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What is digestion?
It is a chemical and mechanical breakdown of large organic molecules into smaller units that can pass across the plasma membrane.
Why is digestion necessary?
- - food must be broken down
- - the smaller units are then able to be absorbed by cells
What are the 4 main steps for substances to become available to cells?
- - Ingestion of food: when food is captured and taken into an aminals mouth. (eating)
- - Mechanical breakdown of ingested food:Large pieces of food are broken down into smaller pieces
- - Chemical breakdown of large molecules into small molecules
- - absorption of molecules into the blood stream.
Describe what ingestion of food involves:
Describe mechanical digestion and why it is important.
What happens in the mouth?
- Chemical and Mechanical digestion:
- Chemical when the amalyse in saliva starts to break down starch; and
- Mechanical when the teeth chew up the food into smaller pieces.
- The mixture forms a 'bolus' that is swallowed.
In what way do the teeth of herbivores, carnivores and omnivores differ?
Carnivore - such as the Tasmanian devil, have well developed canine teeth for tearing meat from bones.
Herbivore - such as the whiptail wallaby, have incisor teeth that enable them to clip the grass and other vegetation that they eat. There is an absence of canine teeth.
Omnivore - such as humans, have teeth that are appropriate for a varied diet.
Gnawing Animal - such as rats, have well developed incisor teeth that enable them to gnaw through heavy grasses, twigs and in some cases, trees.
Describe peristalsis, and where does this occur?
Peristalsis is the movement of food along the gut by means of contraction and relaxation of muscles in the gut wall.
What does the oesophagus do?
it is a soft muscular tube that transports food from mouth to stomach by paristalsis.
Describe chemical digestion and its importance.
Chemical digestion is the chemical change of complex molecules into simpler ones, so that the simpler molecules can pass through plasma membranes into cells.
What does the absorption of food involve?
The absorption of food involves the organic molecules passing through membranes of cells lining the digestive tract and then into body fluids.
What happens in the stomach?
- Mechanical and Chemical digestion.
- The stomach is a large pouch where food is stored. The walls of the stomach secrete enzymes and hydrochloric acid, and the digestion of protein begins.
What is gastric juice?
Gastric juice is a mixture of mucus, enzymes and hydrocholic acid.The components of gastric juice are secreted by different kinds of cells in the stomach wall.
What separates the stomach and the small intestine? How does it work? Why is it important?
The Pyloric Sphincter separates the stomach from the small intestine. Small amounts of food are forced out of the stomach through this muscular opening.
What is the name of the first part of the small intestine?
What happens in the duedenum?
- The duodenum is about 25cm long and is the first part of the small intestine. It contains enzymes and substances that help in the breakdown of food.
What is the function of the pancreas in digestion?
The function of the pancreas in digestion is to secrete substances into the duodenum via the pancreatic duct. These substances include bicarbonates, amylases, protein digesting enzymes, lipases and nucleases which all help in the breakdown of food.
What is the function of the liver in digestion?
The function of the liver in digestion is to produce bile which is used to break up large fat droplets into smaller droplets through a process called emulsification.
What is bile? What does it do? Where is it stored?
- Bile is a greenish fluid which contains, Bile salts and Cholesterol and pigments.
- It helps to emulsify fats.
- It is stored in the gall bladder.
Name the 3 parts of the small intestine:
The three main parts of the Small intestines are the duodenum, jejunum and ileum
Describe the action of digestive enzymes:
The role of digestive enzymes is to act upon food being eaten and break it down multiple times, until it is small enough to be absorbed into the bloodstream through the villi in the small intestine. Many enzymes are released by the pancreas, and different enzymes act on different nutrients to digest.
Why does the small intestine have a large blood supply?
Since nutrients are absorbed through the bloodstream, the more blood in the small intestine, the more nutrients that can be absorbed for use in the body.
What is absorbed into the blood stream?
Nutrients such as glucose, amino acids, some fatty acids and glycerol are absorbed into the bloodstream through the capillaries in the villi.
What are lacteals?
- - Lacteals are blind extensions of the lymphatic system.
- - They transport most glycerol and fatty acids to the veins near the neck where they enter the bloodstream.
Describe the path of the blood after it leaves the small intestine.
What is the function of the jejunum and ileum?
- - Continue the chemical digestion of food.
- - Cells of the jejunum and ileum secrete aminopeptidases, which complete protein digestion.
- - Cells also secrete enzymes that act on specific carbohydrates, which complete the digestion of disaccharides.
- - Absorption of nutrients.
Descibe the structure of the small intestine.
- - The wall lining is made of folds instead of being flat; this increases the SA/V ratio.
- - Each fold is covered in finger-like projections called villi.
- - Each villi is covered in microvilli, this further increases the SA/V ratio of the small intestine.
What process allows the products of digestion to pass through the gut lining, and where do they go?
- - Products of digestion are absorbed through the cells lining the gut by diffusion.
- - The absorbed products pass through the gut lining and into the lymph and blood vessels below the epithelial cells of the small intestine.
- - Some active transport also occurs. The cells absorbing the products must expend energy to absorb the material against a concentration gradient.
What do the capillaries in the villi do?
They transport amino acids and monosaccharides to the liver via the hepatic portal vein.
How much of the total nutrient absorption takes place in the small intestine, and where does the rest occur?
- - Approximately 90% of the absorption of nutrients takes place in the small intestine.
- - The other 10% occurs in the stomach and large intestine.
How much water enters the intestines a day? Describe where they enter from.
- - 2300 mL enters the alimentary canal after being obtained from food and fluids.
- - 7000 mL enters the alimentary canal as enzymes and mucus are secreted by the canal wall cells.
- - 9000 mL is absorbed a day, 8500 mL of this is absorbed along with the products of digestion in the small intestine.
What is the cause of diarrhoea?
If the water is not absorbed into the body properly, the continued loss of water dehydrates the body, and causes the faeces to become watery.
By what method is water absorbed by the intestine? How much is left for the large intestine after this has occurred?
- - Osmosis allows water to be absorbed by the cells of the small intestine.
- - After osmosis has occurred, approximately 500 mL of water remains for the large intestine.
What gives the large intestine and the small intestine its names?
The diameter. The large intestine has an average diameter of about 6.5 centimetres where as the small intestine has an average diameter of around 2.5 centimetres.
What is the major function of the large intestine?
The major function of the large intestine is is to transport waste out of the body and to absorb water from the waste before it leaves.
What is peristalsis?
The movement of food along the gut by means of contraction and relaxation of muscle in the gut wall.
What are the two main parts of the large intestine?
- The colon, which extracts water and salt from solid wastes
What is a herbivore?
Herbivores are animals that eat plant material
How are herbivores able to digest cellulose?
Cellulose can be changed into a form that can be absorbed by the body. To do this these animals make significant use of bacteria to ferment the grasses that they eat. The broken down products from the bacteria are absorbed by the stomach, and energy from the cellulose becomes available for use by the herbivore.
Describe, with an example, a foregut fermenter:
The stomach or part of the oesphagus is vastly enlarged to accomode bacterial digestion. For example in cattle an expanded stomach can have up to 300 litres and constitute 15 per cent of the body mass.
Describe, with an example, a ruminant:
One stomach but has many compartments, an example is cattle, sheep and goats, they are all known as ruminants.
Describe, with an example, a hindgut fermenter:
Some mammals have modified regions of the colon and caecum for bacterial digestion, for example Dugongs are hindgut fermenters.
Why do nectar and pollen feeders have short digestive systems?
- ~The nectar requires no digestion because it is already a simple sugar, and provides immediate sugar and water for the honey possum
- ~Usually the pollen grains are digested within 6 hours
Explain the digestive system between foregut and hindgut fermenters in relation to herbivores?
Foregut fermenters- four chamered stomach with large rumen. Have small and large intestines are long.
Hindgut fermenters- small stomach with a large caecum.
Both contain bacteria to aid in the digestion of cellulose.
Why do carnivores have short digestive systems?
- ~ Carnivores have a reduced or small caecum compared to herbivores
- ~Canivores can digest protein very easily compared to the digestion of plant material eaten by herbivores
Why are photosynthesis and cellular respiration essential for all ecosystems?
- Photosynthesis provides oxygen for cellular respiration and glucose to provide energy
- Cellular respiration provides energy for all organisms.