First 695 words of the document:
The human digestive system is made up of a long muscular tube and its associated glands. These certain
glands produce enzymes that break down large molecules into small ones ready for absorption. The
digestive system provides an interface with the environment because food substances enter the body
The major parts of the digestive system are listed below in correct order;
Salivary Glands; Are situated near the mouth. They pass their secretions via a duct into the mouth. These
secretions contain the enzymes amylase which breaks down starch into maltose.
Oesophagus; Carries food from the mouth tot the stomach it is adapted for transport than for digestion, as
it's made of a thick muscular wall.
Stomach; Is a muscular sac with an inner layer that produces enzymes. Its role is to store and digest food,
and especially proteins, as it has glands that produce enzymes which digest proteins. Other glands in the
stomach produce mucus; this mucus prevents the stomach being digested by its own enzymes.
Pancreas; Is a very large gland situated below the stomach. It produces a secretion called pancreatic juice.
This secretion contains proteases to digest proteins, lipase to digest lipids and amylase to digest starch.
Small Intestine; Is a long muscular tube. Food is further digested in the small intestine by enzymes that are
produced by its wall and by glands that pour their secretions into it. The inner walls of the small intestine are
folded in villi which gives them a large surface area. The surface area of these villi is further increased by
millions of tiny projections, called microvilli on the epithelial cells of each villus. This adapts the small
intestine for its purpose of absorbing the products of digestion into the bloodstream.
Large Intestine; Absorbs water, most of the water that is reabsorbed comes from the secretions of the
many digestive glands. The food within the large intestine therefore becomes drier and thicker in consistency
and forms faeces.
Rectum; Is the final section of the intestine, the faeces are stored here before periodically being removed via
the anus in a process called egestion.
Digestion in humans as with many organisms, takes place in two stages;
1. Physical Breakdown
If the food is too large, it is broken down into smaller pieces by means of structures such as the teeth this
not only makes it possible to ingest the food but also provides a large structure area for chemical digestion.
Food is churned by the muscles in the stomach wall and this also physically breaks it up.
2. Chemical Breakdown
Chemical digestion breaks down large, insoluble molecules into smaller soluble ones. It is carried out by
enzymes. All digestive enzymes function by hydrolysis. Hydrolysis is the splitting up of molecules by adding
water to the chemical bonds that hold them together. The general term for such enzymes is hydrolyses.
Enzymes are specific and so it follows that more than one enzymes is needed to break down a large
molecule. Usually one enzyme splits a larger molecule into sections and these sections are then hydrolysed
into smaller molecules by one or more additional enzymes. There are different types of digestion enzymes,
three of which are very important.
Carbohydrates Break down carbohydrates, ultimately to monosaccharide's
Lipases Break down lipids (fats and oils) into glycerol and fatty acids
Proteases Break down proteins, ultimately to amino acids.
Once the large food molecules have been hydrolysed into monosaccharide, glycerol, fatty acids and amino
acids, they are absorbed by various means from the small intestine into the blood. They are carried to
different parts of the body and are often built up again into large molecules, although these are not
necessarily of the same type as the molecules from which they were derived. These molecules are
incorporated into body tissues and/or used in processes within the body. This is called assimilation.