Carnivore Upper Digestive Tract

What are the digestive organs?

What about the accessory organs?

• Oesophagus

• In abdominal cavity

  • Stomach

  • Small Intestine

  • Large Intestine

• Accessory

  • Pancreas

  • Liver

Where is the oesophagus located?

• Runs from back of pharynx to stomach

• Starts dorsal to larynx (Above larynx/cricoid cartilage)

• Accompanies the trachea (left side + dorsal) along neck and into the thorax

• In thoracic cavity

  • Runs mediastinum dorsal to trachea

  • Central compartment between lungs

  • Passes right side of aortic arch, left side of azygous v.

  • Ventral to descending aorta

• Through oesophageal hiatus, an opening in diaphragm

• Enters stomach at cardia

What is the mediastinum?

The mediastinum is the space in the chest between the lungs that contains many important organs and structures

Is a normal esophagus visible on radiographs?

• No

• May be seen if we use contrast studies

Is the oesophagus visible on ultrasound?

• Might be able to see the cervical (Neck region) of oesophagus

  • Can use advanced imaging

  • Endoscopy

What are the main features of the peritoneum?

• Thin serous membrane lining, lining all of abdominal cavity, covers most organs

• Provides some lubrication + fluid, support

What are the two parts of the peritoneum?

1.) Parietal Peritoneum

• Layer attaching to abdominal wall

2.) Visceral Peritoneum

• Layer attaching to organs

• GIT, spleen, liver, pancreas, bladder, reproductive

**Should be noted that this is the same membrane, although we divide it into two parts, it is simply folding on itself, the organs, and body wall

What is the peritoneal cavity?

• Region between the parietal and visceral peritoneum layers

What do the folds of the peritoneum do?

• Enclose peritoneal organs

• Suspend them from dorsal abdominal wall

What are retroperitoneal organs?

Organs not enclosed by the peritoneum membrane

• Kidneys, adrenals

What is inflammation or infection of the peritoneum?

peritonitis

What is the omentum?

• The omentum is a fold of the peritoneum, the thin tissue that lines the abdomen. It's made up of multiple layers and contains fat and lymph nodes.

Describe the greater and lesser omentum.

Greater

• Extends from the greater curvature of the stomach

• Has dorsal and ventral folds which form a sac between folds = Omental Bursa (Space is quite flat due to the weight of other organs)

  • Accessed by epiploic foramen, opening in the sac, caudal to liver

  • Entrapment of SI in horse

• Fat deposition

  • Gives “lacy” appearance

Lesser

• Extends from the lesser curvature from the the stomach and attaches to the liver

The omentum is a serous membrane, what does this allow it to do?

• Allows it to “glue” to other structures if there is inflammation or infection

• Has the ability to wall off and isolate areas of infection

• We can use to our advantage with surgeries in abdominal cavity, we can pull the omentum to further cover up and seal off incisions

What is the the mesentery?

• Where peritoneum extends into abdominal cavity to wrap around GIT structures, wraps around surface of organs to suspend them

• Provides access for vascular, nervous and lymphatic structures

Where does the mesentary attach?

• Only attaches one side of the intestine (Mesenteric border)

• The area opposite this is the antimesenteric border, which is where we will do the incision

Briefly describe the differences between the peritoneum, omentum and mesentery?

• Peritoneum: This is the broad, continuous membrane that lines the abdominal cavity and covers most abdominal organs.

  • Visceral / Parietal

• Omentum: This is a specific part of the peritoneum. It's a fold or double layer of peritoneum that connects the stomach to other organs, like the intestines/liver. The omentum primarily functions in fat storage, immune response, and protection.

  • Lesser / Greater

• Mesentery: This is also a part of the peritoneum, but it specifically refers to the fold that attaches the intestines to the back wall of the abdomen, helping support and stabilize them while also housing blood vessels and nerves.

What provides the oxygenated arteriole blood?

Systemic Circulation

What supplies the arterial and venous drainage for the digestive system?

Arterial Supply - Abdominal Aorta

Venous Drainage - systemic veins to caudal vena cava

• Organs that drain include the…

• Liver

  • Hepatic veins drain into caudal vena cava

• Terminal Rectum

  • Via the internal iliac vein into vena cava

• Most of oesophagus

What is the hepatic portal system?

The hepatic portal system is a circulatory system that moves blood from the digestive tract and spleen to the liver

• Drains the GI tract (Including terminal oesophagus and proximal rectum), pancreas, spleen

• Hepatic portal vein drains to the liver

The abdominal aorta runs along the ____ of the body, near the ______ column.

There are three main branches of this artery, which organs does each artery supply?

trunk, vertebral

• Coeliac Artery

  • Liver

  • Stomach

  • Spleen

  • Pancreas

  • Cranial Duodenum

• Cranial Mesenteric Artery

  • Pancreas

  • Caudal duodenmum

  • Jejunum

  • Ileum

  • Caecum

  • Ascending and transverse colon

• Caudal Mesenteric Artery

  • Descending Colon

  • Rectum

Organs and regions may be supplied by several arteries or branches, what does this mean in terms of potential complications?

• Reduces complications of vascular obstruction due to having several routes

What is the portal system?

• Carries blood from digestive tract to the liver, it contains nutrients from digestion

• Can connect to systemic veins at periphery

• Multiple routes of drainage

How does the drainage of the portal system work?

• Caudal mesenteric vein —> Cranial mesenteric vein + splenic vein + gastroduodenal vein —> Drain into Hepatic portal vein —> Liver

Describe the sympathetic innervation in the digestive tract.

• Use ganglia - send sympathetic impulses

  • Are located around the three main arteriole branches

  • Coelic Ganglia

  • Cranial Mesenteric Ganglia

  • Caudal Mesenteric Ganglia

• Postganglionic fibers run parallel to arteries

If we increase sympathetic stimulation, we have decreased GIT activity.

Describe the parasympathetic innervation in the digestive tract.

• Mainly via the Vagus (X) - affecting cranial structures

• Pelvic nerve - affecting colon and rectum

Parasympathetic stimulation results in increased GIT activity

What are features of lymphatic drainage in the digestive tract?

• Stomach and intestine rich in lymphatic tissue

• Numerous lymph nodes drain digestive tract

  • Fatty products also absorbed via this route

  • Helps provide immune surveillance

• Nodes generally lie within mesentary

  • Jejunal, Colonic, etc.

  • Named by area they are associated with

How does the GI tract look on radiographs and ultrasound?

Radiographs

• Contrast often needed for GI tract

• Shows course of tract more clearly

• Can also allow assessment of transit times of intestinal contents

Ultrasound

• Useful for all digestive organs

• Can be hampered by gas in the intestines

**Advanced imaging preferable

What is the stomach like in our carnivorous species?

What is the capacity like?

What is the main function?

• Simple stomach due to simple, concentrated diet

• Depends on animal: capacity of 0.5 - 6 liters

  • Easily distensible

• Important for mechanical and chemical breakdown of food

• Absorption of water drugs, and alcohol

How can we divide the stomach

• Greater curvature

  • Longer edge of stomach

  • Where greater omentum arises from

• Lesser Curvature

  • Smaller edge of stomach

  • Where lesser omentum arises from

What is the main ligament in the stomach?

Where does it attach?

• Gastrophrenic LIgament

• Attaches stomach from fundus to the left side of the diaphragm

What are the different parts of the stomach?

• Cardia

  • Where oesophagus enters

  • Smallest part

  • Has cardiac sphincter which regulates flow

• Fundus

  • Dome rising above cardia

    • Often has air (visible on radiographs)

• Body

  • Largest part

• Pylorus

  • Antrum (wider)

  • Pyloric Canal (narrow)

    • Contains pyloric sphincter - a muscular junction to duodenum which regulates flow

From oesophagus to anus - the GI wall has the same component layers, what are these layers?

1.) Mucosa - epithelium

2.) Submucosa - consisting of connective tissue with blood vessels and glands

3.) Muscularis externa

• Inner circular muscle

• Outer longitudinal muscle

4.) Serosa / Adventitia

• Inside abdominal cavity = peritoneum

• Outside in oesophagus = adventitia

What is the general layering of the stomach tissue from outside to inside?

• Serosa

• Muscularis Externa (3 Layers)

  • Longitudinal Layer (Parallel to tube)

  • Circular Layer

  • Oblique Layer

• Submucosa

  • Adheres mucosa to muscularis

  • Vascular plexuses

  • Elastic - creates gastric folds

• Mucosal Region

  • Varies between anatomic regions

  • Covered in mucus

  • Color varies depending on glands, lies in folds or rugae

When considering the mucosal region of the stomach, what does each area secrete?

• Cardia

  • Small area of mucous secreting glands

  • Mucous protects the lining of the stomach

• Fundus / Body

  • Gastric Gland region

  • Secretes the gastric juices (Hydrochloric Acid, Pepsin)

  • More red appearance

• Pylorus

  • Pyloric gland region

  • Mucous and endocrine cells, gastrin release

At the end of the stomach, we have the junction of the stomach and small intestine, what marks this transition?

Gastro-Duodenal Junction, marked by the pyloric sphincter

• Marks transition in GI mucosa

• Glandular stomach → Absorptive Villous duodenum

• At level of sphincter, there is a thick muscularis externa layer, since we need muscle contraction to control digesta

How does the stomach appear on the radiograph/ultrasound?

Radiographs

• Can be seen on radiographs

• Fundus is often filled with gas

Ultrasound

• Assessment of stomach wall