embryology 2

Question 1

define gastrulation

Answer 1

the stage following the implantation of the embryo into the endometrium. During this phase the bilaminar disc is converted into a trilaminar disc.

Question 2

stomach formation

Answer 2

dilatation, differential growth of the tube to form the curvatures. There is then rotation, 90’ around the longitudinal axis, and then an anterior-posterior rotation

Question 3

omental bursa formation

Answer 3

omental burse is produced by the rotation of the ventral and dorsal wall attachment of the stomach known as the mesogastrium, the dorsal portion is rotated along the longitudinal axis to the left to generate the omental bursa.

Question 4

liver formation

Answer 4

liver primordium appears by the third week, outgrowth endoderm in the distal foregut. It grows into the septum transversum, the connection forms the bile duct and ventral outgrowth of the duct forms the gall bladder and cystic duct.

Question 5

spleen development

Answer 5

end of the 4rth week, mesenchymal condensation develops in the dorsal mesogastrium near the body wall. 5th week it differentiates into the spleen, until week 14 it is a haematopoietic organ. 15-17 weeks become lobular and colonised with T-lymphocytes. Week 23 the B cell precursors arrive and becomes lymphatic.

Question 6

pancreas formation

Answer 6

pancreas forms from 2 buds from the endodermal lining of the duodenum. As duodenum rotates the buds move closer. They fuse together.

Question 7

mid gut formation

Answer 7

rapid elongation of the gut tube. Cephalic part of the primary intestinal loop becomes the distal duodenum, jejunum and proximal ileum. The caudal part of the primary intestinal loop will become the distal ileum, caecum, appendix, ascending colon, and proximal 2/3rd’s of the transverse colon. Begins 6th week around the axis of the superior mesenteric artery, rotation of 90’ degrees anti-clockwise. As it rotates the gut tube herniates into the extraembryonic cavity. Week 10 the intestinal loops begin to move the cord back into the abdominal cavity, jejunum enters first. The caecum is last part to re-enter, then there is further 180 degrees rotation anti-clockwise.

Question 8

hind gut formation

Answer 8

terminal portion of the hindgut with the posterior part of the cloaca. The allantois enters the anterior part of the cloaca. The cloaca is endoderm lined cavity with ectoderm at its ventral boundary. Separating the two Is the cloacal membrane. Septum merges to cover the yolk sac and allantois, the embryo grows the tip of the urorectal septum lies close to the cloacal membrane. By week 7 the cloacal membrane ruptures opening the hindgut. The ectoderm of the anal canal proliferates closing the caudal end, week 9 the canal re-opens.

Question 9

foregut abnormalities

Answer 9

incomplete separation results in oesophageal atresia and trachea-oesophageal fistula.
ventral bud fails to migrate around the duodenum causing an annular pancreas resulting in stenosis. Pancreatic migration results in accessory pancreatic tissue.

Question 10

mid gut abnormalities

Answer 10

omphalocele herniation of abdominal viscera through the enlarged umbilical ring, failure of retraction. Gastrochisis herniation directly through the body wall into the amniotic cavity. Remnants of vitelline ducts forms the Meckel’s diverticulum, may form a fistula or ligament.

Question 11

hind gut abnormalities

Answer 11

incomplete separation of the hindgut from the urogenital sinus by the urorectal septum resulting in a anorectal fistula, or imperforate anus.

Question 12

describe the pharyngeal branches

Answer 12

series of arches that develop around the mouth and pharynx. They support the primitive pharynx and develop into the face and neck. 6 arches develop, but we are eventually left with 5. On the exterior is the ectoderm, in the middle is mesoderm forming cartilage and muscles, and endoderm on the inside forming pouches between the arches.

Question 13

arch 1 forms and nerve

Answer 13

mandible + V3

Question 14

arch 2 forms + nerve

Answer 14

styloid process + facial

Question 15

arch 3 forms + nerve

Answer 15

greater horn of hyoid bone + glossopharyngeal

Question 16

arch 4 forms + nerve

Answer 16

thyroid cartilage + superior laryngeal nerve

Question 17

arch 6 forms + nerve

Answer 17

cricoid cartilage + recurrent laryngeal nerve

Question 18

face development

Answer 18

face develops from 5 processes; 1 frontonasal process, 2 maxillary and 2 mandibular. Two mandibular processes fuse together in the midline. The ectoderm thickens from the frontal nasal process and invaginates to form the nasal pit. Medial growth of the nasal process forms the philtrum. The palate forms from the medial nasal process growing downward to form the primary palate, the maxillary process two palatine shelves grow inwards, and form a secondary palate.

Question 19

cranial vault formation

Answer 19

cranial vault consisting of flat bones forms from membranous bones by membranous ossification. The base of the skull consists of irregular bones produced by endochondral ossification, and the viscerocranium is produced by the branchial arches and sensory capsules. They consist of somites that develop into cartilage and then ossify into bones.

Question 20

head and neck developmental abnormalities

Answer 20

1st pharyngeal arch abnormality treacher collin’s syndrome
craniosynostosis.
cleft lip and palate.

Question 21

development of the neural tube

Answer 21

following on from gastrulation then the formation of the three germ layers from the epiblast. There is the formation of the ectoderm which is the top layer that differentiates into the nervous system and the epidermis. There is migration of the ectoderm and thickening anterior to the primitive node to form the neural plate, is edges thicken and move upwards to form folds. They fuse at the midline to form a tube.
tube forms brain vesicles.

Question 22

mesencephalon forms

Answer 22

(superior and inferior colliculi),

Question 23

prosencephalon forms the

Answer 23

telencephalon (cerebral hemisphere, hippocampus, basal ganglia) and the diencephalon (thalamus, hypothalamus, pituitary gland, pineal),

Question 24

telencephalon is the

Answer 24

telencephalon (cerebral hemisphere, hippocampus, basal ganglia)

Question 25

diencephalon forms the

Answer 25

diencephalon (thalamus, hypothalamus, pituitary gland, pineal),

Question 26

rhombencephalon forms the

Answer 26

forms the metencephalon (cerebellum, pons) and the myelencephalon(medulla).

Question 27

metencephalon forms the

Answer 27

cerebellum and pons

Question 28

myelencephalon forms the

Answer 28

medulla

Question 29

CNS Neuroepithelium forms

Answer 29

most of the cells, and motor component of the spinal cord bar microglia which is produced by mesenchymal cells migrating.

Question 30

Neural crest cells form

Answer 30

PNS neurones and glia, as well as the sensory aspect of the spinal cord

Question 31

anterior neuropore closes around

Answer 31

25th day

Question 32

posterior neuropore closes around

Answer 32

27th day

Question 33

anencephaly is

Answer 33

the failure of the anterior neuropore to close, the skull fails to form resulting in brain tissue degeneration which is incompatible with life

Question 34

encephalocele is

Answer 34

the herniation of tissue through a defect in the skull, a failure in closure of the rostral neural tube, it’s most frequent in the occipital region with variable degrees of deficits.

Question 35

spina bifida is the

Answer 35

defective closure of the caudal neural tube, it affects the tissue overlying the spinal cord resulting in the non-fusion of the vertebral arches.

Question 36

prenatal diagnosis of spina bifida

Answer 36

maternal blood screening; high levels of alpha fetoprotein 16-20 weeks
amniocentesis; AFP in amniotic fluid
US; anencephaly from 12 weeks, spina bifida from 16-20 weeks

Question 37

what embryological tissue gives rise to the kidney

Answer 37

intermediate mesoderm gives rise to the kidney and the ureter, in particular it is the metanephros which gives rise to the definitive adult kidney, the metanephric blastema

Question 38

metanephric blastema forms

Answer 38

the excretory tubules; bowman’s capsule PCT, loop of Henle, DCT

Question 39

ureteric bud forms

Answer 39

From the ureteric bud we get the collecting portions of the kidney; collecting ducts, calyces, ureters.

Question 40

cloaca forms

Answer 40

urethra and bladder

Question 41

what part of the urogenital sinus forms the bladder

Answer 41

cranial part

Question 42

trigone is developed from

Answer 42

The trigone is derived from the absorption of the caudal ends of the mesonephric ducts

Question 43

ascent of the kidneys is stopped by

Answer 43

adrenal glands

Question 44

abnormalities of kidney development

Answer 44

polycystic kidney, aberrant renal arteries, lobulated kidney, transposition of the kidney, horseshoe kidney, pancake kidney. May have a hourglass bladder or ectopia vesicae in which trigone and ureteric openings can be seen on the surface