The Digestive System Objectives: Identify the function and origin of various digestive enzymes/acids. Explain the numerous roles of hydrochloric acid.

The Digestive System

Objectives:

Identify the function and origin of various digestive enzymes/acids.

Explain the numerous roles of hydrochloric acid.

Describe an ulcer, its possible locations, causes and treatments.

Evaluate the functions of each digestive organ.

Describe common digestive disorders.

Vocabulary:

Alimentary canal * maxilla * mandible * incisors * canines * bicuspids/premolars * molars * amylase * bolus * esophagus * cardiac (lower esophageal)sphincter * hiatal hernia * pharynx * epiglottis * peristaltic waves * pepsin * ulcer (gastric/duodenal) * chyme * pyloric sphincter * duodenum * jejunum * ileum * gallstones * lactase * villi * rectum * flora * ascending, transverse, descending, and sigmoid colon * intrinsic factor

Digestion begins in the mouth with the mechanical breakdown of

food by the teeth. The teeth are anchored to the maxilla (upper jaw

bone) and the mandible (lower jaw bone). The outer portion of each

tooth is made of enamel, It’s the hardest substance in our body (yet

acid producing bacteria can dissolve it away - so think what an acidic

diet does to our bones). Children have about 20 teeth and adults have

32. The front teeth are called incisors. The pointy teeth behind the

incisors are the canines, Next are 2 bicuspids, or premolars followed

by the molars. Wisdom teeth are just late erupting molars. While

incisors and canines are great for tearing and ripping, and bicuspids for

shredding, the molars are best at grinding food and mixing it with

saliva.

The primary digestive enzyme released in the saliva is amylase.

Amylase begins the breakdown of some starches into the disaccharide,

maltose (carbohydrate digestion).

At the back of the mouth, the pharynx, where air from the nose joins food, a flap called the epiglottis prevents food from entering the trachea (windpipe). The mixture of food and saliva that slides down your throat is called a bolus. This will be pushed down the muscular esophagus. The contractile waves along the entire esophagus and gastrointestinal tract are called peristaltic waves. The bolus will enter the stomach through the cardiac sphincter (first valve to the stomach) into the stomach. The cardiac sphincter, or lower esophageal sphincter, prevents the acid mix in the stomach from backing up into the esophagus. This sphincter is normally anchored at the level of the diaphragm. Occasionally, the sphincter pushes up above the diaphragm and part of the stomach billows up and through the diaphragm Muscle as well. This is called a hiatal hernia.

Once in the stomach (about 12 inches long & 6 inches wide, in the upper abdominal cavity, slightly left of center), the bolus is subjected to hydrochloric acid. The stomach muscles churn the food into the acid to facilitate the breakdown of the food. Hydrochloric acid primarily acts to continue breaking down carbohydrates and assists in breaking down proteins and dissolves minerals. Another digestive enzyme, pepsinogen, is converted to active pepsin in the presence of HCl and also works here to breakdown proteins. Another important digestive product is called intrinsic factor. It is needed to absorb vitamin B12 (methycobalamin or cyanocobalamin). The elderly often don’t make enough intrinsic factor and become B12 deficient (numb feet, etc.)

Low hydrochloric acid in the stomach creates numerous problems. First, pepsinogen will not become active pepsin without HCl, so protein digestion will be hindered. Second, HCl works to kill harmful bacteria and parasites in food. If HCl is low, people are far more susceptible to food poisoning or other infections. Third, low HCl can actually cause heartburn because poor digestion in the stomach leads to fermentation (rotting) of the food which then produces gas that pushes on the cardiac sphincter and allows upward flow of stomach contents. The acid felt in heartburn is not usually from HCl but from the acids produced by bacteria, etc. in the poorly digesting food bolus. Most heartburn can be prevented by taking betaine HCl (from beets) or digestive enzymes. Even apple cider vinegar at meals can help somewhat. Once heartburn is started, regardless of the cause, licorice root usually stops it and has a healing effect on any ulcers present. (Note: deglycerated, or DGL licorice is best if high blood pressure is a problem) An ulcer is an injured, raw area of the stomach, esophageal, or intestinal lining. A gastric ulcer is located in the stomach, a duodenal ulcer is in the small intestine. It is often associated with Helicobacter pylori bacteria. Antibiotics can cure ulcers. H. pylori flourish when HCl is low in the stomach. Normally the stomach lining is not harmed by HCl due to mucus secretions in the stomach but once these bacteria take hold, enough blood can be lost to cause anemia or even death.

After 2 to 3 hours in the stomach, the food mix is slowly released into

the small intestine through the pyloric sphincter. At this point, the food

mix is referred to as chyme. While the stomach works to dissolve

minerals and to breakdown proteins, carbohydrates, etc., the majority

of nutrient absorption occurs in the small intestine.

The small intestine is about 23 feet (7 meters) long. The first 10

inches is called the duodenum, the next section is called the jejunum

and the final section is called the ileum. The small intestine continues

the breakdown of food with the help of digestive enzymes from the

pancreas and liver. While the term “digestive system” includes all

organs that aid in digestion, the term “alimentary canal” refers only to

the organs that actually touch the food as it moves through the body.

Since the liver and pancreas do not touch the food, they are not part of

the alimentary canal.

The liver is located on the upper right of your abdomen. It plays a major role in detoxification of substances entering the body via absorption through the digestive tract. It immediately tries to detoxify foreign substances. This is often why many drugs taken orally are not nearly as effective as they should be at a particular dosage. The liver detoxifies them too quickly. On the other hand, an unhealthy liver might not detoxify substances as well as it should. This is why the elderly often cannot tolerate the same dosage of a prescription drug as younger people can. Numerous nutrients are needed in the 2 major detoxification pathways of the liver. In addition, certain substances, like grapefruit, can greatly impact the breakdown of prescription medications! But, these processes are not directly considered part of the liver’s role in digestion.

The liver makes bile which acts like dish soap by breaking fats into tiny droplets. This increases their surface area so that lipases (enzymes that breakdown lipids/fats into their monomers) can more readily do their job. The gallbladder stores the bile until it is needed for fat digestion in the small intestine. Occasionally, gallstones form. These are often a combination of cholesterol and calcium. They can block the “common bile duct”, preventing the release of bile from the gallbladder when it contracts. People with gallstones often experience pain on the right side of the upper abdomen shortly after eating fats. Magnesium, vitamin C, D, and K2 may help prevent formation of gallstones. Many liver flushes also rely on large amounts of magnesium to dilate the common bile duct to release gallstones.

The pancreas, like the liver, has a role outside of direct digestion.

For example, it secretes insulin in response to increased blood sugar

levels. Insulin moves sugar inside of the cell to be burned for energy.

The pancreas’s more direct role in digestion is very important as

well. The pancreas secretes sodium bicarbonate to help neutralize

stomach acid as chyme enters the small intestine. The change in pH is

necessary for the digestive enzymes to do their part in the small

intestine. Without this pH change, fat breakdown would be impossible.

The pancreas also secretes: pancreatic amylase to continue breaking

down carbohydrates; lipase to break fats into fatty acids and glycerol;

trypsin, chymotrypsin, and carboxypeptidase to breakdown proteins

into small peptides. These enzymes enter the small intestine through

the common bile duct.

The small intestine itself also makes several digestive enzymes. One of the most important is the enzyme lactase which is needed to breakdown the milk sugar “lactose”. Lactase is produced at the ends of fingerlike projections called “villi”. The primary purpose of villi, and their fingerlike projections called “microvilli”, to increase the surface area of the small intestine to allow increased nutrient absorption.

If the tips of the intestinal villi become irritated and damaged, usually due to a hidden food allergy (wheat gluten being the most common), they no longer produce lactase. The undigested lactose then becomes food for bad bacteria which ferment it and cause gas, bloating, cramps, and diarrhea. This is what is called “lactose intolerance”. After breakdown into monosaccharides, amino acids, fatty acids, and glycerol, nutrients are absorbed through the small intestine into blood and lymph vessels. Lymph vessels are usually considered part of the immune system. About 70% of our lymph vessels surround theintestine. Any allergens or microorganisms trying to enter the body through the intestines are immediately attacked. This can wear us down if we are consuming foods that are causing sub-clinical allergies.

All fatty acids and glycerol enter the body through the lymph vessels,

called lacteals, surrounding the small intestine. The lymph eventually

joins the bloodstream through ducts by the clavicles. Amino acids and

monosaccharides enter the blood through capillaries and are taken to

the liver. If necessary, the liver will convert excess dietary glucose into

glycogen for storage for future use. The liver will also detoxify other

substances that entered the blood through the digestive tract.

The remaining material in the small intestine will travel to the large

intestine, or colon. At the juncture between the small and large

Intestines, in the lower right abdominal region, we find the appendix.

The appendix might still have a function in producing enzymes that

destroy bacteria entering the large intestine from the small intestine.

Often bacteria or pinworms get trapped in the appendix causing

appendicitis. Removal to avoid bursting and spilling of bacteria into the

bloodstream may become necessary.

Friendly flora (bacteria), like Lactobacillus acidophilus, are often

found in the large intestine. They manufacture small amounts of

vitamin K which helps with normal blood clotting. Antibiotics can kill the

friendly flora and allow overgrowth of yeasts, like Candida albicans.

The primary function of the large intestine is the absorption of

remaining minerals and the re-absorption of water. The first part of the

large intestine rises from the lower right side of the abdomen to the

upper right. This section is called the ascending colon. The next

section travels from the right to the left side of the upper abdomen and

is called the transverse colon. The colon then descends on the left side

and is called the descending colon. Next it makes an “S” curve and is

called the sigmoid colon. The rectum is the final sac-like region just

before the anal opening.