EMBRYO

Question 1

What is the difference between extra embryonic and intraembryonic mesoderm? Where do they originate from?

Answer 1

Extraembryonic mesoderm: derives from the trophoblast and form a fine, loose connective tissue, which is located outside the embryo.

Intraembryonic mesoderm: the third germ layer between the epiblast and hypoblast layers. Origin: epiblast.

Question 2

List the components of the extraembryonic mesoderm.

Answer 2

Somatopleuric mesoderm Splanchnopleuric mesoderm Connecting stalk
Chorionic mesoderm

Question 3

From which germ disk does the blood, lens of eye, epithelium of kidney tubules, and thymus develop?

Answer 3

Blood ­ mesoderm

Lens of eye ­ ectoderm Kidney tubules ­ mesoderm Thymus ­ endoderm

Question 4

From which germ disk does the bone, hypophysis, chief cells of the parathyroid glands and the

Answer 4

bone ­ mesoderm
hypophysis ­ ectoderm
chief cells of the parathyroid gland – placod plate thyroid gland ­ endoderm

Question 5

What is the “placode” and what are its derivatives?

Answer 5

Placode: thickenings of the surface ectoderm at the head region of the embryo.

Hypophyseal placode (I): Rathke’s pouch. (adenohypophysis) Nasal placode (2): olfactory epithelium.

Lens placode (2): lens of eye

Trigeminal placode (2): semilunar ggl.

Acoustic placode (2): sensory epithelium of vestibular and cochlear receptors, ganglions.

Epibranchial placode (2): sensory epithelium of taste buds.

Branchial: placode (2): sensory ganglia of VIIth, IXth, Xth cranial nerves.

Question 6

What are the derivatives of the paraxial, intermediate and the lateral plate of mesoderm?

Answer 6

· Paraxial mesoderm: breaks up into blocks of somites, and somitomers at the cephalic region. The somites differentiate into sclerotom, dermatome, myotome.
· Intermediate: in the cervical and upper thoracic region it gives rise to the nephrotomes. Caudally the nephrogenic cord develops from it.
· Lateral plate: somatic or parietal mesoderm layer, splanchnic or visceral mesoderm layer, intraembryonic celomic cavity.

Question 7

What is meant by the a) cephalo­caudal and b) lateral foldings of the embryo?

Answer 7

·
What is meant by the a) cephalo­caudal and b) lateral foldings of the embryo? Folding of a flat trilaminar embryonic disc into a somewhat cylindrical embryo.
a)
membrane and overhangs the developing heart. Caudally the tail region projects over the cloacal membrane.
Cephalo­caudal fold: Cranially, the developing forebrain grows beyond the buccopharyngeal
b) Lateral/transverse folds: Each lateral body wall folds towards the median plane in a ventral direction.

Question 8

Which bones develop from the viscerocranium?

Answer 8

· Maxilla, mandible, zygomatic bone, squamous and tympanic parts of temporal bone, styloid process of temporal bone, nasal bone, lacrimal bone, vomer, hyoid bone, inf. concha, medial plate of the pterygoid process of the sphenoid bone, palatine bone.

Question 9

From which structures does the diaphragm develop?

Answer 9

· Septum transversum, pleuroperitoneal membranes, dorsal mesentery of esophagus, muscular component of the lateral and dorsal body wall.

Question 10

Name and characterize the most common malformation of the thoracic diaphragm! Describe also mechanism of malformations!

Answer 10

· Diaphragmatic hernia: caused by failure of the pleuroperitoneal membrane(s) to close the pleuroperitoneal canal(s). The peritoneal and pleural cavities are continuous with each other along the posterior body wall.
· Parasternal hernia: a small muscular part of the anterior portion of the diaphragm fails to develop. · Esophpageal hernia: is due to a congenital shortness of the esophagus.

Question 11

What are the derivatives of the ventral mesentery?

Answer 11

Lesser omentum, falciform ligament.

Question 12

Define the term “dorsal mesentery” and describe its extension!

Answer 12

· A double layer of peritoneum that encloses the gastrointestinal tract. It extends from the lower end of the esophagus to the cloacal region of the hindgut and connects the gastrointestinal tract to the posterior abdominal wall.

Question 13

List the major parts of the dorsal mesentery!

Answer 13

Dorsal mesogastrium, dorsal mesoduodenum, mesentery proper, dorsal mesocolon.

Question 14

What are the derivatives of the dorsal mesogastrium?

Answer 14

· Gastrophrenic ligament, gastrolienal ligament, phrenicolienal ligament, lienorenal ligament, greater omentum.

Question 15

When does the mesentery of the jejunoileal loops become separated from the mesocolon transversum?

Answer 15

· Around the 6th embryonic week, when the caudal limb of ansa umbilicalis moves to the right side of the abdominal cavity and the dorsal mesentery twists (90° counter­clockwise) around the origin of the superior mesenteric artery.

Question 16

What is the location of the cardiogenic area in the presomite embryo?

Answer 16

In the splanchnic mesoderm in front of the neural plate on both sides of the embryo.

Question 17

Which veins can be first distinguished in the embryo?

Answer 17

Three pairs of major veins: vitelline or omphalomesenteric veins, umbilical veins, cardinal veins

Question 18

From which veins does the portal vein develop and how?

Answer 18

Vitelline veins
Before entering the sinus venosus, the vitelline veins form a plexus around the duodenum and pass through the septum transversum. The liver cords growing into the septum interrupt the course of the veins and an extensive vascular network of hepatic sinusoid is formed. The anastomoting network around the duodenum develops into a single vessel: portal vein.

Question 19

What is the ductus venosus and what role does it play in the embryonic circulation?

Answer 19

Communication between the former left umbilical vein and right hepatocardiac channel. The ductus venosus bypasses the sinusoidal plexus of the liver.

Question 20

What are the main changes that occur at the vascular system at birth?

Answer 20

Closure of the umbilical arteries and vein
Closure of ductus venosus.
Closure of the ductus arteriosus.
Closure of the oval foramen.

Question 21

When, where and in which form does the primordium of the respiratory system appear first?

Answer 21

When the embryo is approximately 4­week­old the primordium of the respiratory system appears first as a groove on the ventral wall of the foregut (Laryngotracheal groove).

Question 22

From which branchial arches does the larynx develop?

Answer 22

· The cartilages and muscles of the larynx develop from the mesenchyme of the 4th, 5th and 6th pharyngeal arches.

Question 23

Characterise the pseudoglandular and the canalicular phases, and the terminal sac period in the development of the lung

Answer 23

(a) Pseudoglandular phase: (five to 17 weeks) the developing lung resembles an exocrine gland up to the 7th prenatal month.
b) Canalicular phase: the bronchioli continuously divide into more and smaller canals and the vascular supply increases steadily.
c) Terminal sac period: (from the beginning of the 7th prenatal month) cuboidal lining of bronchioli changes into thin flat cells: the alveolar epithelial cells, which are intimately associated with blood capillaries.

Question 24

What are the derivatives of the foregut?

Answer 24

Pharyngeal gut, tracheobronchial diverticulum, esophagus, stomach, upper part of duodenum, gall bladder, pancreas, liver.

Question 25

What are the derivatives of the midgut?

Answer 25

Lower part of duodenum, jejunum, ileum, cecum, vermiform appendix, ascending colon, prox. 2/3 of transverse colon.

Question 26

How do the shape and position of the stomach primordium change during development?

Answer 26

· First it runs in the long axis of the embryo, as a fusiform dilatation of the foregut.
· Later it rotates clockwise causing its left side to face anteriorly, and its right side posteriorly.
· During the rotation, the original posterior wall of the stomach grows faster than the ant. portion and this results in the formation of the lesser and greater curvatures.
· The cephalic and caudal ends of the stomach are originally located in the midline, but during further growth the caudal part moves to the right and upward and the cephalic portion to the left and slightly downward.

Question 27

From which structures do (a) the parenchyma and b) the stroma of the liver develop? What is the principal function of the liver in the foetus?

Answer 27

(a) Epithelium of the distal end of the foregut derived from endoderm.
(b) Septum transversum. Hemopoietic function, bile formation.

Question 28

Which parts of the pancreas develop from the ventral and from the dorsal pancreatic bud? How is the duct developed?

Answer 28

Ventral: uncinate process and the inf. part of the head of the pancreas.

Dorsal: the remaining parts of the gland.

Main pancreatic duct is formed by the distal part of the dorsal pancreatic bud and the entire ventral pancreatic bud.

The accessory duct develops from the proximal part of the dorsal pancreatic bud.

Question 29

Which parts of the intestinal canal develop from the primary intestinal loop and which artery supplies them?

Answer 29

Jejunum, ileum, cecum, appendix, ascending colon, proximal two­thirds of the transverse colon, Meckel’s diverticulum.

Superior mesenteric artery

Question 30

What is the Meckel’s diverticulum, describe its location and developmental origin?

Answer 30

The outpocketing of the ileum located about 40-­60 cm from the ileocecal valve on the antimesenteric border of the ileum.

One of the possible remnants of the vitelline duct.

Question 31

What is meant by the “physiological umbilical herniation” which occurs during the 6th week of embryo development?

Answer 31

· As a result of the rapid growth of the primary intestinal loop and the simultaneous expansion of the liver the abdominal cavity temporarily becomes too small to contain all the intestinal loops, so they enter the extraembryonic celom in the umbilical cord temporarily.

Question 32

What do the rotation and the retraction of the herniated intestinal loops during development mean?

Answer 32

· Rotation: Parallel with the growth in length, the primary intestinal loop rotates around an axis formed by the superior mesenteric artery. This rotation occurs in counterclockwise direction.
· Retraction : At the end of the 3rd month, the herniated intestinal loops begin to return to the abdominal cavity due to expansion (growth) of abdominal cavity.

Question 33

What are the derivatives of the hindgut?

Answer 33

· Distal third of the transverse colon, descending colon, sigmoid, rectum, upper part of the anal canal, urinary bladder, urethra, lower part of vagina, prostate.

Question 34

Which organs develop from the cloaca?

Answer 34

· Urinary bladder except the trigone,

urethra, prostate,

lower part of vagina,

rectum,

upper part of the anal canal.

Question 35

Define the word “proctodeum”!

Answer 35

An external depression opposite to the anal membrane formed by the mesenchymal swellings.

Question 36

Define the term “pharyngeal arches”!

Answer 36

Surface elevations at the future head and neck region, consisting of bars of mesenchymal tissue and separated from each other by pharyngeal clefts.

Question 37

List the swellings (prominences) which surround the stomodeum in a 4­-5 week old embryo!

Answer 37

· Frontonasal prominence, maxillary swellings (2), mandibular swellings (2).

Question 38

Characterise the malformations defined as median and lateral cleft lip, and cleft palate! How are formed during development?

Answer 38

Incomplete fusion of the two medial nasal swellings or the maxillary processes in the midline during the development of lip and palate.
Median cleft lip: incomplete fusion of the two medial nasal swellings in the midline.

Lateral cleft lip: incomplete fusion of the medial nasal swelling and maxillary swelling.

Cleft palate: nonunion of the secondary palates or nonunion of the secondary and primary palate.

Question 39

Which structures separate the nasal and oral cavities during development?

Answer 39

· Medial nasal prominences (primary palate).

· Palatine shelves of maxillary prominences (the secondary palate).

Question 40

Where is the nasolacrimal groove and which structure develops from it in the embryo?

Answer 40

· It is located between the maxillary and lateral nasal swellings.
· The nasolacrimal duct and lacrimal sac develop from it.

Question 41

Which structures form the upper lip during development?

Answer 41

Two medial nasal swellings and two maxillary swellings.

Question 42

Which structures contribute to the development of the tongue?

Answer 42

Lateral lingual swellings (2), tuberculum impar, copula, anterior part of the epiglottal swelling.