Journey Begins as We Enter

¶ … journey begins as we enter the human body through the mouth and are masticated by teeth as we are mixed with saliva that will help us move along our journey through the digestive system to the circulatory system, and finally our exit through the urinary system. Please note the different types of teeth present: as we move from the center of the mouth to the back not that there are two sets of incisors, a set of canines, the premolar and first and second molars.

The mucosal substance that surrounds us is salivary amylase. This mucosal coating allows for smooth passage through the esophagus into the stomach. Below us is located the tongue with the hard and soft palates located directly above. Before we descend into the pharynx, take a look at the uvula hanging from the soft palate. As we pass through the pharynx, we connect to the esophagus which will take us the rest of the way to the stomach.

The esophagus is approximately 10 inches long and will push us down through the upper abdominal cavity into the stomach. As we enter the stomach into the fundus, the cardiac sphincter will close behind us in order to prevent food from being reintroduced into the esophagus once the stomach contracts. As the stomach contracts, food mixes with gastric juices and is broken down into chyme. These stomach contractions, known as peristalsis, will propel us down the digestive tract.

The lining that covers the stomach walls contains thousands of gastric glands that secrete gastric juice and hydrochloric acid into the stomach. Partial digestion will occur as we are held in the stomach by the pyloric sphincter and before we descend into the small intestine.

We will rest in the stomach for approximately three hours before we continue our journey through the pyloric sphincter and into the first portion of the small intestine As we pass through the pyloric sphincter into the small intestine, note the similar mucosal membrane that covers the intestinal walls. The intestinal glands contained in the walls secrete intestinal digestive juice which will further aid in digestion. Also note the corrugated appearance of the intestinal lining. These circular folds are called plicae and are covered with villi.

Notice the small brush-like cells covering the villi? These are called microvilli. These microvilli and villi help to absorb nutrients as we pass through the digestive system. Most of the digestion on our tour will occur in the duodenum. As we pass through the duodenum you will notice two ducts that empty pancreatic digestive juices and bile into the intestine. As we approach the ileum and reach the end of the small intestine we will take a detour to the circulatory system through the kidney.

On this second part of our journey, we pass through the ileum lumen to the simple columnular cells of the villi to the villi's interstitial fluid. From here we will pass through to the ileum's capillaries to the venules and through the small and medium veins of the ileum to the superior mesenteric vein. The capillaries in the human body allow for the transportation and absorption of nutrients, oxygen, and waste through the blood via capillary walls.

The blood in which we are traveling in is composed of red blood cells called hemoglobin, plasma, platelets, and white blood cells. Blood is transported through the body by the heart's pumping action. As we continue, we will enter the hepatic portal vein, which delivers blood from the gastrointestinal tract to the liver, into the ascending aorta, up towards the heart.

As we approach the heart, it's pumping will pull us up into its chambers and through to the lungs where we will get oxygen and continue our journey to the kidneys. As we return to the heart, we will pass through the aortic arch and descend through the thoracic aorta continuing past the descending abdominal aorta until we reach the renal artery. We will make a left turn and pass through the glomeruli through the kidney's tubules and conclude this phase of our journey into the left kidney.

The last stage of our journey will take us through the kidney and into the urinary system where we will conclude our tour as we exit the human body. The human kidney is made up of the cortex, medulla, pyramids, papilla, renal pelvis, and calyces. In order to complete our journey, we must pass through a nephron back into the glomerulus. Each glomerulus is covered by the Bowman's capsule. Please note the high level of pressure present. This pressure is a necessary component of filtration in the kidneys.

The glomeruli and Bowman's capsule make up a renal corpuscle. Filtration begins when the blood flowing through the glomeruli exerts pressure pushing water and dissolved substances out of the glomeruli and into the Bowman's capsule and continues filtration through the glomerular-capsular membrane. This glomberular filtration usually occurs at a rate of 125 ml per minute. Water (reabsorbed through osmosis), sodium, glucose, and other nutrients are subsequently reabsorbed through tubules. Unwanted wastes and substances move into urine through the distal and collecting.