Liver, Gall Bladder, Pancreas and Spleen Development

00:01 In this lecture on foregut development, we’re gonna discuss how to various glands associated with the foregut, the liver, the gallbladder, and pancreas develop from the endoderm that lines the gut tube.

00:13 Now, during the third week of development, a bud off of the foregut called the hepatic diverticulum develops.

00:20 This is also sometimes called the liver bud and it will indeed become the liver.

00:24 It’s gonna grow anteriorly into the septum transversum and it will eventually form the liver.

00:30 The septum transversum and the hepatic diverticulum contribute different tissues to the developing liver.

00:37 So they are both necessarily.

00:38 The connection of the hepatic diverticulum to the foregut is gonna become the common bile duct.

00:45 And if you think about the mature anatomy, the common bile duct does indeed connect the liver to the foregut at the descending portion of the duodenum.

00:54 Now, one bud was not enough for our hepatic diverticulum and yet, another bud develops off of it.

01:01 The gallbladder is gonna develop as an out-pouching of this common bile duct and is going to develop on the inferior surface of the liver, much like its location in the mature adult on the underside of the liver.

01:14 The connection of the gallbladder to the common bile duct will become the cystic duct.

01:20 So at the point, we’ve already got the connections between the liver, gallbladder, and duodenum established.

01:27 Now, if the cystic diverticulum to create the gallbladder weren’t enough, we develop two more buds coming off of the foregut.

01:36 Just inferior to the cystic diverticulum is the ventral pancreatic bud.

01:40 And if there’s a ventral pancreatic bud, it should be a surprise to no one that there is also going to be a dorsal pancreatic bud.

01:47 These two separate developments off of the foregut are gonna be brought together by rotation of the stomach and migration of the liver.

01:55 As those organs develop, enlarge, and rotate, the ventral pancreatic bud, cystic duct, and common bile duct are all moved into a posterior position and if you know your anatomy, you may remember that the common bile duct enters the duodenum on its posterior side.

02:13 That’s a remnant of this set of rotations.

02:17 So by the time we’re done, we’ve got the gallbladder developing on the underside of the liver, the ventral pancreatic bud has swung posteriorly and fused with the dorsal pancreatic bud making a single pancreas.

02:31 The main pancreatic duct is going to be the remnant of the drainage system and connection to the duodenum of the ventral pancreatic bud.

02:40 Whereas the accessory pancreatic duct is what’s left of the connection of the dorsal pancreatic bud to the same region.

02:47 Occasionally, the accessory pancreatic duct will rescind and the pancreas will have one and only one outlet for its secretory products into the duodenum.

02:57 I should note that because of this rotation and fusion of the pancreas, the ventral pancreatic bud is gonna create the uncinate process and part of the pancreatic head.

03:06 Whereas the dorsal pancreatic bud is going to form the rest of the pancreatic head, its body, and its tail.

03:15 Things that can go wrong in this process include poor migration of the pancreas and most commonly, this manifests as a pancreatic ring.

03:26 In this case, a portion of the ventral pancreatic bud goes posteriorly like we’d expect but another portion travels anteriorly and forms a continuous ring around the duodenum as it attaches to the dorsal pancreatic bud.

03:41 This results in what’s called an annular pancreas or a ring-shaped pancreas.

03:45 That in it of itself is not problematic.

03:48 The problem is it constricts the duodenum and narrows its lumen.

03:53 So this must be differentiated from other reasons for duodenal atresia or duodenal stenosis.

03:59 Because the pancreas develops off of the endoderm in a specific location due to the signals that are present in that location, those signals can induce the formation of pancreatic tissue in other places such as the small intestine or the stomach.

04:14 Problems with the gallbladder and its drainage can be very serious.

04:18 Failure of the gallbladder to form in the first place is gallbladder agenesis.

04:23 This is actually not as severe as you might think because the bile that the liver produces can still drain to the small intestine and be expelled.

04:33 You can have the gallbladder develop in an unusual location.

04:37 A sessile gallbladder may occur when it develops directly off the common bile duct and there’s no cystic duct.

04:44 Just complete immediate connection between the gallbladder and the common bile duct.

04:49 You can also have an additional pouch developing off of the gallbladder called a Hartman’s pouch.

04:54 Again, not a problem that you encounter due to itself but maybe a problem when you’re doing surgery to remove a gallbladder and have to account for an unusual drainage pattern or an unusual shape of the gallbladder.

05:07 Those variants are typically asymptomatic as are small little additional bulbs coming off the top of the gallbladder such as a Phrygian cap, a midline separation inside the gallbladder called a Septate gallbladder where there is in fact a little wall or septum within.

05:25 You can have duplication or double gallbladders, not problematic, but if you’re trying to remove a gallbladder, you may have to be prepared to find two of them in that location.

05:35 And occasionally, the gallbladder forms so high off of the common bile duct and in such close coordination with the hepatic diverticulum that it’s actually located within or partially within the liver and in this case, to remove the gallbladder can be problematic since you have to make sure you’re not lacerating the liver in the process.

05:56 Problems with the drainage of bile from the liver can be very, very serious.

06:02 The liver produces bile and it does not stop and if that bile cannot drain to the common bile duct and intestine or be held temporarily in the gallbladder, it has no choice but to back up into the vascular system causing jaundice, damage to the liver, and eventual death So absence of the entire biliary system, biliary atresia is incredibly important and it causes immediate jaundice of an infant.

06:29 Now, jaundice is a typical presentation in infants and will typically resolve but it does need to be tracked and the cause of that jaundice, properly identified.

06:39 Partial atresia of the bile duct can also occur, leading to the same problem.

06:43 If the bile cannot leave the liver and get to the intestine, it will cause jaundice, cirrhosis, and eventual death.

06:50 Other things that are not as problematic are aberrations in the biliary tree that still allow it to drain into the intestine.

06:58 An accessory bile duct that enters the gallbladder directly can be found and has to be accounted for during gallbladder removal and what is known as a choledochal cyst can occur when you have ballooning of part of the biliary tree.

07:13 These must be accounted for and can cause problems but are not as severe as problems that cause jaundice, cirrhosis, and death due to backup of bile.

07:23 Lastly let’s come to the development of the spleen. The spleen is derived from mesenchymal cells which are found between the layers of the dorsal mesogastrium. Its characteristic shape is obtained very early in development and is retained during adult mature form. Because of the rotation of the stomach, the mesogastrium fuses with the peritoneum over the left kidney. This forms the lienorenal ligament. Moreover, because of this rotation, the splenic artery is found to have a course behind the peritoneum on its way to the spleen. The mesenchymal cells of the spleen differentiate into splenic capsule, connective tissue, and parenchyma. The spleen is a major hematopoietic organ in fetal life. It is involved with the production of lymphocytes and monocytes during adult life.

08:15 Thank you very much for your attention and we’ll return to finish up on foregut development.