embryology exam 2

Question 1

describe the development of the mesodermal germ layer and its division into paraxial, intermediate, and lateral plate mesoderm

Answer 1

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

Question 2

what are the fates of each mesoderm layer

Answer 2

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

Question 3

describe the two mechanisms involved in somitogenesis

Answer 3

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

Question 4

difference between somitomere and somite

Answer 4

somitomeres become somites which are more dense blocks of mesoderm that form along the notochord

Question 5

what is the relationship of ephrin B, Wnt-6, snail, and paraxis to somite formation?

Answer 5

dorsal somites release Wnt-6 which activates paraxis which inhibitis snail expression converting the mesenchymal cell to an epithelial cell = somitocoel formation

Question 6

relate Shh, noggin, Pax1, and Pax9 to the formation of the sclerotome

Answer 6

notochorde releases Shh and noggin which activate Pax1 and Pax 9 genes in ventral part of somite which forms sclerotome

Question 7

list the derivatives from the final subdivisions of the somites

Answer 7

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

Question 8

list the factors involved in the formation of the intermediate mesoderm and list the derivatives

Answer 8

BMP + activin (Hox-4 and Hox-11 contribute to cranial and caudal extent)
derivatives: pronephros and mesonephros aka. kidney

Question 9

differentiate between the intraembryonic coelom and the extraembryonic coelom

Answer 9

intraembryonic coelem is made from the lateral plate mesoderm and becomes the pericardial cavity
extraembryonic coelom is the embryonic sac

Question 10

distinguish between somatic and splanchnic mesoderm

Answer 10

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

Question 11

describe the formation of the lateral plate mesoderm and distinguish between the somatopleaure and the spanchnopleure

Answer 11

somatopleaure: inside the tube mesoderm + endoderm
splanchnopleaure: outside the tube mesoderm + ectoderm

Question 12

describe the early formation of the heart

Answer 12

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.

Question 13

list the genes important in early heart formation

Answer 13

Nkx2-5, MEF2, GATA4

expressed by cells of cardiac crescent

Question 14

what is the secondary heart field

Answer 14

splanchnic mesoderm

Question 15

which signaling factor is necessary for the formation of endoderm

Answer 15

nodal

Question 16

describe the relationship of the expression of nodal and FDF-4 to the establishment of the anterior-posterior gradient

Answer 16

high nodal= anterior

low nodal + FGF-4 = posterior

Question 17

describe the role of Cdx-2 in the formation of the hindgut and foregut

Answer 17

Cdx-2 is expressed in the posterior gut- promotes hindgut development and supresses formation of anterior gut structures

Question 18

describe the relationship of Shh and BMP-4 in the formation of the anterior and posterior intestinal portals

Answer 18

expression of Shh followed by BMP-4 in posterior intestinal portal
expression of Shh in anterior intestinal portal

Question 19

list each of the three major circulatory arcs in the 4 week human embryo and the components and function of each

Answer 19

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

Question 20

list and describe the four extraembryonic tissues and the germ layers fromwhich they are derived

Answer 20

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

Question 21

list the two trophoblastic derivatives that comprise the fetal-maternal interface

Answer 21

placenta

chorion

Question 22

explain the function of the amnion

Answer 22

buffer against mechanical injury, accomodates growth, allows normal movements, protects fetus from adhesions

Question 23

describe the following conditions and indicate what circumstances these are often associated: hydramnios, oligohydramnios

Answer 23

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

Question 24

describe the development of the allantoic vessels and the relation of the allantois to the urinary bladder and the median umbilical ligament

Answer 24

develop in mesoderm of allantois, used for respiratory organ and urinary waste, forms urinary bladder and umbilical ligament

Question 25

what tissue in the mature placenta directly interfaces with the maternal uterine connective tissue

Answer 25

chorion/chorionic platw

Question 26

list and describe the layers from the amnion outward to the outer layer of the endometrium

Answer 26

amnion-chorionic cavity- chorionic plate- trophoblastic covering (outer cytotrophoblastic shell)

Question 27

what is the fate of the decidua capsularis

Answer 27

overlies the embryo and its chorionic vesicle

Question 28

describe/trace the maternal fetal blood flow pattern and indicate where the exchange of material occurs

Answer 28

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

Question 29

describe fetal alcohol syndrom

Answer 29

excessive alcohol ingestion by mother leading to birth defects

Question 30

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?

Answer 30

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

Question 31

list functions of placent

Answer 31

diffuse oxygen and CO2 diffuse foodstufss excrete waste

Question 32

compare the early placenta with the late placenta

Answer 32

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

Question 33

describe the oxygen pressure gradient (near end of pregnancy) and explain why adequate oxygenation can occur with such a low pressure gradient

Answer 33

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

Question 34

describe the Bohr effect and explain what is meant by the double Bohr effect

Answer 34

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

Question 35

describe the timing, method of secretion, targets, and effects of human chorionic gonaotropin

Answer 35

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)

Question 36

describe each of the four theories of why mother's immune system does not recognize the fetus as foreign tissue

Answer 36

1. lack of expression of major histocompatibility antigens by placenta components 2. paralysis of mother's immune system during pregnancy 3 . decidual immune barrier 4. inactivation of mother's immune system components by molecules formed on fetal placenta surface

Question 37

infectious agents that result in birth abnormalities

Answer 37

rubella, cytomegalic inclusion disease, herpes simplex, vricella-zoster, influenza, mumps

Question 38

effects of thalidomide on birth abnormalities

Answer 38

thalidomide: limb defects, ear defects, cardiovascular anomalies

Question 39

causes and symptoms of neotatal respiratory distress syndrome, hydrops, and eclampsia

Answer 39

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

Question 40

prematurity and fetal growth restriction is the second most common cause of neonatal mortality. list major risk factors of prematurity

Answer 40

preterm premature rupture of placental membranes intrauterine infections uterine, cervical, and placental structural abnormalities multiple gestation

Question 41

describe the timing, method of secretion, targets, and effects of estrogen

Answer 41

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

Question 42

describe the timing, method of secretion, targets, and effects of preogesterone

Answer 42

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

Question 43

describe the timing, method of secretion, targets, and effects of human chorionic somatomammotropin

Answer 43

secreted by placenta begining in 5th week of pregnancy functions: causes decreased insulin sensitivity and decreased utilization of glucose by mother, general metabolic hormone

Question 44

teratology

Answer 44

"the study of monsters", study of confenital malformations

Question 45

teratogen

Answer 45

agent that produces birth defects

Question 46

malformation

Answer 46

primary errors of morphogenesis

Question 47

disruption

Answer 47

disturbance in otherwise normal morphogenetic processes

Question 48

deformation

Answer 48

disturbances in otherwise normal morphogenetic processes and are typically caused by abnormal biomechanical forces such as uterine constraint

Question 49

dysplasia

Answer 49

abnormality of a tissue due to an abnormal intrinsic developmental process

Question 50

sequence

Answer 50

series (cascade) of events triggered by one initiating factor

Question 51

syndrome

Answer 51

a group of malformations of different structures due to a single primary cause but acting though multiple developmental pathways

Question 52

association

Answer 52

a group of anomalies seen in more than one individual that cannot yet be attributed to a definitive cause

Question 53

critical period

Answer 53

embryos are more susceptible to agents or factors causing abnormal development, between weeks 3 and 8

Question 54

describe the source of dermal cells in various parts of the skin: dorsal , ventral , lateral, cranial, anterior neck, limb

Answer 54

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

Question 55

describe the signaling pathways leading to the differentiation of dermal cells

Answer 55

ectoderm releases Wnt which stimulates mesenchymal cells to develop tight junctions and become dermal cells

Question 56

compare characteristics of dermal cells and mesenchymal cells

Answer 56

dermal cells are loosely aggregated, interconnected by tight junctions, secrete thin watery matrix rich in glycogen and hyaluronic acid

Question 57

describe how recombination experiments between mesoderm and ectoderm, demonstrate instructive induction

Answer 57

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

Question 58

list commonalities in the development of epidermal derivatives

Answer 58

(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

Question 59

describe the adult hair cycle including the specific stages: anagen, catagen, telogen, and exogen

Answer 59

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

Question 60

explain the importance of hormones in the development of mammary glands

Answer 60

estrogen: stimulates duct growth progesterone: stimulate formation of secretory alveoli prolactin: milk, protein, and fat synthesis oxytocin: milk letdown

Question 61

describe the mesenchymal origin of each major part of the skeleton

Answer 61

mesodermal sclerotomes: vertebral column, ribs, sternum lateral plate mesoderm: limb bones, girdles head mesoderm: calcaria and base of skull neural crest: facial bones

Question 62

differentiate the Hox gene boundaries for the different regions of the vertebral column

Answer 62

``` occipital-cervical boundary: Hox 3 cervical-thoracic boundary: Hox6 Attached-floating ribs boundary: Hox9 thoracic-lumbar: Hox10 lumbar-sacral: hox 11 sacral-coccygeal: Hox13 ```

Question 63

describe results of experiments involving Hox gene knockouts (single gene, hox 10 paralog, hox 11 paralog, mutation of hox gene)

Answer 63

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

Question 64

describe the origin of the sternum

Answer 64

derived from lateral plate mesoderm, arises as a pair of cartilaginous bands

Question 65

describe the origin of the clavicle

Answer 65

arise from neural crest, follows intramembranous pathway, one of the first bones to become ossified

Question 66

describe/compare the subdivisions of the developing skull

Answer 66

neurocranium: surrounds the brain viscerocranium: surrounds oral cavity and pharynx and upper respiratory occipital sclerotomes: base of occipital bone

Question 67

describe the generalized neurocranium/chondrocranium

Answer 67

cartilaginous: part of occipital, sphenoid, thmoid, parts of temporals membranous: part of occipital, parietal, frontals, part of temporal

Question 68

describe the generalized viscerocranium and the bones that develop from the viscerocranium

Answer 68

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

Question 69

define fontanelle

Answer 69

intersections between sutures where more than two bones meet, occupied by connective tissue

Question 70

common pathway (bone/cartilage differentiation)

Answer 70

N-cadherin promotes mesenchymal cell condensation TGF-beta stimulates synthesis of fibronectin and N-CAM agreggated state of mesenchymal cells is stabilized

Question 71

membranous bone pathway

Answer 71

Runx-2 and Osx | mesenchymal cells differentiate into osteoblasts

Question 72

permanent cartilage pathway

Answer 72

mesenchymal condensation forms chondroblasts sox-9 causes chondroblasts to secrete collagen II and catilage matrix, sox-9 is continually expressed in permanent cartilage

Question 73

endochondral bone pathway

Answer 73

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

Question 74

describe each stage in the differentiation of skeletal muscle tissue

Answer 74

myogenic cells --> myoblasts --> myotubes --> muscle fibers

Question 75

differentiate between primary and secondary myotyubes

Answer 75

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,

Question 76

describe the role of satellite cells

Answer 76

fuse with muscle fiber to provide growth, function as stem cells, replace damaged muscle

Question 77

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

Answer 77

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

Question 78

adult structures that develop from each region of the pentapartite brain

Answer 78

telencephalon: paleocortex, corpus stiatum, neocortex diencephalon: epithalamus, thalamus, hypothalamus, infundibulum mesencephalon: tectum, tegmentum, cerebral peduncles metencephalon: cerebellum, pons myelencephalon: medulla

Question 79

describe the stages of the neural tube wall from that of a simple cuboidal epithelium to a stratified epithelium

Answer 79

early neural epithelium: simple cuboidal neural plate: simple columnar epithelium early neaural tube wall: pseudostratified epithelium

Question 80

describe and explain the importance of the orientation of the metaphase plate during proliferation of cells within the neural tube

Answer 80

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

Question 81

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

Answer 81

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

Question 82

describe effects of following expreiments: grafting a second notochord removing notochord slit neural plate on one side of the floor plate

Answer 82

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

Question 83

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

Answer 83

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

Question 84

describe the relationship between rhombomeres, cranial nerves, and pharyngeal arches. which pharyngeal archees are associated with which cranial nerves

Answer 84

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

Question 85

how is the segmented nature of spinal nerves related to the somitic mesoderm pattern

Answer 85

it is segmented like somitic meso derm because motor neurons can penetrate the antior but not posterior mesoderm of somites

Question 86

what is the role of isthmis organizer and what signaling are involved

Answer 86

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

Question 87

how does shh determine the midbrain dorsoventral axis

Answer 87

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

Question 88

what role do prsomeres P1-P3 plat in forebrain patterning

Answer 88

p1-p3 define the diencephalon | p2-p3 define dorsal and ventral thalamus

Question 89

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

Answer 89

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

Question 90

list cues involved in axon guidance

Answer 90

caudal half of somite, fibronectin and laminin, integrins, cadherences

Question 91

describe steps in the formation of synaptic junction

Answer 91

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