Digestion is the process that helps humans to survive,because it produces energy for life,but also creates some waste that needs to be eliminated from the humans body.
Human digestive system starts at the mouth and ends at the anus. It is made up of a of muscles that coordinate the movement of food and other cells that produce enzymes and hormones to aid at dissolution of food. There are also three other organs that are needed for digestion: the liver, gallbladder, and the pancreas.
Food’s journey through the human digestive system
Digestion starts at the mouth even before you take the first bite of a meal. That’s because the smell of food triggers the salivary glands in your mouth to secrete saliva, causing your mouth to water. When you actually taste the food, saliva increases.Once you start to chew and break the food down into pieces small enough to be digested other mechanisms come into play. More saliva is produced to begin the process of breaking down food into a form your body can absorb and use. In addition, “juices” are produced that will help to further break down food.
2- The Pharynx and Esophagus
The pharynx,or the throat, is the part of the digestive tract that receives the food from your mouth. Branching off the pharynx is the esophagus, which carries food to the stomach, and the trachea or windpipe, which carries air to the lungs.
The act of swallowing takes place in the pharynx partly as a reflex and partly under voluntary control. The tongue and soft palate — the soft part of the roof of the mouth — push food into the pharynx, which closes off the trachea. The food then enters the esophagus.
The esophagus is a muscular tube extending from the pharynx and behind the trachea to the stomach. Food is pushed through the esophagus and into the stomach by means of a series of contractions called peristalsis.
There is an important ring-shaped muscle called the lower esophageal sphincter wich opens to letfood pass into the stomach and closes to keep it there. If your LES doesn’t work properly, you may suffer from a condition called GERD, or reflux (the feeling of food coming back up).
3- The Stomach and Small Intestine
The stomach is a organ that looks like a bag,but with strong muscular walls. It serves as the mixer and grinder of food. The stomach secretes acid and powerful enzymes that continue the process of breaking the food down and changing it to a consistency of liquid orpaste. After that food goes to the small intestine. Between meals the non-liquefiable remnants are released from the stomach and ushered through the rest of the intestines to be eliminated.
The small intestine is made of three segments — the duodenum, jejunum, and ileum.It also breaks down food using enzymes released by the pancreas and bile from the liver. Peristalsis is also at work in this organ, moving food through and mixing it up with the digestive secretions from the pancreas and liver, including bile. The duodenum is largely responsible for the continuing breakdown process, with the jejunum and ileum being mainly responsible for absorption of nutrients into the bloodstream.Problems with any of these components can cause a variety of conditions.While food is in the small intestine, nutrients are absorbed through the walls and into the bloodstream. The waste moves into the large intestine.Everything above the large intestine is called the upper GI tract. Everything below is the lower GI tract
4-The Colon, Rectum, and Anus
The colon (large intestine) is muscular tube that connects the small intestine to the rectum. It is made up of the ascending (right) colon, the transverse (across) colon, the descending (left) colon and the sigmoid colon, which connects to the rectum. The appendix is a small tube attached to the ascending colon. The large intestine is a highly specialized organ that is responsible for processing waste so that defecation is easy and convenient.
Stool, or waste, passes through the colon by means of peristalsis, first in a liquid state and ultimately in solid form. As stool passes through the colon, any remaining water is absorbed. Stool is stored in the sigmoid (S-shaped) colon until a “mass movement” empties it into the rectum, usually once or twice a day.
It normally takes about 36 hours for stool to get through the colon. The stool itself is mostly food debris and bacteria. These bacteria perform several useful functions, such as synthesizing various vitamins, processing waste products and food particles, and protecting against harmful bacteria. When the descending colon becomes full of stool it empties its contents into the rectum to begin the process of elimination.
5-Rectum and anus
Rectum has three main operations. It receives stool from the colon,lets the person know there is stool to be evacuated.and holds the stool until evacuation happens.
When gas or stool comes into the rectum, sensors send a message to the brain. The brain then decides if the rectal contents can be released or not. If they can, the sphincters relax and the rectum contracts, expelling its contents. If the contents cannot be expelled, the sphincters contract and the rectum accommodates so that the sensation temporarily goes away.
The last part of the digestive tract is anus. It consists of the muscles that line the pelvis (pelvic floor muscles) and two other muscles called anal sphincters .One is internal and the other one is external.
The pelvic floor muscle creates an angle between the rectum and the anus that stops stool from coming out when it is not supposed to. The anal sphincters provide fine control of stool. The internal sphincter is always tight, except when stool enters the rectum. It keeps us continent (not releasing stool) when we are asleep or otherwise unaware of the presence of stool. When we get an urge to defecate , we rely on our external sphincter to keep the stool in until we can get to the toilet.
As we mentioned at the begginig,there are also three organs very significant for digesting the food.
Pancreas the chief factory for digestive enzymes that are secreted into the duodenum and these enzymes break down protein, fats, and carbohydrates.
Liver has multiple functions, but two of its main functions are to make and secrete an important substance called bile and to process the blood coming from the small intestine containing the nutrients just absorbed. The liver purifies this blood of many impurities before traveling to the rest of the body.
Gallbladder is a storage sac for excess bile. Bile serves two main purposes. First, it helps absorb fats in the diet and secondly, it carries waste from the liver that cannot go through the kidneys Bile made in the liver travels to the small intestine via the bile ducts. If the intestine doesn’t need it, the bile travels into the gallbladder where it awaits the signal from the intestines that food is present..