Embryology Practice Questions with Answers

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Shout out to swayze for forwarding this file to me

1. The part of the sperm containing proteolytic enzymes to digest the zona pellucida is the:

A. capacitor
B. head
C. corona
D. acrosome
E. cumulus

D. is correct.
The acrosome is the part of the sperm containing proteolytic enzymes to digest the zona pellucida. It is exposed by the process of capacitation. Then, under the influence of substances released by corona radiata cells, it releases its proteolytic enzymes and penetrates the oocyte.

2. The ovulated mammalian oocyte is arrested at:

A. prophase of meiosis I
B. metaphase of meiosis I
C. prophase of meiosis II
D. metaphase of meiosis II
E. none of the above

D. is correct.
The 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 II until fertilized.

3. The seven-day blastocyst:

A. has a single layer of trophoblast at the embryonic pole
B. has an amniotic cavity
C. is attached to the endometrial epithelium
D. is surrounded by a degenerating zona pellucida
E. is called the hypoblast

C. is correct.
The decidual reaction of the endometrium creates a nourishing environment for the conceptus a it buries itself by invasion of the uterine endometrial wall. Progesterone produced by the corpus luteum stimulates glandular secretion in the endometrium during the secretory phase of menstruation or early pregnancy.

4. Haploid nuclei that fuse at fertilization are called:

A. homunculi
B. mitotic figures
C. centrioles
D. nucleoli
E. pronuclei

E. is correct.
After the sperm reaches the ovum, it deposits its genetic load, the male pronucleus, into the cytoplasm of the egg. After finally completing the meiotic division that had begun years before, the female pronucleus fuses with the male pronucleus to create the diploid nucleus of the zygote

5. The first week of human development is characterized by formation of the:

A. inner cell mass
B. hypoblast
C. trophoblast
D. blastocyst
E. all of the above

E. is correct.
At four days, the blastocyst cavity of blastocele forms within the morula. Trophoblast are outer cells of the blastocyst, while a knot of cells appears, protruding into the blastocele. This is the inner cell mass. Trophoblast becomes 2 layers: syncytiotrophoblast and cytotrophoblast. Inner cell mass becomes epiblast and hypoblast.

6. During implantation, the blastocyst:

A. implants in the endometrium
B. usually attaches to endometrial epithelium at its embryonic pole
C. usually implants in the posterior wall of the body of the uterus
D. causes change in the endometrial tissues
E. all of the above are correct

E. is correct.
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.

7. Capacitation of the sperm:

A. is caused by the zona pellucida
B. occurs in the male
C. prevents polyspermy
D. is essential for fertilization
E. removes the head of the sperm

D. is correct.
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. Capacitation occurs within the female genital tract, and without its occurrence, fertilization could not occur.

8. The early stages of cleavage are characterized by:

A. formation of a hollow ball of cells
B. formation of the zona pellucida
C. increase in the size of the cells in the zygote
D. increase in the number of cells in the zygote
E. none of the above

D. is correct.
The earliest stages of cleavage are marked by a series of mitotic divisions that increase the number of cells in the zygote without an increase in size. As the cleavage continues the zygote becomes a morula or a solid ball of 12-16 cels. A cavity forming within the morula transforms it into a blasocyst, at about day 4.

9. The most common site for implantation in ectopic pregnancy is:

A. internal os of the uterus
B. mesentery
C. ovary
D. uterine tube
E. other

D. is correct.
The most common site of ectopic implantation is the uterine tube. The growth of the embryo in this site usually causes rupture of the tube and severe hemorrhage in the mother. Abdominally, an ectopic pregnancy often occurs in the rectouterine pouch, an area between the uterus and the rectum.

10. With the light microscope, the zona pellucida appears as a translucent membrane surrounding the:

A. primary oocyte
B. zygote
C. morula
D. very early blastocyst
E. all of the above are correct

E. is correct.
The zona pellucida persists until early it the blastocyst stage. It dissolves during the blastocyst stage in order that implantation may occur.

11. The amniotic cavity develops:

A. on the tenth day
B. within the outer cell mass
C. within the inner cell mass near the cytotrophoblast
D. in extraembryonic mesoderm
E. none of the above

C. is correct.
The amniotic cavity begins to develop around the 8th ay as a slit-like area within the epiblast near the cytotrophoblast. It usually ha a thin strip of epiblast cells, called amnioblasts, between it and the cytotrophoblast.

12. During the second week of development, the trophoblast differentiates into:

A. syncytiotrophoblast
B. ectoderm
C. intraembryonic mesoderm
D. yolk sac (secondary)

A. is correct.
The trophoblast gives rise to both the syncytiotrophoblast and the cytotrophoblast, as well as the extraembryonic mesoderm. The ectoderm is a derivative of the epiblast, and the secondary yolk sac comes from endoderm cells that line the exocoelomic cavity or the primitive yolk sac.

13. The first two intraembryonic germ layers to differentiate are the:

A. ectoderm and hypoblast
B. epiblast and hypoblast
C. ectoderm and endoderm
D. ectoderm and mesoderm

B. is correct.
The epiblast and hypoblast develop from the inner cell mass during the 2nd week. During the 3rd week, the epiblast produces cells between itself and the hypoblast, called the mesoderm. Epiblast also replaces the hypoblast with endoderm cells. Epiblast then changes its name to ectoderm, completing the process of gastrulation.

14. The blastocoele becomes the:

A. amniotic cavity
B. extraembryonic coelom
C. primary yolk sac
D. chorionic cavity
E. secondary cavity

C. is correct.
Around the 9th day, cells from the hypoblast spread around the blastocoele, forming the exocoelomic or Heuser's membrane. When the blastocoele is surrounded by this membrane, it is referred to as the primary yolk sac or exocoelomic cavity.

15. The bilaminar germ disc:

A. consists of epiblast and mesoblast
B. is derived from the outer cells of the morula
C. forms the embryo proper
D. synthesizes human chorionic gonadotropin, HCG

C. is correct.
The bilaminar germ disc develops from the inner cells of the morula and inner cell mass of the blastocyst. It is composed to epiblast and hypoblast layers, and it is also called the embryoblast because it becomes the embryo. The outer cells of the morula and blastocyst become cyto- and syncytiotrophoblast. The latter produces HCG.

16. The primitive streak first appears at the beginning of the _____ week.

A. first
B. second
C. third
D. fourth
E. fifth

C. is correct.
Gastrulation, the process of formation of the three germ layers, occurs during the third week. Epiblast cells form a thickening called the primitive streak, with a primitive knot or node located at its cranial end. Epiblast cells invaginate from this streak to form the mesoderm layer and to replace hypoblast with endoderm.

17. Which of the following structures is believed to be a primary organizer or inducer during organogenesis?

A. somites
B. notochord
C. metanephric blastema
D. lens placode
E. none of the above

B. is correct.
The notochord is thought to be an important structure in induction of nervous system development, axial skeleton development and other organogenic events.

18. Cells from the primitive streak DO NOT become:

A. endoderm
B. intermediate mesoderm
C. paraxial mesoderm
D. lateral plate mesoderm
E. amnioblasts

E. is correct.
All mesoderm is a derivative of the invaginating cells at the primitive streak. The invagination occurs at the beginning of the third week. It is interesting that endoderm cells are also derived from the epiblast during gastrulation, replacing the hypoblast.

19. The primitive streak:

A. is derived from the outer cells of the morula
B. is formed during the second week in development
C. persists as the cloacal membrane
D. is the site of involution of epiblast cells to form mesoderm
E. was done in a bathing suit, for those who remember streaking

D. is correct.
The primitive streak begins to form on the surface of the epiblast at the beginning of the third week. It is at the primitive streak that epiblast cells invaginate to form the mesoderm, through the process of gastrulation. Streaking was a fad of the 1970's that involved running naked in public, definitely not a winter sport.

20. In the third week of human embryonic development:

A. the amnion appears
B. a bilaminar embryonic disc is formed
C. the body stalk moves ventrally and joins with the yolk sac stalk to form the umbilical cord
D. the neural plate is induced by the notochordal process and associated mesoderm
E. the uteroplacental circulation is established

D. is correct.
It is during the third week that the notochordal process and its associated mesoderm induce the neural plate. The hollow notochordal process eventually becomes the solid notochord, the forerunner of the axial skeleton.

21. During development, the notochordal process:

A. arises from involuting endodermal cells
B. extends from the prochordal plate to the primitive node
C. is involved in the induction of the primitive gut
D. becomes the appendicular skeleton

B. is correct.
The notochordal process extends from the primitive node up to the prochordal plate. It develops into the notochord, around which the vertebral column forms. The notochord is not endodermal, and does not induce the primitive gut. It persists in the adult only as the nucleus pulposus of the intervertebral discs.

22. The following organs are derived from mesoderm EXCEPT:

A. skeletal musculature
B. musculature of blood vessels
C. cardiac musculature
D. suprarenal cortex
E. suprarenal medulla

E. is correct.
The suprarenal or adrenal medulla is actually a part of the sympathetic nervous system. Therefore, it is a derivative of neural crest cells, and neural crest cells are ectodermal in origin.

23. Somites:

A. differentiate into myotomes which give rise to skeletal muscle in trunk and limbs
B. differentiate into sclerotomes which give rise to vertebrae
C. arise from segmentation of the paraxial mesoderm
D. differentiate into myotomes which give rise to skeletal muscle of the limbs
E. all of the above are correct

E. is correct.
Somites differentiate into sclerotomes, myotomes and dermatomes. The sclerotomes give rise to the vertebrae. The myotomes give rise to skeletal muscle of the trunk and limbs. The dermatomes give rise to the dermal skin component. The skeletal muscle of the face arises from the pharyngeal arches.

24. Almost all of the internal organs are well laid down at _____ months.

A. 1
B. 2
C. 3
D. 4
E. 5

B. is correct
By the end of the embryonic period at about two months of the development almost all of the internal organs are well established. This is important, in that most malformations occur within the first two months, while the internal organs are being formed. The rest of the gestational period allows for growth and maturation.

25. Which of the following structures does not turn under onto the ventral surface of the embryo during folding of the head?

A. prochordal plate
B. heart
C. notochord
D. pericardial cavity
E. septum transversum

C. is correct.
The buccopharyngeal membrane, heart, pericardial cavity and septum transversum all end up as ventral structures in the embryo, whereas the notochord remains dorsal. Remember, though, that before the folding of the embryo, the heart begins its development extraembryonically in a region anterior to the prochordal plate.

26. When the amount of amniotic fluid exceeds two liters, the condition is called:

A. oligohydramnios
B. polyhydramnios or hydramnios
C. amniotitis
D. bag of waters
E. hydrogravida

B. is correct.
Polyhydramnios is a condition of excess amniotic fluid exceeding 1.5 liters. It is often caused by failure of the fetus to drink the normal amount of amniotic fluid, and may be due to anencephaly, esophageal atresia, or an upper GI tract blockage. Oligohydramnios, too little amniotic fluid, may indicate urinary problems.

27. The wall of the chorionic sac is composed of:

A. cytotrophoblast and syncytiotrophoblast
B. two layers of trophoblast lined by extraembryonic somatic mesoderm
C. trophoblast and exocoelomic membrane
D. extraembryonic splanchnic mesoderm and both layers of trophoblast
E. none of the above

B. is correct.
The outer layer of chorionic sac is the cytotrophoblast shell; the sac is lined with extraembryonic mesoderm of somatic type, because it does not contact the yolk sac; lining the intervillous space is syncytium. Later, the amniotic sac pushes up against and fuses to the chorionic sac, obliterating the chorionic cavity.

28. The most distinctive characteristic of a primary chorionic villus is its:

A. outer syncytiotrophoblastic layer
B. cytotrophoblastic shell
C. extraembryonic somatic mesodermal core
D. bushy appearance
E. cytotrophoblastic core

E. is correct.
All chorionic villi possess an outer layer of syncytiotrophoblast. The cytotrophoblast shell is a feature of the mature chorion. Extraembryonic somatic mesoderm forms the core of secondary villi, becoming tertiary with vascular development. Primary villi, at 14 days, are syncytial processes with a core of cytotrophoblast.

29. Chorionic villi are designated as secondary chorionic villi when they:

A. contact the decidua basalis
B. are covered by syncytiotrophoblast
C. develop a mesenchymal core
D. give rise to branch villi
E. none of the above

C. is correct.
All chorionic villi possess an outer layer of syncytiotrophoblast. The cytotrophoblast shell is a feature of the mature chorion. Extraembryonic somatic mesoderm forms the core of secondary villi, becoming tertiary with vascular development. Primary villi, at 14 days, are syncytial processes with a core of cytotrophoblast.

30. When chorionic villi become vascularized they are called _____ villi.

A. branch
B. stem
C. tertiary
D. anchoring
E. mature

C. is correct
As secondary chorionic villi become vascularized, they become known as tertiary villi. Maturation of the villi involves thinning of the placental barrier, so that only a thin layer of syncytium, extracellular matrix and endothelium separates maternal and fetal blood.

31. The most important region of the decidua for the nourishment of the conceptus is the decidua ___________.

A. frondosum
B. capsularis
C. parietalis
D. basalis
E. laeve

D. is correct.
The placenta is made of maternal tissue, the decidua basalis, and fetal tissue, the chorion frondosum or bushy/villous chorion. The smooth chorion or chorion laeve is covered by decidua capsularis, which disappears as the fetus grows and smooth chorion pushes up against he decidua parietalis.

32. The intervillous space contains all of the following substances EXCEPT:

A. oxygen
B. carbon dioxide
C. maternal blood cells
D. fetal blood
E. electrolytes

D. is correct
Maternal blood cells find their way through the dark intervillous space with electrolytes, oxygen and other good things, and they carry away bad things like carbon dioxide and fetal waste products. However, fetal blood does not normally enter the intervillous space but is separated from it by the placental barrier.

33. The portion of the decidua which does not survive until the end of pregnancy is the:

A. capsularis
B. basalis
C. laeve
D. parietalis
E. frondosum

A. is correct
Chorion frondosum and the decidua basalis make up the placenta. Chorion laeve, or smooth chorion, is covered by decidua capsularis. As the fetus and chorion enlarge the chorion laeve pushes against the decidua parietalis and the capsularis disappears.

34. Which of the following is NOT a component of the mature placental barrier?

A. the endothelial lining of fetal capillaries
B. the cytotrophoblast
C. the syncytiotrophoblast
D. the basement membrane of fetal capillaries
E. all of the above are part of the mature placental barrier

B. is correct.
In the last half of pregnancy, the cytotrophoblast and extraembryonic mesoderm layers are lost from the placental barrier, leaving only syncytium, capillary basement membrane and capillary endothelium between maternal and fetal circulations.

35. Failure of the brain to grow may result in:

A. plagiocephaly
B. craniostenosis
C. acrocephaly
D. scaphocephaly
E. microcephaly

E. is correct.
If the brain does not grow, neither will the skull. This results in microcephaly. Premature closure of cranial sutures is called craniostenosis. Early sagittal suture fusion causes scaphocephaly or a long skull. Early coronal fusion causes acrocephaly or tower skull. Asymmetric fusions produce plagiocephaly.

36. Somitomeres, paraxial mesoderm cranial to the somites, give rise to much of the skeletal muscle in the head EXCEPT:

A. extrinsic muscles of the eye
B. temporalis tongue muscles
C. muscles of facial expression
D. muscles of mastication

B. is correct.
Somitomeres provide myotomal tissue for skeletal muscle development to the head. Muscles of somitomere origin include the extrinsic eye muscles, the muscles of facial expression and the muscles of mastication, of which temporalis is one. Tongue muscles and the muscles of the larynx are from somitic myotomes.

37. The sphenoid bone is derived from which portion of the embryonic skull?

A. cartilaginous neurocranium
B. membranous neurocranium
C. cartrilaginous viscerocranium
D. membranous viscerocranium
E. branchial cartilage

A. is correct.
The skull consists of two parts, the neurocranium, which forms the vault protecting the brain, and the viscerocranium, which forms the bones of the face. The base of the skull, of which sphenoid is part, develops from the cartilaginous neurocranium because it forms by endochondral ossification. Skull vault is membranous.

38. The notochord is replaced by the:

A. ependyma
B. nucleus pulposus
C. spinal canal
D. dorsal roots
E. spinal cord

B. is correct.
The notochord is the forerunner of the vertebral column. As it is replaced by the vertebral column, it degenerates. All that remains of the notochord in the adult is the nucleus pulposus in the intervertebral discs, surrounded by the sclerotome-derived annulus fibrosus.

39. The intraembryonic coelom located cranial to the oropharyngeal membrane becomes the:

A. oral cavity
B. cranial foregut
C. stomodeum
D. pericardial cavity
E. nasal cavity

D. is correct.
The cardiogenic region lies cranial to the prochordal plate and its descendant, the oropharyngeal membrane. The heart tubes form on the endoderm side of intraembryonic coelom in the cardiogenic region. Following the head and lateral body folding, heart and its portion of intraembryonic coelom called pericardial cavity lie in the chest.

40. The derivatives of the embryonic ventral mesentery include the following structures EXCEPT:

A. hepatoduodenal ligament
B. hepatogastric ligament
C. falciform ligament
D. ligamentum teres hepatis
E. lesser omentum

D. is correct.
The ligamentum teres hepatis is a remnant of the fetal umbilical vein. Although it is contained within the ventral mesentery, it is not a derivative of it.

41. The following peritoneal ligaments are derived wholly or in part from the embryonic dorsal mesogastrium EXCEPT:

A. hepatogastric ligament
B. splenorenal or lienorenal ligament
C. gastrosplenic or gastrolienal ligament
D. gastrocolic ligament
E. transverse mesocolon

A. is correct.
Splenorenal, gastrosplenic and gastrocolic ligaments are derived from the dorsal mesogastrium, while transverse mesocolon fuses with dorsal mesogastrium. The nepatogastric ligament, on the other hand, is derived from the ventral mesentery.

42. After folding of the head region, the structure lying just caudal to the pericardial cavity is the:

A. developing heart
B. connecting stalk
C. primitive streak
D. liver
E. septum transversum

E. is correct.
The septum transversum is the diaphragm's earliest progenitor. After folding of the head region brings the heart and its coleom region ventrally, the septum transversum is the structure that lies immediately caudal to it. Liver is not a bad guess, but remember that the diaphragm lies between it and the thorax in the adult.

43. The hypobranchial eminence contributes to formation of:

A. anterior portion of the tongue
B. posterior portion of the tongue
C. musculature of the tongue
D. epiglottis
E. palatine tonsil

B. is correct.
Hypobranchial eminence forms the posterior third of the tongue. It is served by the nerve of the 3rd branchial arch, glossopharyngeal. Tongue musculature arises from occipital somites and is innervated by CN XII, hypoglossal. Epiglottis arises as an epiglottic swelling on the 4th arch. Palatine tonsil is from the 2nd pouch.

44. The fact that general and special sensory information from the posterior part of the tongue is carried by glossopharyngeal nerve indicates that this part of tongue is from branchial arch _____.

A. I

C. is correct
Hypobranchial eminence forms the posterior third of the tongue. It is served by the nerve of the 3rd branchial arch, glossopharyngeal, or cranial nerve IX. Glossopharyngeal carries general sense and the special sense of taste fromthis part of the tongue. In anterior tongue, trigeminal does general and facial does special sense.

45. Myoblasts from the occipital myotomes are believed to give rise to the muscles of the:

A. eye
B. face
C. ear
D. jaw, for mastication
E. tongue

E. is correct.
Most of the muscles of the head arise from the somitomeres located cranial to the occipital somites. Occipital myotomes supply muscle for tongue, and are innervated by cranial nerve XII, hypoglossal.

46. As a resident in pediatrics, you are called to see a newborn who has a unilateral cleft lip and a unilateral cleft of the primary palate. This condition is most likely the result of:

A. failure of fusion of the mandibular prominences
B. failure of fusion of the medial nasal processes
C. failure of fusion of the maxillary prominence with the medial nasal prominence
D. failure of fusion of the lateral palatine processes with the nasal septum
E. failure of fusion of the paired lateral palatine processes.

C. is correct.
This type of cleft is a failure of fusion, or secondary rupture of the union, of maxillary prominence with medial nasal prominence. If the palatine shelves or processes of maxillary prominences rupture or fail to fuse, a midline defect of the secondary palate will result.

47. Which of the following structures is NOT part of the first branchial arch?

A. malleus
B. mandibular process
C. sphenomandibular ligament
D. stylohyoid ligament
E. maxillary process

D. is correct.
Mandibular and maxillary processes are both from first arch, as are malleus and incus bones of the ear. Sphenomandibular ligament is the remnant of the perichondrium of Meckel's cartilage, around which the mandible forms. Second arch cartilage gives rise to stapes, styloid process, stylohyoid ligament, lesser horns and upper part of hyoid.

49. Which structures are derived from the intermaxillary segment of the embryonic face?

A. philtrum
B. anterior portion of the palate
C. anterior portion of the upper jaws
D. upper incisor teeth
E. all of the above are correct

E. is correct.
The intermaxillary segment gives rise to the philtrum, the upper incisors, the anterior portion of the upper jaws, and the primary palate, which lies anteriorly.

50. The nasolacrimal groove separates the:

A. mandibular and maxillary swellings
B. lateral nasal swelling and maxillary swelling
C. medial nasal swelling and maxillary swelling
D. first and second branchial arches
E. otic and optic vesicles

B. is correct.
The nasolacrimal groove lies between the maxillary swelling or prominence and the lateral nasal swelling. This groove ultimately forms the nasolacrimal duct and lacrimal sac. In the adult, it is the passage used by tears to travel from the eye to inferior meatus of the nasal cavity, to make your nose run when you cry.

51. Many facial malformations are believed to be due to:

A. a failure of the oral membrane to rupture
B. a failure to neural crest cells to migrate into the facial processes
C. a failure in growth of the head fold
D. an abnormal persistence of the pharyngeal clefts
E. none of the above

B. is correct
Proper migration of neural crest cells into the face area is vitally important to facial development. Neural crest tissue will form much of the facial skeleton.

52. The foramen cecum of the adult tongue:

A. marks the point of embryonic evagination of the thymus gland
B. divides the tongue into two parts, an anterior one-third and a posterior two-thirds
C. marks the point of embryonic evagination of the thyroid gland
D. develops into taste buds
E. has no embryologic significance

C. is correct.
The foramen cecum on the tongue is the point from which the thyroid gland evaginated and began its journey down into the neck. It lies at the apex of the V-shaped terminal sulcus, which divides the tongue into anterior 2/3rds, from the lateral lingual swellings and truberculum impar, and posterior 1/3rd, from the copula.

53. Each pharyngeal arch includes:

A. derivatives of ectodermal neural crest cells
B. an aortic arch artery
C. a mesodermal core from paraxial mesoderm
D. a cranial nerve
E. all of the above

E. is correct.
The pharyngeal arches have their own mesodermal core, giving rise to cartilaginous and muscular components, cranial nerve components, vascular components and derivatives of neural crest cells, which supplement much of the connective tissue of the face.

54. Which of the following are associated with the 2nd pharyngeal arch?

A. the malleus bone
B. facial nerve
C. glossopharyngeal muscle
D. the lower portion of the hyoid bone
E. anterior belly of digastric

B. is correct.
The stapes, styloid process, stylohyoid ligament, lesser horn of hyoid and upper part of hyoid body all come from 2nd arch. The nerve of the 2nd arch is CN VII or facial nerve, and the muscles are stapedius, stylohyoid, posterior belly of digastric and the muscles of facial expression.

55. Branchial cysts or lateral cervical cysts:

A. are found along the anterior border of the sternocleidomastoid muscle
B. are formed from a rupture of the membrane between pharyngeal pouches and branchial clefts
C. are remnants of the thyroglossal duct
D. are found in front of the ear

A. is correct
Lateral cervical cysts are remnants of the cervical sinus, which forms when the 2nd arch grows over the 3rd and 4th arches. The cysts are found along the anterior border of the sternocleidomastoid muscle, usually just below the angle of the jaw. They have nothing to do with the rupture or anything.

56. The heart is derived from:

A. splanchnic mesoderm
B. somatic mesoderm
C. septum transversum
D. intermediate mesoderm
E. paraxial mesoderm

A. is correct
The heart tubes form within the cardiogenic region cranial to the oropharyngeal membrane and beneath the intraembryonic coelom. If it is beneath the intraembryonic coelom, then it lies toward the yolk sac and must be splanchnic mesoderm. Somatic mesoderm would be the other side, or roof, of the intraembryonic coelom.

57. The most superior part of the inferior vena cava is derived from:

A. left vitelline vein
B. right vitelline vein
C. right umbilial vein
D. left umbilical vein
E. sinus venosus

B. is correct.
The vitelline veins, as they pass through the developing liver, break up into hepatic sinusoids. When the left sinus horn regresses, blood is shunted from the left vitelline vein to the right, which enlarges and ultimately forms the posthepatic portion of the inferior vena cava.

58. The embryonic origin of the ligamentum arteriosum is from the:

A. second arch artery
B. third arch artery
C. fourth arch artery
D. fifth arch artery
E. sixth arch artery

E. is correct
The sixth arch is the pulmonary arch, from which pulmonary arteries are derived. On the left side, this arch maintains its connection with the dorsal aorta. In the fetus, this connection is patent and is called the ductus arteriosus. Postnatally, it closes and persists as the ligamentum arteriosum.

59. The following are true statements with regard to the fetal circulation EXCEPT:

A. Since the fetal liver is a hemopoietic organ, it is large and well supplied with oxygenated blood.
B. Fetal brain receives relatively pure arterial blood.
C. Fetal and maternal blood vessels anastomose in the placenta
D. In early developmental stages, one pulmonary vein buds from the left atrium of the heart.
E. Foramen primum of the interatrial septum closes after the formation of the foramen secundum.

C. is correct.
In the placenta, there is no anastomosis between the maternal and fetal vessels. Maternal blood from the spiral arteries enters the cotyledons, where it bathes the villi from the fetus. This all occurs without anastomosis.

60. Each of the following statements are correctly paired EXCEPT:

A. right vitelline vein - inferior vena cava
B. left vitelline vein - liver sinusoids
C. right anterior cardinal vein - part of superior vena cava
D. right umbilical vein - definitive umbilical vein
E. left sinus horn - coronary sinus

D. is correct.
The right umbilical vein totally disappears. The definitive umbilical vein is the left one. After birth, it closes and becomes the ligamentum teres hepatis.

61. The following embryonic structures are involved in the formation of the definitive right atrium EXCEPT:

A. primitive atrium
B. right sinus venosus
C. left sinus venosus
D. right sinus horn
E. left sinus horn

E. is correct.
The left sinus horn regresses during development to form coronary sinus. Oblique vein of left atrium, from left common cardinal, drains to it. Coronary sinus drains blood from the heart into the right atrium.

62. Each of the following ligaments in the adult are derived from fetal blood vessels EXCEPT:

A. medial umbilical ligament
B. median umbilical ligament
C. round ligament of the liver (ligamentum teres hepatis)
D. ligamentum venosum
E. ligamentum arteriosum

B. is correct.
Median umbilical ligament, attaching to upper part of bladder, is a remnant of the urachus, which itself was a remnant of the allantois. The allantois was a connection between the urinary bladder and the yolk sac, not a fetal blood vessel.

63. Of the following the one most closely associated with the ligamentum teres hepatis is:

A. umbilical vein
B. umbilical artery
C. vitelline vein
D. 3rd aortic arch
E. 6th aortic arch

A. is correct.
The ligamentum teres hepatis is the remnant of the umbilical vein after the umbilical vein closes at birth. It can be found in the falciform ligament, a ventral mesentery derivative.

64. Of the following, the one most closely associated with the portal vein is:

A. umbilical vein
B. umbilical artery
C. vitelline vein
D. 3rd aortic arch
E. 6th aortic arch

C. is correct.
The protal vein forms when an anastomotic network around the duodenum forms one vessel. This anastomotic network is from the veins of the gut, the vitelline veins.

65. The sinus venosus:

A. has a right horn which persists in the adult as the coronary sinus
B. has a left venous valve which develops into the valve of the coronary sinus
C. forms the smooth-walled portion of the adult right atrium
D. receives blood directly from the portal vein

C. is correct.
The left sinus horn regresses and persists as the main vein of the heart, the coronary sinus, whose valve arises from the inferior part of the right venous valve. The right sinus horn is incorporated into the right atrium, where it forms the smooth-walled part. The portal vein does not send blood to the sinus venosus.

66. Ostium secundum defect:

A. is characterized by a large opening between left and right atria
B. may be caused by excessive resorption of septum primum
C. may be caused by inadequate development of septum secundum
D. may be accompanied by intracardiac shunting of blood
E. all of the above are correct

E. is correct.
An ostium secundum defect is a large opening between the atria that can be caused either by excessive resorption of the septum primum or inadequate development of the septum secundum. Depending on the size of the defect, there can be shunting of the blood between the atria.

67. In the development of the heart:

A. the coronary sinus is formed from the left horn of the sinus venosus
B. the oblique vein of the left atrium is formed from the left posterior cardinal vein
C. the valve of the coronary sinus is formed from the left sinus valve
D. the valve of the inferior vena cava is formed from the left sinus valve

A. is correct.
Left horn of sinus venosus forms coronary sinus and left common cardinal vein becomes oblique vein of the left atrium. The right sinus valve becomes the valve of the coronary sinus and the valve of inferior vena cava. Left sinus valve becomes part of interatrial septum.

68. The mesenchymal cells which aggregate to form blood islands are called:

A. hemoblasts
B. mesoblasts
C. fibroblasts
D. angioblasts
E. none of the above

D. is correct.
Angioblasts are the cells that form the blood islands. These blood islands then develop into the blood cells and the endothelium of the blood vessels. This early blood cell and blood vessel formation occurs first in the extraembryonic mesoderm of the yolk sac, chorion and connecting stalk.

69. Closure of the foramen primum results from fusion of the:

A. septum secundum and the fused endocardial cushions
B. septum secundum and the septum primum
C. septum primum and the fused endocardial cushions
D. septum primum and the septum spurium
E. septum primum and the sinoatrial valves

C. is correct.
The septum primum and the endocardial cushions fuse to close the foramen primum. Subsequently, perforations in the upper part of the septum primum coalesce to form the foramen secundum. It is this foramen that closes postnatally when left atrial pressure equals right atrial pressure.

70. The most common type of cardiac septal defect is:

A. muscular type ventricular septal defect, or VSD
B. secundum type atrial septal defect, or ASD
C. membranous type VSD
D. primum type ASD
E. sinus venosus

C. is correct.
Although the most common ATRIAL septal defect is the secundum type ASD, the overall most common cardiac septal defect is the membranous type VSD.

71. The fetal left atrium is mainly derived from the:

A. primitive pulmonary vein
B. primitive atrium
C. right pulmonary vein
D. sinus venarum
E. sinus venosus

A. is correct.
The primitive pulmonary vein becomes incorporated into the wall of the fetal left atrium, forming most of it. The original left atrium becomes a trabeculated atrial appendage called the left auricle, because it resembles an "ear" on the heart.

72. The fetal right atrium is mainly derived from:

A. primitive pulmonary vein
B. primitive atrium
C. right pulmonary vein
D. sinus venarum
E. sinus venosus

E. is correct.
The right sinus horn of the sinus venosus enlarges and forms the fetal right atrium. The left sinus horn regresses to form the main vein draining the heart muscle, the coronary sinus. The original right atrium becomes the right auricle and also part of right atrium anterior to the crista terminalis.

73. The remnant of the first aortic arch artery is:

A. stapedial artery
B. internal carotid artery
C. maxillary artery
D. common carotid artery
E. the 1st arch artery regresses without remnants

C. is correct.
First arch becomes maxillary; 2nd arch remnants are stapedial and hyoid arteries; 3rd arch becomes common and proximal internal carotid arteries; 4th arch becomes proximal right subclavian and part of arch of aorta; 6th arch becomes proximal pulmonary arteries and ductus arteriosus.

74. The aortic sac:

A. is the area immediately distal to the ventricles
B. is connected to the dorsal aorta via the aortic arch arteries
C. is preserved as the region of the semilunar valves in the adult heart
D. is also known as the truncus arteriosus
E. none of the above

B. is correct.
The aortic sac receives blood from the truncus arteriosus and sends it into the aortic arch arteries which branch from it and connect it to the paired dorsal aortae. Aortic sac becomesthe proximal part of aortic arch and the brachiocephalic trunk. Semilunar valves arise from the walls of truncus arteriosus.

75. The crista terminalis is derived from:

A. right horn of the sinus venosus
B. left horn of the sinus venosus
C. primitive atrium
D. AV canal
E. Right cusp of the valve of the sinus venosus

E. is correct.
This is pretty picky. Cristal terminalis is the ridge on the inner surface of the right atrium that demarcates the smooth walled part derived from sinus venosus and the pectinate muscle-containing part from primitive right atrium. It marks where the right cusp of the sinoatrial valve was before the sinus became part of atrium.

76. The region of the atrioventricular canal develops into:

A. the semilunar valves
B. the atrial septum
C. the mitral and tricuspid valves
D. the base of the ventricle
E. the trabeculated portion of the right atrium

C. is correct.
With a name like atrioventricular canal, you might hope it would become something to do with the atrioventricular valves. The single canal is divided by the ingrowth of the endocardial cushions. The right atrioventricular valve is the tricuspid, while the left AV valve is bicuspid, known as the mitral valve.

77. Meckel's diverticulum is an adult remnant of the:

A. urachus
B. hindgut
C. pars cystica
D. vitelline duct
E. dorsal pancreatic duct

D. is correct.
Vitelline duct is a connection between embryonic midgut and yolk sac, from which gut developed. As development proceeds, vitelline duct normally regresses. If it does not, it may persist as a Meckel's diverticulum, a vitelline duct cyst, an umbilical/vitelline fistula, or a fibrous cord connecting gut to umbilicus.

78. The following events in the development of the abdominal cavity are greatly affected by the rapid growth of the liver:

A. urorectal septum formation
B. dorsal mesentery morphogenesis
C. formation of inferior recess of lesser sac
D. herniation of midgut loop

D. is correct.
The rapid growth of the liver has considerable effect on the development of the ventral mesentery, and it promotes the herniation of the midgut by occupying space in the abdominal cavity. It does not affect urorectal septum formation or the inferior recess of the lesser sac.

79. The embryonic foregut differentiates into all or part of the:

A. liver
B. ventral pancreas
C. esophagus
D. lung
E. all of the above are correct

E. is correct
Derivatives of embryonic foregut include pharynx, esophagus, lungs and respiratory tract, stomach, the part of the duodenum cranial to the hepatic diverticulum, the pancreas, liverand gall bladder.

80. Abnormal intestinal rotation during fetal development may produce the following:

A. congenital umbilical hernia
B. annular pancreas
C. infarction and gangrene
D. diaphragmatic hernia
E. Meckel's diverticulum or diverticulum ilei

C. is correct.
Abnormal rotation of the intestinal loop causes it to return to the abdomen in a different order, with the colon being the first to return to the gut. This positions things backwards, and the gut may twist abnormally. Such twisting or volvulus can obstruct the blood supply to the gut, resulting infarction and gangrene.

81. All of us has "suffered" which one of the following types of hernia?

A. inguinal
B. umbilical
C. lumbar
D. diaphragmatic
E. femoral

B. is correct.
The herniation of the midgut out through the umbilicus is a normal event in development. However, the intestinal contents may fail to return to the abdomen, resulting in an omphalocele. Viscera may herniate later through the weak umbilical region, and this is a true umbilical hernia.

82. In the digestive system:

A. failure of the intestinal loops to return into the abdominal cavity forms Meckel's diverticulum
B. an omphalocele would most likely develop around the 10th-12th week of gestation
C. stenosis of the gut most frequently occurs in the large intestine
D. an annular pancreas is caused by a failure in normal migration of the dorsal pancreas

B. is correct.
Return of the intestinal loops to the abdomen occurs toward the end of the third month. Failure to do so results in an omphalocele. Stenosis of the gut is most common in the duodenum. An annular pancreas results when the left portion f the ventral pancreas migrates in a direction opposite normal.

83. In the development of the gut:

A. the celiac trunk represents the blood supply to the midgut
B. the early embryo maintains a connection between the midgut and the yolk sac via the allantois
C. muscle, connective tissue and blood vessels in the gut wall are derived from splanchnic mesoderm
D. the primitive gut tube is in open communication with the amniotic cavity


84. The liver:

A. receives blood from the placenta via the umbilical vein which runs in the falciform ligament
B. forms as a diverticulum from the foregut endoderm
C. contains hemopoietic and connective tissue cells derived from mesoderm of the septum transversum
D. contains hepatic sinusoids derived from the vitelline veins
E. all of the above are correct

E. is correct.
Liver develops from an endodermal hepatic diverticulum, but also contains mesodermal hemopoietic and connective tissue. Blood from the placenta reaches liver via the left umbilical vein but by-passes the sinusoids through the ductus venosus. The sinusoids are derived from the vitelline veins.

85. In the development of the midgut:

A. the superior mesenteric artery is the axis for clockwise rotation of the midgut loop
B. the persistence of part of the vitelline duct leads to urachal fistala
C. a vitelline cyst may result from abnormal remodeling of the vitelline veins
D. an omphalocele is not synonymous with congenital umbilical hernia

D. is correct.
The midgut rotates in a counterclockwise direction around superior mesenteric artery. Persistence of the vitelline duct may cause a vitelline fistula or cyst. Omphalocele results from a failure of midgut to return to the abdominal cavity, while congenital umbilical hernia is a later herniation of gut through abdominal wall.

86. A persistence of the vitelline duct may result in:

A. ileal diverticulum
B. Meckel's diverticulum
C. Vitelline cyst
D. Umbilical fistula
E. All of the above

E. is correct.
If the vitelline duct remains patent, there will be an umbilical or vitelline fistula, leaking meconium or fetal feces at the umbilicus. Partial closure of vitelline duct may result in a vitelline cyst or a Meckel's/ileal diverticulum. The latter are found on the anti-mesenteric side of ileum within 2 feet of cecum.

87. The terminal dilated part of the hindgut is called the:

A. cloaca
B. yolk stalk
C. allantois
D. cecum
E. coelom

A. is correct.
The folding of the embryo brings the allantois and the hindgut into association. The dilated terminal part of the hindgut is called the cloaca, and it communicates with the allantois. Later in development the cloaca is divided by the urorectal septum into the primitive urogenital sinus and the anorectal canal.

88. The tracheoesophageal septum separates the:

A. laryngotracheal tube and nasopharynx
B. esophagus and nasopharynx
C. laryngotracheal tube and esophagus
D. laryngotracheal tube and oropharynx
E. esophagus and oropharynx

C. is correct.
Pharynx is the common food/air tube, so it would not be wise to put a septum between pharynx and esophagus or trachea. However, the lungs bud from the foregut as an anterior diverticulum between the 4th and 6th branchial arches, explaining why superior laryngeal and recurrent laryngeal nerves from vagus innervate larynx.

89. The omental apron of the greater omentum:

A. communicates with the peritoneal cavity via the epiploic foramen of Winslow
B. becomes retroperitoneal in the adult
C. has the ascending colon located within its superior boundary
D. is a quadruple layer of peritoneum
E. is lost during embryonic development

D. is correct.
The omental apron is the portion of the greater omentum, continuous with gastrocolic ligament, which hangs from the transverse colon. Early in development, it is an open sac, communicating with the lesser sac or omental bursa. The walls of the sac are two layers of peritoneum, forming a quadruple layer when the bag fuses.

90. Which duct is NOT associated with urinary system development?

A. ureteric bud
B. paramesonephric duct
C. Wolffian duct
D. pronephric duct
E. mesonephric duct

B. is correct.
The paramesonephric duct arises along the urogenital ridge, separate from the urinary system. In the female, the paramesonephric duct develops into the uterine tubes, uterus and upper part of the vagina.

91. The penile urethra is derived from the:

A. urogenital sinus
B. pelvic part of the vesicourethral canal
C. phallic part of the vesicourethral canal
D. cloaca
E. mesonephric duct

A. is correct.
The penile urethra, all but navicular portion, develops from the urogenital sinus. The urogenital sinus also produces the urinary bladder, prostate and bulbourethral glands.

92. The structure dividing the cloaca into two parts is the:

A. distal retention band
B. transverse septum
C. urogenital sinus
D. urorectal septum
E. cloacal membrane

D. is correct.
The urorectal septum divides the cloaca into the urogenital sinus and rectum, during the second month of development.

93. After the sinovaginal bulbs have proliferated and fused, they form a solid core of endodermal cells known as the:

A. sinus tubercle
B. prostatic utricle
C. vaginal plate
D. uterovaginal primordium
E. vault of the vagina

C. is correct.
The sinovaginal bulbs are evaginations from the urogenital sinus in the female. They proliferate, fuse, and form the vaginal plate, which then canalizes to form the lumen of vagina.

94. The embryonic origin(s) of the labia minora is/are:

A. urethral folds
B. genital tubercle
C. genital swellings
D. sinovaginal bulbs
E. cloacal membrane

A. is correct.
The labia minora develop from the urethral or urogenital folds. In the male, the urethral folds ultimately fuse, forming the ventral aspect of the penis. The labia majora and the scrotum arise from the genital folds or swellings.

95. The embryonic origin(s) of the penile urethra is/are:

A. urethral folds
B. genital tubercle
C. genital swellings
D. sinovaginal bulbs
E. cloacal membrane

A. is correct.
The labia minora develop from the urethral or urogenital folds. In the male, the urethral folds ultimately fuse, enclosing the penile or spongy urethra. However, the urethra passing through the glans is formed by canalization of the glandular plate.

96. The embryonic origin(s) of the scrotum is/are:

A. urethral folds
B. genital tubercle
C. genital swellings
D. sinovaginal bulbs
E. cloacal membrane

C. is correct.
The scrotum in the male and the labia majora arise from the genital swellings or folds. Cloacal membrane is subdivided into the urorectal membrane and anal membrane by the urogenital septum. These membranes should rupture during the 9th week.

97. The following structures are directly or indirectly derived from the mesonephric or Wolffian duct EXCEPT:

A. part of the epididymis
B. part of the kidney
C. part of the urinary bladder
D. seminal vesicles
E. prostate

E. is correct.
The prostate is derived from the urogenital sinus, with no contribution from the mesonephric ducts. Ureteric bud, from mesonephric duct, gives rise to the collecting system of the kidney. A portion of the mesonephric ducts becomes incorporated into the trigone region of the bladder. Seminal vesicles bud from the mesonephric duct.

98. The following structures are the derivatives of the primitive urogenital sinus EXCEPT:

A. most of the urinary bladder
B. male urethra
C. female urethra
D. lower vagina
E. ejaculatory ducts

E. is correct.
The ejaculatory ducts are derivatives of the mesonephric ducts. All of the others have at least some contribution fromthe urogenital sinus.

99. The derivatives of the Wolffian duct include each of the following except:

A. longitudinal duct of Gartner
B. round ligament of uterus
C. ductus deferens
D. duct of the epididymis
E. ejaculatory duct

B. is correct.
Gartners duct, like the appendix of the epididymis, holds more importance to National Board examiners than anyone else. It is a vestigial remnant of the mesonephric duct in the female. The round ligament of the uterus is derived from the gubernaculum, rather than the mesonephric duct.

100. Of the following, the one most closely associated with the oviduct is:

A. mesonephric tubules
B. mesonephric duct
C. paramesonephric duct
D. genital swellings
E. urogenital sinus

C. is correct.
Paramesonephric ducts give rise to the oviducts or uterine tubes, uterus and upper portion of the vagina. In males, the prostatic utricle and the appendix of the testis are vestigial remnants of the paramesonephric ducts.

101. Of the following, the one most closely associated with the efferent ducts of the testes is:

A. mesonephric tubules
B. mesonephric duct
C. paramesonephric duct
D. genital swellings
E. urogenital sinus

A. is correct.
The efferent ductules of the testes are the only functional derivatives of the mesonephric tubules.

102. Of the following, the one most closely associated with the vestibule in the female is:

A. mesonephric tubules
B. mesonephric duct
C. paramesonephric duct
D. genital swellings
E. urogenital sinus

E. is correct.
In the male, the urogenital sinus gives rise to the urinary bladder, all but distal urethra, prostate and bulbourethral glands. In the female, it gives rise to the urinary bladder, urethra, lower part of vagina, vestibule, urethral and paraurethral glands and greater vestibular glands.

103. Of the following, the one most closely associated with the urethra in the female is:

A. mesonephric tubules
B. mesonephric duct
C. paramesonephric duct
D. genital swellings
E. urogenital sinus

E. is correct.
In the male, the urogenital sinus gives rise to the urinary bladder, prostate, bulbourethral glands and all but distal urethral. In the female, it gives rise to the urinary bladder, urethra, lower part of vagina, vestibule, urethral and paraurethral glands and greater vestibular glands.

104. Which of the following associations are correct?

A. renal pelvis - ureteric bud
B. ureter - ureteric bud
C. urethra - urogenital sinus
D. median umbilical ligament - urachus
E. all of the above are correct

E. is correct.
Ureteric bud gives rise to everything from collecting ducts through ureters. Derivatives of UG sinus include bladder and urethra of both sexes, prostate and bulbourethral glands, lower vagina and urethral, paraurethral and vestibular lands. Allantois becomes urachus, which then becomes median umbilical ligament.

105. Embryologically, each uriniferous tubule consists of two parts which become confluent at the junction of the:

A. ascending limb of Henle's loop and the distal convoluted tubule
B. renal corpuscle and the proximal convoluted tubule
C. descending and ascending limbs of the loop of Henle
D. proximal convoluted tubule and the loop of Henle
E. distal convoluted tubule and the collecting tubule

E. is correct.
Everything from Bowman's capsule to the distal convoluted tubule develops from the metanephric cap. Everything from the collecting tubules through the ureter develops from the ureteric bud. Therefore the junction between the two occurs between the distal convoluted tubule and the collecting tubule.

106. The ureteric bud appears as an outgrowth from the:

A. metanephric mass
B. lateral plate mesoderm
C. urogenital sinus
D. allantoic duct
E. mesonephric duct

E. is correct.
The ureteric bud is an outgrowth of the mesonephric duct. It forms the ureter, renal pelvis, calyces and collecting ducts

107. The paramesonephric ducts in female embryos give rise to the:

A. uterine tubes and uterus
B. epoohoron
C. inferior fifth of the vagina
D. round ligament of the uterus
E. ovarian ligament

A. is correct.
The paramesonephric ducts in the female develop in the uterine tubes, the uterus and the upper 1/3 of the vagina. The epoophoron come fromthr mesonephric tubules. The lower portion of the vagina develops from the urogenital sinus. The round ligament and the ovarian ligament are from the gubernaculum.

108. Which of the following gives rise to the labia majora?

A. genital folds
B. genital swellings
C. genital tubercle
D. urorectal gold
E. inguinal fold

B. is correct.
Labia majora arise from the genital swellings. Their counterpart in the male is the scrotum, which also arises from the genital swellings. The genital tubercle forms the distal end of penis and most of clitoris.

109. The optic nerve is derived from what embryonic tissue?

A. neural crest
B. head mesenchyme
C. endoderm
D. mesoderm
E. ectoderm

E. is correct.
The optic nerve is derived from nervous tissue, therefore ectoderm, but not neural crest. Optic sulci of the neural folds forming the forebrain send out the optic vesicles, which then develop into the optic cups connected to forebrain by the optic stalk. The optic stalk becomes the optic nerve.

110. Neural crest cells differentiate into:

A. postganglionic sympathetic cell bodies
B. cells of the inferior mesenteric ganglion
C. adrenal medullary cells
D. cells of the enteric plexus
E. all of the above are correct

E. is correct.
Neural crest cells give rise to the peripheral parts of the autonomic nervous system, which includes all sympathetic and parasympathetic ganglia. Neural crest cells form all sensory ganglia of the peripheral nervous system. Neural crest cells also populate the adrenal medulla.

111. Of the following, the item most closely associated with the regulation of visceral and endocrine functions is:

A. telencephalon
B. diencephalon
C. mesencephalon
D. metencephalon
E. myelencehalon

B. is correct.
The hypothalamus of the diencephalon is the control center for visceral and endocrine functions.

112. Of the following, the item most closely associated with the pons is:

A. telencephalon
B. diencephalon
C. mesencephalon
D. metencephalon
E. myelencephalon

D. is correct.
The metencephalon differentiates into the cerebellum, the coordination center for posture and movement and the pons, which serves as a neural relay center.

113. Of the following, the one most closely associated with the cerebrum is:

A. telencephalon
B. diencephalon
C. mesencephalon
D. metencephalon
E. myelencephalon

A. is correct.
The cerebrum arises from the telencephalon. Telencephalon, the most rostral part of the brain vesicles, develops from the prosencephalon as lateral outgrowths, the cerebral hemispheres and an intermediate area, the lamina terminalis. Lamina terminalis develops into the commissures connecting the hemispheres.

114. Of the following, the one most closely associated with the 3rd ventricle is:

A. telencephalon
B. diencephalon
C. mesencephalon
D. metencephalon
E. myelencephalon

B. is correct.
The 3rd ventricle lies within the thalamic area in the diencephalon. The lateral ventricles are cavities of the forebrain cerebral vesicles, from telencephalon. The 4th ventricle lies within the metencephalon.

115. Cerebrospinal fluid:

A. is produced in choroid plexuses
B. circulates in the ventricular system of the brain and in the subarachnoid spaces
C. re-enters the venous blood at the arachnoid
D. granulations
E. blockage of its circulation can lead to internal or external hydrocephalus
F. all of the above are correct

E. is correct.
Cerebrospinal fluid is produced by ependymal cells of the choroid plexus. It circulates within the ventricles of the brain, the central canal of the spinal cord and the subarachnoid space. It is resorbed into the venous system via arachnoid granulations. If flow is blocked, CSF accumulates and creates hydrocephalus.

116. In the development of the nervous system:

A. there are five primary brain vesicles
B. during the 5th week, each brain vesicle subdivides into 2 parts
C. the pontine flexure is in a direction opposite the mesencephalic and cervical flexure
D. neural epithelial cells are found in the marginal layer

C. is correct.
There are initially 3 brain vesicles: prosencephalon, mesencephalon and rhombencephalon. The pros- and rhombencephalon divide into 2 parts. The pontine flexure is opposite to the mesencephalic and cervical flexures. The marginal layer contains the nerve fibers arising from the neuroblasts.

117. In the development of the nervous system:

A. the sulcus limitans is found in the diencephalon
B. the infundibulum is an outgrowth of the telencephalon that develops into the neurohypophysis
C. sensory nuclei in the hindbrain lie ventral to the sulcus limitans
D. the inner ear is derived from surface ectoderm

D. is correct.
The sulcus limitans is a lateral, longitudinal groove dividing basal and alar plates. The infundibulum is an outpouching of the hypothalamic region that becomes neurohypophysis. Sensory nuclei lie dorsal to the sulcus limitans. Internal ear is from thickened surface ectoderm (otic placode) near rhombencephalon.

118. In the development of the nervous system:

A. the neural groove forms from the neural plate
B. the neural folds are composed of neuroepithelial cells
C. the neural tube maintains temporary contact with the amniotic cavity via neuropores
D. neuroepithelial cells give rise to both neuroblasts and glia blasts
E. all of the above are correct

E. is correct.
The neural groove forms the neural plate when lateral parts of the plate elevate to form neural folds. Neural folds are composed of neuroepithelium which gives rise to neuroblasts, gliablasts and ependymal cells. After the neural tube forms, it maintains contact with the amniotic cavity via cranial and caudal neuropores.

119. With respect to the nervous system, which of the following is NOT correct:

A. a muscle's nerve supply can be used as an indicator of its level of origin and path of migration
B. Rathke's pouch is an outgrowth of oral ectoderm that becomes the anterior lobe of the hypophysis
C. the sulcus limitans marks the boundary between motor and sensory areas
D. sensory nuclei in the hindbrain lie ventral to motor nuclei

D. is correct.
The nerve supply travels with the muscle, indicating its origin and migration path. Rathke's pouch, from which the anterior pituitary is formed, is from oral ectoderm. Sulcus limitans divides motor and sensory areas. Sensory nuclei in the hindbrain lie dorsal to the motor nuclei.

120. Congenital absence of neural crest cells could result in:

A. absence of sympathetic chain ganglia
B. facial malformations
C. absence of adrenal medulla
D. absence of pigment cells
E. all of the above are correct

E. is correct.
Neural crest cells form all sensory and autonomic ganglia, Schwann cells, meninges of the brain and spinal cord, adrenal medulla, pigment cells of the skin and connective tissues of the head and neck, including odontoblasts for dentin of the teeth.

121. The brain flexure which develops between the metencephalon and the myelencephalon is called the:

A. pontine
B. hindbrain
C. cervical
D. cephalic
E. midbrain

A. is correct.
The pontine flexure occurs between the metencephalon, which forms the pons and cerebellum, and the myelencephalon, which forms the medulla. The two other flexures, the cephalic and the cervical, flex in a direction opposite that of the pontine.

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