THE BIOLOGICAL SOURCES DEVELOPMENTAL DISABILITIES
Wednesday, July 16, 2008

GAMETES

n Are the human reproduction cells which are created in the reproductive organs.

n The ovaries of the female produce the ovum or egg cells.

n The testicles or testes of the male produce spermatozoa or sperm cells.

MEIOSIS

n Is the process of cell division in which each pair of chromosomes in the cell separates, with one member of each pair going into each gamete or daughter cell. Thus, each gamete, the ovum and the sperm, has twenty three unpaired chromosomes.

OVUM

n Is the only about one-fourth the size of a period, but it is the largest cell in the Human body. When a female is born, she already has about 400,000 immature ova in her two ovaries. Each ovum is contained in its own small SAC or follicle.

n After a female matures sexually (as early as age of nine to as late sixteen) and until menopause, ovulation takes place once every twenty-eight days when a mature follicle in one of her ovaries ruptures an d expels its ovum.

n The ovum is about 90,000 times as large as the sperm cell. Thousands of sperm cells must combine to break down the ovum’s membrane barrier to allow even a single sperm cell to penetrate it.

SPERM

n Is tadpole like one and only six hundredth (1/600^th) inch from head to tail is one of the smallest cells in the body furthermore.

n Sperms are much more numerous, several millions, and more active than the ova.

n A mature male testicle normally produces several hundred million sperms a day which are ejaculated in the semen at several climax.

n An estimated twenty million sperms must enter a woman’s ovary at one time to make fertilization likely.

FERTILIZATION

n The fertilization of female’s ovum by male’s sperm starts the process of human reproduction.

n Fertilization results in the formation of a single cell called the zygote. In the zygote, two sets of twenty-three unpaired chromosomes. In this manner, each parent contributes fifty percent or half of the zygote’s genetic code or genome.

CRITICAL PERIODS AND DEVELOPMENTAL VULNERABILITY DURING PREGNANCY

n Vulnerability- refers to how susceptible the organism is being injured or altered by a traumatic incident.

n A traumatic incident includes such broad occurrences as teratogens or toxic agents, cell division mutation and other deviations from the usual sequence of developmental.

n Deviancy- from the normal course of prenatal development results to the occurrence of developmental disabilities.

n The organism in utero, the zygote, the embryo and the fetus are vulnerable to injuries and developmental risks.

n Postnatal development, the newborn, the infant and the child are all vulnerable and susceptible to injuries that can persist for the duration of the person’s life.

THE COURSES OF PRENATAL DEVELOPMENT

Developmental in utero covers about thirty-eight (38) weeks or two hundred eighty (280) days or nine months of gestation or growth in the mother’s womb.

THREE PHASES OF PRENATAL DEVELOPMENTAL

1. The Germinal Phase- initial stage of prenatal development which covers the first two weeks after fertilization.

THREE SIGNIFICANT DEVELOPMENTS

n Creation of the zygote- begins with fertilization of a female’s ovum by a male sperm.

- Ovulation occurs once every twenty-eight days or so, as an ovum out of hundreds of ova matures and the single ripe ovum burst from its follicle. The ovum is drawn into the fallopian tube during the ninth to the sixteenth day of the menstrual cycle which is the fertile period. Ovulation sends a chemical signal to unleash a carefully tuned sequence of biochemical substances. One chemical substance dissolves the jellylike veil surrounding the ovum. Another chemical substance softens the ovum. Another substance softens the ovum’s tough outer shell. Millions of sperms deposited by the male race to penetrate the ovum’s shell. Only one strong and healthy sperm succeeds. Once it enters the ovum, an electric charge flies across the membrane and a signal causes the ovum to close, blocking the entry of other sperms.

-fertilization takes place with the union of the genetic materials in the ovum and sperm cells. The process occurs in the upper third of the fallopian tube within eighteen to twenty four hours after sexual intercourse, “the womb weeps” and the menstrual cycle continues the following month. When an ovum is fertilized, the menstrual cycle ceases.

Zygote- is a new cell which results from the transmission of the genetic materials twenty-four to thirty hours after fertilization.

- it weighs about one twenty-millionth of an ounce. This is one sixteenth of a pound (2-2 pounds equals one kilo).

-it carries the human genetic code of genome, the instruction that orchestrates one’s physical and mental traits and sociobiological tendencies and the new person’s entire lifelong blue print of characteristics.

n Continuous cell division and cell tissue differentiation

- chemical reactions occur that cause the zygote to divide repeatedly and generate new cells and tissues of different types.

Cell division- occurs rapidly in the first few days and progresses with considerable speed.

- The zygote divides into two cells after thirty-six hours; four cells after forty-eight hours.

- in three days there is a small compact ball of sixteen to thirty-two cells.

- in four days, a hollow ball has sixty four to one hundred twenty-eight cells. By approximately one week, the zygote has divided into about one hundred fifty cells.

Cell differentiation- continues as the inner and outer layers of the organism are formed. The inner layer of cells which develops into the embryo later on is called blastocyst. The outer layer of cells that provides nutrition and support for the embryo is called trophoblast.

n Implantation or Attachment of the zygote to the uterine wall.

- implantation starts on the sixth to the seventh day when the blastocyst starts to attach itself to the uterine wall. Two weeks after, from the eleventh to the fifteenth day. The blastocyst invades or fully attaches itself into uterine wall and becomes implanted in it.

What can go wrong during the germinal phase?

1. Dominant and recessive diseases like Tay Sachs disease, galactosemia, phenylketonuria (PKU), genetic mutations;

2. Sex-linked inheritances such as Lesch Nyhan Syndrome, Fragile X Syndrome;

3. Polygenic inheritances;

4. Chromosomal deviations, the most common of which is Down Syndrome;

5. Other sex chromosomal anomalies like Klinefelter Syndrome, Tuner Syndrome; and

6. Cranial or skull malformations such as anencephaly or absence of major portions of the brain, microcephaly and hydrocephaly.

Biological causes of developmental disabilities

n congenital or inherited genetic materials as well as prenatal factors associated with teratogens or toxic substances, maternal disorders, substance exposure or too much ingestion of alcoholic and drugs and too much smoking.

The Embryonic Phase

n The second phase of human development occurs from the end of germinal phase of the second month of pregnancy. The mass of cells is now called the embryo. The three main processes of the support systems for continued cell development and organogenesis or the appearance of te different organs of the body.

Intensification of cell differentiation

n During the implantation, the mass of cells form three layers from which every part of the human body will develop.

1. The ectoderm- the outermost layer cells. It develops the surface body parts, such as the outer skin or the epidermis including the cutaneous glands ( the hair, nails and lens of the eye).

2. The mesoderm- is the middle layer that will develop into the body parts surrounding the internal areas, such as the muscles, cartilage, bone, blood, bone ureter, gonads, genital ducts, suprarenal cortex and the joint cavities.

3. The endoderm- is the inner layer of cells that will develop into the epithelium of the pharynx, tongue, auditory tube, tonsils, thyroid, larynx, trachea, lungs, digestive tube, bladder, vagina and urethra.

Development of the life support systems

n The life support systems develop from the embryo for the transfer of substances from the mother to the zygote and vice versa. Very small molecules of oxygen, water, salt, and food from the mother’s blood are transferred to the embryo. Carbon dioxide and digestive waste from the embryo’s blood are transferred to the mother’s blood.

1. The placenta- is a disk-shaped mass of tissues in which small blood vessels from the mother intertwine.

2. The umbilical cord- contains two arteries and one vein that connects the embryo to the placental

3. The amnion or amniotic fluid- is a bag of water that contains clear fluid where the embryo floats. The amnion provides an environment that is temperature and humidity controlled and shock proof. The amnion comes from the fetal urine that the kidney of the fetus produces at the sixteenth week until the ninth month or the end of pregnancy.

Organogenesis

n Is the process of organ formation and the appearance of body organs during the first two months.

1. By the third week, the neural tube forms and eventually becomes the spinal cord. At the same time, the eye buds begin to appear.

2. By the twenty-fourth day, the cells for the heart begin to differentiate.

3. The fourth week is marked by the first appearance of the urogenital systems. The arm and leg buds appear. The four chambers of the heart take shape and blood vessels surface.

4. On the fifth to the eight week, the arms and legs differentiate further. The face starts to form but it is not very recognizable. The intestinal tract develops and the facial structures fuse.

What can go wrong during the embryonic phase?

n The cells divide very rapidly during organogenesis. The organs and systems that are developing are especially vulnerable to environmental changes. Induced abortion in case of unwanted pregnancy can disturb normal processes of organogenesis. Chromosomal abnormalities can cause spontaneous abortion mostly in the second or third month.

n Central nervous system is the primary system that is developing, the cells that constitute the central nervous system- the brain and the spinal cord- divide more rapidly than the other organs. At this time the central nervous system is most vulnerable to trauma. Ingestion of dermatogens or toxic agents from alcohol, drugs and nicotine, artificial food additives, stress and accidents can cause trauma and affect the development that is taking place.

n Physical abnormalities at birth, there are infants born with extra or missing limbs and fingers, ears and other body parts, a tail-like protrusion, heart or brain, digestive or respiratory organs outside the body. Facial development and body shapes can be affected by what scientists describe as “accidents in cell development.” Some clusters of cells that are meant to develop into certain organs and parts of the body fail to follow the precise genetic instructions and appear at birth as inhuman, with the face for example, resembling that of a frog or other animals, statues, or even pictures. Scientific explanation goes back to the disturbances in development during the pregnancy.

The Fetal Phase

n It covers seven months that lasts from the third to the ninth month of pregnancy on the average. The length and weight of the fetus mentioned below are for average Caucasian babies.

1. At three months, the fetus is both three inches long and weighs about one ounce. It is active, moves its arms, legs and head, opens and closes its mouth. The face, forehead, eyelids, nose, chin. Upper and lower arms are distinguishable. Genitals can be identified as male or female.

2. At four months, the fetus is five and a half inches long, weighing about four ounces. Growth spurt occurs in the body’s lower parts. Prenatal reflexes are stronger. Arms and leg movements can be felt by the mother.

3. At five months, the fetus is ten to twelve inches long and weighs one-half to one pound or almost half kilo. Structures of the skin, toenails and fingernails have formed. The fetus is more active and shows preference for a particular position in the womb.

4. At six months, the fetus is fourteen inches long and has gained one-half to one pound. The eyes and eyelids are completely formed. A thin layer of hair covers the head. Grasping reflex is present. Irregular breathing occurs.

5. At seven months, the fetus is almost seventeen inches long, has gained one pound and weighs about three pounds.

6. During the eight and ninth months, the fetus continues to grow longer to about twenty inches and gains about four pounds. Fatty tissues develop and the functioning of the organ systems steps up.

What can go wrong during the fetal phase?

n The same effects of teratogens can occur and disturb normal development. The fetus continues to be vulnerable to trauma that can result to the occurrence of disabilities. Deliberate termination of pregnancy or abortion, if unsuccessful can lead to disabilities. Inadequate birth weight due to malnutrition or early birth places the infant at developmental risks.

Birth of the infant- after full of gestation for thirty-eight weeks, the fetus leaves the intrauterine environment of the mother’s womb and begins life in the outside world. Some of the changes are:

1. rearrangement of the muscle structure of the uterus to facilitate fetal expulsion or to permit the normal passage of the fetus through the birth canal.

2. shortly before birth and during the onset of labor which lasts for seven to twelve hours on the average, the upper part of the cervical area undergoes expansion. By the time the fetus is passing through the birth canal, the muscle structure of the cervix has loosened and expanded. The process is called effacement that enables the fetus to be expelled.

n The normal and desirable position of the fetus when labor begins is with the head toward the cervix. As the fetus begins to move downward into the birth canal, the pelvic girdle or the bony hip structure stretches more. The pressure of the pelvic girdle also molds the head of the fetus.

n All the movements during birth are generated by the muscle contractions of the uterus called labor.

n The respiratory tract is immediately cleared of the remaining amniotic fluid and mucus.

What can go wrong during the birth process?

n Physical trauma or mechanical injury- during birth may injure or damage the brain impair intellectual functioning.

> In precipitious birth- where labor is short (less than two hours) skull molding that should be slow and smooth may affect and injure the brain.

> In breech birth- where the buttocks instead of the head presents itself first poses substantial danger because the head reaches the pelvic girdle during the later stages of labor when there is more pressure exerting on it.

The abnormal pressure generated in breech birth rapidly compresses the still soft skull which crushes portions of the brain. Also, the rapid pressure and shifting of cranial bones can damage the circulatory system around the brain and lead to hemorrhage in the skull and brain damage.

Usually, a fetus in breech position is delivered by caesarian section.

> In the transverse position- where the fetus lies across the birth canal, the same problems in breech birth are present.

n Anoxia or asphyxia- occurs in breech delivery and deprive the infant of adequate supply of oxygen for a period long enough to damage the brain. The infant must depend entirely on the umbilical cord as a source of oxygen until birth is completed. However, the breech position makes the umbilical cord too short to remain attached while the head is being expelled. The placenta can become partially or completely detached while the head is still inside the birth canal. This eliminates oxygen supply and severe brain injury can happen.

Newborn Screening

n Republic Act No. 9288 “Newborn Screening Act of 2004,” is an act promulgating a comprehensive policy and national system for ensuring newborn screening. The law was developed jointly by the Department of Health and the National Institute of Health of UP Manila. It insures that every baby born in the Philippines is offered newborn screening; the establishment and integration of a sustainable newborn screening system within the public health delivery system; that all health practitioners are aware of the benefits of NBS.

n What is newborn screening?

- a simple test given 24 to 72 hours after birth can mean the difference between having a normal child or mentally retarded child.

- this test is aptly called Newborn Screening.

- is a very simple test that should be given to the baby 24 hours after giving birth. It is a blood test wherein a blood sample will be taken from the heel of the child.

-the test primarily checks for five metabolic disorders that could affect the health of the child within the first week of life.

The five metabolic disorders

n Congenital Hypothyroidism-

n Congenital Adrenal Hyperplasia

n Galactosemia-a metabolic disorder inherited as an autosomal recessive trait in which galactose accumulates in the blood due to deficiency of an enzyme catalyzing its conversion to glucose

n Phenylketonuria-a metabolic disorder that is caused by an enzyme deficiency resulting in the accumulation of phenylalanine and its metabolites (as phenylpyruvic acid) in the blood and their excess excretion in the urine, that is inherited as an autosomal recessive trait, and that causes usually severe mental retardation, seizures, eczema, and abnormal body odor unless phenylalanine is restricted from the diet beginning at birth -- abbreviation

n Glucose Six Phosphate Dehydrogenase deficiency

Principles of Normal Development in Infancy and early Childhood

n When the problems in prenatal development and birth as discussed earlier, deviations from the normal development milestones in infancy and early childhood can be expected.

1. Normal development progresses in orderlt step-by-step sequences.

2. All areas of development are interrelated.

3. The skills acquired earlier determine how well later skills will be learned.

4. Although there are developmental milestones in each of the growth areas, children manifest individual differences in their rate of development. Each child develops at his or her pace.

When is developmental disability present?

n A deviation from the developmental milestones from four to six months is enough ground to suspect that there might be a disability. For example at six months the infant is still not able to raise his/her chin when made to lie on the stomach, a gross motor skill that is observable at one month. At two years, the child cannot walk alone with support. There is no receptive language yet at one-and-half years of age, that is, the child does not respond to the adult’s motivation.

Posted byDoc Junhel at 12:10 AM  

0 comments:

Post a Comment