Development of the general body form 陳建榮 http://web.nchu.edu.tw/~chenjr/index.htm
FOLDING OF THE EMBRYO • Folding of the Embryo in the Median Plane • THE HEAD FOLD • THE TAIL FOLD • Folding of the Embryo in the Horizontal Plane Horizontal plane Median plane
THE HEAD FOLD • Septum transversum橫中膈develops into the central tendon of the diaphragm • The longitudinal infolding turns yolk sac inward as foregut (primordium of pharynx, etc.).
THE TAIL FOLD • Cloacal 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.
Folding 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.
GERM LAYER DERIVATIVES • Ectoderm • Mesoderm • Endoderm
CONTROL OF EMBRYONIC DEVELOPMENT • Embryonic development is essentially a process off growth and increasing complexity of structure of structure and function. • Genetic plan in chromosomes • Environmental factors • Development is growth and increasing complexity • Interaction between tissues during development (induction誘導作用)
The methods of signal transduction: • Diffusion of signal substances • Matrix-mediated interaction • Cell contact-mediated interaction
Highlights of fourth to eighth weeks (organogenetic period) 24 days -Mandibular (1st) arch--mandible & maxillary -Hyoid (2nd) arch -Slightly curves (head and tail folds) -Heart prominence Carnegie stage 11 咽弓
26 days -Pharyngeal (branchial) arches -Rostral neuropore closes -Forebrain elevation -C-shaped curvature Carnegie stage 12
28 days -4th pair pharyngeal arches -Upper and lower limb buds show -Lens placodes, attenuated tail are visible -Caudal neuropore closes Carnegie stage 13
Fifth Week • Brain rapid grows; face contacts heart prominence • Hyoid (2nd) arch overgrows 3rd and 4th arches • Forms cervical sinus頸竇 • Upper limb with elbow and hand plate • Mesonephric ridges中腎脊indicate the sites of kidneys • Spontaneous movements
Carnegie stage 16 Carnegie stage 17
Carnegie 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
Carnegie stage 18 Carnegie stage 19
Carnegie stage 19 • Seventh Week • Umbilical herniation臍疝氣with intestine • Notches between digital rays of hand
Carnegie stage 20 Carnegie stage 21
Carnegie stage 21 • Eighth Week • Final week of embryonic period • Webbed digits of hand • Notches between digits of foot • Tail still present • Scalp vascular plexus頭皮血管叢
Carnegie stage 22 Carnegie stage 23
Carnegie stage 23 • End of 8th week • All region of limbs apparent, limbs move • Head takes half of the embryo • Neck established • Intestine is still in the umbilical cord • Sexual difference exists but sex still can not be told
ESTIMATION OF EMBRYONIC AGE 1. Onset of LNMP 2. The probable time of fertilization 3. Measurements of the chorionic sac and embryo 4. External characteristic of embryo
Methods of Measuring Embryos Greatest length (GL)--3rd and early 4th weeks, straight embryo Crown-rump length (CRL) or sitting height--neck-rump measurement Crown-heel length (CHL) or standing height Carnegie Embryonic Staging system (Table 5-1)
Viability of fetus • Immature infants (extremely low birth weight, ELBW)--less than 500 gm, usually do not survive, but with expert postnatal care some may survive • Low-birth-weight babies--full term but caused by intrauterine growth retardation • Premature infants (1500 to 2500 gm) most may survive but with difficulties.
ESTIMATION 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 month Trimester--each lasting 3 calendar months The end of the first trimester--all major systems develops, crown-rump length (CRL) is used for measuring The end of the second trimester--may survive if born prematurely At 35 weeks--fetus weighs 2500 gm, usually survive if born prematurely
External 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)
Ninth to Twelve Weeks • Beginning of 9th week • Head = 1/2 CRL • Legs are short, thighs are small • End of 9th week • External genitalia show difference • 11th week • Intestine return to abdomen • 12th week • -Fetal form of ext. genitalia established • End of 12th week • Head < 1/2 CRL • Primary ossification center appears • Erythropoiesis site transfer from liver to spleen • Between 9th to 12th week • Urine forms and discharge to amniotic fluid, which is swallowed by fetus
Thirteen to Sixteen Weeks • 14th week • Rapid growth • Coordinated limb movement • Active ossification of skeleton • Eye movements occur • Scalp hair pattern determinated • 16th week • Bones can be seen on radiographs • Ovaries differentiated and contain primordial follicles
Seventeen to Twenty Weeks • Fetus grows 50 mm within period • Fetal movements (quickening胎動) felt by mother • Delivery day is 147 +/- 15 days after first movement • Skin is covered and protected by vernix caseosa胎垢 • 20th week • Covered by lanugo胎毛(fine downy hair) • Eyebrows and head hairs are visible • Testes begins to descend
Twenty-one to Twenty-five Weeks • Substantial weight gain • Skin is wrinkles and translucent, pink to red • 21st week • -Rapid eye movements begin • 22nd to 23 weeks • -Responds to noise (blink-startle responses) • 24th week • -Type II pneumocytes secrete surfactant • -Fingernail present • 22nd to 25th weeks • -Born prematurely may survive under intensive care
Twenty-six to Twenty-nine Weeks • Can breath air by functioning lungs • CNS controls rhythmic breathing, body temperature • 26th week • Eyes reopen • Toenails are visible • Subcutaneous fat flattens wrinkled skin • 28th week • Spleen has been an important site of hematopoiesis • Hematopoiesis shifts to bone marrow by the end of 28th week.
Thirty to Thirty-four Weeks 30th week -Pupillary light reflex 32nd week -Born prematurely usually survive -Born as normal weight (premature by date) -White fat = 8% body weight
Thirty-five to Thirty-eight Weeks 35th week -Grasp, spontaneous orientation to light 36th week -Circumferences of head is equal to that of abdomen -CRL 360 mm, weight 3400 gm -Slow growing before birth -White fat = 16% body weight 37th to 38th weeks -Nervous system is mature for integrative functions 38th week -Add 14 gm per day in last week Full term -Testes in scrotum
FACTORS INFLUENCING FETAL GROWTH • Maternal Malnutrition • Cigarette Smoking • Multiple Pregnancy • Social Drugs • Impaired Uteroplacental Blood Flow • Genetic Factors and Growth Retardation
Diagnostic Amniocentesis羊膜穿刺 • A common technique for detecting genetic disorder • After 14 weeks there is about 200 ml amniotic fluid, and 20-30 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 age • previous birth of a trisomy child • chromosome abnormality in either parent • a X-linked recessive disorders carrier • neural tube defects in the family • carriers of inborn errors of metabolism
Alpha-fetoprotein (AFP) Assay • Produced by liver, yolk sac and instestine • neural tube defects (NTDs) and ventral wall defects (VWDs): AFP ↑ • 唐氏症,三染色體18：AFP ↓
Sex Chromatin Patterns--sex-linked hereditary diseases, e.g. hemophilia and muscular dystrophy
Chorionic Villus Sampling (CVS)絨毛膜取樣 • trophoblasts obtained by needle through mother's abdominal and uterine wall under ultrasound guidance • Risk of fetal loss 1%; risk of limb defects if done too early.
Fetoscopy胎內內視鏡--few use Ultrasonography超音波--measuring placental and fetal size, multiple births, and abnormal presentations, even male genitalia Computed Tomography (CT) and Magnetic Resonance Imaging (MRI)--providing more information for treatment, but expensive and limited resolution Amniography羊膜攝影 and Fetography胎兒攝影--injecting water-soluble or oil-soluble radiopaque substance into amniotic cavity Fetal Monitoring胎兒監測--for fetal heart rate monitoring (fetal distress胎兒窘迫-abnormal heart rate)