Quality Controllers of the Blood
Kidneys
What are nephrons?
The nephrons are specialised tubules that carry out blood filtration and
selective reabsorption. Each kidney has about 1.25 million nephrons (140
km of micro-tubing).
Salt - the good and the bad
This lesson presents important facts about the kidneys and their function
in maintaining a state of homeostasis or ‘balance’ in the body’s internal
environment. It also shows how you can avoid health problems caused by
too much salt in your diet.
Water Reabsorption
Salt is a very important component in our diets. However, it
is one of those things that we only need a certain amount of.
An excess of salt can be extremely damaging to our health.
That is why safefood the Food Safety Promotion Board
has designed a safefood public information programme to
raise our level of knowledge about salt and its effects.
Quality Contr
for reabsorption become the excretory liquid called urine. The functional
subunits of the kidney are the nephrons.
Water Reabsorption
Salt - the good and the bad
The
The
Kidneys
for reabsorption become the excretory liquid called urine. The functional
subunits of the kidney are the nephrons.
Clean blood
Salt is a very important component in our diets. However, it Blood
with wastes
What are nephrons?
is one of those things that we only need a certain amount of.
ADH Concentration
ADH Concentration
An excess of salt can be extremely damaging to our health.
The nephrons are specialised tubules that carry out blood filtration and
Nephron
Fig.2 Water reabsorbtion against ADH con
What is homeostasis?
Glomerulus
selective reabsorption. Each kidney has about 1.25 million nephrons (140
Board
That is why safefood the Food Safety Promotion
Homeostasis is the ability of a living organism to maintain a constant
km of micro-tubing).
Is salt necessary in the diet?
safefood
public
information
programme to
hasenvironment
designed
achanges
internal
despite
in the external
environment.
It is the
ability to remain stable. The human body is a society of cooperative living
Salt, which is NaCl, is a source of sodium and chlorine, and is
raise
our
level
of
knowledge
about
salt
and
its
effects.
Clean blood
cells, about 10 in fact. These cells are surrounded by a very thin layer of
Wastes (urine)
14
tissue fluid. In order to ensure that this tissue fluid environment can meet
presents
important
kidneys
theThis
needslesson
of the cell,
it is necessary
to keep thefacts
bloodabout
in good the
condition.
and their function
in maintaining a state of homeostasis or ‘balance’ in the body’s internal
Which
major Itblood
environment.
also shows how you can avoid health problems caused by
Tubule
characteristics
influence
too much salt in your
diet. homeostasis?
to the bladder
Blood
with wastes
Blood concentration, volume and pressure greatly affect the continuous
Fig.1 Nephron and its vascularisation
refreshment and renewal of tissue fluid. The supply of ‘fuel’ and other
Nephron
essential raw materials to the tissue cells is determined by the blood’s
nutrient composition and concentration. The pH of the blood must be kept
Glomerulus
How is the blood filtered?
tightly at 7.4, as even slight changes in cellular pH have a major affect
the ability
of waste
a living
organism
to maintain
a occurs
constant
Filtration
in the glomerulus. This set of capillaries is extremely porous
on Homeostasis
enzyme action. By is
keeping
the blood’s
concentration
low the
and leaky. About
a fifth of the blood plasma, minus its dissolved protein,
various
metabolic
wastes can bedespite
removed rapidly
from the
cells and environment.
internal
environment
changes
in tissue
the external
It is the
passes into Bowman’s capsule. This process is known as glomerular
delivered to the excretory organs for expulsion. Finally, the temperature of
ability
to
remain
stable.
The
human
body
is
a
society
of
cooperative
living
filtration. Only those substances that are smaller than the pores in the
37°C, must be regulated to ensure a high constant rate of enzyme action
cells, normal
aboutmetabolism.
1014 in fact. These cells are surrounded by a very
thincapillaries
layer ofpass out of the blood. Every minute, just over 100 cm3
glomerular
to sustain
of
water with
tissue fluid. In order to ensure that this tissue fluid environment
candissolved
meet materials escapes from the blood at the kidneys
What is homeostasis?
Dotheany
of our
organs
homeostasis?
needs
of the
cell, it isaffect
necessary
to keep the blood in good condition.
How are important materials
Every organ in the body plays a role in homeostasis because the blood
returned to the blood?
is altered as it flows through each. The major homeostatic organs are the
Which major blood
The proximal convoluted tubule (PCT) reabsorbs about 70% of the water
Tubule
by osmosis. The PCT reabsorbs 70% of the salts
(mostly sodium chloride)
characteristics
influence
homeostasis?
and all the glucose and amino acids by active transport.
What are the main functions
kidneys, lungs, skin, liver and brain.
ofBlood
the kidneys?
the remaining water is reabsorbed by the loop of Henle along with
concentration, volume and pressure greatly affectHalf
theof continuous
the diet. As society has moved away from individuals growin
food, a need has developed for foods to have a longer shelf li
one of the most common preservatives used.
The recommended daily amount of salt for teenagers is 400
4g, but the average modern diet is about 10000mg or 10g.
Excessive sodium intake has to be excreted from the body bu
is limited in the amount of sodium that it can excrete at any o
build up of excessive sodium in the body circulates in the bloo
high intake of sodium can lead to high blood pressure (hype
influencing blood control. A diet high in salt can influence the d
of hypertension from an early age. However hypertension oft
manifest itself until middle to later life.
Too much salt can cause heart proble
Wastes
(urine)chloride – NaCl. Your body needs salt because
Salt is sodium
tofluids
the bladder
contain sodium. However, only a small amount of salt is
maintain a healthy body. Too much sodium can be very harmful.
problems, it can cause high blood pressure and this is a serious c
heart disease. The Irish Heart Foundation estimates that over 900
be prevented each year if each person reduced salt intake by ha
per day.
How much should you take every day?
Over 60% of us can’t answer this question. In fact, adults nee
grams and not more than six grams, which is about one teaspo
and teenagers
needand
less. its vascularisation
Fig.1
Nephron
thirds of the salts.
How much salt do you take every day?
of about
‘fuel’two
and
other
Most of us don’t know how much salt is in the food we eat. In fact
Further
water
reabsorption
from
the
distal
convoluted
tubule
(DCT)
and
raw materials
the
cells issalts
determined
by the blood’s
• essential
Excretion: nitrogenous
wastes – to
urea,
urictissue
acid, creatinine,
and
65% to 70% of the salt we eat comes from processed food, fast fo
collecting duct depends on the blood concentration. Only if the blood
any excesscomposition
water.
we buy in restaurants. We usually don’t check the labels* when
nutrient
and concentration. The pH of the blood
must
be
kept
needs to be diluted will these regions
reabsorb
water.
This fine
adjustment filtered?
How
is
the
blood
in shops and have no idea how much a restaurant might add w
• tightly
Regulation
bloodas
concentration.
concentration
atof7.4,
even slight changes in cellular pH haveof ablood
major
affect is under the influence of antidiuretic hormone
We also add another 15% ourselves when cooking or eating a
(ADH). When osmoreceptors in the
hypothalamus
of
the
brain
detect
an
• on
Maintainance
of
the
blood
at
pH
7.4.
remaining
naturally in
food.
Filtration occurs in the glomerulus. This
set ofoccurs
capillaries
isthe
extremely
porous
enzyme action. By keeping the blood’s waste concentration low the
increase in blood concentration above normal, the pituitary gland secretes
Take
care
leaky.ADH
About
a fifth
of the blood
plasma,
minus its dissolved protein,
various metabolic wastes can be removed rapidly from theADH.
tissue
If a cells
drop inand
blood pressureand
is detected
will also
be secreted
It is too important to ignore the facts about salt. Take the time to
How
do the
kidneys
carry
outfor
excretion?
reabsorb more water,
blood volume
raising the capsule.
blood
passes
into and
Bowman’s
This
process is known as glomerular
delivered
to the
excretory
organs
expulsion. Finally, thetotemperature
of increasing
brochures How much salt is good for you and What’s a pinch? w
back to normal.
The37°C,
kidneysmust
first expel
lots of materials
from the blood
by filtration
and rate ofpressure
filtration. Only those substances that
aresafefood
smaller
than
in the
be regulated
to ensure
a high
constant
enzyme
action
at 1850
404 the
567 inpores
the Republic
of Ireland or 08
get from
then reabsorb the useful materials back into the blood. This is just like
NorthernEvery
Ireland. minute, just over 100 cm3
The reabsorption of salt by the DCT
will depend capillaries
on how muchpass
is needed
glomerular
out of theinblood.
to
sustain
normal
metabolism.
clearing out a cluttered wardrobe – empty out all the clothes and only put
to maintain normal blood salt concentration. A different hormone,
*Food labels will tell you how many grams of sodium the food
of water with dissolved materials escapes
from the blood at the kidneys
back what is worth keeping. The materials not selected by the kidneys
aldosterone from the adrenal glands, regulates salt reabsorption.
refreshment
and extremely
renewal important
of tissue
fluid. The
supply
The
kidneys have three
functions,
namely:
Do any of our organs affect homeostasis?
Every organ in the body plays a role in homeostasis because the blood
is altered as it flows through each. The major homeostatic organs are the
kidneys, lungs, skin, liver and brain.
What are the main functions
of the kidneys?
The kidneys have three extremely important functions, namely:
•
Excretion: nitrogenous wastes – urea, uric acid, creatinine, salts and
any excess water.
•
Regulation of blood concentration.
•
Maintainance of the blood at pH 7.4.
How do the kidneys carry out excretion?
The kidneys first expel lots of materials from the blood by filtration and
then reabsorb the useful materials back into the blood. This is just like
clearing out a cluttered wardrobe – empty out all the clothes and only put
back what is worth keeping. The materials not selected by the kidneys
convert to grams of salt, multiply by 2.5.
How are important materials
returned to the blood?
The proximal convoluted tubule (PCT) reabsorbs about 70% of the water
by osmosis. The PCT reabsorbs 70% of the salts (mostly sodium chloride)
and all the glucose and amino acids by active transport.
Half of the remaining water is reabsorbed by the loop of Henle along with
about two thirds of the salts.
Further water reabsorption from the distal convoluted tubule (DCT) and
collecting duct depends on the blood concentration. Only if the blood
needs to be diluted will these regions reabsorb water. This fine adjustment
of blood concentration is under the influence of antidiuretic hormone
(ADH). When osmoreceptors in the hypothalamus of the brain detect an
increase in blood concentration above normal, the pituitary gland secretes
ADH. If a drop in blood pressure is detected ADH will also be secreted
to reabsorb more water, increasing blood volume and raising the blood
pressure back to normal.
The reabsorption of salt by the DCT will depend on how much is needed
to maintain normal blood salt concentration. A different hormone,
aldosterone from the adrenal glands, regulates salt reabsorption.
The
Kidneys
Quality Controllers of the Blood
ntrollers of the Blood
What are nephrons?
The nephrons are specialised tubules that carry out blood filtration and
selective reabsorption. Each kidney has about 1.25 million nephrons (140
km of micro-tubing).
Clean blood
This lesson presents important facts about the kidneys and their function
in maintaining a state of homeostasis or ‘balance’ in the body’s internal
environment. It also shows how you can avoid health problems caused by
too much salt in your diet.
Blood
with wastes
Water Reabsorption
Salt is a very important component in our diets. However, it
is one of those things that we only need a certain amount of.
An excess of salt can be extremely damaging to our health.
That is why safefood the Food Safety Promotion Board
has designed a safefood public information programme to
raise our level of knowledge about salt and its effects.
for reabsorption become the excretory liquid called urine. The functional
subunits of the kidney are the nephrons.
Water Reabsorption
Salt - the good and the bad
ADH Concentration
ADH Concentration
What is homeostasis?
Nephron
Water Reabsorption
Water Reabsorption
Which major blood
characteristics influence homeostasis?
Fig.2 Water reabsorbtion against ADH con
Glomerulus
Homeostasis is the ability of a living organism to maintain a constant
internal environment despite changes in the external environment. It is the
ability to remain stable. The human body is a society of cooperative living
cells, about 1014 in fact. These cells are surrounded by a very thin layer of
tissue fluid. In order to ensure that this tissue fluid environment can meet
the needs of the cell, it is necessary to keep the blood in good condition.
Is salt necessary in the diet?
Salt, which is NaCl, is a source of sodium and chlorine, and is
the diet. As society has moved away from individuals growin
food, a need has developed for foods to have a longer shelf li
one of the most common preservatives used.
Wastes (urine)
to the bladder
The recommended daily amount of salt for teenagers is 400
4g, but the average modern diet is about 10000mg or 10g.
Tubule
ADH Concentration
Blood concentration, volume and pressure greatly affect the continuous
Fig.1 Nephron and its vascularisation
ADH Concentration
refreshment and renewal of tissue fluid. The supply of ‘fuel’ and other
essential raw materials to the
tissue
cells
is
determined
by
the
blood’s
Fig.2 Water reabsorbtion against ADH concentration
nutrient composition and concentration. The pH of the blood must be kept
How is the blood filtered?
was established
tightly at 7.4, as even slight changes in cellular pH have a major affect
Filtration occurs in the glomerulus. This set of capillaries is extremely porous
on enzyme action. By keeping the blood’s waste concentration low the
Agreement in December
and leaky. About a fifth of the blood plasma, minus its dissolved protein,
various metabolic wastes can be removed rapidly from the tissue cells and
withprocess
responsibility
for:
passes into Bowman’s capsule. This
is known as
glomerular
delivered to the excretory organs for expulsion. Finally, the temperature of
Only those
Salt,must
which
is NaCl,
a source
of sodium
chlorine,
andfiltration.
is essential
in substances that are smaller than the pores in the
37°C,
be regulated
to is
ensure
a high constant
rate ofand
enzyme
action
glomerular
capillaries
pass
out
of
the
blood.
Every
minute,
just
over
100 cm3
to
sustain
the
diet.normal
As metabolism.
society has moved away from individuals growing their own
of water with dissolved materials escapes from the blood at the kidneys
safefood
safefood
Is salt necessary in the diet?
Excessive sodium intake has to be excreted from the body bu
is limited in the amount of sodium that it can excrete at any o
build up of excessive sodium in the body circulates in the bloo
high intake of sodium can lead to high blood pressure (hype
influencing blood control. A diet high in salt can influence the d
under
the termsfrom
of an
theearly
Good
Fridayhypertension oft
of hypertension
age. However
until middle
to later
life.
1999.manifest
It is aitself
cross
border
organisation
food, a need has developed for foods to have a longer shelf life and salt is
Do any of our organs affect homeostasis?
• Promotion of food safety
one of the most common preservatives used.
How are important materials
Every organ in the body plays a role in homeostasis because the blood
returned to
• Research into food safety
is
altered
as it flows throughdaily
each. The
major homeostatic
organs
are the
The
recommended
amount
of salt for
teenagers
is 4000mg/day
orthe blood?
kidneys, lungs, skin, liver and brain.
Too much salt can cause heart proble
Salt is sodium chloride – NaCl. Your body needs salt because
fluids contain sodium. However, only a small amount of salt is
maintain a healthy body. Too much sodium can be very harmful.
problems, it can cause high blood pressure and this is a serious c
heart disease. The Irish Heart Foundation estimates that over 900
be prevented each year if each person reduced salt intake by ha
per day.
reabsorbs about 70% of the water
4g, but the average modern diet is about 10000mg or 10g. The proximal convoluted tubule (PCT)
• Communication of food alerts How much should you take every day?
by osmosis. The PCT reabsorbs 70% of the salts (mostly sodium chloride)
Over 60% of us can’t answer this question. In fact, adults nee
the glucose and amino acids by active transport.
What
aresodium
the main
functions
Excessive
intake
has to be excreted from the body and
butallthe
kidney
grams and not more than six grams, which is about one teaspo
• Surveillance
of diseases
carried
by food
of
the
kidneys?
and teenagers need less.
Half
of
the
remaining
water
is
reabsorbed
by
the
loop
of
Henle
along
with
is limited in the amount of sodium that it can excrete at any one time. The
about two thirds of the salts.
How much salt do you take every day?
the blood system. A
• Promotion of scientific cooperation
between laboratories
Most of us don’t know how much salt is in the food we eat. In fact
Further water reabsorption from the distal convoluted tubule (DCT) and
intakenitrogenous
of sodium
can– urea,
leaduric
to acid,
highcreatinine,
blood pressure
(hypertension) by
•high
Excretion:
wastes
salts and
65% to 70% of the salt we eat comes from processed food, fast fo
collecting duct depends on the blood concentration. Only if the blood
any excess water.
we buyschemes
in restaurants. We usually don’t check the labels* when
• reabsorb
Development
ofadjustment
laboratory testing
influencing
blood control. A diet high in salt can influence theneeds
development
to be diluted will these regions
water. This fine
in shops and have no idea how much a restaurant might add w
•of Regulation
of bloodfrom
concentration.
of blood
concentration
is under the influence of antidiuretic hormone
hypertension
an early age. However hypertension often
does
not
We also add another 15% ourselves when cooking or eating a
(ADH). When osmoreceptors in the hypothalamus of the brain detect an
• Maintainance of the blood at pH 7.4.
remaining occurs naturally in the food.
manifest itself until middle to later life.
increase in blood concentration above normal, the pituitary gland secretes
Take care
ADH. If a drop in blood pressure isTo
detected
ADH will also
be lesson
secreted it provides specific information on salt
complement
this
It is too important to ignore the facts about salt. Take the time to
How do the kidneys carry out excretion?
to reabsorb more water, increasing blood volume and raising the blood
is good
for yousalt
and What’s
and how to use it safely. It allowsbrochures
you to How
findmuch
outsalthow
much
is a pinch? w
pressure back to normal.
Too
much
canfrom
cause
problems
The
kidneys
first expel salt
lots of materials
the blood heart
by filtration and
get from safefood at 1850 404 567 in the Republic of Ireland or 08
contained in various types of foods.
Other
then reabsorb the useful materials back into the blood. This is just like
in Northern
Ireland.information on food
The reabsorption of salt by the DCT will depend on how much is needed
Salt is out
sodium
chloride
– –NaCl.
Your
body
needs
saltputbecause
clearing
a cluttered
wardrobe
empty out
all the
clothes
and only
to many
maintainbodily
normal blood salt concentration.
A different
hormone,
labeling, fridge
hygiene,
bacteria and
food
poisoning
is also
*Food
labels
will tell you how
manyprovided
grams of sodium the food
back
is worthsodium.
keeping. The
materials only
not selected
by the
kidneys of saltaldosterone
fluidswhat
contain
However,
a small
amount
is required
from to
the adrenal glands, regulates salt reabsorption.
convert to grams of salt, multiply by 2.5.
so
you
can
learn
how
to
prevent
food
poisoning
when
buying,
maintain a healthy body. Too much sodium can be very harmful. Among other
cooking and storing food.
problems, it can cause high blood pressure and this is a serious contributor to
heart disease. The Irish Heart Foundation estimates that over 900 deaths could
be prevented each year if each person reduced salt intake by half a teaspoon
per day.
How much should you take every day?
Over 60% of us can’t answer this question. In fact, adults need about four
grams and not more than six grams, which is about one teaspoon. Children
and teenagers need less.
How much salt do you take every day?
Most of us don’t know how much salt is in the food we eat. In fact, as much as
You can find out more about safefood at
65% to 70% of the salt we eat comes from processed food, fast food and food
www.safefoodonline.com or at
we buy in restaurants. We usually don’t check the labels* when we buy food
www.sciencetechnologyaction.com.
in shops and have no idea how much a restaurant might add when cooking.
We also add another 15% ourselves when cooking or eating at home. The
safefood is a user friendly, colourful site containing
remaining occurs naturally in the food.
both food safety and nutrition information.
Take care
It is too important to ignore the facts about salt. Take the time to read the two
brochures How much salt is good for you and What’s a pinch? which you can
get from safefood at 1850 404 567 in the Republic of Ireland or 0800 085 1683
in Northern Ireland.
*Food labels will tell you how many grams of sodium the food contains. To
convert to grams of salt, multiply by 2.5.
The
kidneys
three extremely
important
functions,
namely: in
build
up ofhave
excessive
sodium
in the body
circulates
Quality Controllers of the Blood
Kidneys
for reabsorption become the excretory liquid called urine. The functional
subunits of the kidney are the nephrons.
What are nephrons?
The nephrons are specialised tubules that carry out blood filtration and
selective reabsorption. Each kidney has about 1.25 million nephrons (140
km of micro-tubing).
Syllabus Reference
Activities
Clean blood
This lesson presents important facts about the kidneys and their function
in maintaining a state of homeostasis or ‘balance’ in the body’s internal
LeavingIt also
Certifi
environment.
shows cate
how youBiology:
can avoid health problems caused by
too much salt in your diet.
Blood
with wastes
Water Reabsorption
Salt is a very important component in our diets. However, it
is one of those things that we only need a certain amount of.
An excess of salt can be extremely damaging to our health.
That is why safefood the Food Safety Promotion Board
has designed a safefood public information programme to
raise our level of knowledge about salt and its effects.
Quality Contr
Water Reabsorption
Salt - the good and the bad
The
The
Kidneys
Draw a labelled diagram of the human urinary system.
ADH Concentration
3.3.5 Blood Transport of Nutrients – transport of waste products
Nephron
to kidneys,
3.4.6 Excretory system in the Human
What
is homeostasis?
Draw a labelled diagram of a kidney in vertical section
and show the
ADH Concentration
position of the nephron and the collecting duct thatFig.2
it isWater
connected
to.against ADH con
reabsorbtion
Homeostasis is the ability of a living organism to maintain a constant
H3.4.8
The Nephron
as ina the
Unit
of the
Kidney
internal
environment
despite changes
external
environment.
It is the
ability to remain stable. The human body is a society of cooperative living
14
cells,
about 10
in fact. These
are surrounded by a very thin layer of
Junior
Certifi
catecells
Science:
tissue fluid. In order to ensure that this tissue fluid environment can meet
the needs of the cell, it is necessary to keep the blood in good condition.
Draw a labelled diagram of the nephron and its associated blood supply.
Glomerulus
Unit 1A6 – Excretion, OB20, OB23
Which major blood
characteristics influence homeostasis?
Is salt necessary in the diet?
Outline the process of selective reabsorption
carried
out by
the nephron
Salt, which is NaCl,
is a source
of sodium
and chlorine, and is
Wastes (urine)
the diet. As is
society
away from individuals growin
and
duct. Note: selective secretion
not has
on moved
the syllabus.
to thecollecting
bladder
food, a need has developed for foods to have a longer shelf li
one of the most common preservatives used.
Practical Activity
Tubule
The recommended daily amount of salt for teenagers is 400
4g, but the average modern diet is about 10000mg or 10g.
sodium intake
to be
from the body bu
Purchase two lamb or pig kidneys atExcessive
the butchers.
Cuthas
one
inexcreted
transverse
Blood concentration, volume and pressure greatly affect the continuous
is limited in the amount of sodium that it can excrete at any o
Fig.1 Nephron and its vascularisation
section
across the narrow middle and
the other in vertical section along
refreshment and renewal of tissue fluid. The supply of ‘fuel’ and other
build up of excessive sodium in the body circulates in the bloo
the long axis (opens like the wingshigh
of intake
a butterfl
y). Examine
theblood
internal
essential raw materials to the tissue cells is determined by the blood’s
of sodium
can lead to high
pressure (hype
nutrient composition and concentration. The pH of the blood must be kept
control.in
A diet
high
in salt
can influence the d
structure of the kidney and compareinfluencing
with theblood
diagram
your
text
book.
How is the blood filtered?
tightly at 7.4, as even slight changes in cellular pH have a major affect
of hypertension from an early age. However hypertension oft
On
completing
this
student
shouldFiltration
be able
occurs to:
in the glomerulus. This set of capillaries is extremely porous
on
enzyme
action. By keeping
the section,
blood’s wastethe
concentration
low the
manifest itself until middle to later life.
and leaky. About a fifth of the blood plasma, minus its dissolved protein,
various metabolic wastes can be removed rapidly from the tissue cells and
• Explain
the meaning
homeostasis
passes into Bowman’s capsule. This process is known as glomerular
delivered
to the excretory
organs forof
expulsion.
Finally, the temperature of
Too
much
salt
can cause
heart
filtration. Only those substancesWhy
that are
smaller
thankidney
the pores
in the slightly
37°C, must be regulated to ensure a high constant rate of enzyme action
is the
right
usually
lower
in the
abdominal
cavity
thanproble
glomerular capillaries pass out of the blood. Every minute, just over 100 cm3
Describe
the blood characteristics which influence homeostasis
to•sustain
normal metabolism.
Salt is sodium chloride – NaCl. Your body needs salt because
left from
kidney?
Hint:
review
of the digestive system in the
of water with dissolved materials the
escapes
the blood
at the
kidneys the arrangement
fluids contain sodium. However, only a small amount of salt is
maintain a healthy body. Too much sodium can be very harmful.
abdominal cavity.
• any
Describe
theorgans
function affect
of the kidneys
in maintaining homeostasis
Do
of our
homeostasis?
problems, it can cause high blood pressure and this is a serious c
How are important materials
heart
disease.
Thecommon
Irish Heart Foundation
estimates
Every
organ in the the
bodykidney
plays a role
in homeostasis
because the blood
Why is infection of the urinary bladder
much
less
in males
than that
in over 900
• Describe
processes
of excretion
returned
to
the
blood?
be prevented each year if each person reduced salt intake by ha
is altered as it flows through each. The major homeostatic organs are the
females? Hint: review the structure ofper
the
urinary and reproductive systems
day.
kidneys, lungs, skin, liver and brain.
The proximal convoluted tubule (PCT) reabsorbs about 70% of the water
• Explain how important materials are returned to the blood.
How much should you take every day?
males
and(mostly
females.
by osmosis. The PCT reabsorbs of
70%
of the salts
sodium chloride)
Over 60% of us can’t answer this question. In fact, adults nee
all the glucose and amino acids by active transport.
What
are the
• Identify
the main
health functions
problem associated with excess salt and
consumption
grams in
andthe
not urinary
more thanbladder?
six grams, which is about one teaspo
Why is urine stored, though temporarily,
of the kidneys?
and teenagers need less.
Half of the remaining water is reabsorbed by the loop of Henle along with
about two thirds of the salts.
How
much
salt
do
you
take
every day?
Explain why ‘standing on your head’ will not stop the bladder
from filling
The kidneys have three extremely important functions, namely:
Most of us don’t know how much salt is in the food we eat. In fact
Further water reabsorption fromwith
the distal
convoluted tubule (DCT) and
urine.
• Excretion: nitrogenous wastes – urea, uric acid, creatinine, salts and
65%
to
70%
of
the
salt
we
eat
comes
from
processed food, fast fo
collecting duct depends on the blood concentration. Only if the blood
any excess water.
we buy in restaurants. We usually don’t check the labels* when
needs to be diluted will these regions
reabsorb
water.
Thisurine
fine adjustment
Explain
why
fresh
can
be
used
as
an
antiseptic.
in
shops
and
have
no
idea
how
much
a
restaurant
might add w
• Regulation of blood concentration.
of blood concentration is under the influence of antidiuretic hormone
We also add another 15% ourselves when cooking or eating a
(ADH). When osmoreceptors in the hypothalamus of the brain detect an
• Maintainance of the blood at pH 7.4.
remaining occurs naturally in the food.
increase in blood concentration above normal, the pituitary gland secretes
Take care
ADH. If a drop in blood pressure is detected ADH will also be secreted
• The
body iscarry
a cooperative
society of about toone
hundred
It is too important to ignore the facts about salt. Take the time to
How
do human
the kidneys
out excretion?
reabsorb more water, increasing blood volume and raising the blood
brochures How much salt is good for you and What’s a pinch? w
thousand billion cells.
pressure back to normal.
The kidneys first expel lots of materials from the blood by filtration and
get from safefood at 1850 404 567 in the Republic of Ireland or 08
then reabsorb the useful materials back into the blood. This is just like
in Northern Ireland.
The reabsorption of salt by the DCT will depend on how much is needed
clearing
out acells
cluttered
wardrobe
empty out all the known
clothes and
put fluid.to maintain normal blood salt concentration. A different hormone,
• Our
exist
in an –environment
asonly
tissue
*Food
labels
will tell(T)
you how
grams
of sodium the food
Indicate whether the following
are
true
or many
false
(F)
back what is worth keeping. The materials not selected by the kidneys
aldosterone from the adrenal glands, regulates salt reabsorption.
convert to grams of salt, multiply by 2.5.
Learning Objectives
Investigative Activities
General Learning Points
True or False
•
Homeostasis is essential to maintain efficient metabolism.
•
Characteristics of the blood are critical to ensure homeostasis.
•
The kidneys maintain correct blood concentration, pH and chemical
condition by excreting nitrogenous metabolic wastes plus other
substances in excess such as water and salts.
•
•
•
•
Homeostasis involves the complex co-operative activity of all the
organ systems.
Conserving water due to insufficient water intake is harder work on
the kidneys than dealing with an excessive intake of water.
Water intake equivalent to eight glasses is considered necessary for
the average person each day.
Understanding the workings of human anatomy and physiology helps
to understand the factors involved in the maintenance of a healthy
lifestyle.
by drawing a circle around T or F.
a) The kidneys are important homeostatic organs.
T
F
b) The inner part of the kidney is called the cortex.
T
F
c) The efferent arteriole delivers blood to the glomerulus.
T
F
d) The glomeruli are present in the cortex.
T
F
e) Kidneys form urine by plasma filtration and selective reabsorption. T
F
f)
The glomerular capillaries are impermeable.
T
F
g) Glomerular filtrate passes into Bowman’s capsule.
T
F
h) The PCT has a minor role in selective reabsorption.
T
F
i)
Glucose, amino acids and salts are reabsorbed by diffusion.
T
F
j)
The loop of Henle does not have a role in selective reabsorption. T
F
k) The DCT selectively reabsorbs water and salts.
T
F
l)
T
F
T
F
ADH influences the selective reabsorption of glucose.
m) The CD delivers urine to the renal pelvis.
Check your answers to these questions on
www.sciencetechnologyaction.com
The
Kidneys
Quality Controllers of the Blood
ntrollers of the Blood
What are nephrons?
The nephrons are specialised tubules that carry out blood filtration and
selective reabsorption. Each kidney has about 1.25 million nephrons (140
km of micro-tubing).
Examination Questions
Clean blood
This lesson presents important facts about the kidneys and their function
in maintaining a state of homeostasis or ‘balance’ in the body’s internal
environment. It also shows how you can avoid health problems caused by
too much salt in your diet.
2005 Ordinary Level
•
Dialysis was initially used to help damaged kidneys to recover by
removing the poisonous drugs present in the blood. The first workable
ADH Concentration
dialysis machine for people was in operation byADH
1944.
From the early
Concentration
1960s dialysis has been used for the long term Fig.2
treatment
of patients
Water reabsorbtion against ADH con
suffering from kidney failure.
•
Is salt
necessary
in with
the dogs.
diet?
The first artificial kidney was designed
in 1934
and trialed
Blood
with wastes
The diagram shows a section through a human kidney.
(i) Name
A, B, C, D.
What
is homeostasis?
(ii) To what
structure
connect
Homeostasis
is the
ability of does
a livingDorganism
to maintain a constant
internal
environment
the
kidney?despite changes in the external environment. It is the
Nephron
Glomerulus
�
ability to remain stable. The human body is a society of cooperative
living
(iii) Filtration
anThese
essential
cells,
about 1014 inis
fact.
cells areprocess
surroundedinby a very thin layer of
tissuethe
fluid.formation
In order to ensure
that this
environment can meet
of urine.
In tissue
whatfluid
part
the needs of the cell, it is necessary to keep the blood in good condition.
does it take place?
Which
major blood
(iv) Reabsorption
of useful substances
�
characteristics
influence
takes place in the
kidney. Inhomeostasis?
what
�
�
Tubule
Water Reabsorption
Salt is a very important component in our diets. However, it
is one of those things that we only need a certain amount of.
An excess of salt can be extremely damaging to our health.
That is why safefood the Food Safety Promotion Board
has designed a safefood public information programme to
raise our level of knowledge about salt and its effects.
for reabsorption become the excretory liquid called urine. The functional
subunits of the kidney are the nephrons.
Water Reabsorption
Salt - the good and the bad
Wastes (urine)
to the bladder
Biographical Notes
Salt, which is NaCl, is a source of sodium and chlorine, and is
the diet. As society has moved away from individuals growin
food, a need has developed for foods to have a longer shelf li
one of the most common preservatives used.
The recommended daily amount of salt for teenagers is 400
4g, but the average modern diet is about 10000mg or 10g.
Excessive sodium intake has to be excreted from the body bu
does this
occur?
Bloodpart
concentration,
volume
and pressure greatly affect the continuous
is limited in the amount of sodium that it can excrete at any o
Fig.1 Nephron and its vascularisation
refreshment and renewal of tissue fluid. The supply of ‘fuel’ and other
build up of excessive sodium in the body circulates in the bloo
(v) Name an excretory substance
essential raw materials to the tissue cells is determined by the blood’s
high intake of sodium can lead to high blood pressure (hype
present
in urine.
nutrient
composition
and concentration. The pH of the blood must be kept
influencing blood control. A diet high in salt can influence the d
How is the blood filtered?
tightly at 7.4, as even slight changes in cellular pH have a major affect
an early age.
However hypertension oft
found that the capsule (now calledof hypertension
Bowman’sfrom
capsule)
surrounding
(vi)enzyme
Name
an excretory
organ
in waste
the human
body
the kidney.
occurs in the glomerulus. This set of capillaries is extremely porous
on
action.
By keeping the
blood’s
concentration
lowother
the thanFiltration
manifest itself until middle to later life.
each
glomerulus
in
the kidney
is continuous
with the renal tubules. This
and
leaky.
About
a
fifth
of
the
blood
plasma,
minus
its
dissolved
protein,
various
metabolic
wastes
can
be
removed
rapidly
from
the
tissue
cells
and
Name a substance, other than the one you named in (v), excreted by
passes into Bowman’s capsule.
This
known as glomerular
was
ofprocess
prime isimportance
to his filtration theory of urine formation, key to
delivered to the excretory organs for expulsion. Finally, the temperature of
Too much salt can cause heart proble
filtration. Only those substances that are smaller than the pores in the
37°C, this
must organ.(30)
be regulated to ensure a high constant rate of enzyme action
understanding kidney function.3
glomerular
capillaries
pass
out
of
the
blood.
Every
minute,
just
over
100
cm
to sustain normal metabolism.
Salt is sodium chloride – NaCl. Your body needs salt because
of water with dissolved materials escapes from the blood at the kidneys
fluids contain sodium. However, only a small amount of salt is
maintain a healthy body. Too much sodium can be very harmful.
Do any of our organs affect homeostasis?
problems, it can cause high blood pressure and this is a serious c
How are important materials
disease. The Irish Heart Foundation estimates that over 900
Every organ in the body plays a role in homeostasis because the blood
contributed pioneer work on the heart
microscopic
structure
of reduced
tissues,
(a)
What
is
homeostasis?
State
the
role
of
the
kidneys
in
homeostasis.
(9)
returned
to
the
blood?
be
prevented each year
if each person
salt intake by ha
is altered as it flows through each. The major homeostatic organs are the
per name,
day.
including
the
renal
tubules
that
bear
his
epithelium,
hair,
and
blood
kidneys, lungs, skin, liver and brain.
The proximal convoluted tubule (PCT) reabsorbs about 70% of the water
How much should you take every day?
vessels.
by osmosis.
PCT reabsorbs
70% of theHe
saltsanticipated
(mostly sodiumPasteur
chloride) in his theory that microorganisms cause
(b) (i) Draw a labelled diagram of a nephron. Include blood vessels
inThe
your
Over 60% of us can’t answer this question. In fact, adults nee
and all the glucose and amino infectious
acids by active
transport.
What diagram.
are the main functions
diseases.
grams and not more than six grams, which is about one teaspo
of the
kidneys?
and teenagers need less.
Half
of
the
remaining
water
is
reabsorbed
by
the
loop
of
Henle
along
with
(ii) Filtration and reabsorption are vital processes that take place in the
about two thirds of the salts.
How much salt do you take every day?
The kidneys
have three
extremely
important
functions,
namely:
Read about other famous
scientists at
nephron.
Describe
how
each of
these processes
occurs.(27)
Most of us don’t know how much salt is in the food we eat. In fact
Further water reabsorption from the distal convoluted tubule (DCT) and
www.sciencetechnologyaction.com
• Excretion: nitrogenous wastes – urea, uric acid, creatinine, salts and
65%
to
70%
of the salt we eat comes from processed food, fast fo
collecting duct depends on the blood concentration. Only if the blood
any excess water.
we buy in restaurants. We usually don’t check the labels* when
needs tocheck
be diluted will these regions reabsorb water. This fine adjustment
For
further examples of past paper exam questions
in
shops
and
have no idea how much a restaurant might add w
• Regulation of blood concentration.
of blood concentration is under the influence of antidiuretic hormone
We also add another 15% ourselves when cooking or eating a
out www.sciencetechnologyaction.com
(ADH). When osmoreceptors in the hypothalamus of the brain detect an
• Maintainance of the blood at pH 7.4.
remaining occurs naturally in the food.
increase in blood concentration above normal, the pituitary gland secretes
Take care
ADH. If a drop in blood pressure is detected ADH will also be secreted
It is too important to ignore the facts about salt. Take the time to
How do the kidneys carry out excretion?
to reabsorb more water, increasing blood volume and raising the blood
brochures How much salt is good for you and What’s a pinch? w
pressure back to normal.
The kidneys first expel lots of materials from the blood by filtration and
get from safefood at 1850 404 567 in the Republic of Ireland or 08
then reabsorb the useful materials back into the blood. This is just like
in Northern Ireland.
The reabsorption of salt by the DCT will depend on how much is needed
clearing out a cluttered wardrobe – empty out all the clothes and only put
to maintain normal blood salt concentration. A different hormone,
*Food labels will tell you how many grams of sodium the food
back what is worth keeping. The materials not selected by the kidneys
aldosterone from the adrenal glands, regulates salt reabsorption.
convert to grams of salt, multiply by 2.5.
Sir William Bowman
2004 Higher Level
Friedrich G. Henle
Did You Know?
•
Marcello Malpighi in 1660 suggested that the kidneys worked like sieves.
•
Jacob Henle discovered the tubules of the kidney, the muscular
coat of arteries, the minute anatomy of the eye and a variety of skin
structures.
•
First surgical removal of a kidney was performed in 1861. The patient
died two weeks later. Kidney transplants began in 1951 but the death
rate of recipients was extremely high. The first successful human
kidney transplant was in 1954 from one identical twin brother to the
other twin. This stimulated the transplanting of other organs.
•
Living donors can be used for kidney transplant because everyone
has two kidneys but only needs one.
•
Executed criminals in China have their organs harvested for transplant
surgery.
•
In some developing countries poor people sell their kidneys.
•
If transplant fails then dialysis is available. Dialysis is the separation
of particles in a liquid according to their capacity to pass through a
membrane into another liquid.
Revise the Terms
Can you recall the meaning of these terms? Reviewing the
terminology is a powerful aid for recall and retention.
Homeostasis; organism; environment; cell; tissue fluid; blood;
nutrient; metabolism; pH; enzyme; tissue cells; excretion;
organ; filtration; nitrogenous waste; reabsorb; urine; nephron;
tubule; selective reabsorption; blood pressure; glomerulus;
capillary; plasma; protein; BOWMAN’S capsule; glomerular
filtration; proximal convoluted tubule; osmosis; active transport,
salt; glucose; amino acids; loop of HENLE; distal convoluted
tubule; collecting duct; antidiuretic hormone; osmoreceptors;
hypothalamus; brain, pituitary gland; hormone; adrenal gland;
sodium; chlorine; milligram; diet; agriculture; plant; PCT; DCT;
CD; ADH.
Check the Glossary of Terms for this lesson at
www.sciencetechnologyaction.com