Lecture 2 -- Comparative Abdominal Anatomy

Which species’ spleen is shown in this picture? What are its characteristics?

Horse

• Comma-shaped

Which species’ spleen is shown in this picture? What are its characteristics?

Cattle

• Tongue shaped

Which species’ spleen is shown in this picture? What are its characteristics?

Sheep

• Oval

Which species’ spleen is shown in this picture? What are its characteristics?

Dog

• Hockey stick shaped

Which species’ spleen is shown in this picture? What are its characteristics?

Pigs

• Elongated

Which species’ liver is shown in this picture? What are its characteristics?

Ruminant

• No separation on both left and right lobe of the liver

  • 90 degree displaced → No contact with diaphragm → Breathing is not impinged by the liver

• Caudate lobe

  • Papillary process is larger in sheep

  • Caudate process is larger in cow

Which species’ liver is shown in this picture? What are its characteristics?

Dog

Which species’ liver is shown in this picture? What are its characteristics?

Horses

• Only left lobe are separated into medial and lateral lobe

  • 45 degree displaced to the right → Only left lobe comes into contact with the diaphragm

• Difficult to identify left medial lobe and quadrate lobe (Left medial + Quadrate lobe are named as sission’s lobe)

• Strips in quadrate lobe

• No papillary process of the caudate lobe

• No gall bladder

Which species’ liver is shown in this picture? What are its characteristics?

Pig

• No renal notch (Since pig is elongated, there is no attachment between the right liver and the kidney)

Why are there two pancreatic ducts? What are they?

Development of pancreas: Two separate lobes and each of them with a duct = Two ducts (Pancreatic duct + accessory duct) → Then it fuses together into one 

Which species have both pancreatic duct and accessory pancreatic duct?

Horses + Dogs

Which species have only pancreatic duct?

Sheep

Which species have only accessory pancreatic duct?

Cattle and pigs

Describe the embryological development of the stomach in the dog, pig, horse, and ruminants based on the type of epithelium

What are the special characteristics in pigs’ stomach?

1. Gastric diverticulum

   • A blind-ending extension of the fundus of the stomach

   • Derived from cardiac region embryologically, which is lined with glandular epithelium = Only secrete mucous → Pigs produce large amounts of salivary amylase

   • This mucus-secreting region protects salivary amylase from acid and pepsin → Allows continued carbohydrate digestion in the stomach

2. Torus pyloricus

   • Thickened muscular ridge at the pylorus that can be palpated

   • Unknown function

What are the special characteristics in horses’ stomach?

1. Saccus caecus

   • Enlargement of fundus

   • Derived from the oesophageal region embryologically, which is lined with stratified squamous

   • For protection

2. Margo plicatus

   • Derived from cardiac region embryologically

   • Narrow ridge marking the boundary between non-glandular and glandular stomach

Why can horses not vomit?

Due to the strong cardiac sphincter and the extreme angle of the esophagus as it passes through the diaphragm

What is the main function of the greater omentum?

Provides a large surface area for white blood cell migration → Seals off infection

Which species are highly susceptible to peritonitis?

Horse

• They have a poorly developed greater omentum

Why are ruminants resistant to peritonitis?

Due to the massive development of the greater omentum associated with their large stomach

What is the epiploic foramen? How do we identify the epiploic foramen?

• Opening that allows entry into the omental bursa

• Locate the hepatic portal vein and caudal vena cava → Epiploic foramen is right between the two vessels

What is the significance of the epiploic foramen in horses?

Small intestine is long and has a same diameter to the epiploic foramen -> Get trapped easily = Epiploic foramen entrapment 

Which part of the ruminant stomach is shown in this picture?

Reticulum

• Honeycomb structure

• Heavy materials e.g. stones directly enters to the reticulum from the oesophagus → Muscular ridge contracts, preventing those materials from entering other parts of the stomach

Which part of the ruminant stomach is shown in this picture? What is its function?

Rumen

• Largest part of the ruminant stomach

  • Responsible for fermentation of food

  • Composed of papillae that increase surface area for absorption of end product of fermentation - Volatile fatty acids

Which part of the ruminant stomach is shown in this picture? What is its function?

Omasum

• Leaf-like fold = Omasal laminae

  • Increase surface area for absorption of water and the remaining fermentation products

Which part of the ruminant stomach is shown in this picture? What is its function?

Abomasum

• Glandular stomach → Secrete pepsinogen and HCl → Digestion of microbes as source of protein

Where is the caecum normally located in different species, and which species are an exception?

Normal location: 

• Right side

Exception: 

• Pig 

• Left side

How is the ascending colon arranged in pigs?

Centripetal coils (Outer part)

• Sacculated

• Have taenia bands

Centrifugal coils (Inner part)

• Smooth

Why is the horse ascending colon highly modified?

Horses are hindgut fermenters → Ascending colon is greatly enlarged and adapted for fermentation

Describe the pathway of the large intestine in horses.

Ascending colon

• Right ventral colon → 180degree turn at the sternum = Sternal flexure → Left ventral colon → Another 180 degree return upwards in the pelvis → Pelvic flexure → Left dorsal colon → 180degree turns right by the diaphragm → Diaphragmatic flexure → Right dorsal colon)

Traverse colon

Descending colon (Small colon)

What features of the horse large intestine aid in mixing and propulsion?

• Sacculated (haustrated)

• Taenial bands (longitudinal muscle bands)

How many taenial bands are present in each segment of the horse large intestine?

Segment	Taeniae
Caecum	4
Right ventral colon (RVC)	4
Left ventral colon (LVC)	4
Left dorsal colon (LDC)	1
Right dorsal colon (RDC)	3
Transverse colon	2
Small colon	2

Does the horse have an anti-mesenteric ileal artery?

NO

• In dogs, the caecum is too small. Therefore, the caecal branch of ileo-colic artery branches off anti-mesenteric artery to supply the ileum

• BUT in horses, the caecum is too large that not able to free up the ileo-colic artery

How is the horse caecum supplied?

By lateral and medial caecal arteries

What supplies the ventral colon in horses?

Colic branch of ileocolic artery

What supplies the dorsal colon in horses?

Right colic artery

What are the arterial supplies for the pig ascending colon?

Centripetal (proximal) coils: 

• Colic branch of ileocolic

Centrifugal (distal) coils: 

• Right colic

In ruminants, which stomach parts come from the lesser curvature of the embryonic stomach?

Omasum and lesser curvature of abomasum

What are the arterial supplies for the ruminant omasum and lesser curvature of abomasum?

Left and right gastric artery

In ruminants, which stomach parts come from the greater curvature of the embryonic stomach?

Ruminoreticulum and greater curvature of abomasum

What are the arterial supplies for the ruminant ruminoreticulum and greater curvature of abomasum?

left and right gastroepiploic arteries