MCQ Flashcards
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.
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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 B. II C. III D. IV E. VI
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.
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.
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.
