explan the process of digestion answers
Answers
The processes of digestion include six activities: ingestion, propulsion, mechanical or physical digestion, chemical digestion, absorption, and defecation.
The first of these processes, ingestion, refers to the entry of food into the alimentary canal through the mouth. There, the food is chewed and mixed with saliva, which contains enzymes that begin breaking down the carbohydrates in the food plus some lipid digestion via lingual lipase. Chewing increases the surface area of the food and allows an appropriately sized bolus to be produced.
This image shows the peristaltic movement of food. In the left image, the food bolus is towards the top of the esophagus and arrows pointing downward show the direction of movement of the peristaltic wave. In the center image, the food bolus and the wave movement are closer to the center of the esophagus and in the right image, the bolus and the wave are close to the bottom end of the esophagus.
Figure 1. Peristalsis moves food through the digestive tract with alternating waves of muscle contraction and relaxation.
Food leaves the mouth when the tongue and pharyngeal muscles propel it into the esophagus. This act of swallowing, the last voluntary act until defecation, is an example of propulsion, which refers to the movement of food through the digestive tract. It includes both the voluntary process of swallowing and the involuntary process of peristalsis. Peristalsis consists of sequential, alternating waves of contraction and relaxation of alimentary wall smooth muscles, which act to propel food along (Figure 1). These waves also play a role in mixing food with digestive juices. Peristalsis is so powerful that foods and liquids you swallow enter your stomach even if you are standing on your head.
Digestion includes both mechanical and chemical processes. Mechanical digestion is a purely physical process that does not change the chemical nature of the food. Instead, it makes the food smaller to increase both surface area and mobility. It includes mastication, or chewing, as well as tongue movements that help break food into smaller bits and mix food with saliva. Although there may be a tendency to think that mechanical digestion is limited to the first steps of the digestive process, it occurs after the food leaves the mouth, as well. The mechanical churning of food in the stomach serves to further break it apart and expose more of its surface area to digestive juices, creating an acidic “soup” called chyme. Segmentation, which occurs mainly in the small intestine, consists of localized contractions of circular muscle of the muscularis layer of the alimentary canal. These contractions isolate small sections of the intestine, moving their contents back and forth while continuously subdividing, breaking up, and mixing the contents. By moving food back and forth in the intestinal lumen, segmentation mixes food with digestive juices and facilitates absorption.
In chemical digestion, starting in the mouth, digestive secretions break down complex food molecules into their chemical building blocks (for example, proteins into separate amino acids). These secretions vary in composition, but typically contain water, various enzymes, acids, and salts. The process is completed in the small intestine.
Food that has been broken down is of no value to the body unless it enters the bloodstream and its nutrients are put to work. This occurs through the process of absorption, which takes place primarily within the small intestine. There, most nutrients are absorbed from the lumen of the alimentary canal into the bloodstream through the epithelial cells that make up the mucosa. Lipids are absorbed into lacteals and are transported via the lymphatic vessels to the bloodstream (the subclavian veins near the heart). The details of these processes will be discussed later.
In defecation, the final step in digestion, undigested materials are removed from the body as feces.
Answer:
Explanation:
Digestion: Digestion is the process by which food is broken down into simple absorb able substances. Digestion of food takes place in the digestive system. Digestive system is made up of alimentary canal and associated glands.
Parts of alimentary canal:
The mouth, esophagus, stomach, small intestine and large intestine form the alimentary canal. It is also known as the digestive tract.
Mouth is guarded by upper lip and lower lip. The process of taking in food through mouth is called as ingestion.
Buccal cavity is the inner region of the mouth. It encloses teeth and tongue.
Teeth are of different types namely, incisors, canines, premolars and molars.
Incisors are used for biting food.
Canines are sharp and pointed and are used to pierce or tear food.
Premolars and molars are the principal grinders helping to chew and grind the food.
Tongue is a muscular organ attached to the floor of the buccal cavity at the back. It helps in mixing of food with saliva and swallowing it. It also helps in tasting different types of food with the help of taste buds present on it. The buccal cavity leads into pharynx.
Pharynx is at the back of buccal cavity. The pharynx is the common channel for food and air. When you swallow food, a flap-like valve called the epiglottis closes the windpipe. It prevents the entry of food particles into respiratory tract.
Esophagus also called as food pipe helps in conveying the food from buccal cavity to stomach. The esophagus is also known as the gullet. It is about 25 centimeters long. Food inside the esophagus reaches the stomach by peristalsis movements.
Stomach is the widest part of the alimentary canal. It is a J-shaped muscular organ with stomach occurs with the help of digestive juice. Digestive juice comprises of hydrochloric acid, mucous and some enzymes.
Small intestine is made up of three regions namely duodenum, jejunum and ileum. Partially digested food called the chyme from the stomach is received by the duodenum. Duodenum also receives bile form the liver, enzymes from pancreas and secretes some enzymes on its own. All these substances bring about digestion of food in the intestine. The inner walls of the small intestine have millions of small finger like projections called the villi. Villi increase the surface area for digestion as well as absorption of digested food by eight times.
Large intestine comprises of colon and rectum. Undigested food is sent into large intestine. Water from the food is reabsorbed to a great extent in the large intestine. Undigested waste is stored in the rectum for defecation.
Anus is the opening of the alimentary canal to the exterior. This helps in the elimination of faeces by the process of egestion.
Associated glands:
These glands include salivary glands, gastric glands, intestinal glands, liver and pancreas.
Salivary glands are present inside the buccal cavity. They secrete saliva. This saliva plays an important role in breaking down complex components like starch into simple sugars.
Gastric glands present inside the stomach secrete gastric juice which helps in the digestion of food.
Intestinal glands secrete various enzymes which aid in the process of digestion of food.
Liver is the largest gland in our body. The liver secretes a yellowish green watery fluid called bile. It is temporarily stored in a sac called the gall bladder. Bile plays an important role in the digestion of fats. Bile is sent into duodenum through a narrow tube-like structure called the bile duct. Bile breaks the larger fat molecules into tiny droplets, thereby increasing their surface area, which helps in the digestion of fats easily.
Pancreas is the mixed gland. It acts as a both endocrine and exocrine gland. The pancreas secretes the pancreatic juice that helps to digest carbohydrates, proteins and fats. The pancreatic juice converts carbohydrates into simple sugars and glucose, proteins into amino acids, and the lipids into fatty acids and glycerol.
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