1. How Does Food Change in Consistency and Form?
Food changes to various consistency as it travels through the digestive system due to multiple mechanical and chemical processes in different organs:
A. Mouth (Chewing and Digestion)
-
Mechanical digestion occurs through chewing or also known as mastication, breaking food into smaller pieces to form a soft, swallowable mass called bolus.
-
Chemical digestion begins as salivary glands release salivary amylase, which breaks down starch into simple sugars.
B. Stomach (Processing)
-
The bolus enters the stomach, traveling from the esophagus, where gastric juices mix with it, breaking it down further into a semi-liquid form called chyme.
C. Small Intestine (Digestion and Absorption)
-
In the small intestine, chyme is exposed to digestive enzymes from the pancreas and bile from the liver (stored in the gallbladder).
-
These processes emulsify fats and break food into its smallest components, allowing nutrient absorption to occur.
D. Large Intestine (Absorption and Formation)
-
In the large intestine, water, electrolytes, and vitamins are absorbed.
-
The remaining undigested material solidifies into feces, ready for elimination.
Phases of Food in the Digestive System:
Food → Bolus → Chyme → Feces
2. How Does the Body Absorb Nutrients from Food?
Nutrient absorption occurs in different parts of the digestive tract, each absorbing a specific set of nutrients:
A. Stomach
-
The stomach absorbs some water, alcohol, aspirin, and lipid-soluble drugs. However, its epithelial lining is impermeable to most nutrients. This also protect the escape of the hydrochloric acid from the stomach.
B. Small Intestine
-
The small intestine is where most nutrients are absorbed:
-
Fats are emulsified by bile salts and broken into fatty acids. These are absorbed into epithelial cells, reassembled as triglycerides, and transported as chylomicrons via the lymphatic system.
-
Carbohydrates are broken into simple sugars, and proteins into amino acids. These are absorbed into the bloodstream via active transport and facilitated diffusion.
-
Vitamins and Minerals: Fat-soluble vitamins (A, D, E, K) are absorbed with fats, while water-soluble vitamins and minerals are absorbed through diffusion or specialized transport mechanisms.
-
Absorbed nutrients are either sent to the liver for processing or distributed through the bloodstream and lymphatic system.
-
C. Large Intestine
-
The large intestine absorbs water, electrolytes, and vitamins as chyme moves through.
-
Undigested material solidifies into feces, which is eventually expelled through the anus.