11 Accessory Organs: Liver, Gall Bladder, Pancreas

Accessory organs:

In a car factory there is the main assembly line which manufactures cars using parts and bolts, yet even the best factories require oil and lubricants to ensure the parts are assembled efficiently. Similarly, The accessory organs while not directly included in the alimentary canal (pathway of food and chyme) they are integral to the breaking down of large food contents. The accessory organs including the liver, gallbladder and pancreas are integral for their accessory functions and are discussed in detail below.

Liver:

The liver, the second heaviest organ outside of the skin, lies in the upper right quadrant of the body. It is divided into 2 separate lobes connected by the falciform ligament. The liver itself can be divided into 4 differently sized lobes as depicted in the figure below: left, right, caudate(medial and superior) and quadrate(medial and inferior).

The liver, like a “jack-of-all-trades” has several functions:

1. Produce bile to break down fats
2. Produce various proteins to help carry fats through the body
3. Convert excess glucose into glycogen
4. Regulate blood levels of amino acids
5. Process hemoglobin
6. Convert ammonia to urea to be excreted in urine
7. Clear blood of drugs

Gallbladder:

The gallbladder, a small greenish coloured organ inferior to the liver, has the responsibility of storing and concentrating bile produced from the liver.

Imagine cleaning a greasy pan with only water; the grease will not be cleaned off, you need soap! Like dish soap, bile can emulsify fatty acids, breaking them down into smaller droplets which can be processed easier. When you are eating, your gallbladder will contract and release bile into the small intestine to break down fatty acids.

Interestingly, bile’s main pigment, bilirubin which when broken down in the small intestine releases stercobilin which gives feces its brown colour.

Pancreas:

The pancreas, an elongated organ does not directly receive any chyme or foodstuffs just like the liver and gallbladder, but is prominent for its secretions both exocrine and endocrine. Exocrine meaning secretions go through ducts or ampullas onto bodiy surfaces, while endocrine refers to releasing messengers into the bloodstream to have affects elsewhere.

The pancreas itself can be broken down into 3 separates areas:

1. Head: the widest and more rightward portion of the pancreas
2. Body: the mid section
3. Tail: the tapered left side which leads to the spleen

With regards to the digestive tract, the pancreas releases several exocrine products through the sphincter of Oddi, yet its path is a bit more complex, as depicted in the figure below. However, these secretions are bicarbonate rich to neutralize the highly acidic stomach contents like a fire extinguisher.

From the pancreas, exocrine secretions enter the pancreatic duct into the common bile duct from which the final product leaves through the sphincter of oddi into the duodenum.

With regards to the pancreas’s structure, it is ~99% acini cells which create the exocrine secretions, and ~1% of cells known as islets of langerhans can be divided into 2 separate cell types:

1. Alpha cells – secrete glucagon
2. Beta cells – secrete insulin

Both of these secretions are relevant to glucose metabolism(more info available in chapter 2)

Below represents a visual depiction of all the accessory organs and there relative locations with respect to each other: