The Digestive System
The physiological aspect of the digestive system is that humans obtain energy and nutrients from food by four actions; which are ingestion, digestion, absorption, and elimination. Anatomically, the digestive system is a “tube” (alimentary canal) running from mouth to anus and is about 9 meters long. The main organs of the human digestive system are the mouth, the pharynx (throat), esophagus, stomach, small intestine, large intestine, rectum, and anus. The accessory organs associated with the digestive system are the salivary glands, liver, gallbladder, and pancreas.
The main goal of the digestive system is to break down large macromolecules (proteins, fats and starch), which cannot be absorbed as-is, into smaller molecules (amino acids, fatty acids and glucose) that can be absorbed across the wall of the tract, into the circulatory system for diffusion around the body, and excretion. There are two types of digestion which are mechanical digestion (breaking food into smaller pieces ie. chewing) and chemical digestion (enzymes ie. salivary amylase). Mechanical digestion in the mouth helps begin chemical digestion by mixing the food with enzyme-containing saliva. After leaving the mouth, a swallowing reflex moves food from the pharynx into the esophagus. Peristalsis then moves food through the esophagus, which is separated from the stomach by a ring of muscles that controls the passage of food called a sphincter.
The stomach, an organ consisting of smooth muscle, is divided into cardiac, fundic, body, pyloric regions and a pyloric canal. The functions of the stomach include mixing and churning food with gastric fluid to produce chyme, storage of ingested foods, controlling passage into the small intestine (through the pyloric canal), and protein digestion. From the stomach food is moved to the small intestine where digestion of all nutrients is completed. The small intestine consists of the duodenum, jejunum, and ileum in...