embryology exam 2 Flashcards
describe the development of the mesodermal germ layer and its division into paraxial, intermediate, and lateral plate mesoderm
epiblast –> bottle cells and spread laterally to form a layer between ectoderm and endoderm
paraxial: thick column closest and parallel to the notochord
intermediate : narrow column on other side of paraxial than notochord
lateral plate: thin plate lying next to the intermediate
what are the fates of each mesoderm layer
paraxial: segmented into somites
intermediate: urogenital system (kidney, gonads)
lateral plate: forms lining of body cavities and mesoderrm of most internal organs as well as limbs
describe the two mechanisms involved in somitogenesis
wavefront: increase in FGF-8 stimulates mitosis in mesenchymal cells in posterior primititve streak
increase in retinoic acid in the anterior opposes action of FGF-8, balance of retinoic acid and FGF-8 result in cellular determination towards somitogenesis. Mesp-2 present
segmentation clock: molecules in Notch expressed in oscillating expression on a time line. lunatic fringe: concentrated at future anterior border of somite, c-hairy: future posterior border, cells at anterior will express Eph A (receptor) and posterior cells will express Eph B (ligand) which will allow fissure between adjacent somites
difference between somitomere and somite
somitomeres become somites which are more dense blocks of mesoderm that form along the notochord
what is the relationship of ephrin B, Wnt-6, snail, and paraxis to somite formation?
dorsal somites release Wnt-6 which activates paraxis which inhibitis snail expression converting the mesenchymal cell to an epithelial cell = somitocoel formation
relate Shh, noggin, Pax1, and Pax9 to the formation of the sclerotome
notochorde releases Shh and noggin which activate Pax1 and Pax 9 genes in ventral part of somite which forms sclerotome
list the derivatives from the final subdivisions of the somites
dermomyotome: dorsal lateral somite, becomes axial dermis and skeletal muscle
syndetome: cells between myotome and scleretome become tendons
scleretome: ventral medial somite, becomes vertebral column
list the factors involved in the formation of the intermediate mesoderm and list the derivatives
BMP + activin (Hox-4 and Hox-11 contribute to cranial and caudal extent)
derivatives: pronephros and mesonephros aka. kidney
differentiate between the intraembryonic coelom and the extraembryonic coelom
intraembryonic coelem is made from the lateral plate mesoderm and becomes the pericardial cavity
extraembryonic coelom is the embryonic sac
distinguish between somatic and splanchnic mesoderm
divded by the intraembryonic coelem
somatic: below/ventral to the endoderm; bones, ligaments, connective tissue, blood vessels
splanchnic: above/dorsally the endoderm; forms heart, visceral pericardium, blood vessels, smooth muscle of GI and respiratory
describe the formation of the lateral plate mesoderm and distinguish between the somatopleaure and the spanchnopleure
somatopleaure: inside the tube mesoderm + endoderm
splanchnopleaure: outside the tube mesoderm + ectoderm
describe the early formation of the heart
cells migrate through primitive streak: anterior = outflow track, middle= ventricles, posterior= atria. which all form the cardiac crescent
cardiac tubes form from the crescent and fuse: outer layer= myocardium, inner layer= endocardium.
list the genes important in early heart formation
Nkx2-5, MEF2, GATA4
expressed by cells of cardiac crescent
what is the secondary heart field
splanchnic mesoderm
which signaling factor is necessary for the formation of endoderm
nodal
describe the relationship of the expression of nodal and FDF-4 to the establishment of the anterior-posterior gradient
high nodal= anterior
low nodal + FGF-4 = posterior
describe the role of Cdx-2 in the formation of the hindgut and foregut
Cdx-2 is expressed in the posterior gut- promotes hindgut development and supresses formation of anterior gut structures
describe the relationship of Shh and BMP-4 in the formation of the anterior and posterior intestinal portals
expression of Shh followed by BMP-4 in posterior intestinal portal
expression of Shh in anterior intestinal portal
list each of the three major circulatory arcs in the 4 week human embryo and the components and function of each
vitelline arc: carries blood from embryo to yolk sack and back
allantoic arc: umbilical, nurishment, waste disposal, and blood oxygenation
embryonic arc: aorta, veins, atrium, ventricle
list and describe the four extraembryonic tissues and the germ layers fromwhich they are derived
amnion: inner cell mass, ephiblast derivative
yolk sac: inner cell mass, hypoblast derivitave
chorion: fetal maternal interface
allantois: inner cell mass, interfaces with placenta via umilical chord
list the two trophoblastic derivatives that comprise the fetal-maternal interface
placenta
chorion
explain the function of the amnion
buffer against mechanical injury, accomodates growth, allows normal movements, protects fetus from adhesions
describe the following conditions and indicate what circumstances these are often associated: hydramnios, oligohydramnios
hydramnios: excessive amniotic fluid >2000mL (normal = 500-1000 mL)related to esophageal atresia or anencephaly- gross defects of the head, inability to swallow
oligohydramnios: too little amniotic fluid <500 mL, associated with bilateral renal agenesis (absent kidneys) could be consequence of preterm rupture of amniotiv membrane
describe the development of the allantoic vessels and the relation of the allantois to the urinary bladder and the median umbilical ligament
develop in mesoderm of allantois, used for respiratory organ and urinary waste, forms urinary bladder and umbilical ligament
what tissue in the mature placenta directly interfaces with the maternal uterine connective tissue
chorion/chorionic platw
list and describe the layers from the amnion outward to the outer layer of the endometrium
amnion-chorionic cavity- chorionic plate- trophoblastic covering (outer cytotrophoblastic shell)
what is the fate of the decidua capsularis
overlies the embryo and its chorionic vesicle
describe/trace the maternal fetal blood flow pattern and indicate where the exchange of material occurs
maternal blood enters intervillous space from spiral arteries where materials are exchanges in the lacunae, the fetal capillaries in villi pick up the material, the maternal blood then returns to maternal veins in decidua basalis
describe fetal alcohol syndrom
excessive alcohol ingestion by mother leading to birth defects
describe the following pathological conditions and relate to the structure of the placenta: hydatidiform mole, placenta previa. what is the genetic basis for the hydatidiform mole?
hydatidiform mole: chorionic villi have nodular swellings like bunches of grapes and will not have vascularization, embryo is either absent or non viable; paternally derived: 46, XX
placenta previa: abnormal implantation site in uterine cavity, hemorrhge is common
list functions of placent
diffuse oxygen and CO2
diffuse foodstufss
excrete waste
compare the early placenta with the late placenta
early placenta: thick, low permeabiity, small surface are, miniscule total diffusion conductance
late placenta: thin, high permeability, large surface area, lare increase in placental diffusion
describe the oxygen pressure gradient (near end of pregnancy) and explain why adequate oxygenation can occur with such a low pressure gradient
p02 mother: 50 mmHg
pO2 fetus: 30 mmHg
diffusion pressure= 20 mmHg, which is low but adequate oxygenation can still occur because: fetal hemoglobin has a higher affinity for oxygen, fetal blood has 50% greater hemoglobin concentration than maternal, and Bohr affect
describe the Bohr effect and explain what is meant by the double Bohr effect
bohr affect: low PCO2 blood has higher affinity for oxygen. both mothers is high in CO2 and baby’s is low in PC02 so this is a double Bohr affect
describe the timing, method of secretion, targets, and effects of human chorionic gonaotropin
timing: measurable 8-9 days aftr ovulation, max at 10th-12th week of pregnancy
method of secretion: secreted by syncytial trophoblasts into maternal fluids
effects: prevents involution of corpus leteum, causes CL to increase secretion of progesterone and estrogens, increase CL growth, exerts interstitial cell-stimulating effects on tests of male fetus (causes testosterone production until birth)
describe each of the four theories of why mother’s immune system does not recognize the fetus as foreign tissue
- lack of expression of major histocompatibility antigens by placenta components
- paralysis of mother’s immune system during pregnancy
3 . decidual immune barrier - inactivation of mother’s immune system components by molecules formed on fetal placenta surface
infectious agents that result in birth abnormalities
rubella, cytomegalic inclusion disease, herpes simplex, vricella-zoster, influenza, mumps
effects of thalidomide on birth abnormalities
thalidomide: limb defects, ear defects, cardiovascular anomalies
causes and symptoms of neotatal respiratory distress syndrome, hydrops, and eclampsia
neonatal respiratory distress syndrome: immaturity of the lungs due to premature birth
hydrops: accumulation of edema fluid in fetus during intrauterine growth, until recently most common cause was immune: hemolyric anemia (blood group incompatibility) ; nonimmune: cardiovascular defects such as congenital cardiac defects and arrhythmias as well as turner syndrome
preeclampsia: pregnancy induced hypertension, persistance blood pressure of 140/190, weight gain and edema
eclampsia: extremely serious, extremely high blood pressure, grand mal seizures or coma
prematurity and fetal growth restriction is the second most common cause of neonatal mortality. list major risk factors of prematurity
preterm premature rupture of placental membranes
intrauterine infections
uterine, cervical, and placental structural abnormalities
multiple gestation
describe the timing, method of secretion, targets, and effects of estrogen
timing: highest toward end of pregnancy
secreted by syncytiotrophoblast cells in placenta
functions: uterine enlargement, breast enlargement, growth of breast ductal structure, enlargement of maternal external genitalia, relaxation of pelvic ligaments
describe the timing, method of secretion, targets, and effects of preogesterone
secreted early in small quantities by corpus luteum and large quantities by placenta
functions: causes decidual cells to develop in the endometrium, decreases contractility of pregnant uterus, increases secretions of fallopian tubes and uterus, may work with estrogen to prepare breasts for lactation
describe the timing, method of secretion, targets, and effects of human chorionic somatomammotropin
secreted by placenta begining in 5th week of pregnancy
functions: causes decreased insulin sensitivity and decreased utilization of glucose by mother, general metabolic hormone
teratology
“the study of monsters”, study of confenital malformations
teratogen
agent that produces birth defects
malformation
primary errors of morphogenesis
disruption
disturbance in otherwise normal morphogenetic processes
deformation
disturbances in otherwise normal morphogenetic processes and are typically caused by abnormal biomechanical forces such as uterine constraint
dysplasia
abnormality of a tissue due to an abnormal intrinsic developmental process
sequence
series (cascade) of events triggered by one initiating factor
syndrome
a group of malformations of different structures due to a single primary cause but acting though multiple developmental pathways
association
a group of anomalies seen in more than one individual that cannot yet be attributed to a definitive cause
critical period
embryos are more susceptible to agents or factors causing abnormal development, between weeks 3 and 8
describe the source of dermal cells in various parts of the skin: dorsal , ventral , lateral, cranial, anterior neck, limb
dorsal: mesenchyme from dermatome
ventral and lateral: mesenchyme from lateral plate mesoderm
cranial and anterior neck: mesenchyme mostly from cranial neural crest
limb: lateral plate mesoderm
describe the signaling pathways leading to the differentiation of dermal cells
ectoderm releases Wnt which stimulates mesenchymal cells to develop tight junctions and become dermal cells
compare characteristics of dermal cells and mesenchymal cells
dermal cells are loosely aggregated, interconnected by tight junctions, secrete thin watery matrix rich in glycogen and hyaluronic acid
describe how recombination experiments between mesoderm and ectoderm, demonstrate instructive induction
instructive induction: dermis influences the development of epidermis and the derivitives and a reciprocal influence by the epidermis on the dermis
this was shown by separating them in experiment and neither of them differentiated
list commonalities in the development of epidermal derivatives
(hair, nails, mammary glands)
involve ectodermal-mesodermal interactions and inductions
begin as epidermal downgrowths into mesenchyme
ectoderm contributes to: hair follicle, hair shaft, sebaceous glands, nails, eponychium, hyponychium, secretory ducts and duct components
mesenchyme contributes to hair papilla, outer hair follicle, and arrector muscles
describe the adult hair cycle including the specific stages: anagen, catagen, telogen, and exogen
anagen: hair is actively growing (5-6 years)
catagen: (1-2 weeks) hair follicle regresses to only a fraction of its original length
telogen: (5-6 weeks) hair stops growing
exogen: hair is shed
explain the importance of hormones in the development of mammary glands
estrogen: stimulates duct growth
progesterone: stimulate formation of secretory alveoli
prolactin: milk, protein, and fat synthesis
oxytocin: milk letdown
describe the mesenchymal origin of each major part of the skeleton
mesodermal sclerotomes: vertebral column, ribs, sternum
lateral plate mesoderm: limb bones, girdles
head mesoderm: calcaria and base of skull
neural crest: facial bones
differentiate the Hox gene boundaries for the different regions of the vertebral column
occipital-cervical boundary: Hox 3 cervical-thoracic boundary: Hox6 Attached-floating ribs boundary: Hox9 thoracic-lumbar: Hox10 lumbar-sacral: hox 11 sacral-coccygeal: Hox13
describe results of experiments involving Hox gene knockouts (single gene, hox 10 paralog, hox 11 paralog, mutation of hox gene)
single Hox gene knockout: minor morphological effects
Hox10 paralog knock out: ribs form on all the lumbar and sacral vertebrae
hox 11 paralog knockout: sacrum doesnt form
mutant in hox gene: minor defect
describe the origin of the sternum
derived from lateral plate mesoderm, arises as a pair of cartilaginous bands
describe the origin of the clavicle
arise from neural crest, follows intramembranous pathway, one of the first bones to become ossified
describe/compare the subdivisions of the developing skull
neurocranium: surrounds the brain
viscerocranium: surrounds oral cavity and pharynx and upper respiratory
occipital sclerotomes: base of occipital bone
describe the generalized neurocranium/chondrocranium
cartilaginous: part of occipital, sphenoid, thmoid, parts of temporals
membranous: part of occipital, parietal, frontals, part of temporal
describe the generalized viscerocranium and the bones that develop from the viscerocranium
cartilaginous: pharynggeal arch I- meckels cartilage, malleus, incus; oharyngeal arch II- reichert’s cartilage, stapes, styloid
membraneous: part of temporal, zygomatic, maxillary, nasal, lacrimal, palantine, vomer, pterygoid plates, mandible, tympanic ring
define fontanelle
intersections between sutures where more than two bones meet, occupied by connective tissue
common pathway (bone/cartilage differentiation)
N-cadherin promotes mesenchymal cell condensation
TGF-beta stimulates synthesis of fibronectin and N-CAM
agreggated state of mesenchymal cells is stabilized
membranous bone pathway
Runx-2 and Osx
mesenchymal cells differentiate into osteoblasts
permanent cartilage pathway
mesenchymal condensation forms chondroblasts
sox-9 causes chondroblasts to secrete collagen II and catilage matrix, sox-9 is continually expressed in permanent cartilage
endochondral bone pathway
Runx-2, ihh, and BMP-6 induce this cartilage to undergo hypertrophy
hypertrophic cartilage cells secrete bone proteins and vascular endothelial growth factor
invading blood vessels erode the hypertrophic cartilage and bring in osteoblasts to replace cartilage with bone
describe each stage in the differentiation of skeletal muscle tissue
myogenic cells –> myoblasts –> myotubes –> muscle fibers
differentiate between primary and secondary myotyubes
primary: formed by fusion of earliest myoblasts, dofferentiation occurs before innervation
secondary: smaller than primary, formed later, presence of axons may be necessary for them to form,
describe the role of satellite cells
fuse with muscle fiber to provide growth, function as stem cells, replace damaged muscle
describe the role/function of each of the following myogenic regulatory factors: Myf-5, Pax-3, Pax-7, FGF, TGF-beta, MyoD, Myogenin, and Myf-6
FGF and TGF-beta: maintain myogenic cells in labile state
MyoD: able to convert non-muscle cells to cells capable of expressing muscle proteins
Pax-3, Pax-7 and Myf-5: can separately activcate MyoD causing myogenic cells to become myoblasts
Myf-6: leads to expression of myofiber genes
adult structures that develop from each region of the pentapartite brain
telencephalon: paleocortex, corpus stiatum, neocortex
diencephalon: epithalamus, thalamus, hypothalamus, infundibulum
mesencephalon: tectum, tegmentum, cerebral peduncles
metencephalon: cerebellum, pons
myelencephalon: medulla
describe the stages of the neural tube wall from that of a simple cuboidal epithelium to a stratified epithelium
early neural epithelium: simple cuboidal
neural plate: simple columnar epithelium
early neaural tube wall: pseudostratified epithelium
describe and explain the importance of the orientation of the metaphase plate during proliferation of cells within the neural tube
if the plate is perpendicular to the neural tube, two resulting daughter cells will remain proliferative
if the plate is parallel with the neural tube only the one closest to it will remain proliferative while the other will express notch recepter, be postmitotic, move to the external limiting membrane and become a neuroblast
describe the hierarchy of basic cell lineages in the development of the nervous system and note when mitosis ceases in each lineage and differentiation begins
neuroepithelium= initial epithelial layer of neural tube
bipotential progenitor cell= cell is restricted to becoming neuronal lineage progenitor or glial lineage progenitor
neuronal lineage cell: develope into neurons, postmitotic
glial lineage cells: have a number of paths leading to type of glial cells
describe effects of following expreiments:
grafting a second notochord
removing notochord
slit neural plate on one side of the floor plate
grafting an extra notochord near the neural tube induces a secondary floor plate
in the absence of a notochord, a very incomplete floor plate forms and nerve fibers exit from multiple sites around the spinal courd
slitting the neural plate on one side of the floor plate removes the wall of the neural tube from the influence of the notochord, allowing the disorganized exit of nerve fibers from that part of the spinal cord
describe the signaling pathways and factors that establish the dorsal-ventral axis of the developing neural tube. what roles do the notochord and non-nervous ectoderm play
ventral signaling: notochord releases sonic hedgehog to form the floor plate, floor plate releases sonic hedgehog to form motorneurons
dorsal: ectoderm flanking the neural plate uses BMP to induce snail-2 in future neural crest and later to maintain pax-3 and pax-7 to create a dorsalizing effect which is suppressed by shh from floor plate to supress dorsalizing effect in the basal plate
describe the relationship between rhombomeres, cranial nerves, and pharyngeal arches. which pharyngeal archees are associated with which cranial nerves
cranial nerves mostly supply structures derived from the pharyngeal arches
first pharyngeal arch: Cranial nerve V- rhombomere 2 and 3 joins 2
second arch: cranial nerve VII- rhombomere 4 and axons from 5 join 4
third pharyngeal arch: CN IX- rhombomere 6 and axons from 7 join 6
how is the segmented nature of spinal nerves related to the somitic mesoderm pattern
it is segmented like somitic meso derm because motor neurons can penetrate the antior but not posterior mesoderm of somites
what is the role of isthmis organizer and what signaling are involved
signaling center:
principal signaling molecule = FGF-8 (FGF-8/Wnt-1 induce expression of En-1, En-2, pAX-2, pAX-5 which all decrease away from isthmic organizer)
organizes and polarizes dorsal midbrain and cerebellum
how does shh determine the midbrain dorsoventral axis
shh restricts Pax-7 expression and similar molecules
pax-7 forms alar plate
pax-6 eye formation and inhibits en-1 and vice versa which creates diencephalic-mesencephalic border
what role do prsomeres P1-P3 plat in forebrain patterning
p1-p3 define the diencephalon
p2-p3 define dorsal and ventral thalamus
describe steps and outgrowth of motorneuron and compare with sensory neuron what are growth cones? how do environmental factors afftect growth? what role do netrins and semaphorins play? what are boundary caps and what role do they play in axon growth
motor neurons grow out from the motor neuroblasts in the basal plate of spinal chord
cell bodies of sensory neurons are derived from neural crest cells and form snesory spinal ganglia and axons grow toward spinal cord and periphery
growth cone: expanded region of cytoplasm with filopodia which advance via extension/resorption via actin filaments
environmental factors: chemoattraction, contact attraction, chemorepulsion, contact repulsion
netrins : attractant
semaphorin: repulsive
boundary caps maintain spearation betwen CNS and PNS
list cues involved in axon guidance
caudal half of somite, fibronectin and laminin, integrins, cadherences
describe steps in the formation of synaptic junction
axon outgrowth ceases
neuron preps to release neurotransmitter molecules: synaptoc vesicles fill with ACh
muscle fiber prepares for signal transduction: ACH receptors become concentrated in postsynaptic folds, ACH-esterase accumulates in basal lamina
