- 7/5/2025
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LearningTranscript
00:00Hello everyone, my name is Megan and welcome to another anatomy tutorial.
00:05In this tutorial we will be covering the mesentery which is found in the abdominal cavity.
00:10I'm going to also cover some of the related structures and organs.
00:15Before we begin talking about the mesentery, I quickly want to go through a brief overview of the peritoneum.
00:22The peritoneum is a double layer of serous membrane or mesothelium.
00:26It lines the walls of the abdominal cavity and most of the viscera.
00:32Throughout the abdominal cavity there are peritoneal folds that connect organs together or connect these organs to the abdominal wall.
00:40Some of these folds also contain vessels and nerves that supply the organs.
00:45Their function is twofold as they also stabilise and help maintain the position of the organs.
00:51The subdivisions of the peritoneum include the amenta, the mesentries and the peritoneal ligaments.
01:01In this image we can see the male pelvis.
01:04We can see the peritoneum highlighted in green.
01:07It's covering the superior aspect of the bladder and continues over the superior surface of the rectum.
01:12In the next illustration we can see the female pelvis.
01:18In the female pelvis the peritoneum also covers the bladder.
01:23It then covers the uterus to form the broad ligament of the uterus.
01:27Once it has done that it then continues to run over the rectum.
01:31Now that we know what the peritoneum is, we can look at the two different types of peritoneum.
01:38The peritoneum consists of the parietal and visceral peritoneum.
01:43So as I said before, the parietal peritoneum is a mesothelial layer
01:48and covers the internal surface of the abdominal walls and is supplied by the regional vasculature.
01:55Whereas the visceral peritoneum covers the viscera inside of the peritoneal cavity.
02:00So let's start with the mesentries.
02:03The mesentries are peritoneal folds that contain the viscera and attach them to the posterior abdominal wall.
02:10The most important mesentry is the mesentry proper.
02:15It is a fan-shaped double layer of peritoneum that connects the jejunum and the ileum to the posterior abdominal wall.
02:23Its superior attachment is at the junction between the duodenum and the jejunum.
02:27This attachment then travels obliquely downwards and to the right where it ends at the ileocecal junction.
02:36The two peritoneal layers of the mesentery contain fat and the arteries, veins and nerves that supply the jejunum and ileum.
02:43The lymphatic vessels that drain the jejunum and the ileum are also in the mesentery proper.
02:49In the next illustration we have a better view of the superior aspect of the mesentery proper.
02:56The reason we can see it clearer is because the large intestine and the transverse mesocolon have been cut away.
03:03Here we can see where the stomach would have been.
03:05It then continues as a duodenum in a C-shaped loop before it gets to here, which is the junction between the duodenum and the jejunum.
03:14We can see the superior aspect of the mesentery proper here.
03:18It then continues as a fan downwards.
03:22The transverse mesocolon is also a double layer of peritoneum.
03:26It connects the transverse colon to the posterior abdominal wall.
03:31Its two layers leave the posterior abdominal wall from the anterior surface of the head and body of the pancreas.
03:39We can see that here highlighted in green.
03:42It then passes outwards to surround the transverse colon.
03:46Similar to the mesentery proper, the transverse mesocolon contains the arteries, veins, nerves and lymphatic vessels for the structure it surrounds.
03:55The next part of the mesentery is the sigmoid mesocolon.
03:59It's an inverted V-shaped peritoneal fold that attaches the sigmoid colon to the abdominal wall.
04:07The apex of the V is near the division of the left common iliac artery into its internal and external branches.
04:15The sigmoid and superior rectal vessels, along with the nerves and lymphatics associated with the sigmoid colon, pass through the sigmoid mesocolon.
04:24In the next illustration, we have an isolated view of the sigmoid mesocolon so that we can see it better.
04:31We've now covered the mesentries, so let's look at another fold of peritoneum that is visible from this perspective, which is the greater omentum.
04:39The greater omentum is also a double fold of peritoneum.
04:45It hangs down from the greater curvature of the stomach and reflects back on itself to attach to the transverse colon.
04:52In this image here, you can see the transverse colon and its associated mesentery underneath the greater omentum.
05:00The greater omentum contains variable amounts of fat.
05:04It also contributes to the immune system through its store of macrophages,
05:08and it's important in the isolation of wounds and infections in the peritoneal cavity.
05:13The vascular supplied to the greater omentum comes from the left and right gastroepiploic arteries,
05:20which are branches of the splenic and gastroduodenal arteries.
05:23So, on a clinical note, the greater omentum is an important site for the metastasis of tumours.
05:33Direct omental spread of cancer cells via the transcolemic route is common for cancer of the ovaries.
05:40As the metastasis develops within the greater omentum, it becomes significantly thickened.
05:46The thickened greater omentum is then referred to as an omental cake in a CT scan.
05:51In this image, we can see the greater omentum hanging from the edge of the greater curvature of the stomach
05:57and covering up the transverse colon.
06:01So next, we're going to look at the viscera that come into contact with the mesentery.
06:06First, we're going to look at the jejunum.
06:08The jejunum is the middle segment of the small intestine between the duodenum and the ileum.
06:14It is approximately 2.5 metres long.
06:17The internal surface of the jejunum is lined by villi,
06:21which increase the surface area and improve absorption of nutrients.
06:26The wall of the jejunum is composed of two muscular layers,
06:30a circular and a longitudinal layer of smooth muscle.
06:34These are responsible for peristalysis.
06:37Sympathetic innervation to the jejunum is supplied by the celiac ganglia.
06:41Parasympathetic innervation, on the other hand, is supplied by the vagus nerve.
06:47In the previous image, we saw the start of the jejunum and then the mesentery,
06:52but in this image, we can see the jejunum suspended from the mesentery in the abdominal cavity.
06:59The other portion of the small intestines we can see here is the ileum.
07:03The ileum is the terminal portion of the small intestine.
07:06It measures approximately 3.5 metres in length.
07:11It is a continuation of the jejunum and ends at the ileocecal valve.
07:16This ileocecal valve separates it from the cecum.
07:20The inner lining of the ileum is also covered by villi that increase the surface area for absorption.
07:27The main function of the ileum is to absorb bile salts, vitamin B12 and any other nutrients that haven't been absorbed yet.
07:34The ileum receives its vascular supply from the ileal arteries, which are branches of the superior mesenteric artery.
07:44It receives sympathetic innervation from the superior mesenteric ganglion and parasympathetic innervation from the vagal trunk.
07:53In this illustration, we can see the ileum highlighted in green.
07:57We can also see that it's continuous with the jejunum.
08:00Now that we've looked at the small intestine from this perspective, let's move on to the large intestine.
08:07The large intestine begins with the ileocecum valve I mentioned before.
08:12The first part of the large intestine is the cecum.
08:15This is a pouch just below the ileocecal valve.
08:19The next part is the ascending colon, which starts immediately after the cecum and travels up to the right colic flexure.
08:26This flexure, which is known as the hepatic flexure because of its proximity to the liver, marks the end of the ascending colon.
08:35In these illustrations, we can see the cecum, the ascending colon and the right colic flexure highlighted in green.
08:43The next part of the large intestine is the transverse colon, highlighted here in green, is the most mobile part of the large intestine.
08:54It's lifted up here to show the mesentery.
08:58The transverse colon travels across the abdomen to the other colic flexure, the left or splenic colic flexure.
09:05It's called the splenic flexure, for as you might have guessed, its proximity to the spleen.
09:12The next part of the large intestine is the descending colon.
09:15It's located on the left side of the abdomen and it travels straight down to the sigmoid colon.
09:21The sigmoid colon is highlighted in green here.
09:25This segment of the large intestine is intraperitoneal, which means it's completely surrounded by peritoneum.
09:32It is a continuation of the descending colon.
09:37The sigmoid colon transports faeces from the descending colon into the rectum.
09:42It is also responsible for the absorption of water, nutrients and vitamins.
09:47The final part of the large intestine is the rectum.
09:51When the rectum pierces the pelvic floor, it becomes the anal canal.
09:56Now that we've seen the various parts of the large intestine,
09:59let's look at the intestines as a whole and look at some of their features.
10:02On the external surface of the large intestine, there are these whitish bands of tissue.
10:09They are called tinea coli.
10:11They are three thickened bands of longitudinal muscle.
10:15They measure approximately one centimetre in width and they're found on the outer surface of the colon.
10:21They converge at the root of the appendix.
10:24On the inner surface of the muscles that make up the anterior abdominal wall,
10:29there is an artery called the inferior epigastric artery.
10:33This artery arises from the external iliac artery.
10:38It anastomoses with the superior epigastric artery, the umbilical artery and the lower intercostal arteries.
10:45So in the next illustration, we have an isolated view of the inferior epigastric artery.
10:51We can see the origin of this artery from the left external iliac artery.
10:56We can then see it passing upwards to anastomose or connect with the superior epigastric artery,
11:03the umbilical artery and the lower intercostal arteries.
11:08Accompanying the inferior epigastric artery, there is an inferior epigastric vein.
11:14You can see them here running right next to the artery.
11:17The inferior epigastric vein arises from the superior epigastric vein
11:22and drains into the external iliac vein.
11:25Again, we're going to look at the inferior epigastric vein in isolation.
11:30We can see that it's following an extremely similar pattern to the artery
11:34and that it drains into the external iliac vein here.
11:38Next, we're going to look at the medial umbilical folds.
11:41They're a paired structure that cover the medial umbilical ligaments
11:45and they are in close relation to the two vessels that we've just talked about.
11:50The medial umbilical ligaments are the remnants of the fetal umbilical arteries.
11:55Before we end this tutorial, there is one last structure we need to talk about,
11:59the median umbilical fold.
12:01It's an unpaired structure that extends from the apex of the bladder to the umbilicus
12:07and covers the median umbilical ligament.
12:10This ligament is a remnant of the uracus,
12:13a canal that connects the bladder to the umbilicus during fetal development.
12:26The medial umbilical ligaments, which they can probably attach the laptop to the brain.
12:31In this tutorial, you can find the 97-8-0-0-1 to the umbilical ligaments of the other
12:34and aophane.
12:36All right.
12:37Thanks for that.
12:40Thanks for that.
12:41Thanks.
12:42Thanks.
12:43Thanks.
12:47Thanks, sehen You.
12:49Thanks.
12:50Thanks.
12:52Thanks.
12:53Thanks.
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