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Section D:Digestive System & human nutrition (human Alimentary canal…
Section D:Digestive System & human nutrition
human Alimentary canal
the mouth
Mechanical digestion happens here- your jaw action.
A bolus is created; this is a ball of food covered in saliva. This is help full as the food is lubricated to enable swallowing and enzymes in the saliva can begin to break down the food. (amylase)
The oesophagus
this tube connects you mouth and stomach. It is next to the trachea which is covered by the epiglottis when you swallow so the food only enters the oesophagus.
Peristalsis- or muscular contractions- moves the food downward
The stomach
Churning mechanically digests whilst enzymes do so chemically.
Chyme is the name for liquid food existing in the stomach.
the small intestine
This absorbs digested molecules into the blood stream.
Villi cover the inside giving it a large surface area which many molecules can diffuse through into the blood.
Large intestine
This absorbs water from undigested food, producing faeces.
Pancreas
This produces the enzymes lipase, amylase and protease.
Prosess
INGESTION: Taking food into the body.
DIGESTION: Breaking down large insoluble molecules in food into smaller soluble molecules
ABSORPTION: Taking digested food into the blood
EGESTION: Expelling undigested material from the body via the anus in faeces.
ASSIMILATION: Using the absorbed nutrients and converting it into living tissue
how and why food is moved through the gut by peristalsis
A bolos is a mouthful of food that you swallow
the muscles before the bolus of food contract and forces the bolos down and the muscles after it relax to let it through
Peristalsis doesn't just happed in the oesophagus.
the gut is the whole of the digestive tract starting at the mouth and finishing at the anus
Role of Digestive Enzymes
the digestion of starch to glucose by amylase and maltase,
the digestion of proteins to amino acids by proteases
the digestion of lipids to fatty acids and glycerol by lipases
Bile
Bile is made in the liver.
• It is then secreted by the liver and stored in the gall bladder until it is needed.
• During digestion bile is released into the small intestine. Here it helps emulsify fat in our food. This means that large fat droplets are broken up into smaller fat droplets.
• This provides a larger surface area for the enzyme lipase, which breaks down fats into fatty acids and glycerol.
• Bile is also alkaline. Thus when mixed with the acidic Mixture of semi-digested food and enzymes coming from the stomach, the mixture is neutralised before it continues on its way through the gut.
Villus
Human Nutrition
sources and functions of
components of the diet
Carbohydrates are used for energy supply
Fats (Lipids) are used as an Energy store, insulation
Protein is used for growth and Cell repair
Fibre adds bulk to the food and allows peristalsis and prevents constipation.
Water is used for excretion, cooling and chemical reactions
