Human Digestive and Respiratory System Functions
Intestinal Juice and Nutrient Absorption
Intestinal juice is produced by cells in the small intestine and acts upon nutrients to break them down into their simplest components. As a result of digestion in the small intestine, chyme transforms into chyle, a slurry that is significantly more liquid and milky. The inner wall of the small intestine features numerous folds, which in turn present villi and microvilli. These structures greatly increase the absorbing surface area of the intestine, facilitating the passage of nutrients into the bloodstream.
Functions of the Large Intestine
The unabsorbed chyle passes through the large intestine, which measures approximately 1.5 meters and is divided into three main parts:
- Cecum (including the appendix)
- Colon (ascending, transverse, and descending)
- Rectum
In the large intestine, water and mineral salts are absorbed into the blood. Consequently, the chyle thickens and acquires a more solid consistency, forming stool. This waste accumulates and is stored in the rectum before being expelled.
The Path of Food Through the Body
The digestive process begins in the mouth, where food is chewed by the teeth and softened by the tongue and salivary glands. Here, carbohydrate digestion starts, and saliva acts as a bactericide. The resulting bolus passes through the pharynx, which connects the mouth to the esophagus. The epiglottis prevents the bolus from entering the airways.
The bolus then travels through the esophagus via peristalsis—a series of muscular contractions that carry it to the stomach. In the stomach, food is stored and kneaded until it becomes chyme. From the stomach, it enters the duodenum, where it transforms into chyle. It then moves through the small intestine, the large intestine, and finally exits through the anus.
Components of the Respiratory System
The respiratory apparatus consists of two primary components. The respiratory tract includes the following structures:
- Nose and Mouth
- Pharynx and Larynx
- Trachea
- Bronchi and Bronchioles
- Alveoli
- Lungs
Anatomy of the Lungs
The lungs are two spongy organs located in the thorax and protected by the rib cage. The right lung is divided into three lobes, while the left lung is smaller and divided into only two lobes to accommodate the space where the heart is located.
The Process of Cellular Respiration
Nutrients obtained from food reach every cell in the body via the blood and enter the mitochondria. Simultaneously, oxygen inhaled through the respiratory tract enters the blood and is transported by red blood cells to all body cells. This oxygen enters the mitochondria and is used to "burn" nutrients to gain energy. This combustion process results in waste substances such as CO2 (carbon dioxide) and water vapor. These wastes are released from the cells, cross back into the blood, and reach the respiratory system to be expelled.