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The Digestive System, Mouth - Coggle Diagram
The Digestive System
Process of digestion
The digestive system is designed to turn food that is eaten into nutrients, which the body uses for energy, growth and cell repair.
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The process of digestion begins in the mouth where food is chewed until it reaches a consistency whereby it can be swallowed. The following accessory structures aid this early stage of digestion:
Tongue — a muscle that is covered by tastebuds. It assists the process of chewing and manoeuvres food to a position where it can be swallowed easily.
Salivary glands — begin the process of chemical digestion through the secretion of the enzyme, salivary amylase. This enzyme begins the process of breaking down carbohydrates. Saliva also moistens food which helps it to be swallowed more easily.
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Oesophagus
The oesophagus is the tube or gullet connecting the mouth to the stomach. It lies in front of the vertebral column and behind the trachea (breathing tube) and heart.
Stomach
Intestines: Digested material is moved through the intestine via a process of wavelike muscular contractions called peristalsis. The process of digestion is completed in the small intestine. At this stage the nutrients that the body needs are absorbed through the walls of the small intestine (ileum).
The waste material then moves into the large intestine where water is reabsorbed; thereby changing it into a more solid form, ready to be excreted through the rectum.
Food remains in the stomach for 3 to 4 hours. During this time it is further broken down by the muscular churning action of the stomach. Powerful gastric juices that contain enzymes are secreted by the cells of the stomach, contributing to chemical digestion. The food ends up in a semi-liquid form that is called chyme.
Liver
The liver is a large gland that is divided into four lobes. It carries out many vital metabolic functions such as:
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Gallbladder
The gallbladder concentrates and stores bile that is produced in the liver. It then releases the bile when it is needed for digestion after a fatty meal.
Pancreas
The pancreas is what is called both an endocrine and exocrine gland. It produces pancreatic juices, containing enzymes, which play an important role in the chemical digestion of food. The pancreas also produces the hormones insulin and glucagon directly into the bloodstream, which is termed an endocrine function.
Function
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Absorption is where substances pass through the walls of parts of the digestive tract into the bloodstream. 90 % of the absorption of all nutrients takes place in the ileum of the small intestine through small projections called villi. The other 10 % take place in the stomach and large intestines.
Elimination is the process by which undigested foods leave the body. Any undigested food and water moves into the colon. Movement is slow in this section and it is anywhere from 16-24 hours before waste is evacuated. This evacuation is a reflex action and is called defecation. It occurs as the rectal sphincter responds to a filling of the colon and can be voluntarily inhibited by keeping the external sphincter contracted.
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