How Food Is Broken Down In The Body
• What Is The Digestive System?
|What Is The Digestive System?
It is a group of organs in the body which work together to digest food. Digestion is the process by which our body breaks down food into substances we can take in (absorb) and use. Food travels through the alimentary canal which starts at mouth and ends at the anus. The alimentary canal is also known as the digestive tract or gut. As well as the mouth and anus, it includes the esophagus, stomach and intestines. If you could lay your gut out straight it would be 6 times your height.
|What Are The Stages Of Digestion?
There are four stages of digestion:
What Are The Bowels? Bowels is another name for the small and large intestines combined.
Studies estimate that it takes food 50 to 53 hours to travel from the mouth to out the other end as feces.
|Stage 1: The Mouth and Esophagus
In the mouth the action of teeth and saliva combine in the first stage of breakdown, chewing and partially digesting the food so that it will pass more easily along the esophagus. The ball of food that leaves the mouth is known as a bolus.
What Is Saliva?
Saliva (spit) is a liquid secreted by 3 pairs of salivary glands: the parotid gland (situated below the ear), the submandibular gland and the sublingual gland (both situated below the tongue). It contains water, mucus and the enzyme salivary amylase.
What Is An Enzyme?
If we think about the food we eat, and the difference in size between it and the microscopic cells and tissues that it will feed in our body, it is easy to understand why a digestive system that breaks food down into different units is needed. Enzymes are an important part of the process. If the digestive system is a conveyor belt, enzymes are the machines and workers which slowly change whatever is on the belt to make it smaller and smaller so that, eventually, it can be carried around the body in blood. They are made of protein and act as catalysts - that is, they make chemical changes happen in other substances, while themselves remaining unchanged. They act on food, changing it into smaller particles.
What Is The Tongue?
How Does Food Get From The Mouth To The Stomach?
Through the action of swallowing and through the portion of the gastrointestinal tract known as the esophagus. The tongue pushes the bolus to the back of the mouth, towards the pharynx, a muscular tube behind the mouth. The food passes into the pharynx and down to the esophagus. The epiglottis, a small flap of cartilage which forms part of the larynx (the windpipe) moves upwards and forwards, blocking the entrance to the larynx. This stops the food from 'going down the wrong way' and prevents choking.
What Is The Esophagus?
|Stage 2: What Is The Stomach?
The stomach is a J-shaped, elastic organ which expands and contracts depending on what is in it. Food enters it from the esophagus via the esophageal sphincter, a valve that stops back flow of the stomach's contents. It leaves the stomach through the pyloric sphincter into the duodenum, the first part of the small intestine. The wall of the stomach is a combination of layers of muscle fiber with an inner mucous membrane. The inner mucous membrane has lots of folds, called rugae. When the stomach is full they stretch out, enabling expansion, then they contract when it empties.
|What Does It Do?
The Chemistry Of Digestion
The whole digestive process is a combination of different chemical reactions that act on the food we eat, reducing it to the building blocks of nutrients for absorption and use by the body. Every piece of food we eat is composed of fats, carbohydrates and proteins. These must be broken down into their relative chemical compounds in order for the body to use them i.e. by the time the bread you eat reaches your muscles as energy it has been chewed, churned, liquefied and the starch changed to useable glucose. The following shows the main chemical reactions and breakdowns at different stages of digestion.
What Are Proteins?
Proteins foods include dairy products, meat, fish and beans. Proteins are large molecules that are made up long chains of polypeptides. They are the building material for the body. In order to be used by the body they must be broken down into their smaller components - amino acids. There are approximately 20 amino acids classified by whether they are essential (those the body cannot make, that must therefore be supplied in the diet) and non-essential (those the body can make).
What Are Fats?
Fats are classified as saturated, monounsaturated or polyunsaturated. Saturated fats can be found in dairy products and meat. Monounsaturated fats can be found in olive oil and avocados. Polyunsaturated fats can be found in sunflower oil and oily fish. Some polyunsaturated fats cannot be made by the body and are therefore also classified as essential fats and must be consumed in the diet. In order to be used by the body, fats must be broken down to fatty acids and glycerol.
What Are Carbohydrates?
Carbohydrates are classified as monosaccharides, disaccharides or polysaccharides. Monosaccharides include fructose in fruit. Disaccharides include lactose in milk. Polysaccharides include starch and fiber in cereals, potatoes and other plant sources, and glycogen in meat. All carbohydrates are broken down to monosaccharides for absorption and all eventually become glucose to supply the body with energy.
The small intestine, ironically, is not that small. It is seven 7 long and divided into 3 different parts: the duodenum, the jejunum and the ileum. The walls have several layers, including a muscular layer, a layer containing blood vessels, lymph vessels and nerves and an inner mucous membrane. The inner wall is covered with villi, tiny finger-like projections which increase the surface area for absorption and contain a network of blood and lymph vessels.
What Does The Small Intestine Do?
It completes the chemical digestion of food and the subsequent absorption of nutrients takes place in the small intestine. Nutrients are absorbed through the villi into the blood and lymph vessels. Hardly any food is absorbed elsewhere in the digestive system.
How Does Digestion And Absorption Happen In The Small Intestine?
1. Waves of muscular contractions called peristaltic movements mix food with intestinal and pancreatic juices as well as bile. The movements push the food against the villi. Intestinal juices are composed of enzymes:
Other Functions Of The Small Intestine
To protect the digestive system from infection. It is the only section of the digestive system with a direct link to the protective lymphatic system.
What Is The Large Intestine?
The large intestine deals with waste. It is about 1.5 meters long and sits draped around the small intestine. It consists of the caecum, appendix, colon, rectum, anal canal and anus.
Feces is the unwanted leftovers from food, combined with cellulose (roughage which is indigestible, found in foods like vegetables and bran), dead blood cells, bacteria (both living and dead), fatty acids and mucus used to help move the feces through the large intestine. The color comes from the dead blood cells and bilirubin, a bile pigment.
Summary: Functions Of The Large Intestines
• Absorbs nutrients, vitamins, salt or water left in digestive waste.
There are several other organs involved in the digestive process: the tongue, teeth and salivary glands, liver, pancreas and gall bladder. They are known as accessory organs because, although they do not form part of the gastrointestinal tract, they help the digestive process by breaking down foodstuffs and the toxins/ waste produced during digestion. The role of the tongue, teeth and salivary glands has been mentioned earlier in the chapter.
What Is The Liver? PICTURE OF LIVER
What Is The Gall Bladder?
What Is The Pancreas? PICTURE OF PANCREAS
What Is Insulin?
Insulin is a hormone secreted by specialized cells in the pancreas known as the islets of Langerhans. It regulates blood sugar level. When we eat, the blood sugar level rises. The sugar in the blood is in the form of glucose. Insulin helps cells absorb glucose and turns any excess glucose into glycogen, an insoluble sugar which is stored in the liver until the body needs it. Thus the blood sugar level drops. A lack of insulin causes diabetes. Type 1 diabetes is caused by auto-immune damage to the pancreas resulting in low or no insulin production. Type 2 diabetes is strongly linked to obesity and although insulin may still be produced it is unable to work properly in the body (insulin resistance). In either type, glucose cannot be properly absorbed into the body resulting in the following symptoms — a dangerously high level of blood sugar (hyperglycemia), the loss of glucose through excretion, thirstiness and excessive urine production. Low levels of blood sugar is known as hypoglycemia.
|Diseases Of The Digestive System
Irritable Bowel Syndrome
The digestive system links to:
Circulatory System: This system transports nutrients from the digestive system to every system of the body.
The digestive system:
Other Systems Of The Body
| Other Useful Guides
Recommended health screenings for women: Tests for every woman, every age.
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