Understanding Human Digestion and Respiration
The Digestive System: A Detailed Look
Chewing: This is a mechanical process that involves grinding food into smaller pieces to facilitate digestion. Chewing is performed by the teeth, aided by the tongue. Teeth are hard structures containing calcium and fluoride, responsible for crushing food. Types of teeth include:
- Incisors: Used to cut food.
- Canines: Also called tusks, used to tear food.
- Premolars and Molars: Known as molars, their function is to grind food.
Salivation: Saliva, secreted by the salivary glands, mixes with the crushed food to form a bolus. Saliva has several functions:
- Facilitates the passage of the bolus.
- Initiates the digestion of starches.
- Destroys bacteria in food.
Swallowing: After the bolus forms, it is swallowed. The bolus moves through the esophagus via peristalsis, a contraction of the muscle layers in the esophageal wall.
The stomach, shaped like a bagpipe, connects to the small intestine through the pylorus, a valve that is normally closed. The inlet valve of the stomach is called the cardia and is always open.
The Small Intestine
The small intestine is a tube about 6-7 meters long, extending from the pylorus to the ileocecal valve, which separates it from the large intestine. It is divided into three sections:
- Duodenum: A short, 25cm horseshoe-shaped portion.
- Jejunum and Ileum: The largest tract and final part, respectively, which empties into the large intestine.
The Liver
The liver is a large organ located on the right side of the abdomen, partially covering the stomach. It has a violet color due to its high blood content. The liver produces bile, which is secreted into the duodenum via the Vater papilla. Bile is stored in the gallbladder and released when food enters the intestine. Bile does not contain digestive enzymes but contains bile salts, which facilitate fat digestion.
The Pancreas
The pancreas is an elongated gland located behind and below the stomach. It has a dual role: it secretes hormones and produces pancreatic juice. Pancreatic juice contains enzymes that digest all types of food molecules, as well as sodium bicarbonate, which neutralizes the acidity of chyme.
The Large Intestine
The large intestine has three sections:
- Cecum: The initial pouch-like portion with a narrow extension, the appendix.
- Colon: Divided into ascending, transverse, and descending sections. Symbiotic bacteria in the colon constitute the intestinal flora and produce essential vitamins.
- Rectum: The end portion that opens to the anus.
The Respiratory System: How We Breathe
Airways
Airways are ducts that collect air, extract oxygen, and prepare it for use. These pathways include the nostrils, pharynx, trachea, and bronchi.
The Lungs
The lungs are where gas exchange (oxygen and carbon dioxide) occurs between the blood and the air.
The Respiratory Process
Gas exchange involves capturing oxygen from the air and transferring it to the blood for transport to body cells. Simultaneously, carbon dioxide is collected from the blood and expelled.