S2-3) Development of the Gut Flashcards Preview

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In the 4th week, the embryo folds.

Describe the result of its lateral folding


- Creates ventral body wall

- Primitive gut becomes tubular 


In the 4th week, the embryo folds.

Describe the result of its craniocaudal folding


- Creates cranial & caudal pockets from yolk sac endoderm

- Beginning primitive gut development


What is the gut tube?

- The gut tube is an endoderm-lined tube

- It runs the length of the body and opens at the umbilicus



Describe some features found on the primitive gut tube

- Blind pouches at the head and tail ends

- Splanchnic mesoderm covering


Identify and describe the divisions of the gut tube

Foregut and hindgut begin as blind diverticula

- Midgut has an opening at first and is continuous with the yolk sac


Identify the derivatives of the foregut

- Oesophagus

- Stomach

- Pancreas, liver & gall bladder

- Duodenum (proximal to entrance of bile duct) 


Identify the derivatives of the midgut

- Duodenum (distal to entrance of bile duct)

- Jejunum

- Ileum

- Cecum

- Ascending colon

- Proximal 2/3 transverse colon 


Identify the derivatives of the hindgut

- Distal 1/3 transverse colon

- Descending colon

- Sigmoid colon

- Rectum

- Upper anal canal

- Internal lining of bladder & urethra 


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

-  Arterial supply reflects embryonic development

- Each embryonic segment receives blood supply from a distinct branch of the abdominal aorta 


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

Relate this to the duodenum

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

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


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

- Superior pancreaticoduodenal artery (CT)

- Inferior pancreaticoduodenal artery (SMA) 


Describe the formation of the intraembryonic coelom

- Formed as the embryo folds

- Begins as one large cavity

- Later subdivided by the future diaphragm into abdominal and thoracic cavities 


Explain the specialisation of intraembryonic coelom and its membrane

- One membrane lining the whole intraembryonic cavity

- Specialises as the cavities specialise:

I. Pericardium

II. Pleural membrane 


What are mesenteries and why are they needed?

- 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 


How are mesenteries formed?

The new primitive gut is suspended within the intraembryonic coelom:

- Splanchnic mesoderm surrounds new gut

- Mesentery formed from a condensation of this mesoderm 


Where are the mesenteries?

- Dorsal mesentery suspends the entire gut tube from the dorsal body wall

- Ventral mesentery is only in the region of the foregut 


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

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 


What are omenta?

Omenta are specialised regions of peritoneum 


Describe the formation of the greater omentum

- Formed from the dorsal mesentery

- First structure seen when the abdominal cavity is opened anteriorly


Describe the formation of the lesser omentum

- Formed from the ventral mesentery

- Free edge conducts the portal triad 


What is meant by the term peritoneal reflection?

A change in direction:

- From parietal peritoneum to mesentery

- From mesentery to visceral peritoneum, etc


What influences the position of the greater and lesser sacs? 

Rotation of the stomach during development 


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

What does this mean?

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


What is meant by the term secondarily retroperitoneal?

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 


Identify some secondarily retroperitoneal structures of the foregut

- Duodenum 

- Pancreas


Describe the location of the foregut

Extends from the lung bud to the liver bud 


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) 


A variety of oesophageal abnormalities occur as a consequence of abnormal positioning of the tracheoesophageal septum.

Identify two


Which mesentery do the liver and biliary system (foregut-derived glands) develop from?

Ventral mesentery 


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