PARASITES: ECTOPARASITES (present in skin or on bodysurface)
Common examples
How acquired
• Head lice
• Ticks
• Bedbugs
• Cat/Dog fleas
• Aquatic leeches
Suck host’s blood
Through contact with other
people (lice, scabies mites,
warts), animals (ringworm fungi,
ticks), vegetation (ticks, mites),
or water (aquatic leeches).
Bedbugs live in bedroom walls or
mattresses and visit humans at
night. Cat and dog fleas may visit
humans when the pet is absent.
• Scabies mites
Burrow in skin
• Ringworm fungi
• Wartviruses
Multiply in skin
Common examples
How acquired
• Tapeworms
• Flukes
• Roundworms
• Threadworms
• Hookworms
Adults live in human
gut, blood vessels, bile
ducts, or elsewhere and
produce eggs that are
passed out of the body.
By eating infected meat,
swallowing eggs on food,
contaminating fingers with
faecal material, or contact with
infected water.
• Various disease-
causing protozoa,
fungi, bacteria, and
Organisms multiply
locally or spread
throughoutthe body,
causing disease.
By inhalation, water- or food-borne
transmission, sexual transmission,
or blood-borne infection, among
other mechanisms.
of thoughts), telekinesis (movement of
objects with the m ind), and precogni-
tion (being able to see into the future).
Many “paranormal” experiences can
probably be explained by mental distur-
coincidence, self-deception, or fraud.
p a ra q u a t
A weedkiller, available in high concentra-
tions for agricultural use, w hich can be
fatal if swallowed, inhaled, or absorbed
through the skin. Paraquat poisoning
requires urgent medical attention. Symp-
toms may include breathing difficulty,
mouth ulcers, nosebleeds, diarrhoea, and
later, respiratory and kidney failure.
Treatments include eating activated
charcoal or Fuller’s earth.
H a e m o d ia ly s is
(removal of toxic substances from the
blood) may also be used.
p a ra site
Any organism living in or on another
living creature (the host) and deriving
advantage from it, while causing the host
disadvantage. In contrast, some organ-
isms live on other creatures but have a
symbiotic, or mutually beneficial, rela-
tionship with their host (see
c o m m e n s a l
Parasites obtain nourishment from the
host’s blood, tissues, or ingested food.
The organisms may spend only part of
their life-cycle with the host or remain
symptoms, while others cause disease
or even death.
Animal parasites of humans include
p ro t o z o a
w o rm s
f lu k e s
le e c h e s
lic e
t ic k s
m it e s
V ir u s e s
and disease-causing
f u n g i
b a c t e ria
are also parasites.
p a ra s ito lo g y
The scientific study of paras/'tes.Although
viruses and many types of bacteria and
fungi are parasites, their study is conduct-
ed under the title of
m ic ro b io lo g y
p a ra s u ic id e
s u ic id e , a tte m p te d
p a ra s y m p a th e tic n e rv o u s
s y ste m
One of the two divisions of the
a u t o -
n o m ic n e rv o u s s y s t e m
w hich controls the
automatic activities of organs, glands,
blood vessels, and other tissues through-
out the body. In contrast to the function
of the sympathetic system, w hich pre-
pares the body for action, the parasym-
pathetic system controls everyday func-
tions such as breathing, digestion, and
excretion of waste products.
p a ra th io n
An agricultural
o rg a n o p h o s p h a t e
cide that is highly poisonous.
p a ra th y ro id e c to m y
Surgical removal of abnormal tissue from
p a ra t h y ro id g la n d s
may be performed to treat
h y p e rp a ra th y -
ro id is m
(excess secretion of parathyroid
hormones). Less commonly, it may be
used to treat parathyroid cancer.
If hyperparathyroidism is caused by an
a d e n o m a
(a small, benign tumour), usu-
ally only one of the parathyroid glands is
involved and needs to be removed. If all
the glands are enlarged and overactive,
more parathyroid tissue may be removed.
p a ra th y ro id g la n d s
Two pairs of oval, pea-sized glands that
lie behind the
th y ro id g la n d
in the neck.
The glands produce parathyroid hor-
mone (PTH), w hich helps to regulate
the level of calcium in the blood.
Blood calcium levels are monitored
continuously by the body because even
small variations can impair muscle and
nerve function. If the calcium levels
drop too low, the parathyroid glands
These glands are
embedded in the
back of the thyroid
gland, in the front
of the neck, and are
situated on either
side of the trachea.
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