Human Digestive and Respiratory Systems: Health & Function
Digestive System: Function and Processes
Digestion takes place in the organs of the digestive tract.
Mouth
Digestion begins here through the mechanical actions of the teeth and tongue, and the chemical action of the enzyme amylase, present in saliva. Amylase transforms complex carbohydrates into simple sugars. This transformation contributes to the formation of the bolus.
Stomach
Gastric digestion of the bolus occurs here. The stomach walls secrete gastric juices that contain hydrochloric acid and enzymes like pepsin. Peristaltic contractions mix the gastric juices with the bolus, turning it into a thick, very acidic liquid called chyme.
Small Intestine
In the small intestine, the chyme is affected by peristaltic movement, bile, and enzymes from pancreatic and intestinal juices. Peptidases break down proteins into amino acids, and amylases break down starch into sugars.
Nutrient Absorption
The nutrients obtained in digestion pass through the walls of the digestive tract to the blood, where they are carried to the cells.
- Small intestine: Absorption of glucids occurs via intestinal villi and microvilli (epithelial cells).
- Large intestine: Absorption of water, salts, and minerals. Intestinal flora produces vitamin K.
Formation of Feces
Some foods that cannot be digested are converted into waste to be eliminated. This waste is compacted in the large intestine, where it loses water and mineral salts. As a result, feces are formed and accumulate in the final section of the large intestine. They are expelled during defecation.
Main Diseases of the Digestive System
These diseases are sometimes the result of a lack of hygiene or poor eating habits.
- Caries: An infectious disease caused by mouth bacteria. Bacteria produce acids from sugary foods that weaken dental enamel and cause holes.
- Peptic Ulcer: A break in the lining of the stomach or duodenum. Caused by H. pylori infection, alcohol, or smoking.
- Constipation: Difficult defecation due to hard, dry feces, caused by diets poor in fiber and water, or stress.
- Gastroenteritis: Inflammation of the gut caused by infection, food poisoning, or contact with affected people. Symptoms include vomiting, diarrhea, and fever.
- Appendicitis: Swelling of the appendix due to obstruction. This could lead to infection or perforation, and eventually to peritonitis if not treated.
- Hepatitis: Liver inflammation caused by viruses, toxins, or alcohol.
The Respiratory Tract
The respiratory tract is made up of passages, or tubes, through which oxygen-rich air enters the lungs and carbon dioxide is expelled from the body.
- Nasal Passages: Air enters the nose and continues through these passages, where it is moistened and warmed. Dust is retained there.
- Pharynx: This organ is part of both the digestive and respiratory systems. When you swallow, the epiglottis closes to prevent food from entering the trachea.
- Larynx: A short tube made up of cartilage. As air passes through the larynx, the vocal cords vibrate.
- Trachea: A short, flexible tube formed by C-shaped cartilage. The inside of this tube is lined with cells that have hair-like projections. These cells send a constant flow of mucus toward the pharynx.
- Bronchi and Bronchioles: Very small, thin passages that end in tiny, rounded sacs with very thin walls called pulmonary alveoli.