General Review
The food that we eat is made up of the biomacromolecules which is eventually broken up by the digestive tract. The energy of the food that we consume is stored in the chemical bonds of the food, when this bond is broken (catabolism), energy is made available to the body. This happens with glucose then fats then to the extreme limits with proteins. Every bit of the food that we eat is broken down and the rest which the body can no longer use is passed out of the body in the form of feces. As well as energy, food gives us vitamins and minerals which are essential for life and cannot be synthesized in the body. The nutrients are then passed into the blood stream whose role is to distribute that around the body to provide energy to other cells throughout the body.
Mechanical Digestion
The food at the start is broken up by mechanical digestion, an example is the work of teeth on foods which breaks it down into smaller sizes therefore increasing the surface area to volume ratio. This allows enzymes to easily and quickly act upon them. The human teeth or any carnivorous organisms are composed of sharp teethes which are used to tear and slice meat. They also have flat teethes which is useful for grinding vegetables. In the mouth a chemical reaction also occurs by the enzyme amylase which is found in the saliva. This acts on carbohydrates (starch) and breaks it down into simpler diasaccharides (maltose). Saliva also lubricates food, softens it and forms it into a bolus. Another example is the churning of the stomach which more or less serves the same function.
Stomach
The Stomach
The stomach is an organ of digestion. It has a saclike shape and is located between the oesophagus and the intestines.
The human stomach is a muscular, elastic and a pear-shaped bag, it changes size and shape according to its position of the body and the amount of food inside. The stomach is about 12 inches (30.5 cm) long and is 6 inches, (15.2 cm) wide at its widest point. The stomach's capacity is about 1 to 1.5 litres in an adult.
Food enters the stomach from the oesophagus. The connection between the stomach and the oesophagus is called the cardiac sphincter. The cardiac sphincter prevents food from passing back to the oesophagus. Heart burn is the sensation when stomach juices (gastric juice) is allowed to seep through the sphincter into the oesophagus. Once the food enters the stomach, gastric juices are used to break down the food. The other end of the stomach empties into the duodenum. The duodenum is the first section of the small intestine. The pyloric sphincter separates the stomach from the duodenum.The three important main functions of the stomach are:
The stomach is a highly acidic environment due to hydrochloric acid production and secretion which produces a pH range usually between 1 and 2 depending on a whole range of factors such the, food intake, time of the day, drug use, and other factors. Combined with digestive enzymes, such an environment is able to break down large molecules (such as from food) to smaller ones so that they can eventually be absorbed from the small intestine. Pepsin and rennin and is present in hydrochloric acid and is a necessity in protein digestion.
The human stomach is a muscular, elastic and a pear-shaped bag, it changes size and shape according to its position of the body and the amount of food inside. The stomach is about 12 inches (30.5 cm) long and is 6 inches, (15.2 cm) wide at its widest point. The stomach's capacity is about 1 to 1.5 litres in an adult.
Food enters the stomach from the oesophagus. The connection between the stomach and the oesophagus is called the cardiac sphincter. The cardiac sphincter prevents food from passing back to the oesophagus. Heart burn is the sensation when stomach juices (gastric juice) is allowed to seep through the sphincter into the oesophagus. Once the food enters the stomach, gastric juices are used to break down the food. The other end of the stomach empties into the duodenum. The duodenum is the first section of the small intestine. The pyloric sphincter separates the stomach from the duodenum.The three important main functions of the stomach are:
- To kill and destroy any bacteria in the stomach.
- Break down large molecules of food into small molecules so it’s easier for digestion. Proteins are broken down by protease, lipids by lipase and carbohydrates by amylase
- To hold food and release it at a constant rate.
The stomach is a highly acidic environment due to hydrochloric acid production and secretion which produces a pH range usually between 1 and 2 depending on a whole range of factors such the, food intake, time of the day, drug use, and other factors. Combined with digestive enzymes, such an environment is able to break down large molecules (such as from food) to smaller ones so that they can eventually be absorbed from the small intestine. Pepsin and rennin and is present in hydrochloric acid and is a necessity in protein digestion.
Small Intestine
When the food is processed from the stomach it is passed to the small intestine via the pyloric sphincter. The major break down of food occurs in the small intestine, in here it is mixed with three different liquids:
- Bile which works by emulsifing fats to allow greater absorption. This substance is produced by the liver and then stored in the gallbladder. The bile in the gallbladder is much more concentrated.
- Pancreatic juice made by the pancreas.
- Intestinal enzymes, these include enzymes like maltase, lactase and sucrase (all three of which process only sugars), trypsin and chymotrypsin.
Large Intestine
The overall digestive system
The food finally reaches the large intestine, a 1.5 meter long intestine with another three parts to it, these are the cecum, the colon and the rectum. Within the large intestine, digestion is retained for long periods that is long enough to allow fermentation due to the action of gut bacteria. These gut bacteria breaks down some of the substance that remain in the small intestine and some of the broken down products are also absorbed. The large intestine stores feces until it can be egested and also absorbs water from the bolus. The feces is stored in the rectum which is associated with the large intestine and is eliminated from the body due to the contraction and relaxation through the anus.