Human Digestive System

Correct answer. Ribonuclease A (RNase A) is a small (124 amino acids) digestive enzyme secreted by the pancreas and is an endonuclease specifically designed to hydrolyse RNA phosphodiester bonds which covalently link ribonucleotides particularly those linked to pyrimidine bases such as uracil. It can be inhibited by ribonuclease inhibitor protein, by heavy metal ions (like Pb²⁺, Hg⁺  etc.), and by uridine-vanadate complexes.

The duodenum is the first and shortest section of the small intestine, approximately 25-30 cm long, connecting directly to the stomach at the pyloric sphincter. It receives partially digested food (chyme) from the stomach, along with bile from the liver and digestive enzymes from the pancreas. The caecum marks the beginning of the large intestine, while the ileum and jejunum are the middle and final sections of the small intestine, respectively. The duodenum's primary function is neutralizing stomach acid and continuing chemical digestion.

Plastic materials, if taken in by cows choke their wind pipe and make it difficult for them to breathe. Since it cannot be digested, then it cannot affect their digestive or excretory system in the way it affects the respiratory system. 

Enterogastrone is a hormone secreted by the intestinal mucosa when acidic chyme enters the small intestine. It inhibits gastric acid secretion and stomach motility, protecting the duodenum and slowing gastric emptying. Option C correctly describes this inhibitory function.

Secretin is the primary hormone that stimulates the pancreas to secrete pancreatic juice (rich in bicarbonate to neutralize acidic chyme). It is released from S cells in the duodenum when acidic chyme enters the small intestine. Trypsinogen is a pancreatic enzyme precursor, enterokinase activates trypsinogen, and cholecystokinin stimulates enzyme secretion but fluid/bicarbonate secretion is mainly secretin-driven.

Different phases of digestion take place including the cephalic phase, gastric phase and intestinal phase. The cephalic phase occurs at the sight, thought and smell of food, which stimulate the cerebral cortex. Taste and smell stimuli are sent to the hypothalamus and medulla oblongata.

Water and lipids are absorbed by passive diffusion throughout the small intestine.

Pancreatic amylase digests all the remaining starch in the duodenum. Amylase digests starch molecules from the ends of the chains in two-glucose units, forming the disaccharide maltose. Glycogen is also digested here.

The muscularis externa consists of an inner circular layer and a longitudinal outer muscular layer. The circular muscle layer prevents food from traveling backward and the longitudinal layer shortens the tract.

Pepsin (in gastric juice) digests proteins to peptides, 6-12 amino acids long. Pepsin is an endopeptidase, which means it hydrolyses peptide bonds in the middle of a polypeptide chain. It is unusual in that it has an optimum pH of about 2 and stops working at neutral pH.

After passing through the small intestine, food passes into the large intestine. In the large intestine, some of the water and electrolytes (chemicals like sodium) are removed from the food. Many microbes (bacteria like Bacteroides, Lactobacillus acidophilus, Escherichia coli, and Klebsiella) in the large intestine help in the digestion process.

After passing through the small intestine, food passes into the large intestine. In the large intestine, some of the water and electrolytes (chemicals like sodium) are removed from the food. Many microbes (bacteria like Bacteroides, Lactobacillus acidophilus, Escherichia coli, and Klebsiella) in the large intestine help in the digestion process.

The stomach has a priority to destroy the bacteria and viruses using its highly acidic environment but also has a duty to protect its own lining from its acid. The way that the stomach achieves this is by secreting mucin and bicarbonate via its mucous cells, and also by having a rapid cell turn-over.

The pancreas is also the main source of enzymes for digesting fats (lipids) and proteins. The enzymes that digest polysaccharides, by contrast, are primarily produced by the walls of the intestines.

Amylases are used in breadmaking and to break down complex sugars, such as starch (found in flour), into simple sugars. Yeast then feeds on these simple sugars and converts it into the waste products of alcohol and CO2. This imparts flavour and causes the bread to rise.