Chapter 6 Flashcards
The _____, or period of organogenesis, occurs from the third to the eighth weeks of development and is the time when each of the three germ layers, ectoderm, mesoderm, and endoderm, gives rise to a number of specific tissues and organs
embryonic period
The embryonic period, or period of ____, occurs from the third to the eighth weeks of development and is the time when each of the three germ layers, ectoderm, mesoderm, and endoderm, gives rise to a number of specific tissues and organs
organogenesis
The embryonic period, or period of organogenesis, occurs from the ____ of development and is the time when each of the three germ layers, ectoderm, mesoderm, and endoderm, gives rise to a number of specific tissues and organs
third to the eighth weeks
The embryonic period, or period of organogenesis, occurs from the third to the eighth weeks of development and is the time when each of the three germ layers, ___, ____, and _____, gives rise to a number of specific tissues and organs
ectoderm, mesoderm, and endoderm
The third to eighth weeks are also cited as the time when the majority of birth defects are induced; prior to this time, any insult to the embryo results in its death and spontaneous abortion. Although this tenet holds true for many insults to normal development, it is important to note that ___ begins late in the first week at the blastocyst stage and that a great variety of birth defects can be attributed to disruptions in cell signaling during specification of the cranial-caudal and left-right axes
axis formation
The third to eighth weeks are also cited as the time when the majority of birth defects are induced; prior to this time, any insult to the embryo results in its death and spontaneous abortion. Although this tenet holds true for many insults to normal development, it is important to note that axis formation begins late in the ____ at the blastocyst stage and that a great variety of birth defects can be attributed to disruptions in cell signaling during specification of the cranial-caudal and left-right axes
first week
Appearance of the notochord and prechordal mesoderm induces the overlying ectoderm to thicken and form the ____
neural plate
Cells of the plate make up the ____, and their induction represents the initial event in the process of neurulation
neuroectoderm
Cells of the plate make up the neuroectoderm, and their induction represents the initial event in the process of _____
neurulation
Upregulation of fibroblast growth factor (FGF) signaling together with inhibition of the activity of ____, a transforming growth factor-B (TGF-B) family member responsible for ventralizing ectoderm and mesoderm, causes induction of the neural plate
bone morphogenetic protein 4 (BMP4)
Upregulation of _____ signaling together with inhibition of the activity of bone morphogenetic protein 4 (BMP4), a transforming growth factor-B (TGF-B) family member responsible for ventralizing ectoderm and mesoderm, causes induction of the neural plate
fibroblast growth factor (FGF)
Upregulation of fibroblast growth factor (FGF) signaling together with inhibition of the activity of bone morphogenetic protein 4 (BMP4), a _____ family member responsible for ventralizing ectoderm and mesoderm, causes induction of the neural plate
transforming growth factor-B (TGF-B)
FGF signaling probably promotes a neural pathway by an unknown mechanism while it represses BMP transcription and upregulates expression of ___ and ___, which inhibit BMP activity
CHORDIN and NOGGIN
Secretion of three other molecules, ____, ____, and _____, inactivates BMP
noggin, chordin, and follistatin
Induction of caudal neural plate structures (hindbrain and spinal cord) depends on two secreted proteins, ___ and ___. In addition, retinoic acid (RA) appears to play a role in organizing the cranial-to-caudal axis because it can cause the respecification of cranial segments into more caudal ones by regulating expression of homeobox genes
WNT3a and FGF
Induction of caudal neural plate structures (hindbrain and spinal cord) depends on two secreted proteins, WNT3a and FGF. In addition, ____ appears to play a role in organizing the cranial-to-caudal axis because it can cause the respecification of cranial segments into more caudal ones by regulating expression of homeobox genes
retinoic acid (RA)
Induction of caudal neural plate structures (hindbrain and spinal cord) depends on two secreted proteins, WNT3a and FGF. In addition, retinoic acid (RA) appears to play a role in organizing the cranial-to-caudal axis because it can cause the respecification of cranial segments into more caudal ones by regulating expression of _____
homeobox genes
As the neural plate lengthens, its lateral edges elevate to form ____, and the depressed midregion forms the neural groove
neural folds
As the neural plate lengthens, its lateral edges elevate to form neural folds, and the depressed midregion forms the ____. As a result, the neural tube is formed.
neural groove
As the neural plate lengthens, its lateral edges elevate to form neural folds, and the depressed midregion forms the neural groove. As a result, the ____ is formed.
neural tube
Until fusion is complete, the cephalic and caudal ends of the neural tube communicate with the amniotic cavity by way of the ____ and posterior (caudal) neuropores, respectively
anterior (cranial)
Until fusion is complete, the cephalic and caudal ends of the neural tube communicate with the amniotic cavity by way of the anterior (cranial) and ____, respectively
posterior (caudal) neuropores
Neurulation is then complete, and the central nervous system is represented by a closed
tubular structure with a narrow caudal portion, the ___, and a much broader cephalic portion characterized by a number of dilations, the brain vesicles
spinal cord
Neurulation is then complete, and the central nervous system is represented by a closed
tubular structure with a narrow caudal portion, the spinal cord, and a much broader cephalic portion characterized by a number of dilations, the _____
brain vesicles
This cell population, the _____, undergoes an epithelial-to-mesenchymal transition as it leaves the neuroectoderm by active migration and displacement to enter the underlying mesoderm.
neural crest cells
This cell population, the neural crest cells, undergoes an _____ as it leaves the neuroectoderm by active migration and displacement to enter the underlying mesoderm.
epithelial-to-mesenchymal transition
(____ refers to cells derived from the epiblast and extraembryonic tissues. Mesenchyme refers to loosely organized embryonic connective tissue regardless of origin.)
Mesoderm
(Mesoderm refers to cells derived from the epiblast and extraembryonic tissues. ___ refers to loosely organized embryonic connective tissue regardless of origin.)
Mesenchyme
Crest cells from the trunk region leave the neuroectoderm ____ of the neural tube and migrate along one of two pathways:
(1) a dorsal pathway through the dermis, where they will enter the ectoderm through holes in the basal lamina to form melanocytes in the skin and hair follicles, and (2) a ventral pathway through the anterior half of each somite to become sensory ganglia, sympathetic and enteric neurons, Schwann cells, and cells of the adrenal medulla
after closure
Crest cells from the trunk region leave the neuroectoderm after closure of the neural tube and migrate along one of two pathways:
(1) a dorsal pathway through the dermis, where they will enter the ectoderm through holes in the basal lamina to form ___ in the skin and hair follicles
(2) a ventral pathway through the anterior half of each somite to become sensory ganglia, sympathetic and enteric neurons, Schwann cells, and cells of the adrenal medulla
melanocytes
Crest cells from the trunk region leave the neuroectoderm after closure of the neural tube and migrate along one of two pathways:
(1) a dorsal pathway through the dermis, where they will enter the ectoderm through holes in the basal lamina to form melanocytes in the skin and hair follicles, and (2) a ventral pathway through the anterior half of each somite to become ____, ____, ____, and ____
sensory ganglia, sympathetic and enteric neurons, Schwann cells, and cells of the adrenal medulla
NCC also form and migrate from cranial neural folds, leaving the neural tube ___ in this region
before closure
These cells contribute to the ___ as well as neurons for cranial ganglia, glial cells, melanocytes, and other cell types
craniofacial skeleton
These cells contribute to the craniofacial skeleton as well as ____, ____, _____, and other cell types
neurons for cranial ganglia, glial cells, melanocytes
NCC are so fundamentally important and contribute to so many organs and tissues that they are sometimes referred to as the ____
fourth germ layer
Give the Different neural crest derivatives
Connective tissue and bones of the face and skull
Cranial nerve ganglia
C cells of the thyroid gland
Conotruncal septum in the heart
Odontoblasts
Dermis in face and neck
Spinal [dorsal root] ganglia
Sympathetic chain and preaortic ganglia
Parasympathetic ganglia of the gastrointestinal tract
Adrenal medulla
Schwann cells
Glial cells
Meninges [forebrain]
Melanocytes
Smooth muscle cells to blood vessels of the
face and forebrain
They are also involved in at least ____ of all birth defects and many cancers, such as melanomas, neuroblastomas, and others
one-third
By the time the neural tube is closed, two bilateral _____, the otic placodes and the lens placodes, become visible in the cephalic region of the embryo
ectodermal thickenings
By the time the neural tube is closed, two bilateral ectodermal thickenings, the ____ and the lens placodes, become visible in the cephalic region of the embryo
otic placodes
By the time the neural tube is closed, two bilateral ectodermal thickenings, the otic placodes and the _____, become visible in the cephalic region of the embryo
lens placodes
During further development, the otic placodes invaginate and form the ___, which will develop into structures needed for hearing and maintenance of equilibrium
otic vesicles
At approximately the same time, the ___ these placodes also invaginate and, during the fifth week, form the lenses of the eyes
lens placodes
At approximately the same time, the lens placodes appear. These placodes also invaginate and, during the fifth week, form the ____ of the eyes
lenses
___ result when neural tube closure fails to occur
Neural tube defects [NTDs]
If the neural tube fails to close in the cranial region, then most of the brain fails to form, and the defect is called ___
anencephaly
If closure fails anywhere from the cervical region caudally, then the defect is called ___
spina bifida
The ___ genes are part of the planar cell polarity pathway that regulates convergent extension, the process that lengthens the neural tube and is necessary for normal closure to occur
VANGL
Regardless of the region or country where
NTDs occur, and rates have been reduced significantly following ___ administration
folic acid
It is estimated that 50% to 70% of NTDs can be prevented if women take ___ of folic acid daily [the dose present in most multivitamins] beginning 3 months prior to conception and continuing throughout pregnancy
400 pg
If a woman has had a child with an NTD or if there is a history of such defects in her family, it is recommended that she take 400 pg of folic acid daily and then ___ per day starting 1 month before she tries to become pregnant and continuing through the first 3 months of pregnancy.
4,000 pg
By approximately the 17th day, however, cells close to the midline proliferate and form a thickened plate of tissue known as __
paraxial mesoderm
More laterally, the mesoderm layer remains thin and is known as the ___
lateral plate
Together, these layers line a newly formed cavity, the ___, which is continuous with the extraembryonic cavity on each side of the embryo.
intraembryonic cavity
With the appearance and coalescence of intercellular cavities in the lateral plate, this tissue is divided into two layers:
1. A layer continuous with mesoderm covering the amnion, known as the _____
2. A layer continuous with mesoderm covering the yolk sac, known as the ___
somatic or parietal mesoderm layer
splanchnic or visceral mesoderm layer
These segments, known as ___, first appear in the cephalic region of the embryo, and their formation proceeds cephalocaudally.
somitomeres
___ connects paraxial and lateral plate mesoderm
Intermediate mesoderm
In the head region, somitomeres form in association with segmentation of the neural plate into ____ and contribute to mesenchyme in the head
neuromeres
Formation of segmented somites from un-segmented presomitic (paraxial) mesoderm depends on a____ established by cyclic expression of a number of genes
segmentation clock
The cyclic genes include members of the ___ and ___ signaling pathways that are expressed in an oscillating pattern in presomitic mesoderm
NOTCH and WNT
Boundaries for each somite are regulated by retinoic acid (RA) and a combination of ___ and ___
FGF8 and WNT3a
Boundaries for each somite are regulated by ___ and a combination of FGF8 and WNT3a
retinoic acid (RA)
RA is expressed at high concentrations cranially and decreases in concentration caudally, whereas the combination of ___ and ___ proteins is expressed at higher concentrations caudally and lower ones cranially
FGF8 and WNT3a
Number of somites at 20 days
1-4
Number of somites at 21 days
4-7
Number of somites at 22 days
7-10
Number of somites at 24 days
13-17
Number of somites at 23 days
10-13
Number of somites at 25 days
17-20
Number of somites at 26 days
20-23
Number of somites at 27 days
23-26
Number of somites at 28 days
26-29
Number of somites at 30 days
34-35
When somites first form from presomitic mesoderm, they exist as a ball of mesoderm (fibroblast-like) cells. These cells then undergo a process of ___ and arrange themselves in a donut shape around a small lumen
epithelization
By the beginning of the fourth week, cells in the ventral and medial walls of the somite lose their epithelial characteristics, become mesenchymal (fibroblast-like) again, and shift their position to surround the neural tube and notochord. Collectively, these cells form the ___ that will differentiate into the vertebrae and ribs
sclerotome
The secreted protein products of the ____ genes and ___, produced by the notochord and floor plate of the neural tube, induce the ventromedial portion of the somite to become sclerotome
NOGGIN - sonic hedgehog (SHH)
Hence, each somite forms its own ___ (the tendon cartilage and bone component), its own ___ (providing the segmental muscle component), and its own ___, which forms the dermis of the back
sclerotome - myotome - dermatome
Once induced, sclerotome cells express the transcription factor ___, which initiates the cascade of cartilage- and bone-forming genes for vertebral formation
PAX1
Expression of ___, regulated by __ proteins from the dorsal neural tube, marks
the dermomyotome region of the somite
PAX3 - WNT
WNT proteins from the dorsal neural tube also target the dorsomedial portion of the somite, causing it to initiate expression of the muscle-specific gene ___ and to form primaxial muscle precursors
MYF5
The midportion of the dorsal epithelium of the somite is directed by ____, secreted by the dorsal region of the neural tube, to form dermis
neurotrophin 3 (NT-3)
In cervical and upper thoracic regions, it forms segmental cell clusters (future __), whereas more caudally, it forms an unsegmented mass of tissue, the nephrogenic cord
nephrotomes
In cervical and upper thoracic regions, it forms segmental cell clusters (future nephrotomes), whereas more caudally, it forms an unsegmented mass of tissue, the ___
nephrogenic cord
___ splits into parietal (somatic) and Visceral (splanchnic) layers, which line the intraembryonic cavity and surround the organs, respectively
Lateral plate mesoderm
Lateral plate mesoderm splits into ___ and ___, which line the intraembryonic cavity and surround the organs, respectively
parietal (somatic) and Visceral (splanchnic) layers
Mesoderm cells of the parietal layer surrounding the intraembryonic cavity form thin membranes, the ____ or ____, which will line the peritoneal, pleural, and pericardial cavities and secrete serous fluid
mesothelial membranes, or serous membranes
Blood cells and blood vessels also arise from
mesoderm. Blood vessels form in two ways: ____, whereby vessels arise from blood islands, and ____, which entails sprouting from existing vessels
vasculogenesis - angiogenesis
These islands arise from mesoderm cells that are induced to form ___, a common precursor for vessel and blood cell formation
hemangioblasts
The definitive ____ are derived from mesoderm surrounding the aorta in a site near the developing mesonephric kidney called the aorta-gonad-mesonephros region (AGM)
hematopoietic stem cells
The definitive hematopoietic stem cells are derived from mesoderm surrounding the aorta in a site near the developing mesonephric kidney called the ____
aorta-gonad-mesonephros region (AGM)
___ induces blood island development from competent mesoderm cells that form hemangioblasts
FGF2
Hemangioblasts are directed to form blood cells and vessels by ____, which is secreted by surrounding mesoderm cells
vascular endothelial growth factor (VEGF)
The signal to express VEGF may involve HOXBS, which upregulates the VEGF receptor ___
FLKl
Hemangioblasts in the center of blood islands form ____, the precursors of all blood cells, whereas peripheral hemangioblasts differentiate into angioblasts, the precursors to blood vessels
hematopoietic stem cells
Hemangioblasts in the center of blood islands form hematopoietic stem cells, the precursors of all blood cells, whereas peripheral hemangioblasts differentiate into ___, the precursors to blood vessels
angioblasts
Maturation and modeling of the vasculature are regulated by other growth factors, including ____ and ___, until the adult pattern
is established
platelet-derived growth factor (PDGF) and TGF-B
In turn, VEGF expression induces the ____ (a transmembrane receptor pathway), which specifies arterial development through expression of ____ (ephrins are ligands that bind to Eph receptors in a pathway involving tyrosine kinase signaling)
NOTCH pathway - EPHRINBZ
In turn, VEGF expression induces the NOTCH pathway (a transmembrane receptor pathway), which specifies arterial development through expression of EPHRINBZ (ephrins are ligands that bind to ____ in a pathway involving ____)
Eph receptors - tyrosine kinase signaling
_____ are abnormally dense collections of capillary blood vessels that form the most common tumors of infancy, occurring in approximately 10% of all births
Capillary hemangiomas
NOTCH signaling also upregulates expression of _____, a vein-specific gene, but how this gene and others specify venous development is not clear
EPHB4
On the other hand, _____, a homeodomain-containing transcription factor, appears to be the master gene for lymphatic vessel differentiation
PROXI
Failure of the lateral body folds to close the body wall results in ____
ventral body wall defects
The tube is divided into three regions:
the ____, ___ and ___
foregut, midgut, and hindgut
The midgut communicates with the yolk sac by way of a broad stalk, the ___
Vitelline (yolk sac) duct
At its cephalic end, the foregut is temporarily bounded by an ectodermal—endodermal membrane called the ____
oropharyngeal membrane
This membrane separates the ___, the primitive oral cavity derived from ectoderm, from the pharynx, a part of the foregut derived from endoderm
stomodeum
The hindgut also terminates temporarily at an ectodermal—endodermal membrane, the _____
cloacal membrane
This membrane separates the upper part of the anal canal, derived from endoderm, from the lower part, called the ____, which is formed by an invaginating pit lined by ectoderm
proctodeum
Another important result of cephalocaudal growth and lateral folding is partial incorporation of the allantois into the body of the embryo, where it forms the ___
cloaca
_____ genes are known for their homeodomain, a DNA-binding motif, the homeobox
Homeobox
During further development, endoderm gives rise to the following:
- The epithelial lining of the respiratory tract
- The ____ of the thyroid, parathyroids, liver, and pancreas
- The reticular stroma of the tonsils and the thymus
- The epithelial lining of the urinary bladder and the urethra
- The epithelial lining of the tympanic cavity and auditory tube
parenchyma
Homeobox genes are known for their ___, a DNA-binding motif, the homeobox
homeodomain
Homeobox genes are known for their homeodomain, a DNA-binding motif, the ___
homeobox
Many homeobox genes are collected into ____, although other genes also contain the homeodomain
homeotic clusters
An important cluster of genes specifying the craniocaudal axis is the homeotic gene complex ____ in Drosophila
Hom-C
These genes are conserved in humans, existing as four copies—___, ____, ____, and ___, — which are arranged and expressed like those in Drosophila
HOXA, HOXB, HOXC, and HOXD
These genes, which contain the ___ and ___ classes of homeotic genes, are organized on a single chromosome as a functional unit
Antennapedia and Bithorax
Genes with the same number, but belonging to different clusters, form a ___ group, such as HOXA4, HOXB4, HOXC4, and HOXD4
paralogous
The pattern of expression of these genes, along with evidence from ____ experiments in which mice are created that lack one or more of these genes, supports the hypothesis that they play a role in cranial-to-caudal patterning of the derivatives of all three germ layers
knockout
Because counting somites becomes difficult during the second month of development, the age of the embryo is then indicated as the ____ and expressed in millimeters
crown-rump length (CRL)
The former are located dorsal to the pericardial swelling at the level of the fourth cervical to the first thoracic somites, which explains their innervation by the ____
brachial plexus
These grooves, known as ___, appear in the hand region first and shortly afterward in the foot, as the upper limb is slightly more advanced in development than the lower limb
rays
Crown - rump length is 10-14mm in what week?
6
Crown - rump length is 5-8mm in what week?
5
Crown - rump length is 17-22mm in what week?
7
Crown - rump length is 28-30mm in what week?
8
Most major organs and organ systems are formed during the ____. This period, which is critical for normal development, is therefore called the period of____ or ___
third to eighth weeks - organogenesis or embryogenesis
The ____ gives rise to the organs and structures that maintain contact with the outside world:
- Central nervous system
- Peripheral nervous system
- Sensory epithelium of ear, nose, and eye
- Skin, including hair and nails
- Pituitary, mammary, and sweat glands and
- enamel of the teeth
ectodermal germ layer
Characteristic feature: Apperance of primitive streak - what days of embryonic period?
14-15
Characteristic feature: Notochordal process appears; hemopoietic cells in yolk sac - what days of embryonic period?
16-28
Characteristic feature: Intraembryonic mesoderm spreads under cranial ectoderm; primitive streak continues; umbilical vessels and cranial neural folds begin to form. - what days of embryonic period?
19-20
Characteristic feature: Cranial neural folds elevated and deep neural groove established; embryo begins to bend - what days of embryonic period?
20-21
Characteristic feature: Fusion of neural folds begins in cervical region; cranial and caudal neuropores open widely; visceral arches 1 and 2 present; heart tube begins to fold. - what days of embryonic period?
22-23
Characteristic feature: Cephalocaudal folding under way; cranial neuropore closing or closed; optic vesicles formed; otic placodes appear - what days of embryonic period?
24-25
Characteristic feature: Caudal neuropore closing or closed; upper limb buds appear; three pairs of visceral arches - what days of embryonic period?
26-27
Characteristic feature: Fourth visceral arch formed; hind limb buds appear; otic vesicle and lens placode - what days of embryonic period?
28-30
Characteristic feature: Forelimbs paddle-shaped; nasal pits formed; embryo tightly C-shaped - what days of embryonic period?
31-35
Characteristic feature: Digital rays in hand and foot plates; brain vesicles prominent; external auricle forms from auricular hillocks; umbilical herniation initiated - what days of embryonic period?
36-42
Characteristic feature: Pigmentation of retina visible; digital rays separate; nipples and eyelids formed; maxillary swelling fuse with medial nasal swellings as upper lip forms; prominent umbilical herniation - what days of embryonic period?
43-49
Characteristic feature: Limmbs long, bent at elbows, knees; fingers, toes free; face more humanlike; tail disappears; umbilical herniation persists to end of third month - what days of embryonic period?
50-56
