The myenteric interstitial cells of Cajal act as the "pacemaker" of the gastrointestinal tract. They cause spontaneous smooth muscle cell contractions in the stomach, small intestine, and large intestine. These contractions play and integral role in mechanical digestion and motility of digestates.

The stimulus is spread to the gastrointestinal tract via gap junctions; however, the action potential does not originate from the junctions themselves and must be initiated by the cells of Cajal. Acinar cells are found in several regions and are defined by their clustered formation to form an exocrine gland. Acinar cells secrete pancreatic enzymes and saliva in the mouth. The cells of Cajal act via spontaneous depolarization and are not under the direct control of gastrointestinal neurotransmitters.

Diarrhea is a condition that causes living organisms to have loose bowel movements. This means that the bowel movements contain a high amount of liquid water. Recall that the main function of the large intestine is to reabsorb water back into the body. If there is a decrease in water reabsorption, then more water will be excreted via bowel movements; therefore, decreased water reabsorption in the large intestine will lead to loose bowel movements and, subsequently, diarrhea.

Most of the pathogens are not killed in the large intestine; they are killed in the acidic environment of the stomach. TheE. colifound in large intestine function to release vitamins, such as vitamin B12. They do not participate in water reabsorption; lack of microbes (E. coli) in the large intestine does not cause diarrhea.

The large intestine contains a bacterium calledEscherichia coli, orE. coli. It is not a pathogen, and instead participates in a symbiotic relationship with the human.E. coliactively synthesize and secrete essential vitamins such as vitamin B12 (required for proper functioning of the nervous system). Recall that the lumen (inside) of the large intestine does not contain any oxygen; therefore, a living organism that thrives inside the large intestine must be able to survive without oxygen.E. coliis a type of facultative anaerobe; this means that it can survive in oxygen rich conditions and in oxygen poor conditions (such as the lumen of large intestine).

Ebola is a type of virus and is usually not found inside the large intestine. Ebola virus is very harmful because it causes hemorrhagic fever, a fatal disease that leads to excessive blood loss from the circulatory system.

The question states that chyme is a semifluid food mass that enters the intestines. Recall that this food mass will first enter the small intestine, where the majority of digestion will take place. In the small intestine, chyme contains large amounts of undigested nutrients. The small intestine will absorb most of the nutrients (carbohydrates, fats, and proteins) and will send the digested food mass to the large intestine.

In the large intestine, water and undigested nutrients are reabsorbed from the chyme. The remainder of chyme is considered waste and is excreted through the rectum; therefore, chyme will enter the large intestine after the small intestine and will mostly consist of water and waste products. Most of the water is reabsorbed and the remaining chyme (waste products and a small amount of water) is excreted.

The large intestine is the last organ in the digestive tract. The food mass exits the stomach as chyme and enters the small intestine, where 90% of chemical digestion occurs. The digested chyme is transported to the large intestine where most of the water and undigested nutrients in the chyme are reabsorbed; therefore, the majority of the digestion occurs in the small intestine, while the majority of water reabsorption occurs in the large intestine. This makes statement I false.

The large intestine also containsE. coli, a bacterial species that thrives in the anaerobic environment of the large intestine. Presence ofE. coliis beneficial to humans because the bacteria synthesize vital vitamins such as vitamin B12. This makes statement II true.

Recall that the stomach is characterized by its highly acidic environment. This means that the lumen of the stomach contains a low pH and, therefore, a high concentration of hydrogen ions. Other organs involved in digestion, such as the large intestine, do not contain a highly acidic environment. The pH of the large intestine is higher than that of the stomach and, consequently, it has a lower concentration of hydrogen ions than stomach. This makes statements III true.

The correct answer shows the proper order, and you should pay special attention to the names of the two sphincters. The cardiac sphincter is by the heart, and comesbeforethe stomach. The pyloric sphincter is at the bottom of the belly and comesafterthe stomach. Food does not pass through the larynx, which is used in breathing and speaking.

The digestive system begins in the mouth with fragmentation. Mucous helps roll the food into a bolus and salivary amylase begins the process of chemical breakdown.

脂类消化开始发生the mouth because of the enzyme lipase. Saliva in the mouth incorporates both lipase, to begin lipid digestion, and amylase, to being carbohydrate digestion. Lipids are also broken down later in the digestive pathway by lipase in the small intestine. Protein digestion does not begin until food enters the stomach.

Vitamins A, D, E, and K (ADEK) are fat soluble vitamins, and require the ingestion and absorption of fat in order to maintain adequate stores of the vitamins in the body. Any problems with bile salt function or absorption of bile salt and fat miscelles in the small intestine can lead to a deficiency in vitamins A, D, E, and K. All other vitamins can be absorbed without the help of fat.

The gastrointestinal, or digestive, system is primarily designed to break down (catabolize) nutrients and absorb them into the blood for use by the body. Digestion of nutrients by stomach and pancreatic enzymes allows for their absorption in the small intestine. The large intestine is responsible for water absorption.

Filtration occurs in three primary areas in the body: the kidney, the liver, and the spleen/lymph nodes. The kidney is part of the excretory system, in which fluids are filtered from the blood to remove solute waste from the body. The liver filters the blood in circulation, and is responsible for removing toxins that may have been absorbed during digestion. It is not, however, part of the gastrointestinal tract. The spleen and lymph nodes filter the interstitial fluid to screen for antigens and pathogens.