The Digestive System (4) Flashcards
What is digestion?
the breakdown of large insoluble food molecules into small soluble food molecules
Explain absorption
After digestion, the digested food products are them absorbed into the blood and transported around the body
How is the digestive system organised?
The parts of the digestive system are organised so that different processes take place in the different regions.
Label the digestive system
On flashcard or in booklet (Left side labels) - tongue - salivary glands - liver - bile duct - gall bladder - duodenum (small intestine) - caecum - appendix ( right side labels) - salivary glands - epiglottis - stomach - oesophagus - stomach - pyloric sphincter - pancreas - ileum (small intestine) - colon ( large intestine) - rectum - anus
The main processes that take place in the digestive system are:
Ingestion - taking food into the alimentary canal through the mouth
Digestion - large, complex food materials are broken down into simple, soluble molecules
Absorption - the passage of small, soluble molecules across the wall of the small intestine into the blood stream
Assimilation - digested food molecules are absorbed into body cells where they are used in respiration to release energy, stored, or built up into new complex molecules
Egestion - passing out undigested food material (faeces) from the anus
Explain the process in the mouth (Buccal cavity)
Food enters the mouth (Buccal cavity).
Physical digestion occurs through the action of the teeth. The teeth grind and chew the food and break it up into smaller pieces, increasing the surface area of the enzyme action .
Explain what saliva is used for
Saliva is added to the food in the mouth by the salivary glands.
It has two functions:
- it contains mucus which lubricates the food so that it is easy to swallow
- it contains the digestive enzyme amylase. This enzyme breaks down large insoluble starch molecules into glucose molecules (chemical digestion)
Explain what happens as food passes through the oesophagus
The oesophagus is the tube at the back of the throat that the food passes through before entering the stomach. This tube has layers of muscle in its walls. The food passes down the oesophagus by a wave of muscular contraction
Explain the process in the stomach
The stomach is a muscular, elastic bag that can stretch when food enters it. The muscles in the wall contract rhythmically, mixing the food thoroughly and turning it into a thick liquid called chyme.
Glands in the lining of the stomach produce gastric juice which contains:
- protease enzymes (pepsin) - thus breaks down proteins into amino acids. It works best in acidic conditions
-
What is the digestive system composed of & and what is its function?
The digestive system is composed of the alimentary canal (gut), which is a long tube with several organs attached to it. The alimentary canal runs from the mouth to the anus .
The function of the digestive system is to carry out digestion of the food we eat.
Explain what happens in the small intestine
The small intestine consists of the duodenum and the ileum. It is the longest part of the gut and may be over 6 metres long. The small intestine continues work already started in the stomach.
Explain what happens in the duodenum
The duodenum is the first part of the small intestine. The semi-liquid food released from the stomach is acted upon by a number of secretions in the duodenum:
- The pancreas (pancreatic juice)
- The duodenum wall (intestinal juice)
- The gall bladder (bile)
Explain pancreatic juice
Is produced by the pancreas and is secreted into the duodenum. It contains the enzymes:
Amylase - starch to glucose
Protease - protein to amino acids
Lipase - fat to fatty acids & glycerol
Carbohydrases - starch to glucose or carbs to glucose
Explain intestinal juice
Is produced by the walls of the duodenum (duodenal wall). It contains a number of enzymes (amylase, protease, lipase and carbohydrases) that finish the digestion process.
Explain bile
Bile is a green liquid that is produced in the liver and stored in the gall bladder. It has two functions in the duodenum:
- it is alkaline and therefore helps to neutralise the acidic food passing through from the stomach. It makes the duodenum slightly alkaline.
- it emuisities fats. Emulsification is the breakdown of large fat globules into smaller fat globules. This increases the surface area of the fat to make it easier for the lipase enzymes to break it down.
Explain what happens in the ilium
The ilium is the second part of the small intestine. More enzymes are secreted (amylase, lipase and protease) to ensure all the large molecules are now broken down to small, soluble molecules. The small molecules are then absorbed into the blood.
This is known as absorption and occurs by diffusion. Once in the bloodstream, the digested food molecules are carried around the body to where they are needed.
Only small, soluble substances can diffuse across the wall of the small intestine. Large insoluble substances cannot pass through.
Adaptions of the small intestine
The ilium is adapted for the process of absorption in many ways:
- Has a large surface area
- Good blood supply
- Thin and permeable membranes
Explain the ilium’s large surface area
A large surface area allows absorption to happen quickly and efficiently. If the small intestine had a small surface area, a lot of digested food might pass out of the body before it had a chance to be absorbed.
The small intestine has a large surface area because:
- it is long (over 6 metres)
- it has folds or twists along its length
- it’s inner surface contains millions of microscopic finger-like projections called villi (singular - villus). These stick out into the middle (lumen) of the small intestine
Explain the ileum’s good blood supply
Each villus has its own network of blood capillaries (tiny blood vessels) to transport the products of digestion (e.g. Amino acids, glucose) once they have been absorbed. This ensures that a steep concentration gradient is maintained.
Fats are dealt with differently. Inside each villus is a structure called a lactuel. Instead of going into the blood capillaries, fatty acids and glycerol are absorbed into the lactuel ( part of the system of tubes called the lymph system). Eventually these products will be returned back into the bloodstream.
Label diagram of a villus
On flashcard or in booklet
Left side
- a lactuel - absorbs breakdown products of fat (fatty acids & glycerol) and returns them to the blood later.
- lumen of gut
Right side
- a capillary network in the villus - absorbs breakdown of product of protein (amino acids) and starch (glucose)
- single later of surface cells
Describe villi’s thin & permeable membranes
The surface lining of each villus is thin and permeable due to the small number of cells between the lumen of the gut and the capillaries and lacteals. This makes it easier for dissolved food substances to pass through to the blood capillaries
Explain what happens in the large intestine (colon)
Some of the food we war is indigestible because we do not have the correct enzyme to digest it. Thus consists mainly of fibre (cellulose) from plant material. This undigested food cannot be absorbed in the ileum. It leaves the ileum and enters the next stretch of the alimentary canal called the large intestine (colon). Fibre helps food progress long the alimentary canal.
In the large intestine water is removed from this material and is absorbed back into the blood. The colon is adapted by having a large surface area.
Explain what happens in the rectum and anus
The remaining waste material accumulates and is stored in the rectum where it forms faeces. This can be removed (egested) through the anus at intervals.
Summary of enzyme action in digestion
Enzyme | Amylase Food digested | starch products of digestion | glucose Region of body | mouth, duodenum, ileum Source of enzyme | salivary glands, pancreatic juice, intestinal juice
Enzyme | protease
Food digested | protein
Products of digestion | amino acids
Region of body | stomach, duodenum, ileum
Source of enzyme | gastric, pancreatic and intestinal juice
Enzyme | lipase
Food digested | fat
Products of digestion | fatty acids & glycerol
Region of body | duodenum, ileum
Source of enzyme | pancreatic and intestinal juice
