digestive 2

• Accessory digestive organs include the liver and pancreas.
• Salivary glands are also accessory digestive organs.
• Salivary glands were discussed in a previous lecture.

Liver Function

• Produces bile, which is essential for fat digestion.
• Removes toxins biochemically that enter through the gastrointestinal tract (GIT).
• Kupffer cells are macrophages that scan for and remove foreign germs coming from the GIT.
• Stores, metabolizes, and releases nutrients as needed.

Hepatic Circulation

• About 75% of the blood entering the liver comes from the portal vein and is venous blood.
• The venous blood from the small intestine, stomach, pancreas, and spleen enters the portal vein.
• The remaining 25% of the incoming blood is arterial blood from the hepatic artery.
• The liver gets "first choice" of everything absorbed in the small intestine.

Liver Organization

• Hepatic histology includes the central vein (CV) and portal canal (triad).
• Portal canal is also known as a portal triad
• The arrows indicate the borders of the liver.
• The "classical" liver lobule is the functional unit drained by a central vein.

Bile Composition

• Bile salts are a component of bile.
• Phospholipids are a component of bile.
• Cholesterol is a component of bile.
• Bile pigments are a component of bile.
• Horses do not have a gallbladder, and cow livers are entirely on the right side without lobes.

Bile Function & Transport

• Bile emulsifies fats.
• In canines, hepatic ducts move bile from the gallbladder to the duodenum
• In felines, there is a common bile duct.
• Connections from the pancreas to the duodenum in cats do not have a direct duct; instead, it merges with the bile duct before entering the duodenum.

Clinical Significance

• Clinical applications explain importance

Hormones Involved in Digestion

• Gastrin is a hormone that is released from the G cells in the pylorus.
• Secretin and CCK are hormones from the duodenum
• See stomach and duodenum notes from previous lectures.

Bile Processing

• After lipids are digested and absorbed, bile acids travel along the GIT and are re-absorbed in the ileum.
• Bile goes to the liver via the hepatic portal vein and is recycled by the liver in enterohepatic circulation.

Hepatic Portal Vein

• The liver rests between the heart and GIT
• Processes blood leaving GIT before it goes into the general circulation.
• Blood then percolates through the liver and down through the central vein, eventually joining the caudal vena cava.
• Portosystemic shunts redirect blood from the portal vein to systemic circulation.

Pancreas

• The pancreas has dual functions as both an exocrine and endocrine organ.
• Exocrine function involves digestion in the darker pink areas.
• Acinar cell contents go to the duodenum.
• Pancreatic enzymes include amylase, protease and lipase.

Pancreatic Secretions

• Stimulated by the duodenum's release of CCK and secretin.
• Vagal release of Ach, stomach stretching, and anticipation of food also stimulates.
• Sends bicarbonate and enzymes to the duodenum.

Related Enzymes

• Salivary amylase (ptyalin) is produced in the salivary glands and functions in the mouth.
• Pancreatic amylase is from the pancreas and functions in the duodenum.
• Maltase, Isomaltase, Sucrase and Lactase are produced in the intestinal glands and function in the duodenum.
• Pepsin(ogen) originates in the gastric glands and works in the stomach.
• Lipase originates in the pancreas (acinar cells) and works in the duodenum.

Exocrine Pancreatic Insufficiency (EPI)

• Exocrine Pancreatic Insufficiency is a condition that requires supplementation.

Monogastric Digestion Questions?

• Questions revolve around monogastric digestion

Ruminant Digestion

• Ruminant digestion includes an esophagus and the 4 chambered stomach
• Insectivore stomachs are short and have no cecum
• Carnivore stomachs short intestines and small cecum

Ruminant Stomach/Digestion: In a Nutshell

• The ruminant stomach includes the rumen/reticulum, omasum, and abomasum.
• Omasum is not in camel types of ruminants
• The first three compartments are the forestomach, while the abomasum is the true glandular stomach.
• Entire left side of the abdomen is just rumen, no kidney or liver on the left side

Forestomach

• Rumen/reticulum is also known as reticulorumen.
• It lacks glands and pits in the mucosa but has many papillae.
• rumen/reticulum has Stratified squamous epithelium that is keratinized.
• The rumen contains bacteria, fungi, and protozoa which are part of the microbial fermentation vat.
• There is a lot of bicarb in saliva mixed in.
• Hardware disease can be a cause of reticulopericarditis/pericarditis.
• The reticulum has a special honeycomb pattern to the papillae.
• The omasum has leaves/pages, which are folds of mucosa.
• Function is to increases surface area and Absorb water and salts.

Abomasum Function

• Acts like a monogastric stomach.
• Secretes HCl, pepsinogen, and rennin.
• The microbes produce gas.
• Rumen contractions mix the matter and rumination regurgitates matter

Ruminant Digestion Specifics

• Microbes residing in the organ break down complex carbohydrates from the plant cell walls and produce VFAs.
• VFAs serve as the primary energy source for ruminants.
• Proteins - microbes use them
• Then the microbes are digested by the host
• These processes require alkaline conditions.

Ruminant Lipid/Protein Digestion

• Lipids are a small part of a ruminant's diet.
• Proteins made by the host are digested and absorbed in SI

Ruminant VFA Usage

• Ruminants use VFAs for cellular respiration
• Tissues like the brain use glucose
• Made by the liver from gluconeogenesis
• Hindgut fermentation is microbial digestion that occurs after the stomach and small intestine.
• Starches and other simple carbohydrates are digested in the small intestine.
• Fermentation occurs in the cecum and LI (large intestine), producing VFAs.
• Glands in the wall of the LI (large intestine) make bicarbonate.

Equine Digestion

• Equine digestion includes the digestive tract, cecum, and colon
• Hindgut digestion is the microbial digestion AFTER the stomach and small intestine.
• In horses, urea (protein breakdown product in the liver) goes via blood to the cecum and colon, acting as a protein source.

Rabbit Specifics

• Fermented fibre from the cecum still has undigested nutrients.
• Cecotropes (cecal droppings) get excreted.
• They contain 2X protein compared to regular poops and contain vit K and B vitamins.
• Chinchillas and hares also practice caprophagy.