Embryology

Question 1

From what does the intraembryonic coelom develop?

Answer 1

lateral plate mesoderm

Question 2

The intraembryonic coelom splits the mesoderm into what 2 portions?

Answer 2

Somatic (parietal) mesoderm - lines body wall

Splanchnic (visceral) mesoderm - lines gut tube

Question 3

What 2 locations have endoderm and ectoderm directly connected?

Answer 3

Stomodeum (primordial mouth) & cloacal membrane (primordial anus)

Question 4

What is pulled anteriorly during embryonic head folding?

Answer 4

septum transversum, primordial heart, pericardial coelom, and oropharyngeal membrane

Question 5

What is pulled anteriorly during embryonic tail folding?

Answer 5

allantois, connecting stalk, cloacal membrane, and primitive streak

Question 6

What occurs to the dorsal and ventral mesenteries?

Answer 6

Dorsal remains surrounding ABD organs; Ventral disappears

Question 7

What is the outcome of lateral body folding?

Answer 7

a uniform body wall is created anteriorly except at the connecting stalk (umbilical cord)

Question 8

What 3 body cavities does the intraembryonic coelom divide into?

Answer 8

pericardial cavity
pleural cavity
peritoneal cavity

Question 9

What do the pleuropericardial folds separate?

Answer 9

Separate pleural cavities and pericardial cavity (separates heart from lungs and lungs from each other)

Question 10

What do the pleruoperitoneal folds separate?

Answer 10

separate pleural cavities from peritoneal cavity

Question 11

How is the pleuropericardial membrane formed and what does it create?

Answer 11

formed by enlarging pleuropericardial folds squeezing together in the midline; leads to formation of primitive mediastinum and fibrous pericardium

Question 12

Explain how the pleuroperitoneal membrane grows and closes?

Answer 12

attach to the posterior body wall and grow forward; right fold slightly smaller due to liver growth; myoblasts (precursor to muscle) complete closure process

Question 13

What makes up the diaphragm?

Answer 13

septum transversum - central tendon
pleuroperitoneal membrane - primordial diaphragm
Dorsal mesentery
Myoblasts (crura - 2 arms of diaphragm)
Phrenic N.

Question 14

What will form from the laryngotracheal groove?

Answer 14

primordial of the tracheobronchial tree and laryngotracheal diverticulum (lung bud)

Question 15

What is the purpose of the tracheoesophageal folds?

Answer 15

to create the tracheoesophageal septum that will divide the laryngotracheal tube (trachea) and the esophagus

Question 16

What parts of the respiratory system stem from splanchnic mesoderm and NCC?

Answer 16

larynx cartilage is NCC and the rest of the respiratory system is splanchnic mesoderm

Question 17

Define recanalization

Answer 17

laryngotracheal groove is converted into a T shaped inlet by arytenoid swellings and then covered by layngeal epithelium; 10th week - the epithelium is removed and subsequent structures develop (recanalization)

Question 18

Why is the larynx in a high position in newborns?

Answer 18

epiglottis is in contact w/ soft palate -> allows infants to nurse without milk going into oropharynx or trachea; will descend over 2 years

Question 19

When do lung buds develop and in what direction to they grow?

Answer 19

develop in the 4th week off of the distal end of the laryngotracheal diverticulum; grow ventrocaudally (forward and downward)

Question 20

What are bronchopulmonary segments?

Answer 20

segmental bronchi + mesenchyme (develop in 7th week)

Question 21

Pseudoglandular Stage

Answer 21

1st stage of lung maturation (5-17 weeks) - majority elements form except gas exchange

Question 22

Canalicular Stage

Answer 22

2nd stage of lung maturation (16-25 weeks) - vascularization, respiratory bronchioles and primitive alveoli

Question 23

Terminal Sac Stage

Answer 23

3rd stage of lung maturation (24 weeks to birth) - alveoli form; pneumocytes form; gas exchange can occur

Question 24

Alveolar Stage

Answer 24

4th stage of lung maturation (32 weeks to 8 years) - primitive alveoli (development completed by 3 years); mature alveoli (majority grow postnatally to handle growing body)

Question 25

Explain extra embryonic vasculogenesis

Answer 25

day 17; mesoderm differentiates into hemangioblasts that group to form blood islands; create either hematopoietic stem cells or endothelial precursor cells

Question 26

Explain intraembryonic vasculogenesis

Answer 26

day 18; direct formation of endothelial precursor cells (EPCs) from endoderm; EPCs divide into cysts and combine to make vasculogenic cord

Question 27

What is the difference between angiogenesis and intussusception?

Answer 27

angiogenesis is outgrowth of existing blood vessels formed during vasculogenesis; intussusception is the division of blood vessels after angiogenesis

Question 28

What is definitive hematopoiesis?

Answer 28

hematopoietic stem cells are programmed in the liver to generate both myeloid and lymphoid lineages; come from endothelial cells found in aortic-gonadal-mesoneprhic AGM region

Question 29

What forms the majority of the heart?

Answer 29

angiogenic clusters (EPCs) that form in the splanchnic mesoderm

Question 30

How is the transverse pericardial sinus formed? What does the rest of the tissue do?

Answer 30

created by rupture in the dorsal mesocardium (holding onto heart tube); caudal end of dorsal mesocardium forms a proepicardial organ that will migrate and cover entire heart (source of epicardium)

Question 31

What is the flow of the heart tube?

Answer 31

inflow of blood at the sinus horns (left and right) into the sinus venosus -> primitive atrium -> primitive ventricle -> constricts to create outflow tract -> conus and trunks regions -> aortic sac

Question 32

What veins are on either side of the sinus horns?

Answer 32

anterior cardinal V. posterior cardinal V. umbilical V. Vitelline V.

Question 33

What happens to the sinus horns overtime?

Answer 33

Differential expansion occurs on the left side which moves larger veins to the right; left sinus horn will disappear except for part that becomes coronary sinus

Question 34

What will occur w/ right vitelline V.?

Answer 34

it becomes a portion of the inferior vena cava

Question 35

What will happen to the sinus venosus?

Answer 35

it will be incorporated into the RA wall (sinus venarum)

Question 36

Explain how septum form within the heart

Answer 36

as chambers expand, they leave behind a portion of wall (muscular septum); cushion cells fill in the rest of the septum (fibrous membrane of septum)

Question 37

What does atrioventricular cushion tissue do?

Answer 37

fills in gap between atria and ventricles; also plays a part in creation of bicuspid and tricuspid valves

Question 38

Describe atrial separation

Answer 38

septum primum (thin muscular septum) develops w/ foramen primum -> apoptosis creates foramen secundum high up -> septum secundum develops (much thicker) and has a hole at the bottom (foramen ovale) -> blood flows through RA, foramen ovale, and foramen secundum into left atrium (can't flow backwards)

Question 39

Name the 2 shortcuts through the heart

Answer 39

Foramen ovale - blood passes between RA to LA | Ductus arteriosus - blood passes from pulmonary A to aorta (bypasses lungs)

Question 40

What does the conotrunchal septum do?

Answer 40

divides the conus region into pulmonary trunk and aorta and then spirals down between 2 ventricles (creates pulmonary and systemic circulation)

Question 41

What do the veins of the sinus horn drain?

Answer 41

anterior cardinal V - anterior body posterior cardinal V - posterior body umbilical V. - umbilical cord vitelline V - yolk sac

Question 42

What happens to the vitelline and umbilical veins in the liver?

Answer 42

vitelline veins swallowed up by liver buds and become hepatic sinusoids; right umbilical V. disappears and left hepatocardiac channel (left vitelline v) disappears; right hepatocardiac channel (future IVC); distal left umbilical V. remains and sends all umbilical blood through liver

Question 43

What happens to the left umbilical V. and ductus venosus after birth?

Answer 43

left umbilical V. = ligamentum trees hepatisus | ductus venosus = ligamentum venosum

Question 44

What does the anastomosis between anterior cardinal veins become?

Answer 44

left brachiocephalic V.