Digestive and Respiratory System Embryology

Question 1

1) What does the digestive system consist of?
2) Development of head and tail processes as well as the ventral merger of lateral body folds results in what?
3) What does endoderm become?
4) What does splanchnic mesoderm form?

Answer 1

1) mouth, pharynx, esophagus, stomach, liver, pancreas, small intestine, large intestine (colon, cecum, rectum and anal canal) and salivary glands
2) transforms splanchnopleure into foregut, midgut and hindgut (midgut is continuous with yolk sac)
3) epithelial lining of GI tract
4) CT and smooth muscle components

Question 2

1) What does the foregut become?
2) What does midgut become?
3) What does hindgut become?
4) (adult) Derivatives of foregut, midgut and hindgut are structures supplied by what?

Answer 2

1) pharynx, esophagus, stomach, liver, pancreas, cranial duodenum
2) remaining small intestine, cecum, ascending colon and part of transverse colon
3) remaining transvere colon, descending colon, and cloaca which forms rectum and most of anal canal
4) celiac (foregut), cranial mesenteric (midgut) and caudal mesenteric arteries (hindgut) resp

Question 3

1) The adult pharynx is a __________
2) initially, the pharynx is closed cranially by what?
3) It must do what
4) #3 must happen to allow what two events?
5) What do pharyngeal pouches give rise to?
6) midline evagination of floor of pharynx (?) gives rise to what?

Answer 3

1) common respiratory-digestive chamber
2) oropharyngeal membrane
3) degenerate
4) communication with oral and nasal cavity outgrowths
- migration of tongue muscle from pharynx into oral cavity
5) several adult structures which retain continuity with pharyngeal cavity –> auditory tube and fossa of palatine tonsil
6) laryngotracheal groove; larynx, trachea and lungs

Question 4

1) Esophagus develops from ________
2) what’s its principal morphogenic development?
3) What is associated with both the esophagus and pharynx?
4) What is it derived from?
5) It’s innervated by what?

Answer 4

1) foregut
2) elongation
3) skeletal muscle
4) somites that migrate toward pharyngeal arches
5) vagus nerve

Question 5

1) Most domestic animals have what kind of stomach versus ruminants?
2) stomach develops from what?
3) Describe morphogenic changes
4) What does endoderm form?

Answer 5

1) simple vs complex
2) tubular segment from foregut
3) tube become convex dorsally (greater curvature) and concave ventrally (lesser curvature) –> growth is more rapid dorsally

tube rotates 90 degrees to L (dorsal to L, ventral to R)

long axis becomes transverse –> liver pushes cranial end of stomach to L side

incrased growth along L cranial margin of future greater curvature –> fundus region

4) epithelium lining of stomach –> differentiates

Question 6

5) 3 compartments of ruminant are lined by what?

6) what is the last compartment?
7) rumen develops as what?
8) reticulum arise as?
9) omasum develops as?
10) abomasum develops?
11) What happens with rumen later in development?

Answer 6

5) rumen, reticulum, omasum –> stratified squamous

6) abomasum –> glandular compartment
7) expansion of fundus
8) caudoventral pocket of rumen
9) bulge along lesser curvature
10) rest fo stomach
11) rumen flips caudally –> lays on top of abomasum adn reticulum is cranial

Question 7

along with general tubular elongation…..

1) where yolk sac is attached, what happens?
2) eventually what happens in response to #1)
3) What’s next step?
4) What happens with caudal limb of loop?

Answer 7

1) midgut forms an elongate loop that herniates through umbilicus (out of embryo and into coelom of umbilical stalk)
2) eventually as embryo grows, loop returns into embryonic coelom (abdominal cavity)
3) elongating loop rotates 360 degrees clockwise (viewed dorsally) around R vitelinne artery (adult cranial mesenteric a)
4) develops a diverticulum, future cecum

Question 8

5) in ungulates, what happens with colon?’

6) What is temporary atresia? What must occur?
7) What is persistent atresia or stenosis?
8) What happens if yolk sac isn’t absorbed by midgut (jejunum)?

Answer 8

5) loop of colon forms just distal to cecum (loop of ascending colon)

pig and ruminant - loop coils (spiral or coiled colon)

horse - loop enlarges and bends on itself; cecum enlarges

6) intestinal tract and esophagus occlude lumen as a result of epithelium proliferation. Recanalization occurs by formation of vacuoles that coalesce to form ultimate lumen
7) failure to recanalize or narrow lumen - congenital anomaly –> localized sites
8) jejunal diverticulum , fistulous (hollow) cord to umbilicus or a fibrous connection btw jejunum and umbilicus –> source of colic

Question 9

1) The hindgut terminates as what?
2) the caudal wall of cloaca is what? define
3) what happens with allantois?
4) What species does cloaca persist?

Answer 9

1) cloaca - chamber that communicates with urinary, digestive and genital systems
2) cloacal membrane - endoderm apposed to surface ectoderm
3) envaginates from hindgut at cranial end of cloaca
4) avians, reptiles and amphibianas

Question 10

1) How is the rectum formed?
2) What does the dorsal chamber become?
3) What does the ventral chamber become?
4) What does urinary bladder and urethra develop from?

Answer 10

1) mesenchyme partiition (urorectal septum) divides cloaca into dorsal and ventral chambers
2) rectum and most of anal canal, including a temporary anal membrane (contiuous with hindgut)
3) is the urogenital sinus, continuous with allantois
4) proximal allantois and urogenital sinus

Question 11

1) How is cranial part of anal canal formed?
2) What is this part lined by?
3) What is the caudal part lined by?
4) How does it form?
5) What is the proctodeum
6) What does the laterla diverticula of proctodeum ectoderm become in carnivores?

Answer 11

1) along with rectum
2) mucosal epithelium derived from endoderm (most of canal)
3) stratified squamous (caudal to adult anocutaneous line)
4) external tissue surrounding anal membrane grows caudally creating a proctodeum
- proctodeum becomes incorporated in anal canal when anal membrane degenerates (atresia ani or intact anal membrane - congenital anomaly)
5) ectoderm lined depression
6) anal sacs

Question 12

1) What does the liver originate as?
2) Where does it arise from? which will become?
3) What does the diverticulum give rise to?
4) How are lobes of liver formed?
5) the gall bladder develops from?
6) bite duct is derived from?
7) heptaic diverticulum originates where, but what happens?

Answer 12

1) from endoderm as a hepatic diverticulum
2) arises from region of foregut which will become future descending duodenum
3) multiple branches –> hepatic ducts, cystic ducts and pancreatic duct
4) during continued growth and branching of hepatic duct primordia
5) end of cystic duct
6) initial part of hepatic diverticullum
7) ventrally but differential growth of duodenal wall –> bile duct entering duodenum dorsally –> pancreatic duct on major duodenal papillae

Question 13

1) pancreas originates from what?
2) one diverticulum arise where?
3) what does it form?
4) other diverticulum arise where?
5) forms what?
6) What happens with R and L lobes?
7) where do endocrine islet cells develop from?
8) pancreatic ducts…

Answer 13

1) 2 separate endoderm diverticula –> elongates, branches and forms acini in typical glandular fashion
2) ventrally as bud of hepatic diverticulum
3) pancreatic duct and R lobe of pancreas
4) dorsally from duodenum (minor duodenal papillae)
5) accesory pancreatic duct and L lobe of pancreas
6) cross one another and fuse –> body of pancreas; ducts anastomose to form common drainage system
7) endoderm of diverticula
8) one duct destined to be smaller or disappear –> depends on species –> dog - accesory larger –> cat - accesory smaller and majority don’t have one and assoc minor duodenal papillae

Question 14

1) Features of avian GI tract

Answer 14

1) crop - diverticulum of esophagus
2) 2-compartment stomach
- proventiculus (glandular)
- ventriculus (gizzard) - stratified squamous and heavy muscles for grinding
3) pair of ceca
4) cloaca –> opens externally by means of vent

Question 15

1) embryonic coelom separates what?
2) mesoderm lining transforms into what?
3) Mesenteries formed by what?
4) caudal to pharynx……__________ persist as _______
5) in abdomen, _____ persists but _______ is absent in ___________

Answer 15

1) splanchnic mesoderm from somatic mesoderm
2) serous membranes making coelom a serous cavity
3) splanchnic mesoderm at same time embryo gut it created as embryo assumes tubular shape
4) ventral and dorsal mesenteries of esophagus persist as mediastinum in thorax
5) dorsal mesentery persists but ventral mesentery is absent in midgut

Question 16

1) what does dorsal mesentery become?
2) original dorsal mesogastrium forms what?
3) what else develops here?
4) How is root of mesentery formed?
5) what does ventral mesogastrium become?
6) what else develops

Answer 16

1) greater omentum, mesoduodenum, mesentery, mesocolon and mesorectum
2) elongates as forms greater omentum
3) L lobe of pancreas within dorsal portion of greater omentum
- spleen (from blood vessels that accumulate - greater curvature)
4) as midgut elongates and rotates around cranial mesenteric artery –> portions of mesojejunum and mesoileum come in contact near dorsal body wall and fuse (parts of mesoduodenum and mesocolon also fuse)
5) lesser omentum and coronary and falciform ligaments of liver; caudally it becomes median ligament of urinary bladder
6) liver

Question 17

1) What does the respiratory consist of?
2) Epithelium lining nasal cavity is derived from what?whereas rest of the epithelium lining remaing resp. system comes from?
3) Larynx, trachea and lungs originate as what?
4) called what?
5) How is tracheoesophageal septum formed?
6) septum creates what?
7) where does larynx develop?

Answer 17

1) nasal cavity, pharynx, larynx trachea and lungs
2) ectoderm; endoderm
3) envagination of endoderm along floor of pharynx
4) laryngotracheal groove
5) from lateral walls of laryngotracheal groove –> fuses along midline
6) laryngotracheal tube (future trachea and lung buds) separate from esophagus
7) rostrally where lumen of groove communicates with pharynx

Question 18

1) pharyngeal arch splanchic mesoderm forms what?
2) swellings border what?
3) growth of laryngeal swellings give rise to what?
4) diverticulum of lateral laryngeal wall produces what?
5) laryngeal muscles formed from what?

Answer 18

1) bilateral laryngeal swellings and a rostral epiglottal swelling
2) laryngeal openings (btw groove and pharynx)
3) cartilages of the larynx
4) lateral ventricle and vocal fold, bilaterally
5) somtie myotomes that migrate into pharyngeal arches

Question 19

1) what happens with laryngotracheal tube?
2) splanchnic mesoderm contributes to what?
3) endoderm contributes to what?
4) blind, caudal end of tube develops what?
5) outgrowths of each principal bronchus form what? which give rise to________that become____________; each of which give rise to_______
6) smallest branches are?
7) give rise to what?
8) True or False: bronchial branchings continue to occur throughout fetal and postnatal period

Answer 19

1) grows caudally; elongation shifts bronchi caudally into thoracic splanchnic mesoderm
2) cartilage and CT to trachea and lungs
3) respiratory epithelia to trachea and lungs
4) bi-lobed bronchial buds –>future principal bronchi
5) lobar bronchi which give rise to outgrowth that become segmental bronchi each of which give rise to dozens of bronchial branches
6) terminal bronchioles
7) lung terminal sacs and alveoli
8) True

Question 20

1) in domestic animals, R principal bronchus divides into how many lobar bronchi?
2) while L gives rise to how many?
3) exceptions in horse? humans? ruminants and swine?

Answer 20

1) 4 (cranial, middle, caudal and accesory)
2) 2 (cranial and caudal)
3) horses - lack a middle lobe

humans lack accesory

rum and swine - R cranial lobe supplied by tracheal bronchus

Question 21

1) endoderm-lined bronchial tree grows into (thru) what? to form what?
2) continued branching results in?
3) coated by?
4) initially bronchiole-lung branches are?
5) eventually terminal branches become?
6) How are alveoli formed?
7) some alveolar cells become? and produces what?
8) what’s its fn?
8) species differ in degree of lung maturity at birth; which regions are less mature?
9) formation of new alveoli occur?
10) lung growth is due to?

Answer 21

1) splanchnic mesoderm to form cartilage, fascia, smooth muscle and vessels of lung
2) lung tissue
3) visceral pleura
4) solid cores of cells
5) hollow, dilated sac-like with thin epithelium (endoderm) –> terminal sacs
6) formation of septae that partition terminal sacs
7) cuboidal and produce surfactant
8) reduces surface tension and facilitates alveolar expansion; fetal lungs contain fluid –> facilitates breathing movements that take place in utero to prepare postnatal respiration; at birth lung fluid drains or is absorbed as air is breathed
8) distal
9) postnatal
10) hypetrophy , increased size of alveoli and air passageways