The digestive system is one of the main systems of the body. It is responsible for breaking down the food that we eat and processing it into useable molecules for the cells of the body. Massage students preparing for the MBLEx in 2021 should have a good understanding of the digestive system anatomy and physiology. It is also important for massage therapists to understand how the digestive system interacts with other systems of the body. And know how massage can affect the digestive system.
This post gives an overview of the digestive system anatomy and physiology, and focuses on key terms that massage therapists are most likely to encounter on the massage exam.
Primary functions of the digestive system
The primary function of the digestive system is to process food into a useable form, so that it can supply nutrients and be converted into energy. The food we eat goes through two basic processes before the cells of the body can metabolize the nutrients: digestion and absorption.
Digestion begins at the mouth with the ingestion of food. Digestion includes mechanical digestion, which is chewing or mastication. The churning of food by the stomach muscles is another form of mechanical digestion. Chemical digestion also begins at the mouth, as enzymes help to break down food into simpler molecules.
Absorption can begin once the food is broken down into simple molecules. These molecules are absorbed through the cell membranes of the small intestine walls into capillaries of the circulatory system or lymphatic system. The inner walls of the small intestine are lines with small fingerlike projections called villi and microvilli. These tiny projections increase the surface area to enhance absorption.
Elimination is the process of removing waste products and unused material from the body. Both the digestive system (defecation) and urinary system (urination) assist the body with elimination.
Components of the digestive system
The digestive system, also called the gastrointestinal (GI) system, is composed of two parts: the GI tract and the accessory digestive organs.
Gastrointestinal (GI) tract: the continuous tube from the mouth to the anus. It is also called the alimentary canal. Technically substances in the GI tract are “outside” of the body because they haven’t yet passed through any cell membranes into the body. The gastrointestinal tract of the digestive system is often divided into the upper GI tract and the lower GI tract, divided by the duodenum.
There are four layers, or tunics, in the walls of the digestive tract:
- Mucosa: the innermost layer, consisting primarily of epithelium tissue.
- Submucosa: is a thick layer of loose connective tissue.
- Muscular layer: consists of an inner and outer layer.
- Serosa or adventitia: produces watery fluid to lubricate the outer walls of the tract.
Accessory digestive organs: the gallbladder, liver, pancreas, salivary glands, teeth and tongue.
The digestive system begins at the mouth, where food is ingested. Food is broken down through both mechanical digestion and chemical digestion.
Mechanical digestion is chewing or mastication. Muscles involved with mastication include: masseter, temporalis, medial and lateral pterygoid.
Chemical digestion also begins in the mouth through the work of enzymes in saliva. The salivary glands of the mouth include:
- Parotid gland
- Sublingual gland
- Submandibular gland
These glands produce an enzyme called salivary amylase, which starts breaking down starches (carbohydrates) into simpler sugars.
The pharynx is the passageway that connects the oral and nasal cavities to the esophagus and larynx. It is divided into the nasopharynx, oropharynx and laryngopharynx.
The esophagus is about 9 inches long, and positioned just posterior to the trachea. It descends through an opening in the diaphragm called the esophageal hiatus, and then connects to the stomach.
The stomach is divided into 4 regions:
- Fundus: uppermost region
- Cardiac region: near where the stomach connects with the esophagus
- Body: main stomach region
- Pyloric region: near the connection to the duodenum
Other significant features of the stomach are that it has an additional layer of muscle. It also has folds in the mucosa layer called rugae, which allow the stomach to expand as it fills up.
Parietal cells of the stomach secrete hydrochloric acid, which helps to kill bacteria. The acidity or pH in the stomach can range from 1-5.
The chief cells of the stomach secrete pepsinogen. This is converted to the enzyme pepsin by the hydrochloric acid in the stomach. Pepsin breaks down proteins into peptides.
The small intestine is the primary site for absorption of nutrients from ingested food. The length of small intestine can vary greatly, from 10 feet to over 30 feet, mainly as a function of a person’s height. But it is generally between 20-23 feet.
The duodenum is the first and shortest section of the small intestine, about 8-12 inches long. Its primary function is to continue breaking down food, which is now a semifluid mixture called chyme. The duodenum receives bile from the liver and gallbladder, and digestive enzymes from the pancreas. It also mixes in bicarbonate to reduce the acidity of the chyme to a neutral or slightly alkaline pH.
The jejunum is the next section of the small intestine. It is about 8 feet long and is where the absorption process begins in the small intestine.
The ilium is the last section of the small intestine, and is about 10 feet long. It continues the absorption function and is the site of B12 absorption.
Large intestine or colon
The large intestine, or colon, is the final section of the gastrointestinal tract. It is around 6 feet in length and is divided into several distinct parts. Contents flows through the large intestine in this order:
- Ascending colon
- Transverse colon
- Descending colon
- Sigmoid colon
The primary function of the large intestine is to reabsorb water. A large intestine that is not working properly can result in dehydration, among other problems.
Accessory organs of the digestive system
As mentioned previously, the accessory organs of digestion include the teeth, tongue, salivary glands, liver, pancreas and gall bladder.
The liver is located in the right upper quadrant of the abdomen, beneath the diaphragm and behind the stomach. Its role as an accessory digestive organ is to produce and secrete bile into the duodenum. It also metabolizes lipids, proteins and carbohydrates.
The gallbladder is a small organ that stores and concentrates bile. The liver continuously produces bile, so the gallbladder stores the bile until it is needed.
The pancreas is a long flat organ that performs both endocrine and exocrine functions. One of its exocrine functions is to produce enzymes to aid in chemical digestion. These enzymes include:
- Pancreatic amylase (to break down carbohydrates)
- Pepsin, Trypsin, Elastase, Carboxypeptidase (to break down proteins)
- Pancreatic lipase (to break down lipids, or fats)
Pancreatic juice also has a high concentration of bicarbonate ions which raises the pH and make the chyme more alkaline.
How the digestive system interacts with other body systems
The digestive system supports other body systems by providing nutrients and water, and eliminating waste products. The list below gives a brief description of how the digestive system anatomy and physiology interacts with other systems of the body.
Capillaries of the circulatory system pick up the nutrients that are absorbed at the small intestine, and transports them to the liver. The circulatory system transports hormones that affect GI motility and secretions of the accessory organs of the digestive system. The large intestine absorbs water that is needed to maintain blood volume.
Muscles are involved in mechanical digestion including chewing food (skeletal muscles) and churning of the stomach (smooth muscles). The muscles of the GI tract enable peristalsis, which is the wavelike rhythmic contractions of smooth muscle to move contents through the intestines. The liver metabolizes lactic acid produced through muscle contraction.
Bones of the skeletal system provide support and protection for organs of the digestive system. They also provide insertion points for the muscles of mastication. The teeth, mandible and maxilla bones are involved in the mechanical digestion of food. The digestive system absorbs calcium and phosphate necessary to grow, maintain and repair bone.
The integumentary system stores excess calories as adipose tissue in the subcutaneous layer. The digestive system absorbs nutrients needed for the growth, maintenance and repaid of skin.
The respiratory system provides oxygen needed by the cells of the digestive system.
Water absorbed by the digestive system helps the urinary system to help flush out waste products and excrete toxins. Some of these toxins are byproducts created by normal liver function, which include urea and metabolized hormones and drugs.
Hormones produced by the endocrine system affect the function of the digestive system. The hormones insulin and glucagon affect the glucose metabolism in the liver. Hormones, which are messengers, influence the secretion of various enzymes by the pancreas and gall bladder. The digestive system provides the endocrine system the nutrients it needs for hormone synthesis.
Lacteals in the lymphatic system absorb lipids and fat-soluble vitamins from the digestive system. The acidity in the stomach aids the lymphatic system in its immune function by destroying most of the toxins in the stomach. Lymphoid tissue along the GI tract also helps to provide defense against pathogens.
Signals from the autonomic nervous system influence movement of contents through the digestive system (motility). The nervous system also influences activity of the accessory digestive organs. Nutrients absorbed by the digestive system are used in the synthesis of neurotransmitters and ATP. These nutrients also help to maintain and repair the nervous system.
The digestive system provides nutrients needed for development of reproductive structures as well as fetal development. Hormones produced by the gonads effect the metabolic rate.
How massage therapy effects the digestive system
Massage therapy has both physiological effects and psychological effects on the digestive system. Relaxation that occurs from massage will stimulate the parasympathetic division of the autonomic nervous system. The PNS is also called the “rest and digest” system.
Activating the parasympathetic nervous system results in the following events that effect the digestive system:
- Increased saliva production
- Stimulates stomach secretions
- Stimulates the liver to release bile
- Increased peristaltic movement of the GI tract
- Increases blood flow at digestive organs
A mechanical effect of massage therapy is that it can improve mobilization of GI contents. So abdominal massage can be a useful treatment for constipation. Massage therapists can educate clients on abdominal self-massage techniques. Massage may also aid in preventing or reducing adhesions that affect the gastrointestinal tract.
These were some of the most important details of the digestive system that new massage therapists are most likely to see on the MBLEx. If you’re ready, go ahead and try one of our free practice quizzes.