In order to stimulate digestion in the stomach G cells secrete gastrin, which stimulates parietal cells. Pepsinogen is released by chief cells. The parietal cells release hydrochloric acid into the stomach lumen. The lowered acidity cleaves pepsinogen and creates pepsin, which begins to degrade proteins.

Mucous cells have the nondigestive role of lubricating the stomach lumen and protecting the stomach epithelium from degradation by the highly acidic gastric juices.

The pyloric sphincter, between the antrum of the stomach and the duodenum of the small intestine, regulates the passage of chyme from the stomach to the small intestine. The antrum has rhythmic contractions that force chyme against the pyloric sphincter, allowing approximately five milliliters to flow through every contraction; thus, the pyloric sphincter allows for the gradual but continual digestion of gastric contents.

The upper and lower esophageal sphincters are involved in the process of swallowing, while the ileocolic sphincter joins the small intestine and large intestine.

The colon extracts water and salts while forming feces. The colon also absorbs some nutrients that made it through the small intestine without being absorbed, but its main job is water and salt absorbtion.

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 contains E. coli, a bacterial species that thrives in the anaerobic environment of the large intestine. Presence of E. coli is 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 most important function of the large intestine is the resorption of water that comes from intake or the pancreas. Waste is still hydrated while in the small intestine.

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.

A renal afferent arteriole is directed toward the glomerulus, while a renal efferent arteriole is directed away from the glomerlus. If the radius of the afferent arteriole is increased, there is more flow through it toward the glomerulus, and if there is a smaller radius in the efferent arteriole, there is a resultant back pressure in the glomerulus. This is can be imagined as trying to squeeze a high-pressure hose through a small pipe. This pressure increases the force within the glomerulus to increase filtration, and subsequently increase reabsorption.

Antidiuretic hormone (ADH) secretion has a neglible effect on the radius of renal arterioles. Blood flow to the kidney is increased when afferent arteriole radius is increased (this also increases the arteriole flow).

A renal afferent arteriole is directed toward the glomerulus, while a renal efferent arteriole is directed away from the glomerlus. If the radius of the afferent arteriole is increased, there is more flow through it toward the glomerulus, and if there is a smaller radius in the efferent arteriole, there is a resultant back pressure in the glomerulus. This is can be imagined as trying to squeeze a high-pressure hose through a small pipe. This pressure increases the force within the glomerulus to increase filtration, and subsequently increase reabsorption.

Antidiuretic hormone (ADH) secretion has a neglible effect on the radius of renal arterioles. Blood flow to the kidney is increased when afferent arteriole radius is increased (this also increases the arteriole flow).

As we are told in the passage, phase I metabolism occurs by the transfer of electrons, commonly called an oxidation-reduction reaction. Phase I metabolism in the liver serves primarily to oxidize endogenous and exogenous molecules by passing electrons from a substrate to iron, and finally to oxygen. These oxidation reactions are carried out by the cytochrome P450 system and allow metabolites to become more soluble in urine for excretion. The other reactions listed are carried out by various transferases during phase II metabolism in the liver.

As we are told in the passage, phase I metabolism occurs by the transfer of electrons, commonly called an oxidation-reduction reaction. Phase I metabolism in the liver serves primarily to oxidize endogenous and exogenous molecules by passing electrons from a substrate to iron, and finally to oxygen. These oxidation reactions are carried out by the cytochrome P450 system and allow metabolites to become more soluble in urine for excretion. The other reactions listed are carried out by various transferases during phase II metabolism in the liver.