digestive system, comparative anatomy of the liver and pancreas

Describe the topography of the liver and pancreas in the domestic species ✓ Describe the lobulation of the liver and pancreas in the domestic species ✓ Identify the isolated liver and the pancreas of each of the domestic species ✓ Describe the microscopic structure of the associated organs within the digestive system ✓ Describe the type of cells within the associated organs ✓ Describe the function and the ducts of the liver and the pancreas ✓ Describe the blood supply and venous drainage of the liver and the pancreas

what are the functions of the liver?

Detoxification and excretion (waste products)

Secretion (Bile)

Storage (lipids, vitamins A and B, glycogen)

Synthesis (Albumin, clotting factors, globulins)

Protein, carbohydrate and lipid metabolism

Immune function (Kupffer cells)

how do we compare the liver in the body?

it is the largest gland in the abdominal cavity, caudal to the diaphragm

bulk lies to the right in all species and in ruminants entirely moved to the right

gall bladder between the right medial and quadrate lobe

some species have no gallbladder in the fossa (horses, rats)

A=dog

D=ruminant

whats the surface of the liver like?

strongly convex surface towards the diaphragm (parietal surface or diaphragmatic surface)

concave towards viscera (lies against and impressed by stomach, duodenum, etc) hence visceral surface

the visceral surface is marked by the porta (gate) of the liver

what is the porta of a liver

image shows dog lying on its back (paws on top)

the visceral surface of the liver

bile duct, portal vein, and hepatic vessels enter and leave)

porta is allso known as. the hilar region on the liver

what is the topography of the liver

Located cranial part of the abdomen

Cranial to liver is diaphragm

Caudal to liver is the stomach, intestinal mass, and right kidney

The right kidney makes contact with liver

Adopts to the form of adjacent organs (e.g. renal impression

of the caudate lobe)

what is the liver lobes

lobes are created by fissures (indentations)

where is the liver located in the dog?

Liver is related on the left to the stomach (spleen); and on the right to the pancreas,

kidney, and duodenum; and ventrally to the greater omentum

Liver reaches the umbilical region on the ventral abdominal wall

Its most caudal part covers the cranial extremity of the right kidney and reaches the 13th thoracic vertebra

Extends slightly beyond the costal arch (lower edge of ribs cartilage bit -where it connects to sternum) ventrally (more so in pups and in congestive heart failure)

Liver biopsy-puncture caudal to the xiphoid process

xyphoid process=tip of sternum - can pulpate - where you puncture to get biopsy of liver

where is the liver located in the horse?

Lies completely within the ribcage

Located obliquely across the diaphragm with the left lobe ventral and right lobe dorsal

Caudal margin reaches the 15th ICS

You can do liver biopsy at either the :

• 12th ICS (intercostal space- count from caudal end): on a line between the tuber coxae (hip) and point of the shoulder (right-hand side)

• 8th ICS: at the level of the deltoid tuberosity of the humerus (right-hand side)

liver in rabbit

The liver has five lobes with a deep cleft dividing it into right and left lobes

Caudate lobe has a narrow attachment to the porta region of the liver and could be a site of liver torsion

Gallbladder present

Liver biopsy-Ultrasound-guided biopsy can be taken ventrally from

any lobe

cow liver

Liver reaches dorsally as far as the last rib

The gall bladder also rests 10th ICS

Note the left lobe of the liver here (1), right lobe would be 24/25 (imagine liver rotated forward)

Liver biopsy -10th ICS, ¼ of the length of the rib

what are the peritoneal folds and ligaments

Peritoneal folds serve more to fix organs in position than as channels for blood vessels. These are called ligaments: -supportive function- attach liver firmly

Coronary ligament- surround the caudal vena cava-attaches liver to the central tendon of the diaphragm

Triangular ligaments extend between the dorsal part of the liver on each side of the diaphragm

Right and left triangular and coronary ligaments that pass to the diaphragm from the parietal surface have fibrous cores

Liver is covered by serosa (visceral peritoneum) overlying a thin connective tissue capsule (tunica fibrosa-especially strong in Pigs)

Some peritoneal folds have no supportive function but carry blood Vessels, nerves, and lymphatics

Falciform ligament- between the liver and the diaphragm, and the ventral abdominal wall

Round ligament –a fibrous strand in the free edge of the falciform ligament (umbilical vein remnant)

Hepatoduodenal (liver to duodenum) and Hepatogastric (liver to stomach) ligament- (Lesser omentum)

what is the blood supply like in liver?

dual

Hepatic artery

-Fresh oxygenated (nutritional) blood

-Branch of the coeliac artery

Hepatic portal vein

- Large vein carrying nutrient-rich (functional) blood from the unpaired organs (like intestines, pancreas, stomach, spleen, not kidneys cos theres two of them) into the liver

-Supplying 60-70% of the blood flow

then the blood coming from the artery and portal vein mix once theyre in the liver

tell me more about the blood vessels in the dual blood supply of the liver

image shows how the blood from the artery and vein join in one tube in the middle (sinusoid)

The hepatic portal vein receives the venous blood form all unpaired abdominal organs (stomach, pancreas, spleen and intestines)

Blood from the portal vein and hepatic artery branches mixes within the hepatic sinusoids before collecting in central veins

These central veins merge and eventually form hepatic veins that drain into the abdominal portion of the caudal vena cava

what is the hepatic lobule?

The basic structure of the liver is the hepatic lobule-hexagon shaped

At each corner - an arteriole (from hepatic a.); a venule (from portal vein) and a small bile duct form the bile duct

These three structures are commonly referred to as portal triad

Each portal triad may provide blood to the several adjacent hepatic lobules

surrounded by hepatocytes

lets break down this portal triad

sinusoids are very leaky to soak the hepatocytes

kupffer cells catch harmful like pathogens or tumours

Arteriole and venule empty their blood into the spongy liver lobule

Blood capillary beds that run between portal triad and central vein

Capillary beds are lined by fenestrated, leaky endothelium known as liver sinusoids

Blood flowing into the lobule is drained out via the central vein

central vein then eventually goes to the cranial vena cava - its a loop in terms of circulation

what is the bile and bile duct

whilst theres a portal triad we also have the bile duct next to it

Bile is produced by the sheets of hepatocytes

Discharged into bile canaliculi (microscopic channels)

Canaliculi unite to form the interlobular ducts -lobular ducts

Hepatic ducts joins with cystic duct (the one that attaches to gall bladder-think of it as like holding the cyst) and the bile duct (its the one that enters the small intestine)

hepatic ducts are slightly larger than bile duct

what is the pancreas

it is located in the dorsal part of the abdominal cavity, often abuts the stomach and liver

Small lobulated gland with two lobes joined by the body which is in contact with the pylorus

Right lobe (7) is within mesoduodenum next to DD

Left lobe (5) lies in the deep leaf of the greater omentum

Coeliac and cranial mesenteric a. branches supply blood

what are the pancreatic ducts

Pancreatic duct (greater) opens into the duodenum together or just beside the bile duct

Accessory pancreatic duct (lesser) opens on the opposite

In some species only one duct commonly survives (sheep, pig)

what do the pancreatic and bile ducts compare in each species

Horse- Bile and pancreatic ducts open at the first bend of the duodenal sigmoid flexure

Dog-common bile duct enters the duodenum at the major duodenal papilla adjacent to, the pancreatic duct

Cat-common bile duct and the pancreatic duct conjoin just before they enter into the major duodenal papilla

how is the liver innervated?

Liver is innervated both sympathetic and parasympathetic nerves

It receives fibers from the vagal trunk and sympathetic axons from celiac plexus/ganglion

Vagal axons reach the abdomen by passing through the diaphragm with the oesophagus