Digestive system

The small intestine, which consists of three different regions, begins with the exit from the stomach (pyloric sphincter) and ends with the entrance to the large intestine (ileocecal valve). It is attached by mesentery to the posterior body wall of the abdominal cavity.

Mesentery

Thin walls of small intestine with blood supply

Most of the arterial blood supply to the small intestine is via the superior mesenteric artery

Venous drainage of the small intestine is via the hepatic portal vein

The duodenum is the first portion of the small intestine and it is mostly located retroperitoneally. The duodenum receives secretions from the liver and the pancreas.

The duodenum is continuous with the jejunum at the duodenojejunal flexure

The major duodenal papilla is a projection the protrudes into the duodenum the allows the exit of bile and pancreatic fluid

The jejunum is about 7.5 feet long and is the portion of the small intestine where the most absorption takes place.

Some absorption occurs in the duodenum and ileum, but most occurs in the jejunum.

Bruising on abdomen where the jejunum and greater omentum were crushed against the spine by an impact with the steering wheel during an automobile collusion.

The ileum (about 10 feet long) is the final portion of the small intestine and it empties into the cecum via the ileocecal valve

Note the circular folds (plicae circulares) of the small intestine.

Intestinal villi

Intestinal villi

Microvilli on the surface of villi

Each villus contains blood capillaries and a lymph capillary (lacteal). Each villus is covered with microvilli.

Carbohydrates and amino acids enter the blood capillaries in villi

Lipids and lipid soluble vitamins enter into lymph capillaries (lacteals).

Adhesions often form following abdominal surgery or after an abdominal infection (peritonitis).

The large intestine has a larger diameter than the small intestine and is about 5 feet long.

The large intestine absorbs most of the remaining water and salts and forms relatively solid feces, which are later expelled from the body.

The cecum is a short blunt pouch in humans

The ileocecal valve opens into the cecum and the appendix is attached to the cecum.

The cecum of sheep is an elongated blunt pouch that is harvested when sheep are slaughtered.

Natural membrane condoms are made from harvested sheep ceca

The vermiform (“wormlike”) appendix is attached to the cecum.

Endoscopic view of appendix

Cecum

Inflammation or blockage of the appendix can lead to appendicitis. The main concern is that if the appendix ruptures it will spill bacteria and feces into the peritoneal cavity causing peritonitis. Read the clinical view in the text.

Anterior superior iliac spine

Umbilicus

McBurney’s point is one third the distance from the anterior superior iliac spine towards the umbilicus

Hordes of bacteria normally found in feces of large intestine. If they escape into the peritoneal cavity, potentially lethal peritonitis may follow.

Fatal peritonitis. Note swollen intestines and pus on inner surface of parietal peritoneum.

Peritonitis can also follow penetrating abdominal injury

The four regions of the colon

Note the right colonic flexure (hepatic flexure) and the left colonic flexure (splenic flexure).

The four regions of the colon

Diverticulosis is the development of sacs or pouches along the intestine, usually in the colon. If these sacs or pouches become inflamed, then it is called diverticulitis.

Endoscopic view of colon showing internal openings of diverticuli. These sacs or pouches are mostly caused by a lack of fiber in a persons diet.

If a diverticulum ruptures, peritonitis will most likely follow.

The last 7.5 inches of the GI tract is called the rectum. Its exit is guarded by the anal sphincters.

Note the rectal valves, which are inner folds of the rectum

Rectal valves

Close-up of anal canal and anal sphincters.

External hemorrhoids

A hemorrhoid can be grasped and have a ligating rubber band slipped over its base to cut off its blood supply so it will necrose and fall off.

This elderly man felt that inserting a glass Mason jar into his rectum would “loosen up his plumbing”. Unfortunately, he could not retrieve it and went to the local ER for assistance. If the jar should break during its removal, severe lacerations to the rectum and anus might occur!

An ER doctor came up with this solution for such slippery jar removal!

Note the longitudinal bands (tenia coli), the many sacs (haustra), and the lobules of fat (epiploic appendages) of the large intestine.

Read the clinical view about how polyps may develop into colorectal cancer.

A plastic bag is taped over the colostomy opening to catch the feces gradually expelled by peristalsis.

Read the clinical view in the text about inflammatory bowel disease

The liver is positioned immediately below the diaphragm and is the largest organ in the body.

The falciform ligament divides the liver into two major lobes

Venous blood is brought to the liver by the hepatic portal vein and arterial blood is brought to the liver by the hepatic artery.

The liver contains thousands of hepatic lobules, which are the structural and functional units of the liver. These lobules contain hepatocytes.

Not the portal triads at the periphery of each hepatic lobule.

The sinusoids of liver lobules allow both arterial and venous blood from the periphery to mix as the blood travels towards the central vein at the center. Note that separate bile canaliculi produce bile which travels from the center to the periphery where it is collected into the bile duct.

Hepatic lobule

The liver has numerous functions that are mentioned in your notes

The liver, among its many functions, produces several clotting proteins that help your plasma to coagulate when injuries occur. When the liver is damaged, excessive bleeding can take place

Ethyl alcohol is toxic to the liver

Chronic alcoholism will typically lead to damage of the liver characterized by scarring of the hepatic sinusoids so they no longer permit easy blood flow. The damaged liver often turns an orange color. This damage of the liver is called “cirrhosis”. Cirrhosis is less commonly caused by viruses and some toxic chemicals.

This person has fluid accumulation in the abdominal cavity because of alcoholic cirrhosis. Note that since the blood flow to the liver is partially obstructed, the venous blood will seek alternate routes to return to the heart by traveling through superficial skin veins. This process is called “collateral circulation”.

Cirrhosis of the liver

Liver cirrhosis

Note extensive scarring

One route that collateral circulation can occur in cirrhosis is via the esophageal veins. The increased blood flow leads these veins to weaken and bleed (become varicose). These esophageal varicosities will bleed extensively!

The esophageal veins provide an alternate route for venous return (collateral circulation) when hepatic portal hypertension exists because of cirrhosis.

Esophageal varicose veins in patient with alcoholic cirrhosis

Stomach and esophagus turned inside out to reveal numerous varicose veins. Now you know why patients with cirrhosis become chronic gastrointestinal bleeders (chronic G.I. bleeders). Since they lose blood, they also lose iron. Iron deficiency anemia soon develops.

The inner esophageal veins can be surgically closed to help control bleeding. However, this does nothing to solve the underlying cirrhosis.

This cirrhotic patient is vomiting blood from the esophagus, has turned yellow because of accumulated bile pigments, and is suffering brain damage (encephalopathy) because natural toxins in ingested foods are NOT being detoxified by the liver.

The gallbladder is attached to the inferior surface of the liver. It stores and concentrates bile that is produced by the liver for later release.

Liver

Gallbladder

Endoscopic view of liver and gallbladder

Read about cholelithiais (presence of gallstones in gallbladder or nearby ducts) in the clinical view in the text.

Blockage of the common bile duct by gallstones may lead to accumulated bilirubin (obstructive jaundice).

Note that the cystic duct connects the gallbladder to the common bile duct.

The pancreas is a mixed gland because it exhibits both endocrine (produces insulin and glucagon) and exocrine functions (produces digestive enzymes that are released into the duodenum. It has a head, body, and tail. The tail leads towards the spleen.

Note the main pancreatic duct

The pancreas is adjacent to the stomach and is retroperitoneal

Biliary apparatus

Sphincter of Oddi controls release of secretions from the hepatopancreatic ampulla into the duodenum.

• EVERYTHING PAST THIS POINT IS EXTRA OR FOR EXAMS

The gallbladder concentrates bile produced by the liver and stores it for later release.

The small intestine receives secretions from the liver and pancreas, breaks down food from the stomach, absorbs most of the nutrients, and transports the remaining undigested material to the large intestine.

Peristalsis propels food through the G.I. tract

The large intestine is supplied by the superior and inferior mesenteric arteries and drained by the hepatic portal vein

The defecation reflex is triggered by stretch receptors in the rectum

Defecation

spleen

Note that tail of pancreas always leads to spleen

Dysentery, which is characterized by the excessive stools of mucus, pus, and blood, can lead to severe dehydration and illness. Note sunken eyes on this child

Hepatitis is inflammation of the liver.

Jaundice

Jaundice in a newborn

In the past, penetrating bullet wounds to the large intestine were almost invariably fatal when peritonitis soon followed.

Cystic fibrosis

Liver cirrhosis

Liver cirrhosis

Hepatitis B virus

Gallbladder

Liver

Intestine

Liver fatally ruptured by blunt trauma

Figure 26.15abc

Figure 26.16

Figure 26.18b

Figure 26.20

Figure 26.p817

Figure 26.p820b

Figure 26.p820a

Liver cirrhosis

Cirrhosis

Peritoneal edema (ascites) in a patient with liver disease

Peritioneal edema (ascites) is typically associated with liver disease.