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Biology 30S
THE EXCRETORY SYSTEM
(This workbook adapted from Manitoba Blackboard)
Student: ______________________
Instructor: _____________________
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Lesson 1: Excretory Organs
What goes in, must come out… This applies to living things. We started
our study of the human body with the digestive system. The digestive
system deals with the processes that involves taking in nutrients into the body and simplifying them so that they can enter the cells.
Whatever is left over, would be waste and need to be eliminated,
exhaled/expired, or excreted.
This unit deals with the excretion of the wastes from the circulatory
system. The liquid wastes are excreted through the excretory organs.
Every metabolic process in the human body uses energy and generates
wastes. If these waste products are not removed, they would quickly
accumulate in harmful proportions. In fact, some wastes are poisonous
and pose a serious threat to health if they are not removed promptly.
The process of getting rid of metabolic wastes is called excretion.
There are many organs and systems responsible for excretion. For
example, the skin removes salts and nitrogen-based wastes, the lungs remove carbon dioxide and the liver converts poisons and toxins to a
form that can be eliminated by the kidneys.
In the last unit, we studied the body’s blood and immune system and
the vital importance of these systems to your health. In this unit, we will
study the structure and function of the excretory system.
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Introduction
The human body is about 60% water. Two thirds of the water is in the
cells while the rest is in the fluid around the cells. The chemical
composition of this intercellular fluid must be carefully balanced. If it becomes too salty, the cells can become dehydrated. If it gets too
watery the cells can bloat. If too much acid or base accumulates, the
cells' enzymes can stop working. If metabolic wastes collect, the cells
can die of poisoning. Homeostatic mechanisms within the body keep
the chemical composition of the intercellular fluid constant when
conditions change.
Excretory systems regulate the chemical composition of these body
fluids by removing metabolic wastes and retaining the proper amounts of water, salts, and nutrients. Components of the excretory system in
humans include the kidneys, liver, lungs, and skin.
How does excretion differ from the elimination of wastes from the digestive system?
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Outcomes
In this lesson, you will study the excretory organs and their importance in maintaining homeostasis in the body. By the end of this lesson, you
should be able to:
Define the term excretion.
Describe how excretion aids in maintaining homeostasis in the
body.
List the primary metabolic wastes produced in human body (i.e.,
carbon dioxide, water, ammonia, mineral salts) and the source of
each. Compare the role of the major excretory organs (kidneys, lungs,
skin, liver) in the excretory process.
Excretion and Homeostasis
Cells produce water and carbon dioxide as by-products of metabolic
breakdown of sugars, fats, and proteins. Chemical groups such as
nitrogen, sulfur, and phosphorous must be stripped, from the large
molecules to which they were formerly attached, as part of preparing
them for energy conversion. The continuous production of metabolic
wastes establishes a steep concentration gradient across the plasma membrane, causing wastes to diffuse out of cells and into
the extracellular fluid.
Multicellular organisms such as humans must have a specialized
organ system to concentrate and remove wastes from the interstitial
fluid and eventually from the body. The process of getting rid of
metabolic wastes is called excretion.
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Excretion aids homeostasis by removing metabolic wastes and
regulating the salt and water balance. The blood picks up carbon
dioxide, excess salts, nitrogen compounds, and any excess water that may be present in the interstitial fluid and carries them to the
excretory organs, which channel the wastes out of the body.
Therefore, the excretory system regulates volume of internal body
fluids as well as eliminates metabolic wastes from the internal
environment.
Fortunately, atoms and molecules do not wear out, but may be
changed or rearranged and used over and over again. Many of the
end products of various cell activities can be recycled and used in other processes. As a result, the amount of waste that actually
needs to be discharged from the body is very small in relation to the
amount of work done by all the cells of the human body.
Several organs take part in human excretion. The skin, lungs, liver,
and the transport system play very important roles. However, the
main excretory organs are the kidneys.
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The metabolic wastes produced and the organs that excrete them
are summarized in the table below.
Wastes Formed From Organ of
Excretion
1. Carbon Dioxide Cellular Respiration lungs
2. Water Cellular Respiration &
Dehydration Synthesis
kidneys, skin,
lungs
3. Nitrogenous
Wastes
Metabolism of Proteins (Amino
Acids)
kidneys, liver,
skin
a) Ammonia
(extremely toxic)
deamination of amino acids by
the liver
liver
b) Urea ammonia combined with
carbon dioxide
kidneys, skin
c) Uric Acid product of the breakdown of
nucleic acids, such as DNA
liver
4. Mineral Salts (NaCl, KSO4)
Metabolism of Various Food Substances
kidneys, skin
Table 7.1.1 Metabolic Wastes
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Lesson 1 Overview
Following is a list of topics covered in this lesson.
Excretion and Homeostasis
Skin and Homeostasis
Excretion in the Lungs
Role of Liver in Excretion
Kidneys: Major Organs of Excretion
Skin and Homeostasis
The skin has many functions in the body. These include protection, regulation of body temperature, sensory reception, water balance,
excretion, synthesis of vitamins and hormones, and absorption of
materials. The skin's primary functions are to serve as a barrier to
the entry of microbes and viruses, and to prevent water and
extracellular fluid loss.
Your skin has approximately 2 million sweat glands. These tiny,
coiled tubules are found in the dermis layer of skin, below the
surface layer or epidermis. See the diagram below.
http://www.nigms.nih.gov/news/features/artificial_skin.html
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These glands secrete sweat continuously, even when you are not
exercising. Sweat consists primarily of water, along with salts, and
some urea (nitrogen-based waste). These materials pass from the blood vessels in the skin into the sweat glands. The wastes travel up
the tubules and onto the surface of the skin through tiny openings
called pores. The wastes form perspiration on the skin, which
eventually evaporates. The solid wastes in the perspiration remain
on the surface of the skin or on clothing. Perspiration itself has no
odour. However, bacteria living on the skin decompose the urea in
perspiration, producing new compounds that do have odours.
Did you know that the skin and kidneys excrete the similar waste products? The composition of sweat and urine are very
similar (except urine is much more concentrated)!
Heat and cold receptors are also located in the skin. When the body
temperature rises, the hypothalamus, the region of the brain
responsible for coordinating many nerve and hormone functions,
sends a nerve signal to the sweat-producing skin glands, causing
them to release about 1-2 liters of water per hour, cooling the body
through evaporation. The hypothalamus also causes dilation of the blood vessels of the skin, allowing more blood to flow into those
areas, causing heat to be dissipated from the skin surface.
When body temperature falls, the sweat glands constrict and sweat
production decreases. If the body temperature continues to fall, the
hypothalamus will trigger the body to engage in thermiogenesis, or
heat generation, by raising the body's metabolic rate and by
shivering.
This is an excellent example of negative feedback mechanisms in
action.
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Excretion in the Lungs
Carbon dioxide and water are produced by all cells during cellular
respiration. The blood carries these to the lungs. Carbon dioxide
diffuses into the alveoli and is removed from the body when we exhale.
Some water also leaves the lungs as water vapour.
The lungs can also eliminate alcohol, which, since it is made up of small molecules, can be rapidly passed from the bloodstream into the alveoli
of the lungs and exhaled. This is why the breathalyzer test is an
effective and simple way of determining the amount of alcohol that
people have taken into their systems.
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Role of Liver in Excretion
Although, we obtain most of our energy from carbohydrates and fats,
we sometimes use proteins for energy. Some proteins and other
nitrogenous compounds are broken down in the liver by a process called deamination. The extraction of energy from proteins
produces ammonia (NH3), a highly toxic substance. The liver converts
ammonia to a non-toxic substance called urea by combining it with
carbon dioxide. The blood then delivers urea to the kidneys, where it is
excreted.
The liver also breaks down red blood cells. About 120 days after they
are formed, erythrocytes are destroyed by special cells in the liver.
These cells engulf the red blood cells and break down their hemoglobin. Iron released from the hemoglobin is carried by the blood to various
parts of the body. In the bone marrow the iron is used in the
manufacture of new hemoglobin. Another part of the broken down
hemoglobin is the yellow pigment bilirubin. This pigment enters the bile,
passes into the small intestine, and is eventually removed from the
body with the feces.
The liver is also responsible for removing potentially hazardous
chemicals from the blood. It "detoxifies" the blood. For this reason, alcoholics and other types of drug addicts have a higher incidence of
liver disease. The liver breaks down harmful and foreign substances,
such as many ingested poisons and drugs after they are absorbed by
the digestive system and before they reach the rest of the body. Since
the liver has the enzymes to break down the natural materials, it is also
able to destroy certain drugs. This function can be life-saving, because it makes destructive substances harmless, and prevents hormones,
medications, and other chemicals from accumulating to harmful levels.
Cortisone and sulfur-containing medicines are examples of drugs that
the liver breaks down.
The liver's ability to make substances harmless has limits. Materials can
accumulate in the liver and destroy its tissues. For example, alcohol
taken in excess over a period of time can deteriorate the liver.
Pollutants, such as PCBs (polychlorinated biphenyls) and pesticides, such as DDT, can also harm the liver.
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Kidneys: Major Organs of Excretion
The kidneys are the major organs of excretion in the human body. They
form part of the urinary system and function primarily in filtering wastes
from the blood. The kidneys also play a key role in fluid balance in the
body.
In the next lesson, you will study the urinary system and the function of
the kidneys in detail.
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Lesson 1 Questions
Please answer the following six questions.
1. Define the term excretion.
2. Describe two ways that excretion contributes to homeostasis?
3. Complete the following table.
Wastes Formed From Organ of Excretion
1. Cellular Respiration lungs
2. Water Cellular Respiration &
Dehydration Synthesis
3. Nitrogenous
Wastes
Metabolism of Proteins (Amino
Acids)
kidneys, liver,
skin
a) Ammonia
(extremely toxic)
liver
b) ammonia combined with carbon dioxide
kidneys, skin
c) Uric Acid product of the breakdown of
nucleic acids, such as DNA
4. Mineral Salts
(NaCl, KSO4)
Metabolism of Various Food
Substances
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4. Describe the role of the skin in temperature regulation of the
human body.
5. How does the formation of urea prevent poisoning?
6. Why is it said that the liver "detoxifies" the body?
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Activity - Mammalian Diving Reflex
What happens to the heart rate when a person falls into cold water?
Test the mammalian diving reflex with this activity and see how your
body responds.
Materials: pan filled with about 8 cm of cold water, stopwatch or clock
with second hand, towel, partner
1. Have your partner measure your resting pulse for 15 seconds and
calculate your beats per minute.
2. Hold your breath and submerge your face in the pan of cold water
for 15 seconds. Before you start, predict what will happen to your pulse rate. Have your partner measure your pulse rate for the 15
seconds that your face is submerged. Calculate your beats per
minute.
3. Switch roles and repeat the procedure.
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Answer the following questions:
1. What happens to your pulse rate when your face
is submerged in water?
2. Why do you think this happens?
3. How might this help someone who has fallen
into very cold water?
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Lesson 1 Summary
In this lesson, you have studied that excretory systems regulate the
chemical composition of body fluids by removing metabolic wastes and
retaining the proper amounts of water, salts, and nutrients. You have also learned about the role of the liver, lungs, and skin in excretion. In
the next lesson, you learn about the role of the urinary system in
maintaining homeostasis.
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Lesson 2: The Urinary System
The kidneys remove metabolic wastes from the body by filtering the
blood. The entire blood volume is filtered through the kidneys about 65
times per day by way of the renal arteries. After the blood is cleaned, it flows back into the body through the renal veins. The kidneys work
continuously, processing all of the blood in the body every 20 minutes.
At this rate, every 24 hours the kidneys filter approximately 325 litres of
blood. Of these 325 litres, only 1 to 2 litres of fluid are excreted as urine.
In the last lesson, you studied the function of the skin, lungs and liver in
excretion. In this lesson, you will study the role of the urinary system in
excreting wastes and balancing fluids in your body.
Outcomes
When you have completed this lesson, you will be able to:
Identify on a diagram or model and describe the function of the
following structures of the human urinary system:
o kidneys
o renal cortex o renal medulla
o renal pelvis
o renal arteries and veins
o ureters
o urinary bladder
o urethra
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Identify from a diagram or model and describe the function of the
following structures of the nephron:
o afferent and efferent arterioles
o glomerulus o Bowman's capsule
o proximal convoluted tubule
o peritubular capillaries
o Loop of Henle
o distal convoluted tubule
o collecting duct
Differentiate between the terms filtration, reabsorption, and
secretion as they relate to nephron function.
Analyze and compare water and solute concentrations in various
parts of the nephron and urine.
Describe the role of antidiuretic hormone (ADH) in maintaining
water balance in the body.
Describe the role of aldosterone in maintaining blood pressure in
the body.
Explain the effect of diuretics such as caffeine and alcohol on
water loss.
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Lesson 2 Overview
Following is a list of topics covered in this lesson.
The Urinary System
Importance of Kidneys
Structure of Kidneys
Nephron Kidney Function
Kidneys and Water Balance
Kidneys and Blood Pressure
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The Urinary System
The human urinary system consists of two kidneys, two ureters, the
urinary bladder, and the urethra. Normally, there are two of kidneys,
one on either side of the spine under the lower ribs. The ureters lead from the kidneys to the urinary bladder, which lies low in the abdominal
cavity. The urethra extends from the bladder to the exterior of the body,
carrying urine through the urogenital organs, either the penis or vagina.
Refer to the diagram below.
Figure 7.2.1 Urinary System
http://www.kidney.ca/publications-eng.htm
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Importance of Kidneys
Your kidneys are important because they do these essential things.
1. Regulate water
For your body to work properly, it must contain just the right
amount of water. One of the important jobs of the kidneys is to
remove excess water from the body or to retain water when the
body needs more.
2. Remove wastes
Many of the substances in the blood and body fluid must be kept
at the correct level for the body to function properly. For example,
sodium and potassium are minerals which come from food. These
minerals are needed by the body for good health, but they must
be kept at specific levels. When the kidneys are working properly,
excess minerals, such as sodium and potassium, are excreted
from the body in the urine. The kidneys also help to regulate the
levels of other minerals, such as calcium and phosphate, which
are important for the formation of bone.
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3. Wastes, such as urea and creatinine, must also be removed from
the body. Urea and other wastes are made when the body breaks
down protein, such as meat. Creatinine is a waste product of the
muscles. As kidney function decreases, the levels of urea and
creatinine in the blood increase. Many waste products are toxic
(poisonous) if they are not removed from the body fluids. For
example, when certain drugs are taken, chemical wastes are
produced which must be removed from the body by the kidneys.
4. Produce hormones
Normal kidneys also make important chemical messengers called
hormones. These hormones circulate in the bloodstream and
regulate some body functions such as blood pressure, the making
of red blood cells, and the uptake of calcium from the intestine.
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Structure of Kidneys
Kidneys are reddish brown in colour and shaped like kidney beans.
Each kidney is about the size of your clenched fist. If you were to cut a
kidney in half, you would see the following parts:
renal capsule - a thin, outer membrane that helps protect the
kidney
cortex - a lightly colored outer region
medulla - a darker, reddish-brown, inner region
renal pelvis - a flat, funnel shaped cavity that collects the urine
into the ureters
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Figure 7.2.2 Kidney Structure
Image from Purves et al., Life: The Science of Biology, 4th Edition, by
Sinauer Associates
(www.sinauer.com) and WH Freeman (www.whfreeman.com)
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Nephron
The working units of the kidney are microscopic structures
called nephrons. Each kidney contains about one million nephrons. A nephron contains a network of capillaries called the glomerulus, which
filters blood into a cup-shaped structure known as the Bowman's
capsule. The filtrate then passes into a series of tubules. Water and
waste products are separated from the blood by the filtering process
and the flow into and out of the tubules. Much of the water is
reabsorbed by the tubules and the wastes are concentrated into urine.
Figure 7.2.3 Nephron Location
http://www.kidney.ca/publications-eng.htm
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The main parts of the nephron are as follows:
Glomerulus - coiled capillaries inside the Bowman's capsule.
Bowman's (Glomerular) capsule - closed end at the beginning of
the nephron. It is located in the cortex.
Proximal convoluted tubule - first twisted region after the
Bowman's capsule. It is also in the cortex.
Loop of Henle - long, loop after the proximal tubule. It extends
from the cortex down into the medulla and back.
Distal convoluted tubule - second twisted portion of the nephron
after the loop of Henle. It is also in the cortex.
Collecting duct - long straight portion after the distal tubule that is
the open end of the nephron. It extends from the cortex down
through the medulla.
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Figure 7.2.4 Nephron Structure
http://botany.indstate.edu/hughes/endo/412pics/
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The nephron also has a unique and rich blood supply compared to
other organs. They are listed below.
Renal artery - supplies blood to the kidney from the circulatory
system
Renal vein - returns blood from the kidney to the circulatory
system
Afferent arteriole - connects the renal artery with the glomerular
capillaries.
Efferent arteriole - connects the glomerular capillaries with the
peritubular capillaries.
Peritubular capillaries - located after the glomerular capillaries and
surrounding the proximal tubule, loop of Henle, and distal tubule.
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Draw the nephron and label the parts. Identify what happens in each
part.
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Kidney Function
Many of the substances in the blood and body fluids must be kept at the
correct level for the body to function properly. Regulating the
composition of these fluids involves the following:
Keeping the concentrations of various ions and other important
substances constant.
Keeping the volume of water in your body constant.
Removing wastes from your body.
Keeping the acid/base concentration of your blood constant.
The kidney performs these functions by a combination of:
Filtration - the passage of substances through the capillaries of
the glomerulus into Bowman's capsule. Reabsorption - the transfer of essential solutes and water from
the nephron back into the blood
Secretion - the movement of materials from the blood back into
the nephron.
Anything (fluid, ions, small molecules) that has not been reabsorbed
from the nephron gets swept away to form the urine, which ultimately
leaves the body. Through these processes, the blood is maintained with
the proper composition, and excess or unwanted substances are
removed from the blood into the urine. See diagram below.
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Figure 7.2.5 Filtration, Reabsorption and Secretion
http://www.sirinet.net/~jgjohnso/urinary.html
Filtration
The blood supply to the kidneys is carried by the large renal arteries
(right and left). These large vessels divide into many smaller vessels as
soon as they enter the kidneys. The result of the decrease in diameter
of the artery is to produce an increase in the pressure of the blood. In
addition, the efferent arterioleleaving the Bowman's capsule is considerably smaller than the afferent arteriole which delivers blood to
Bowman's capsule. This increases the blood pressure within the
glomerulus. In the kidney, blood pressure in the capillaries is 60 to 70
mm Hg, whereas elsewhere in the body capillary blood pressure is only
25 mm Hg or less. As a result of this high pressure in the glomerulus,
about 20% of the blood plasma entering the kidneys is passed rapidly
and easily into Bowman's capsule, creating a filtering effect.
The substances that pass from the glomerulus into Bowman’s capsule comprise what is called the filtrate. Blood cells and large protein
molecules are too large to pass through the tiny pores in the capsule
capillaries. Other substances such as, salts, sugars, water, and wastes
are composed of smaller molecules and can pass easily through the
pores to enter the capsule. About 80% of the plasma component of the
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blood entering the kidney is left behind and does not become part of the
filtrate, but re-enters the bloodstream.
Reabsorption
The filtrate that enters Bowman's capsule contains metabolic waste
products and other materials not needed by the body. It also however, contains salts, water, amino acids, and other useful substances which
must be retained and recycled back into the blood.
Sometimes it is necessary to move molecules from an area of low
concentration to an area of high concentration. Such movement is
known as active transport. It requires energy and the presence of
special carrier molecules, which temporarily associate with the
substance to help it pass through a membrane.
As the filtrate passes through the proximal tubule of the nephron,
glucose, amino acids, and some salts are reabsorbed back out of the
tubules into the bloodstream by active transport. The efferent arteriole, which leaves the glomerulus, branches out into a network of capillaries
called the peritubular capillaries which surround the tubules. It is this
bed of capillaries that is constantly reabsorbing the needed products
from the filtrate and enabling them to re-enter the bloodstream. The
waste substances remain in the tubules, becoming gradually more
concentrated until they are formed into urine.
The cells of the proximal tubule are filled with mitochondria which
produce energy for active transport to take place. The cells of the proximal tubules also contain microvilli which increase the efficiency of
absorption by increasing the surface area of the tubule.
As salts (and ions) are forced out of the proximal tubule, the
concentration of the filtrate changes. Eventually, there are more salts
outside the tubule and more water inside the tubules. This establishes
the condition under which normal diffusion takes place; water then flows
out of the tubules by osmosis and is reabsorbed into the capillaries.
Water continues to diffuse out of the top portion of the descending loop
of Henle. However, water does not pass out of the remainder of Henle's
loop. Sodium ions (Na+) are moved out of the ascending portion of the loop by active transport, into the intercellular fluid. The walls of the
ascending loop of Henle are impermeable to water, so no water leaves
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the loop as it would if the membrane did not block it. Sodium ions
diffuse into the descending loop and increase the concentration of the
filtrate there, so that a point is reached when the concentration of dissolved materials in the filtrate is equal to or greater than the
concentration of the blood in the nearby capillaries and water ceases to
diffuse out. The diagram below summarizes this process.
Figure 7.2.6 Reabsorption
www.columbia.edu/cu/biology/courses/w2501/kidney_notes.html
Secretion
Secretion is the movement of wastes from the blood into the nephron.
Nitrogen-containing wastes, excess hydrogen ions, and other minerals
are balanced by secretion. Even drugs such as penicillin can be
secreted. Cells loaded with mitochondria line the distal tubule. Like reabsorption, tubular secretion occurs by active transport, but unlike
reabsorption, molecules are transferred from the blood into the
nephron.
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Kidneys and Water Balance
As mentioned earlier in the lesson, for your body to work properly, it
must contain just the right amount of water. One of the important jobs of
the kidneys is to remove excess water from the body or to retain water
when the body needs more.
Water conservation by the kidney is controlled by a hormone called antidiuretic hormone or ADH. ADH is produced in the pituitary
gland in the brain. Low water levels in the blood signals the pituitary to
release more ADH. The blood carries the ADH to the kidneys and
increases the permeability of the tubule cell membranes to water
causing more water to be reabsorbed from the tubule into the blood,
producing more concentrated urine. If, on the other hand, a person has too much water, less ADH is released. Then the cell membranes of the
tubules become impermeable to water. As a result, they do not allow
water to return to the blood and the urine is very dilute.
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Kidneys and Blood Pressure
The kidneys play a role in the regulation of blood pressure by adjusting
for blood volumes. A hormone called aldosterone acts on the nephrons
to increase sodium ion reabsorption. This hormone is produced in the cortex region of the adrenal glands that lie on the upper surface of the
kidneys. As Na+ reabsorption increases, the osmotic gradient increases
and more water moves out of the nephron by osmosis.
Low blood pressure through the body (resulting perhaps from loss of
blood through a wound or loss of water and salts in diarrhea) is
reflected in a lowering of the blood pressure in each glomerulus of the
kidneys. This decreases the amount of plasma that leaves the
glomerulus and enters the Bowman's capsule. Accordingly, this lowered blood pressure decreases the amount of water and salts filtered into the
kidney tubules, helping to conserve them.
High blood pressure results in an increase in the volume of filtrate in the
glomeruli (plural form of glomerulus) and the excretion of more water
and salts from the body. However, the activities of the tubule cells
increase in an attempt to cause more water and salts to be reabsorbed
into the bloodstream.
While we think of the kidney as an organ of excretion, it is more than
that. It does remove wastes, but it also removes normal components of
the blood that are present in greater-than-normal concentrations. When excess water, sodium ions, calcium ions, etc. are present, the excess
quickly passes out in the urine. On the other hand, the kidneys can step
up their reclamation of these same substances when they are present
in the blood in less-than-normal amounts. Thus the kidney continuously
regulates the chemical composition of the blood within narrow limits.
The kidney is one of the major homeostatic devices of the body.
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Lesson 2 Questions
1. Label the following diagram.
2. Describe the three main functions of the kidneys.
3. What are the functional units of the kidney?
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4. List the function of the following structures:
a. Glomerulus
b. Bowman's (Glomerular) capsule
c. Proximal convoluted tubule d. Loop of Henle
e. Distal convoluted tubule
f. Collecting duct
g. Renal artery
h. Renal vein
i. Afferent arteriole j. Efferent arteriole
k. Peritubular capillaries
5. Label the following diagram. Also, indicate the processes associated with the green, blue and red arrows..
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6. List and explain the three main processes that are involved in
urine formation.
7. Place the following processes in the correct order.
a. urine is stored in the bladder.
b. blood enters the afferent arteriole c. fluids pass from the glomerulus into Bowman’s capsule
d. urine is excreted by the urethra
e. sodium ions, glucose and amino acids are actively
transported from the nephron to the bloodstream
f. water is diffused from the nephron to the bloodstream
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8. How do the blood vessels in the glomerulus contribute to
filtration?
9. Explain the role of ADH in water balance.
10. How does the kidney contribute to the maintenance of blood
pressure?
11. A micropipette was used to extract fluids from various structures within the kidney. The data in the following table is an
analysis of the substances collected. All quantities are in g/mL.
Answer the following questions providing an explanation for each.
Substance
found in body
fluid
Blood plasma
from afferent
arteriole
Glomerular filtrate
from Bowman’s
capsule
Urine
protein 7.00 0.00 0.00
urea 0.04 0.04 2.00
glucose 0.10 0.10 0.00
sodium ions 0.32 0.32 0.35
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12. a. Which substance is not filtered from the blood into
Bowman’s capsule?
b. Which substance provides evidence of secretion?
c. Which substance provides evidence of reabsorption?
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Research Assignment
Investigate the effects of caffeine and alcohol on water loss. Can you relate these findings to the so-called "hangover"?
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Lesson 2 Summary
In this lesson, you have studied the role of the urinary system in
excreting wastes and balancing fluids in your body. In the next lesson,
you will study some of the major disorders that effect the urinary system. You will also examine some of the treatments available for
these disorders and consider the issues surrounding kidney transplants.
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Lesson 3: Diseases and Disorders
Did you know?
Kidney disease can strike anyone at any age.
Every day an average of 10 Canadians learn that their kidneys
have failed and that their survival depends on dialysis or a kidney
transplant.
Kidney diseases rank 6th among diseases causing death in
Canada.
Leading causes of kidney failure are diabetes, renal vascular
disease (including high blood pressure), and glomerulonephritis
(inflammation of the tiny filters in the kidney which clean the
blood).
People aged 65 to 74 are the fastest growing group newly
diagnosed with kidney failure.
At the end of 2001, 3,500 Canadians were on a waiting list for an
organ transplant. Of those, 80 % were waiting for a kidney.
In 2002 there were 25,000 Canadians with kidney failure who are
living with dialysis or a kidney transplant.
In the last lesson, you studied the function of the urinary system in
maintaining homeostasis in the body. In this lesson, you will study some
common disorders and diseases that can upset the homeostatic
balance of the urinary system.
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Outcomes
When you have completed this lesson, you will be able to:
Describe how the following diseases/disorders affect the urinary
system:
o diabetes (Type I and II)
o nephritis o kidney stones
o urinary tract infection
o high blood pressure
Explain the function of the kidney dialysis machine.
Identify urinary system disorders through urinalysis results.
Discuss patient options when kidney failure occurs (i.e. kidney
dialysis technology, organ transplant).
Lesson Overview
Following is a list of topics covered in this lesson.
Kidney Disease
Diabetes
Nephritis
Kidney Stones
Urinary Tract Infections
High Blood Pressure
Kidney Failure
Dialysis
Kidney Transplant
Testing for Healthy Kidney Function
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Kidney Disease
Proper urinary and kidney function is essential for maintaining
homeostasis in the body. Kidney disease usually progresses silently,
often destroying most of the kidney function before causing any symptoms. Therefore, people at risk of developing kidney disease
should be evaluated regularly. These people include those with
diabetes, high blood pressure or blood vessel diseases, and close
relatives of people with hereditary kidney disease. Sometimes even
people with serious kidney disease may not have any symptoms. That
is why a blood or urine test may be necessary to check for kidney
problems.
Some of the Signs and Symptoms That May Indicate Kidney Disease
High blood pressure (hypertension)
Puffiness of the eyes, hands and feet Passage of bloody, cloudy or tea-coloured urine
Presence of protein in the urine
Excessive foaming of the urine
Frequent passing of urine during the night
Passing less urine or difficulty passing urine
Fatigue Loss of appetite or weight
Persistent generalized itching
When the kidneys fail, wastes and fluids accumulate in your body. As a
result, you need dialysis treatments or a kidney transplant.
We will now explore some of the most common disorders of the urinary
system.
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Diabetes
Diabetes is the most common cause of kidney failure, accounting for
more than 40 percent of new cases. Diabetes is a disease which is caused by the lack of insulin in the body or the body's inability to
properly use normal amounts of insulin. The body converts the food we
eat into sugar (glucose). The body needs this sugar, in the form of
energy, to perform its functions. The hormone insulin, produced by the
pancreas, regulates the amount of glucose (sugar) in the blood. If the
body lacks insulin or does not use the insulin properly, then this imbalance results in high blood sugar. Eventually, many unhealthy
changes can occur in different body organs, including the kidneys.
Even with the use of injected insulin, people who have had diabetes for
some time often suffer from damage to the small blood vessels of the
body. This may cause damage to the retina of the eye and result in loss
of vision. Also, the delicate blood vessels in the nephrons of the kidney
may be damaged. At the early stage, this damage is shown by finding
protein in the urine.
Sometimes at a later stage, so much protein is lost from the blood that
water from the blood moves into the body tissues and causes swelling (edema). After a number of years, the kidneys' nephrons can become
so damaged by diabetes that the kidneys fail. Because smoking also
damages the blood vessels, it worsens the complications of diabetes.
People with diabetes should try to stop smoking completely.
Diabetes can also damage the nerves in many parts of the body. When
the bladder is affected, it may be difficult to pass urine. If urine builds up
in the bladder, the pressure can cause it to back up to the kidneys
causing damage there.
The urine of people with diabetes has high sugar content. This
encourages the growth of bacteria and kidney infections may occur. People with diabetes must take special care to avoid infections and
have them treated immediately.
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There are different types of diabetes. The most common ones are Type
1 and Type 2.
Type 1 - Juvenile Onset Diabetes
Occurs mainly in young people
Is caused by an inability of the pancreas to produce enough
insulin
Requires regular insulin injections
Type 2 - Adult Onset Diabetes
Usually develops in people over the age of forty (usually
overweight people)
The pancreas produces close to normal amounts of insulin, but
the body is unable to use it properly
Making proper food choices and/or taking oral medication can
control the abnormal blood sugar level
About 40% of people with Type 1 diabetes (juvenile onset) and 10% of
people with Type 2 diabetes (adult onset) will eventually develop kidney disease which will lead to permanent chronic renal insufficiency (kidney
failure).
A person could have serious kidney damage without being aware of it.
There are usually no specific symptoms of diabetic kidney disease until
the kidneys fail completely. However, there are certain early signs or
risk factors to watch for:
High blood pressure (over 130/85 mm Hg*) or a family history of
high blood pressure
Protein in the urine
Burning or difficulty during urination
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Nephritis
Nephritis, also called Glomerulonephritis (GN) is a disease of the
kidneys in which the glomeruli, the tiny filters in the kidneys that help to
clean the blood, become inflamed or damaged. This allows protein and
red blood cells to pass into the urine.
If glomerulonephritis does not respond to treatment, the glomeruli may slowly be destroyed and the kidneys may lose their ability to clean your
blood.
As we studied in the last lesson, each kidney consists of about a million
tiny units called nephrons. Each nephron is made up of a very small
filter called a glomerulus which is attached to a tubule. The glomeruli
clean the blood by filtering out excess water and waste products. In a
normal kidney, the glomeruli allow small-sized waste products to be
filtered out of the blood, while at the same time preventing protein and
red blood cells from passing into the urine.
Glomerulonephritis has many different causes. These include infection, certain drugs, and in rare cases, even cancer. However, in the great
majority of cases, the cause is unknown. Most cases of
glomerulonephritis are sporadic. This means the disease arises
spontaneously and is not inherited.
There is some evidence that GN may be caused by a problem in the
body's immune system. This system protects the body against invasion
by foreign materials such as viruses and bacteria. However, if the
immune system is not working properly, it may harm the kidneys. The immune system may mistakenly attack the kidneys' filters (glomeruli)
and cause them to become inflamed.
There are many types of glomerulonephritis. These may be grouped as
primary and secondary. In primary GN, only the kidneys are affected. In
secondary GN, the kidneys are damaged as part of a more generalized
disease that can affect other parts of the body.
The exact diagnosis can be made by a test called a kidney biopsy. This
is a medical procedure in which a very tiny tissue sample from one
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kidney is removed using a special needle. This tissue sample is
examined to determine the pattern of kidney damage, and to give more
information about the type of GN. A kidney biopsy is not required for
every patient so a kidney specialist will decide whether one is needed.
Unfortunately, the presence of glomerulonephritis is difficult to detect. In early stages, there may be no symptoms or signs of the disease. A test
to measure the protein and red blood cells in the urine will confirm
whether or not a person has GN.
As the disease progresses, the following symptoms may become
evident:
high blood pressure
excessive foaming of the urine
change in the colour of the urine (to red or dark brown)
puffiness of the eyes, hands and feet
nausea and vomiting difficulty breathing
headaches
In mild cases, kidneys may recover on their own, or following specific
treatment. Even if the disease is more advanced, it may be slowed by
lowering blood pressure with medication and by making changes in diet.
A kidney specialist may recommend other specific treatments as well. In
rare cases, temporary dialysis treatments (to clean your blood) may be
needed until the kidneys respond. However, in some cases when the damage is severe, the kidneys become unable to perform their usual
functions adequately, and eventually regular dialysis treatments or a
kidney transplant may be required.
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Kidney Stones
A kidney stone can develop when certain chemicals in urine form
crystals that stick together. The crystals may grow into a stone ranging
in size from a grain of sand to a golf ball. Small stones can pass through the urinary system without causing problems. However, larger
stones might block the flow of urine or irritate the lining of the urinary
tract.
Most stones form in the kidney and some travel to the ureter or bladder.
Most stones (70 to 80 percent) contain mainly calcium oxalate crystals.
A smaller number are uric acid stones or cystine stones.
One out of ten Canadians will have a kidney stone at some point in their
life. Kidney stones occur much more commonly in men than in women.
They tend to affect people in middle age, and occur more frequently hot
climates.
Normally, urine contains chemicals which prevent crystals from forming.
However, some people seem to be more prone to kidney stones than others. If you are prone to kidney stones, there are several factors
which contribute to their formation:
Recurrent urinary tract infections
Drinking too little fluid
Blockage of the urinary tract
Limited activity for several weeks or more
Consuming too much calcium oxalate or uric acid in your diet
Consuming too much Vitamin C or D Certain medications
Certain metabolic diseases
Symptoms of kidney stones include:
Severe pain that usually starts suddenly in the small of the back under the ribs or in the lower abdomen, and which may move to
the groin; the pain may last for minutes or hours, followed by
periods of relief.
Blood in the urine
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Nausea and vomiting
Sometimes, stones can also develop if a person has a persistent kidney
infection. If there is a urinary tract infection, symptoms may include:
Burning during urination and the urge to urinate frequently
Cloudy or foul-smelling urine
Fever, chills and weakness
Kidney stones are diagnosed by a complete medical examination, X-
rays and other tests. A doctor will usually start with a physical
examination and asking questions about past kidney illness, diet, use of medications, lifestyle and family background. An X-ray of the kidneys,
ureters and bladder can reveal the presence of most stones.
Sometimes, stones which are less common can be seen using dye
injections or an ultrasound test. Blood and urine tests may be needed to
find out what is causing the stones to form.
Most small stones pass through the body by themselves within hours or
a few days. To help this process, a doctor may advise the patient to
drink a lot of fluids and follow a special diet. Medication may also be prescribed. Certain types of stones can be dissolved using medication.
However, the most common stones (those containing calcium) cannot
be dissolved.
Stones that do not pass by themselves are treated with Extra-corporeal
Shock Wave Lithotripsy (ESWL). This treatment is a non-surgical
technique which uses high energy shock waves to break the stones into
small fragments (about the size of grains of sand). They can then be
passed during urination during the next few weeks. This treatment is successfully used in many cases where the stones are less than two
centimetres in size. When stones are larger than two centimetres, a
surgical procedure is often needed.
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Kidney stones recur in about 50 percent of cases. There are steps that
can be taken in consultation with a doctor and a dietitian, to help
prevent this from happening.
Drink a glass of water every hour during the day and whenever
you get up at night. Be sure to drink plenty after meals and exercise.
If you have calcium oxalate stones, do not consume very large
amounts of dairy products or foods high in oxalate content (such
as tea or chocolate). Do not take very large doses of Vitamin C (4
grams or more daily) and avoid heavy use of antacids.
If you have uric acid stones, cut down on the amount of red meat
you eat.
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Urinary Tract Infections
The urinary tract is made up of the kidneys, the ureters, the bladder and
the urethra. Each plays an important role in helping the body eliminate
waste products in the form of urine. The main job of the kidneys is to remove wastes from the blood and return the cleaned blood back to the
body. The ureters carry the waste products, as urine, from the kidneys
to the bladder. Urine is stored in the bladder until urination. It passes
out of the body through a tube called the urethra.
A urinary tract infection (UTI) is an inflammation usually caused by
bacteria attacking the kidneys, ureters, bladder or urethra. Under
normal circumstances the urinary tract is free of bacteria. A UTI most
often occurs when bacteria enter the urethra and travel to the bladder, causing a bladder infection. A kidney infection results if bacteria climb
further from the bladder to the kidneys. The bacteria that most often
cause UTIs sit on the skin in the genital area and are called Escherichia
coli (E. coli).
Although this is by far the most common cause, there are other ways
the body can get a UTI. Some people get an infection because the
normal flow of urine is blocked, or is backed up from the bladder into
the kidneys. Sometimes kidney or bladder stones can cause repeated infections. In rare cases, bacteria can reach the kidneys through the
bloodstream.
People are more inclined to get a UTI if they have an abnormal urinary
tract. People are also more susceptible to develop a UTI during
pregnancy, if they have diabetes or if they have an indwelling urinary
catheter (a tube placed in the bladder to help drain urine).
Women have a much greater tendency than men to get a UTI. In fact,
Canadian women make about 500,000 visits to doctors per year, due to
UTIs.
Women are more prone than men to develop UTIs because a woman's
urethra is much shorter than a man's, and bacteria have a shorter
distance to travel from the outside into the bladder. If a woman is prone to developing bladder infections she should avoid wiping her genitals
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from back to front as this might transport bacteria from the anus to the
vagina or urethra, causing infection.
Pregnant women are at increased risk of having a bladder infection
progress and develop into a kidney infection. The drainage system from
the kidney to the bladder dilates during pregnancy and does not empty as rapidly. This reduced flow of urine makes it easier for bacteria to
climb from the bladder to the kidney and for infection to set in. UTIs
during pregnancy may result in a smaller, premature baby.
After menopause, UTIs might increase due to a lack of certain
hormones. An increase in sexual activity might trigger symptoms of a
urinary tract infection in some women. Bladder and kidney infections
are generally not transmitted by sexual intercourse.
Bladder infection (cystitis) is the most common UTI. Symptoms include:
Feeling an urgent need to pass urine often, although the amount
of urine may be small
Burning during urination
Cloudy or foul-smelling urine
Pain in the lower abdomen
If a person also suffers from any of the following, they might have an
infection of the kidneys or prostate gland:
Blood or pus in the urine Fever, chills or vomiting
Diabetes or chronic illness
A history of kidney infection or disease
Pain on urination during pregnancy
Bad back pain
In some cases a person might have mild symptoms (e.g. urge to urinate
frequently), without having a UTI. Smoking, anxiety, drinking a lot of
coffee, food allergies or premenstrual syndrome may cause symptoms similar to a UTI. If mild symptoms have not disappeared within a day or
two, then a urine test is recommended. Infections are usually treated
with antibiotics.
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High Blood Pressure
Proper control of high blood pressure can prevent many of its
complications. If high blood pressure is not well-controlled, it can lead to
stroke, heart attack, heart failure, kidney failure (also called chronic renal insufficiency), and damage to the blood vessels of the legs
leading to amputation.
If a person has diabetes as well as high blood pressure, they must be
especially careful about blood pressure control. For people with kidney
disease, blood pressure control can slow down the decrease in kidney
function.
Some people who already have kidney disease can develop high blood
pressure. The opposite is also true: people with high blood pressure
can develop kidney disease. In fact, high blood pressure is the cause of
kidney failure in about 10% of new patients. High blood pressure
damages the blood vessels of the kidneys. This reduces the blood
supply to the kidneys so they are unable to remove fluids and waste products from the blood. This can lead to kidney failure. When the
kidneys fail, dialysis treatment or a kidney transplant is needed.
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Kidney Failure
Acute kidney failure occurs when kidneys fail suddenly. In this situation,
kidney function usually returns to normal, but dialysis may be needed
until the kidneys begin to work again. There are a number of reasons
why acute kidney failure happens.
Slow and progressive deterioration of kidney function is called chronic kidney failure or chronic renal insufficiency (CRI). It is usually
irreversible. Chronic kidney failure occurs when the tiny filters in the
kidney (nephrons) that remove wastes stop working. Damage to the
nephrons can be caused by conditions such as diabetes and high blood
pressure. In some cases, control of these conditions may slow or even
prevent the development of complete kidney failure.
There is no cure for chronic renal insufficiency. In the early stages,
proper food choices, medications and good blood pressure control may be all that is required to slow the damage to the kidneys. However,
once the kidneys are functioning at less than 10-20% of their normal
rate, either dialysis or transplantation is needed to keep on living. This
period is called end-stage renal disease or ESRD.
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Dialysis
Dialysis is a way to clean the blood by removing wastes and excess
water. There are two types: hemodialysis and peritoneal dialysis.
During hemodialysis, the blood is passed through an artificial kidney.
The artificial kidney cleans the blood in almost the same way that
healthy kidneys do. The treatment is performed usually three times a week. It can take between three and five hours each time and is called
a run.
Figure 7.3.1 Dialysis Machine
http://www.kidney.ca/publications-eng.htm
Hemodialysis can be done in a hospital dialysis unit, in a self-care
centre (with some assistance from the staff), or at home with the aid of
a partner. Special training is required for self-care or home dialysis.
Peritoneal dialysis works on the same principle as hemodialysis, but the blood is cleaned inside the body rather than through an artificial kidney.
Your abdomen or "belly" has a peritoneal cavity lined by a thin
membrane called the peritoneum that surrounds the intestines and
other internal organs.
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In peritoneal dialysis, your peritoneal cavity is filled with a special
dialysis fluid. Excess water and wastes pass through the peritoneum
into the dialysis fluid. This fluid is then drained from the body and discarded. The process is repeated between four to five times a day
(continuous ambulatory peritoneal dialysis, CAPD), or a machine called
an automatic cycler can perform exchanges while you sleep. In most
cases, this treatment can be performed without assistance, at home or
at work. Peritoneal dialysis is sometimes done in a hospital, but more
often, you are trained to do this independently at home.
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Kidney Transplant
A kidney transplant is a surgical procedure in which a healthy donated
kidney is transplanted into another body. A successful kidney transplant
will allow the person to return to a more normal lifestyle and will free them from dialysis treatments. However, a kidney transplant is not a
cure. It is the treatment of choice for chronic renal insufficiency for those
who are considered suitable candidates for a transplant.
There are two types of kidney transplants: a living donor transplant and
a cadaveric transplant.
In a living donor transplant, a kidney from a donor, usually a blood
relative is transplanted. The most suitable donors are usually members
of the immediate family. Sometimes a spouse, distant relative, or close
friend can also be a suitable donor.
The donor's blood group and tissue type must be compatible, and
extensive medical tests will be done to determine the health of the
donor. People who donate a kidney can live a normal life with one kidney and there are few risks to healthy donors. For this type of
transplant, there is a shorter waiting period and the transplant operation
is planned at a time convenient for you and your donor.
Living donor transplants have a 90 to 95% success rate. That means
that after one year, 90 to 95 of every 100 transplanted kidneys are still
working.
A transplant from a non-living donor is called a cadaveric transplant. In
this type of transplant, a healthy kidney from someone who has died
suddenly is transplanted. Before a cadaveric donor's organs can be
transplanted, a series of medical tests is done to determine if they are healthy. In addition, the family of the donor must consent to organ
donation.
After a series of tests, the person will be put on a transplant waiting list
until a kidney is found that is compatible. The length of time a person
will have to wait is hard to predict because it depends on how hard the
match is and how many kidneys become available. Unfortunately, the
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waiting time for a cadaveric organ transplant is getting longer.
Cadaveric transplants have an 80 to 85% success rate.
The transplant operation usually takes two to four hours. The new
kidney and ureter (the tube through which the urine flows into the
bladder) are placed in the lower abdomen near the groin. They are surgically attached to the blood vessels and bladder. The old kidneys
are not removed unless they are so large there is no room for the new
kidney, or they are chronically infected.
Figure 7.3.2 Kidney Transplant
http://www.kidney.ca/publications-eng.htm
A catheter is placed in the bladder for a few days to drain the urine
made by the new kidney. Sometimes a drainage tube is placed near the
transplanted kidney to remove fluids that build up. In some cases,
dialysis may be required following the transplant until the new kidney
starts to work. Fluids and medications are given through intravenous lines, often inserted in the arm and neck. After the transplant, the
person receives anti-rejection medication. Many tests are done to make
sure the new kidney is working properly and to watch for any signs of
rejection.
Rejection occurs when the body recognizes that the transplanted kidney
is not its own and mobilizes the immune system to fight against it.
Various anti-rejection medications (called immunosuppressives) are
used to prevent or treat rejection. They work by blocking the activity of the immune system. Some of these medications may cause side
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effects. Rejection is more common in the early months but can occur at
any time after the transplant. It may occur even when medications are
taken faithfully. Rejection episodes can usually be treated successfully. If the transplanted kidney stops working, the person will be able to go
back on dialysis. The transplanted kidney may not be removed. Many
factors influence its long term functioning. Some kidneys have lasted as
long as 25 years and more.
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Testing for Healthy Kidney Function
Healthy kidneys remove wastes and excess fluid from the blood. Blood
tests show whether the kidneys are failing to remove wastes. Urine
tests can show how quickly body wastes are being removed and
whether the kidneys are leaking abnormal amounts of protein.
Blood Tests
Serum creatinine - Creatinine is a waste product that comes from
meat protein in the diet and from the normal wear and tear on muscles of the body. Higher levels may be a sign that the kidneys
are not working properly. As kidney disease progresses, the level
of creatinine in the blood increases.
Blood urea nitrogen (BUN) - Urea nitrogen also is produced from
the breakdown of food protein. As kidney function decreases, the
BUN level increases.
Urine Tests
Some urine tests require only a few ounces of urine. But some tests
require collection of all urine produced for a full 24 hours. A 24-hour
urine test shows how much urine your kidneys produce in 1 day. The
test is sometimes used to measure how much protein leaks from the kidney into the urine in 1 day. However, protein leakage can also be
accurately determined in a small sample of urine by measuring its
protein and creatinine concentration. Following are some common
substances tested in urine.
Ketones - A urine test that uses a reagent strip to check for the
presence of ketones. Ketones spill into the urine when the body
metabolizes, or breaks down, fat for fuel in the absence of
glucose. They are often identifiable by their fruity odor. Presence in urine may indicate ketoacidosis (diabetic coma). This test may
also be performed as part of a routine urinalysis.
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Protein - Also known as the Proteinuria test or "dipstick" test, it
detects protein in the urine. Healthy kidneys filter and absorb
proteins; damaged or diseased kidneys are unable to properly
process proteins and instead excrete them into the urine. Presence may indicate renal or kidney disease. This test may also
be performed as part of a routine urinalysis. Proteinuria can also
signal other urinary tract disorders.
Microalbumin - Also known as the Microalbuminuria test, the
microalbumin test checks for albumin, a protein, in the urine over
a period of 24 hours. It is a more sensitive test than a "dipstick"
protein test. It may be performed along with a creatinine clearance
test. Presence may indicate deterioration of the kidneys due to
diabetes. Bladder infection and/or nephritis can also cause an
elevated microalbumin level.
Creatinine Clearance - A urine test that measures the kidney's
ability to filter creatinine from the blood. Creatinine is a metabolic byproduct of creatine, the acid that supplies energy for muscle
contractions. Normal kidneys should filter creatinine into the urine
at a constant rate. If kidney function is impaired, creatinine levels
will be low. Low levels indicate kidney disease (i.e., polycystic
kidney disease, glomerulonephritis, renal cancer), congestive
heart failure, or and/or severe dehydration.
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Glucose - Also known as the Glucosuria test or urinary sugar test,
it is a test for the presence of glucose in the urine. It measure
glucose levels from several hours earlier, and results vary depending on the concentration of the urine. This test may be
performed as part of a routine urinalysis. It generally is not used
as a standalone measure of glucose levels any more, as blood
glucose testing has replaced this function. Elevated levels of
glucose indicate the presence of sugar in the urine, which may
indicate diabetes.
Urine Culture - This is a test for the presence of bacteria in urine.
Under normal conditions, urine is sterile. The presence of bacteria
typically indicates a urinary tract infection (UTI).
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Homework Questions
1. List five symptoms that may indicate kidney disease.
2. Differentiate between Type I and Type II diabetes.
3. How does diabetes lead to kidney disease?
4. Why is nephritis such a potentially serious kidney disease?
5. Describe 3 treatments for kidney stones.
6. What is the most common cause of a urinary tract infection?
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7. What is chronic kidney failure and how is it treated?
8. Differentiate between hemodialysis and peritoneal dialysis.
9. Why would living donor transplants have higher success rate than
cadaveric transplants?
10. Describe three substances that are analyzed in urine
samples.
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Project Assignment
Debate: Xenotransplants
Statement: The government should allow xenotransplants in Canada.
Procedure:
1. Choose a partner to work with from your class.
2. Read the background information on the next page.
3. Research the issue of xenotransplants in newspapers, periodicals
and the Internet (some web references are provided on the
following page). 4. Discuss the issue with your partner and others in preparation for a
debate.
5. Prepare a joint report (you and your partner) with the information
in the points below.
6. Your teacher will give you specific instructions about how to post
or submit your report.
1. Write a list of points and counterpoints
that you and your partner considered.
2. Decide whether your group agrees or
disagrees with the statement.
3. Defend your group’s position. 4. What responsibility do governments have
to ensure that all groups have a voice in
the debate?
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Background Information
Canada but only 1,667 received one (including 378 kidneys donated by
living people). More than 3 out of 4 people on the waiting list needed a
kidney. The rest were waiting for livers, hearts, lungs or pancreases.
available. It appears that the number of people waiting for organs will
continue to grow as the number of people over the age of 60 grows.
transplants in Canada.
from one animal species to another for medical purposes. We use the
term here to refer to animal-to-human transplants. The transplanted
material is called a xenotransplant.
-to-human transplants
could potentially be treated by xenotransplantation. Organ
xenotransplants could include whole hearts, lungs, livers, kidneys or
pancreas of animals. Tissue xenotransplants could include skin grafts for burn victims, corneal transplants for the visually impaired or bone
transplants for limb reconstruction. Cellular xenotransplants may be a
way to treat people who have diabetes or Parkinson's disease.
transplants, is not new and the procedure has largely been
unsuccessful. The main scientific challenges to xenotransplantation are
immune rejection and infection. While drugs have been available for
some time to sufficiently suppress the immune system for human-to-human transplants, they have not been successful in animal-to-human
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transplants. To date, survival times for recipients of xenotransplants
have been poor although some cellular xenotransplants seem better
able to resist immune rejection.
genes to animal cells to make them more acceptable to a patient's immune system. Genetically modified animals are called "transgenic"
animals. Transgenic pigs have been developed in various countries and
shipped to researchers in Canada.
lot of questions. Is this a good way to save lives and cure people? Is it
safe? Who should pay for it? Should humans use animals in this way?
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Web References
Public Consultation on Xenotransplantation
(http://www.xeno.cpha.ca/english/index_e.htm) Information on the status of xenotransplantation in Canada and the
issues surrounding it can be found on this Canadian Public Health
Association Web site. The function of the site is to inform Canadians
about the government's Public Consultation on Xenotransplantation
program and to involve citizens in the decisions concerning the use of
this technology in our country. The results of this public consultation are published here. Also included is a list of links to Canadian documents
and Web sites on the topic.
Xenotransplantation
(http://www.hc-sc.gc.ca/dhp-mps/brgtherap/activit/fs-fi/xeno_fact-fait-
eng.php http://www.phac-aspc.gc.ca/publicat/ccdr-rmtc/01vol27/27s1/index.html)
This report published by Health Canada defines Xenotransplantation
and outlines some of the potential problems associated with it. The
main function of this report is to describe government plans to keep a
close watch on the effects of xenotransplantation on the population.
Background to the Current Regulatory Framework for
Xenotransplantation in Canada
(http://www.hc-sc.gc.ca/dhp-
mps/brgtherap/activit/consultation/xenotransplant/forum_rep-rap_xeno-
eng.php )
Background to the Current Regulatory Framework for Xenotransplantation in Canada is a long document that is part of the
Report of the Xenotransplantation Surveillance Workshop, Health
Canada. It outlines the current status of xenotransplantation in Canada,
and the issues and perceived risks associated with it.
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Organ Farm
(http://www.pbs.org/wgbh/pages/frontline/shows/organfarm/) Organ Farm is a PBS Frontline report on xenotransplantation. It
provides excellent coverage of the risks and business of
xenotransplants. Options for viewing include video excerpts, interviews,
and some historical background of the experiments.