Anatomy and Physiology - Process of Digestion of a Meal - Assignment Example

Food is an essential source of energy on which our body works. The ingested food takes a route inside the body which consists of three steps digestion, absorption, and elimination. Digestion is the processing of ingested food inside our body. This processing takes place with the help of digestive system which is also referred as gastrointestinal tract (GIT). The entry of food inside our body is through oral cavity. Then, the sequential parts of the GIT are pharynx, esophagus, stomach and intestines. Then, for the defecation process the processed unwanted food enters into the rectum and expelled through anus. Various accessory organs like salivary glands, liver, pancreas and gall bladder also plays an important role in mechanical and chemical breakdown of food. The enzymes secreted from these accessory organs help in decomposition of food into necessary and easily absorbable nutrients. These nutrients are the source of energy for our body. The breakdown products of proteinacious food are amino acids, starches get converted to simple sugars, while fats breakdown into fatty acids and glycerol. The watery part in the food meets the requirement of needed body fluid. Rhythmic and efficient peristaltic movements of the muscular walls of GIT help to propel the food throughout GIT. When the food is ingested, both mechanical as well as chemical digestion starts in the first organ of GIT system i.e. mouth. Mechanical digestion is a process in which food is mechanically broken down into small pieces. Chemical digestion is a process of digestion of food with the help of various enzymes which the complex food is converted into simple water soluble and easily absorbable substances. The muscular ring called sphincter is present throughout the GIT, which aids in movement of food only in one direction, and also thus prevent the mixing of food from two different parts. The teeth inside the oral cavity help to chew the food by mechanical process called Mastication. The tongue helps for the movement of food inside oral cavity. Salivary gland secretions moisten the food. In addition to this they secrete amylase like enzyme (glycoprotein) which helps to process starch, complex carbohydrates type of food into simple absorbable sugars. For example plain baked potato primarily contains starch, and also broccoli contains some about of carbohydrates as mentioned later. These carbohydrates are converted into sugars like maltose and glucose. Maltose is broken down into glucose in the small intestine by maltase. These simple sugars can be absorbed through oral mucosa. The remaining food is passed onto pharynx and esophagus through swallowing process. The muscular tube of esophagus which is inside circular and outside longitudinal transports food components from mouth into stomach. Smooth muscles perform peristaltic contractions which squeeze food particles and help in forward movement of the food. The cardial orifice controls the movement of food from esophagus to fundus (superior) part of the stomach. The J shaped stomach is divided into four parts. The gastric glands are situated in the body (middle) part of the stomach. This is the place where the food is stored for short duration to get processed. Stomach wall has folds called rugae, which allows flexibility to stomach to stretch and expand when the food is inside. The peristaltic contraction of the muscles causes churning and mixing movements of bolus; which aids in mechanical breakdown of food particles. The gastric cells secrete acid and enzyme called pepsin, which breakdown protein part of food (protein of potato, steak and broccoli) into smaller amino acids. In this process a bolus is converted into a liquid mass termed as chyme. Steak mainly contains protein; therefore major digestion of this proteinacious type of food takes place in the stomach. Hydrochloric acid also kills germs and unwanted microbes in the food. Autodigestion of the stomach is prevented by a thick mucus layer that lines the stomach walls. Then, the food enters into pylorus (last) curved part of stomach. Then the contents of the stomach are emptied into the intestine where chemical digestion and absorption of nutrients takes place. The intestine is the largest organ of GIT and occupies major portion of the abdominal cavity. The chyme from the stomach enters into proximal duodenum (first part of small intestine) through the pyloric sphincter. The duodenum is responsible for complete digestion of partially digested food particles. The digestive juices or secretions from the accessory organs like pancreas and liver enter into duodenum at the Ampulla of Vater and are blended with the partially digested food contents in the duodenum. The enzymes from the pancreas and bile salts from the liver and gallbladder act on the food. Proteolytic enzymes like trypsin and chymotrypsin help in protein digestion in the steak which is not digested in the stomach by pepsin. Carbohydrases like amylase aids in carbohydrate digestion, and hydrolases like lipase assist in lipid digestion of steak into fatty acid, glycerol or cholesterol . Bile salts emulsify fat part of steak and aids in breakdown of fatty material. The small intestine is lined with numerous permanent folds of plicae circulares. Plicae have many finger like mucosal projections called villa. Each villus is lined by epithelium with small projections called microvilli. These microvilli forms brush border of the small intestine. The mucosal cells of the small intestine secrete enzymes to digest the food particles and also secrete mucous to protect intestinal lining. In the jejunum part (second part of small intestine) digested food is absorbed. This implies the proteins, fats, and carbohydrates part of food is converted to simple absorbable components and absorbed through mucosal components of microvilli (brush border) of small intestine. All these mucosal folds increase surface area of small intestine thereby increasing efficiency of intestinal wall for nutrient absorption. Thus, the completely digested food enters into blood stream at villi through capillaries. Small water soluble nutrients like Calcium, vitamin A, vitamin B (thiamin and riboflavin) are absorbed in upper part duodenum. While longer lipid soluble molecules like fats are absorbed by jejunum, and vitamin B12 is absorbed by ileum. Chelation reaction helps in amino acids and mineral absorption. The products of protein and carbohydrate digestion like amino acids and simple sugars respectively, in addition to vitamins, minerals and glycerol, short chain fatty acids are introduced into microscopic blood vessels (capillaries) at this point. The emulsified fatty material (fatty acids, cholesterol) is absorbed into the mucosal cells by passive transport mechanism and again large fatty molecules are formed. These digested fatty food components admits into blood circulation through Lymph vessels called lacteals which are present within the villi. These digested constituents transport to the one of the most vital organ, liver through hepatic portal vein. In this hepatic organ, detoxification process takes place with the help of liver cells called hepatocytes. The blood containing harmful substances such as alcohol and ammonia are filtered in liver. Glucose is utilized for energy. Fat is carried to storage depots to different organs and amino acids. Amino acids are transported to cells through circulatory system to build the walls and other parts of cells. Fat-soluble vitamins and surplus substances such as sugars are stored in hepatocytes for future use when extra energy is required. Glucose is stored in the form of glycogen. Thus, the absorbed nutrients are circulated to all the body organs through circulatory system. Fats and fat soluble vitamins of lymphatic system first enters into heart, followed by liver, and consequently are released by assimilation process to different parts for their functioning. The unabsorbed food enters into large intestine from ileum (last part of small intestine) at ileo-caecal valve. Large intestine is horse-shoe shaped and borders around the small intestine. The appendix, caecum, ascending, transverse, descending and sigmoid colon, and the rectum are the six parts of large intestine. The entered unabsorbed material in the caecum, gets compressed to make a small mass named as faecal material. This faecal matter then passed though colon. Colon walls have many pouches called haustra which are connected to three thick bands of muscle named taenia coli. At the bottom of the caecum, worm shaped appendix is present. Lymphoid tissue of the appendix blocks the pathogenic microorganisms that might have got entry into the digestive tract. The faecal matter is accumulated and stored in rectum part of large intestine. It is notable that large intestine does not bear villi like projections. Only intestinal glands are present on the flat mucosal surface. The mucous secreting goblet cells in the rectum lubricate solidified faecal matter. The water, salts, sugar and vitamins which might be present in the waste material is reabsorbed in large intestine. Then, the faecal matter enters into anorectal canal to the anus, and expelled at appropriate time. Reddish brown liver is situated in the upper part of the abdomen. Liver is a vital accessory organ of digestive system. The bile secretion of liver enters into intestine. The bile salts secreted by liver cells are responsible for mechanical digestion of fatty food like steak. Bile salts emulsifies lipids in steak and breakdown into smaller particles (fatty acids and glycerol) to increase surface area so that enzymes can readily act on them. This versatile organ plays an important role in the metabolism of nutrients, detoxification of metabolites, breakdown of bilirubin and estrogen, and production of albumin and blood clotting factors. The pear shaped gall bladder helps to store and concentrate bile produced by liver. It is released by muscular contraction in response to hormones produced due to food filled duodenum. Pinkish Pancreas which is situated behind the stomach has exocrine and endocrine functions. The Islets of Langerhans in Pancreas produce insulin, glucagon and other substances (endocrine function) which help to maintain blood sugar level. The numerous acini (small glands) of Pancreas secrete Pancreatic enzymes consisting of carbohydrases, lipases, nucleases and proteolytic enzymes in an inactive form. When these inactive enzymes enter into food filled duodenum, they become active. These enzymes aids in digestion and breaking down of all type of food and conevert into small building blocks. The mucosa of the stomach and small intestine releases regulatory hormones like gastrin, secretin, and cholecystokinin (CCK). These digestive hormones circulates from GIT to heart and again back to GIT. In GIT they stimulate digestive secretions and allows the organs to function properly. Gastrin stimulates the production of acid which plays vital role in digestion and antimicrobial activity. It also provides normal growth of the lining of the stomach, small intestine, and colon. Secretin plays crucial role in production of digestive chemicals in pancreas, stomach and liver. Secretin stimulates production of pancreatic enzymes with significant amount of bicarbonate, pepsin in the stomach and bile in the liver. CCK aids in growth and formation of pancreas and pancreatic enzymes respectively. CCK also functions in emptying of gall bladder. The major nutrients are carbohydrates, proteins, fats, vitamin, minerals and water. Carbohydrates and proteins supply energy (4 calories per gram). Carbohydrates also provide fiber. Proteins assist in building and repairing body tissues, and fighting against infection. Fats supplies 9 calories per gram and are carrier of oil soluble vitamins like A, D, E, and K. Vitamins keep GIT healthy and extract energy from food. Vitamin C (Ascorbic Acid) plays important role to strengthen blood vessels, healing of wounds and bones. Thiamin (B1) and Niacin (B3) maintains nerves healthy. Vitamin A helps to maintain well being of eyes. Vitamin D absorbs calcium and is vital for strong bones and teeth. Vitamin E supports the involuntary nervous system, vascular system, and involuntary muscles. Vitamin K is crucial in blood clot formation. Folate supports formation of erythrocytes and decreases the neural tube birth defects. Biotin helps to decompose the food items. Pantothenic Acid aids in the metabolism of fat. Biotin aids in the formation of cholesterol and hormones. Cyanocobalamin (B12) helps in the development of normal growth. Minerals like Calcium, Manganese and Phosphorus are needed for bone rigidity and blood clotting. Magnesium plays role in temperature regulation, muscle contractions. Sodium, Chloride, Potassium control the flow of fluids in the body, the nervous system and muscle function. Iron & Copper helps in hemoglobin formation. Zinc aids in the formation of body protein. Selenium protect cell damage. Chromium controls glucose uptake into cells. Iodine helps in thyroxine production. Fluoride protects decaying of tooth. Nutrients Steak 100 g of pork steal contains 30.1 grams protein and 6.7 grams fat, 86 grams of cholesterol. Minerals: Potassium - 320 mg, Phosphorus - 198 mg, Calcium - 15 mg, Sodium - 64 mg Magnesium - 18.7 mg, Iron - 1.1 mg, and contains small amounts of selenium, manganese, copper and zinc. Vitamins: Vitamin A, Vitamin E, Vitamin K, Vitamin B1-B6, Pantothenic Acid, Folate and contains some other vitamins in small amounts. (Mikibo, 2006) Broccoli Half cup cooked with no added salt contains 2.3 grams protein and 2.3 grams fiber. Minerals: Potassium - 228 mg, Phosphorus - 46 mg, Calcium - 36 mg, Sodium - 28 mg Magnesium - 18.7 mg, Iron - .65 mg, Vitamin K - 110 mcg, and contains small amounts of selenium, manganese, copper and zinc. Vitamins: Vitamin A - 1083 IU, Vitamin C - 58 mg, Niacin - .45 mg, Pantothenic Acid - .4 mg, Folate - 39 mcg, and contains some other vitamins in small amounts. Plain baked potato One medium baked potato without salt contains 3.0 grams of protein and 2.3 grams of fiber. Minerals: Potassium - 610 mg, Phosphorus - 78 mg, Magnesium - 39 mg, Calcium - 7.8 mg, Sodium - 7.8 mg, Iron - .55 mg, Selenium - .46 mg, Zinc - .45 mg, and contains small amounts of manganese and copper. Vitamins: Vitamin C - 20 mg, Niacin - 2.18 mg, Pantothenic Acid - .9 mg, Vitamin B6 - .5 mg, Folate - 14 mcg, and contains some other vitamins in small amounts. References http://www.virtualmedicalcentre.com/anatomy.asp?sid=7. It is a snapshot of the page as it appeared on 2 Mar 2009. Lippincott Williams & Wilkins, Elizabeth Rosto. 2008. Pathophysiology Made Incredibly Easy!, Springhouse Publishing Company Staff, Edition: 4, illustrated, revised Published by Lippincott Williams & Wilkins, 2008. Decuypere, J. (2009). Dr. Decuyperes Nutrient Charts™ Vegetables Chart http://www.healthalternatives2000.com/vegetables-nutrition-chart.html. (Mikibo, 2006). http://www.mikibo.com/nutrients/meat-poultry-game/food.php?f=Pork,%20steak (ADAM, 2009) http://www.besthealth.com/besthealth/bodyguide/reftext/html/dige_sys_fin.html. http://www.zhion.com/Diseases/major_nutrients.html] http://www.chemistrydaily.com/chemistry/Gastrointestinal_tract. Kirschmann, John D. (2006). Nutrition Almanac, Inc Nutrition Search Edition: 6, illustrated, Published by McGraw-Hill Professional. Read More