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What is disease?
A disease is defined as a physical or
mental disorder or malfunction with a
characteristic set of signs or symptoms.
Diseases may be caused by a single
factor such as a pathogenic
microorganism or be multifactorial and
have many causes some of which may
depend on lifestyle.…read more

Slide 2

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· Pathogenic microorganisms include bacteria, viruses and
· Each pathogen has a specific method by which it causes
disease. Some such as the influenza virus damage host
cells whereas others, such as Vibrio cholera produce toxins
which have a harmful effect on the body.
· The ability of the pathogen to cause disease depends on
­ Location - what tissue is colonised
­ Infectivity - how easily a bacterium can enter the host cell
­ Invasiveness - how easily a bacterium or its toxin spreads within
the body
­ Pathogenicity - how a bacterium causes disease
· Common entry points for pathogens are the gas exchange
and digestive system.…read more

Slide 3

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· Lifestyle
· A healthy lifestyle involves:
­ Maintaining a healthy weight
­ Taking regular exercise
­ Eating a balanced diet
­ Drinking a limited amount of alcohol
­ Not smoking
· Lifestyle has an effect on human health:
­ Exposure to carcinogenic chemicals (i.e. those found in tobacco smoke)
or radiation (i.e. X-rays) may increase a person's chance of contracting
­ Coronary heart disease is associated with diets that are rich in fat and a
sedentary lifestyle
­ Alterations to a person's lifestyle can have a dramatic effect on the
likelihood of them contracting these conditions…read more

Slide 4

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The Digestive System
· The digestive system is a tube through which
food passes from the mouth where food is
ingested to the anus where it is egested. It
consists of a series of organs, each with a
distinct structure and function. During the
digestive transit food is broken down into
substances suitable for absorption into the
The gut wall has the same basic structure
along its length. There are three main layers:
· An outer, muscular layer. Circular and
longitudinal layers of smooth muscles are
present. Alternate contraction of these
muscles moves food along the digestive tract
· A middle layer of connective tissue
- submucosa
· An inner layer - mucosa…read more

Slide 5

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intestine/large intestine/rectum.
· Oesophagus
· Muscular tube carrying food from the mouth to the stomach
· Stomach
· Elastic and muscular organ which can expand
· Highly folded mucosa
· Gastric pits secreting gastric juices containing digestive enzymes (proteases)
· Contraction and relaxation of the muscular wall mix the food thoroughly
· Small Intestine
· The site of chemical digestion and absoption of the products of lipids, polysaccharides and
· Highly folded mucosa - arranged in villi (finger like projections to increase surface area for
· Epithelial cells lining the small intestine have a folded cell membrane - microvilli to further
increase the surface area for absorption
· Large Intestine
· The site of absorption of water
· Undigested food matter forms faeces
· Rectum
· Faecal matter is stored here before egestion…read more

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· Large molecules (starch, proteins, TAG) are too big and insoluble to be
­ Polymers have to be broken down into monomers
­ With help of hydrolytic enzymes - reaction requires H2O
­ Note: TAGs are not polymers but also need to be broken down
· Different enzymes break down different food
­ Work best at body temperature (37°)
­ Work in different conditions at different pH (stomach is acidic,
intestine is alkaline)
· Hydrolysis
­ Proteins amino acids
· Essential amino acids: cannot be synthesised and must be present
in diet
· Non-essential amino acids: synthesised from essential amino acids
by transamination in the liver
­ TAG glycerol and fatty acids
­ Polysaccharides monosaccharides…read more

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