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Respiration
The term “respiration” refers to two separate processes, both of which occur in living
things and are related to the generation of energy. One is physiological respiration,
the process by which an organism takes in oxygen and excretes carbon dioxide.
The second is cellular respiration, a series of biochemical reactions that allow a
cell to generate energy.
Physiological Respiration
There are four stages to this process in humans and other mammals, and they plot
the progress of oxygen from inhalation into the lungs to absorption by internal
organs and other tissues. It also covers the exhalation of carbon dioxide.
Ventilation
The first stage is ventilation, in which air moves in and out of the alveoli of the
lungs. These are fibrous collagen structures that expand during inhalation, to take
in the maximum amount of oxygen; upon exhalation, they contract and release
carbon dioxide. Alveoli are present only in mammalian lungs; however, similar
structures exist in other vertebrate animals, such as reptiles and birds.
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Illustrated Handbook of Drugs & Alcohol Related Health Issues
Pulmonary Gas Exchange
In this stage, oxygen from the alveoli enters the circulatory system through the
pulmonary capillaries. The alveoli and the pulmonary capillaries are separated by
a barrier just two cells thick; once across this barrier, oxygen molecules bind to
the hemoglobin, a special protein, in red blood cells.
Gas Transport
Gas transport begins in the pulmonary capillaries. In this step, oxygen bound to
hemoglobin moves through the blood vessels of the circulatory system, eventually
entering capillaries throughout the body. Capillaries feed organs, glands, and other
tissues, which need a constant supply of oxygen to function.
Peripheral Gas Exchange
The final stage is peripheral gas exchange, in which oxygen moves from the capillaries
into cells. This happens similarly to the way gases diffuse between alveoli and
pulmonary capillaries in the lungs. Waste gases, such as carbon dioxide excreted
by cells, enter the capillaries and move though the circulatory system to the lungs,
where they are released during exhalation.
Other Physiological Systems
Respiration is not exclusive to organisms with lungs. For example, in most species
of fish it occurs in gills, which allow the animals to extract oxygen from water. In
amphibians, most gas exchange occurs across the skin; the lungs provide a means
of controlling the body’s oxygen levels, by acting as a secondary source of oxygen.
Plants produce oxygen via photosynthesis, and take in more through diffusion
across their leaves. Regardless of the physical process, all of these organisms take
in oxygen and excrete carbon dioxide, just as mammals do.
Cellular Respiration
The oxygen that is brought to the tissues via physiological respiration is used in all
cells for the biochemical process of cellular respiration. This process, which is also
referred to as oxidative metabolism, is a set of chemical reactions, many involving
oxygen, that allow the body to convert certain molecules into usable energy. In
animal and plant cells, the reactions occur that convert nutrients into an energyrich molecule called adenosine triphosphate (ATP).
Oxygen is needed for cellular respiration because many oxidation-reduction reactions,
also called redox reactions, occur throughout the respiration process. This gas is a
powerful oxidizing agent, which means that, in chemical reactions, it can readily
give its available electrons. This makes it very useful in reactions. The reactions
that occur are also referred to as catabolic, because they break large nutrient
molecules into smaller ones. These molecules are sugars, which are derived from
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carbohydrates; fatty acids from dietary fat; and amino acids, derived from protein.
Electrons are released when the nutrients are broken down, and the electrons are
used in reactions that produce ATP. This energy-rich molecule is then used in cells
to power almost all reactions that occur within them.
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Anaerobic Cellular Respiration
In animals and plants, as well as many bacterial species, the type of cellular respiration
that occurs is aerobic, which simply means that it uses oxygen. In some species
of bacteria, respiration is anaerobic, which means it does not use oxygen. Instead,
these organisms use molecules such as nitrate or sulfur as a substitute. Some have
even evolved to the point where they can only live in oxygen-free environments.
Cancer and Malignancies
Smoking is a direct cause of:
■ lung cancer
■ oral cavity cancers (tongue, pharynx)
■ esophageal and stomach cancer
■ cancer of the larynx
■ kidney and bladder cancer
■ pancreatic cancer
■ leukaemia
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■ cancer of the liver
The incidence of cancer is related to the amount and duration of smoking. Concomitant
heavy alcohol consumption further increases risk, especially with oral, pharyngeal
and laryngeal cancer.
Illustrated Handbook of Drugs & Alcohol Related Health Issues
Gastrointestinal
Gastrointestinal diseases refer to diseases involving the gastrointestinal tract, namely
the esophagus, stomach, small intestine, large intestine and rectum, and the accessory
organs of digestion, the liver, gallbladder, and pancreas. Smoking is a risk factor for
both peptic ulcer disease and Crohn’s disease and exacerbates gastrooesophageal
reflux.
What are gastrointestinal problems?
The gastrointestinal (GI) system is made up of the GI tract plus accessory organs.
In essence, the GI tract is a long hollow tube that extends from your oral cavity
where food enters your body, via the oesophagus, stomach, small intestine, large
intestine, rectum, and finally to the anus where undigested food is expelled. The
accessory organs include the salivary glands, pancreas and liver. These secrete
important enzymes into the digestive tract. The gall bladder, which stores bile, is
also considered part of the GI system.
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The function of the GI system is to process nutrients and energy from food and fluids
that you ingest. To do this, the GI system first needs to break foods down or ‘digest’
them into their simplest forms. The main components of food are carbohydrates, fats,
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proteins, vitamins, minerals and fibre. Food also contains varying amounts of water.
The process of digestion breaks starch and sugars from carbohydrate-rich foods such
as bread, potatoes and pasta into simple sugars such as glucose and fructose. Fats
in butter, cheese, meat etc are converted into cholesterol and fatty acids. Proteins,
for example in meat, eggs and fish, are broken down into amino acids.
When you eat and drink, digestion begins when you chew food to break it down
into smaller pieces and enzymes within your saliva (excreted from salivary glands)
begin to break the foods down into the component parts. Swallowed food and
fluids travel down your throat into your oesophagus and then into your stomach.
Once within the stomach, the food and fluids are mixed with strong acids that
dissolve the solids, and digestive enzymes continue to break the food down. Next,
the mixture passes into the small intestine where it is digested further by juices
from your pancreas, liver (which produces bile) and small intestine. The nutrients
are then in an accessible form and can travel through the wall of the intestine into
the bloodstream (a process known as absorption) to be delivered to cells throughout
your body. Undigested food in the small intestine moves into the large intestine
(where some of the water is reabsorbed into the body) and is then expelled from
the body as faeces or ‘stools’.
In people with GI problems, these functions are impaired. Digestion of foods can
be reduced, so fewer nutrients are converted into a usable form. Alternatively, food
may be digested correctly but nutrients may not be absorbed into the bloodstream
for use by the body. Finally, food and nutrients may be expelled too soon or specific
nutrients and fluids may be lost via the faeces.
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Some of the most common GI problems are constipation, diarrhoea, nausea and
vomiting. These may be mild, self-limiting and temporary or may persist over the
long term and affect your health. For instance, sustained constipation can lead to
diverticular disease (where the intestine becomes damaged from passing hard stools
and then form pocket-like sacs) and impaction (causing the intestine and rectum
to become blocked). Sustained diarrhoea can make your blood pressure drop,
which can lead to fainting or heart rhythm abnormalities. Nutrient and fluid loss
from your body due to diarrhoea or vomiting can lead to dehydration, electrolyte
imbalances, vitamin deficiencies, weight loss and malnutrition. Similarly, nausea,
indigestion and constipation can reduce your appetite, and thus reduce your food
intake leading to nutritional deficits. The nutritional effects of GI problems can be
particularly serious for people who are already malnourished or ill.
What is Gastrointestinal Physiology?
Gastrointestinal (GI) physiology is the study and treatment of the digestive tract, with
a focus on its physical functions. This area of medical practice includes evaluating
patients with suspected GI tract disorders and providing appropriate treatment
for patients with conditions like diverticulitis or Crohn’s disease. Practitioners in
this area of medicine are usually gastroenterologists, specialists in the care of the
stomach and gut.
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The gastrointestinal tract utilizes a number of different systems to accomplish the
goal of processing food. This includes motility, or the movements of the gut to force
foods through, as well as secreting various compounds to assist with digestion and
uptake of necessary nutrients. It also includes interactions between the circulatory
system and the gut to supply it with oxygen and pick up nutrients as they metabolize
in the intestines. Gastrointestinal physiology is a study of the whole system from
mouth to anus.
Illustrated Handbook of Drugs & Alcohol Related Health Issues
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A number of conditions can involve the GI tract. Patients may develop infections
and inflammation, ulcerations, tumors, and other types of injuries in response to a
variety of environmental pressures. Pharmaceutical companies have to understand
how gastrointestinal physiology works in order to develop effective medications.
Enteric coatings on medications to slow absorption rely on mechanisms in the gut,
as do things like the structure of molecules in medications to make sure they can
pass through the intestinal lining to reach the bloodstream.
This system also connects with the circulatory system as well as structures like the
liver, pancreas, and gallbladder. Gastrointestinal physiology includes an understanding
of these systems and how they interact with the GI tract. It can be necessary to
treat disorders like gallstones that lead to digestive disorders, or to determine how
toxins reach the liver after traveling through the intestines.
Specialists in gastrointestinal physiology can be involved directly in patient care
or may conduct research. Researchers work on the development of new diagnostic
tools, medications, and treatment protocols. They can conduct clinical trials to
test their medications as well as participate in activities like the study of new
microorganisms to determine how best to tackle them when they show up in patients.
Gastrointestinal physiology is also highly variable in different species. Horses and
humans, for instance, digest and metabolize their food differently. Specialists may
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focus on a particular species to provide the best medical care and nutrition. This work
can include the study of some rather exotic and unusual approaches to digestion;
starfish, for example, eat by regurgitating their stomachs and engulfing their prey.
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Complications related to Pregnancy and Reproduction
Complications of pregnancy are health problems that are caused by pregnancy.
There is no clear distinction between complications of pregnancy and symptoms
and discomforts of pregnancy. However, the latter do not significantly interfere
with activities of daily living or pose any significant threat to the health of the
mother or baby. Still, in some cases the same basic feature can manifest as either a
discomfort or a complication depending on the severity. For example, mild nausea
may merely be a discomfort (morning sickness), but if severe and with vomiting
causing water-electrolyte imbalance it can be classified as a pregnancy complication
(hyperemesis gravidarum).
Smoking contributes to placental insufficiency and is a cause of placental abruption,
premature labour, spontaneous abortion, stillbirth, neonatal and sudden infant death
syndrome (SIDS).
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Babies of mothers who smoke are more likely to:
■ be born with a cleft lip and palate
■ have a lower than average birthweight
■ have a higher incidence of asthma, chronic serous otitis media, behavioural
problems, SIDS
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Women who smoke have a higher incidence of amenorrhoea, early menopause and
problems with ovulation. Men who smoke are more likely to develop impotence
and have a low sperm count.
Illustrated Handbook of Drugs & Alcohol Related Health Issues
Degenerative Disease
Degenerative disease is the result of a continuous process based on degenerative cell
changes, affecting tissues or organs, which will increasingly deteriorate over time,
whether due to normal bodily wear or lifestyle choices such as exercise or eating
habits. Degenerative diseases are often contrasted with infectious diseases. Smoking
accelerates the ageing process of skin, delays wound healing and contributes to
osteoporosis.
Chronic Degenerative Diseases
If you live somewhere where there’s snow, you may be familiar with the wear and
tear on the roads over time. Such wear and tear is particularly common during the
winter, when ice and snow freeze the pavement, causing cracks as the underlying
surface expands and contracts at a different rate than the asphalt. Plow trucks and
salt also work to break apart the smooth surface. Even though it is unintended, the
result is a patchy, pothole-ridden road in the spring.
A similar process happens in our body and it’s called degenerative disease, but
snow and ice are not the culprit here. In degenerative diseases, parts of the body
break down at a faster rate than normal over time. These might be caused by
environmental factors or genetics, and some causes aren’t fully understood yet.
Below, we’ll look at four major examples of degenerative diseases: Huntington’s
disease, Parkinson’s disease, macular degeneration and osteoarthritis.
Degenerative Disc Disease
Does your back ever hurt? You are not alone! Up to 80% of people will suffer
from some type of back pain in their lifetime. There are different issues that cause
this, some perfectly temporary, but some are irreversible and can worse over time.
Degenerative disc disease is one such case.
The name is a little misleading, because degenerative disc disease is not actually
a disease at all; rather, it’s a natural process affecting the spinal discs that occurs
with aging. It’s also the leading diagnosis for people experiencing back pain.
Spinal discs are the soft, compressible tissue found between each vertebra in the
spine. These discs are what allow you do bend, twist, and move comfortably;
without them, you would have major limitations on spinal movement. If it helps,
you can also think of them as shock absorbers, similar to what you have on your
car to prevent you from feeling every bump on the road.
Problems arise when we injure a disc or when the disc naturally starts to erode
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away due to age, and that’s what degenerative disc disease is: the natural aging
process where the spinal discs wear down and stop functioning properly. This can
lead to pain and reduced mobility of the spine. Injuries can spur the onset of natural
degeneration, but how does natural degeneration actually occur?
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Degenerative Joint Disease
Degenerative joint disease is an umbrella term for conditions leading to the
deterioration of joint cartilage. Synonymous with osteoarthritis (OA), it can be
brought on by such conditions as trauma to the afflicted joint, developmental
disorders in which the disks in the joint never fully formed or did not form properly,
or hereditary conditions. Whatever the cause, degenerative joint disease typically
presents with localized or radiating pain at the joint, tenderness, stiffness, and
difficulty in movement. It is a major cause of disability, common in older adults.
While it cannot be cured, it can be treated with a combination of chiropractic and
physical therapy, the avoidance of movements or behaviors that cause pain, and
pain-relieving medication.
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Osteoarthritis can affect many of the movable joints of the body but is most often
seen in the intervertebral joints of the spine, the hip joint, the knee joint, and the
joints of the hands and feet. Symptoms include pain that is invariably described
as a stiff, aching pain, and pain in the surrounding muscles and tissues. Swelling
may also be present as the joint becomes filled with fluid, particularly in the hands
and knees, a condition known as effusion. In addition, certain movements may
exacerbate this pain or be difficult to perform, such as bending forward in the case
of degenerative joint disease in the spine.
Degenerative joint disease can be classified two ways: primary OA or secondary OA.
While symptoms and treatments are the same for each, the two are differentiated by
the cause of the condition. Primary OA tends to be brought on with age as the water
content of the cartilaginous disk separating the bones in the joint diminishes. This
leaves the joint vulnerable to wearing down, and bony growths called osteocytes,
also known as bone spurs, may develop on one or both of the adjacent bones as
a means of adaptation to the changing joint structure.
Secondary OA, on the other hand, is brought on by non-age-related factors such
as disease, injury, or excessive wearing on the joint caused by dysfunctional body
mechanics or obesity. Diseases that may lead to OA include diabetes, inflammatory
conditions like Lyme disease, other forms of arthritis, and various genetic disorders.
Past injury to the joint can also lead to degenerative joint disease if the damaged
joint tissues do not heal properly. Finally, carrying excess body weight or repetitively
performing weight-bearing activities, as in manual labor, can over time compress
the joint, leading to deterioration of the disk.
Illustrated Handbook of Drugs & Alcohol Related Health Issues
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