The Digestion Pathway
From MyMCAT
Contents |
Introduction
Understanding the digestive system involves learning about the function of each organ and how together they allow the body to absorb nutrients. Throughout the gastrointestinal tract, there are two basic movements that can occur: propulsion, or peristalsis, and mixing.
The Mouth
The first step in digestion is mechanical breakdown of food particles, also called mastication. This process serves two functions: To increase the surface area of food allowing ptyalin, or salivary amylase to break down starch quicker and to make the food particles small and wet enough for safe travel in the esophagus.
The Esophagus
The esophagus is used to transport food from the mouth to the stomach. The swallowing mechanism, deglutination, ensures that food does not accidentally get lodged in the lungs. Peristalsis, the rhythmic movement of muscles in the esophagus allows the process to occur smoothly and subconsciously. Food enters the stomach through the gastroesophageal (or cardiac) sphincter.
The Stomach
Once in the stomach, mechanical digestion continues through a process called churning. The rugae, or many folds of the stomach ensure that an increase in food volume does not lead to an increase in pressure initially.
Hydrochloric acid is released from the parietal cell in the oxyntic glands, and break down food into a semi-fluid called chyme.
Liver
Gall Bladder
Bile, used to emulsify fats, is stored and concentrated in the gall bladder. Gall bladder removal, for example in a patient with gall stones, does not significantly impact the physiology in the gut, and digestion can proceed normally. In this case, the bile backs up the bile duct to the liver, instead of being stored in the gall bladder.
Small Intestine
The small intestine is broken up into three sections: the duodenum, the jejunum, and the ileum.