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Physiology Sem 2 > Development of the GI tract > Flashcards

Development of the GI tract Flashcards

1
Q

The gut is divided into

A

Foregut
Midgut
Hindgut

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2
Q

When does GI tract development occur

A

3rd to 12th weeks embryonic age

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3
Q

Describe the formation of the blastocyst from the zygote

A

Zygote undergoes mitosis -> 1 cell to 8-16 cells to form morula.

Embryo undergoes compaction, cells form epithelial tight junctions between cells on the outer side. Outside cells form trophectoderm, inner cells form inner cell mass to form the embryo.

Inner cell mass cells differentiate into epiblast and hypoblast layers.

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4
Q

Where does the primitive streak form

A

Forms at caudal of the embryo, moves towards cranial end.

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5
Q

Describe gastrulation

A

Epiblast cells condense towards middle of embryo. These cells undergo epithelial to mesenchymal transformation. They then fill the space between the epiblast and hypoblast layers (involution and ingress). The cells then migrate and differentiate.

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6
Q

Describe the primary germ layers

A

Mesoderm - Surrounding muscle, connective tissue and mesenteries
Endoderm - Epithelium of the gut tube
Ectoderm - Innervation of the gut

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7
Q

The primitive streak is surrounded by

A

the primitive groove

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8
Q

The ectoderm is patterned by

A

the mesoderm

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9
Q

What are notochordal cells

A

Mesodermal cells which form a rod like structure, which patterns the above layer (ectoderm)

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10
Q

Describe initial gut folding and tube formation

A

Gut tube formed by folding of sheets of cells in two directions
Folding towards midline along the cranial-caudal axis
Folding towards the yolk sac at the cranial and caudal ends

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11
Q

Gut tubeis closed by

A

Pharyngeal membrane at cranial end, cloacal membrane at caudal end.

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12
Q

What are mesenteries

A

Important in anchoring gut tube to body wall. Neural ectoderm folds upwards , so edges come together to form closed neural tube. Lateral folding of lateral sides to the midline of the embryo to enclose the yolk sac. The endoderm sides fuse to form an enclosed tube. The mesoderm attaches the gut to the body wall.

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13
Q

The foregut includes

A

Pharynx
Oesophagus
Stomach
Cranial half of duodenum
Ampulla of Vater

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14
Q

The midgut includes

A

Caudal duodenum
Jejunum
Ileum
Cecum
Appendix
Ascending colon
Proximal 2/3 of transverse colon

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15
Q

The hindgut includes

A

Distal 1/3 of transverse colon
Descending colon
Rectum

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16
Q

Hox gene expression boundaries

A

Boundaries of hox gene expression along the cranial-caudal axis specify the position of GI tract structures

17
Q

Which arteries supply blood to each part of the gut

A

Celiac -> Foregut
Superior mesenteric -> Midgut
Inferior mesenteric -> Hindgut

18
Q

Arterial blood supply to the GI tract

A

Gut surrounded by plexus of blood vessels, joining vitelline vessels to aorta. Plexus resolves to form aerteries that supply the GI tract from the aorta.

These define the boundaries
5 branches to the thoracic oesophagus.

19
Q

Innervation of the gut tube

A

Sympathetic ganglia develop next to major branches of the aorta
Post-ganglionic sympathetic axons innervate the same tissues that the arteries supply with blood.

20
Q

What are the principles of foregut development

A

Regionalised development of the gut tube occurs simultaneously
Gut development is a dynamic three-dimensional process
Driven throughout by growth, expansion, rotation

21
Q

Describe stomach expansion and rotation

A

Gut tube undergoes swelling. Left side of vagal nerve lies ventral, right side lies dorsal. (anterior and posterior). Curvature of gut tube occurs, more rotation along craniocordal axis.

22
Q

What is the pylorus

A

A construction at the outlet of the stomach.

23
Q

What are the mesenteries attaching the stomach to the body walls

A

Dorsal mesogastrium (as the stomach rotates, this is drawn with it) which extends and encloses the omental bursa. Folds to form the greater omentum, obliterating the bursa

Ventral mesogastrium -> Lesser omentum (stomach and liver)
Falciform ligament -> Liver and ventral body wall

24
Q

What fixes the mature gut in place in the body

A

Fusion of the mesenteries with the posterior abdominal wall

25
Q

What is pyloric stenosis

A

Obstruction of the pylorus, caused by overgrowth of smooth muscle that surrounds the opening (smooth muscle hypertrophy)

Results in projectile vomit after feeding

26
Q

How does the liver bud from the foregut

A

Heart induces signal for liver to bud. Hepatic diverticulum grows into mesenchyme of septum transversum. Cords of hepatic endoderm, bile drainage ducts and blood vessels proliferate, arranged as sinusoids. Liver expands into ventral mesentery.

27
Q

How does the pancreas bud from the foregut

A

Two pancreatic buds - Dorsal from duodenal endoderm, ventral from hepatic diverticulum

Duodenum rotates, ventral and dorsal buds meet and fuse

Ventral bud bifid, one rotates around duodenum, annular pancreas forms, which can obstruct duodenum

28
Q

How are the intestines arranged in the midgut

A

Attached by dorsal mesentery
Mesentery and gut grow at different rates
Ventral branch of the aorta supplies the midgut: superior mesenteric artery
Intestines rotate around SMA, herniates into umbilical stalk at 6/7 weeks. At 10 weeks, intestines return and unherniate.

29
Q

What is umbilical hernia

A

Intestines return normally, but body wall has not closed properly over intestines (failed fusion). Gut is covered in skin.

30
Q

What is omphalocele

A

Failure of intestinal loops to return into abdomen: heria coverd in amnion. Associated with materal obesity, alcohol/tobacco, SSRI use.

31
Q

What is gastroschisis

A

Failure of ventral body to fuse, no covering around the gut or intestines. Associated with young maternal age, low BMI and drug misusage.

32
Q

What is the persistence of yolk duct

A

The yolk duct is normally obliterated
Yolk duct attached to ileum, near ileo-cecal junction, apex of midgut loop

33
Q

What is Meckel’s diverticulum

A

Asymptomatic defect
Can contain ectopic gastric cells: ulceration
Can be connected to umbilicus by ligament

34
Q

What is Hirschsprung’s disease

A

Ganglia present in dilated/hypertrophic region
Aganglionic segment shows contraction

Affects hidngut, dilatation of sections of the colon, lack of tone, peristalsis, leading to constipation
Absence of parasympathetic enteric ganglia
Lack of neural crest cells - > Tonic contraction

35
Q

What are neural crest cells

A

Originate from dorsal region of the neural tube
Contribute to parasympathetic innervation of the gut

Physiology Sem 2 (53 decks)

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