Friday, October 22, 1999

Structure and Function of the Human Body week 10

Answer each of the questions below using information gathered from your readings, lectures, and outside research. You should provide at least a paragraph response for each of the questions.
1. Describe the role of the following organs within the digestive system: stomach, liver, salivary glands, small intestine and gallbladder. Also, describe what complications could occur within the functions of the digestive system if each listed organ was damaged or dysfunctional.

Our digestive system provides the body a means to transfer nutrition from the external environment into the cellular level in order to sustain life.

Salivary glands, controlled by the autonomic nervous system, is located in the oral cavity. It's main role is to secrete saliva in the oral cavity. There are three pairs of salivary glands. Parotoid savary gland lies under the skin on each side of the mandible. These glands secrete amylase, an enzyme that breaks down starches. The parotoid duct implies empties into the vestibile at the level of the second upper molar. The sublingual duct is (located under the tongue) between the mucus membrane of the floor of the mouth and the submandibular duct is located in the floor of the mouth. Both the sublingual and submandibular glands secrete saliva that contains more buffers and mucus. (p. 539-40)

Saliva (mucus) consists of 99.4% water, mucins and an assortments ions, buffers, and waste products and enzymes. The mucines absorbs water and form the mucus. During meal time, the saliva lubricates the mouth along with dissolved chemicals that stimulates the taste buds. The mucus coats the food, and reduces friction making swallowing easier. The continuous flow of saliva also flushes and cleans the oral surfaces while controlling oral bacteria through salivary antibodies (IgA and lysozyme). The pH of saliva during meal time raises from slightly acidic (pH 6.7) to more alkaline (pH 7.5).

Radiation and emotional distress can cause a reduction of salivary secretions. This then can create an unhealthy oral cavity environment due to increased bacteria population. Over time, the complications caused by the decreased salivary secretions are infection and erosion of the teeth and gums. (p.540)

The stomach is another component of the digestive system which is located within the left upper quadrant of the abdominal cavity. It is a muscular J-shaped organ that is positioned inferior of the esophagus and superior to the small intestines. There are four primary functions the stomach has to offer. First, it becomes a temporary storage for ingested food. Food is stored in the stomach while it is physically broken down for chemical digestion. Second, it provides a mechanical means to break down ingested food. The stomach is an area where there is a lot of mixing of the food, so added strength to the muscularis external layer is needed. Instead of two layers in the muscular external, the stomach's has three layers, a longitudinal layer, a circular layer, and an inner oblique layer. Thirdly, it provides an acidic environment that causes a break down of the chemical bonds in food through the actions of acids and enzymes. The pH of 2.0 in the stomach makes the environment acidic. The ingested foods, mixed with stomach's secretion, produces an acidic soupy mixture of partially digested food called chyme. Lastly, the stomach is responsible for the production of the intrinsic factor, a compound necessary for the absorption of vitamin B-12. (p.544)

Gastric ulcers is one complication that can occur in the stomach. Ulcers are caused either bacterium Helicobacter pylori or by medication such as aspirin that irritates the mucus membrane. This irritation causes erosion of the mucus membrane; which either creates an excessive production of acid or an inadequate production of alkaline mucus that defends the epithelium against the acid. Treatment can lean toward a medication such as cimetidine, a drug that inhibits acidity in the stomach, or it can be treated with antibiotics for bacterial infection depending on the cause. Meal time still would include a complete diet, but staying away from high fat, high acidic foods like tomatoes, and spicy foods. In atropic gastritis, there is chronic inflammation in the stomach which produces a lower acid production capability. When this happens, the intrinsic factor is affected , trapping vitamin B12 within the food. People in this case would need to take a vitamin B12 supplement.

The small intestines main function is in the digestion and absorption of nutrients. Ninety percent of nutrient absorption occurs in the small intestine. The duodenum is the segment in the small intestine that receives chyme from the stomach and digestion secretions from the pancreas. It also contains duodenal glands which secrete alkaline mucus that helps buffer acids in the chyme. The bulk of chemical digestion and nutrient absorption occurs in the jejunum. The small intestines receives and raises the pH of the materials arriving from the stomach. Most of the important digestive processes are completed in the small intestine where the final products of digestion (simple sugars, fatty acids, amino acids) are absorb along with most of the water contents. (p. 548)

Crohn's disease is one complication found in the small intestine. It is a chronic auto-immune inflammatory disorder that occurs in intervals active (flares) disease altering in periods of remission . Treatment varies from special diets, medication like Cortisone and surgery (possible ileostomy). Crohn's disease is not curable. Treatment only covers the symptoms caused by the disease progression. Over time, the inflammation of the small intestine can result in scaring and thickening of the walls of the affected structure. With this disease, absorption of nutrition can lead to difficulties. The inflammation causes damages to the lining of the intestine so that it cannot absorb nutrients, water, and fats from the food eatened. This can result in malnutrition, dehydration, vitamin and mineral deficiencies. (emedicinehealth, 2011)

The liver is an essential part to the digestive process. The liver has three functional roles: metabolic regulation, hematological, and bile production. The basic functional unit of the liver is its 100,00 lobules. Within each lobule there are liver cells called hepatocytes .
In metabolic regulation, the liver's main goal is to regulate the composition of the circulating blood. It does this through the hepatocytes. The hepatocytes extract and absorbed nutrients or toxins from the blood prior to reaching the general circulation. Hepatocytes also monitors/adjusts the circulating levels of organic nutrients. Excesses are removed and stored; while deficiencies are corrected by utilizing stored reserves or synthesizing the necessary compounds. Toxin and metabolic wastes are removes for later inactivation and excretion. Fat-cell vitamins such as A,D,K, and E are absorbed and stored. ( p.555-6)

With hematological regulation, the liver becomes the blood reservoir. As the blood passes through the liver, phagocytes (kupffer ) cells remove spent/or damaged RBCs, debris, and pathogens from the circulation. The hepatocytes synthesizes plasma proteins ( which determines blood's osmotic concentration), transports nutrients, and makeup the clotting and complement systems. ( p.556)

The bile production is derived from the hepatocyte secretions. Bile may either flow into the common bile duct, which empties into the duodenum, or enters into the cystic duct, which leads into the gallbladder. Bile consist of water, ions, bilirubin (pigment from hemoglobin), cholesterol, and bile salts (an assortment of lipids). The bile's water and ions dilute and buffer acids in chyme as it enter the small intestine. The bile salts (synthesized from cholesterol) are required for normal digestion and absorption of fats. Bile breaks down large lipid droplets into smaller lipid particles in order for the digestive enzymes to become more effective. ( p.556)

After revealing the main functions the liver provides, any condition that can damage or make the liver dysfunctional can be life threating to the body. One example is hepatitis which is an inflammation of the liver producing swelling in the liver. There are many virus that can cause hepatitis depending in how it is transmitted, but the main ones are A, B, and C. If left untreated, in some cases hepatitis can lead to cirrhosis which is a progressive degenerate disease that results in the loss of organ/tissue function due to scar tissue. Further progression of the disease could eventually lead to liver failure. Unlike a healthy liver, the liver would not be able fight infection, clean the blood and help digest food and store energy; thus, leaving the body, toxic.

The gallbladder is a hollow pear-shape organ that stores and concentrates bile made in the liver. Bile is secreted continuously (approx1 liter/day); however, it is only release into the common duct to the duodenum when fatty foods enters the digestive tract and through the stimulation of a duodenum's hormone CCK (cholecystokinin). The CCK stimulates contractions in the walls of the gallbladder, releasing the bile into the small intestine. In the absence of CCK, bile leaving the liver through the common duct is redirected into the cystic duct delivering bile into the gallbladder for storage.
The concentration of bile changes its composition while in the gallbladder's storage. Water is absorbed and the bile salts along with other bile components become increasing concentrated. Sometimes bile salts become too concentrated through stasis (due to no-fat diet) or infection which alters the ratio of bile salts and water content, forming gallstones. ( pg.550, 556-7)

Gallstones can be a complication of the gallbladder. Gallstones can develop when bile contains too much cholesterol, too much bilirubin, or not enough bile salts, or when the gallbladder does not completely empty or emptied enough. Most people are unaware they have a problem. If a person is asymptomatic, no treatment necessary. Only those with sever discomfort or repeated attacks from gallstones receive treatment. This usually requires surgery for removal of the gallbladder (cholecystectomy). People can live without their gallbladder because bile is made continuously and the gallbladder is just a reservoir for bile. If any change in life style it would be in diet (low-fat) and frequently of meals. (, ) ( p.557)

Explain how the small intestine’s anatomy is geared to increase surface area. Why is increased surface area important in the small intestine?

The length of the small intestine is approximately 20 feet long. The intestinal lining consist of transverse folds (plicae circulares) composed of multitude of finger like projections called villi.
These structures are covered with simple columnar epithelium that are covered with microvilli, in other words the epithelium looks like bristles on a hair brush. If the small intestine was smooth and simple , the total absorption area would be about 3.6 feet long. Instead, the small intestine is composed of multiple arrangement of the intestinal wall, which consist of plicae circulares layered with villi; villi is layered with epithelium; epithelium that is layered with microvilli; thus makes the total increase absorption area approximately 2,200 feet.

3. Describe the role of each of the four layers in the stomach including the mucus cells and parietal cells of the mucosa layer.

The four layers of the stomach are the mucosa layer, submucosa layer, muscularis externa, and serosa layer.
The mucosa layer of the stomach is the inner lining consisting of mucosal (glandular secreted) membrane that is composed of simple columnar epithelium dominated by mucus cells. The role of these mucus cells this is to secrete alkaline mucus that covers and protects epithelial cells from acids, enzymes, and abrasive material. Gastric pits are shallow depressions open onto the gastric surface. The mucus cells at the base of each gastric pit divide and replace the superficial cells of the mucus epithelium which is then shed into the chyme. The gastric pit corresponds with the gastric glands which secrete the gastric juice. The cells that produce the components of the gastric juice as the parietal cells. The parietal cells secrete the intrinsic factor and hydrochloric acid. The intrinsic factor is needed to facilitate the absorption of Vitamin B-12 across the intestinal lining. The hydrochloric acid lowers the pH of the gastric juices which keeps the stomach pH contents at approximately 2. The acidity of the stomach kills micro organisms, helps break down plant cell walls, and connective tissues in meat and also activates the enzyme secretions of the chief cells. The main purpose of chief cells is the production of the enzyme pepin (a protein digesting enzyme) Within both the mucosa and sub-mucus are distinct ridges or folds called rugae. The folds increase the surface area for absorption and permits expansion (flattens out) for food. Ducts between the rugae opens onto the epithelial surface and carries the gastric glands that secrete digestive juices.

The sub-mucosa layer is the second layer that is composed loose connecting tissue which contain large blood vessels, lymphatic vessels, and nerve fibers( sensory neurons and parasympathetic motor neurons). Its main role is in controlling and coordinating contraction of the smooth muscle layers and in regulating secretion.
Muscularis externa makes up the third layer of the stomach. This layer consist of bands of smooth muscle cells which contains a longitudinal layer, a circular layer, and an inner oblique layer. These three portions of the muscularis externa provides strength and assists in the mixing and churning essential to forming chyme.

The serosa layer (visceral peritoneum) covers the outer surface of the stomach. It has no role except to stabilize the stomach in the peritoneal cavity.

4. We discussed the endocrine role of the pancreas when we studied the endocrine system but it has an exocrine role within the digestive system. Please explain what type of dysfunction would occur if the pancreas didn’t secrete its pancreatic juices. What type of dysfunction would occur if someone had to have their gallbladder removed?

The pancreas is primary an exocrine organ that produces digestive buffers and enzymes. The four enzymes: carbohydrases (digest surgars and starches), lipases (break down lipids), nucleases (break down nucleic acids), and proteases (break protein apart). Specific enzymes are the pancreatic amylase (breaks down carbohydrates), pancreatic lipase (group of nucleases and several proteases), and trypsin and chymotrypsin are all part of the proteases enzymes Proteases accounts for 70% of the enzyme production. The main buffer is sodium bicarbonate which increases the pH of the chyme. (pg 552-553)

If the pancreas becomes dysfunctional, these pancreatic and enzymes would be missing in the duodemum. Inadequate digestion would take place. Your sugars, starches, fats, and proteins would be incompletely digested, because of the missing enzymes. In pancreatitis, inflammation occurs from blockage of excretory ducts, bacterial infection, or drug reaction (alcohol), This can cause injury in the exocrine cells. The lysosomes within the damaged cells then activated the pancreatic enzyme which attack the normal pancreatic cells and there is a chain reaction which produces destruction. In most cases, with treatment, this can be reversed/stopped. However, there are a few cases where this auto-digestion continues and destroys the organ. In that case, two conditions result: diabetes mellitus that requires insulin and nutrient malabsorption where oral pancreatic enzymes need to be taken. (pg 563)

In the case of the gallbladder, people can live without their gallbladder, because the only function of the gallbladder is a reservoir for bile from the liver. Bile will continue the flow into the small intestines without a problem. It might be a little more or less depending on the food quantity and substance.

5. What is the importance of adenosine triphosphate (ATP)? Carbohydrate metabolism is our body’s main source of ATP production. Explain where carbohydrate metabolism occurs in the cell, what additional “ingredient” is needed and what waste product is produced in this process.
The primary function of ATP is the transfer energy from one location to another, not the long term storage of energy. The energy a cell produces in the form of ATP supports cell growth division, contraction, secretion, and all functions that vary from cell to cell and tissue to tissue. Cells in the body generate most ATP through aerobic (oxygen-required) metabolism in the mitochondria ;however,the initial steps occur through glycolysis (anaerobic -with out oxygen) in the cystosol of the cytoplasm. Oxygen is the key ingredient needed in mitochondria energy production. Aerobic (oxygen) metabolism in the mitochondria provide most (95%) of the energy needed to keep cells alive. Most of the energy deriving from carbohydrates are produced in the mitochondria. Energy is stored and transferred in a high energy bond of ATP in order to move from place to place. The by-product of areobic metabolism is carbon dioxide. Glycolysis involves enzymatic steps that breakdown glucose to pyruvic acid molecules. These molecules are then absorbed by the mitochondria. Glycolysis (anarobic) can also continue to provide ATP when the oxygen availability is limited for mitochondrial production. This usually occurs during the body's peak activity, such in the case of a long distance runner. The body cannot provide enough O2 to maintain the metabolism in the metochondria. This the time where glycolysis becomes the prime source for ATP. (p.77, 210, 577)