnancies and easier deliveries. However, when


of 16

pregnant mothers do a lot of stressful housework, there is a tendency for them to deliver premature babies. Pregnant mothers must be aware that their fetus will share whatever they consume. Drugs taken by pregnant mothers are dangerous for the unborn child. The American Academy of Pediatrics recommended that pregnant mothers should not take any drugs even for medical reasons unless it's for the survival of the unborn child or the mother. Medical drugs known to be harmful include the antibiotics streptomycin and tetracycline; the sulfonamides; excessive amounts of vitamins A, B6, C, D, and K; certain barbiturates, opiates, and other central nervous system depressants; several hormones, including birth control pills, progestin, diethylstilbestrol (DES), androgen, and synthetic estrogen; acutance, a drug often prescribed for severe acne; and even aspirin. The next factor that influences the unborn child is maternal illness. Since the mothers' blood is shared with the fetuses through the placenta, HIV infected mothers will automatically transfer the disease to the child. An illness like rubella can affect the fetus but most diseases can be cured by immunization. Diabetes, tuberculosis and syphilis may contribute difficulties in prenatal development. While gonorrhea and genital herpes may complicate delivery at birth. A pregnant mother may catch a common cold, which is due to a parasitic infection called toxoplasmosisa. This may cause brain damage, blindness or even death to the baby. This parasite can be found in cattle, sheep or pigs and the intestinal tracts of cats. Medical X-rays is another factor that could influence the unborn child. Radiation from medical x-trays can cause gene mutations. Therefore, a pregnant mother should avoid medical x-rays during the first three months of pregnancy because this is the most critical period during which the greatest damage to the fetus may occur. The other maternal factor that influences the unborn child is known as environmental hazards. Environmental hazards like radiation, chemicals, extreme heat and humidity can affect prenatal development. For example, nuclear radiation is extremely dangerous to the unborn child because it can change the genes and chromosomes and consequently cause major birth defects and other abnormalities.


of 16

Prenatal Care It is essential for pregnant mothers to have some knowledge in prenatal care. This is to ensure the safety of the unborn child. An education on prenatal care is important especially for first timers. Nowadays, education on prenatal care is provided in most hospitals. The education teaches expecting mothers on proper breathing and useful muscular exercises to ensure easy labor. There are also medical services and consultations available to make the mothers aware of potential prenatal hazards and preventive measures during the prenatal period. In addition, social privileges are also available, or should be made available, like paid maternity leaves by employers and low cost of prenatal and postnatal care programs. This is to ensure that the mothers and their babies are really taken care of. However, a lot of women do not bother to give good prenatal care to their unborn child. This maybe due to the mother's lack of education or financial resources. We hope that you have understood what prenatal care is. It is basically more towards education, medical-care services or schedule of visits to the hospital. Take into account that prenatal care is very important to make sure that the unborn baby and the mother are in good health.


of 16

1.3 After Birth

In this topic, we shall look into the followings:

i. Size and Appearance The average newborn or neonate is about 20 inches long or about 50 centimeters and weighs approximately 7 ½ pounds or about 3.4 kilograms. Boy babies tend to be longer and heavier than girl babies. Apart from sex, there are other factors that influence the size of a child. The factors are related to race, parents' size, the mother's health and nutrition.

Figure 18: Graph on Weight and Height

Do not feel shocked when you see the newborn's appearance. Normally, a newborn has a large head that is ¼ of the body length and a receding chin. The appearance of all newborns is almost the same. They have pinkish skin due to the fact that their skin is so thin that the underlying capillaries through which the blood flows show on the surface. They are also covered with a protective layer of oil called vernix caseosa that will dry off after a few days.

In addition, the pressure of traveling through the narrow passage of his/her mother's pelvis during delivery causes the newborn's head to be long and misshapen after he/she is born. The ability to adjust his/her head to the size of the passage is due to the fact that the skull bones are not yet fused. The soft spots on the skull are called fontanels.

Furthermore, some newborns are very hairy at birth because some lanugo, or fuzzy prenatal hair, has yet to fall off.

ii. Body System Before birth, babies rely totally on their mothers for survival. However, after birth, they need to readjust their body systems as they have to do everything themselves to continue to survive.


of 16

Figure 19: Body System of A Newborn

a. Circulatory System Previously in the womb, the mother and her baby have separate circulatory systems and heartbeat. However, the fetus's blood is cleansed through the umbilical cord back and forth to the placenta to be recycled. After birth, this system must be operated by the newborn alone. At birth, a newborn's heartbeat would be fast and irregular. It only reaches stabilization when he/she reaches the tenth day of life.

b. Respiratory System While in the womb, the fetus receives oxygen from the umbilical cord, which also carries out carbon dioxide. This has to be done by a baby on his/her own right after birth. However, if breathing does not begin in the first five minutes, brain damage due to anoxia may occur.

c. Gastrointestinal System In the uterus, an unborn child depends on the umbilical cord to receive food from the mother. The umbilical cord also acts as a canal to move away the fetus's body wastes. At birth, the baby has a strong reflex to suck in milk, and also his/her own gastrointestinal reserve to digest it. In the first few days, the baby's waste or meconium, is automatically ejected from the body when his/her bladder and bowels are full. The baby's sphincter muscles will open automatically for this. However, this is an uncontrollable action for months.

d. Temperature Regulation An infant stays healthy after birth by regulating his/her own temperature by producing extra heat through extra activity if the surrounding temperature drops. An infant also has layers of fat to keep him/her warm.

iii. The Brain and Reflex Behavior Reflex can be defined as an automatic action a human being does in response to external stimulation. The first early reflexes, called primitive or newborn reflexes, are needed for early survival. These include rooting for food and grasping the mother's hair. Normally these primitive reflexes will disappear after a year and what remain will be reflexes of the protective kind like blinking, yawning and shivering. The pupillary reflex will also remain, a reflex that controls the dilation of the pupil in the dark.


of 16

Figure 20: Types of Reflex Behavior However, the disappearance of the reflexes, such as the Moro reflex (the baby extends leg, arms and fingers when he/she is dropped or hears a loud noise) and the Babinski reflex (the infant fans out his/her toes and twists in the foot when his/her sole is stroked), is not a setback, but instead a sign that the cortex is maturing and developing. From birth, human beings are endowed with certain reflex behavior that is connected to the brain. The brain starts to develop from the 25th day of gestation right up to birth. Basic biological functions such as breathing are developed first, controlled by the brain stem. This is how our brain develops. As the brain grows and develops, the front upper part of it becomes bigger to form the cerebrum. The cerebral cortex, that is specific areas of the gray matter of the brain, has specific functions to control sensory and motor activities. The cerebellum maintains balance and motor coordination while the subcortex handles reflex behavior and other functions of the lower levels. However, a large part of the brain is free from any specific task and is reserved for other higher cognitive requirements like thinking and reasoning. Fetal brain development from 25 days through birth. The brain stem, which controls basic biological functions such as breathing, develops first. As the brain grows, the front part expands greatly to form the cerebrum (the large, convoluted upper mass). Specific areas of the cerebral cortex (the gray outer covering of the brain) have specific functions, such as sensory and motor activity; but large areas are "uncommitted" and thus are free for higher cognitive activities, such as thinking, remembering, and problem solving. The subcortex (the brain stem and other structures below the cortical layer) handles reflex behavior and other lower-level functions. The cerebellum, which maintains balance and motor coordination, grows more rapidly during the first year of life.


of 16

ADDITIONAL MATERIALS Printed Materials • Levine, Ellen (ed.) 1995. The Good Housekeeping Book of Child Care. USA: St. Remy Press

Inc. • Fenwick, Ellen 1996. The Complete Book of Mother and Baby Care. Great Britain: Dorling

Kindersley Ltd. • Papalia, Diane E.; Olds, Sally W.; Feldman, Ruth D. 1998. Human Development. USA:

McGraw-Hill. • Santrock, John W. 1997. Children. USA: Brown and Benchmark Publishers. • Santrock, John W. 1999. Life-Span Development. USA: McGraw-Hill. • Sdorow, Lester M. 1998. Psychology. USA: McGraw-Hill. • Smith, Tony (ed.) 1996. Complete Family Health Encyclopedia. Great Britain: Dorling

Kindersley Ltd.

021 prenatal development notes

Documents