Human Body Systems: Digestion and Respiration Explained
The Importance of Nutrients and Body Systems
The cells of all organisms need nutrients to grow and function. Heterotrophic organisms, like us, can’t produce their own nutrients. They obtain them from food. Multicellular organisms have many organs. These organs are grouped together into different systems that perform diverse functions. Five important systems work together to maintain our organisms correctly: Digestive, Respiratory, Circulatory, Excretory, and Lymphatic systems.
Digestion: Breaking Down Food
Like all animals, human beings obtain fats, sugars, and proteins from food. This is done by the digestive system. The movement of food through the digestive tract is achieved through peristaltic movements. This involves the narrowing of the tube through the contraction of muscles in the walls.
The Digestive System: A Journey Through the Body
The digestive tract is approximately 8 meters long, starting in the mouth and finishing at the anus.
- Mouth: The food enters here, where it is cut and broken down. This is a result of salivation (a chemical process) and mastication (a physical process).
- Salivary Glands: Organs that secrete substances into the digestive tract.
- Pharynx: Shared by the digestive and respiratory systems. During digestion, food goes to the esophagus, and during respiration, air goes to the larynx.
- Epiglottis: Prevents food from entering the lungs by controlling the larynx.
- Esophagus: The food bolus is swallowed and travels to the stomach.
- Stomach: After swallowing, the food reaches the stomach, where gastric digestion begins. Physical and chemical digestion also occur here. The food moves and is softened thanks to the walls of the stomach (peristaltic movements), and it is mixed with gastric juices. After this process, a pulp (chyme) is created.
- Liver: A large organ located in the top-right of the abdomen. It creates bile and destroys most toxic molecules.
- Gallbladder: Stores the bile.
- Pancreas: Produces hormones to regulate the amount of glucose in the bloodstream. It also secretes pancreatic juice, which enters the duodenum. This contains digestive enzymes and sodium bicarbonate, which neutralizes the acidic chyme.
- Small Intestine: Further breaks down the chyme.
- Large Intestine: Consists of the ascending, transverse, and descending colon. The ascending and transverse colon recover water and some ions, while the descending colon stores the feces.
- Rectum: When a certain amount of feces has formed, it passes to the rectum.
- Anus: The place where we expel waste products.
Respiration: Breathing Life In
Cells need oxygen, which is crucial for cellular respiration. Cellular respiration creates waste products, including CO2, which must be eliminated. The respiratory system captures oxygen from the air, which then enters the blood and is transported to all cells in our body.
The Respiratory System: From Air to Cells
- Transport and Modification of Air:
- Nasal Cavity: Air enters our body through the nostrils. The blood inside the capillaries of the nasal cavity warms the air. Mucosa cleans the air.
- Pharynx: (Shared passage)
- Larynx: Controlled by the epiglottis. This flap of tissue closes when food is in the pharynx, preventing food from entering the airways during swallowing.
- Trachea: Approximately 12cm long. The mucus in the trachea traps any foreign particles present in the air. The inside of the trachea is formed by vibrating filaments called cilia. The cilia move the mucus, which then goes to the esophagus.