MCQs

Embryology

Following fertilization, the zygote

Develops a thick outer coat known as

the zona pellucida.

Has the adult haploid number of chromosomes.

Usually reaches the uterus in one to two days.

May occasionally remain in the abdominal cavity.

A F. The zona pellucida is the covering of the ovum and remains
for some time after fertilization.

B F. The zygote has the adult diploid number of chromosomes.

C F . The zygote takes 36 days to pass into the uterine cavity, progress being by muscular contraction and ciliary activity.
D T . This condition is known as an ectopic pregnancy.


22 The morula:

Contains cells known as blastomeres.

Has two distinctive cell types.

Absorbs uterine fluid and produces a central cavity known as the blastocyst.

Becomes implanted in the uterine wall after loss of the zona pellucida.

23 The embryoblast:

Gives rise to the germ disc.

Has an endodermal germ layer adjacent to the amnion.

Has an ectodermal germ layer adjacent
to the trophoblast.

Is separated from the amnioblast cells by the amniotic cavity.

A T . The zygote becomes the morula once the 1216 cell stage has been reached.
B T. The smaller outer trophoblast and the larger inner cell mass.


C T. The latter is destined to become the future embryo.

D T .

A T. This comprises the ectodermal and endodermal germ layers.

B F. This layer lies adjacent to the primitive cavity of the blastocyst (exocoelomic cavity).

C T. The amniotic cavity develops within the area of the trophoblast, the cells away from the ectoderm being called

D T. amnioblasts.

24 The extra-embryonic mesoderm:

Is the primary mesenchyme.

Surrounds the yolk sac.

Splits to form the extra-embryonic calomel.

Contributes to the development of the chorion.


25 In the decidual reaction:

Endometrial glands are reduced in number.

Endometrial vascularity increases.

The endometrium becomes intimately related to the cytotrophoblast.

The decidua parietalis lies between the embryo and the uterine muscle.

A T. This is known also as Heusers membrane.

B T.

C T.

D T. The outer splanchnopleuric part of the mesoderm together with the trophoblast make up the chorion.

A F. The number of glands increases.

B T .


C F. The endometrium is related to the outer syncytiotrophoblast.

D F. The decidua basalis part of the decidua capsularis lies between the embryo and uterine muscle, the decidua parietalis is the remainder, lining the uterine cavity.
26 In the 14-17 day embryo:

The embryonic disc and adjacent amniotic and yolk sacs are surrounded by splanchnopleure.

A midline ectodermal thickening
develops known as the prochordal plate.

The primitive streak develops in the caudal half of the embryonic disc.

The mesodermal germ layer is laid down.

27 he head process:

Grows cranially from the primitive knot.
Grows between the ectoderm and amniotic cavity.
Becomes canalised about the 1 8th day.
Cells placed dorsal to the neurenteric canal form the notochord.

A T .

B F. The prochordal plate develops in the endoderm. It is the future mouth area, the oropharyngeal membrane.

C T. Cells stream cranially between the ectoderm and endoderm from the region of the streak and form the mesoderm on

D T. each side of the midline.

A T .

B F . The process grows between the ectoderm and endodermal layers.

C T. The neurenteric canal temporarily unites the amniotic and

D T. yolk sacs. This connection is obliterated by the developing

solid notochord, the endoderm re-uniting ventrally.

The cloacal membrane:

Arises cranial to the primitive streak.

Receives no ectodermal contribution.

Gives rise to the allantois.

Becomes the urogenital membrane.

29 In the embryonic period:

The yolk sac becomes elongated cranio-caudally and forms the primitive gut.

The head-fold brings the cloacal membrane on to the ventral surface of the embryo.

The yolk sac becomes the vitelline duct in the body stalk.

Communications develop between the intra- and extra- embryonic coelomes.

A F . The mid-line ectoderm caudal to the primitive streak fuses

B F . with the endoderm layer and forms the membrane.

C F . This is a diverticulum from the yolk sac adjacent to the membrane.

D T . Also the anal membrane.


A T . The foregut, midgut and
hindgut can be identified during
this time (from 4th to 8th weeks).

B F . This is brought about by the

tail-fold. The head-fold brings
the pericardial sac and primitive heart caudal to the oropharyngeal
membrane.

C T . The duct and the yolk sac are

positioned in the body stalk.

D T . These communications soon

close.

30 The somites of the mesodermal layer:

Develop from the lateral plate mesoderm.

Are arranged serially as blocks of mesoderm on each side of the notochord.

Start to develop about the middle of the embryo and progress cranially and caudally.

Differentiate into a ventromedially placed dermo myotome.

A F. They develop from the paraxial mesoderm.

B T. The number of pairs is used as

an indication of the stage of
development. Most cranial and
caudal somites disappear, the final
number approximating to the adult
number of 31 spinal nerves.

C F. The process starts adjacent to the cranial end of the

notochord and progresses caudally.

D F. This is the site of the

sclerotome, the dermomyotome is
placed dorsolaterally.

31 The dermomyotome:

Forms the viscerocranium.

Gives rise to the hypomere.

Gives rise to the dermis of skin.

Gives rise to the muscles of facial expression.

32 The intra - embryonic coelome:

Develops as clefts in the

dermomyotome.

Communicates with the pericardial cavity.

Is lined by splanchnopleuric mesoderm.

Communicates with the cavity of the allantois.

A F. This and the neurocranium are formed from sclerotome.


B T. Also to the smaller dorsally placed epimere.

C T. Migration from the dermomyotome beneath the ectoderm produces the dermis and subcutaneous tissues.

D F. These are derivatives of the 2nd pharyngeal arch mesenchyme.

A F. It develops in clefts in the lateral plate mesoderm.

B T. The pericardioperitoneal canals are so formed on each side and are the future pleural sacs.
C T . This lines the endoderm
whereas the somatopleuric
mesoderm lines the ectoderm.
D F. The allantoic diverticulum from the cloaca grows into the body stalk and lies alongside the coelomic cavity in the umbilical cord.

33 The diaphragm:

Is formed mainly from a dorsal mass of mesenchyme known as the septum transversum.

Receives contributions from the

pleuropericardial membranes.


Receives contributions from the ventral mesentery.

Receives contributions from the body wall.

A F. The septum grows from the ventral body wall to contribute
to the diaphragm.

B F. These folds are over the common cardinal veins and separate the pleural and pericardial cavities.

C F . The dorsal mesentery of the oesophagus does contribute.

D T . Additional paired transverse dorsal folds, the pleuroperitoneal
membranes, grow out and fuse with the septum transversum in front, and the dorsal mesentery of the lower oesophagus behind.

34 The mesonephros:

Forms the secretory part of the adult kidney.

Gives rise to the paramesonephric duct.

Is a derivative of the lateral plate mesoderm.


Opens via its duct into the cloaca.

A F . This is derived from the

metanephros.

B F . The paramesonephric (Mullerian) duct is a separate tube appearing in the 6th week. The ducts from each side form, in the female, the uterine tubes, uterus and upper vagina.
C F. It, like the pro- and metanephros, is derived from the intermediate cell mass (nephrogenic cord).

D T . The mesonephric (Wolffian) duct persists in the male as the

ductus deferens. A diverticulum from the duct, the ureteric bud, forms the collecting system of the adult kidney.

35 The primitive urogenital sinus receives the:

Pronephric duct.

Mesonephric duct.

Paramesonephric duct.

Allantois.

A F . This duct does not persist jn the embryo.

B T. This becomes incorporated into the sinus and forms the trigone of the bladder.

C T. In the female the fused paramesonephric ducts enter the distal part of the sinus.

D T. The communication between the bladder and the allantois, the urachus, may persist but usually forms the median

36 During the development of the external genitalia the:

Primitive streak mesoderm migrates around the cloacal membrane.
Laterally placed cloacal eminences develop into the body of the penis.

Cloacal swellings form the glans penis.

Genital folds form the labia majora.

A T. This takes place at the end of 3rd week.

B F. The cloacal eminence is a single midline structure developing adjacent to the midline allantois. It becomes known as the genital tubercle and forms the
clitoris in the female and the glans penis in the male.


C F. The cloacal (labioscrotal) swellings form the labia majora in the female and the scrotum in the male.

D F . The genital folds form the labia minora in the female and the body of the penis in the male.

37 In the development of the cardiovascular system the:

Blood vessels are developed from migrating endodermal cells.

Heart is formed by the fusion of two tubes which invaginate the pericardium and form its dorsal mesentery.

Dorsal mesentery of the pericardium breaks down and forms the oblique sinus.

First heart beat occurs about the 4th week.

A F. Primitive mesodermal cells known as angioblasts form the endothelium of the vessels.

B T.

C F. The defect in the mesentery becomes the transverse sinus lying between the arterial and venous ends of the tube.

D T . Although the circulation is not established at this time.

38 During development the inferior vena cava receives contributions from the:

Right subcardinal vein.

Left subcardinal vein.

Right supracardinal vein.

Right anterior cardinal vein.

39 In the development of the venous system the:

Superior vena cava is formed from the right anterior cardinal veih.

Coronary sinus is derived from the left common cardinal vein.

Ductus venosus links the left umbilical vein and the inferior vena cava.

Azygos vein is derived from the primitive right prevertebral plexus.

A T . Further contributions are received from the right posterior


B F . cardinal vein, the right renal vein, and separate links

C F . between the subcardinal and hepatic veins.

D F .

A T . The left anterior cardinal vein usually disappears.

B T .

C T It usually closes before birth, thus making the umbilical blood pass through the liver sinusoids.

D T . The azygos system of veins drains the posterior thoracic wall.

40 In the development of the 6 paired aortic arches the:

Definitive adult aortic arch develops from the 3rd left arch.

4th arches disappear.


Communication between the left 3rd and 6th arches persists as the ductus arteriosus.

6th arch contributes to the pulmonary arteries.

42 During development of the endodermal layer the:

Oropharyngeal membrane breaks down in the 4th to 5th week of intra-uterine life.

Tracheobronchial diverticulum bifurcates into the lung buds in the 6th week of intra-uterine life.

Lung buds invaginate the pericardioperitoneal canals and acquire a covering of spanchnopleuric mesoderm.

Gut tube possesses both ventral and dorsal mesenteries over its whole length.

A F. The adult aortic arch and the right subclavian artery are derived from the left and right 4th arches respectively.

B F.

C F. The ductus arteriosus unites the left 4th and 6th arch derivatives.

D T . The pulmonary arteries grow out from the 6th arch near the ventral aorta.

A T. The mouth and foregut are then in continuity.

B T. The diverticulum descends in front of the oesophagus.

C T. This mesoderm develops into the connective tissue, smooth muscle and blood vessels of the adult lung and into the pleura.

D F. ventral mesentery is limited to the

foregut.

42 The liver:

Develops as a dorsal bud from the primitive gut.

During development, divides the ventral mesentery into the falciform ligament and the lesser omentum.

Bud arises near to the junction of the primitive fore- and midgut.

Bile ducts are derived from the mesoderm of the septum transversum.

A F . The liver bud grows from the ventral surface of the primitive gut.

B T . The liver occupies most of the available space and the mesentery is stretched over it.

C T

D F . Cords and plates of liver cells, derived from the liver bud,
penetrate the septum transversum and come alongside the sinusoids derived mainly from the vitelline and umbilical
veins. The extrahepatic biliary system is derived from the proximal part of the liver bud.

43 The primitive midgut:

Outgrows the peritoneal cavity and
so is extruded into the body stalk
between the 6th and 12th weeks of
intra-uterine life.

Loop has the inferior mesenteric artery as its axis.

Loop rotates clock-wise through 180
as it returns to the abdominal cavity,
(viewed from the ventral surface).
Extends to approximately the unction
of the middle and distal thirds of the adult transverse colon.


A T . This is the stage of herniation in the development of the gut.

B F . The superior mesenteric artery is its axis of rotation.

C F . The rotation is 270counterclockwise.

D T . This is near the splenic flexure.

44 In development of the ectodermal germ layer:

The neural plate gives rise to the neural

crest.

The neural crest becomes differentiated

into the dorsal root ganglia.

The mammary glands are derived from this layer.

Rathkes pouch is derived from this
layer.


A F . The plate becomes differentiated in to the future central nervous system. Neural crest cells are derived from adjacent ectoderm.

B T. It also forms the cranial, peripheral and autonomic ganglia, and the suprarenal medulla.

C T . Anywhere along the milkline from axilla to groin.

D T . As is the rest of the stomodeum from which it develops.

45 The placenta:

Develops from the trophoblast opposite the body stalk.

Is divided into approximately 20 cotyledons on its maternal surface.

Maternal vessels form a dense capillary network over the trophoblastic villi.

maternal blood is partly mixed with the fetal circulation.

A T . The trophoblastic villi become increased in size and number
over this area. They invade the decidua.


B T . The weight is approximately 500 grams, the organ is 34 cm
thick and 1520cm in diameter.

C F . The uterine (maternal) vessels open into lakes of blood around the villi. These lakes are lined by maternal endothelium.

D F . The maternal uterine vessels open into lakes of blood around the villi which contain the fetal blood vessels. Fetal endothelium, mesenchyme and trophoblast separate the two circulations.