Gastrointestinal Tract Flashcards
Describe the peritoneum.
A serosal layer lining abdominal and pelvic cavities.
- Flattened mesothelial cells supported by fibrous connective tissue.
- Has a parietal and visceral layer, lubricated by a serous fluid.
- Has a large surface area so any fluid that escapes can be quickly reabsorbed and allows for a method of distributing drugs in the body via intraperitoneal injection.
What is a use of some of the mesenteries being very long?
Allowing organs to be moved around during surgery for access to different structures.
What is the blood supply of the parietal and visceral peritoneums?
Parietal peritoneum lines the abdominal wall. Its blood supply, innervation and lymphatic drainage are the same as the overlying structures.
Visceral peritoneum envelops organs. Its blood supply, innervation and lymphatic drainage are the same as the organs is surrounds.
What is the structure of the mesenteries?
Reflection of 2 layers of peritoneum to make a fold suspending an organ:
- Mesoduodenum,
- Mesojejunoileum/great mesentery
- Mesocolon
Blood supply, innervation and lymphatic drainage run between peritoneal layers. These branch out from the root of the mesenteries.
What are the embryonic derivations of the mesenteries?
• Dorsal mesogastrium becomes the dorsal mesentery
• Ventral mesogastrium becomes the ventral mesentery
Separated by the GI tract
What are the omentums?
Peritoneal attachments associated with the stomach from the mesogastrium.
- Greater omentum arises from greater curvature of the stomach and has 2 double layers
- Lesser omentum connects the liver and the lesser curvature of the stomach and has 1 double layer
Name the peritoneal ligaments.
• Right and left triangular ligaments, coronary ligament, falciform ligament – all double layers of peritoneum travelling to and from the liver.
• Duodenocolic ligament – connects the duodenum and colon
• Iliocaecal fold – connects the ileum and caecum
• Hepatorenal ligament
• Gastrosplenic ligament
• Vesical ligament
What are the 7 fixed points of the abdominal viscera?
• Cardia of stomach – attached to the diaphragm
• Hepatic ligaments – attached to the diaphragm
• Mesoduodenum – short, therefore duodenum lies in the dorsal abdomen
• Dorsal extremity of spleen – near origin of greater omentum
• Dudenocolic ligament – attached duodenum to colon
• Mesorectum – short, therefore rectum lies in the dorsal abdomen
• Bladder – vesical ligaments are short but cranial movement is possible
Describe the structure of the stomach.
- Oesophagus enters the stomach at the cardiac sphincter, a ring of muscle that can contract to block the tube.
- Fundus is the region of the stomach that is between the cardiac region and the body of the stomach. This varies between species.
- Pyloric region has he pyloric sphincter, the circular ring of muscle that controls the movement of food out of the stomach and into the duodenum. Important that food stays in the stomach long enough to be churned and release nutrients to be absorbed by the small intestine.
- Has the lesser and greater curvatures of the stomach.
- Internal surface of the stomach has an arrangement of folds called Mugabe. These help direct food through the stomach.
what are the 3 branches of the coeliac artery and what do they supply?
• Left gastric artery – stomach. Gastric arteries supply the lesser curvature of the stomach
• Splenic artery – spleen. Has a branch called the left gastroepiploic artery – supplies the greater curvature of the stomach. Spleen supplied by left gastroepiploic artery.
• Hepatic artery – liver. Supplied by right gastric artery and right gastroepiploic artery.
What is the gross structure of the small to large bowel?
Stomach > duodenum > jejunum > ileum > caecum > colon > rectum
What is the blood supply to the small and large bowel?
• Cranial mesenteric supplies the caudal duodenum, the jujunoilium, ascending and transverse colon
• Caudal mesenteric artery supplies the descending colon and rectum
What are the divisions of the GI tract?
• Foregut – distal oesophagus to cranial duodenum, liver and pancreas. The spleen has the same blood and nerve supply but not derived from the foregut. Coeliac artery
• Midgut – caudal duodenum and pancreas to transverse colon. Cranial mesenteric artery
• Hindgut – descending colon and rectum. Caudal mesenteric artery
Describe venous drainage of the GI tract.
Do not have paired veins of unpaired branches. This is because the GI tract is absorbing all the nutrients and, if fed directly back into the systemic circulation, there would be toxic levels of chemicals and substances. So blood must be filtered before it enters the systemic circulation again.
- Gastroduodenal, splenic, cranial mesenteric and ileocolic veins feed into the hepatic portal vein.
- Hepatic portal vein drains to the liver, where blood can be processed and filtered.
- Blood then drains into the caudal vena cava to enter the systemic circulation.
Describe innervation of the abdominal viscera.
Motor (autonomic) – general visceral efferent:
Parasympathetic
- Vagus nerve innervates the foregut and midgut
- Pelvic nerves from S1, 2 and 3 supply the hindgut and pelvic organs
Sympathetic via sympathetic chain. T1 – L2.
- Smooth muscle of the GI tract
- Coeliac ganglia – foregut
- Cranial mesenteric ganglion – midgut
- Caudal mesenteric ganglia – hindgut and supplies hypogastric nerves that supply the pelvic viscera
Sensory – general visceral afferent
State the 3 functions of the liver.
• Protein, carbohydrate and fat metabolism
• Bile production
• Processing of digestion products
Name the lobes of the liver.
• Left medial lobe
• Right medial lobe
• Left lateral lobe
• Right lateral lobe
• Quadrate lobe
What vasculature enters and exits the liver via the porta?
• Hepatic artery
• Hepatic portal vein
• Caudal vena cava
What 4 ligaments attach the liver to the body wall?
Left and right triangular ligaments
Coronary ligament
Falciform ligament
What impressions does a fixed liver have?
Stomach
Right kidney
Lesser omentum
Gall bladder
Describe blood flow in the liver lobules.
- Blood flow entering the porter is going to detach a lot of extension and
they will put blood vessels inwards which will continue to divide. - The parenchyma of the liver also follows the same pattern
- Tunis phyprocessor encloses the parenchyma has teh same path and creates the pattern (lobules)
Blood vessels divided down and down into smaller blood vessels. The central veins collect the remaining blood once it has been processes by the hepatocytes which will then empty into larger and larger veins until they empty into the hepatic vein which will drain into the caudal vena cava.
What is the pathway of bile secretion?
As food travels down the GI tract, the gall bladder is stimulated and releases the stored bile into the duodenum, which mixes with the ingesta as it travels down the tract.
- Hepatic duct system begins with tiny ducts called canaliculi within liver lobules.
- These open up into larger ducts called ductules.
- These become hepatic ducts.
- Bile duct exist the liver via the porta.
- At the porta, hepatic ducts combine to form a common trunk that goes to the duodenum.
- Side branch called the cystic duct goes to the gall bladder.
- Common trunk distal to the cystic duct goes to the bile duct.
What is the location of the pancreas and its lobes?
Nestled in the curve of the duodenum.
- At the duodenum papilla, there is a common opening for bile duct and pancreatic duct.
- The lobes of the pancreas are located behind the stomach.
- Has a distinct left and right lobe that from a v shape a the cranial flexure of the duodenum.
- Right lobe runs within the duodenum in the mesentery to the duodenum
- Left lobe is shorter and thicker and extends over the caudal surface of the stomach and towards the spleen.
What are the functions of the pancreas?
Has an exocrine function and produces digestive enzymes that empty into the proximal duodenum through the pancreatic duct.
Has endocrine function and islands of Langerhans that have alpha and beta cells producing insulin, glucagon and gastrin.
What are the 2 openings when the pancreas empties into the duodenum?
• The major duodenal papilla is the opening for the major pancreatic duct (and bile duct). This drains the left lobe and some of the right lobe.
• Also has a minor duodenal papilla, draining the right lobe of the pancreas
How is colic in horses detected using imaging?
Horses often experience colic, abdominal pain, and is often associated with the GI tract in horses. In horses, there are few x-ray machines to penetrate the skin so relies on ultrasounds.
Lots of black on an ultrasound connotes lots of fluid in the tract, which could mean there is a blockage or obstruction somewhere preventing the fluid from moving.
How do horses’ diets affect their GI tracts?
Do not adapt well to changes in diet and are out on high starch diets in order to give them energy for things like racing. They ferment this and it can become acidic, which can cause problems with the microbial flora in the gut.
Horses are triple grazers and only take in a small amount of food over short periods of time, so have a smaller stomach.
Wild horses with graze for 16 hours a day on poor quality grass.
Domesticated horses are fed 2-3 times a day on concentrated food, and if given too much at these 3 meals, the stomach can be overloaded. Food will overflow into the small and large intestines before it has had time to be properly processed in the stomach.
What are the 2 regions of the equine stomach surface? What are they separated by?
• Fundus/saccus caecus – dorsal non-glandular region, lined with stratified squamous epithelia.
• Fundic region – ventral glandular region, lined with simple columnar epithelium.
Separated by a ridge called the margo plicatus.
What is the cardiac sphincter and its effect?
Horse stomachs have a very well developed oblique cardiac sphincter. Sits obliquely due to the oesophagus entering the stomach at an angle. This result in food only being able to travel one way in the stomach, and so horses cannot vomit. If a horse ingests something toxic, it is not until the horse becomes very sick that the cardiac sphincter relax sufficiently to allow food to travel back up the oesophagus. This means horses can become sick very quickly, as the toxin is trapped in the stomach and can be absorbed easily into the body.
Describe the components of the non-glandular region of the stomach.
- Fundic and fundus regions are separated by a cardiac region, and is where the margo plicatus is found.
- Margo plicatus is important, as the fundic regions produces stomach acid and the fundus region has no protection against this.
- In a wild horse, gravity means that acid will stay in the fundic region.
- Botflies attach to the non-glandular region.
Describe gastric ulceration syndrome.
In domestic horses, if the stomach is overloaded, the acid component can be forced up past the cardiac region and margo plicatus and into the fundus region.
This condition is gastric ulceration syndrome. Acid begins to digest the walls of the non-glandular region.
Horses under stress may produce more acid or horses doing a lot of jumping and galloping may have acid splash and have more ulceration.
