Embryology/Limb dev

Question 1

what are the 2 important sites of the sperm?

Answer 1

acrosome, w enzymes for the acrosomal reaction

tail, movement

Question 2

what happens to the chromosome number during gametogenesis?

Answer 2

the chromosome number is reduced by 1/2, and the shape of the cells is altered (each cell contains haploid number)

Question 3

definition of fertilization

Answer 3

fusion of pronucleus of the sperm with the pronucleus of the ovum to form the zygote

Question 4

where does fertilization occur?

Answer 4

the ampulla of the uterine tube

Question 5

what are the four phases of fertilization?

Answer 5

1) capacitation and acrosomal reaction
2) penetration
3) zona reaction

Question 6

what happens during the acrosomal reaction?

Answer 6

the sperm penetrates the corona radiata, and upon binding to the zona pellucida, enzymes in the acrosome of the sperm degrade the layer after a rise in Ca

Question 7

what happens after the acrosomal reaction occurs? what is the exception?

Answer 7

the oocyte will block other sperm from entering (blocking of polyspermy), except for in the case of twins
- this occurs via the cortical reaction, which causes the zona pellucida to harden

Question 8

what are the results of fertilization?

Answer 8

1) restoration of normal diploid number of chromosomes

2) chromosomal sex determination of embryo

Question 9

what occurs during the cleavage stage?

Answer 9

after fertilization occurs (zygote), lots of CD occurs giving lots of blastomeres –> morula
- early blastocyst forms when the morula hollows out, fills w fluid, and zona pellucida degenerates

Question 10

what is the initiating factor for implantation during cleavage?

Answer 10

the degradation of the zona pellucida (that was still present at the morula)

Question 11

what happens as the early blastocyst starts to form?

Answer 11

cells start to rearrange, going to one side: site of the inner cell mass, which will be the future embryo

Question 12

what defines an implanting blastocyst?

Answer 12

it consists of a spherical lining of cells (trophoblast) around the inner cell mass that give fingerlike projections to help the embryo/inner cell mass to be implanted

Question 13

what are the 2 layers of the trophoblast?

Answer 13

1) cyto - well-defined cell boundary. appears early, disappears w time
2) synchtio - ill-defined, continuous, secretes HCG

Question 14

what happens if the zona pellucida disappears ebfore early blastocyst formation?

Answer 14

the zygote will implant in the fallopian tubes - ectopic pregnancy

Question 15

what is the site of implantation?

Answer 15

in the posterior superior wall of the uterus

Question 16

where is the most common site of an ectopic pregnancy?

Answer 16

sometimes in the ovary, but tubal most common

Question 17

what are the symptoms of an ectopic pregnancy?

Answer 17

uterine bleeding, sudden onset of abdominal pain (appendicitis), missed period, positive HCG test

Question 18

HCG

Answer 18

a glycoprotein produced by synctio, can be assayed in maternal blood and urine

Question 19

what may low HCG levels indicate?

Answer 19

spontaneous abortion, ectopic

Question 20

what may high HCG levels indicate?

Answer 20

multiple pregnancy, trophoblastic diseases

Question 21

what is meant by “period of 2” in the 2nd week of dev?

Answer 21

embryoblast –> epi and hypoblast (bilaminar disc)
trophoblast –> cyto and synctio
2 cavities –> amniotic cavity and yolk sac

Question 22

what happens during the invasion of the blastocyst?

Answer 22

fix the position of the blastocyst in the uterus at this stage, using chorionic villi to position the embryo

Question 23

what is the role of the trophoblast when the embryo needs to be implanted?

Answer 23

trophoblast will extend fingerlike projections, chorionic villi, to the endometrium

Question 24

compare the number of types of chorionic villi at the 3rd week and then at the beginning of the 4th week

Answer 24

3rd week: 3 types of chorionic villi (cyto, synctio, endothelium)
4th week: only have 2 layers left (no cyto anymore)

Question 25

decidua basalis

Answer 25

part of the embryo that attaches to the uterus, the maternal part of the placenta

Question 26

during EARLY pregnancy, how many layers are in the placental barrier, and what are they?

Answer 26

4: 1) synctio 2) ctyo 3) connective tissue 4) fetal endothelium

Question 27

during LATE pregnancy, how many layers are present in the placental barrier, and why are these layers needed?

Answer 27

2 1) synctio: secrete HCG, continuation of placenta 2) fetal endothelium: for exchange of O2 (these are the only 2 that are continuous)

Question 28

what are the maternal and fetal components of the placenta?

Answer 28

maternal: decidua basalis fetal: chorionic villi

Question 29

what is the function of the placenta?

Answer 29

- gas exchange (O2 and CO2) - nutrients: glucose, fatty acids, AAs, electrolytes - hormonal and immunologic exchange

Question 30

where is everything exchanged btw fetus and mother?

Answer 30

arteries from the endometrium come into the INTERVILLOUS SPACE around villi, which is where all exchange occurs

Question 31

why is week 3 of dev known as the period of 3?

Answer 31

- primitive streak and notochord formation - gastrulation of epiblast (trilaminar germ disc): exto, endo, mesoderm - neurulation: neural plate, groove, tube - mesoderm differentation: 3 types of mesoderm

Question 32

what happens during gastrulation?

Answer 32

epiblast gets rid of the hypoblast, which becomes the endoderm. - epiblast will change to ectoderm. layer btw the 2 is mesoderm - all 3 layers come out of the epiblast as it "updates" the embryo via the neural groove "epiblast gives renovation"

Question 33

why is the mesoderm important during gastrulation?

Answer 33

starts to specify the embryo's shape (cranial and caudal ends) - starts to form a midline of the embryo, primitive streak where the mesoderm originates and spreads btw ecto and endo

Question 34

formation of notochord

Answer 34

some of the mesoderm will form the notochord, will become the intervertebral discs

Question 35

what are the 3 layers of the mesoderm?

Answer 35

somite intermediate lateral plate

Question 36

neural tube formation

Answer 36

the neural groove folds around the thick ectoderm, will fuse together to form the neural tube (future SC and brain)

Question 37

steps of neurulation

Answer 37

``` neural plate neural groove neural crest neural folds neural tube ```

Question 38

what are the results of folding following gastrulation?

Answer 38

endoderm becomes enclosed inside the embryo, forming the gut tube ectoderm covers the embryo from outside, and amniotic sac to expand to surround the embryo - the oral mem and cloacal mem become ventral - pericardium and septum transversum (future diaphragm) become ventral

Question 39

the ectoderm germ layer will give rise to ...

Answer 39

- epidermis, hair, nails, glands of skin - brain, SC - neural crest/derivatives (cranial, spinal, sympathetic ganglia, associated nerves, adrenal medulla, pigment cells of skin)

Question 40

the endoderm germ layer will give rise to ...

Answer 40

epithelial lining and glands of digestive and resp tracts

Question 41

mesoderm germ layer will give rise to ...

Answer 41

- notochord (intervertebral discs) - somite (sclerotome - vertebrae and ribs, dermatome - dermis of dorsal body region, myotome - trunk and limb musculature) - intermediate (kidneys, gonads) - lateral plate (somatic and sphlanchic, connective tissues of limbs (bones, joints, ligaments), wall of digestive and respiratory tracts (except epithelial lining), heart, blood vessels

Question 42

describe the general stages of limb development

Answer 42

- 4 limb buds develop from ventrolateral body wall - circular groove appears separating a hand plate from upper limb, foot plate from lower - digital rays --> notches --> webbed fingers --> separated digits - a second groove appears

Question 43

limb rotation (degrees)

Answer 43

upper limb - 90 degrees laterally | lower limb - 90 degrees medially

Question 44

flexors/extensors are posterior/anterior? in the upper vs lower limb

Answer 44

upper: flexors (anterior) extensors (posterior) opposite for lower limb

Question 45

what are the medial and lateral bones of the upper and lower limbs?

Answer 45

upper: radius (lateral) ulna (medial) fibia (lateral) tibia (medial)

Question 46

what are the bones of the upper/lower limb used for rotation, which direction do they point

Answer 46

upper: thumb (lateral) elbow (backwards) lower: big toe (medial) knee joint (forwards)

Question 47

amelia

Answer 47

absence of entire limb

Question 48

meromelia

Answer 48

absence of part of limb

Question 49

polydactyly

Answer 49

extra digit

Question 50

syndactyly

Answer 50

fusion of digits

Question 51

during the later stages of pregnancy, maternal blood is separated from fetal blood by the ...

Answer 51

synctio and fetal epithelium (placental barrier)

Question 52

what must degenerate for blastocyst implantation to occur?

Answer 52

zona pellucida

Question 53

US of 20 y/o pregnant woman in the 20th week of pregnancy revealed abnormal limb dev of her fetus, showing one arm to be shorter than the other. what condition is likely described?

Answer 53

meromelia