Our digestive system runs from mouth to anus and includes esophagus, stomach, and small and large intestines. Liver, gallbladder and pancreas which produce juices to help digestion are also involved. The whole digestive system is around 9 meters long.
Digestion is a process in which our body breaks food we eat down to a form our body can use to build and nourish cells and provide energy. It is a form of catabolism, i.e., a breakdown of large food molecules to smaller ones so that they are more easily absorbed into a blood stream. In a healthy human adult this process can take between 24 and 72 hours. Food digestion physiology varies between individuals and upon other factors such as the characteristics of the food and size of the meal.
In general, when food enters the mouth its digestion starts by a form of mechanical digestion called mastication (Chewing) and the contact of saliva. Saliva is secreted (~2 litres/day) by three pairs of exocrine salivary glands (parotid, submandibular, and sublingual) in the oral cavity.
The oral step is rapid but plays an important role in digestion. Mouth secretes saliva. Saliva contains salivary amylase, an enzyme which starts the digestion of starch in the food. Mastication reduces the particle size, and hydrates and lubricates the food by mixing it with saliva. Mastication also reduces viscosity of starchy food by the rapid action of salivary amylase (Read more on this).
After undergoing mastication and starch digestion, the food will be in the form of a small, round slurry mass called a bolus. It will then travel down the esophagus and into the stomach by the action of peristalsis. Peristalsis is an advancing wave of contraction of the walls of a flexible conduit, forcing the contents forward.
Gastric juice that mainly contains hydrochloric acid and pepsin starts protein digestion in the stomach. The acid itself does not break down food molecules, rather it provides an optimum pH for the reaction of the enzyme pepsin and kills many microorganisms that are ingested with the food. It can also denature proteins. This is the process of reducing polypeptide bonds and disrupting salt bridges, which in turn causes a loss of secondary, tertiary, or quaternary protein structure.
After typically an hour or two the resulting thick liquid called chyme enters the duodenum when the pyloric sphincter valve opens through a process known as Gastric emptying. Gastric emptying is slower in elders and females.
Chyme mixes with digestive enzymes from the pancreas, and then passes through the small intestine, in which further digestion continues. When the chyme is fully digested, it is absorbed into the blood. 95% of absorption of nutrients occurs in the small intestine. Water and minerals are reabsorbed back into the blood in the colon (large intestine) where the pH is slightly acidic about 5.6 ~ 6.9. Some vitamins, such as biotin and vitamin K produced by bacteria in the colon are also absorbed into the blood in the colon. Waste material is eliminated from the rectum during defecation.
Improper food habits and life styles could alter the GUT and lead to many types of digestive disorders or gastrointestinal tract (GI) diseases. This includes diseases of the oesophagus, stomach, duodenum, jejunum, ileum, the ileo-cecal complex, large intestine (ascending, transverse, and descending colon), sigmoid colon, and rectum..
In each disorder the symptoms may vary widely but in general, you should see doctor if you have
- Blood in your stool
- Changes in bowel habits
- Severe abdominal pain
- Unintentional weight loss
- Heartburn not relieved by antacids
The most common digestive disorders today, to mention a few, are:
- Celiac disease
- Crohn’s disease
- Diverticulosis and diverticulitis
- Hiatal hernia
- Irritable bowel syndrome
- Ulcerative colitis
Major Check Points
Check Point 1: MOUTH
Chewing the food thoroughly is considered very beneficial:
– creates less stress on the rest of the digestive tract and also reduces appetite
For example study conducted to determine whether eating the same meal at varying speeds elicits different postprandial gut peptide responses concluded that “Eating at a physiologically moderate pace leads to a more pronounced anorexigenic gut peptide response than eating very fast”.
– lowers calorie intake
For example study conducted on ‘the effects of mastication on energy intake and gut hormones in both obese and lean subjects suggests that “improving chewing activity could become a useful tool for combating obesity.”
– can aid weight loss (because the hormones that leave us feeling satiated don’t kick in until 20 to 40 minutes after you begin eating)
Therefore, make an effort to study further on this and meanwhile consider the following tips:
- First thing is first: Turn off TV and any distracting activities while eating
- Take sufficient time to eat your meal – don’t eat in hurry
- Prefer small bites over bigger ones
- Focus on the food you eat and feel the taste, texture etc.
- Chew the food thoroughly (tip: chew each mouthful 15 times at least)
- Bon appetit and stay healthy for years to come
Check point 2: STOMACH
Two chemicals, HCl and Pepsin, may damage the stomach wall and may lead to stomach or gastric ulcers. “In the digestive system, persistent inflammatory conditions have been linked with tumor growth: patients who have stomach ulcers or gastritis (inflammation of the stomach lining) are more susceptible to gastric cancer, while inflammation of the colon, called colitis, is associated with an increased risk of developing colon cancer.” (Read more on this). Thus mucus neck cells present in the gastric glands of the stomach secrete mucus, which along with gastric juice plays an important role in lubrication and protection of the mucosal epithelium from excoriation by the highly concentrated hydrochloric acid.
Check point 3: DUODENUM
Gastric emptying has attracted medical interest because of the fact that gastric emptying is influenced by many biological factors such as age, body mass index, hormonal factor, gender, the blood glucose level, posture, stress, depression and also diseased states.
Gastric emptying are of two types: 1. Rapid gastric emptying. 2. delayed gastric emptying. And each type is related to a certain disorder in the system, for example:
Thus Control of gastric emptying is essential for ensuring optimal digestion.
Read more on this at:
Check point 4:
….to be continued
It is my sincere appeal to the readers, experts in the field that please feel free to send in your inputs to expand the each point with logic and new developments with references. Improve the subject matter with your invaluable additions to the subject matter at and any point of the entire digestive process. Share text, images, tables, references and all your contributions will be suitably acknowledged.
“Lets make an effort together to prevent the preventable”
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Special thanks to Social Media and other Open access information sources for the invaluable information to continually curate with a hope and belief to make it as one stop “Education Booklets” on “Health and Disease”.
- The truth about stomach acid: Why low stomach acid is jeopardizing your health (thepaleonurse.com)
- Digestion (easylearnit.wordpress.com)
- Stomach Enzymes For Digestion | Yeast Infection No More : Candida Yeast Infection Cure (ajkaif8s.wordpress.com)
- Healthy Foods for Digestive System (healthylifestylesliving.wordpress.com)
- Cooking is an anticipation of digestion…. (carljungdepthpsychology.blogspot.com)
- Gut Check – Monthly Mission June 2013 (dkfitsolutions.com)