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GI - A > Embryology > Flashcards

Embryology Flashcards

1
Q

What are the three phases of human development?

A
  1. Growth- cell division and elaboration of products.
  2. Morphogenesis- Development of shape, size of a particular organ or part of the body.
  3. Differentiation- Maturation of physiological processes
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2
Q

What can be viewed as the most important weeks of embryo development and why?

A

Weeks 4-8
Major organs form and develop.
Teratogens like drugs and virus’ have a large effect during this period.

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3
Q

What happens during gastrulation?

A

The bilaminar embryonic disc is converted into the trilaminar disc.
These three layers are the 3 germ layers.
Axial orientation is also established.

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4
Q

What structures arise from the embryonic ectoderm?

A

Epidermis, CNS, PNS, Retina and other structures

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5
Q

What structures arise from the embryonic endoderm?

A

Epithelial lining of the respiratory system, Gastrointestinal tract, Glands, Liver and pancreas

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6
Q

What structures form from the embryonic mesoderm?

A

Most of the CVS, Connective tissues, muscles, blood cells, and bone marrow, vessels associated with organs and tissues.

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7
Q

During which week does the primordial gut form?

A

4th Week

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8
Q

What structure is the primordial gut derived from?

A

Endoderm lining the yolk sac.

When the embryo folds to form head and tail some of the yolk sac is “absorbed” and the endoderm is pulled inside the embryo to become the foregut, midgut and hindgut.

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9
Q

The precursor to the mouth is called what?

A

Stromodeum.

It is lined by ectoderm and separated from the foregut by the oropharyngeal membrane.

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10
Q

The primordial gut is closed at each end by which two membranes?

A

Oropharyngeal membrane and the cloacal membrane.

The cloacal membrane covers the cloaca. As the human embryo grows and caudal folding continues the urorectal septum divides the cloaca into a urogenital sinus and anorectal canal. Before the urorectal septum fuses with the cloaca the cloacal membrane ruptures forming the two exists to the body

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11
Q

Where does the foregut develop from?

A

The cranial part of the primitive gut tube.

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12
Q

What structures do the pharyngeal pouches form?

A

The pharyngeal pouches form most of the facial structures.

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13
Q

What important structure develops from the ventral wall of the foregut just after the pharyngeal pouches?

A

Laryngo-tracheal diverticulum (lung bud).

The tracheo-oesophageal septum divides the foregut into trachea and oesophagus. If this deviates incorrectly then there will be an incomplete separation of the laryngo-tracheal tube.

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14
Q

Define Atresia

A

Where an orifice or passage in the body is abnormally closed or absent.

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15
Q

Define fistula

A

An abnormal or surgically made passage between two hollow organs or between a hollow organ and the body surface.

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16
Q

How does the foregut initially form the stomach?

A

During week 4 the foregut dilates to form the early stomach

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17
Q

What does differential growth of the stomach create?

A

Differential growth of the stomach creates the greater and lesser curvatures.

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18
Q

How does the stomach rotate?

A

The stomach rotates 90 degrees clockwise along its longitudinal axis (anteroom-posterior rotation).
The ventral border now becomes the left side and the dorsal border becomes the right side.
The stomach also adapts its shape to fit with other developing organs.

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19
Q

How does the rotation of the stomach affect its vagal supply?

A

The left vagus is rotated to the anterior and the right vagus is rotated to the posterior as a result of the stomachs antero-posterior rotation.

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20
Q

How is the stomach attached to the dorsal and ventral walls of the embryo?

A

The stomach is attached by a mesentery called mesogastrium

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21
Q

How is the Omental Bursa (lesser sac) formed?

A

The mesogastrium rotates clockwise, pulling the dorsal mesentery to the left and the ventral mesenogastrium to the right.
Disproportionate growth on the dorsal side leads to the formation of the mental bursa.

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22
Q

What two major abdominal vessels supply the duodenum and why?

A

The duodenum is supplied by the Coeliac axis and superior mesenteric artery.
This is because it is formed from the caudal part of the foregut and the cranial part of the midgut.

23
Q

What effect does the rotation of the stomach have on the duodenum?

A

The duodenum also rotates and becomes “C” shaped.

Some of the dorsal mesentery fuses with the peritoneum of the posterior abdominal wall resulting in the lower duodenum being retroperitoneal.

24
Q

What is the septum transversum?

A

The septum transverse originates as the most cranial part of the mesenchyme.
During craniocaudal folding it assumes a position caudal to the developing heart.

It therefore is a mesodermal structure between the heart (pericardial cavity) and gut (yolk stalk).

It will go onto forming part of the diaphragm

25
Q

How does the liver form?

A

An outgrowth appears in the endoderm at the distal end of the foregut.
This is the hepatic diverticulum (liver bud) growing out of the primordial duodenum and into the septum transversum.

26
Q

The connection between the liver bud and foregut (duodenum) undergoes what further changes?

A

It narrows to form the bile duct.

Ventral outgrowth from this newly formed bile duct forms the gall bladder and the cystic duct.

27
Q

Does the spleen arise from the gut tube like other GI organs?

A

No.
The spleen is a mesodermal derivative not an endodermal derivative of the gut tube.

It forms in the dorsal mesogastrium near the body wall as a mesenchymal condensation.

28
Q

How does the function of the spleen change during development?

A

Up to week 14 the spleen acts as a haematopoietic organ.

During weeks 15 to 17 the spleen acquires its lobular shape and is colonised by T-lymphocyte cells.

During week 23 the B-Cell precursors arrive

The spleen can then start its lymphoid function.

29
Q

How does the pancreas buds form?

A

The pancreas forms from 2 buds, which grow from the endodermal lining of the duodenum in week 5.

The larger dorsal pancreatic bud lies in the dorsal mesentery.

The ventral pancreatic bud lies close to the bile duct.

As the duodenum rotates the ventral bud also moves to lie close to the dorsal bud (weak 6)

30
Q

What is the relation of the ventral bud compared with the dorsal bud of the pancreas once the duodenum has rotated?

A

The ventral bud lies directly behind and below the dorsal bud.

31
Q

How do the pancreatic buds form the adult pancreas once the duodenum has rotated?

A

The dorsal and ventral buds fuse to form the head of the pancreas.

32
Q

How are the developing liver and gall bladder affected by the rotating stomach and duodenum?

A

They are held in place so don’t move.

This creates the arrangement of vessels you see in the adult

33
Q

What condition can occur when the ventral pancreas fails to migrate around the duodenum correctly?

A

Annular Pancreas.

This may cause duodenal stenosis.

Another abnormality can be the formation of pancreatic tissue in other areas of the foregut. This is simply called accessory pancreatic tissue

34
Q

Which parts of the GI tract make up the midgut?

A
  1. Distal part of the duodenum
  2. Jejunum
  3. Ileum
  4. Caecum
  5. Appendix
  6. Ascending colon
  7. Proximal 2/3rds of the transverse colon
35
Q

What is classified as the distal duodenum?

A

The duodenum below the bile duct.

36
Q

How is the primary intestinal loop formed?

A

The development of the midgut involves rapid elongation of the gut tube and its associated mesentery.

37
Q

What will arise from the cephalic (cranial) part of the primary intestinal loop?

A

Distal duodenum, jejunum and proximal ileum.

The cephalic part is above the caudal part

38
Q

What will arise form the caudal part of the primary intestinal loop?

A

Distal ileum, caecum, appendix, ascending colon and the proximal 2/3rds of the transverse colon.

39
Q

What connects the primary intestinal loop to the yolk sac?

A

The apex of the primary intestinal loop is connected to the yolk sac by the vitalise duct which lies in the umbilical cord.

40
Q

Why does the primary intestinal loop herniate through the umbilicus to the extra embryonic cavity in the umbilical cord?

A

The abdominal organs are growing faster than the abdominal cavity itself. There is simply not enough room for the midgut to grow inside the abdomen.

This is called physiological herniation.

41
Q

How does rotation of the midgut differ from that of the foregut?

A

The primary intestinal loop rotates 90 degrees anti-clockwise around the superior mesenteric artery.
(As if your looking at the embryo)

42
Q

After a 90 degree rotation what positions are the cephalic and caudal limbs of the primary intestinal loop in now?

A

The cephalic limb is now on the right side of the body and the caudal limb is on the left.

Remember the primary intestinal loop rotates 90 degrees anticlockwise as if your facing the embryo.

43
Q

Describe the process of retraction of the herniated loops

A

During week 10 the abdominal cavity becaomes relatively more spacious.

The intestinal loops begin to move from the umbilical cord back into abdomen.

While this happens there is another rotation of 180 degrees anticlockwise.

The proximal part of the jejunum enters first and towards left side

As the rest of the loops re-enter they lie further to the right.

The caecum is the last part to re-enter.

This establishes the adult patter of the transverse colon lying infant of the duodenum

44
Q

Why does the abdominal cavity become spacious enough for the midgut to fit back in?

A
  1. Growth of abdominal cavity
  2. Kidneys decrease in size and move more posteriorly in abdominal wall.
  3. Liver growth slows
45
Q

What abnormalities can occur if the rotation of the primary intestinal loop is wrong?

A

Abnormal rotation can cause all the small intestine lying to the right with large intestine to the left.

Reversed rotation can lead to the duodenum lying over the colon, possibly creating a blockage

46
Q

Define Omphalocele

A

Herniation of the abdominal viscera through an enlarged umbilical ring.

This is where the intestines fail to return to the abdominal cavity.

It may include the liver, stomach and intestinal loops.

The viscera will be covered by a layer of amnion.

47
Q

Define Gastroschisis

A

Herniation of abdominal contents directly through the body wall into the amniotic cavity.

Not covered by peritoneum or amnion.

Usually through a weak area right of the umbilicus.

Not associated with chromosomal abnormalities or other defects but possibly coke use

48
Q

Define Ileal (Meckel’s) diverticulum

A

This is when a portion of the vitalise duct fails to deteriorates and instead persists..

It may form a fistula (feces may exit umbilicus), a cyst or a ligament

49
Q

What structures make up the hindgut?

A
  1. Distal 1/3rd transverse colon
  2. Descending colon
  3. Sigmoid colon
  4. Rectum
  5. upper part of the anal canal
50
Q

As well as the handgun itself what does the endoderm of the handgun also form?

A

The lining of the bladder and urethra

51
Q

What does the terminal portion of the hindgut join with?

A

The posterior part of the cloaca (primitive anal canal)

52
Q

What role does the allantois play in handgun development.

A

The allantois is present in the umbilicus and joins the hindgut before the hindgut joins the cloaca.

This creates a space between the allantois and the handgun called the urorectal septum.

The urorectal septum grows towards the cloaca but the cloacal membrane ruptures before it reaches creating the urogenital and rectal tracts

53
Q

What is the histological description of the cloaca?

A

The cloaca is an endoderm lined cavity with surface ectoderm at its ventral boundary.

54
Q

What is the urorectal septum derived from?

A

It is a mesenchymal structure

GI - A (8 decks)

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