Prenatal Development PDF

How did you come to be who you are? From beginning as a one-cell structure to your birth, your prenatal development occurred in an orderly and delicate sequence. Prenatal development refers to the process in which a baby develops from a single cell after conception into an embryo and later a fetus....

How did you come to be who you are? From beginning as a one-cell structure to your birth, your prenatal development occurred in an orderly and delicate sequence. Prenatal development refers to the process in which a baby develops from a single cell after conception into an embryo and later a fetus. The average time for prenatal development to complete is 38 weeks from the date of conception. During this time, a single-celled zygote develops in series of stages into a full-term baby. The three primary stages of prenatal development are the germinal stage, the embryonic stage, and the fetal Let\'s take a look at what happens to the developing baby in each of these stages. Stages of Prenatal Development 1\. Germinal Period (Weeks 1-2) A mother and father\'s DNA is passed on to the child at conception. Conception occurs when sperm fertilizes an egg and forms a zygote. A zygote begins as a one-cell structure created when a sperm and egg merge. The genetic makeup and sex of the baby are set at this point. During the first week after conception, the zygote divides and multiplies, going from a one-cell structure to two cells, then four cells, then eight cells, and so on. Mitosis is the process of cell division. As the cells divide, they become more specialized, forming different organs and body parts, In the germinal stage, the mass of cells has yet to attach itself to the lining of the mother\'s uterus. +-----------------------------------+-----------------------------------+ | Germinal Stage | What\'s happening | +-----------------------------------+-----------------------------------+ | 24 to 30 hours after | The sperm and egg chromosomes | | fertilization | unite. | +-----------------------------------+-----------------------------------+ | 36 hours | In the fertilized ovum, the | | | zygote divides into two cells. | +-----------------------------------+-----------------------------------+ | 2 days | The two cells become four cells. | +-----------------------------------+-----------------------------------+ | 3 days | The four cells become a small | | | compact ball, 16- | +-----------------------------------+-----------------------------------+ | 4 days | There is now a hollow ball of | | | 64-128 cells. | +-----------------------------------+-----------------------------------+ | 4 to 5 days | The inner cell mass called | | | blastocyst is still free | +-----------------------------------+-----------------------------------+ | 6 to 7 days | The blastocyst attaches to the | | | wall of the uterus. | | | | | | The blastocyst invades the | | | uterine wall of the | +-----------------------------------+-----------------------------------+ | 11-15 days | uterus and becomes implanted in | | | it. This is called implantation. | +-----------------------------------+-----------------------------------+ Embryonic Period (Weeks 3-8) The embryonic stage begins after implantation and lasts until eight weeks after conception. After implantation, the cells continue to divide rapidly, and differentiation occurs. It is a cluster of cells that begins to take on different functions. Gastrulation leads to the formation of three distinct layers called germ layers: the outer layer (ectoderm), the middle layer (mesoderm), and the inner layer (endoderm). As the embryo develops, each germ layer differentiates into different tissues and structures. For example, the ectoderm eventually forms skin, nails, hair, brain, nervous tissue and cells, nose, sinuses, mouth, anus, tooth enamel, and other tissues. The mesoderm develops into muscles, bones, heart tissue, lungs, reproductive organs, lymphatic tissue, and other tissues. The endoderm forms the lining of the lungs, bladder, digestive tract, tongue, tonsils, and other organs. The differentiation process takes place over a period of weeks, with different structures forming simultaneously. Embryonic Stage ----------------- -- -- ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- Week 3 Beginning development of the brain, heart, blood cells, circulatory system, spinal cord, and digestive system. Week 4 Beginning development of bones, facial structures, and limbs (presence of arm and leg buds); continuing development of the heart (which begins to beat), brain, and nervous tissue. Week 5 Beginning development of eyes, nose, kidneys, and lungs; continuing development of the heart (formation of valves), brain, nervous tissue, and digestive tract. Week 6 Beginning development of hands, feet, and digits; continuing development of brain, heart, and circulation Week 7 Beginning development of hair follicles, nipples, eyelids, and sex organs (testes or ovaries); first urine formation in the kidneys, and the first evidence of brain waves. Week 8 Facial features are more distinct, internal organs are well developed, the brain can signal for muscles to move, heart development ends, and external sex organs begin to form. 3\. Fetal Stage (Weeks 9-40) Prenatal development is most dramatic during the fetal stage. When an embryo becomes a fetus at eight weeks, it is approximately 3 centimeters (1.2 inches) in length from crown to rump and weighs about 3 grams (0.1 ounces). By the time the fetus is considered full-term at 38 weeks gestation, he or she may be 50 centimeters (20 inches) or 3.3 kilograms (7.3 pounds). Although all organ systems were formed during embryonic development, they continue to develop and grow during the fetag embr +-----------------------------------+-----------------------------------+ | Fetal Stage | | +===================================+===================================+ | Weeks 9 to 12 | The fetus reaches approximately 8 | | | cm. (3.2 in.) in length; the head | | | is approximately half the size of | | | the fetus. External features such | | | as the face, neck, eyelids, | | | limbs, digits, and genitals are | | | well formed. The | | | | | | beginnings of teeth appear, and | | | red blood cells begin to be | | | produced in the liver. The fetus | | | is able to make a fist. | +-----------------------------------+-----------------------------------+ | Weeks 13 to 15 | The fetus reaches approximately | | | 15 cm. (6 in.) in length. | | | | | | Fine hair called lanugo first | | | develops on the head; structures | | | such as the lungs, sweat glands, | | | muscles, and bones continue to | | | develop. The fetus is able to | | | swallow and make sucking motions. | +-----------------------------------+-----------------------------------+ | Weeks 16 to 20 | The fetus reaches approximately | | | 20 cm. (8 in.) in length. | | | | | | Lanugo begins to cover all skin | | | surfaces, and fat begins to | | | develop under the skin. Features | | | such as finger and toenails, | | | eyebrows, and eyelashes appear. | | | The fetus becomes more active, | | | and the mother can sometimes | | | begin to feel fetal movements at | | | this stage. | +-----------------------------------+-----------------------------------+ | Weeks 21 to 24 | The fetus reaches approximately | | | 28.5 cm. (11.2 in.) in length and | | | weighs approximately 0.7 kg (1 | | | lb. 10 oz.). | | | | | | Hair grows longer on the head, | | | and the eyebrows and eye lashes | | | finish forming. The lungs | | | continue to develop with the | | | formation of air sac (alveoli); | | | the eyes finish developing. A | | | startle reflex develops at this | | | time. | +-----------------------------------+-----------------------------------+ | Weeks 25 to 28 | The fetus reaches approximately | | | 38 cm. (15 in.) in length and | | | weighs approximately 1.2 kg (2 | | | lb. 11 oz.). | | | | | | The next few weeks mark a period | | | of rapid brain and nervous system | | | development. The fetus gains | | | greater control over movements | | | such as opening and closing | | | eyelids and certain body | | | functions. The lungs have | | | developed sufficiently that air | | | breathing is possible. | +-----------------------------------+-----------------------------------+ | Weeks 29-32 | The fetus reaches approximately | | | 38-43 cm. (15-17 in.) in length | | | and weighs approximately 2 kg (4 | | | lb. 6 oz.). | | | | | | Fat deposits become more | | | pronounced under the skin. | | | | | | The lungs remain immature but | | | breathing movements begin. The | | | fetus\'s bones are developed but | | | not yet hardened | +-----------------------------------+-----------------------------------+ | Weeks 33 to 36 | The fetus reaches approximately | | | 41-48 cm, (16-19 in.) in length | | | and weighs 2.6-3.0 kg (5 lb. 12 | | | oz. to 6 lb. 12 oz.). Body fat | | | continues to increase, lanugo | | | begins to disappear, and | | | fingernails are fully grown. The | | | fetus has gained a high degree of | | | control over body functions. | +-----------------------------------+-----------------------------------+ | Weeks 36 to 38 | The fetus reaches 48-53 cm. | | | (19-21 in.) in length is | | | considered to be full-term by the | | | end of this period. | | | | | | Lanugo has mostly disappeared and | | | is replaced with thicker hair on | | | the head. Fingernails have grown | | | past the tips of the fingers. In | | | a healthy fetus, all organ | | | systems are functioning. | +-----------------------------------+-----------------------------------+ Hazards to Prenatal Development Prenatal development is a complicated process and may not always go as planned. About 45% of pregnancies result in a miscarriage, often without the mother ever being aware it has occurred (Moore & Persaud, 1993). +-----------------------------------+-----------------------------------+ | Physical Hazards | What might occur | +===================================+===================================+ | a\. Starvation | The zygote will die of starvation | | | if it has too little yolk to keep | | | it alive until it can lodge | | | itself in the uterine wall or if | | | it remains too long in the tube. | +-----------------------------------+-----------------------------------+ | b\. Lack of Uterine Preparation | Implantation cannot occur if, as | | | a result of glandular imbalance, | | | the uterine walls are not | | | prepared in time to receive the | | | zygote. | +-----------------------------------+-----------------------------------+ | c\. Implantation in the wrong | If the zygote becomes attached to | | place | a small fibroid tissue in the | | | uterine wall or to the wall of | | | the Fallopian tube, it cannot get | | | nourishment and will die. | +-----------------------------------+-----------------------------------+ | d\. Miscarriages | Unfavorable conditions in the | | | prenatal environment are likely | | | to occur between the tenth and | | | eleventh week after conception. | +-----------------------------------+-----------------------------------+ | e\. Developmental Irregularities | Maternal malnutrition, vitamin, | | | and glandular deficiencies. | +-----------------------------------+-----------------------------------+ | f\. Problems brought by aging | Older women tend to have more | | | health problems than younger | | | women, e.g., high blood pressure | | | is more common in older people. | | | Having high blood pressure before | | | pregnancy can increase the risk | | | of preeclampsia. But studies also | | | show that older women who do not | | | have any health conditions can | | | still have complicated | | | pregnancies. | +-----------------------------------+-----------------------------------+ | | | +-----------------------------------+-----------------------------------+ | Environmental | Example | | | | | Hazards | | +-----------------------------------+-----------------------------------+ | Extreme Exposure | Exposure to radiation, | | | pollutants, toxic wastes, and | | | harmful substances such as | | | cigarettes and alcohol | +-----------------------------------+-----------------------------------+ | Prescription and Nonprescription | Taking harmful drugs such as | | | antibiotics and some | | Drugs | nonprescription drugs such as | | | diet pills, aspirin, and coffee. | +-----------------------------------+-----------------------------------+ | Psychoactive Drugs | Taking nicotine, caffeine, and | | | illegal drugs such as marijuana, | | | cocaine, and heroin. | +-----------------------------------+-----------------------------------+ | Diseases | Rubella (German measles), | | | syphilis, genital herpes, | +-----------------------------------+-----------------------------------+ and AIDS