2FOLDING OF THE EMBRYOFolding of the Embryo in the Median PlaneTHE HEAD FOLDTHE TAIL FOLDFolding of the Embryo in the Horizontal PlaneMedian planeHorizontal plane
3THE HEAD FOLDSeptum transversum橫中膈 develops into the central tendon of the diaphragmThe longitudinal infolding turns yolk sac inward as foregut (primordium of pharynx, etc.).
4THE TAIL FOLDCloacal membrane泄殖膜 on the caudal end of primitive streak develops into future anus.Neural tube growing over cloacal membrane causes infolding and turns part of yolk sac into embryo as hind gut.Connecting stalk turns to ventral surface, and allantois is incorporated into embryo.
5Folding of the Embryo in the Horizontal Plane Lateral folding rolls the sides of embryo disc and turns part of yolk sac into embryo as midgut and the rest left outside (yolk stalk) and will be incorporated into umbilical cord.
8CONTROL OF EMBRYONIC DEVELOPMENT Embryonic development is essentially a process off growth and increasing complexity of structure of structure and function.Genetic plan in chromosomesEnvironmental factorsDevelopment is growth and increasing complexityInteraction between tissues during development (induction誘導作用)
9The methods of signal transduction: Diffusion of signal substancesMatrix-mediated interactionCell contact-mediated interaction
19Fifth Week Brain rapid grows; face contacts heart prominence Hyoid (2nd) arch overgrows 3rd and 4th archesForms cervical sinus頸竇Upper limb with elbow and hand plateMesonephric ridges中腎脊 indicate the sites of kidneysSpontaneous movements
21Carnegie stage 17 Sixth Week Rapid growth of upper limbs hand plates with digital rays指放射Groove between 1st and 2nd arch develops (external acoustic meatus)Swelling around it (auricular hillock耳狀丘)Respond to touch
27Carnegie stage 23 End of 8th week All region of limbs apparent, limbs moveHead takes half of the embryoNeck establishedIntestine is still in the umbilical cordSexual difference exists but sex still can not be told
29ESTIMATION OF EMBRYONIC AGE 1. Onset of LNMP2. The probable time of fertilization3. Measurements of the chorionic sac and embryo4. External characteristic of embryo
30Methods of Measuring Embryos Greatest length (GL)--3rd and early 4th weeks, straight embryoCrown-rump length (CRL) or sitting height--neck-rump measurementCrown-heel length (CHL) or standing heightCarnegie Embryonic Staging system (Table 5-1)
32Viability of fetusImmature infants (extremely low birth weight, ELBW)--less than 500 gm, usually do not survive, but with expert postnatal care some may surviveLow-birth-weight babies--full term but caused by intrauterine growth retardationPremature infants (1500 to 2500 gm) most may survive but with difficulties.
33ESTIMATION OF FETAL AGE By ultrasonic measurements to determine the size of infant.To provide the date of confinement (EDC預產期) the calculation of age is done by:1. Gestational age--the onset of the last normal menstrual period (LNMP)2. the estimated day of fertilization; the month is by calendar monthDaysWeeksCalendar monthsLunar months (28 days)Fertilization266 days38 weeks8 3/49 1/2LNMP280 days40 weeks9 1/410Trimester--each lasting 3 calendar monthsThe end of the first trimester--all major systems develops, crown-rump length (CRL) is used for measuringThe end of the second trimester--may survive if born prematurelyAt 35 weeks--fetus weighs 2500 gm, usually survive if born prematurely
34External Characteristics of Fetuses Measuring with ultrasonography and weight in the second and third trimesters:1. Biparietal diameter (BPD)2. Head circumference頭圍3. Abdominal circumference腹圍4. Femur length股骨長度5. Foot length足長度6. Fetal weight胎兒重量 (may have discrepancy when mother has diabetes mellitus)
37Ninth to Twelve WeeksBeginning of 9th weekHead = 1/2 CRLLegs are short, thighs are smallEnd of 9th weekExternal genitalia show difference11th weekIntestine return to abdomen12th week-Fetal form of ext. genitalia establishedEnd of 12th weekHead < 1/2 CRLPrimary ossification center appearsErythropoiesis site transfer from liver to spleenBetween 9th to 12th weekUrine forms and discharge to amniotic fluid, which is swallowed by fetus
38Thirteen to Sixteen Weeks 14th weekRapid growthCoordinated limb movementActive ossification of skeletonEye movements occurScalp hair pattern determinated16th weekBones can be seen on radiographsOvaries differentiated and contain primordial follicles
39Seventeen to Twenty Weeks Fetus grows 50 mm within periodFetal movements (quickening胎動) felt by motherDelivery day is 147 +/- 15 days after first movementSkin is covered and protected by vernix caseosa胎垢20th weekCovered by lanugo胎毛 (fine downy hair)Eyebrows and head hairs are visibleTestes begins to descend
40Twenty-one to Twenty-five Weeks Substantial weight gainSkin is wrinkles and translucent, pink to red21st week-Rapid eye movements begin22nd to 23 weeks-Responds to noise (blink-startle responses)24th week-Type II pneumocytes secrete surfactant-Fingernail present22nd to 25th weeks-Born prematurely may survive under intensive care
41Twenty-six to Twenty-nine Weeks Can breath air by functioning lungsCNS controls rhythmic breathing, body temperature26th weekEyes reopenToenails are visibleSubcutaneous fat flattens wrinkled skin28th weekSpleen has been an important site of hematopoiesisHematopoiesis shifts to bone marrow by the end of 28th week.
42Thirty to Thirty-four Weeks 30th week-Pupillary light reflex32nd week-Born prematurely usually survive-Born as normal weight (premature by date)-White fat = 8% body weight
43Thirty-five to Thirty-eight Weeks 35th week-Grasp, spontaneous orientation to light36th week-Circumferences of head is equal to that of abdomen-CRL 360 mm, weight 3400 gm-Slow growing before birth-White fat = 16% body weight37th to 38th weeks-Nervous system is mature for integrative functions38th week-Add 14 gm per day in last weekFull term-Testes in scrotum
46Diagnostic Amniocentesis羊膜穿刺 A common technique for detecting genetic disorderAfter 14 weeks there is about 200 ml amniotic fluid, and ml can be safely withdraw under guidance of ultrasonography.The risk of inducing an abortion is about 0.5%Who may need amniocentesis:> 38 years of maternal ageprevious birth of a trisomy childchromosome abnormality in either parenta X-linked recessive disorders carrierneural tube defects in the familycarriers of inborn errors of metabolism
47Alpha-fetoprotein (AFP) Assay Produced by liver, yolk sac and instestineneural tube defects (NTDs) and ventral wall defects (VWDs): AFP ↑唐氏症,三染色體18：AFP ↓
48Sex Chromatin Patterns--sex-linked hereditary diseases, e. g Sex Chromatin Patterns--sex-linked hereditary diseases, e.g. hemophilia and muscular dystrophy
49Chorionic Villus Sampling (CVS)絨毛膜取樣 trophoblasts obtained by needle through mother's abdominal and uterine wall under ultrasound guidanceRisk of fetal loss 1%; risk of limb defects if done too early.
50Fetoscopy胎內內視鏡--few use Ultrasonography超音波--measuring placental and fetal size, multiple births, and abnormal presentations, even male genitaliaComputed Tomography (CT) and Magnetic Resonance Imaging (MRI)--providing more information for treatment, but expensive and limited resolutionAmniography羊膜攝影 and Fetography胎兒攝影--injecting water-soluble or oil-soluble radiopaque substance into amniotic cavityFetal Monitoring胎兒監測--for fetal heart rate monitoring (fetal distress胎兒窘迫-abnormal heart rate)