The primitive gut tube is derived from the extraembryonic part of embryo's yolk sac. True or false.
Extraembryonic yolk sac = 2ndary yolk sac --> provides nutrients to the embryo while utero-placental circulation is estsablished; later assimilited into umbilical cord.
Intraembryonic yolk sac = primitive gut
How is the gut tube formed from the 3 germ cell layers?
Endoderm: epithilial lining of digestive tube & digestive organs (liver, gallbladder, & pancreas) arise as buds
Mesoderm: through lateral folding, eventually surrounds the gut tube forming connective tissue & muscular walls.
Ectoderm: forms the neural tube that gives rise to the neural crest cells that invade the mesoderm forming neurons & glial cells intrinsic to GI tract
What are the 3 parts of the endodermal gut tube?
Foregut, midgut, & hindgut
What parts of the digestive system arises from the foregut?
Esophagus, stomach, proximal duodenum (to ampulla of Vater)
What artery supplies blood to the foregut?
What parts of the digestive system arise from the midgut?
Small intestine (including duodenum distal to the bile duct)
Part of the large intestine: cecum, appendix, ascending colon & proximal transverse colon (2/3 of transverse colon)
What artery supplies blood to the midgut?
What parts of the digestive system arise from the hindgut?
Large intestines: distal transverse colon, descending colon, sigmoid colon, rectum, superior part of anal canal
What parts of the endodermal gut tube (foregut, midgut, & hindgut) give rise to organs that are not part of the digestive system?
Foregut = Lower respiratory system & pharynx --> in the book known as a 4th section of the primitive gut, the Pharyngeal gut (includes the 2 mentioned above & the upper esophagus), the foregut is the lower esophagus down
Hindgut = epithelium of urinary bladder & most of urethra
What eventually forms into the liver, gallbladder, and pancreas?
By the 4th-6th week, what is a major early hematopoietic organ of the embryo?
When does the bone marrow take over hematopoiesis from the liver?
Approx 6 months
At birth a child's liver is equivalent to an adult's size. True or false.
False, at birth, the liver is 20% of the adult size --> will continue to grow for 25-30 years.
What attaches the liver to the ventral wall?
What is the respiratory diverticulum?
In the embryo, arising frm the foregut, the respiratory diverticulum grows from the ventral wall of the esophagus at its border with the pharyngeal gut.
What is the esophagotracheal septum?
The separation between the respiratory diverticulum & the foregut portion that eventually becomes the esophagus
What are the 4 layers of the GI tract? (inside to outside, include the sublayers)
Mucosa, submucosa, muscularis, & serosa
Mucosa (epithelium, lamina, muscularis mucosae)
Muscularis (Circular muscle layer, longitudinal muscle layer)
Serosa (connective tissue layer, peritoneum)
By which week of gestation does the respiratory diverticulum separate from the foregut that eventually becomes the esophagus?
What are the steps forming the enteric nervous system?
1) neural crest cells enter the gut
2) crest cells proliferate
3) crest cells migrate along the gut
4) crest cells differentiate & form connections w/ their targets.
How is the GI tract innervated?
ANS - sympathetic slows it down, parasympathetic (vagus nerve) speeds it up
Also have intrinsic innervation - submucosal plexus (Meissner plexus) & myenteric plexus (Auerbach plexus)
Describe the innervation of the stomach.
Extrinsic - originate outside stomach --> parasympathetic fibers frm vagus nerve & sympathetic fibers frm the celiac plexus
Intrinsic - originate w/in stomach & respond to local stimuli --> myenteric plexus
What is peristalsis?
Coordinated sequential contraction & relaxation of the outer longitudinal & inner circular layers of muscles.
What gestation age does the gut develop normal propulsive motility/peristalsis?
What gestational age can you swallow?
What gestational age does non-nutritive sucking develop?
What gestational age does coordinated esophageal peristalsis occur?
What gestational age does nutritive sucking occur?
34-35 wks when there is rapid growth of the fetal stomach & small intestine motility
What is the percentage of the blood supplied by hepatic artery and portal vein in the liver?
hepatic artery = 25%
portal vein = 75%
What is deglutition?
the act of swallowing
What are gastric glands and gastric pits? Location.
Location: stomach's mucosa
Gastric pits: depressions in the epithelial lining of the stomach --> a duct where gastric glands empty into.
Gastric glands: found at the bottom of gastric pits - tubular in nature --> chief cells secrete gastric juice, parietal cells secrete stomach acid.