Embryo Exam 3 TQs

Intraembryonic coelom

embryonic body cavity

Week 4

When is the intraembryonic coelom formed by embryonic folding?

Septum transversum

Develops into the central tendon of the diaphragm

Parietal wall

Which wall is covered with somatic mesoderm?

Visceral wall

Which wall is covered with splanchnic mesoderm?

Mesentery

double layer of peritoneum which attaches a segment of gut to the body wall.

Ventral mesentery

Attaches the gut to the ventral wall of the intraembryonic coelom

Dorsal mesentery

attaches the gut to the posterior wall of the intraembryonic coelom

Ventral mesentery

Which mesentery disappears?

Pericardial cavity

cavity around the heart

Pleural cavity

cavity around the lungs

Peritoneal cavity

cavity around abdominal visceral

Pleuropericardial folds

form partitions that separate the pericardial cavity from the pleural cavities, which surround each lung

Pleuroperitoneal folds

separate diaphragm, grow into pericardioperitoneal canals, forming pleuroperitoneal membranes

Diaphragm

most important muscle for inspiration (breathing), dome-shaped fibromuscular structure that separates the thoracic cavity from the abdominal cavity

Septum transversum, pleuroperitoneal membranes, dorsal mesentery of the esophagus, and muscle of the lateral walls

4 parts that make up the diaphragm

Septum transversum

crescent shaped, shelf-like structure formed of mesoderm

Dorsal mesentery

forms the left and right crus of the diaphragm

Aorta hiatus

opening through which the aorta passes

Esophageal hiatus

opening through which the esophagus passes, formed by the right crus

C3, C4, and C5

Keep the phrenic nerve of the diaphragm alive

Level of the third through fifth cervical somites

Where does the septum transversum lie during the fourth week of development?

Congenital diaphragmatic hernia

Herniation of the abdominal viscera into thorax due to presence of posterolateral defect of diaphragm, usually unilateral, most common cause of pulmonary hypoplasia, results in severe breathing difficulties

Endoderm

The _____ of the laryngotracheal groove will form the respiratory epithelium and glands on the larynx, trachea, and bronchi.

Splanchnic mesoderm

The ______ external to the foregut will form the cartilages and smooth muscle of the trachea and bronchi.

Endoderm

forms epithelium and glands of visceral organs

Splanchnic mesoderm

forms stroma and smooth muscle visceral organs

Ventral part

Part of the laryngotracheal diverticulum that forms the larynx, trachea, bronchi, and lungs

Dorsal part

Part of the laryngotracheal diverticulum that forms the esophagus as a direct continuation of the pharynx

Epiglottic

Which laryngeal cartilages does NOT develop from the fourth and sixth pharyngeal arches?

Fourth and sixth pharyngeal arches

What do all laryngeal cartilages except the epiglottic cartilage develop from?

Caudal part of hypopharyngeal eminence

What do the epiglottis and its cartilage develop from?

Myoblasts of 6th pharyngeal arch

8 of the 9 intrinsic muscles of the larynx develop from _____.

Cricothyroid muscle

The ONLY muscle of the larynx that develops from the fourth pharyngeal arch.

4th pharyngeal arch

Which arch does the cricothyroid develop from?

High position in the neck (dorsal to the soft palate)

Where the larynx of most mammals is found

Low position

Where the larynx migrates to in adult humans

Infancy

Term for 0 - 1.0 years in a human’s life

1.5 to 2 years

When does the human’s larynx descend from the high infant position to the low adult position?

Endoderm

The ________ lining the laryngotracheal tube forms the respiratory epithelium and glands of the trachea.

Splanchnic mesoderm

The __________ external to the laryngotracheal tube forms the C-ring cartilages and smooth muscle of the trachea.

Tracheoesophageal fistula

Abnormal opening between the trachea and esophagus, results from an incomplete division of laryngotracheal tube from esophagus. Usually associated with esophageal atresia

Esophageal atresia

upper part of esophagus ends as a blind pouch

Right

Which bronchus splits into an upper and lower division AND splits again to from the superior, middle, and inferior lobe of the lung.

Left

Which bronchus splits only ONCE, into the superior and inferior lobar bronchi, which supply the superior and inferior lobes of the left lung?

Week 7

When have the lobar bronchi formed ten segmental bronchi in each lung?

Splanchnic mesoderm

What surrounds the segmental bronchi?

10 bronchopulmonary segments of each lung

Together, the bronchi and mesoderm will form the ….

Splanchnic mesoderm

Forms bronchopulmonary segments, cartilage, and smooth muscle of bronchi, and visceral pleura

Somatic mesoderm

forms parietal pleura

Pseudoglandular stage

stage at 6-16 weeks

Canalicular stage

stage at 16-26 weeks

Terminal sac stage

stage at 26 weeks to birth

Alveolar stage

stage from 32 weeks to eight years

Pseudoglandular stage

By the end, all major parts of the lung have formed except those with gas exchange, which means respiration cannot occur and premature infants born at this time will not survive.

Features of the canalicular stage

Expansion in diameter of bronchi

Vascularization of the lung

Formation of respiratory bronchioles and alveolar ducts

Type 1 Pneumocytes

squamous epithelial cells that are the site of gas exchange, also known as type 1 alveolar cell

Type II Pneumocytes

cells that secrete surfactant

26-28 weeks

When surfactant secretion reaches adequate levels for unassisted survival

Postnatally

When 95% of mature alveoli develop

Adequate surfactant

Formation of functional alveoli

Establishment of pulmonary/systematic circulation

3 factors that determine if a fetus can make the transition successfully from dependence on placenta for gas exchange to air-breathing respiration

Exercise muscles of respiration

Stimulate lung development

Functions of fetal breathing movements

Pulmonary lymphatics

Most important mechanism for clearance of amniotic fluid from lungs

Expulsion through mouth/nose due to pressure on thorax during parturition

Through pulmonary blood vessels

Through pulmonary lymphatics

Clearance of amniotic fluid from the lungs occurs through these three mechanisms

Connection between oligohydramnios and pulmonary hypoplasia

When insufficient amniotic fluid is present, expansion of lungs is restricted due to pressure of uterine walls.

Pulmonary hypoplasia of lungs is a result

Respiratory distress syndrome

rapid, labored breathing which develops shortly after birth, affects 2% of neonates

Surfactant deficiency

most common cause of respiratory distress syndrome

Week 4

When the digestive system begins developing

Oropharyngeal membrane

closes the digestive system at the cranial end

Cloacal membrane

closes the digestive system at the caudal end

Endoderm

germ layer that forms most of the digestive system, including the epithelium of gut and parenchyma of accessory organs (liver/pancreas) and glands

Ectoderm

germ layer that forms the epithelium of the primitive oral cavity (stomodeum) and distal end of the anal canal (proctodeum or anal pit)

Splanchnic Mesoderm

germ layer that forms the smooth muscle and connective tissue of the gut wall and the stroma of accessory organs

Foregut

forms the distal esophagus through the second part of the duodenum where the bile duct enters

Midgut

forms the duodenum below the entrance of the bile duct through the right 2/3 of the transverse colon

Hindgut

Forms the left 1/3 of the transverse colon through the upper part of the anal canal

Celiac trunk

Branches supply the foregut derivatives

Upper third of esophagus

consists of striated muscle derived from mesenchyme from pharyngeal arches 4/6

Middle third of esophagus

consists of mixed striated and smooth muscle

Lower third of esophagus

consists of smooth muscle derived from splanchnic mesoderm surrounding the foregut

Vagus nerve

Nerve that supplies the esophagus and pharyngeal arches four and six

Esophageal atresia

upper part of esophagus ends as blind pouch, usually associated with tracheoesophageal fistula

results from deviation of tracheoesophageal septum in posterior direction

fetus is unable to swallow amniotic fluid

Polyhydramnios

result of esophageal atresia in the fetus

Ventral mesogastrium

attaches stomach to ventral body wall

Dorsal mesogastrium

attaches stomach to dorsal body wall

Developing spleen

What does the dorsal mesogastrium contain?

Omental bursa

Cavity formed as the stomach rotates and the dorsal mesogastrium elongates

Ventral border

after the original 90 degree rotation of the stomach, this comes to lie to the right

Dorsal border

after the original 90 degree rotation of the stomach, this comes to lie to the left

Ventral surface

after the original 90 degree rotation of the stomach, the left surface becomes the _________

Dorsal surface

after the original 90 degree rotation of the stomach, the right surface becomes the _________

Clockwise

What direction does the stomach rotate in?

Greater omentum

Dorsal mesogastrium’s two layers fuse to form …

Duodenum

short C-shaped segment that develops during the fourth week from the caudal foregut and cranial midgut

Entrance of bile duct

Where is the junction BETWEEN the foregut and midgut portions of the duodenum

Ventral mesogastrium

becomes the lesser omentum and falciform ligament of the liver

Hepatic diverticulum

The liver, gallbladder, and biliary duct system develop from the foregut near its junction with the midgut as the …

Liver

The large cranial part of the hepatic diverticulum forms the…

Gallbladder

The small caudal part of the hepatic diverticulum forms the…

Biliary duct system

formed by the stalk of the hepatic diverticulum connected to the duodenum