Unit 9 Project
Anatomy and Physiology II
Once again my mini-sub and I will be miniaturized (8 microns long) and witnessing another ‘Fantastic Voyage’ in a human body. This time I will be swallowed by George, a 55 years old man, while he is eating his meal consisting of a hamburger, French fries and a soda. I will pilot my mini-sub through George’s GI (gastrointestinal tract), which is the tube that starts with the mouth and proceeds to the esophagus, stomach, duodenum, small intestine, large intestine (or colon), rectum and, finally, the anus (Pansky, 2007). Along this pathway I will describe the digestion of George’s meal and the major structures that I will encounter. Arrived to the distal ileum I will divert my journey in to George’s bloodstream at the Superior Mesenteric Vein. I will keep going in to the Renal Artery through the hepatic portal vein, heart and lungs and once I will arrive to the kidney I will travel through George’s urinary tract until I will be able to leave his body via the urethra.
I never thought that one day I would be part of a meal and chewed up, but here I am mixed up with some bread and meat and broken down by George’s teeth. The first part of George’s meal digestion is happening right now in his oral cavity. The compound that George is chewing is a mix of proteins, carbohydrates, lipids and others components. I see floats of a clear fluid mixing with this compound coming from different angles, it is George’s saliva produced by glands such as: Parotid, Submandibular and Sublingual glands (Patton & Thibodeau, 2008). This liquid contains an enzyme called amylase which is breaking the longest molecule of glucose (polysaccharide) into smaller molecules (oligosaccharides); in other words I am assisting at the first mechanical and chemical digestion where teeth and saliva are breaking down food into a small bolus. From the mouth, the bolus and I are moving down into the pharynx and then into muscular tube made up of two layers of smooth muscles called the esophagus or food pipe. I am feeling like I am pushed down by a series of sequential squeezing or muscular contraction, these are definitely peristaltic waves which are leading the bolus and I through the esophageal sphincter or cardiac orifice (Patton & Thibodeau, 2008). This sphincter looks pretty strong and does not allow food to flow back up into the esophagus. I am now inside a muscular sac, is the stomach. The lining of the stomach is covered with millions of deep gastric pits which lead into the gastric glands that produce the stomach secretion called gastric juice. The stomach keep squeezing, churning and mixing the bolus with the gastric juice made up of stomach acids (hydrochloric acids) and enzymes like pepsin (Pansky, 2007). This place is continuing the demolition job begun in the mouth but seems like proteins are a target because the pepsin is breaking them down into smaller peptide chains. The bolus is changing into chyme and resembles now to a thick liquid. The chyme and I are now passing through another sphincter called the pyloric sphincter; we are entering into the duodenum which is the first part of the small intestine (jejunum and ileum are the other two), (Martini & Nath, 2008). The duodenum is C-shaped and about 25 cm. long; it has many fingers like projections called villi which are responsible for the absorption of nutrients. Between these villi I can see the Brunner’s glands important for the secretion of alkaline mucus able to protect the small intestine from the acidity of the chyme (Pansky, 2007). I can also notice that each villus contains, beside blood capillaries, a lymphatic vessel (lacteal) able to absorb lipids. Going towards the middle third part of the duodenum there are two openings, these are the minor and the major duodenal papillae where bile from the liver and pancreatic digestive fluid are released into the duodenum (Patton & Thibodeau, 2008)....