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Summary IGCSE-Biology-Digestive system
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IGCSE-Biology-Digestive system: Summary of the human digestive system (Triple award inculded)
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Digestive system:When we eat, the nutrients we need from food (carbohydrates, proteins etc) are large and insoluble.
This means they cannot be absorbed into the blood, and transported to where they are needed in the
body.
Digestion is the breakdown of food, from large insoluble molecules to small, soluble molecules, which
can be absorbed into the blood.
Mechanical digestion Chemical digestion
Involves the physical breakdown of food into Involves chemical reactions to change the food
smaller particles. particles into different, smaller molecules. This is
aided by enzymes - biological catalysts that speed
up the rate of chemical reactions.
Humans have a digestive system. It is an organ system (group of organs) that work together to digest our
food.There is a long tube (about 8m) that carries food through the body, starting in the mouth,
compromising several organs and ending at the anus. This is called the alimentary canal.
PROCESS OF DIGESTION:
After ingestion, Inside the mouth, mechanical digestion occurs. Chewing breaks down food into smaller
particles, increasing their surface area. Chemical digestion also occurs here - the salivary glands secrete
amylase, an enzyme which helps break down starch into a simpler sugar - maltose.
The oesophagus transports food from the mouth to the stomach.
In the stomach, mechanical digestion occurs - the stomach
muscles contract to churn up the food.
Chemical digestion of proteins also occurs here, catalysed by
pepsin, breaking down protein to peptides. The stomach
contains hydrochloric acid - which gives the optimum conditions
for pepsin. It also kills any bacteria.
The liver makes a digestive juice, called bile. This helps with the
breakdown of lipids. It is stored in the gallbladder. The pancreas
produces digestive enzymes. These then digest food in the small
intestines.
The small intestines is where digestion is finalised and products
of digestion are absorbed into the blood.
The walls of the small intestine produce enzymes, as well as
those from the pancreas. The start of the small intestines is
called the duodenum, the mid section the Jejunum and the final
section the ileum. It is in the ileum where products of digestion
are absorbed into the blood. The large intestine is where water
is absorbed into the blood. This part of the large intestines is
the colon. Any remaining food, such as fibre, and waste
products are stored in the
rectum (end of small
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