development of liver, pancreas.

When does the liver diverticulum appear?

In the 3rd week of development,

→ the liver diverticulum (liver bud) appears as an outgrowth of the endodermal epithelium

from the ventral wall of the caudal portion of the foregut.

In which direction does the liver diverticulum grow?

It grows cranially

and ventrally → into the ventral mesogastrium and septum transversum.

What are the primordia of the hepatocytes?

The cranial end of the liver diverticulum is bifurcated

and branches in strands of cells, which are the primordia of the hepatocytes.

What do the developing liver cells induce?

They induce the development of the hepatic sinusoids.

What are the two hypotheses for the origin of hepatic sinusoids?

Developing liver cords intermingle with vitelline veins,

interrupting their course

and converting them into hepatic sinusoids.

Under the inductive influence of hepatic cords, the angiogenic cells of the mesenchyme of the septum transversum give rise to hepatic sinusoids.

The development of the liver divides the ventral mesogastrium into what structures?

• Posterior part → lesser omentum

• Anterior part → falciform ligament

• Cranial part → coronary ligament and left & right triangular ligaments (at lateral extremities of coronary ligament)

What does the caudal part of the liver bud become?

The bile duct, which gives rise to a small ventral outgrowth (cystic bud) ">"

the primordium of the gall bladder and cystic duct.

What do the biliary ducts induce?

The development of the canals of the biliary tract inside the liver.

What do endodermal strands of cells differentiate into?

Into hepatocytes (parenchymal cells)

and intrahepatic biliary ducts.

What is the origin of the other liver structures (connective tissue, hematopoietic cells, Kupffer cells)?

They are mesodermally derived from the septum transversum.

Describe the early symmetry of the liver.

The liver is initially symmetric, but after the 2nd month, the left lobe regresses due to atrophy of the left horn of the sinus venosus and development of the digestive tract.

What are the three venous sources supplying the liver during development?

Vitelline veins,

umbilical veins,

and the portal vein.

What are the efferent and afferent parts of the vitelline veins?

• Cranial parts → efferent veins (between liver and sinus venosus)

• Caudal parts → afferent veins (between yolk sac and liver)

How are the afferent veins connected?

By three anastomotic canals, forming two anastomotic circles around the foregut:

• Superior and inferior anastomoses in front of the foregut

• Middle anastomosis behind the future duodenum

What remains after parts of afferent and efferent veins disappear?

• From the left vein, only the part immediately below the middle anastomosis remains.

• From the right vein, the part immediately below the middle anastomosis disappears.

• These remaining parts form the portal vein with the superior mesenteric vein.

What happens to the efferent veins?

The left efferent vein disappears,

and the remaining right efferent vein, now the common efferent vein,

→ forms the hepatocardiac portion of the inferior vena cava.

Describe the path of the umbilical veins.

The right and left umbilical veins run lateral to the vitelline veins,

passing through the septum transversumfrom the placenta to the sinus venosus.

What happens to the umbilical veins during liver development?

The right umbilical vein disappears.

The portion of the left umbilical vein between the liver and sinus venosus also disappears.

A direct communication forms between the left umbilical vein and common efferent vein → called the ductus venosus.

What happens to the left umbilical vein and ductus venosus after birth?

They are obliterated, forming the ligamentum teres of the liver and ligamentum venosum.

What happens initially to the gall bladder and bile duct?

They are obliterated due to proliferation of epithelial cells.

What occurs later in the development of gall bladder and bile duct?

The lumen is recanalized; atresia or stenosis occurs if this process fails.

What abnormalities are related to the cystic bud?

Absence of the gall bladder,

its duplication,

or partial subdivision.

What abnormality involves liver lobes?

Atrophy of the hepatic lobes, especially the left lobe.

What abnormality involves extra lobules?

Accessory hepatic lobules, located on the visceral surface of the liver.

From what does the pancreas develop?

From two buds,

ventral and dorsal,

originating from the endodermal epithelium of the caudal part of the foregut.

When do the pancreatic buds appear?

In the 4th week of development, and each bud presents a duct.

How does the ventral pancreatic bud appear?

As an outgrowth of the ventral wall of the foregut,

immediately below the liver bud.

Why do the main pancreatic and bile ducts have a common opening?

Because the ventral pancreatic bud appears below the liver bud, explaining the common opening into the duodenum.

What causes the fusion of the two pancreatic buds?

Unequal development of the duodenal walls and rotation of the duodenum,

causing the ventral bud to migrate dorsally and fuse with the dorsal bud in the 7th week, with an oblique anastomosis between their ducts.

What parts of the pancreas do the buds form?

• Ventral bud → inferior part of the head of the pancreas and uncinate process

• Dorsal bud → remainder of the pancreas

How is the main pancreatic duct formed?

By the distal part of the dorsal pancreatic duct,

the entire ventral pancreatic duct,

and the anastomosis between them.

What does the accessory pancreatic duct represent?

The proximal part of the dorsal duct.

When does the endocrine part of the pancreas develop and function?

The pancreatic islets (islets of Langerhans) develop from pancreatic tissue in the 3rd month,

and insulin secretion starts in the 5th month.

Where may heterotopic pancreatic tissue be found?

In the gastric wall

or in the wall of the small intestine.

What is an annular pancreas?

A ring of pancreatic tissue surrounding the duodenum, which may cause stenosis of the duodenum.

In this abnormality, the ventral bud forms a ring around the duodenum.