N3 Anatomy and Physiology AY 2024-2025

1. How does the food change in consistency and form?
- The food first experiences changes as it enters the mouth or the oral cavity, a process of ingestion. In there, it will undergo mechanical and chemical digestion by the chewing of the food with teeth  and breaking it down into tiny absorbable units with salivary amylase, respectively. From there, the now chewed food, also called bolus, travels down the esophagus with the help of muscle contractions called peristalsis. As it enters the stomach, the bolus is churned and mixed with gastric juices in a process of mechanical digestion. In the stomach as well, gastric juices, including hydrochloric acid and pepsin, break down proteins, turning the bolus into a semi-liquid mixture called chyme. After passing through the stomach, it enters the small intestine. Pancreatic enzymes and bile from the liver further digest carbohydrates, proteins, and fats in the duodenum. In the small intestines, nutrients are absorbed through the intestinal walls into the bloodstream. Afterwards it enters the large intestines where water absorption occurs. The large intestine absorbs water and salts from the remaining indigestible food matter. There, the indigestible and waste material is eliminated as feces through the rectum and out the anus in the process of defecation or elimination.

2. How could the body absorb the nutrients from the foods we eat?
- As food from the stomach, now called as chyme, enters the small intestines, particularly the duodenum, bile from the liver and digestive enzymes from the pancreas are released to help break down fats, proteins, and carbohydrates. These enzymes include lipase (for fats), amylase (for carbohydrates), and proteases (for proteins). Carbohydrates are broken down into glucose; proteins into amino acids and peptides; and fats into fatty acids and glycerol, all of which enter the bloodstream. As the chyme moves through the jejunum and ileum, nutrients are absorbed through the walls of the small intestine. The inner walls of the small intestine have finger-like projections called villi and small hair-like structures called microvilli, which greatly increase the surface area for nutrient absorption. After nutrients are absorbed in the small intestine, the remaining material moves to the large intestine. Here, water, electrolytes, and some vitamins are absorbed. The large intestine also houses beneficial bacteria that help break down remaining fiber and produce vitamins like vitamin K and some B vitamins.