Integration of Cardiovascular and Gastrointestinal Systems

Introduction

The gastrointestinal and cardiovascular systems of the human body work together to break down and transport materials that are ingested — such as food and medication — to the necessary parts of the body, while expelling wastes that are not needed. Independently, these systems serve separate functions, but when working in conjunction, they help to transport necessary nutrients throughout the body while maintaining and promoting homeostasis within the systems. Any imbalance within these systems will greatly affect the body as a whole and can lead to potentially fatal results.

The Gastrointestinal System

The gastrointestinal system is essentially a long tube that runs throughout the body and has specialized sections capable of digesting materials inserted at the beginning of the tract, extracting useful components from those materials, and subsequently expelling waste materials at the end (University of Leicester 2001). The digestive system is comprised of the following organs and structures: the mouth, esophagus, stomach, small intestine, large intestine, rectum, and anus. The entire digestive system is approximately nine meters long, and digestion within a human adult can take anywhere from 24 to 72 hours.

The mouth is designed to aid in breaking down pieces of food introduced into the human body, while the esophagus takes in food from the mouth and pushes it down the gastrointestinal tract via peristalsis to the stomach (Cleveland Clinic 2005). The stomach is a hollow organ that holds food and mixes it with chemicals and enzymes to further break it down during the digestive process. The small intestine is a 22-foot-long muscular tube where digestion continues to occur. The pancreas secretes digestive enzymes into the first section of the small intestine and also produces insulin that is secreted directly into the bloodstream (Cleveland Clinic 2005). The liver helps to process nutrients absorbed by the small intestine. The gallbladder sits below the liver and helps the duodenum — the first section of the small intestine — digest and absorb fats.

The large intestine processes and eliminates unwanted solid wastes from the body. The colon is, on average, six feet long and connects the small intestine to the rectum. The rectum is an eight-inch tube that connects the large intestine to the anus and serves as the holding site for stool until it is evacuated from the body. The anus is a two-inch canal that aids in the evacuation of stool and is comprised of a series of pelvic muscles and two anal sphincters (Cleveland Clinic 2005).

The Cardiovascular System

The cardiovascular system is comprised of the heart, blood, and blood vessels. Its main functions include the transport of materials such as gases, nutrients, wastes, and hormones; housing cells that help combat infections; the stabilization of pH and ionic concentration of bodily fluids; and the maintenance of body temperature through the transportation of heat (Gregory n.d.). The heart consists of two separate pumps: the left side pumps blood to the body, while the right side pumps blood to the lungs. Both sides are made up of an atrium and a ventricle (Gregory n.d.). At rest, the heart beats an average of 60 to 80 times per minute.

Blood cells can be subdivided into three types: erythrocytes (red blood cells), leukocytes (white blood cells), and thrombocytes (platelets) (Cotterill 2000). Plasma is composed of water containing proteins, nutrients, hormones, antibodies, and waste products (Cotterill 2000). Nutrients and blood must pass through the body's various veins into the ascending aorta and then to the heart (Thibodeau 1992). At rest, the cardiovascular system supplies all organs of the body with blood and oxygen, ensuring that these organs remain functional and that the entire body stays healthy. Prior to digestion, the cardiovascular system is triggered by the parasympathetic nervous system to increase blood flow to the digestive system and its organs, causing heart rate to increase slightly in preparation for the digestive process.

The Digestive Process in Detail

The digestive process begins even before food or any other materials are introduced into the body. One of the initial reactions of the digestive system to the introduction of materials into the mouth is salivation. Salivation is controlled by the autonomic nervous system, which governs both the volume and type of saliva produced (University of Leicester 2001). Saliva production may be stimulated parasympathetically or by potent stimuli, which may include the presence of food, thoughts about food, or the presence of an irritating substance in the mouth (Bowen 2002). Within the mouth, saliva serves several important functions: providing lubrication for food within the esophagus, binding masticated food for facilitated passage down the esophagus, solubilizing dry food, regulating oral hygiene, initiating digestion, providing alkaline buffering and fluid, and aiding in evaporative cooling (Bowen 2002).

In order for food to pass down to the esophagus, it must first be masticated. The mouth is also comprised of the tongue, the hard and soft palates, and the uvula, which hangs at the back of the mouth from the soft palate (Thibodeau 1992). At the back of the mouth, before food is passed down to the esophagus, is the pharynx. The esophagus is approximately 25.4 cm (10 inches) in length and pushes food down into the upper abdominal cavity and into the stomach (Thibodeau 1992). As food is pushed into the stomach and into the fundus, the cardiac sphincter closes behind it to prevent food from being reintroduced into the esophagus once stomach contractions begin. When the stomach contracts, food mixes with gastric juices and is broken down into chyme (Thibodeau 1992). These contractions, known as peristalsis, further propel food down the digestive tract. The stomach is lined with thousands of gastric glands that secrete gastric juice and hydrochloric acid; partial digestion occurs in the stomach and lasts approximately three hours (Thibodeau 1992). Partially digested food is then passed through the pyloric sphincter into the first portion of the small intestine to be further broken down.

The small intestine is covered with a mucosal wall. Intestinal glands within these walls secrete digestive juice — as opposed to gastric juice and hydrochloric acid — which helps to advance the digestive process (Thibodeau 1992). The small intestine is also covered with circular folds called plicae, which are covered with villi and microvilli. Villi and microvilli help to absorb nutrients as food passes through the digestive system (Thibodeau 1992). Most of the digestive process occurs in the duodenum, the first section of the small intestine. Two ducts within the duodenum empty pancreatic digestive juices and bile into the intestine to further aid in digestion. The pancreas secretes digestive enzymes and bicarbonate that neutralizes stomach acid (Farabee 2010).

The digestion of carbohydrates, proteins, and fats continues in the small intestine. "Starch and glycogen are broken down into maltose by small intestine enzyme…[while] proteases are enzymes secreted by the pancreas that continue the breakdown of protein into small peptide fragments and amino acids" (Farabee 2010). Bile, secreted by the gallbladder, emulsifies fats before they are acted upon by lipases; bile contains cholesterol, phospholipids, bilirubin, and a mixture of salts (Farabee 2010). The last two sections of the small intestine are the jejunum and the ileum. Solid wastes, from which most nutritionally useful products have been removed, are moved into the large intestine, where they are eventually expelled from the body via the rectum (University of Leicester 2001). It is at the ileum that nutrients can pass from the digestive system into the cardiovascular system (Thibodeau 1992).

Conclusion

Both the digestive system and cardiovascular system work in conjunction to introduce and disseminate nutrients and hormones, and to eliminate wastes from the human body. While food is introduced into the body through the mouth and processed, broken down, and passed into the cardiovascular system by the digestive system, it is the cardiovascular system that transports these nutrients, hormones, and other supplements throughout the body by pumping blood to and from the heart and to the rest of the body. Separately, the digestive system introduces and provides a steady flow of food to be broken down for energy and nutrients, while the cardiovascular system ensures that blood, hormones, and other nutrients are consistently delivered to all parts of the body. Furthermore, a healthy blood supply to the digestive system ensures that its cells remain strong and viable. Together, these two systems are essential to sustaining life and maintaining overall bodily health.