Chylomicrons contain triglycerides, cholesterol, and other lipids and have proteins on their surface. Together, they enable the chylomicron to move in an aqueous environment without exposing the lipids to water. Chylomicrons leave the absorptive cells via exocytosis.
Chylomicrons enter the lymphatic vessels, and then enter the blood in the subclavian vein. Vitamins can be either water-soluble or lipid-soluble.
Fat soluble vitamins are absorbed in the same manner as lipids. It is important to consume some amount of dietary lipid to aid the absorption of lipid-soluble vitamins. Water-soluble vitamins can be directly absorbed into the bloodstream from the intestine.
This website has an overview of the digestion of protein, fat, and carbohydrates. Which of the following statements about digestive processes is true? The final step in digestion is the elimination of undigested food content and waste products. The undigested food material enters the colon, where most of the water is reabsorbed.
The semi-solid waste is moved through the colon by peristaltic movements of the muscle and is stored in the rectum. As the rectum expands in response to storage of fecal matter, it triggers the neural signals required to set up the urge to eliminate. The solid waste is eliminated through the anus using peristaltic movements of the rectum. Diarrhea and constipation are some of the most common health concerns that affect digestion.
Constipation is a condition where the feces are hardened because of excess water removal in the colon. In contrast, if enough water is not removed from the feces, it results in diarrhea. Many bacteria, including the ones that cause cholera, affect the proteins involved in water reabsorption in the colon and result in excessive diarrhea.
Emesis, or vomiting, is elimination of food by forceful expulsion through the mouth. It is often in response to an irritant that affects the digestive tract, including but not limited to viruses, bacteria, emotions, sights, and food poisoning. This forceful expulsion of the food is due to the strong contractions produced by the stomach muscles.
The process of emesis is regulated by the medulla. Animal diet should be balanced and meet the needs of the body. Carbohydrates, proteins, and fats are the primary components of food. Some essential nutrients are required for cellular function but cannot be produced by the animal body. These include vitamins, minerals, some fatty acids, and some amino acids. Food intake in more than necessary amounts is stored as glycogen in the liver and muscle cells, and in fat cells.
Excess adipose storage can lead to obesity and serious health problems. ATP is the energy currency of the cell and is obtained from the metabolic pathways. Excess carbohydrates and energy are stored as glycogen in the body.
Skip to content Chapter Animal Nutrition and the Digestive System. Learning Objectives By the end of this section, you will be able to: Describe the process of digestion Detail the steps involved in digestion and absorption Define elimination Explain the role of both the small and large intestines in absorption. Digestion and Absorption. Table Aminopeptidase Dipeptidase. It connects the throat above with the stomach below. At the junction of the esophagus and stomach, there is a ringlike valve closing the passage between the two organs.
However, as the food approaches the closed ring, the surrounding muscles relax and allow the food to pass. The food then enters the stomach, which has three mechanical tasks to do. First, the stomach must store the swallowed food and liquid.
This requires the muscle of the upper part of the stomach to relax and accept large volumes of swallowed material. The second job is to mix up the food, liquid, and digestive juice produced by the stomach. The lower part of the stomach mixes these materials by its muscle action. The mixture is referred to as chyme. Several factors affect emptying of the stomach, including the nature of the food mainly its fat and protein content and the degree of muscle action of the emptying stomach and the next organ to receive the contents the small intestine.
As the food is digested in the small intestine and dissolved into the juices from the pancreas, liver, and intestine, the contents of the intestine are mixed and pushed forward to allow further digestion.
Finally, all of the digested nutrients are absorbed through the intestinal walls. The waste products of this process include undigested parts of the food, known as fiber, and older cells that have been shed from the mucosa. These materials are propelled into the colon, where they remain, usually for a day or two, until the feces are expelled by a bowel movement. The small intestine has 3 segments:. Duodenum — The chyme first enters into the duodenum where it is exposed to secretions that aid digestion.
The secretions include bile salts, enzymes, and bicarbonate. Pancreatic enzymes help digest carbohydrates and fats. Bicarbonate from the pancreas neutralizes the acid from the stomach. Jejunum — The chyme is then further transited down into the second or middle part of the small intestine, the jejunum. Ileum — The ileum is the last section of the small intestine and leads to the large intestine or colon.
The ileum mainly absorbs water, bile salts, and vitamin B The ileocecal valve is a one-way valve located between the ileum and the cecum, which is the first portion of the colon. This valve helps control the passage of contents into the colon and increases the contact time of nutrients and electrolytes essential minerals with the small intestine.
It also prevents back-flow reflux from the colon up into the ileum, and helps minimize the movement of bacteria from the large intestine up into the small bowel. The primary function of the large intestine or colon is to absorb fluids and electrolytes, particularly sodium and potassium, and to convert remaining luminal contents into more solid stool.
The colon absorbs on average 1—1. Another function of the colon is to break down ferment dietary fiber to produce short chain fatty acids — substances that can be absorbed and provide added nutrition. The first portion of the colon, the cecum, is shaped like a pouch, and is the area of storage for the contents arriving from the ileum. The second portion is the ascending colon, where fluids are absorbed and where some stool formation begins. The glands that act first are in the mouth — the salivary glands.
Saliva produced by these glands contains an enzyme that begins to digest the starch from food into smaller molecules. The next set of digestive glands is in the stomach lining. They produce stomach acid and an enzyme that digests protein.
One of the unsolved puzzles of the digestive system is why the acid juice of the stomach does not dissolve the tissue of the stomach itself. In most people, the stomach mucosa is able to resist the juice, although food and other tissues of the body cannot. After the stomach empties the food and juice mixture into the small intestine, the juices of two other digestive organs mix with the food to continue the process of digestion.
One of these organs is the pancreas. It produces a juice that contains a wide array of enzymes to break down the carbohydrate, fat, and protein in food. Other enzymes that are active in the process come from glands in the wall of the intestine or even a part of that wall. The liver produces yet another digestive juice — bile. The bile is stored between meals in the gallbladder.
At mealtime, it is squeezed out of the gallbladder into the bile ducts to reach the intestine and mix with the fat in our food. The bile acids dissolve the fat into the watery contents of the intestine, much like detergents that dissolve grease from a frying pan.
After the fat is dissolved, it is digested by enzymes from the pancreas and the lining of the intestine. Digested molecules of food, as well as water and minerals from the diet, are absorbed from the cavity of the upper small intestine. Most absorbed materials cross the mucosa into the blood and are carried off in the bloodstream to other parts of the body for storage or further chemical change. As already noted, this part of the process varies with different types of nutrients.
It is recommended that about 55 to 60 percent of total daily calories be from carbohydrates. Some of our most common foods contain mostly carbohydrates. Examples are bread, potatoes, legumes, rice, spaghetti, fruits, and vegetables. Many of these foods contain both starch and fiber. The digestible carbohydrates are broken into simpler molecules by enzymes in the saliva, in juice produced by the pancreas, and in the lining of the small intestine.
Starch is digested in two steps: First, an enzyme in the saliva and pancreatic juice breaks the starch into molecules called maltose; then an enzyme in the lining of the small intestine maltase splits the maltose into glucose molecules that can be absorbed into the blood.
Glucose is carried through the bloodstream to the liver, where it is stored or used to provide energy for the work of the body. Table sugar is another carbohydrate that must be digested to be useful. After some simple digestion in the mouth, the food is pushed down the esophagus and into the stomach.
The stomach plays a necessary role in the digestion of protein and is considered your body's blender, churning the food to make absorption easier for the intestines. Before anything can happen in the stomach, digestion of your food starts in the mouth. When you bite into food, your mouth releases an enzyme, salivary amylase, in the saliva that begins breaking down the food, making it softer and easier to swallow and initiating the digestion of starch.
When you're ready to swallow, the food moves down through the esophagus, where it is slowly pulsed into the stomach. The stomach, working as a blender, has three main functions: store the food, break down the food into a liquid and empty the liquid into the small intestine.
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