Digestion 101

by lydia on March 6, 2012

A North to South Process -Digestion Begins in the Brain. The sight and smell of food triggers the salivary glands to begin producing saliva. The mouth is the physical gateway to the digestive system. This is where the mechanical and chemical breakdown of the food begins. The teeth physically break down food into smaller parts. This is called mastication. The salivary glands secrete saliva to moisten the food and help with swallowing. Saliva = 99.5% water + 0.5% solutes. One of these solutes is the enzyme, salivary amylase, which begins the chemical breakdown of carbohydrates within the mouth. When you swallow, the chewed food now called the bolus enters the esophagus for passage to the stomach. The cardiac sphincter at the bottom of the esophagus opens to allow the bolus to pass into the stomach. The stomach continues the mechanical breakdown of food along with a number of chemical activities. As the bolus enters the stomach, gastric juice is excreted from millions of tiny gastric glands located in the mucosal lining of the stomach. Hydrochloric acid (HCL) and pepsinogen begin breaking down proteins into peptides (smaller strings of amino acids).

Keep in mind that the stomach is all about acid (it is designed for a normal pH of 1.5-3.0). HCL is excreted into the stomach at a pH of 0.8, that is almost pure acid. The acid; bathes & disinfects the stomach, kills bacteria and parasites, activates pepsin so we can digest proteins, stimulates gastrin and breaks down proteins.

After the stomach churns the bolus and mixes it with gastric juice, the food breaks down even more into a paste called chyme (which is very acidic). Chyme is released into the upper part of the small intestine (duodenum) through the pyloric sphincter. As the chyme enters the duodenum the acidic pH (1.5-3.0) of the chyme triggers the small intestine to secrete mucous. Quick note: The small intestine has a dual role as a digestive organ and a gland. At the same time the intestinal walls are secreting mucous, they are also secreting two hormones into the bloodstream, secretin & cholecystokinin (aka – CCK). Secretin stimulates the pancreas to release bicarbonate and pancreatic juice, and CCK stimulates the gallbladder to release bile.

Bile is necessary to emulsify and absorb fats. As part of the pancreatic juice, the pancreas first releases sodium bicarbonate to help raise the pH of the chyme to neutral (7.0). Once the chyme pH reaches neutral, the enzyme portion of the pancreatic juice is released to complete the chemical digestion of carbohydrates, proteins and fats. By the time the chyme leaves the duodenum, it is almost totally digested. Carbohydrates are broken down into glucose molecules. Proteins are broken down into amino acids and polypeptides. Fats are broken down into fatty acids and glycerol molecules.

Peristalsis moves these absorbable  molecules into the jejunum, where millions of villi and macro villi absorb the nutrient molecules into the bloodstream, here they are carried to the entire body. Glucose, amino acids and short chain fatty acids are carried by the villi to the capillaries and into the liver. Long chain fatty acids require bile for proper absorption and end up in the lymphatic system. The leftover chyme from the small intestine (indigestible fibers, bile, water, sloughed off cells) gets passed on to the large intestine through the illeocecal valve.

The large intestine, or the large bowel, consists of 3 sections, the cecum, colon and the rectum and is approximately 5 feet in length. It has the job of; recycling & the waste material which nourishes the colon, capturing any lost nutrients that are still available (with the help of the bowel flora) and converting nutrients to vitamin k/B1/B12 & butryric acid. The cecum is a short pouch, that receives the chyme from the ileum through a short valve. The rectum is the terminal segment of the digestive tract, this is where the feces accumulates just prior to discharge . The feces are discharged through the anus which contains two important musclesthe internal sphincter and the external sphincter. The internal sphincter is always tight, except when feces enter the rectum, in order to keep us continent (eg) when we are asleep. When we get an urge to defecate, we depend upon the external sphincter to keep the stool in until we go to the toilet. In total, it takes about 36-48 hours or longer for waste matter to pass through the large intestine. As in the esophagus and the small intestine, the contents of the large intestine are pushed forward by a sequence of muscular contractions called peristalsis (a type of motility or muscular movement). Peristalsis is regulated by a large network of nerves, hormones and muscles. Malfunction of any of these components may lead to a range of intestinal problems, including indigestion and constipation.

This is what occurs in a healthy properly functioning individual with a healthy digestive tract. Stay tuned for what can go wrong in digestion – this is all too common and pervasive today.

So in review, as digestion works from North to South

1. Digestion starts in the BRAIN

2. MOUTH (food is chewed, salivary glands are releasing saliva)

3. The chewed food/bolus enters the STOMACH

4. The chyme from the stomach enters the SMALL INTESTINE (the liver/gallbladder and pancreas all help with the digestion of the chyme in the small intestine, and nutrients are shuttled through the body through the S.I.)

5. The remains from the small intestine head into the LARGE INTESTINE. This is when we absorb the water and vitamins with help of the bowel flora. And any remaining unusable waste comes out as feces.


LydiaLydia Joy Shatney is certified as a Nutritional Therapy Practitioner through the Nutritional Therapy Association. Additionally, she is a co-chapter leader for the Weston A. Price Foundation in Delaware County, Pa. (Find the group here on Facebook). Lydia is also a member of the Nourished Living Network. Lydia founded Divine Health in March of 2010. You can find Lydia on Facebook, Twitter & Pinterest.

Lydia offers specialized one-on-one counseling for those that are looking to transform their health through dietary advice (both food and supplements), learning cooking techniques, shopping guidance, as well as fitness inspiration and self-empowerment. These personal consultations are tailored to suit your specific needs and can be done over the phone, Skype or in person. Lydia will work with you in person locally or long distance across the globe. Lydia currently offer 3 & 6 month packages. In these packages you will receive phone consultations, email support, food journal evaluations, a thorough nutritional assessment, lots of handouts, supplement recommendations for your specific needs, information, recipes, tips, cooking ‘how to’s’ and more. Contact Lydia to sign up for your free initial consult call today!

{ 5 comments }

Kathy, Puristat Digestive Specialist March 6, 2012 at 9:24 pm

Great post! There is definitely a connection between your brain and your gut. We have all heard the statement “You are what you eat.” Well, this statement is so true. Digestion affects our appetite and the health of our immune system.
When your digestive system is functioning well with enough serotonin production it can mean the difference between feeling well and feeling lousy. Our digestive system is our second brain and we can take actions to keep us healthy. Start with a colon cleanse which will balance the good and bad bacteria in your body shortening transit time which will reduce the amount of time bacteria has to do damage.

Laura Black March 8, 2012 at 5:30 pm

Reading this article reminded me of how important it is to chew my food slowly and well. Digestive issues have plagued me most of my adult life – all diet related. I will be interested to read your follow-up article.

Suzanne June 14, 2012 at 9:25 am

This was very helpful to me for reviewing for my exam.

lydia June 15, 2012 at 3:48 pm

That’s awesome to hear Suz! Good luck, you’ll do great!

Andrea J. October 29, 2012 at 1:01 pm

So it is vital to remember to take care of your teeth. It\’s where digestion begins, without proper mastication, it is hard on your digestive system.

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