QVprep Biology Lessons

Respiratory system, role of the respiratory system, What is the role of the digestive system?, Alimentary canal or the digestive tract, Digestion, small intestine, large intestine, pancreas, Liver



What is the role of the respiratory system?: The respiratory system supplies the body with oxygen. Air is inhaled through the nose or mouth. It then travels into the pharynx, passes through the larynx, and down the trachea. The trachea branch and air reaches the lungs where it will diffuse into the blood via the alveoli. The nose, nasal cavity, larynx, pharynx, bronchi, trachea and lungs make up the main organs in the system. Alveoli are tiny cells in the lungs that are involved in the exchange of oxygen and carbon dioxide.

What is the role of the digestive system?: The digestive system provides the means for processing food and transforming nutrients into energy.

Alimentary canal or the digestive tract: The digestive system comprises the buccal cavity, esophagus, stomach, small intestine, large intestine ending in the rectum and anus. These parts together are called the alimentary canal or the digestive tract.

Digestion: Saliva is secreted by glands into the mouth and this starts the process of chemical digestion with the help of enzymes which break down large molecules of food into smaller molecules that the body is able to absorb. Digestion becomes involuntary after food is swallowed. Food passes down the throat to the esophagus, which is the first among digestive organs. The food is then transported further through muscular contractions known as peristalsis. The stomach secretes many digestive juices including the enzymes pepsin, which targets proteins, and lipase, which works on fats. Hydrochloric acid dissolves the stomach contents and destroys harmful bacteria. The resulting semi fluid paste—chyme—is sealed in the stomach by two ring-like sphincter muscles for many hours and then released in short bursts into the duodenum.

Small intestine: The small intestine is divided into 3 sections – duodenum, ileum and colon. The first of three sections of the small intestine, the duodenum produces large quantities of mucus to protect the intestinal lining from acid in the chyme. Measuring about 20 feet in length, the small intestine is where the major digestion and absorption of nutrients take place. These nutrients are taken into the bloodstream by fingerlike projections called villi, and transported to the liver.

Large intestine: Then whatever is left passes into the large intestine, where it is acted upon by harmless bacteria and mixed with dead cells to form solid feces. Water is reabsorbed into the body while the feces are moved into the rectum to await expulsion.

What are the accessory organs in the digestive system?: Other organs that play a key role in digestion include the liver, gallbladder, and pancreas.

Pancreas: The pancreas is a gland located behind the stomach. It produces enzymes that are pumped into the duodenum. A duct connects the duodenum to the gallbladder. This pear-shaped sac squeezes out green-brown bile, a waste product collected from the liver. The bile contains acids for dissolving fatty matter.

Liver: The liver is the body's main chemical factory, performing hundreds of different functions. It processes nutrients absorbed into the blood by the small intestine, creating energy-giving glycogen from carbohydrates and detoxifies harmful substances.