embryology- practice questions Flashcards
the part of sperm that contains proteolytic enzymes to digest zone pellucida is
acrosome
- acrosome is exposed during process of capacitation
- thus, under influence of substances released by corona radiata cells, it releases its proteolytic enzymes and penetrates oocyte
the ovulated mammalian oocyte is arrested at
metaphase of meiosis II
- long arrest in meiosis occurs in the primary oocyte
- these descendants of oogonia begin meiosis before birth and stop dividing during prophase of the first division
- years later, this first division is completed just prior to ovulation
- ovulated secondary oocytes then stop at metaphase Il until fertilized
true or false & explain: male and female processes of meiosis are equal
false
in males = results in 4 spermatids
females = results in 1 ovum with 3 polar bodies
How does the oocyte assure that only one sperm cell enters it during fertilization?
The zona pellucida becomes impenetrable (impermeable) after one sperm cell enters
progesterone is produced by what organ during the secretory phase of menstruation or early pregnancy?
corpus luteum
decidual reaction
change that happens in lining of uterus(endometrium) when embryo implants to create a nourishing environment for the conceptus as it buries itself by invasion of uterine endometrial wall
- increases blood supply, cell enlargement (fill stromal cells [supportive cells] with glycogen, lipids, and proteins), immune protection
happens during the 7 day blastocyst
Haploid nuclei that fuse at fertilization are called:
pronuclei
- female pronucleus fuses w/ the male pronucleus after completing the meiotic division that had begin years ago to create the diploid nucleus of the zygote
The first week of human development is characterized by formation of the:
inner cell mass, hypoblast, trophoblast, blastocyst
(all of the above answer choice)
trophoblast
forms around days 5-6
- outer layer of the blastocyst, responsible for implantation in the uterus
- later forms the placenta
by day 7-8, divides into 2 layers:
- Cytotrophoblast (inner layer) → Forms the structural part of the placenta, cell divisions happen here
- Syncytiotrophoblast (outer layer) → Helps invade the uterine lining for implantation
also produces the HCG which signals the corpus luteum to keep producing progesterone to maintain uterine lining
trophoblast differentiates into which 2 layers after implantation (day 8-9)
cytotrophoblast (inner layer): single layer of cells that provides structure and gives rise to new trophoblast cells
- forms the chorionic villi, which develop into the placenta
Syncytiotrophoblast (Outer Layer):
multinucleated mass of fused cells that actively invade uterine wall, secretes hCG & helps in nutrient exchange between the mother and embryo, lacks cell boundaries, which allows it to spread easily and establish deeper implantation
what happens during implantation
Implantation occurs when the trophoblast cells at the embryonic pole secrete proteolytic enzymes that allow the blastocyst to penetrate the wall of the uterus, usually the posterior wall. The endometrial lining responds to implantation through the decidua reaction, by which it becomes more succulent for nourishing the blastocyst.
- interactions b/w L selectin on trophoblast & carb receptors on uterine epithelium help with implantation
what is capacitation?
Capacitation involves removing the glycoprotein coat and seminal plasma proteins from the head of the sperm, exposing the acrosome and allowing the acrosome reaction to occur
- occurs within the female genital tract, and without its occurrence, fertilization could not occur
early stages of cleavage are characterized by what?
increase in number of cells in zygote, not size
- earliest stages of cleavage marked by these mitotic divisions that increase # of cells but decrease size in each division = forms morula when gets to 12-16 cells
the most common site of ectopic pregnancy is
uterine tube
growth of the embryo in this site usually causes rupture of the tube and severe hemorrhage in the mother
when does the zona pellucida dissolve
during the blastocyst stage to allow implantation to occur
- in light microscope, zona pellucida appears as a translucent membrane surrounding the morula and early blastocyst
Which of the following is a major characteristic of meiosis I?
pairing of homologous chromosomes
What is the normal complement of chromosomes found in a sperm?
22 autosomes + 1 sex chromosome
Which of the following describes the number of chromosomes and amount of DNA in a gamete?
23 chromosomes, 1N
amount of DNA + number of chromosomes in a normal body cell (somatic)
46 chromosomes, 2N
In the process of meiosis, DNA replication of each chromosome occurs, forming a structure consisting of two sister chromatids attached to a single centromere. What is this structure?
duplicated chromosome
- DNA replication occurs before division, structure of 2 identical sister chromatids attached at single centromere is created
- even though chromosome has been duplicated, still considered one chromosome as long as sister chromatids remain attached
what is a homologous pair
2 different chromosomes (one from mom and one from dad), not a single chromosome with two chromatids
bc 2 sister chromatids is considered 1 chromosome even tho its 2 lines attached together
by when are all primary oocytes formed by
month 5 of fetal life (in female baby)
when does formation of primary spermatocytes begin?
at puberty
in production of female gametes, which type of cell can remain dormant for 12-40 years? what about which ones can remain dormant for 12 years in production of male gametes?
female: primary oocyte
male: primordial germ cell
approx. how many sperm will be ejaculated by a normal fertile male during sexual intercourse?
350 million
A young woman enters puberty with approximately 40,000 primary oocytes in her ovary. About how many of these primary oocytes will be ovulated over the entire reproductive life of the woman?
480
what is a Barr body and how can fetal sex be diagnosed using Barr bodies?
barr body: inactivation of 1 X chromosome in females
- fetal sex can be diagnosed by noting the presence or absence of the Barr Boyd in cells obtained from the amniotic fluid
How much DNA does a primary spermatocyte contain?
primary spermatocyte: diploid (2N) cell that undergoes DNA replication before meiosis begins - means that even tho it has 46 chromosomes, each chromosome has 2 sister chromatids = doubling amount of DNA
final answer= 4N
what is crossing over
pairing of homologous chromosomes, permits large segments of DNA to be exchanged
occurs during meiosis
during ovulation, secondary oocyte resides at what specific stage of meiosis?
metaphase of meiosis II
in oogenesis, when do oogonia enter meiosis I and undergo DNA replication to form primary oocytes?
during fetal life
where do primordial germ cells initially develop?
in the yolk sac at week 4 of embryonic development
when does a secondary oocyte complete its 2nd meiotic division to become a mature ovum?
at fertilization
when after fertilization does blastocyst begin implantation?
by day 7
where does the blastocyst normally implant?
functional layer of the endometrium
In oogenesis, which of the following events occurs immediately following the completions of meiosis II?
formation of a female pronucleus
which plays most active role in invading the endometrium during blastocyst implantation?
syncytiotrophoblast
between which 2 layers is the extraembryonic mesoderm located?
exocoelomic membrane and cytotrophoblast
during week 2 of development, embryo blast receives its nutrients via?
diffusion
the prochordal plate marks the site of the future
mouth
what the components of the definitive chorion? (3 layers)
extraembryonic somatic mesoderm, cytotrophoblast, and syncytiotrophoblast
Carcinoembryonic antigen (CEA) is an on- cofetal antigen that is generally associated with which one of the following tumors?
colorectal carcinoma
at what location does the amniotic cavity develop?
within the epiblast
at the end of week 2 what is the composition of the embryonic disk?
epiblast and hypoblast
the heart is derived from what layer?
splanchnic mesoderm
the notochord is replaced by what structure?
nucelus pulposus
what are components of the mature placental barrier?
- endothelial lining of fetal capillaries
- syncytiotrophoblast
- basement membrane of fetal capillaries
which substances does the intervillous space contain?
- oxygen
- carbon dioxide
- maternal blood
- electrolytes
fetal blood is not present here, its separated from it by the placental barrier
the most important region of the decide for the nourishment of the conceptus is the decidua ___________
basalis
chorionic villi are designated as secondary chorionic villi when they ____
develop a mesenchymal core
most distinctive characteristic of a primary chorionic villus is its ___________
cytotrophblastic core
polyhydraminos or hydramnios
when the amount of amniotic fluid exceeds 2 liters
What is a numerical chromosomal abnormality? Give 2 examples of chromosomal anomalies related to sex chromosome.
numerical chromosomal abnormality: change in the number of chromosomes in a person’s cells
- Trisomy: an extra chromosome (total 47 chromosomes)
- Monosomy: a missing chromosome (total 45 chromosomes)
examples:
1. Turner Syndrome (monosomy X): X (only 1 X chromosome, no second sex chromosome)
- affects females
- features: short stature, webbed neck, underdeveloped ovaries (infertility), no menstrual periods
-
Klinefelter syndrome: XXY (1 extra X chromosome in males)
- affects males
- features: tall stature, small testes, reduced fertility, may have breast development
Define neurulation. Briefly outline steps involved in neurulation.
neurulation: process during embryonic development in which the neural tube is formed, neural tube later develops into the brain and spinal cord (the central nervous system)
- begins around week 3 of development
steps:
1. Formation of Neural Plate: notochord (a rod-like structure from the mesoderm) sends signals to the ectoderm above it = ectoderm thickens to form neural plate
- Shaping of Neural Plate: neural plate widens at the top (cranial end) and narrows at the bottom (caudal end)
-
Formation of Neural Folds and Neural Groove: edges of the neural plate start to rise, forming neural folds
- neural plate folds inwards forming a neural groove -
Fusion of Neural Folds to Form Neural Tube: neural folds move toward each other and eventually fuse in the midline to form the neural tube
- tube closes first in the middle, then toward the head and tail ends -
Formation of Neural Crest Cells: as neural tube closes, some cells at tip of neural folds break off to become neural crest cells
- these cells migrate and form many important structures like sensory nerves, parts of the face, and melanocytes - tube detaches from the surface ectoderm and becomes the future brain & spinal cord
Name the structures that pass through the primitive umbilical ring at 5 weeks of gestation. What about after that?
At 5 weeks, 3 main structures pass through it:
1. Connecting stalk: contains the allantois and umbilical vessels (2 arteries and 1 vein)
- connects the embryo to the chorion (future placenta)
2. Yolk sac duct (Vitelline duct): connects midgut of embryo to yolk sac
- carries nutrients before the placenta is fully functional
3. Canal for the intraembryonic coelom: temporary passage allowing connection b/w the intraembryonic and extraembryonic coeloms (early body cavities)
after 5 weeks: these structures become part of umbilical cord and some (vitelline duct, intraembryonic coelom) disappear
During process of fertilization, explain how the egg responds after entry of spermatocyte in the oocyte.
- Cortical Reaction (Block to Polyspermy): after 1 sperm successfully enters oocyte, small sacs just beneath the oocyte membrane (called cortical granules) release their contents, causing changes in zona pellucida (the outer layer of the egg), making it hard and impenetrable to other sperm
-
Completion of Meiosis II in the Oocyte:
oocyte was arrested in metaphase II of meiosis at the time of ovulation.
- entry of the sperm triggers the oocyte to finish meiosis II, forms: one large cell: ovum (mature egg) & one small cell: second polar body (which eventually degenerates) -
Formation of Female and Male Pronuclei: sperm nucleus swells and becomes the male pronucleus.
- oocyte nucleus becomes the female pronucleus
- both pronuclei move toward each other in the center of the oocyte and fuse resulting in diploid zygote (46 chromosomes) -
Start of Cleavage (First Mitotic Division):
zygote begins to divide through mitosis, starting the process of embryonic development
define dizygotic & monozygotic twins. give relation of placenta & placental membranes in monozygotic twins, if embryo splits at 2 cell stage. what about if it splits at any other cell stage?
Dizygotic Twins (Fraternal Twins): 2 separate eggs are fertilized by 2 different sperm
- always have two placentas and two sets of membranes (chorion and amnion)
Monozygotic Twins (Identical Twins): 1 egg is fertilized by 1 sperm, and the resulting zygote splits into 2 embryos
splits at 2 cell stage: very early so 2 placentas, 2 amniotic sacs, and 2 chorionic sac
splits day 4-8: shared placenta and chorion, 2 separate amniotic sacs (most mono twins in this category)
day 8-13 split: everything shared, higher risk of cord entanglement
splitting any day after that may result in conjoined twins
What is spina bifida? Give its embryological bases in the light of normal process of neurulation. During which weeks of gestation did this defect most likely occur?
type of neural tube defect (NTD) where the vertebral arches (bones of the spine) fail to close properly, leaving the spinal cord or meninges exposed or protruding
defect occurs around 4th week of gestation when the neural tube is supposed to close
What is apical ectodermal ridge? Give its role in the development of the limbs.
specialized thickened area of ectoderm (outer layer of the embryo) found at the tip (apex) of each developing limb bud
- like command center that controls and guides limb growth
role in development of limbs:
1. promotes limb outgrowth: sends signals to underlying mesoderm cells to keep diving & growing
- controls patterning along the proximal-distal axis: tells cells underneath what to become
- prevents premature differentiation: keeps nearby mesenchyme cells “undifferentiated” so they can keep dividing & forming different parts of the limb
Explain the development of trophoblast during the first 3 weeks of development.
week 1 → zygote divides to form blastocyst
- outer layer is called trophoblast
day 6 → trophoblast differentiates into 2 layers: cytotrophoblast (inner layer of mitotically active cells) & syncytiotrophoblast (outer multinucleate layer that invades uterine lining & helps w/ implantation*)
week 2→ lacunae form within syncytiotrophoblast that will later become the maternal blood-filled spaces
- primary villi form which are finger like projections made of cytotrophoblast cells pushing into the syncytiotrophoblast
week 3 → extraembryonic mesoderm invades primary villi, forming secondary villi
- later in week → blood vessels start to form inside these villi (now they are tertiary villi)
Describe briefly the formation and fate of the primitive streak. Explain how it leads to the formation of the 3 germ layers. What is sacrococcygeal teratoma?
formation: appears around day 15 at the caudal (tail) end of the embryonic disc &
grows towards the cranial (head) end
- at tip of streak is a primitive node (also called Hensen’s node), with a central primitive pit
- cells from epiblast move inward through the primitive streak → this process is called gastrulation
how it forms 3 germ layers: during gastrulation, epiblast cells migrate inward through the primitive streak, then spread out and form three new layers (endoderm, mesoderm, ectoderm)
fate: regresses by the end of 4th week
- if persists abnormally, can cause tumor called sacrococcygeal teratoma
sacrococcygeal teratoma: tumor at base of spine that forms bc of remnants of primitive streak that fail to disappear
- usually benign but contains tissues from all 3 germ layers (like teeth, hair, skin, muscle)
What is oligohydraminos? Describe the formation of amniochorionic membrane and give the events that lead to obliteration of the uterine cavity towards end of pregnancy.
oligohydramnios: condition during pregnancy where there is too little amniotic fluid surrounding the fetus
- causes: renal problems in fetus, premature rupture of membranes, placental insufficency
formation of amniochorionic membrane:
- amnion: formed during week 2, cavity forms within epiblast that becomes known as the amniotic cavity
- chorion: around week 2-3, extra embryonic mesoderm forms between trophoblast & amnion/yolk sac, splits into two layers creating the chorionic cavity
- chorion gives rise to chorionic villi for maternal-fetal exchange
- as amniotic sac (amnion) expands with fluid, presses against the chorion and by the end of the first trimester, amnion fuses w/ the chorion forming a single membrane called amniochorionic membrane
obliteration of the uterine cavity: amniochorionic membrane eventually fuses with the decidua parietals (lining of uterus) to eliminate the uterine cavity (theres no space b/w fetus & uterine wall anymore)
discuss derivatives of neural tube in the developing embryo
neural tube gives rise to the central nervous system (CNS)
cranial part: brain: cerebrum, thalamus, brainstem, cerebellum
caudal part: spinal cord: gray & white matter, sensory & motor areas
Give the characteristic congenital anomaly related to gastrulation that may occur in a patient that is habitually alcoholic and is now pregnant
Holoprosencephaly
(birth defect where fetal brain fails to separate into 2 hemispheres)
small head or large head, one eye, closely spaced eyes, intellectual disabilites
diff presentations based on severity of case
Define gastrulation. Explain the events occurring during gastrulation.
gastrulation: during 3rd week of embryonic development, bilaminar embryonic disc is converted into trilaminar disc (3 germ layers)
events of gastrulation:
1. Formation of primitive streak: appearance on the dorsal surface of the epiblast, has 3 parts (primitive groove, primitive node, primitive pit)
- Ingression of epiblast cells: epiblast cells start migrating inward through the primitive streak
-
formation of germ layers: first wave of migrating epiblast cells replaces the hypoblast and forms the endoderm
- next wave spreads b/w epiblast & endoderm to form the mesoderm
- remaining epiblast cells dont migrate to become the ectoderm -
formation of notochord: notochord forms from some mesodermal cells
- acts as signaling centers for development of nervous system & axial skeleton - disappearance of primitive streak: regresses by end of 4th week
derivates of the 3 germ layers
ectoderm: external things (skin, brain, nerves)
- brain, spinal cord, nerves, epidermis, outer white layer of teeth, NEURAL CREST DERIVATIVES!!!
mesoderm: middle things (muscle, bone, heart, blood)
- bones, cartilage, heart, blood vessels, kidneys, gonads
endoderm: internal things (gut, lungs, glands)
- lining of digestive and respiratory tract, glands, lining of urinary bladders & urethra
neural crest derivaties
melanocytes, adrenal medulla, cranial nerves, facial cartilage
Describe the placental circulation in a mature placenta, indicating the vessels carrying oxygenated and deoxygenated blood.
there is no direct mixing of maternal and fetal blood — exchange happens across a thin placental membrane
fetal side of circulation: fetus uses umbilical cord to connect w/ placenta, it contains 3 vessels:
- 2 umbilical arteries: carry DEoxygenated blood from the fetus to the placenta (take waste like CO2 & urea)
- 1 umbilical vein: carries OXYGENATED blood from placenta to fetus (brings nutrients & oxygen from mother)
maternal side of circulation:
- spinal arteries of uterus: open into intervillous space of placenta, deliver oxygen-rich blood & nutrients to intervillous space
- endometrial veins: collect deoxygenated blood from intervillous space & return to mother
exchange site: exchange happens across chorionic villi (contain fetal capillaries)
What is a placental membrane (placental barrier)? Give the components of this membrane during the 4th week of development. (SO IMP)
placental barrier is not the same as the full placenta- its a place for interchange
placental membrane: thin barrier through which exchange occurs b/w fetal & maternal blood
- contains NO MATERNAL TISSUE, only fetal tissue
components:
- syncytiotrophoblast
- cytotrophoblast
- connective tissue (mesodermal core of villus)
- endothelium of fetal capillaries
the 3 phases of fertilization
-
Penetration of Corona Radiata
- outermost layer of cells surrounding oocytes -
Penetration of Zona Pellucida
- glycoprotein shell around egg, located under corona radiata
- sperm releases enzymes that digest through this (acrosome reaction) - Fusion of Sperm and Egg Membranes
