Physiology - Digestive System
The branches of science that will help you understand the body parts and functions are anatomy and physiology. Anatomy deals with the study of the human body (the component parts, structure and position) and physiology the study of how the body functions.
Body Systems
Select the appropriate body system link, in the table below, to view the available information.
| Skeletal | Muscular | Neurological | Endocrine |
| Cardiovascular | Respiratory | Digestive |
Digestive System
The functions of the digestive system are:
- Ingestion - eating food
- Digestion - breakdown of the food
- Absorption - extraction of nutrients from the food
- Defecation - removal of waste products
The digestive system also builds and replaces cells and tissues that are constantly dying.
Digestive Organs
The digestive system is a group of organs (Buccal cavity (mouth), pharynx, oesophagus, stomach, liver, gall bladder, jejunum, ileum and colon) that breakdown the chemical components of food, with digestive juices, into tiny nutrients which can be absorbed to generate energy for the body.
The Buccal Cavity
Food enters the mouth and is chewed by the teeth, turned over and mixed with saliva by the tongue. The sensations of smell and taste from the food sets up reflexes which stimulate the salivary glands.
The Salivary glandsThese glands increase their output of secretions through three pairs of ducts into the oral cavity, and begin the process of digestion. Saliva lubricates the food enabling it to be swallowed and contains the enzyme ptyalin which serves to begin to break down starch. The PharynxSituated at the back of the nose and oral cavity receives the softened food mass or bolus by the tongue pushing it against the palate which initiates the swallowing action. At the same time a small flap called the epiglottis moves over the trachea to prevent any food particles getting into the windpipe. From the pharynx onwards the alimentary canal is a simple tube starting with the salivary glands. |
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The Oesophagus
The oesophagus travels through the neck and thorax, behind the trachea and in front of the aorta. The food is moved by rhythmical muscular contractions known as peristalsis (wave-like motions) caused by contractions in longitudinal and circular bands of muscle. Antiperistalsis, where the contractions travel upwards, is the reflex action of vomiting and is usually aided by the contraction of the abdominal muscles and diaphragm.
The Stomach
The stomach lies below the diaphragm and to the left of the liver. It is the widest part of the alimentary canal and acts as a reservoir for the food where it may remain for between 2 and 6 hours. Here the food is churned over and mixed with various hormones, enzymes including pepsinogen which begins the digestion of protein, hydrochloric acid, and other chemicals; all of which are also secreted further down the digestive tract.
The stomach has an average capacity of 1 litre, varies in shape, and is capable of considerable distension. When expanding this sends stimuli to the hypothalamus which is the part of the brain and nervous system controlling hunger and the desire to eat.
The wall of the stomach is impermeable to most substances, although does absorb some water, electrolytes, certain drugs, and alcohol. At regular intervals a circular muscle at the lower end of the stomach, the pylorus opens allowing small amounts of food, now known as chyme to enter the small intestine.
Small Intestine
The small intestine measures about 7m in an average adult and consists of the duodenum, jejunum, and ileum. Both the bile and pancreatic ducts open into the duodenum together. The small intestine, because of its structure, provides a vast lining through which further absorption takes place. There is a large lymph and blood supply to this area, ready to transport nutrients to the rest of the body. Digestion in the small intestine relies on its own secretions plus those from the pancreas, liver, and gall bladder.
The Pancreas
The Pancreas is connected to the duodenum via two ducts and has two main functions:
- To produce enzymes to aid the process of digestion
- To release insulin directly into the blood stream for the purpose of controlling blood sugar levels
Enzymes suspended in the very alkaline pancreatic juices include amylase for breaking down starch into sugar, and lipase which, when activated by bile salts, helps to break down fat. The hormone insulin is produced by specialised cells, the islets of Langerhans, and plays an important role in controlling the level of sugar in the blood and how much is allowed to pass to the cells.
The Liver
The liver, which acts as a large reservoir and filter for blood, occupies the upper right portion of abdomen and has several important functions:
- Secretion of bile to the gall bladder
- Carbohydrate, protein and fat metabolism
- The storage of glycogen ready for conversion into glucose when energy is required.
- Storage of vitamins
- Phagocytosis - ingestion of worn out red and white blood cells, and some bacteria
The Gall Bladder
The gall bladder stores and concentrates bile which emulsifies fats making them easier to break down by the pancreatic juices.
The Large Intestine
The large intestine averages about 1.5m long and comprises the caecum, appendix, colon, and rectum. After food is passed into the caecum a reflex action in response to the pressure causes the contraction of the ileo-colic valve preventing any food returning to the ileum. Here most of the water is absorbed, much of which was not ingested, but secreted by digestive glands further up the digestive tract. The colon is divided into the ascending, transverse and descending colons, before reaching the anal canal where the indigestible foods are expelled from the body.
Effect of exercise on the digestive system
Most exercise has a positive effect on the digestive system helping to quell appetite and increase metabolism. Some endurance events sometimes cause competitors to have an upset stomach and diarrhoea.
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Human Anatomy & PhysiologyThis heavily illustrated self-teaching course gives you everything you need to know. Find out how human muscles, nerves, bones,organs, glands, connective tissue and more, function and communicate with each other. Discover the molecular-level workings of your glandular, genitourinary, digestive, cardiovascular, and other systems. But that is just part of the story. Select this link for more information on Human Anatomy & Physiology. |
Associated Pages
The following Sports Coach pages should be read in conjunction with this page:
Associated Books
The following books provide more information related to this topic:
- Principles of Anatomy and Physiology, G.J. Tortora et al., ISBN 0 06 046704 5
- Strength Training Anatomy, F. Delavier, ISBN 0 7360 4185 0
- Atlas of Skeletal Muscles, R.J. Stone et al., ISBN 0 697 13790 2
- The Muscle Book, P. Blakey, ISBN 1 873017 00 6
- Advanced Studies in Physical Education and Sport, P Beashel et al., ISBN 0 17 4482345
- Physical Education and the Study of Sport, B. Davis et al., ISBN 0 7234 31752
- Essentials of Exercise Physiology, W.D. McArdle et al., ISBN 0 683 30507 7
- Physical Education and Sport Studies, D. Roscoe et al., ISBN 1 901424 20 0
- The World of Sport Examined, P. Beashel et al., ISBN 0 17 438719 9
- Advanced PE for Edexcel, F. Galligan et al., ISBN 0 435 50643 9
- Examining Physical Education, K. Bizley, ISBN 0 435 50660 9
- Sport and PE, K Wesson et al., ISBN 0 340 683821
- PE for you, J. Honeybourne, ISBN 0 7487 3277 2
Keywords: system, digestive, physiology, body, food, athlete, function, stomach, cardiovascular, liver, gall, bladder, human, anatomy, digestion, study, muscular, intestine, skeletal, cavity, glands, endocrine, respiratory, nervous, pharynx, oesophagus, colon, information, muscle, buccal