Human Digestive and Respiratory Systems Explained
The Digestive System
The digestive system converts food into nutrients, absorbs them, and expels waste. Key glands involved include:
- Salivary Glands: Three types (sublingual, submandibular, and parotid) that keep the mouth moist, clean teeth, enhance taste, dissolve food, lubricate, and initiate digestion.
- Pancreas: Produces pancreatic juice and controls glucose levels via insulin.
- Liver: Manufactures and excretes bile, stores glucose, and regulates metabolic processes.
Digestion of Food
Digestion transforms food into absorbable nutrients through two processes:
- Mechanical: Reduces the size of food particles.
- Chemical: Breaks down molecules for easy intestinal absorption.
Food enters the stomach through the cardias valve. The intestinal mucosa releases intestinal juice to digest proteins, fats, and carbohydrates, while pancreatic enzymes and bile further assist in breaking down nutrients.
Nutrient Absorption
Nutrients pass into the bloodstream through the intestinal walls. The small intestine, measuring 6 meters, features folded walls with villi and enterocytes containing microvilli to maximize absorption.
The Large Intestine and Waste
The large intestine (1.5 meters) absorbs water and mineral salts. Its functions include:
- Fermenting undigested compounds.
- Synthesizing vitamins K and E.
- Protecting against microorganisms.
Waste is stored in the rectum and eliminated through the anus. A low-fiber diet can cause waste to remain in the large intestine too long, leading to water absorption, hardening, constipation, and hemorrhoids.
The Respiratory System
The respiratory airways facilitate breathing:
- Nostrils: Air is moistened, heated, and filtered of dust.
- Pharynx and Larynx: Air passes through the voice box into the trachea.
- Trachea: A tube of cartilaginous rings that divides into two bronchi.
- Lungs: Two spongy organs coated in pleura membranes with pleural fluid to facilitate movement.
Inside the lungs, bronchi branch into bronchioles and pulmonary alveoli.