Embryology Exam 3

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258 Terms

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intraembryonic coelom
embryonic body cavity, formed week 4 via embryonic folding, has 3 divisions
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pericardial cavity
surrounds the heart
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pericardioperitoneal canals
surrounds the lungs, lie lateral to foregut and pass dorsal to the septum transversum
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septum transversum becomes the
central tendon of the diaphragm
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parietal wall
covered with somatic mesoderm, forms the parietal layer of membranes (pleura, pericardium, peritoneum)
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visceral wall
covered with splanchnic mesoderm, forms visceral layer of membranes (pleura, pericardium, peritoneum)
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why might the pleural cavity not be present initially?
because the lungs develop over time
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mesentery
a double layer of peritoneum which attaches a segment of gut to the body wall
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2 initial mesenteries
ventral- attaches gut to ventral wall of intraembryonic coelom, dorsal- attaches gut to posterior wall of intraembryonic coelom; both divide the peritoneal cavity into left and right halves, only ventral disappears through much of its length
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pleuropericardial folds
grow and eventually form partitions that separate the pericardial cavity from the pleural cavities that surround each lung
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pleuroperitoneal folds
grow into pericardioperitoneal canals forming pleuroperitoneal membranes
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diaphragm
most important muscle of inspiration, dome-shaped fibromuscular structure that separates thoracic cavity from abdominal cavity
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diaphragm develops from
septum transversum, pleuroperitoneal membranes, dorsal mesentery of the esophagus, muscle of lateral walls
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septum transversum
crescent shaped, shelf-like structure formed of mesoderm, grows dorsally from ventrolateral body wall and passes between heart and liver to form an incomplete partition between thoracic and abdominal cavities
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pleuriperitoneal membranes
grow ventromedially to fuse with septum transversum and dorsal mesentery of esophagus
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dorsal mesentery of esophagus forms
left and right crus of the diaphragm
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crus of the diaphragm
pass in front of aorta forming aortic hiatus, right crus forms boundaries of esophageal hiatus
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septum transversum movements
travel with nerve fibers from C3-5 in its decent and form phrenic nerve, supplying the diaphragm, 4th week is at the level of the 3rd-5th cervical somites, later through differentiated growth of body wall is lies at adult position of diaphragm between thoracic and abdominal cavity
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congenital diaphragmatic hernia
herniation of abdominal viscera into thorax- due to presence of posterolateral defect of diaphragm, usually unilateral and results from defective formation of pleuroperitoneal membrane, results in large opening in diaphragm though which viscera protrude, most common cause of pulmonary hypoplasia, results in sever breathing difficulties
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respiratory system develops
week 4 with appearance of laryngotracheal groove in caudal anterior wall of pharynx
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endoderm of laryngotracheal groove
forms epithelium and glands of visceral organs
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splanchnic mesoderm external to foregut- larynx, trachea, bronchi
forms stroma and smooth muscles of visceral organs- trachea and bronchi
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the distal end of the laryngotracheal diverticulum enlarges to form ___ while the opening of the laryngotracheal diverticulum into the pharynx becomes the ___
respiratory bud; primordial laryngeal inlet
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the laryngotracheal diverticulum is initially
in open communication with the pharynx
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2 longitudinal tracheoesophageal folds
develop in the laryngotracheal diverticulum as it elongates, grow toward each other and fuse to form tracheoesophageal septum
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tracheoesophageal septum divides laryngotracheal diverticulum into
ventral part- forma larynx, trachea, bronchi, lungs ; and dorsal part- forms esophagus as a direct continuation of pharynx
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respiratory epithelium of larynx develops from
endoderm lining the laryngotracheal tube
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epiglottis and its cartilage
develop from caudal part of hypopharyngeal eminence
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8 of 9 intrinsic muscles of larynx develop from
myoblasts of 6th pharyngeal arch, 1 exception is cricothyroid muscle(controls innervation) that develops from 4th pharyngeal arch
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where is the larynx of most mammals found and what’s the purpose?
in a high position in the neck dorsal to the soft palate, creates separate respiratory and digestive channels allowing mammals to swallow and breathe at the same time
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larynx of adult humans
lies in a low position increasing the size of the pharynx- facilitates speech and prohibits swallowing and breathing at the same time
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where is the larynx in an infant?
it is born high up similar to other mammals, but during the first 1.5-2 years after birth it descends to adult position corresponding to time of speech development
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trachea develops from
laryngotracheal tube distal to larynx
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endoderm lining of laryngotracheal tube forms the
respiratory epithelium and glands of the trachea
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splanchnic mesoderm external to laryngotracheal tube forms
the c-ring cartilages and smooth muscle of the trachea
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tracheoesphageal fistula
an abnormal opening between trachea and esophagus, results from incomplete division of laryngotracheal tube from esophagus due to incomplete fusion of tracheoesphageal folds, usually associated with esophageal atrasia, infant cannot swallow and reflux of gastric acid into lungs may occur- associated with polyhydramnios
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esophageal atrasia
upper part of esophagus ends as a blind pouch
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a single respiratory bud develops where?
the end of the laryngotracheal diverticulum during week 4, it then divides into 2 primary bronchial buds
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beginning of week 5
each primary bronchial bud enlarges to form right and left main bronchi- carry air to and from right and left lung
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right main bronchus splits into
upper division and lower division, lower division then splits again
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upper bronchi division becomes
superior lobar bronchus, supplies superior lobe of right lung
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lower bronchi division
splits again to become middle and inferior lobar bronchi, supply middle and inferior lobes of right lung
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left main bronchus
splits only once into superior and inferior lobar bronchi, supply superior and inferior lobes of left lung
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by week 7 the lobar bronchi form
10 segmental bronchi in each lung
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10 bronchopulmonary segments of each lung
the segmental bronchi and the splanchnic mesoderm that surrounds it
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splanchnic mesoderm surrounding bronchi and bronchioles form
cartilaginous rings and plates of bronchi, smooth muscle of bronchi and bronchioles
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as the outer lungs develop
splanchnic mesoderm on its outer surface forms visceral pleura
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somatic mesoderm covering inside of thoracic wall forms
parietal pleura
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pleural cavity
space between parietal and visceral pleura
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4 stages of lung development
pseudoglandular stage: 6-16 weeks, canalicular stage: 16-26 weeks, terminal sac stage: 26 weeks-birth, alveolar stage: 32 weeks-8 years
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pseudoglandular stage
6-16 weeks, chracterized by branching of bronchioles and formation of bronchopulmonary segments, by end all major parts of lung have formed except those involved with gas exchange
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T/F premature infants born in canalicular stage may survive
F- respiration cannot occur, premature infants at this stage cannot survive
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canalicular stage
16-26 weeks, characterized by expansion in diameter of bronchi, vascularization of the lung, formation of respiratory bronchioles and alveolar ducts, by end some terminal sacs have developed and lungs have become highly vascularized
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T/F a premature infant born toward the end of canalicular stage may survive
T- some gas exchange can occur, however it will require intensive care and mortality risk is high
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terminal sac stage
26 weeks-birth, characterized by formation of numerous terminal sacs which represent primordia of alveoli of mature lung, walls of terminal sacs become thin as cuboidal cells of respiratory bronchioles transform to squamous flattened epithelial cells (type I pneumocytes)
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type I pneumocytes
flattened epithelial cells, make up terminal sac epithelium that’s 1 cell thick, capillary beds surround the terminal sacs and bulge into their walls, facilitates gas exchange
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type II pneumocytes
rounded cells that secrete surfactant
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surfactant
a mixture of phospholipids and proteins that form a thin film over inner walls of terminal sacs and later alveoli, reduces surface tension between air and alveolar surfaces which is essential to allow alveolar sacs to expand and prevent their collapse during expiration
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surfactant secretion begins
20-22 weeks and reaches adequate levels for unassisted survival at 26-28 weeks
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alveolar stage
32 weeks-1 year, characterized by development of mature alveoli, 95% of mature alveoli develop postnatally- mostly complete by 3 years but some form up to 8 years
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3 factors that determine if a fetus can make transition successfully from dependence on placenta for gas exchange to air-breathing respiration
adequate surfactant, formation of functional alveoli, establishment of pulmonary/systemic circulation
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why is it important to advise parents not to smoke around infants/small children?
the alveoli are still developing and inhaling smoke could alter/disrupt the developing alveoli
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at birth lungs are filled with what? what happens to that fluid?
at birth lungs are about half-filled with amniotic fluid, removal of the amniotic fluid is essential to allow inflation of the lungs
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3 ways clearance of amniotic fluid occurs
expulsion through mouth and nose due to pressure on thorax during parturition (c-section babies have more fluid in lungs), via pulmonary blood vessels, via pulmonary lymphatics
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fetal breathing movements occur intermittently during
3rd trimester of gestation and some amniotic fluid is aspirated during these movements
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fetal breathing movements function to
exercise muscles of respiration, stimulate lung development
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are pulmonary lymphatics larger and more numerous in adults or a fetus?
they’re larger and more numerous in a fetus to facilitate drainage of amniotic fluid
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oligohydramnios and hypoplasia
when insufficient amniotic fluid is present, expansion of the lungs is restricted due to pressure from the uterine walls, results in pulmonary hypoplasia
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respiratory distress syndrome
rapid, labored breathing that develops shortly after birth, affects 2% of neonates, major cause is surfactant deficiency
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digestive system is initially closed by the
oropharyngeal membrane (cranial end) and cloacal membrane (caudal end)
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when does the digestive system begin development?
week 4 when folding of the embryo incorporates the dorsal part of umbilical cord
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what germ layer(s) is the digestive system derived from?
all 3- endoderm, mesoderm, ectoderm
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endoderm
forms most of the digestive system, epithelium of gut, parenchyma of accessory organs (liver, pancreas) and glands
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ectoderm
forms epithelium of primitive oral cavity (stomodeum) and distal end of anal canal (proctodeum or anal pit)
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mesoderm
splanchnic mesoderm forms the smooth muscle and connective tissue of gut wall and stroma of accessory organs
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the 3 embryological components the digestive system
foregut, midgut, hindgut
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foregut
forms the distal esophagus through second part of duodenum where the bile duct enters
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midgut
forms the duodenum below entrance of bile duct through right 2/3 of the transverse colon
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hindgut
forms left 1/3 of transverse colon through upper part of anal canal
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foregut derivatives are supplied by
branches of the celiac trunk
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esophagus develops from
pharynx as the laryngotracheal diverticulum and is divided from laryngotracheal tube by tracheoesophageal septum
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the esophagus consists of
upper 1/3, middle 1/3, lower 1/3
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lower third of esophagus
consists of smooth muscle derived from splanchnic mesoderm surrounding the foregut
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middle third of esophagus
consists of mixed striated and smooth muscle
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upper third of esophagus
consists of striated muscle
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esophageal atresia
upper part of esophagus ends as a blind pouch, usually associated with tracheoesophageal fistula, results from deviation of tracheoesophageal septum in posterior direction
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what clinical condition results in a fetus being unable to swallow amniotic fluid and results in polyhydramnios?
esophageal atrasia
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the ventral and dorsal mesenteries of the stomach are called
ventral and dorsal mesogastrium
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ventral mesogastrium
attaches stomach to ventral body wall
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dorsal mesogastrium
attaches stomach to dorsal body wall, contains developing spleen
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which direction does the stomach rotate?
90 degrees clockwise
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stomach
dilation of the foregut occurs week 4, broadens ventrolaterally, dorsal border grows faster than ventral
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ventral and dorsal borders of the stomach becomes which curvatures?
ventral border becomes lesser curvature and dorsal border becomes greater curvature of stomach
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after a 90 degree clockwise rotation the ventral border comes to lie
to the right and the dorsal border comes to lie to the left
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after a 90 degree clockwise rotation the left surface and right surfaces become
the ventral and dorsal surfaces of the stomach
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after a 90 degree clockwise rotation the left and right vagus nerves supply
ventral and dorsal surfaces of the stomach
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as the stomach rotates the dorsal mesogastrium elongates and forms
a cavity that becomes the omental bursa- a subdivision of the peritoneal cavity
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after a 90 degree rotation the left/right vagus nerves become the
anterior/posterior vagal trunks
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the dorsal mesogatrium expands
caudally to overhang intestines and its 2 layers fuse to form greater omentum
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the ventral mesogastrium becomes the
lesser omentum and falciform ligament of liver