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3rd LectureEmbryology
Dr. Khaldoun Darwich
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Developmental Disturbances with Ectoderm
►The Syndrome of Ectodermal Dysplasia involves the abnormal development of one or more ectodermal structures .
►This syndrome has a hereditary etiology and affected persons may have abnormalities of the teeth, skin, hair, nails, eyes, facial structure, and glands, because these are derived from ectoderm or associated embryological tissues
►Children with all the features of this syndrome resemble "little old men."
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Developmental Disturbances with Ectoderm
►The Syndrome of Ectodermal Dysplasia
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Developmental Disturbances with Ectoderm
►Persons with ectodermal dysplasia may suffer from partial or complete anodontia; the absence of some or all teeth in each dentition .
►The teeth present for both dentitions have frequent malformations.
►Partial or full dentures are used for both functional and cosmetic purposes and need to be reconstructed periodically as the jaws continue to grow.
► Implants may be considered after growth halts, if enough alveolar bone is present
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Developmental Disturbances with Ectoderm
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Fourth Week Of Prenatal Development
►During the fourth week of prenatal development, the disc undergoes embryonic folding into an embryo, placing the tissues in their proper positions for further embryonic development.
►The folding of the flat embryonic disc also results in a somewhat tubular embryo.
►This folding results from extensive proliferation of the ectoderm and differentiation of basic tissues.
►This occurs mainly at the cephalic end, where the brain will form.
►This tissue grows beyond the oropharyngeal membrane and overhangs the developing heart.
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Fourth Week Of Prenatal Development
► Folding due to increased growth occurs not only at the cephalic end but also at the caudal end and at the sides of the embryo simultaneously.
►Because of this folding, the positions of the embryonic layers take on a more recognizable placement for the further development of the embryo.
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Fourth Week Of Prenatal Development
►After folding of the disc, the endoderm lies inside the ectoderm, with mesoderm filling in the areas between these two layers .
►This forms one long hollow tube lined by endoderm from the cephalic end to the caudal end of the embryo, specifically from the oropharyngeal membrane to the cloacal membrane.
►This tube is the future digestive tract and is separated into three major regions: the foregut, the midgut, and the hindgut.
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4th Week: Disc – Folding - Embryo
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Fourth Week Of Prenatal Development
►The anterior portion of this tube is the foregut, which forms the primitive pharynx, or throat, and includes a portion of the primitive yolk sac as it becomes enclosed with folding
►The other more posterior portions, the midgut and hindgut , form the rest of the pharynx as well as the remainder of the digestive tract.
►During development of the digestive tract, four pairs of pouches form from evaginations on the lateral walls lining the pharynx.
►These are called the pharyngeal pouches
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Fourth Week Of Prenatal Development
► Finally, during the fourth week, the face and neck begin to develop, with the primitive eyes, ears, nose, oral cavity, and jaw areas. (will be discussed later)
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Developmental Disturbances During the Embryonic Period
►Because the beginnings of all essential external and internal structures are formed during the embryonic period, this is the most critical period of development.
►Developmental disturbances during this period may give rise to major congenital malformations of the embryo .
►Any teratogens can cross by way of the placenta. Thus, teratogens can be present during the active differentiation of an organ or tissue, possibly raising the incidence of these malformations.
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Developmental Disturbances During the Embryonic Period
►An example of a: virus can be transmitted embryo from the pregnant woman.
►This infection of the embryo, can result in cataracts, cardiac defects, and deafness in the child.
►Another infective teratogen for the embryo is the syphilis spirochete , Treponema Pallidum, because it produces defects in the incisors and molars,• as well as blindness, deafness, and paralysis
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Developmental Disturbances During the Embryonic Period
►An example of the result of a teratogenic drug effect during the embryonic period is fetal alcohol syndrome.
►Ethanol ingested by a pregnant woman easily crosses the placenta and can result in prenatal and postnatal growth deficiency, mental retardation, and other anomalies.
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Developmental Disturbances During the Embryonic Period
►An affected child may have a cluster of facial changes such as small head circumference, a low nasal bridge, a short nose, a small midface, widely spaced eyes with epicanthic folds and eyelid fissures, an indistinct philtrum, and a thin Upper lip
►Oral changes such as anterior open bite and crowding of the dentition, mouth breathing, and related gingivitis may occur, possibly because of an increase in the habit of finger sucking.
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Developmental Disturbances During the Embryonic Period
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Developmental Disturbances During the Embryonic Period
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Developmental Disturbances During the Embryonic Period
►Direct exposure to high levels of Radiation can act as an environmental teratogen during the embryonic period.
►Radiation may injure embryonic cells, resulting in celldeath, chromosome injury, and retardation of mental development and physical growth.
►The severity of embryonic damage is related to the absorbed dose, the dose rate, and the state of embryonic or fetal development at the time of exposure.
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Developmental Disturbances During the Embryonic Period
►Human congenital abnormalities have not been proved to be caused by a diagnostic level of radiation, such as that used in dentistry.
►Scattered radiation from a radiographic examination of the oral cavity administers a dose of only a few millirads to a pregnant woman.
►This amount is not teratogenic to an embryo.
►Nevertheless, even this small dose should be avoided unless an emergency situation requires it. Proper protective precautions should be used with all patients and, with health care personnel.
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Developmental Disturbances During the Embryonic Period
► Failure of fusion of the neural tube results in neural tube defects of the tissue overlying the spinal cord, such as the meninges, vertebral arches, muscles, and skin.
► ►One type of neural tube defect is spina
bifida characterized by defects in the vertebral arches and various degrees of disability.
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Developmental Disturbances During the Embryonic Period
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Developmental Disturbances During the Embryonic Period
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Developmental Disturbances During the Embryonic Period
►Nutritional and environmental factors have an important role as teratogens causing neural tube defects.
► Folic acid supplements are now being recommended during pregnancy to help prevent this as well as to prevent cleft lip and palate.
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FETAL PERIOD OF PRENATAL DEVELOPMENT
►The Fetal period of prenatal development follows the embryonic period.
►The fetal period encompass the beginning of the ninth week, or third month, to the ninth month.
►This is a period of time of maturation of existing structures as the embryo enlarges to become a fetus .
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5 months
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FETAL PERIOD OF PRENATAL DEVELOPMENT
►Although developmental changes are not as dramatic as those that occur during the embryonic period, they are important because they allow the newly formed tissues and organs to function.
►Even though the embryo has been breathing since the third week, by the end of the fourth month, the fetal heartbeat can be detected.
►By the end of the 4th month mark, fetal movements can be felt by the pregnant woman.
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Developmental Disturbances During the Feta Period
►Congenital malformations can also occur during the fetal period.
► In amniocentesis , the most common invasive prenatal diagnostic procedure, amniotic fluid is sampled during the fourteenth to sixteenth weeks after the last missed menstrual period.
► It is performed in women of old age groups, when one or both parents have a chromosomal abnormality or neural tube defect, when previous child was affected, or when the parents are carriers of inborn errors of metabolism or X-linkei disorders such as hemophilia.
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Developmental Disturbances During the Feta Period
►Systemic tetracycline antibiotic therapy of the pregnant woman can act as a teratogenic drug during the fetal period.
►This therapy of the woman can result in permanent tetracycline Staining of the child's teeth or primary teeth that, are developing at that time.
►This intrinsic yellow to yellow-brown staining of the teeth can occur in slight, moderate, or severe degrees: The antibiotic becomes chemically bound to the dentin for the life of the tooth, and because of the transparency of enamel, this stain is visible .
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Developmental Disturbances During the Feta Period
►The adult teeth, or permanent teeth, may also be ^tedrft^ drug i, given during their development .
► If the permanent teeth are involved treatment may require full-coverage crowns or veneers to alter the appearance of the teeth Thus this type of antibiotic therapy should be avoided in pregnant women and children..