The digestive system consists of many different organs that digest food to create energy for the human body. The first stage of digestion begins with the mouth. Food is first taken in through the mouth. The mouth contains different type of teeth, which help break up the food. We have teeth that cut ant rip food such as carnivores and teeth that are flat, which grind food like herbivores. Within the mouth, the tongue helps mix the food with saliva. Three pairs of salivary glands secrete saliva into the mouth. Saliva contains amylase, which starts to break down the starch in the food into free sugars. The saliva also lubricates and moistens the food so it can be swallowed and travel down the esophagus with little resistance. The esophagus is a tube that connects the mouth to the stomach. The lower two-thirds of the esophagus is wrapped in smooth muscle, which cause peristalsis, rhythmic waves of muscular contractions that move the food to the stomach. The bottom of the esophagus has a muscular ring called a sphincter that closes the esophagus from the stomach and prevents acids to flow up the esophagus. The first major organ of digestion is the stomach. The main functions of the stomach are temporary storing the food, mechanical breakdown of the food and the unraveling of proteins. The stomach collects ingested food, digests some of the proteins, and sends its contents to the primary digestive organ, the small intestines, in a controlled fashion. The stomach pepsinogen into pepsin ensures that the pepsin won't attack the cells of the gastric pit. The HCl unfolds proteins and the pepsin then creates several long fragments, so the protein can't reform into its original shape after the acid is neutralized in the small intestines. The hormone gastrin regulates the release of HCl, so that there is not too much acid in the stomach, which could cause an ulcer. The primary organ of digestion is the small intestines. The small intestines, which are about 6 meters long, break down large molecules into smaller ones. Only small portions of food are introduced into the small intestines from the stomach so that the acid can be neutralized and the enzymes can act. The main enzymes are secreted from the pancreas. The pancreas secretes digestive enzymes, to break down fats, carbohydrates, and proteins, bicarbonate, to neutralize the acid, and insulin, to regulate the level of glucose in the blood. Most of the energy absorbed for the body is from fats. The liver makes bile salts the break down the fats so that they can be absorbed. The ileum of the small intestines is where most of the water and products of digestion are absorbed into the bloodstream. The lining of the ileum is covered with villi and microvilli, which greatly help in absorption process. The large intestines absorb some water, sodium and vitamin K, but the main purpose of it is to act as a refuse dump. Many bacteria live in the large intestines and play a role in the processing of undigested material into the final excretory product, feces. The rectum is a short extension of the large intestines, which compact the solids. The anus is where the solid material passes out of the body.
Bibliography
None
Word Count: 544
字串2
|
|
|
|
