Digestive and Respiratory Systems: Functions and Processes
The Digestive System
It consists of the gastrointestinal tract and accessory glands. The gastrointestinal tract is a long tube that varies along its route, widening in some places and narrowing in others. It begins at the mouth and ends at the anus. The following parts are distinguished:
- Pharynx
- Esophagus
- Intestine
The accessory glands are organs that pour their secretions into the digestive tube. These are:
- Salivary glands (located in the mouth)
- Stomach
- Intestinal glands (in the intestine)
- Liver
- Pancreas
The liver and pancreas are two larger glands that pour their secretions into the digestive tube.
Digestion in the Mouth
Chewing: This is a mechanical process to crush food into smaller pieces to facilitate the digestive process. It is carried out by the teeth and aided by the tongue. The teeth are very hard structures composed of calcium and fluorine. The tongue is involved in moving food between the teeth.
Insalivation: This consists of mixing the food with saliva produced by the salivary glands. The mixture of saliva and food is called the bolus. Saliva has several functions:
- It facilitates the passage of the bolus to the pharynx and esophagus.
- It initiates the digestion of some food molecules.
- It destroys some bacteria in food.
Swallowing: This is the passage of the bolus to the pharynx and esophagus. The advancement of the bolus is produced by the contraction of the two muscular layers of the wall of the esophagus, originating a characteristic movement called peristalsis.
The Respiratory System
It captures oxygen from the air and delivers it to the blood, which transports it to all body cells. The blood collects the carbon dioxide formed to expel it outside.
Air Transport and Preparation
- Nostrils: This is the air inlet. The inner wall presents abundant blood capillaries, allowing circulating air to be warmed. The existence of nooks and crannies increases the air’s path so that it can be heated better.
- Pharynx: This organ belongs to the digestive system and is a common passage area for the digestive tract and the respiratory system.
- Larynx: Entry is governed by a fibrous structure called the epiglottis, which closes when there is food in the pharynx to prevent it from entering the airways during swallowing and blocking the passage of air.
- Trachea: The interior is lined with mucus, which traps foreign particles in the air, and some cells with filaments called cilia. The cilia vibrate, moving the mucus laden with impurities into the larynx, where it is then driven into the esophagus.
- Bronchi and Bronchioles: The trachea is divided into two bronchi, each of which enters a lung and branches into smaller ducts. The whole of each bronchus with its branches is called the bronchial tree. The ultimate ramifications of the bronchioles end in tiny sacs called alveoli. Each individual’s lungs have around 400 million alveoli.
Pulmonary Ventilation
- Inspiration: This is the respiratory motion through which air enters the lungs. It is due to the contraction of the muscles of the rib cage and the diaphragm, which flattens and lowers. The ribs are elevated to the outside, increasing the capacity of the thoracic cavity. As the chest expands, the walls of the rib cage pull on the pleura, causing them to expand, increase in volume, and allow air to enter.
- Expiration: This is the movement through which air leaves the lungs. The ribs do the opposite motion to inspiration, and the diaphragm relaxes. The air comes out because the volume of the rib cage decreases, forcing the lungs to shrink.