Glimpse into How your Digestive System works: In a Nutshell – Digestion
Have you ever wondered how your digestive system works? Here are a few facts and figures to give you an insight.
The digestive or alimentary tract consists of the:
• mouth
• pharynx
• oesophagus
• stomach
• small intestine (duodenum, jejunum, ileum) – approximately 3 metres in length and 2-4cm in diameter
• large intestine (ascending, transverse and descending colon) -approximately 1 metre long and 6cm in diameter
• rectum and anus
• Accessory organs of digestion are the salivary glands, liver, gall bladder and pancreas.
• Functions: Ingestion, propulsion (peristalsis), digestion (mechanical and chemical), absorption and elimination.
• Structure: from the oesophagus onwards the walls of the digestive tract are formed by four layers of tissue:
Adventitia or outer coating
Muscle layer
Submucous layer
Mucosa (lining)
• Nerve supply: autonomic nervous system, both sympathetic – spinal nerves from thoracic and lumber regions and parasympathetic – vagus nerve and sacral nerves.
Now, what happens to the main food groups I wonder?
Saliva from three salivary glands in the mouth begin starch digestion.
Gastric juices from the stomach wall starts protein digestion and minimal digestion of fats.
The pancreas secretes pancreatic juices via the pancreatic duct into the duodenum, the first part of the small intestine, which acts on starches, proteins and fats.
Intestinal juices from glands in the walls of the small intestine break down complex sugars into simpler forms.
Bile from the liver (between 500 and 1000 mls daily), secreted via the bile duct breaks down fats.
Once the enzymes have done their work, the nutrients we need are absorbed through the walls of the small intestine into the blood stream.
The function of the large intestine is to remove excess water from the fluid contents from the small intestine. Mineral salts, and vitamins are also absorbed into the blood capillaries here. When the rectum is full, nerve receptors are stimulated and defaecation can occur if convenient!
Fun Fact: the hydrochloric acid in the stomach is strong enough to melt metal. One of the few things I remember from my lectures as a student nurse over 50 years ago is that if you dripped some hydrochloric acid on a carpet, it would burn a hole in it.
Strong stuff!
Mary Leonard
The Components of the Digestive System image credit – Blausen.com staff (2014)