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[AMS] Gastro-intestinal System > S2-3) Development of the Gut > Flashcards

S2-3) Development of the Gut Flashcards

1
Q

In the 4th week, the embryo folds.

Describe the result of its lateral folding

A

Lateral:

  • Creates ventral body wall
  • Primitive gut becomes tubular
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2
Q

In the 4th week, the embryo folds.

Describe the result of its craniocaudal folding

A

Craniocaudal:

  • Creates cranial & caudal pockets from yolk sac endoderm
  • Beginning primitive gut development
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3
Q

What is the gut tube?

A
  • The gut tube is an endoderm-lined tube
  • It runs the length of the body and opens at the umbilicus
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4
Q

Describe some features found on the primitive gut tube

A
  • Blind pouches at the head and tail ends
  • Splanchnic mesoderm covering
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5
Q

Identify and describe the divisions of the gut tube

A
  • Foregut and hindgut begin as blind diverticula
  • Midgut has an opening at first and is continuous with the yolk sac
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6
Q

Identify the derivatives of the foregut

A
  • Oesophagus
  • Stomach
  • Pancreas, liver & gall bladder
  • Duodenum (proximal to entrance of bile duct)
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7
Q

Identify the derivatives of the midgut

A
  • Duodenum (distal to entrance of bile duct)
  • Jejunum
  • Ileum
  • Cecum
  • Ascending colon
  • Proximal 2/3 transverse colon
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8
Q

Identify the derivatives of the hindgut

A
  • Distal 1/3 transverse colon
  • Descending colon
  • Sigmoid colon
  • Rectum
  • Upper anal canal
  • Internal lining of bladder & urethra
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9
Q

Explain how the embryonic divisions have implications for blood supply in the adult

A
  • Arterial supply reflects embryonic development
  • Each embryonic segment receives blood supply from a distinct branch of the abdominal aorta
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10
Q

The structures that develop close to the junction between foregut and midgut will have mixed blood supply.

Relate this to the duodenum

A

- Proximal to entry of bile duct: gastroduodenal artery & superior pancreaticoduodenal artery (CT)

- Distal to entry of bile duct: inferior pancreaticoduodenal artery (SMA)

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11
Q

The structures that develop close to the junction between foregut and midgut will have mixed blood supply.

Relate this to the head of the pancreas

A
  • Superior pancreaticoduodenal artery (CT)
  • Inferior pancreaticoduodenal artery (SMA)
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12
Q

Describe the formation of the intraembryonic coelom

A
  • Formed as the embryo folds
  • Begins as one large cavity
  • Later subdivided by the future diaphragm into abdominal and thoracic cavities
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13
Q

Explain the specialisation of intraembryonic coelom and its membrane

A
  • One membrane lining the whole intraembryonic cavity
  • Specialises as the cavities specialise:

I. Pericardium

II. Pleural membrane

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14
Q

What are mesenteries and why are they needed?

A
  • Mesenteries are a double layer of peritoneum suspending the gut tube from the abdominal wall
  • Purpose:

I. Allow a conduit for blood and nerve supply

II. Allow mobility where needed

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15
Q

How are mesenteries formed?

A

The new primitive gut is suspended within the intraembryonic coelom:

  • Splanchnic mesoderm surrounds new gut
  • Mesentery formed from a condensation of this mesoderm
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16
Q

Where are the mesenteries?

A
  • Dorsal mesentery suspends the entire gut tube from the dorsal body wall
  • Ventral mesentery is only in the region of the foregut
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17
Q

Explain the contribution of the dorsal and ventral mesenteries to the lesser and greater sacs of the peritoneal cavity

A

Dorsal and ventral mesenteries divide the cavity into left and right sacs (in foregut only):

  • The left sac contributes to the greater sac
  • The right sac becomes the lesser sac
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18
Q

What are omenta?

A

Omenta are specialised regions of peritoneum

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19
Q

Describe the formation of the greater omentum

A
  • Formed from the dorsal mesentery
  • First structure seen when the abdominal cavity is opened anteriorly
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20
Q

Describe the formation of the lesser omentum

A
  • Formed from the ventral mesentery
  • Free edge conducts the portal triad
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21
Q

What is meant by the term peritoneal reflection?

A

A change in direction:

  • From parietal peritoneum to mesentery
  • From mesentery to visceral peritoneum, etc
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22
Q

What influences the position of the greater and lesser sacs?

A

Rotation of the stomach during development

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23
Q

Structures that are not suspended within the abdominal cavity are retroperitoneal.

What does this mean?

A

Retroperitoneal structures were never in the peritoneal cavity & never had a mesentery

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24
Q

What is meant by the term secondarily retroperitoneal?

A

Secondarily retroperitoneal structures are structures which developed intraperitoneally whose mesentery was lost to fusion with posterior abdominal wall parietal peritoneum due to massive expansion of GI tract during development

25
Identify some secondarily retroperitoneal structures of the foregut
- Duodenum - Pancreas
26
Describe the location of the foregut
Extends from the lung bud to the liver bud
27
What happens in the 4th week of development in relation to the foregut?
A respiratory diverticulum forms in the ventral wall of the foregut at the junction with the pharyngeal gut: - Respiratory primordium (ventrally) - Oesophagus (dorsally)
28
A variety of oesophageal abnormalities occur as a consequence of abnormal positioning of the tracheoesophageal septum. Identify two
29
Which mesentery do the liver and biliary system (foregut-derived glands) develop from?
Ventral mesentery
30
Describe which mesentery is responsible for the development of different areas of the pancreas (foregut-derived gland)
- **Ventral mesentery:** uncinate process and inferior head - **Dorsal mesentery:** superior head, neck, body & tail
31
Explain why the duodenum is regarded as a secondarily retroperitoneal structure?
- Its shape is determined by rotation of the stomach - Rotation of the stomach pushes duodenum to right, then against posterior abdominal wall
32
Describe the formation of the primary intestinal loop
The midgut elongates enormously then makes a loop that: - Has the **SMA** as its axis - Is connected to the **yolk sac** by the vitelline duct - Has **cranial & caudal** limbs
33
How does physiological herniation occur?
- **Primary intestinal loop** elongates rapidly and **liver** also grows rapidly - Abdominal cavity is **too small** to accommodate both & **intestines herniate** into the umbilical cord
34
What immediately follows the rotation of the gut?
The descent of the caecal bud
35
How does incomplete rotation occur and what is the result?
- Midgut loop makes only one 90° rotation - **Result**: left-sided colon
36
How does reverse rotation occur and what is the result?
- Midgut loop makes one 90° rotation clockwise - **Result**: transverse colon passes posterior to the duodenum
37
Most complications arising from midgut defects occur in the neonatal period. Identify two of them
- Strangulation - Ischaemia
38
The vitelline duct can persist resulting in a number of different abnormalities. Identify 3 of these
- Vitelline cyst - Vitelline fistula - Meckel's diverticulum
39
How does a vitelline cyst form?
**Vitelline cyst** – vitelline duct forms fibrous strands
40
Describe the features of a vitelline fistula
**Vitelline fistula** – direct communication between the umbilicus & intestinal tract
41
Meckel's diverticulum is the most common GI anomaly. Describe the incidence of its occurrence
- Affects 2% population - Usually detected in under 2s
42
In some gut structures, cell growth becomes so rapid that the lumen is partially or completely obliterated. Identify three of these
- Oesophagus - Bile duct - Small intestine
43
What does recanalisation do?
Recanalisation occurs to **restore the lumen** of gut structures
44
What happens if recanalisation is wholly or partially unsuccessful?
- **Atresia**: lumen obliterated - **Stenosis**: lumen narrowed
45
What is the most common location for atresia and stenoses?
Duodenum
46
What is pyloric stenosis?
- **Pyloric stenosis** is hypertrophy of the circular muscle in the region of the pyloric sphincter - It is **not** a recanalisation failure
47
What is gastroschisis?
- **Gastroschisis** is the failure of closure of the abdominal wall during folding of the embryo - Gut tube & derivatives are outside the body cavitiy
48
What is omphalocoele?
**Omphalocoele** is the persistence of physiological herniation
49
How does the omphalocoele differ from an umbilical hernia?
**Umbilical hernias** have the covering of skin and subcutaneous tissue
50
How is the anal canal divided?
The anal canal is divided by the **pectinate line** into histologically distinct superior and inferior parts
51
What is the proctodeum?
The proctodeum is the junction between two embryonic germ layers (anal pit)
52
Above the pectinate line, describe the following: - Blood supply - Innervation - Epithelium - Lymphatic drainage
- **Blood supply**: IMA - **Innervation**: S2-4 pelvic parasympathetics - **Epithelium**: columnar - **Lymphatic drainage:** internal iliac nodes
53
Below the pectinate line, describe the following: - Blood supply - Innervation - Epithelium - Lymphatic drainage
- **Blood supply**: pudendal artery - **Innervation**: S2-4 pudendal nerve - **Epithelium**: stratified epithelium - **Lymphatic drainage**: superficial inguinal nodes
54
What is the significance of the contribution of two embryonic tissues to the anal canal?
- **Above the pectinate line:** stretch sensation - **Below the pectinate line:** temperature, touch and pain sensations
55
Describe the nature of visceral pain?
Visceral pain is **poorly localised**
56
Identify the regions of visceral pain and its origins
- Foregut & its derivatives – **epigastrium** - Midgut – **periumbilical** - Hindgut – **suprapubic**
57
Identify 3 different hindgut abnormalities
- Imperforate anus - Anal / anorectal agenesis - Hindgut fistulae
58
Identify the 5 structures which retain the mesenteries
- Jejunum - Ileum - Appendix - Transverse colon - Sigmoid colon
59
Identify 4 structures of the midgut/hindgut with fused mesenteries
- Duodenum - Ascending colon - Descending colon - Rectum

[AMS] Gastro-intestinal System (18 decks)

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