Embryology Exam 3 (learning objectives) Flashcards
describe results of removing part of a limb primordium
the remaining half will form a complete limb
describe the results of splitting a limb primordium into two halves and preventing from fusing
each half will form a normal limb
describe result of superimposing two equivalent limb discs
one limb will form
distinguish between limb field and limb disc
limb disc: actual primordium for the limb
limb field: region around the disc, can give rise to the limb if disc is removed. if the limb field is removed, no limb will form
describe the role of Tbx4 in limb development
initiates future hindlimb development (initial initiator)
describe the role of Tbx5 in limb development
initiates future forelimb development (initial initiator)
describe the role of Pitx-1 in limb development
initiates future hindlimb development
describe the role of Gli-3 in limb development
fix anterior of anterior-posterior axis
describe the role of Hand 2 in limb development
fix posterior of anterior-posterior axis
describe the role of Fgf-8 in limb development
after initial initiation from Tbx5 or Tbx4, the mesoderm releases FGF-10 to the ectoderm
describe the role of FGF-10 in limb development
after ectoderm receives FGF-10 from mesoderm, the ectoderm releases FGF-8 to the mesoderm
what are the 3 axes of the vertebrate limb
dorsoventral, anterior-posterior, proximodistal
what are the 3 axes of the vertebrate limb
describe results of transplanting limb disc on opposite side and rotating limb disc 180 degrees
dorsoventral, anterior-posterior, proximodistal
transplanting a limb disc to the opposite side resulted in normal limb except anterior posterior axis is reversed
rotating the limb disc 180 degrees resulted in a normal limb forming but AP and DV are reversed
explain the contributions of each of the following experiments to our understanding of how these axes are established: Slack, Riddle
Slack: transplanted a portion of flank tissue from posterior of the limb disc to anterior of the limb disc which resulted in a limb with two posterior halves arranged in mirror fashion. he concluded that the posterior region (he called the posterior organizing region) organized the posterior edge of the disc by setting up a gradient of a diffusible substance. it was later found to be retinoic acid
Riddle: discovered that retinoic acid is not the morphogen by is capable of activiating sonic hedgehog (shh) gene which then expresses what might be the actual morphogen, this region of cells in birds is called the ZPA (zone of polarizing activity)
describe the signaling pathways and molecules that help to establish the asymmetry of vertebrate limb development
Hoxb8: ZPA will be positioned at highest concentration, expression is induced by retinoic acid
sonic hedgehog: produced by ZPA, maintains structure and function of AER (apical ectodermal ridge), induces expression of gremlin
gremlin: inhibits BMP-2 which inhibits FGF-4 and AER and inhibits Gli-3 in posterior part of limb bud
Gli-3: in anterior part of limb bud, inhibits expression of shh
describe the role of AER in limb development and its relation to the underlying mesoderm
the AER is located at border between dorsal and ventral ectoderm
it interacts with underlying limb bud mesoderm and promotes outgrowth of limb bud via FGFs and Wnts
(the limb bud mesoderm is more involved in the determination of actual limb bud morphology)
describe the role of Hox genes in the patterning of the limb
Hoxd gene expression is involved in pattern formation of proximodistal limb axis
describe the relationship of Msx expression to the distal mesesnchyme
cells in the distal limb bud express Msx-1
describe the origin of the limb bud mesenchyme
lateral plate mesoderm
mesenchym destined to become limb muscles migrate from somitic ventral dermomyotomes
describe the roles of Wnts, BMPs, and ihh in the mesenchymal cell condesations
overlying ectoderm of the limb bud secretes Wnt-71 which restricts cartilage formation to central core of limb bud
mesenchymal pre-cartilage expresses BMP-2 and BMP-4
BMP-3 is expressed later in the cartilage
BMPs are later restricted to perichondrial cells
cartilage cells begin to hypertrophy and express ihh which may induce expression of BMP-6
describe the stages in joint formation and the roles of noggin and BMP
limbs form as precartilaginous rods which requires BMP, Noggin inhibits BMP in regions of future joint cavity, cell necrosis occurs at region of joint cavity which is then filled with loose connective tissue
describe the sequential steps in limb muscle formation, including the roles of c-met, Pax-3, N-cadherin, Wnt-6, and Tcf-4
proximal cells of limb bud produce scatter factor
premuscle cells in the somite express c-met (receptors for scatter factor) which then migrate to limb bud and express Pax-3 and N-cadherin
Wnt-6 (expressed by limb bud ectoderm) differentiates premuscle cells into muscle in the limb bud
they form into two muscle masses- flexor and extensor muscles
CT secretes TCg-4 which determines muscle morphology
name the three major vertebrate limb plexuses
cervical, brachial, lumbar
in humans at what point in development do motor neurons emerge from the spinal cord
5th week
describe the interactions of AER and limb bud mesoderm and the experimental evidence related to this relationship
instructive induction, the mesoderm instructs the AER ectoderm, mesoderm produces an apical ectodermal maintenance factor (AEMF) which maintains the AER in a healthy state. AER maintains the mesodermal cells below it in a labile and mitotic state, if either are removed growth will cease
describe the pattern of innervation of the dorsal and ventral muscle masses and the anterior and posterior muscles derived from these masses
ventral muscle mass: axons originating from medial locations in the spinal cord
dorsal muscle mass: axons originating from lateral locations
anterior muscles: axons originating anteriorly from spinal cord
posterior muscles: axons originating more posteriorly from the spinal cord
be able to describe each of the historical experiments leading to hypotheses on motor axon guidance
spinal nerves leading to limbs are larger than other spinal nerves
if forelimb is removed, nerves to the brachial plexus remain smaller/thinner
if additional limb is transplanted then nerves increase in thickness
if forelimb is removed before brachial nerve outgrowth and transplanted near the original location, brachial nerves will deviate from original path and toward transplanted limb
if addition limb is transplanted into immediate vicinity of host limb brachial nerves develop additional branches to lead to the additional limb
if blocked by an obstacle, the nerves can go around itand still reach destination
if obstacles or distance of transplant are too great the nerves fail to be attracted to limb, other local nerves grow into the limb but cannot provide limb function
fore limb and hindlimb are interchangeable bu transplant
if eye is transplanted where limb is removed brachial nerves reach out to eye but do not connect (outgrowth is non specific)
describe the vascularization process of limbs
from endothelial cells of aorta, cardinal veins, and angioblast arise a fine capilary network, central artery forms within the meshwork, cappilaries connect central artery to marginal sinuses below the AER, blood in sinuses drains via peripphreal venous channel,
identify the site of origin of neural crest tissue
lateral margins of the neural plate (originally epithelial and then trandform into mesenchymal cells)
describe the inductive process for neural crest from non-neural ectoderm and from mesoderm; identify roles played by BMP, Wnt, Gbx-2, Snail-1, Sox-9, and Snail-2
BMP and Wnt: induce from non-neural ectoderm
FGF-8 and Gbx-2: induce from mesoderm
Snail-1 and Sox-9: specification
Snail-2: emigration
what role do cadherins and other CAMs play in the epithelial-mesenchymal transformation? what role do the following play: SNail-1, Snail-2, and Foxd3
cadherins and other CAMs form the tight junctions
Snail-1, Snail-2, and Foxd3 allow cells to break free
describe the three migratory pathways and state which type of migratory substrate is preferable
ventral/symoathoadrenal: first emigrating cells
ventrolateral: second wave of emigrating cells
dorsolateral: last wave of emigrating cells
basal lamina is preferred substrate
describe the relationship between the timing of neural crest cell migration and the specific migratory pathway
first emigrating cells: ventral/symoathoadrenal path
second wave of emigrating cells: ventrolateral path
last wave of emigrating cells: dorsolateral
what role do the following play in neural crest cell migration: Robo/Slit, Neuropilin/Semaphorin, Ephrin/Eph
these are ligand/receptor pair guidance molecules
list the major neural crest cell divisions
trunk neural crest: sympathoadenal lineage, sensory lineage, melanocyte lineage cranial neural crest circumpharyngeal neural crest cardiac neural crest vagal crest
describe and trace the three migration pathways of the trunk neural crest
symoathoadrenal: follows intersomatic blood vessels around and between somites
ventrolateral: neural crest cells enter and pass through anterior sclerotome compartments. repulsed from posterior compartment by interaction of semaphorinA3F and neuropilin-2. passage is facilitated via thrombospondin
dorsolateral: migrate just beneath ectoderm
what role do Dickopf-1 and Hox genes play in origin of cranial neural crest
Dickkopf-1 inhibits neural crest cells from arising anterior to diencephalon. cells arising from diencephalon posteriorly through R3 do not express Hox genes, cells from R4 and posteriorly do express Hox genes
describe the origin and migration pathways of each of the following neural crest cell divisions and list the fate of the cells taking each of these pathways: cranial neural crest: circumpharyngeal neural crest, cardiac neural crest, vagal crest
circumpharyngeal neural crest: arises from somites 1-7. circumpharyngeal ridge- arc-shaped aggregation of cells passing behind 6th pharyngeal arch, cells migrate ventrally and then cranially to provide pathway for CN CII and related musculature. most neural crest cells from somite levels 1-3 pass into pharyngeal arches 4 and 6 or form cardiac crest. neural crest cells from somite levels 1-3 + 4-7 make up vagal crest and form parasympathetic innervation for digestive tract
describe the lineage of the 3 migration pathways
sympathoadrenal: cells in this pathway give rise to adrenal chromaffin cells, adrenergic sympathetic nerons, cholinergic sympathetic neurons
ventrolateral (sensory): dorsal root ganglia, schwann cells
dorsolateral (melanocyte): melanocytes
describe the origin and migration pathways of the following neural crest cell division and list the fate of the cells taking this pathway: cranial neural crest: circumpharyngeal neural crest
circumpharyngeal neural crest: arises from somites 1-7. circumpharyngeal ridge- arc-shaped aggregation of cells passing behind 6th pharyngeal arch, cells migrate ventrally and then cranially to provide pathway for CN CII and related musculature. most neural crest cells from somite levels 1-3 pass into pharyngeal arches 4 and 6 or form cardiac crest. neural crest cells from somite levels 1-3 + 4-7 make up vagal crest and form parasympathetic innervation for digestive tract
describe the origin and migration pathways of the following neural crest cell division and list the fate of the cells taking this pathway: cranial neural crest: vagal crest
arises from circumpharyngeal crest and exits from levels of somites 1-7
these neural crest cells mostly are associated with the gut enteric system (parasympathetic)
other contributions include: dorsal root ganglia and a few sympathetic ganglia
what role do Slit-2 and Robo play in neural crest cell division
SLit-2 is expressed in the messentary near the gut and prevents neurons from crossing the midline of the ventral nervous system
trunk neural crest cellos express Robo(Slit receptor) and avoid cells that express SLit-2. Vagal crest cells do not express Robo and are able to cross to the gut wall
Waardenburg’s syndrome
Due to Pax-3 mutations
involves pigmentation defects including a white stripe in the hair, deafness, cleft palate, ocular hypertelorism, and sometimes hypoplasia of limb muscles
CHARGE
Coloboma, heart disease, atresia of nasal choanea, retardation of development, genital hypoplasia in males, and anomalies of the ear
autosomal dominant genetic disorder. causes by mutation of the CHD7 gene on chromosome 8
the mechanism suggested are 1. deficiency in migration of cervical neural crest cells into the dricatives of the pharyngeal pouches and arches. 2. deficiency of mesoderm formation. 3. defective interaction between neural crest cells and mesoderm resulting in defects of blastogenesis
DiGeorge syndrome
due to deletion in chromosome 22
hypoplasia, reduced thymus, thyroid, and parathyroid function
cardiovascular defects including persistent truncus arteriosus
related to defects in neural crest associated with 3rd and 4th pharyngeal arches
now referred to as Q22
define ectodermal placode
local thickening in the embryonic ectodermal layer that generally constitutes a primordial group of cells from which a sense organ or ganglion will develop
list major placodes that give rise to major sense organs
hypophyseal placode: Ratheke’s pouch –> Adenohypophysis
olfactory placodes: olfactory epithelium
lens placodes: lens
trigeminal placodes: cranial nerve V
otic placodes: inner ear
epibranchial placodes: sensory neurons supplying visceral structures (CN VII, IX, X)
use fig 13.2 and lecture notes to indicate the role of various signaling pathways, transcription factors, and genes in the formation of the normal eye
see book
define and describe the optic stalk, choroid fissure, and hyaloid artery in relation to the formation of the normal eye
optic stalk: lateral evagination of the diencephalon which enlarges distally to form the optic vesicle
choroid fissure: groove alongside of the cuplike structure formed by optic vesicle invagination, this groove is continuous with groove in optic stalk
hyaloid artery: uses choroid fissure and optic stalk to pass into the posterior chamber of the eye
be able to diagram/describe stages of normal eye formation and inductive events that occur during normal eye formation
insert photo of diagram
what is the relationship of Pax6 in the formation of the eye in drosophila and in mammals
in drosophila: turns on gene sequence needed for eye development (“master gene for eye development”) and absense of gene leads to eyeless mutant
in mammals: absence of gene results in early optic vesicle formation, but the rest of eye formation does not occur. prospective lens ectoderm does not respond to induction by optic vesicle
how do high and low concentrations of Shh affect expression of Pax6 in the formation of the optic stalk and guidance of ganglion cell axons
high concentrations of Shh inhibit expression of pax6
low concentrations of Shh in distal optic stalk permits expression of Pax6 and development of optic vesicle (leading to formation of retina)
high concentrations of Shh in proximal optic stalk decreases expression of Pax6 and induces expression of Pax2 (this will provide guidance of axons of ganglion cells from retina)
describe the inductive interactions leading to the formation of the lends and the signaling molecules, transcription factors and genes involved
insert photo
describe the formation of the lens, including the role of mitosis and the factors involved
lens nucleus is formed by lens fibers derived from inner pole of lens vesicle
lens fiber cells are postmitotic, elongated cells made up of crystalline proteins alpha, beta, and gama
rest of lens fiber cells are derived from mitotic activity of cuboidal cells of anterior lens epithlelium
retinal secretions, especially FGF, accumulate in the vitreous humor and stimulate formation of lens fibers
what role does Pax6 play in corneal formation? what is the primordium of the cornea and what induces the primordium to form the cornea
Pax6 is necessary for corneal induction
underlying lens vesicle induces overlying ectoderm to transform from bilayered epithelium to transparent multi-layered structure
what is the role of neural crest cells, TGF-B, semaphorin 3A, neuropilin-1, and hyaluronic acid in the formation of the cornea
in text book
describe the fixation of retinal polarity. what is the order in which the axes are fixed. what factors and gradients are involved in the fixation of the axes?
the nasotemporal (anterior-posterior) axis is fixed first: the nasotemporal axis is established by gradients composed of ephrins and receptors, ganglion cells differentiate first and bipolar neurons and cones differentiate last, the spread of the gradient is from the center to periphery, Notch genes expression keeps cells from differentiating too early
the dorsoventral axis is fixed second: the dorsoventral axis is established by the antagonistic actions of Shh and BMP, along with ventropin, Tbx-5, pax2, and Vax2
describe sequentially the stages in the formation of the cornea
pax6 is necessary for induction
underlying lens vesicle induces overlying ectoder, to transform from milayered epithelium to transparent multi-layered structure
anophthalmos
absence of an eye due to RAX mutation may be result of lack of formation of optic vessicle sinc it is the inductive trigger for subsequent eye develpment
microphthalamos
can range from an eyeball that is slightly smaller than normal to one that is almost vestigial
common component of rebulla syndrome
coloboma
nonclosure of choroid fissure of the iris during sixth or seventh week of pregnancy
individuals are sensitive to light since pupil cannot contract properly
list and describe the components of the pharyngeal region
pharyngeal pouches: 4 pairs of lateral endodermal outpockets from the foregut
thyroid diverticulum: ventral midline endodermal outpocketings from floor of forefut between pharyngeal pouches I and II
pharyngeal grooves: four pairs of ectodermal inpocketings that lie opposite to the associated pharyngeal pouches
pharyngeal (brachial) arches: five pairs of mesenchymal masses that lie between the pharyngela pouches
aortic arches: single artery within each pharyngeal arch that connects the ventral aorta to the dorsal aorta
describe the derivation of pharyngeal tissues
pharyngeal arch derived musculature: mesoderm from somitomeres
rest of pharyngeal mesenchyme: from neural crest
describe the roles of the neural tube and paraxial mesoderm as signaling centers. what gene group is involved
basic signalling centers that involve Hox gene expression
signal segmentation of neural crest to give rise to neural crest tissue
what roles do retinoic acid, otx-2, and fgf-8 play in patterning of the pharyngeal endoderm
patterning is heacily based on exposure to retinoic acid, first pouch is not dependent of retinoic acid but is dependent on Otx-2. second pouch is somewhat dependent on reinoic acid. pouches 3 and 4 are heavily dependent on retinoic acid. Signals the prepatterning of cranial ectoderm via FGF-8
what roles do retinoic acid, otx-2, and fgf-8 play in patterning of the pharyngeal endoderm
patterning is heacily based on exposure to retinoic acid, first pouch is not dependent of retinoic acid but is dependent on Otx-2. second pouch is somewhat dependent on reinoic acid. pouches 3 and 4 are heavily dependent on retinoic acid. Signals the prepatterning of cranial ectoderm via FGF-8 (not dependant on neural crest)
what signaling mechanisms are involved in the patterning of the pharyngeal arches
depends on signals from pharyngeal pouches. not dependent on neural crest. Dlx genes heavily influence dorsoventral patterning. arch I ectoderm uses EDn-1 to signal migrting neural crest cells and heavily influences the development of arch I
explain how fgf-8 plays a role in the development of the cranial ectoderm
it is prepatterned by FGF-8 signals from pharyngeal endoderm
describe the frontonasal zone and explain how SHH and FGF-8 are involved in the establishment of this zone
it is induced by Shh from forebrain, is an ectodermal signal center involving the establishment of a dorsoventral gradient of FGF-8 (more dorsal) and Shh (more ventral)
involved in shaping tip of snout
list and describe the facial primordia
frontonasal prominence
nasomedial processes
nasolateral processes
name the pharyngeal arch related to the formation fo the jaws and llist and describe the primordia for the jaws. What role does endothelin-1 play
from first pharyngeal arch
maxillary processes: consists of neural crest derived from forebrain and midbrain
mandibular processes: consists of neural crest derived from midbrain and hindbrain
subdivision of first arch into upper and lower jaaw primordia is dependent on endothelin-1
describe the autostylic, holostylic, and craniostylic types of jaw articulation and give representative examples. compare with the mammalian jaw articulation pattern. what is meckel’s cartilage and what are its derivatives? tell the fate of the quadrate, articular, and hyostylic components in the mammalian jaw development
autostylic: amphibian
carniostylic: reptile
hyostylic: shark
mammalian: synovial joint with an articular disk. involves early expression of barx-1. temporal bone articulates with mandibular condyle.
Meckel’s cartilage: slender, elongated cartilaginous rod that develops within the first arch, its derivatives= articular and quadrate
quadrate bone moves into middle ear and becomes incus
articular bone moves into middle ear and becomes the malleus
development of nasolacrimal groove, nasolacrimal duct, lacrimal sac, philtrum, premaxillary portion of upper jaw, and primary palate
between the maxillary process and nasal primordium is nasolacrimal groove. the floor of nasolacrimal groove thickens to form epithelial cord which detaches and canalizes to form nasolacrimal duct and lacrimal sac
the median palatine process forms a triangular bony structure- the primary palate
when does the palate form during development and what are its primordia
palate forms between 6 and 10 weeks of development
median palatine process and lateral palatine process
describe the signaling pathways for the developing palatal shelves
FGF-10 produces in the mesenchyme of the forming palatal shelf is bound to an FGF receptor in the ectoderm which stimulate release of shh from the ectoderm. shh causes release of BMP-2 in the mesenchyme. BMP-2 and Msx-1 which interacts with BMP-4, stimulate proliferation of the mesenchymal cells of the palatal shelf and its resultant growth.
review from text vomoeronasal organs
lined with modified olfactory epithelium
are involved with olfaction of food in the mouth or sexual olfactory stimuli
review from text embryonic basis for kallmann’s syndrome
anosmia and hypogonadotropic hypogonadism
how does the composition of the basal lamina affect the growth potential of the region, especially with regard to collagen and proteoglycan
around the stalk and in clefts, the basal lamina contains types I and IV collagen and a basement membrane-1 proteoglycan. these components are not found in the regions of the lobules that undergo further growth. basal lamina in growing regions lose the collagens and proteoglycans that are associated with stable structures.
how does local contraction of epithelial microfilaments affect branching
branching is associated with the local contraction of ordered microfilaments within the apices of epithelial cells at the branch points
describe the roles of Pax-6, FGF-6, and retinoids in the development of the nose and olfactory apparatus
Pax-6 and retinoids develop nasal placodes
FGF-8 is stimulated by retinoids and stimulate proliferation of mesenchyme in nasaomedial and nasolateral processes
list and stages describe in tooth development
dental lamina: c-shaped bands of oral ectoderm overlying neural crest mesenchym
tooth bud: epithelial downgrowth overlying neural crest mesenchyme and marking position of a single tooth
cap stage: inverted cup-shaped layer of ectoderm capped by stellate reticulum and covering a mass of mesenchyme= dental papilla
bell stage: cone-shaped premordium covered by stellate retiuclum overlying the enamel organ
dental sac: condensation of mesenchymal cells around the developing tooth which will form the cementum and periodontal ligament
outline and describe tissue interactions and signaling pathways in tooth development
Pitx-2 outlines first the entire ectodermal dental field
Dlx-1 and Dlx-2 are expressed in maxillary arch and in proximal part of the mandibular arch
Barx-1 is induced by FGF-8 in proximal ectoderm of the mandibular process
FGF-8 acts proximally to restrict Barx-1 and Dlx-2 to guide the molar producing domain, and BMP-4 acts distally to activate Msx-1 and Msx-2 in guiding formation of incisor teeth
islet-1 is expressed only in the oral surface ectoderm only where incisors will form
Pitx-1 is expressed only in the molar region
Osr-2 inhibits BMP-Msx and consequently tooth formtation on lingual side of jaw
cleft lip
results from lack of fusion of the maxillary and nasomedial processes
cleft palate
results from incompleate or absent fusion of the palatal shelves
highly associated with MSX1 mutations
holoprosencephaly
defective formation of the forebrain which manifest externally as facial malformations, typically reduction in tissue of the frontonasal process. cyclopia in extreme cases. root cause is inability of prechordal plate and anterior endoderm to secrete Shh and other factors requiredd for induction and early development of the ventral forebrain
hypodontia
congenital absence of teeth
can be caused by mutations in MSX1, EDA, AXIN2, PAX9, and WNT10A
hyperdontia
exccessive number of teeth
caused by mutations in TRPS1
microdontia
small teeth
caused by mutations in MSX1
dentinogenesis imperfecta
caused by mutations in DSPP which causes mutations in type I collagen genes
teeth appear blue-gray or amber brown or opalescent
amelogenesis imperfecta
effect enamel development and result in abnormalities in its amount and composition
mutations include ENAM, AMEL, DLX3, and P63
list the components of a pharyngeal arch
artery (aortic arch), cranial nerve, and skeletal component
identify the main organizer of pharyngel arch development and explain the roles of Hox genes, Tbx-1, and FGF-8 in pharyngeal arch development
main organizer= foregut endoderm
craniocaudl segmentation of arches is determined by Hox genes
first arch is independent of Hox expression
arches I and II require Hoxa-2 and Hoxa-3 expression
pharyngeal endoderm releases TBx-1 which stimulates FGF-8 which induces arch formation
for each arch I through IV list the aortic arch, cranial nerve, muscle, and skeletal derivatitives
I: maxillary artery, CN V (trigeminal), muscle of mastication, tensor tympnani, mylohyoid, tensor veli palatini, anterior belly of digastric; malleus, incus, sphenomandibular ligament, Meckel’s cartilage, tympanic ring
II: hyoid artery, stapedial artery; CN VII (facial); muscles of facial expression, stapedius, stylohyoid, posterior belly of digastric; stapes, styloid process, stylohyoid ligament, lesser horn of hyoid, part of body of hyoid
III: internal artery; CN IX (glosso-pharyngeal); stylopharyngeus; greater horn of hyoid, part of body of hyoid
IV: right subclavian artery and aorta; CN X (vagus); pharyngeal and laryngeal muscularture; largyngeal cartilages
list the derivatives for each pharyngeal groove and pouch
1st groove: external auditory meatus
2nd and 3rd grooves: cervical sinus (temporary)
1st pouch: tympanic cavity of middle ear and auditory tube
2nd pouch: fossa for palatine tonsils
3rd: inferior parathyroid and thymus
4th: superior parathyroids, postbrachial (ultimobranchial)body
describe the origin of the thyroid gland and explain the role of Hhex, Nkx2-2, Pax-8, and Foxe-1
the thyroid begins as a node of cells located on the ventral surface of the pharynx between the first and second pairs of pharyngeal arches
node of cells is induced by underlying mesenchyme
the cells that make up the thyroid anlage (node of cells) express transcription factors Hhex, Nkx2-1, Pax-8, and Foxe-1
describe the origin of the hypophysis and explain the roles of BMP-4 and FGF-8
the infundibular process is a ventral downgrowth from floor of diencephalon
the rathke’s pouch is an upgrowth from roof of stomodeum which is stimulated by BMP-4 and FGF-8
both extend and attach
describe the origin of the tongue and list the primordia
lateral lingual swelling (ventral area of 1st pair of pharyngeal arches), tuberculum impar (ventral swelling between 1st and 2nd pair of arches), copula (ventrl swelling between 2nd and 3rd pairs of arches)
be familiar with the common malformations that arise from pharyngeal primordia (clinical correlatioin 14-3)
Pierre robin syndrome: extreme micrognathia (small mandible), cleft palate, and defects in the ear
agnathia: lower jaw basically fails to form and ears remain in ventral cervical region and may join in the ventral midline
treacher collins syndrome: TCOF1 gene operating the Treacle protein is affected which affects the survival and proliferation of cranial neural crest cells. hypoplasia of mandible and facial bones, malformations in outer and innter ear, high or cleft palate, lower eyelids
cyst: completely enclosed epithelial lined cavity
sinus: closed on one end and open to the outside or to he pharynx
fistula: epithelially lined tube that is open in both ends
ectopic thyroid tissue: abnormal structures along the pathway of the thyroglassal
ankyloglossia: regression of the frenulum (thin midline tissue that connects the ventral surface of the tongue to the floor of the mouth) mutation in TBX22
macroglossia and mircroglassia: hyperplasia and hypoplasia of lingual tissue
DiGeorge’s syndrome: cranial neural crest deficieny, defects and hypoparathyroidism. failure of differentiation of thymus and parathyroid gland. malformation in 1st arch structures and defects in outflow tract of the heart
list and describe the factors necessary for the patterning of the anterior and posterior domains of the gut
nodal= anterior
FGF-4= posterior
foregut: inhibition of Wnt and expresses Sox-2, Hhex, nad Foxa-2
hindgut: FGFs, BMPs, Wnts, Retinoic acid; express: Cd-2–> Hox gene expression in midgut and hindgut, Pdx-1 –> sets apart midgut; FGF-10 –> establishes cecum
be familiar with the steps in the formation of the esophageal wall
5 weeks: circular layer of smooth muscle visible
8 weeks: longitudinal layer of smooth muscle visible
early esophagus is a stratified columnar epithelial tube
lumen of esophagus is partially ocluded by the epithelium
large vacuoles appear
lumen recanalizes
multilayered ciliated columbar epithelial lining
16 weeks: epithleium replaced with stratified squamous epithelium
what roles do Shh, patched, and BMP-4 play in esophageal formation
shh: refulates radial orginization. patched = shh receptor
shh inhibits formation of smooth muscle in submucosal layer
shh acts through BMP-4
describe the roles played by Hoxa-5, Barx-1, and FGF-10 in the formation of the stomach
Hoxa-5 and Barx-1 inhibit posteriorizing effects of Wnt
FGF-10 strong in the posterior
explain how the omental bursa and epiploic foramen form
omental bursa: during rotation of stomach the dorsal mesogastrium is carried with it
describe the formation and factors involved in the development of the pyloric sphincter
directed by Sox-9 and Nkx-2.5 whose expression is stimulated by BMP-4
Hox genes are also needed
name the two reference points used to understand and describe the coiling of the intestine
yolk stalk: extends from floor of midgut to yolk sac
superior mesenteric artery: serves as pivot point
what effects does the cooiling of the intestine have on the change in position of the colon
when the small intestine enters it pushes the colon to the left side of the peritoneal cavity
what causes the intestine to undergo the characteristic coiling
rapid growth as a result of FGF-9
describe the portioning of the cloaca
the combined ingrowth of the lateral ridges and growth of the urorectal septum toward the cloacal membrane divide the cloaca into the rectum and urogenital sinus
the area where the urorectal septum and lateral mesodermal folds fuse with the cloacal membrane becomes the perineal body which represents the partition between the digestive and urogenital systems
list the three major phases involved in the histogenesis of the intestinal lining
- an early phase of epithelial proliferation and morphogenesis
- an intermediate period of cellular differentiation in which the distinctive cell types characteristic of the intestinal epithelium appear
- a final phase of biochemical and functional maturation of the different types of epithelial cells
what role do Foxa-2 and GATA-4 play in the anterior regions of the endoderm
restrict overlying endoderm so it only forms the appropriate epithelial cell types which is essential for formation of anterior regions of endoderm
describe the role of Wnt and BMP in the formation of the intestinal crypts and intestinal stem cells
intestinal cypts form at the bases of the cilli
toward the bottom of the crypts are intestinal stem cells which in response to Wnt have a high rate of mitosis
toward the top of the crypt is BMP which counteracts Wnt and thus keeps proliferation deep in the crypt and it facilitates cellular differentiation
meckel’s diverticulum
a blind pouch on antimesentric border of ileum. it represents the persistent proximal portion of the yolk stalk
usually asymptomatic but can occasionally become inflamed or result in ulceration
volvulus
intestine rotates about ligament connectinh meckel’s diverticulum to the umbilicus
vitelline fistula and duct cyst
direct connection between intestinal lumen and outside of the body via umbilicus
cyst along length of vitelline ligament
hirschsprung’s disease
aka aganglionic megacolon
great dilation of certain segments of the colon
absence of parasympathetic ganglia in the affected walls of the colon
imperforate anus
can range from simple membrane covering of anal opening to atresia of various lengths of the anal canal, rectum, or both
absence of anal opening
hindgut fistula
links the patent portion of hindgut to another structure in the region of the original urogenital sinus region
common types connect the hindgut with the vagina, the urethra, or the bladder
