Digestive System
- Created by: emews
- Created on: 26-10-17 12:10
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- Digestive system
- Human alimentary canal
- Mouth
- Salivary glands
- Oesophagus
- Stomach
- Pancreas
- Liver
- Gall bladder
- Small intestine
- Large intestine
- Teeth
- Food is broken down into smaller pieces in the mouth by chewing
- An example of mechanical digestion
- Cut and crush food, then mixed with saliva
- Types of teeth
- Incisor - for biting and cutting
- Canine - for holding and cutting
- Premolar and molar - for crushing and chewing
- Tooth decay
- Tooth decay happens when the hard outer enamel of the tooth is damaged
- Happens when bacteria in the mouth convert sugars into the acids that react with the enamel.
- Ways to prevent it
- Avoiding foods with a high sugar content
- Using toothpaste
- Drinking water containing fluoride
- Fluoride
- Reduces tooth decay by:
- Reducing the ability of bacteria on plaque to produce acid
- Helping to replace calcium ions and phosphate ions lost by tooth enamel because of acid attack
- Arguments against fluoridation of drinking water:
- Some people say that they should not be forced to consume fluoride
- Excessive fluoride can cause grey or brown spots on the teeth
- Reduces tooth decay by:
- Fluoride
- Regular, effective brushing to prevent the build-up of plaque
- Ingestion
- Food enters the digestive system by mouth. This is called ingestion
- Peristalsis
- Food is moved through the digestive system by a process called peristalsis
- Two sets of muscles in the gut wall are involved:
- Circular muscles - reduce the diameter of the gut when they contract
- longitudinal muscles - which reduce the length of the gut when they contract
- The muscles work together to produce wave-like contractions.
- Digestive enzymes
- Digestion is the breakdown of large insoluble food molecules into small, water-soluble molecules using mechanical and chemical processes
- Mechanical digestion includes:
- Chewing in the mouth
- Churning in the stomach
- Enzymes can break down nutrients into small, soluble molecules that can be absorbed
- Types of enzymes
- Salivary amylase breaks down starch
- Protease breaks down protein
- Lipase breaks down lipids (fats and oils)
- Pancreatic amylase breaks down starch
- Maltase breaks down maltose
- Where digestion happens
- Proteases catalyse the breakdown of protein into amino acids in the stomach and small intestine
- Lipases catalyse the breakdown of fats and oils into fatty acids and gllycerol in the small intestine
- Amylase catalyses the breakdown of starch into maltose in the mouth and small intestine
- Maltase catalyses the breakdown of maltose into glucose in the small intestine
- Absorption
- The movement of digested food through the wall of the intestine into the blood or lymph
- Villi
- Tiny, finger-shaped structures that increase the surface area.
- Important features:
- Wall just one cell thick for short diffusion distance
- Network of blood capilliaries to transport glucose and amino acids away from the small intestine in the blood
- Internal structure called a lacteal which transports fatty acids and glycerol away from the small intestine in the lymph
- Egestion.
- Remaining material:
- Water
- Bacteria (living and dead)
- Cells from lining of gut
- Indigestible substances such as cellulose from plant cell walls.
- Remaining material:
- Human alimentary canal
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