Week 4 to 8 - Organogenetic Period Flashcards
During the fourth to eighth weeks period the embryo will develop the ___, the tissues will differentiate fast, so any exposure to teratogens during this period may cause congenital anomalies.
main organ systems
Nervous and cardiovascular systems will begin to develop during weeks ______ which is important to support a live fetus.
4-8
agents such as drugs and viruses that produce or increase the incidence of congenital anomalies.
Teratogens
The normal development of an embryo can be divided into three phases, which are interrelated:
Growth, Morphogenesis, and Differentiation
First phase: consists of cell division
Growth
Second phase: _______, the development of shape, size, or other features of a particular organ or part of the whole of the body.
Morphogenesis
Third phase: maturation of physiologic processes.
Differentiation.
During the fourth week of development a significant event is the establishment of body form by folding of the flat trilaminar disc into a cylindrical embryo.
“Folding of the embryo”
The fast growth of the embryo is responsible for the folding of the _____ and ______ planes.
median and horizontal
Folding at the cranial and caudal ends occurs simultaneously. This causes constriction at the junction of the embryo and _______
umbilical vesicle (yolk sac).
As the embryo’s head folds, heart will be dorsally pushed to directly above the ____. This is important for proper location of the heart. It is rare to see heart beating outside of chest.
diaphragm
HEAD FOLD: During week 4, the neural folds in the cranial region thickened forming the _____ of the brain
primordium
HEAD FOLD: The developing embryo projects into the ____ and as development advances it grows beyond the oropharyngeal membrane and overhangs the developing heart.
amniotic cavity
The _______, primordial heart, pericardial coelom, and oropharyngeal membrane move onto the ventral surface of the embryo. After folding the septum transversum lies caudal to the heart where later it will develop into the central tendon of the diaphragm.
septum transversum or transverse septum
After folding, the pericardial coelom lies ventral to the heart and cranial to the septum transversum and the intraembryonic coelom communicates on each side with the ______
extraembryonic coelom
In week four of development, the heart is located outside of the chest. There is no space or _______ cavity because it is folding.
Pericardial
Head Fold: During folding, part of the endoderm of the umbilical vesicle goes into the embryo as the ____ (primordium of pharynx, esophagus, etc).
foregut
Head fold: The foregut lies between the brain and heart, and the ____.
oropharyngeal membrane
Head fold: The ____ will form the digestive track from the esophagus to a portion of the anus.
Endoderm
Head fold: From the foregut, a small attachment comes interior to the esophagus, forming the ____. The embryo will begin swallowing.
Trachea
Tail fold: The growing of the ______ (spinal cord primordium) causes the tail to grow.
neural tube
The ______ or tail region projects over the cloacal membrane.
caudal eminence
The future site of the anus is called the
cloacal membrane
The ____ or the primordium of the descending colon is incorporated to the embryo during folding and is part of the endodermal layer.
hindgut
The ___ or primordium of the urinary bladder and the rectum forms when the terminal part of the hindgut dilates slightly.
cloaca
The ____ or primordium of the umbilical cord is now attached to the ventral surface of the embryo, and a diverticulum of the umbilical vesicle called the allantois, is partially incorporated into the embryo.
connecting stalk
During ___ the three layers that will give rise to the primordia of all tissues and organs are formed: Ectoderm, Mesoderm and Endoderm.
gastrulation
This germ layer gives rise to the CNS, PNS, sensory epithelia of the eye, ear, and nose. Epidermis and its appendages; mammary glands; pituitary gland and enamel of teeth
Ectoderm
Neural crest cells derived from ___ gives rise to the cells of the spinal and cranial nerves.
neuroectoderm
Germ layer that gives rise to connective tissue; cartilage; bone; striated and smooth muscles; heart blood and lymphatic vessels; kidneys; ovaries; testes; genital ducts; serous membrane lining the body cavities and cortex of suprarenal glands.
Mesoderm
Mesoderm forms the ___, which forms primordia for muscle cells. This will migrate and help information for all of the muscles.
somite
Reproductive system development occurs at week ___ in the male and around week ___ in the female.
7,12
This germ layer gives rise to the epithelial lining of the gastrointestinal and respiratory tracts, parenchyma of tonsils, thyroid and parathyroid glands, thymus, liver and pancreas, epithelial lining of the urinary bladder; urethra, tympanic cavity and pharyngotympanic or auditory tube.
Endoderm
Which germ layer are all digestive tubes a part of?
endoderm
At the beginning of week ___ the embryo has four to 12 somites. The neural tube is formed opposite the somites, widely open at the rostral and caudal neuropores, which are openings at the cranial and caudal regions.
four
In a 24 days old embryo the first two ___ are visible. The first arch is the mandibular arch and will give rise to mandible or lower jaw and the maxilla or upper jaw. The second arch or hyoid arch. The heart produces a large ventral prominence and pumps blood.
pharyngeal arches
The forebrain produces a prominent elevation of the head, called the____.
forebrain prominence.
By day 26, the ___ are seen as small swellings of the ventrolateral body walls
limb buds
The ___, which are the primordia of the internal ears, are also visible by day 26.
otic pits
The ____, are ectodermal thickenings and they indicate the future lenses of the eyes. (day 26)
lens placodes
Towards the end of week four, there is rapid development of the
forebrain
By day 28, ___, the caudal eminence, which is a long tail-like, becomes a characteristic feature.
Carnegie stage 13
At day 28 a rudimentary ____ system, is established.
cardiovascular
By the end of the fourth week, the caudal ___ is usually closed
neuropore
During the fifth week, changes occur mostly on the head, which changes fast due to the growing of the ___ and facial prominences.
brain
In the fifth week, the second ____ overgrows the third and fourth arches, forming a lateral ectodermal depression on each side the cervical sinus.
pharyngeal arch
A six week embryo already show reflex response to ___.
touch
During the sixth week, the upper limbs differentiate and show the elbow, large handplates, and the primordia of the fingers, called ___
digital rays.
The lower limbs develop ___days after the upper limbs.
4 to 5
In the sixth week the ____ and the external acoustic ___ form.
auricular hillocks meatus
During the sixth week, the intestines enter the extraembryonic coelom in the proximal part of the ___.
umbilical cord.
The ____ in the sixth week of development is common in embryos this age, and is because the abdominal cavity is too small at this age.
umbilical herniation
The hernia formed during week six in most embryos is very thick, but by week ___ the diameter decreases significantly.
8
The 7th week of development is characterized by the changes on the ___
limbs.
During the 7th week, ___ appear between the digital rays in the handplates, indicating the future fingers
Notches
In week 7, the communication between the ___ and umbilical vesicle is reduced.
primordial gut
Ossification of the bones of the upper limbs begins during week
7
Cartilage and bone will ossify during week 7. The ___ ossifies first, followed by the femur. The length of the femur is usually measured and compared with other babies of same age.
clavicle
The 8th week marks the end of the ___ period.
embryonic
During the eighth week, digits of the hand are separated, but ___
webbed
The ____ is still present at week 8, but very small
caudal eminence
The ___ appears during week 8 and forms a band around the head.
scalp vascular plexus
Ossification begins in the ___ at week 8
femur
The ___ start closing during week 8
eyelids
In week 8, the ____ are still in the proximal portion of the umbilical cord.
intestines
During the eighth week of development, ____ begins to appear
external genitalia
ONLY after week 8 you will be able to know if formation of __ and ___ is complete
hands and limbs
Obstetricians date pregnancy from the first day of the LNMP= Last Normal Menstrual Period. This is the ___
gestational age.
The ___, begins at fertilization, two weeks after the LNMP
embryonic age
Errors in establishing the LNMP in woman who become pregnant after cessation of oral contraception are frequent, due to the fact that the ___affect the time of ovulation.
hormones
___ assessment of the size of the chorionic (gestational) cavity and its embryonic contents enables clinicians to obtain an accurate estimate of the date of conception.
Ultrasound
Around week four of development, transvaginal US you will see gestational sac. As the embryo grows, cavity of gestational sac will ____
Decrease
____ to ____ length is used to determine the age and expected date of delivery
crown to rump
Estimation of the age of embryos recovered after a ____, is determined from their external characteristics and measurements of their length.
spontaneous abortion
The appearance of the developing ____ is a helpful criterion for estimating embryonic age.
limbs
You count the number of ___ after a spontaneous abortion to estimate embryonic age.
somites
