human nutrition Flashcards
balanced diet
A balanced diet is a diet in which all the components needed to maintain health are present in appropriate proportions.
The necessary food groups are:
Carbohydrates Proteins Lipids Vitamins Minerals Dietary Fibre Water
There are different types of malnutrition depending on the cause of the imbalance
They include:
Starvation
Coronary heart disease
Constipation
Obesity
Protein Energy Malnutrition
In many countries in the world, droughts, natural disasters, wars and a poor economy can lead to mass malnutrition in large areas of the country
The two types of malnutrition most common in these situations are termed ‘protein energy malnutrition’ (PEM)and they are:Kwashiorkor – caused by a lack of protein in the diet, most common in children under 2.
Often caused by poverty as high protein foods tend to be more expensive and scarcer.
Children suffering from kwashiorkor are always underweight for their age but they often have a swollen abdomen as their diet may contain a lot of carbohydrate
Marasmus – the most severe form of PEM, where there is a lack of both protein and energy in the diet.
People suffering from this have a much lower body weight than normal and look emaciated
Dietary Needs of Different Individuals
Food taken into the body goes through 5 different stages during its passage through the alimentary canal (the gut)
Ingestion – the taking of substances, e.g. food and drink, into the body through the mouth
Mechanical digestion – the breakdown of food into smaller pieces without chemical change to the food molecules
Chemical digestion – the breakdown of large, insoluble molecules into small, soluble molecules
Absorption – the movement of small food molecules and ions through the wall of the intestine into the blood
Assimilation – the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells
Egestion – the passing out of food that has not been digested or absorbed, as faeces, through the anus
Ingestion
he taking of substances, e.g. food and drink, into the body through the mouth
Mechanical digestion
the breakdown of food into smaller pieces without chemical change to the food molecules
Chemical digestion
the breakdown of large, insoluble molecules into small, soluble molecules
Absorption
the movement of small food molecules and ions through the wall of the intestine into the blood
Assimilation
the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells
Egestion
the passing out of food that has not been digested or absorbed, as faeces, through the anus
Diarrhoea Causes and Treatment
Diarrhoea is the loss of watery faeces from the anus
If it is severe and continues for a long time, it can lead to death
Severe diarrhoea can cause the loss of significant amounts of water and ions from the body, causing the tissues and organs to stop working properly
It can be effectively treated by oral rehydration therapy
This is a drink with a small amount of salt and sugar dissolved in it
There are many causes of diarrhoea, one of which is infection with Vibrio cholerae bacteria, which causes the disease cholera
How does Vibrio Cholerae Cause Diarrhoea?
ingested via infected water or food, if it enters the small intestine it can cause illness in the following way:
Bacteria attach to the wall of the small intestine
They produce a toxin
The toxin stimulates the cells lining the intestine to release chloride ions from inside the cells into the lumen of the intestine
The chloride ions accumulate in the lumen of the small intestine and lower the water potential there
Once the water potential is lower than that of the cells lining the intestine, water starts to move out of the cells into the intestine (by osmosis)
Large quantities of water are lost from the body in watery faeces
The blood contains too little chloride ions and water
mechanical digestion is mainly carried out by
the chewing action of the teeth, the churning action of the stomach and the emulsification of fats by bile in the duodenum
They are used for
chewing to increase the surface area of the food so that it can be exposed to saliva and other digestive juices and broken down more quickly
Incisors
chisel shaped for biting and cutting
Canines
pointed for tearing, holding and biting
Premolars and molars
larger, flat surfaces with ridges at the edges for chewing and grinding up food
Dental Decay
Tooth decay and gum disease are both caused by bacteria
Many bacteria live in the mouth and most are harmless, however some form a sticky film with saliva, called plaque, which coats teeth and the areas where they attach to gums
To begin with, plaque is soft and easy to remove, however if it hardens and forms tartar, it cannot be removed by brushing
Tartar around the edges of teeth and gums can allow bacteria to work their way into roots, causing gum disease and loss of teeth
If sugar is left in the mouth after eating, bacteria in plaque will feed on it
They use it in respiration and turn it into acids
The acids gradually dissolve the enamel coating of the teeth, working its way into the dentine
Dentine is softer than enamel and so dissolves more easily and quickly
This is tooth decay and if not dealt with, can cause painful infections and loss of teeth
Dental Health
Reducing the amount of sugar eaten can prevent tooth decay
Brushing teeth regularly removes the buildup of plaque that can cause gum disease and removes the sugars in the mouth so bacteria cannot turn them into acids and cause tooth decay
Teeth should be brushed with a fluoride toothpaste as this helps to strengthen enamel and reduce damage from acids
Regular visits to a dentist ensures that any signs of gum disease or tooth decay can be dealt with promptly
The purpose of digestion is to
break down large, insoluble molecules (carbohydrates, proteins and lipids) into small, soluble molecules that can be absorbed into the bloodstream
Digestion mainly takes place chemically, where
bonds holding the large molecules together are broken to make smaller and smaller molecules
Chemical digestion is controlled by …which are produced in different areas of the… system
- enzymes
- digestive
There are three main types of digestive enzymes
carbohydrases, proteases and lipases
Carbohydrases
Amylase is secreted into the alimentary canal in the mouth and the duodenum (from the pancreas) and digests starch to maltose (a disaccharide)
Maltose is digested by the enzyme maltase into glucose on the membranes of the epithelium lining the small intestine
Proteases
Protein digestion takes place in the stomach and duodenum with two main enzymes produced:
Pepsin is produced in the stomach
Trypsin is produced in the pancreas and secreted into the duodenum
Lipases
Lipase enzymes are produced in the pancreas and secreted into the duodenum
They digest lipids into fatty acids and glycerol
The digestion of fats (lipids) to fatty acids and glycerol
The Role of Hydrochloric Acid
The stomach produces several fluids which together are known as gastric juice
One of the fluids produced is hydrochloric acid
This kills bacteria in food and gives an acid pH for enzymes to work in the stomach
How is a Low pH Helpful in the Stomach?
The low pH kills bacteria in food that we have ingested as it denatures the enzymes in their cells, meaning they cannot carry out any cell reactions to maintain life
Pepsin, produced in the stomach, is an example of an enzyme which has a very low optimum pH – around pH 2
The hydrochloric acid produced in the stomach ensures that conditions in the stomach remain within the optimum range for pepsin to work at its fastest rate
The Role of Bile
Cells in the liver produce bile which is then stored in the gallbladder
Bile production and secretion
Bile has two main roles:
It is alkaline to neutralise the hydrochloric acid which comes from the stomach. The enzymes in the small intestine have a higher (more alkaline) optimum pH than those in the stomach
It breaks down large drops of fat into smaller ones. This is known as emulsification. The larger surface area allows lipase to chemically break down the lipid into glycerol and fatty acids faster.
emulsification is an example of …digestion,
mechanical
How is the Ileum Adapted for Absorption?
The ileum is adapted for absorption as it is very long and has a highly folded surface with millions of villi (tiny, finger like projections)
These adaptations massively increase the surface area of the ileum, allowing absorption to take place faster and more efficiently
Structure and Adaptations of a Villi
Microvilli on the surface of the villus further increase surface area for faster absorption of nutrients
Wall of villus is one cell thick meaning that there is only a short distance for absorption to happen by diffusion and active transport
Well supplied with a network of blood capillaries that transport glucose and amino acids away from the small intestine in the blood
Lacteal runs through the centre of the villus to transport fatty acids and glycerol away from the small intestine in the lymph
Structure and Adaptations of a Villus
