Download Chapter 4 Third Week of Human Development

Chapter 4
Third Week of Human
Development
解剖學科
鄭授德
本教材圖片取自於
The Developing Human (9th ed)
Moore, Persaud and Torchia
•
•
•
The 3rd week (the 5th week after the day one of
LNMP) is the beginning of embryonic period.
The 8th week is the end.
Important events
1. Formation of the primitive streak
2. Notochord
3. Three germ layers
•
Cessation of menstruation (~ 5 weeks after LNMP) is the
first indication of pregnancy.
3.5 wk, umbilical vesicle
Gastulation:
Formation of Germ Layers
• Gastrulation: embryonic disc from bilaminar
develops into trilaminar; the embryo is gastrula.
• Each layer of trilaminar develops into specific
tissues and organs
– Embryonic ectoderm: epidermis, nervous system,
and others
– Embryonic mesoderm: smooth muscular coats,
connective tissue, and vessels; also blood cells and
born marrow, skeleton, striated muscles, reproductive
and excretory organs.
– Embryonic endoderm: epithelial linings of
respiratory and GI tracts and glandular cells
Primitive Streak
• At the beginning of the 3rd week, thickened linear band
of epiblast on the dorsal caudal aspect of embryonic disc.
• Primitive node (and pit) is on its cranial end.
• Primitive groove on the primitive streak (Fig. 4-2)
Primitive Streak
• Mesenchyme from inward turning of epiblast cells
through primitive groove forms (intra)embryonic
mesoderm, and displacing hypoblast forms
(intra)embryonic endoderm.
• Epiblast now can be called (intra)embryonic ectoderm.
Fate of Primitive Streak
•
•
•
The process of forming mesoderm
through primitive streak slows down
after the early 4th week
degenerates by the end of 4th week
in the sacrococcygeal region of
embryo.
Sacrococcygeal teratoma
developed from the remnants of
primitive streak
Notochordal Process and Notochord
•
•
Notochordal process - mesenchymal cells migrate cranially from
primitive node and form a cellular cord until it reaches the prechordal
plate (mouth region in future).
Prechordal plate serves as a signaling center for controlling
development of cranial structures.
Notochordal Process and Notochord
•
•
The lumen within it is called notochordal canal.
Mesenchymal cells extend laterally and cranially to the margin of embryonic
disc and continuous with extraembryonic mesoderm.
Notochordal Process and Notochord
•
Some mesenchymal cells migrate cranially alone the sides of notochord
process and meet at cardiogenic area.
Fate of the Notochord
•
•
•
It is the structure around vertebral column in the future, and degenerates as
nucleus pulposus in the intervertebral disc.
Notochord induces the development of neural plate (future central nervous
system).
A small passage, neuroenteric canal connects amniotic cavity with yolk sac,
but will be sealed after notochord completes.
•
Cloacal membrane--caudal to primitive steak, the future sites of
anus.
• Oropharyngeal membrane--remains bilaminar, ectoderm and
endoderm fuse there.
• Mesoderm separates ectoderm and endoderm, except at cloacal
membrane, oropharyngeal membrane and notochord.
Formation of the Notochord
• The notochord defines the primitive axis of the embryo and indicate
the future site of vertebral column.
Allantois
•
•
•
It appears on day 16 as a sausagelike
outpouch from caudal end of yolk sac
into connecting stalk.
It is involved with early blood formation
and associated with urinary bladder
development.
It becomes urachus and remains as
median umbilical ligament.
Neurulation:
Formation of Neural Tube
• The formation of neural plate and neural folds and the
closure of these folds to form the neural tube.
• It is completed by the end of the 4th week. The embryo
is called neurula during neurulation.
Neural Plate and Neural Tube
• Neuroectoderm—
– neural plate induced by notochord and develops into CNS (brain and
spinal cord)
• Neural plate broadens and extends as far as oropharyngeal
membrane and beyond notochord.
•
•
Invagination of neural plate forms neural groove with neural folds on both
sides.
Cranial enlargement of neural fold is the first sign of brain development.
•
•
•
End of the 3rd week, neural folds fuse and neural plate into neural tube.
Both ends of neural tube are rostral and caudal neuropores.
Both close during 4th week when neurulation completes.
Neural Crest Formation
•
•
•
•
The crest of each neural fold detaches when neural tube forms.
These flattened mass is called neural crest, which will forms
sensory ganglia of spinal (dorsal root ganglia) and cranial nerves
(V, VII, IX, X).
Also, it forms the Schwann cells, pia mater, arachnoid, pigment
cells, adrenal medulla, and several skeletal and muscular
components in the head.
Congenital defects:
– meroanencephaly (anencephaly) (p.400).
– spina bifida cystica (p.401).
Development of Somites
•
•
Both lateral sides of notochord
mesoderm forms a paraxial
mesoderm. Lateral to it are the
intermediate and lateral
mesoderms.
Somites - by the end of the 3rd week,
paraxial mesoderm develops into 38
pairs of cuboidal bodies (days 20 to
30). End of 5th week, 42 to 44 pairs.
18-day
20-day
21-day
•
•
Somites are so prominent as to be a
criteria for determining the age of
embryo in 4th and 5th weeks.
Somites appears first at occipital
region at the end of the 3rd week
and give rise to axial skeleton (bone
of head, neck and trunk), associated
musculature and dermis of skin.
18-day
20-day
21-day
Development of the Intraembryonic
Coelom
•
Intraembryonic coelom (cavity)--fusion of
isolated coelomic spaces in the lateral
mesoderm and cardiogenic mesoderm into a
horseshoe-shaped cavity.
•
During the 2nd month, intraembryonic coelom
is divided into 3 body cavities:
1.
2.
3.
Pericardial cavity
Pleural cavities
Peritoneal cavity
Lateral mesoderm
divided into:
• Parietal layer—
– together with extraembryonic mesoderm covering amnion and
ectoderm called somatopleure, embryonic body wall (upper side)
• Visceral layer—
– together with extraembryonic mesoderm covering yolk sac and
endoderm is called splanchnopleure, embryonic gut wall (lower
side)
Early Development of
Cardiovascular System
•
•
•
•
Blood vessel formation (angiogenesis) occurs at the beginning of
the third week in the extraembryonic mesoderm covering yolk sac,
connecting stalk, and chorion.
Without significant amount of yolk, the embryo needs blood vessels
to supply nutrition and oxygen.
At the end of the 2nd week the embryo obtains nutrition from
maternal blood through diffusion;
During the 3rd week it develops a primitive placental circulation.
Vasculogenesis and Angiogenesis
Developing of blood vessels and blood in the embryo
and extraembryonic membranes during the third
week
1. Blood island – angioblasts (a kind of
mesenchymal cell) aggregate in isolated cluster
with cavities
2. Primitive endothelium – angioblasts flatten to
form endothelial cells around cavity
3. Network – cavities fuse together
4. Vessels extend to fuse with vessels in adjacent
area
Primitive blood cells and plasma
•
•
•
develop from endothelial cells of vessels in
umbilical vesicle and allantois at the end of the
3rd week.
It occurs in embryo (liver first, than spleen,
bone marrow and lymph nodes) in the 5th
week.
Fetus and Adults – erythrocytes are derived
from different hematopoietic progenitor cells.
Primitive Cardiovascular System
•
•
•
heart and great vessels are developed from cardiogenic area.
Heart tube is fused from endothelial heart tube by the end of the 3rd
week.
Heart tube joined by vessels in the embryo, connecting stalk,
chorion, and yolk sac form a primitive cardiovascular system.
Primitive Cardiovascular System
•
•
Heart beats and blood circulation start on 21st or 22nd day (5 weeks
after LNMP).
Cardiovascular system is the first organ system to reach a
functional state.
Further Development
of Chorionic Villi
•
•
•
•
Primary chorionic villi--at the end
of the 2nd week
Secondary chorionic villi--the early
3rd week, with mesenchymal core in
the branching villi covering all
surface of chorionic sac
Tertiary chorionic villi--day 15 to
20 arteriocapillary venous networks
develop villi
The end of the 3rd week blood flow
starts; oxygen, nutrients in the
maternal blood exchange with CO2
and waste in embryonic blood by
diffusing through the wall of villiplacental membrane.
Primary
Secondary
Tertiary
Cytotrophoblastic shell
• Cytotrophoblasts extend through syncytiotrophoblastic
layer forming a shell to attach the chorionic sac to the
endometrium.
• Main exchange site—
– stem (anchoring) villi and their branch villi
Abnormal Growth of the Trophoblast
•
Hydatidiform moles
– Without vasculization in tertiary villi;
– Form cystic swellings; produce excessive hCG;
– 3~5% of them form choriocarcinomas, which may spread to
lungs, vagina, liver, bone, intestine, and brain through
bloodstream..
Chapter 5
Fourth to Eighth Weeks of
Human Development
解剖學科
鄭授德
本教材圖片取自於
1. The Developing Human (9th ed) Moore, Persaud and Torchia
2. Human Anatomy (6th ed), Marieb, Mallatt, and Wilhelm
Phases of Embryonic Development
1. Growth - increase in size.
2. Morphogenesis - development of form
3. Differentiation - maturation of physiological processes
• Teratogens - agents (drugs or virus) that produce or
increases the incidence of birth defects.
• Exposure of embryo to the teratogen within the 4th to 8th
weeks may cause major congenital defects.
Folding of the Embryo
• Foldings in median and horizontal planes change the flat
trilaminar embryo disc into a cylindrical embryo.
• Folding of the Embryo in the Median Plane
– Head and tail move ventrally
• Folding of the Embryo in the Horizontal Plane
– Lateral folding rolls the sides of embryo disc and turns part of
endoderm into embryo as midgut
– the rest left outside (yolk stalk) and will be incorporated into
umbilical cord.
22-day
Beginning of 4-wk
26-day
End of 4-wk
28-day
The Head Fold
• Septum transversum (transverse
mesodermal septum), primordial heart,
pericardial coelom, and oropharyngeal
membrane line from cranial to caudal in
the head region of trilaminar embryonic
disc.
• Septum transversum develops into
the central tendon of the diaphragm.
• The end of the 3rd week, primitive brain
protrudes into amniotic cavity. Later, it
grows crainally and hang over
oropharyngeal membrane and
developing heart. The longitudinal
infolding turns endoderm inward as
foregut (primordium of pharynx, etc.).
21 days
26 days
The Tail Fold
• Cloacal membrane on the caudal
end of primitive streak develops into
future anus.
• Neural tube growing over cloacal
membrane causes infolding and turns
part of endoderm into embryo as
hind gut.
• Connecting stalk turns to ventral
surface, and allantois is incorporated
into embryo.
Beginning of 4-wk
End of 4-wk
Germ Layer Derivatives
Ectoderm
• CNS
• PNS
• Sensory epithelial of eye,
ear, and nose
• Epidermis and hairs and
nails
• Mammary glands
• Pituitary gland
• Subcutaneous glands
• Enamel of teeth
Neural crest cells
• Cells of spinal, cranial nn.
and autonomic ganglia
• Ensheathing cells of PNS
• Pigment cells of dermis
• Muscle, connective
tissues, and bone of
pharyngeal arch origin
• Suprarenal medulla
• Meninges of brain and
spinal cord.
Germ Layer Derivatives
Mesoderm
• Connective tissue
• Cartilage
• Bone
• Striated and smooth muscles
• Heart
• Blood and lymph vessels
• Kidneys
• Ovaries
• Testes
• Genital ducts
• Serous membranes lining pericardial, pleural, and
peritoneal cavities
• Spleen
• Cortex of suprarenal glands
Germ Layer Derivatives
Endoderm
• Epithelial lining of GI and respiratory tracts
• Parenchyma of tonsils, thyroid and parathyroid glands
• Thymus
• Liver
• Pancreas
• Epithelial lining of urinary bladder and most of urethra
• Epithelial lining of tympanic cavity, tympanic antrum, and
pharyngotympanic tube
Control of Embryonic Development
Embryonic development is essentially a process of growth
and increasing complexity of structure and function.
•
Genetic plan in chromosomes
•
Environmental factors
•
Development is growth and increasing complexity
•
Interaction between tissues during development
(induction)
1.
2.
•
•
optic vesicle induces the formation of lens
uteric bud induces the formation of tubules in the metanephric
mesoderm.
Molecular mechanism of induction from relating tissue
Intracellular signal transduction pathway
Fourth Week
Early 4th wk Straight embryo
Middle 4th wk Neural tube, widely opened neuropores
24 days
Mandibular (1st) arch - mandible & maxillary
Hyoid (2nd) arch
Slightly curves (head and tail folds)
Heart prominence
26 days
Pharyngeal (branchial) arches
Rostral neuropore closes
Forebrain elevation
C-shaped curvature
26 or 27 days Upper limb buds and otic pits show
Lens placodes, attenuated tail are visible
End of 4th wk 4th pair arches and lower limb buds show
Caudal neuropore closed
Fourth Week
Early 4th week
Middle 4th week
Straight embryo
Neural tube, widely opened neuropores
22-day
23-day
Fourth Week
24 days
24 days
Mandibular (1st) arch - mandible & maxilla
Hyoid (2nd) arch
Slightly curves (head and tail folds)
Heart prominence
Fourth Week
26 days
26 days
Pharyngeal (branchial) arches
Rostral neuropore closes
Forebrain elevation
C-shaped curvature
Fourth Week
26 or 27 days
End of 4th week
28 days
Upper limb buds and otic pits show
Lens placodes, attenuated tail are visible
4th pair arches and lower limb buds show
Caudal neuropore closed
28 days
28 days
Fifth Week
Brain rapid grows; face contacts heart prominence
Hyoid (2nd) arch overgrows 3rd and 4th arches
Forms cervical sinus on lateral sides
Upper limb with elbow and hand plate
Mesonephric ridges indicate the sites of kidneys
Spontaneous movements
33 days Digital rays in hand plates
32 days
32 days
Sixth Week
•
•
•
•
•
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Rapid growth of upper limbs
Elbow, wrist show; hand plates with digital rays
Groove between 1st and 2nd arch develops (external acoustic
meatus)
Swelling around it (auricular hillocks)
Heart prominence against face
Respond to touch
42 days
Seventh Week
•
•
•
Notches between digital rays of hand
Only omophaloenteric duct left communicating between primitive
gut and umbilical vesicle
Prominent umbilical herniation with intestine
48 days
Eighth Week
•
•
•
•
•
Final week of embryonic
period
Webbed digits of hand
Notches between digits of
foot
Tail still present
Scalp vascular plexus
appears near the vertex
(crown) of head.
52 days
Eighth Week
End of 8th week
– All regions of limbs
apparent; limbs move
– Digit lengthened and
separated
– Distinct human
characteristics
– Head takes half of the
embryo length
– Neck established
– Eyelid are obvious
– Intestine is still in the
umbilical cord
– Sexual difference exists but
sex still can not be told
56 days
56 days
Estimation of Embryonic Age
1. Onset of LNMP (gestational age)
2. The probable time of fertilization
3. Measurements of the chorionic sac and embryo
4. External characteristic of embryo
• Spontaneous aborted embryos can be estimated
by the appearance of developing limbs.
Methods of Measuring Embryos
1.
Greatest length (GL)
–
2.
3.
3rd and early 4th weeks, straight embryo
Crown-rump length (CRL) or sitting height
–
neck-rump measurement
Crown-heel length (CHL) or standing height for 8-wk
embryo
4.5-wk
CRL 4.8 mm
5-wk
CRL 2.09 cm
amnion
7-wk
CRL 2.14 cm
Ultrasound Scanner
6-wk
4th
ventricle
Chapter 6
Ninth Week to Birth:
The Fetal Period
解剖學科
鄭授德
本教材圖片取自於
The Developing Human (9th ed)
Moore, Persaud and Torchia
• A notable change of the embryo to fetus period relatively
slow down in the growth of head compared with the rest
of body.
• Viability – the ability of fetuses to survive in the
extrauterine environment.
• 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 expected date of
confinement (EDC) the calculation of age
is done by:
1. Gestational age – the onset of the last normal
menstrual period (LNMP), used clinically
2. The estimated day of fertilization (used in this
book); the month is by calendar month
9-week
Trimester of Pregnancy
• Trimester – each last for 3 calendar months
• The end of the first trimester
– all major systems develop
– crown-rump length (CRL) is used for measuring
• The end of the second trimester
– may survive if born prematurely
• At 35 weeks
– fetus weighed 2500 gm, usually survives if born prematurely
Measurements and Characteristics
of Fetuses
Measuring with ultrasonography and weight in the second
and third trimesters:
1. Biparietal diameter (BPD)
2. Head circumference
3. Abdominal circumference
4. Femur length
5. Foot length
6. Fetal weight
(may have discrepancy when mother has diabetes mellitus)
Nine 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
Intestines return to abdomen
• 12th week
Fetal form of ext. genitalia established
Nine to Twelve Weeks
• 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
11-week
9-week
12-week
Thirteen to Sixteen Weeks
13-week
• 14th week
–
–
–
–
–
Rapid growth
Coordinated limb movement
Active ossification of skeleton
Eye movements occur
Scalp hair pattern determined
• Beginning of 16th week
– Bones can be seen on radiographs
• 16th week
– Ovaries differentiated and contain primordial follicles
Seventeen to Twenty Weeks
•
•
•
•
Fetus grows 50 mm within period
Fetal movements (quickening) felt by mother
Delivery day is 147 ± 15 days after first movement.
Skin is covered and protected by vernix caseosa.
17-week
Seventeen to Twenty Weeks
20-week
• 20th week
– Covered by lanugo (fine downy hair)
– Eyebrows and head hairs are visible
– Testes begin to descend.
• 17th to 20th weeks
– Brown fat is the heat production site.
• 18th week
– Canalization of vagina begins.
18-week
Twenty-one to Twenty-five Weeks
• Substantial weight gain
• Skin wrinkles and is translucent, pink
to red
• 21st week
25-week
fetus
– Rapid eye movements begin
• 22nd to 23rd weeks
– Responds to noise (blink-startle responses)
• 24th week
– Type II pneumocytes secrete surfactant
– Fingernails appear
25-week newborn
• 22nd to 25th weeks
– Born prematurely may survive under
intensive care
Twenty-six to Twenty-nine Weeks
• Can breathe air by functioning lungs
• CNS controls rhythmic breathing and body
temperature
• 26th week
– Eyes reopen
– Toenails are visible
– Subcutaneous fat flattens wrinkled skin
• 28th week
– Spleen has been an important site of
hematopoiesis
– It shifts to bone marrow by the end of 28th week
29-week
26-week
28-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
34-week
Thirty-five to Thirty-eight Weeks
36-week
• 35th week
– Grasp, spontaneous orientation to light
• 37th to 38th weeks
– Nervous system is mature for
integrative functions.
• 36th week
– Circumference of head is equal to that
of abdomen.
– CRL 360 mm, weight 3400 gm
– Slow growing before birth
– White fat = 16% body weight
• 38th week
– Add 14 gm per day in last week
• Full term
– Bluish-pink skin; Testes in scrotum
37-week
Expected Date of Delivery
• 266 days (38 weeks)
– Expected time of birth
– EDC (expected date of confinement)
• 1 to 2 weeks late
– 12% of babies
• 3 weeks late
– 5 to 6%
38-week
Factors Influencing Fetal Growth
•
•
•
•
•
Cigarette smoking
Multiple pregnancy
Alcohol and illicit drugs
Impaired uteroplacental
and fetoplacental blood
flow
Genetic factors and
growth retardation
Procedures for Assessing Fetal Status
Perinatology
Fetus of 26th week after fertilization to newborn infant of 4 weeks
after birth.
1.
Ultrasonography
–
–
–
Primary imaging modality, a major tool for prenatal diagnosis of
fetal abnormalities
Measuring placental and fetal size, multiple births, and abnormal
placental shape and presentations
Wide availability, low cost, and lack of known adverse effects.
3-D Ultrasonogram
28-week
4.5-wk
CRL 4.8 mm
5-wk
CRL 2.09 cm
amnion
7-wk
CRL 2.14 cm
Ultrasound Scanner
6-wk
4th
ventricle
Procedures for Assessing Fetal Status
2.
Diagnostic amniocentesis
–
–
A common technique for
detecting genetic disorder
After 14 weeks there is about
200 ml amniotic fluid, and 15-20
ml can be safely withdrawn
under real-time ultrasonography.
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
3.
Alpha-fetoprotein (AFP) Assay
–
–
4.
neural tube defects (NTDs; e.g. spina bifida)
ventral wall defects (VWDs; e.g. gastroschisis and omphalocele)
Spectrophotometric studies
–
5.
for erythroblastosis fetalis, maternal antibodies destruct fetal blood
cells
Chorionic villus sampling (CVS)
–
–
–
6.
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.
Sex chromatin patterns
–
sex-linked hereditary diseases, e.g. hemophilia and muscular
XXX
XX
dystrophy
XY
XY
indicates condensed X chromosome.
by cresyl echt violet staining
indicates condensed Yq.
by quinacrine mustard staining
7.
Cell cultures and chromosomal analysis
–
–
8.
for fetal sex and chromosomal aberrations.
Also, inborn errors of metabolism
Fetal transfusion
–
for hemolytic disease of the newborn (HDN), blood transfusion
through peritoneal cavity or umbilical cord puncture
Fetoscopy – few used
9.
10. Percutaneous umbilical cord blood sampling (PUBS)
–
–
sampling blood after 18 weeks for aneuploidy, fetal growth restriction,
fetal infection, and fetal anemia.
Treating fetal anemia by transfusion packed RBC
11. Computed tomography (CT) and
Magnetic resonance imaging (MRI)
–
–
providing more information for treatment
MRI has high soft-tissue contrast and
resolution
12. Fetal monitoring
–
for fetal heart rate monitoring (fetal
distress-abnormal heart rate)
MRI
Establishment of openings of the ureters into the bladder at a 21-week fetus