![]() ![]() The waste material travels on to the large intestine where water is absorbed and the drier waste material is compacted into feces it is stored until it is excreted through the anus. ![]() The smaller molecules are absorbed into the blood stream through the epithelial cells lining the walls of the small intestine. Further breakdown of food takes place in the small intestine where bile produced by the liver, and enzymes produced by the small intestine and the pancreas, continue the process of digestion. This acidity kills microorganisms, breaks down food tissues, and activates digestive enzymes. The stomach contents are extremely acidic, with a pH between 1.5 and 2.5. Using peristalsis, or wave-like smooth-muscle contractions, the muscles of the esophagus push the food toward the stomach. The food is then swallowed and enters the esophagus-a long tube that connects the mouth to the stomach. The enzymes present in saliva also begin to chemically break down food. The teeth play an important role in masticating (chewing) or physically breaking food into smaller particles. The process of digestion begins in the mouth with the intake of food. The rise in obesity and the resulting diseases like type 2 diabetes makes understanding the role of diet and nutrition in maintaining good health all the more important. Taking in more food energy than is used in activity leads to storage of the excess in the form of fat deposits. One of the challenges in human nutrition is maintaining a balance between food intake, storage, and energy expenditure. This happens by both physical means, such as chewing, and by chemical means. During digestion, food particles are broken down to smaller components, which are later absorbed by the body. The conversion of the food consumed to the nutrients required is a multistep process involving digestion and absorption. Animals must convert these macromolecules into the simple molecules required for maintaining cellular function. However, the food consumed consists of protein, fat, and complex carbohydrates. At the cellular level, the biological molecules necessary for animal function are amino acids, lipid molecules, nucleotides, and simple sugars. While plants can obtain nutrients from their roots and the energy molecules required for cellular function through the process of photosynthesis, animals obtain their nutrients by the consumption of other organisms. Describe how excess carbohydrates and energy are stored in the bodyĪll living organisms need nutrients to survive.Describe the essential nutrients required for cellular function that cannot be synthesized by the animal body.Describe the ways in which organs work together to digest food and absorb nutrients.Explain the specialized functions of the organs involved in processing food in the body.Explain the processes of digestion and absorption.Lymphatic organs contain lymphocytes that destroy invading organisms.By the end of this section, you will be able to: Lymph nodes and other lymphatic organs filter the lymph to remove microorganisms and other foreign particles. The third and probably most well known function of the lymphatic system is defense against invading microorganisms and disease. The lymph in the lacteals has a milky appearance due to its high fat content and is called chyle. The blood capillaries absorb most nutrients, but the fats and fat-soluble vitamins are absorbed by the lacteals. There are blood capillaries and special lymph capillaries, called lacteals, in the center of each villus. The mucosa that lines the small intestine is covered with fingerlike projections called villi. The second function of the lymphatic system is the absorption of fats and fat- soluble vitamins from the digestive system and the subsequent transport of these substances to the venous circulation. After the fluid enters the lymph capillaries, it is called lymph. Lymph capillaries pick up the excess interstitial fluid and proteins and return them to the venous blood. If this continues, blood volume and blood pressure decrease significantly and the volume of tissue fluid increases, which results in edema (swelling). This further inhibits the return of fluid into the capillaries, and fluid tends to accumulate in the tissue spaces. Small protein molecules may "leak" through the capillary wall and increase the osmotic pressure of the interstitial fluid. The 10 percent that does not return becomes part of the interstitial fluid that surrounds the tissue cells. Of the fluid that leaves the capillary, about 90 percent is returned. First of all, it returns excess interstitial fluid to the blood. The lymphatic system has three primary functions. Acknowledgements Introduction to the Lymphatic System ![]()
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