Lesson 4- The Respiratory System and
the Renal System
Assignment:
• Read Chapters 5 and 6 in the textbook.
• Read and study the lesson discussion.
• Complete Lesson 4 Worksheet
Objectives:
After you have completed this lesson, you will be able to:
• Identify the basic components of the respiratory tract.
• List and discuss the function and control of breathing.
• Identify and name the basic structures in the renal systems.
• Explain the functions of the renal system.
• Identify structures within the kidney and detail the formation of urine and its
regulation.
• Evaluate urine and blood as a measure of the health of the animal and the urinary
system.
• Discuss the clinical significance of the academic material in this lesson.
• Identify common disorders of the respiratory and renal systems.
The Respiratory System
One fundamental concept that you need to remember as you are working through
these lessons is that all animals, including humans, contain about 99% of the same
genetic material. It is the remaining 1% that distinguishes humans from dogs, and
birds from alligators. This is why most of the discussions regarding systems of the
body can be related to all animals, including humans. In other words, anatomy,
physiology, function, and disorders of these systems, for the most part, are very
comparable in all species.
According to information obtained from ThinkQuest.org,
All animals need food, water, and air to survive. The respiratory system of each
animal is what meets these needs. Oxygen is taken from outside and exchanged with
carbon dioxide in the lungs. That exchange is called respiration and is composed of
four basic events:
• pulmonary ventilation—Air inside the lungs is exchanged with fresh air from
the outside.
• external respiration—Fresh air in the lungs is moved into the blood, and used
air in the blood is moved into the lungs to be removed.
• respiratory gas transport—The circulatory system pumps the blood into which
the fresh air has been moved throughout the body.
•
internal respiration—The cells of the body remove air from the red blood
cells and move the carbon dioxide into them.
External Respiration
The subsystem that removes carbon dioxide from the lungs and moves in fresh air
from outside is made up of the nasal cavity (nose), the pharynx, the larynx, the
trachea, the bronchi (and all the smaller branches of the bronchi), and the air sacs,
or alveoli, to which the entire external respiration subsystem leads. The
respiration zone consists of the bronchioles (not the large bronchi), the alveolar
ducts, and the alveoli, all of which basically make up the lungs. This is where the
oxygen and carbon dioxide are exchanged. All other organs in the external
respiration subsystem make up the conducting zone. During the trip that air takes
through the conducting zone, it is humidified, cleaned, and warmed so that it does
not harm any of the delicate organs that it passes through. When the air finally
reaches the alveoli, it is closer to the air in the tropics, which is the kind of air the
lungs prefer.
The nose is the first and last organ that air passes through. The nose serves some
very important functions. As part of the conducting zone, it cleans the air of dust and
other impurities, warms the air if it is too cool, and moistens the air if it is too dry.
Though not related to respiration, the nose also helps humans speak and is the
organ that gives you the power to smell.
After passing
through the
external
nares
(nostrils), air
passes through
the nasal
cavities. The
nasal septum
separates the
two nasal
cavities.
Immediately
after passing
through the
nostrils into
the nasal
cavities, the air
begins to be
purified,
humidified,
and warmed.
The skin of the
vestibule, the part of the nasal cavities behind the nostrils, has sebaceous and sweat
glands and hair follicles, which catch the dirt and other impurities that may be in
the air. The hair growing out of the follicles are called vibrissae.
The olfactory mucosa is what detects scents that are inhaled. The serous glands
excrete enough lysozyme, an enzyme that destroys bacteria, to keep the air
breathed mostly pure, which is about a quart a day.
The pharynx, most commonly known as the throat, serves dual purposes. Not only
does it move the air into the lungs, but it also moves food into the stomach. [The
length of the pharynx varies and depends upon the animal. The pharynx is separated
into three different regions. Location and function determine these separations.]
The nasopharynx is located above the part of the pharynx that food enters. At the
base of the nasopharynx are the soft palate and its pendulous uvula. When
swallowing, there is a possibility that food will enter into the nasopharynx and nose.
This would severely disrupt breathing. So when an animal swallows, the soft palate
and its pendulous uvula point upwards, blocking off the nasopharynx so that neither
air nor food can pass through it … . The middle ear is also connected to the wall of
the nasopharynx so that ear pressure can be equalized. Infections in the
nasopharynx are commonly followed by ear infections because of this.
The mouth leads to the oropharynx. The mucous lining the walls of the oropharynx
change slightly to adapt for handling food as well as air. It is here that the two
tonsils are located. One is at the entrance from the mouth into the oropharynx and
the other is somewhat deeper.
The laryngopharynx also serves as a common passageway for both food and air. At
the base of the laryngopharynx is the esophagus, which directs food and air to
where they should be. Sometimes it can get confused and make mistakes.
Swallowing air can lead to burping more often. Inhaling food or liquid causes an
animal to cough until it is expelled.
The larynx, also known as the voice box, is what allows animals to "speak." The
larynx has an inlet at the top that allows substances to pass through it or not. When
food is being swallowed, the inlet is closed, forcing food into the stomach. When air
is being breathed, the inlet is wide open so that air can enter the lungs.
The trachea, or
windpipe, connects
the larynx to the
bronchi. This organ
differs from others in
the neck in that it is
flexible, stretching to
four or five inches
long and about one
inch in diameter. The
trachea is lined with
mucous called the
mucociliary
escalator, which
represents the
mucous and cilia and
carry the foreign
substances up to be
swallowed.
The trachea is made
up of between sixteen
and twenty cartilage
rings in the shape of a
"C." Because the
trachea is so flexible
and twistable, without
these cartilage rings, it
would collapse under the partial vacuum formed when inhaling. The open part of
the "C" shape is covered with the trachealis muscle, which can stretch itself to
prevent tracheal tearing when swallowing large things. When an animal coughs, the
muscle also contracts to force air out at a faster speed to dislodge food or other
stuck foreign objects.
The trachea branches off into two main bronchi, the left and right primary bronchi,
which lead to the left and right lung, respectively. The right lung is slightly wider,
shorter, and taller than the left, which makes it more vulnerable to foreign invasion.
At this point in breathing, the air has been moistened, purified, and warmed.
The first few levels of bronchi are supported by rings of cartilage. Branches after
that are supported by irregularly shaped discs of cartilage, while the latest levels
have no support whatsoever.
Respiration begins when the terminal bronchioles lead into the respiratory
bronchioles. These bronchioles are covered with thin-skinned air sacs that allow for
gasses to pass through them. These sacs, which contain alveoli, are called alveolar
sacs, and are at the end of the alveolar ducts. The alveoli are very small curves in
the sac walls. The lung has millions of alveoli, which give the lungs an incredible
surface area for gas exchange. Though fairly impossible to measure exactly, the
surface area is approximated at 70-80 square meters or a square between eight and
nine meters on each side.
The alveoli are covered in interlinking capillaries through which blood flows. The
alveoli and the capillary walls form the respiratory membrane. The lungs rely
simply on diffusion to exchange the gasses, and that moves enough gas to have a
steady supply of oxygen in the body. The respiratory membrane is [very thin,] so
diffusion happens pretty efficiently. For maximum efficiency, the amount of blood
passing through a capillary on an alveoli and the amount of gas exchange should
match precisely. When there is not enough gas in the alveoli, certain pulmonary
vessels tighten, slowing the flow of blood, which causes more blood to flow
elsewhere. When there is a lot of gas exchange happening, those vessels widen,
allowing more blood to pass through. A similar process happens to bronchioles.
When an alveoli has a lot of carbon dioxide in it, the bronchioles that connect it to
the outside air widen, allowing it to leave more quickly.
With the lungs coming in direct contact with the air, you would think that it could
supply its own blood supply. This isn’t so. The bronchial arteries, which branch from
the aorta, supply the lungs with oxygen, and the bronchial and pulmonary veins take
old blood away.
The pleurae is a thin, double-layered tissue which lines the walls of the lungs and
heart. Due to the fact that it produces pleural fluid, the pleurae helps the lungs to
glide easily against the rib-lining tissues, the thoracic wall, when the lungs take in
air. Also, the pleurae is essential to breathing because it serves as potential space.
This important function helps the lungs form a vacuum which sucks in air from the
atmosphere. In addition, its capability to stretch and divide the lungs into two
compartments, a lower and an upper lung, allows other organs to move without
interfering with respiration.
As mentioned
before,
respiration is the
result of a
vacuum formed
inside the lungs.
The lungs
themselves don't
have muscles, so
they can't force
themselves to
expand. Instead
of each alveoli or
bronchiole
having a muscle,
there is one big
muscle called the
diaphragm. The
diaphragm lines
the lower part of
the chest cavity,
sealing it off air-tight from the rest of the body. When the animal inhales, the domeshaped diaphragm contracts, straightening itself out. This lowers the pressure in the
chest cavity, causing air outside the lungs to rush in to fill the space. Though air can
expand, … the low pressure inside pulls in air to equalize the pressure. The lungs,
connected at the ends by cartilage, expand, stretching the cartilage to allow room for
the lungs to hold air. With the ribs expanding outward only a few millimeters, and
the diaphragm lowering only a few millimeters, the volume of the chest cavity
increases by about half a liter, which is the average inhaling amount.
The exact opposite is the cause for expiration. When the diaphragm relaxes, moving
upwards, the chest cavity [decreases] in volume, raising air pressure in the lungs
and forcing air out into the atmosphere. Muscles, such as the diaphragm, cannot
push out, but only contract. When an animal inhales, different tissues in the chest
cavity stretch. Relaxing the diaphragm allows them to return to normal size, which
raises the pressure, thus forcing the air out … . If an animal needs to exhale quickly,
such as in coughing or sneezing, the abdominal walls can contract, doing the same
things that the stretched tissues do.
Elasticity is incredibly important. Animals who suffer from asthma type conditions
do so because their lungs have lost most of their original elasticity. As a result, they
must actively breathe out; it doesn't happen automatically anymore. This condition
requires animals to expend extra energy just to stay alive.
Internal respiration is the exchange of carbon dioxide and oxygen in the cells of
the body. It happens in much the same way as gas exchange in the lungs through
diffusion. Red blood cells carry the oxygen to the body and bring back the carbon
dioxide to the lungs.
Watch this video which explains what respiration is and
why living things need to breathe.
The respiratory system is susceptible to a number of diseases, and the lungs are
prone to a wide range of disorders caused by pollutants in the air. The most
common problems of the respiratory system are asthma, bronchiolitis, chronic
obstructive pulmonary disease, cystic fibrosis, lung cancer, and pulmonary
hypertension. Each one of these disorders attacks some part of the respiratory
system and is very comparable to the conditions in humans.
Being able to identify respiratory structures and their associated functions, from the
nose to the lungs, allows veterinarians to diagnose and treat such disease conditions
as pneumonia and roaring. Moreover, the respiratory rate provides a key piece of
information to practitioners when accessing the overall health of animals. The status
of the respiratory system affects the breathing, and therefore the total health, of
animals.
The Renal System
The renal system is also known as the urinary system or the excretory system. This
system can be subdivided into two major functional subdivisions: the first is the
kidney, where the manufacturing of urine takes place. We will consider in this
lesson the structure of the functional unit of the kidney, the nephron, in detail. The
second subdivision of the system is the excretory passage, which consists of all of
the structures for collecting urine and draining it out of the body, including the
ureter, the bladder, and the urethra. We will consider each of these separately a
bit later.
According to Dr. Thomas Caceci, a professor from the Virginia—Maryland Regional
College of Veterinary Medicine, "The kidney did not evolve primarily as an excretory
organ. Though we think of it as one, and though in mammals that is one of its
important functions, the primary purpose of the kidney is to control the flux of ions
out of the body, and to conserve water." In other words, the kidney is responsible
for controlling what is included in waste materials.
If you split a kidney along its long axis, you will be able to differentiate between the
cortex and the medulla. The cortex is the outer region. This is where the first parts
of the urine-producing nephrons and parts of some tubules are located. The
medulla is the deeper region and is composed entirely of tubules (Caceci).
Dr. Caceci continues, "The kidney is a place in which blood is filtered. The blood flow
is the driving force behind urine formation, so it is important to consider vascular
relationships before we look at the process of urine formation in detail. Blood enters
the kidney via the renal artery, and is distributed through a series of smaller
vessels." After entering the kidney, each renal artery breaks up into subdivisions. In
these subdivisions is a network of arteries which directly supplies blood to the
capillaries in the renal system. It is the capillaries that clean the waste from the
blood. Eventually, drainage from all of the capillaries is collected into larger and
larger veins until it leaves the kidney through the renal vein.
According to Dr. Caceci,
The nephron [is] the basic unit of
the kidney. Urine production is
essentially a process of filtration
followed by modification of the
filtrate. Urine starts as an
ultrafiltrate of blood, from which
all of the formed elements and
most of the larger soluble elements
(e.g., proteins) have been removed.
Blood is brought to the renal
corpuscle via the route described
above. Propelled by the pressure
of continuing filtration, the urine is
driven through the rest of the
nephron, and the various parts of
it modify the product until it’s
released and drains out through
the excretory passages. The exact
concentration and composition of
the urine varies, depending on
what needs to be cleared and how
much water is available to do the
job.
There are many complicated
inner-anatomical parts to the
nephron, but, for the purpose of
this course, it is important to
remember that each nephron is a
continuous tubular unit. It empties
through its collecting tubule into a
larger collecting duct. This duct receives input from many nephrons. It could be
compared to several garden hoses emptying into the same tank. Up to a million
nephron can be found in a typical mammalian kidney (Caceci).
The rest of this first phase consists of a complicated mixture of anatomical and
chemical processes that basically filters and prepares urine so that it can be
removed from the body.
Since the body has produced urine, it is now necessary to get rid of it. The urine sets
in the collecting system (ducts) and flows through a series of tubes to the outside.
The renal pelvis is the upper end of the ureter, attached just below the tips of the
kidney's lobes. It catches the urine and drains out. The ureter is simply a muscular
tube that connects the kidneys to the urinary bladder. The urinary bladder is a
temporary storage organ for urine; its capacity is measured in milliliters …. The wall
of the bladder is similar to that of the ureter, but there are said to be three layers of
smooth muscle …. There is
also a fair amount of elastic
connective tissue in the wall
to provide for elasticity and
dispensability (Caceci).
The urethra is the final
passageway of the excretory
system. It is the tube that
releases urine from the vulva
(or penis) out of the body.
The general health of any
animal depends on how well
the urinary system functions.
Waste products build up in
the body when this system
fails to function. Serious
disorders and even death
from toxicity in the body can
result. The following are
common urinary system
disorders:
• Nephritis is an
inflammation of the nephron
in the kidney. This condition
can be caused by almost
anything that irritates the
kidneys. Most of the time, this condition is not fatal, and no damage to other
kidney parts is expected.
• Pyelonephritis refers to the inflammation of the renal pelvis and connective
tissue of the kidney. Bacterial infection or urinary blockage is usually the
cause of this condition; however, it can also be caused by viruses.
• Cystitis is an inflammation of the bladder and most often occurs because of an
infection caused by bacteria that enter the bladder through the urethra.
• Urethritis is an inflammation of the urethra that results most of the time from a
bacterial infection. Most of these inflammatory diseases of the urinary
system lead to difficult or painful urinating.
• Bladder or kidney stones form from the salts of calcium and uric acid. These
stones form by precipitation around some sort of bacteria, blood clumps, or
similar foreign substances. Diet can also predispose bladder or kidney
stones.
• Blood in the urine is a symptom and not a disease. This could mean that there is
the presence of a serious disease in another part of the renal system. Urine
can also be an indicator of cancer in the kidney or bladder.
It is very important that the
kidneys be kept in normal
functioning condition with
sufficient water consumption.
Insufficient water increases the
specific gravity of the
excretion, thus increasing the
work of the excretory system.
This leads to irritation and
inflammation.
Try this drag and
drop quiz about the
parts of a kidney.
Try some target
practice to review the
components of the kidney and nephron.
Summary
Veterinarians depend on their extensive knowledge of the renal system to treat
common illnesses in animals including dehydration and bladder infections, but this
same knowledge is also used to detect other, more serious health issues like
potential kidney failure. Specialized knowledge of urine is also helpful to anyone in
this field of medicine.
Sources Cited:
Caceci, Dr. Thomas. "Urinary System." Veterinary Histology. 1998. 28 Dec. 2006
<http://education.vetmed.vt.edu/Curriculum/VM8304/lab_companion/Histo-Path/VM8054/Labs/La
Oracle Education Foundation. "The Respiratory System." ThinkQuest. 1996. 28 Dec. 2006.
<http://library.thinkquest.org/2935/Natures_Best/Nat_Best_Low_Level/Respiratory_page.L.html>.