Digestion Notes PDF

Digestion ٢ The food we eat needs to be broken down into simpler substances which the body can utilize. This is accomplished by the process of digestion. Complex substances such as carbohydrates, proteins and fats are broken...

Digestion ٢ The food we eat needs to be broken down into simpler substances which the body can utilize. This is accomplished by the process of digestion. Complex substances such as carbohydrates, proteins and fats are broken down into simpler forms by the mechanical action of the teeth and chemical action of various enzymes in the digestive system. ٢ Digestion ٣ Water , minerals , vitamins can be absorbed directly without undergoing any change. Glucose needs no further break down and is immediately absorbed giving instant energy. Both digestion and absorption take place in the digestive tract in the body. ٣ The digestive tract or alimentary canal ٤ in humans comprises the: 1- Mouth. 2- Oesophagus. 7- Caecum. 3- Stomach. 8- Colon. Large intestine 4- Duodenum. 9- Rectum. 5- Jejunum. Small intestine 10- Anus. 6- Ileum. ٤ Digestion ٥ The liver and pancreas are not a part of the digestive tract, but provide vital secretions, namely, bile and pancreatic juice, respectively which aid in the digestion of food. Digestive juices are also secreted by all parts of the digestive tract except the esophagus, rectum, and anus. These juices contain chemical substances called enzymes, which act as catalysts in the breakdown of nutrients. ٥ Digestion of Food ٧ 1- Mouth: The process of digestion begins in the mouth. Food is mechanically broken down by the teeth by chewing and is moistened with saliva produced by salivary glands in the mouth. Saliva contains an enzyme Amylase or Ptyalin which breaks down starch to smaller units into Maltose. ٧ Digestion of Food ٨ 2- Oesophagus: Food passes from the mouth into the stomach through a tube called the oesophagus or food pipe. No digestion takes place in oesophagus. ٨ Digestion of Food ٩ 3- Stomach: In the stomach the food is mixed with gastric juice which contains-Hydrochloric acid (HCL), enzymes such as Pepsin. The stomach muscles contract and churn the food to a liquid consistency called chyme. The enzyme pepsin acts on proteins and enzyme lipase has some effect on emulsified fats. ٩ The action of acidic nature of gastric juice ١٠ making: Destroys harmful bacteria which may be present in food. Activates enzyme pepsin. Swells proteins so that enzymes can easily act on them. Aids in the absorption of calcium and iron. ١٠ Digestion of Food ١١ 4- Small intestine: Maximum digestion of proteins, carbohydrates and fats takes place in the small intestine. Bile which is produced by the liver and stored in the gall bladder is needed for digestion of fat. The small intestine secretes intestinal enzymes and the pancreas secretes pancreatic juice and completes the digestion of proteins, carbohydrates, and fats into amino acids, mono saccharides, and glycerol and fatty acids, respectively. These simple substances are absorbed through the walls of the small intestine into the bloodstream. ١١ Digestion of Food ١٢ 5- Large intestine: Water and digestive juices are reabsorbed in the large intestine giving the intestinal contents a solid consistency. The unabsorbed material is called faeces and it contains small amounts of undigested food mainly fiber, bile salts, cholesterol, mucous, bacteria, and broken down cells. It is excreted via the anus. ١٢ Factors that Affect Digestion ١٣ 1- Consistency, Division and Type of food: Food that are of liquid or well chewed, easily to be digested than solid or which in big size. 2- Bacterial action: Helps in breaking down food and is desirable. 3- Chemical factors: Strong acids, spices, caffeine, and meat extracts stimulate the flow of gastric juice. Fats slow down the flow of gastric juice. ١٣ Factors that Affect Digestion ١٤ 4- Psychological factors: Anger, fright and worry slow down the secretion of gastric juices. The sight, smell and aroma increase saliva and gastric juices. Carbohydrates are digested fastest. A mixture of carbohydrates, proteins and fats gives satiety and remains in the digestive system for a longer time. ١٤ Indigestion and other digestive disorders ١٦ Bad eating habits like over consumption of refined carbohydrates, or lack of dietary fiber can cause constipation, indigestion or can lead to certain specific digestion related conditions such as and Irritable Bowel Syndrome (IBS), or nutritional deficiencies. Lastly ingested food toxins can cause a number of unpleasant digestive complaints or even food poisoning. ١٦ Indigestion ١٧ Do you suffer from indigestion? While the terms “heartburn” and “indigestion” have no medical definition there is usually a medical reason. The most common have no medical reason for these symptoms is a condition known as gastro esophageal reflux (GER) sometimes called gastro esophageal reflux disease (GERD). Reflux happens when the muscle between the stomach and the esophagus fails to contract enough to keep food and digestive juices in the stomach. ١٧ Indigestion ١٨ If you experience pain in the middle of your abdomen or just below your breast bone shortly after eating, wake up with this pain during the night, or have periodic episodes of unexplained asthma. Besides medications that lessen the amount of stomach acid you produce and help the stomach empty faster here are some self –help measures you can try to lessen the regurgitation of acid and foods back up into your esophagus after eating: ١٨ Measures to lessen the regurgitation: ١٩ 1. Eat small frequent meals, or mini meals rather than three large meals a day. 2. Take small bites and chew your food well. Smaller food particles empty faster from the stomach. 3. Eat foods that pass through your stomach quickly primarily proteins and carbohydrates rather than foods that linger in the stomach a while such as high fat foods. ١٩ Measures to lessen the regurgitation: ٢٠ 4. Remain upright and quiet for 30 minutes after eating. Moving around jostles the acid in your stomach aggravating the condition. 5. Don’t go to bed with a full stomach. Eat dinner earlier in the evening and keep it low fat. Remember, don’t dine after nine. 6. Relax. Stress produces stomach acid. ٢٠ Absorption ٢٢ Absorption is the process in which the end products of digestion of nutrients are transferred from the intestine into the blood and lymph circulation. The wall of the small intestine is made up of 4 to 5 million folds or finger like (Villi). Each villus has blood vessels and lymph vessels. The presence of villi increases the total area from which absorption can take place. Most nutrients are absorbed in the duodenum and jejunum and remaining in the ileum. ٢٢ Absorption ٢٣ Nutrients are absorbed across the epithelial cell walls lining of each villi by two methods: 1. Passive diffusions – movement of water and minerals from an area of higher concentration to an area of lower concentration. Sometimes a carrier is required to help ferry water soluble nutrients across a cell membrane with fat like material. 2. Most nutrients are absorbed by active transport from an area of lower concentration to an area of higher concentration. Active transport requires energy for transportation. ٢٣ Absorption ٢٤ The nutrients absorbed into lymph are: o Fatty acids, some molecules of fat and fat soluble vitamins. Glucose, amino acids, water soluble vitamins and minerals are transported by the portal circulation to the liver. ٢٤ Metabolism ٢٥ From the blood stream, nutrients are supplied to all the cells in the body where each nutrient performs its specific functions. It is either oxidized to release energy (catabolism), or it is used in the synthesis of complex substances (anabolism). ٢٥ Metabolism ٢٦ 1) Anabolism - is the term used for all chemical reactions in which simple substances are used to synthesis more complex substances, amino acids are used for specific protein synthesis (building tissues). 2) Catabolism - is the term used for all chemical reactions in which complex substances are further broken down to simpler compounds glucose is oxidized to produce carbon dioxide (Co2), water , and energy (release of energy). ٢٦ Metabolism ٢٧ Glucose and fats are stored as potential energy in form of adipose tissue. Amino acids are used for synthesis of new cells, enzymes and hormones. Minerals and Vitamins carry out regulatory functions. The waste products of digestion, absorption, and metabolism are excreted by the bowels, kidneys, skin and lungs. ٢٧