Biology M3 Excretion & Osmoregulation

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Excretion in Animals
M3 U8 Lesson 4
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Objectives
You should be able to:
1. give examples of excretory substances in animals and
state how they are excreted.
2. describe the structure of the human kidneys.
3. relate the structure of nephrons to their
osmoregulatory and excretory functions.
4. discuss briefly the effect of alcohol on the excretory
processes.
5. define osmoregulation.
6. describe, with the aid of a diagram, the role of the
hormone ADH in osmoregulation.
7. state the importance of osmoregulation to humans.
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What is Excretion?
• Excretion is the removal from the
organism’s body of toxic waste
substances produced during cellular
metabolism (e.g. respiration).
• Excretion helps to maintain homeostasis
in the organism’s internal environment.
• Excretion is a life process carried on by
ALL living organisms - large and small;
simple unicellular and complex multi-
cellular; plants and animals.
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EXCRETION
EXPLAINED

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Defaecation is not Excretion!
Horse’s Faeces
Earthworm’s Faeces
Dog’s Faeces
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EXCRETION
EXPLAINED

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Did You Know?
Excretion in some invertebrate animals
is done as follows:
(Click on underlined names to see a photo!)
• Amoeba → CO2 →diffusion/cell
membrane → Ammonia and Water
through the contractile vacuole
• Hydra → through oral opening
• Flatworms → through flame cells
• Earthworm → through nephridia and
diffusion across moist skin
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EXCRETION
EXPLAINED

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What Waste do Animals Excrete?
The metabolic wastes which are excreted
by animals may be grouped as shown
below:
image.tutorvista.com/content/excretion/classi...
Excretory WastesExcretory Wastes
Respiratory Waste ProductsRespiratory Waste Products
Nitrogenous Waste ProductsNitrogenous Waste Products
Bile PigmentsBile Pigments
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EXCRETORY
SUBSTANCES

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What happens in Respiration?
All animals (and plants) carry on respiration
within their body cell/s. In respiration, oxygen
combines with sugars present in cells to break
molecular bonds, thus releasing the energy
contained in those bonds. How would you
represent respiration? Click the button below to
check your answer.
RESPIRATIONRESPIRATION
GlucoseGlucose OxygenOxygen Carbon
Dioxide
Carbon
Dioxide+ WaterWater
Energy
released
& made
available
Energy
released
& made
available++
C6H12O6
C6H12O6 6O2
6O2 6CO2
6CO2+ 6H2O6H2O
Energy
released
& made
available
Energy
released
& made
available
++
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EXCRETORY
SUBSTANCES

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Respiratory Waste Products
• Carbon dioxide and water are the waste
products of catabolism (breakdown) of all
kinds of complex food molecules. These waste
products are excreted by animals in many
ways.
• In many lower animals, Carbon dioxide is
eliminated by diffusion through the body
surface directly into the environment.
• In humans, CO2 is excreted, along with water
vapour, from the lungs when they exhale.
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EXCRETORY
SUBSTANCES

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Bile Pigments
The liver changes the decomposed
haemoglobin of worn out red blood cells
into bile pigments called bilirubin and
biliverdin.
These pigments are passed into the
alimentary canal with the bile for
elimination.
The liver also excretes cholesterol, steroid
hormones, certain vitamins and drugs
through the bile.
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Bile PigmentsBile Pigments
EXCRETORY
SUBSTANCES

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Nitrogenous Waste Products
Nitrogen-containing waste products are
derived from the deamination of the
excess amino-acids consumed in food and
also from the breakdown of proteins and
nucleic acids.
Read through the next slide to recall the process
of deamination!
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EXCRETORY
SUBSTANCES

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Nitrogenous wastes
The following are the nitrogenous waste
products produced by animals:
•Ammonia
•Urea
•Uric acid
•Amino acids.
On the next slide, look at the various
animal groups that excrete each type of
nitrogenous waste.
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EXCRETORY
SUBSTANCES

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Animals that excrete each kind of
nitrogenous waste
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EXCRETORY
SUBSTANCES

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Excretion of Ammonia
Aquatic animals e.g. fish, usually excrete
ammonia directly into the external environment,
because this compound is highly soluble and
there is ample water available in an aquatic
environment for its dilution.
In lower animals like molluscs (e.g. snails, slugs)
and echinoderms (e.g. starfish, sea eggs) the
excess amino acid gets removed without
undergoing any change.
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EXCRETORY
SUBSTANCES

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Excretion of Uric acid
In birds and reptiles, uric
acid is excreted as a thick
white paste or in the form
of pellets.
This enables these animals
to conserve water. Look
out for wastes passed out
by lizards, e.g. croaking
lizard wastes can often be
seen high up on walls
inside/outside houses.
White Uric acid and dark
faeces of a lizard
http://en.wikipedia.org/wiki/Excretion
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EXCRETORY
SUBSTANCES

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What is Deamination?
• Deamination is the process by which amino
acids are broken down when too much protein
has been taken in.
• It Involves the removal of an amino group (NH2)
from the amino acid and it is then converted to
ammonia (NH3) .
• Ammonia is toxic to the human system, and
enzymes convert it to urea or to uric acid.
• Deamination takes place primarily in the liver
and also in the kidneys.
http://www.ask.com/wiki/Deamination
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EXCRETORY
SUBSTANCES

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Excretion of urea/uric acid via the Skin
Skin plays an important
role in excretion in
humans. It has two types
of glands:
•sebaceous glands that
excrete lipids;
•sweat glands that
excrete cellular
metabolic wastes such as
water containing salts,
urea and lactic acid. This
aids in osmoregulation.
http://www.tutorvista.com/content/biology/biology-iv/excretion/excretionindex.php
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EXCRETORY
SUBSTANCES

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Excretion of Urea
• In higher animals, ammonia undergoes
deamination mainly in the liver and
forms a less toxic substance called urea
which is periodically flushed out of the
system of the animal.
• Humans eliminate nitrogenous waste as
urea formed during deamination in the
liver mainly, but it can also occur in the
kidneys.
http://www.tutorvista.com/content/science/science-ii/excretion/substances-excreted-animals.php
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EXCRETORY
SUBSTANCES

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Excretion in Humans via the Kidneys
ALL mammals have paired kidneys
which, together with the ureters,
bladder and urethra, form the
excretory system proper.
In humans, two kidneys in the lower
back are supplied by the Renal arteries
which bring blood to the kidneys, whose
special structure equip them to remove
harmful wastes from the blood, thus
forming urine.
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EXCRETORY ORGAN
Human Kidney

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Location of the Kidneys in the Body
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Right kidney, seen from in front
http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookexcret.html
EXCRETORY ORGAN
Human Kidney

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External view of a mammalian kidney
Note the colour, size
and shape of this
kidney.
Internally, a kidney
has the: Renal Cortex,
Renal Medulla and
the Renal Pelvis.
Look for those parts on
the next slide.
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http://www.worldofteaching.com/powerpoints/biology
256,1,The kidney
EXCRETORY ORGAN
Human Kidney

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Kidney cut open
24http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookexcret.html
http://www.emc.maricopa.edu/faculty/farabee/biobk/biobookexcret.html
Renal
Pyramid
Renal
Pelvis
EXCRETORY ORGAN
Human Kidney

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Inside the Kidney
Identify the following:
• Renal Cortex
• Renal Pelvis
• Renal Medulla
• Pyramids
• Ureter
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http://www.worldofteaching.com/powerpoints/biology/TheKidney.ppt#
257,4,Cross section
Photo of the inside of
one half of the Kidney,
cut lengthwise.
EXCRETORY ORGAN
Human Kidney

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Nephrons in the Kidneys
• Nephrons are the functional units of the
kidneys.
• There are typically over 1,000 nephrons
in each of the two kidneys in the body.
• Each nephron has a part in the Renal
cortex and a part in the Renal medulla.
• All nephrons empty into the Renal
pelvis.
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EXCRETORY ORGAN
Human Kidney

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The parts of the Nephron
Each nephron has a Bowman’s
capsule, convoluted or coiled
tubules, a Loop of Henle, the
collecting duct and a capillary
network. The Bowman’s capsule (or
Glomerular capsule) surrounds the
glomerulus (ball of capillaries) and is
located in the Renal cortex.
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EXCRETORY ORGAN
Human Kidney

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The parts of a Nephron
• The glomerulus, has blood coming to it
by an afferent arteriole (from the Renal
artery); an efferent arteriole leads blood
away from the glomerulus into the
tubules.
• Bowman’s capsule leads into a Proximal
(near) Convoluted (= coiled) Tubule
(PCT), a Descending limb, Loop of
Henle, an Ascending limb, a Distal (= far)
Convoluted Tubule (DCT) and finally a
Collecting duct/tubule. The walls are
very thin, allowing diffusion to occur.
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EXCRETORY ORGAN
Human Kidney

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The parts of a Nephron
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EXCRETORY ORGAN
Human Kidney

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Parts of a Nephron
In the previous slide, did you notice how
the Descending and Ascending tubules
and the U-shaped Loop of Henle are
surrounded by the blood vessels?
This arrangement of blood vessels
around various parts of the nephron
enables materials inside the tubules to
be removed from these tubules and
diffuse into the blood vessels,
facilitating osmoregulation.
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EXCRETORY ORGAN
Human Kidney

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Osmoregulation in the Nephron
The process has four distinct steps:
1. Ultrafiltration- blood filtered under high
pressure (because of the narrow arterioles of
the glomerulus) to form a glomerular filtrate.
2. Reabsorption- valuable solutes are
reabsorbed in the PCT from the filtrate.
3. Secretion- various solutes, toxins etc. are
added to the filtrate from body fluids.
4. Excretion- the filtrate is passed out as urine.
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EXCRETORY ORGAN
Human Kidney

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Functions of various sections of a
nephron
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1. Filtration: As blood flows into Bowman’s capsule, water
and solutes are forced by blood pressure out through the
selectively permeable membranes of the glomerulus (coiled
capillaries) forming a filtrate in the (PCT) tubule. This is
ultrafiltration.
1. Filtration: As blood flows into Bowman’s capsule, water
and solutes are forced by blood pressure out through the
selectively permeable membranes of the glomerulus (coiled
capillaries) forming a filtrate in the (PCT) tubule. This is
ultrafiltration.
2. Reabsorption: In the Proximal Convoluted Tubule water,
salts, glucose, amino acids are reclaimed from the filtrate and
returned to the body fluids.
2. Reabsorption: In the Proximal Convoluted Tubule water,
salts, glucose, amino acids are reclaimed from the filtrate and
returned to the body fluids.
3. Secretion: Excess H+ ions, Potassium, drugs, toxins are
extracted from body fluids and secreted back into the contents
(filtrate) of the Distal Convoluted Tubule.
3. Secretion: Excess H+ ions, Potassium, drugs, toxins are
extracted from body fluids and secreted back into the contents
(filtrate) of the Distal Convoluted Tubule.
4. Excretion: The filtrate – now urine - leaves the nephron,
passes via the ureter into the bladder, then leaves the
system and the body.
4. Excretion: The filtrate – now urine - leaves the nephron,
passes via the ureter into the bladder, then leaves the
system and the body.
Diagram: http://www.scribd.com/doc/7400291/Osmoregulation-and-Excretion
EXCRETORY ORGAN
Human Kidney

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The Kidneys and Drugs
• A drug is a substance that alters the way the
human body works. Alcohol ( e.g. rum, beer,
stout, wine, vodka) is one of the most
commonly used drugs.
• Once consumed, alcohol is
absorbed from the stomach
and other parts of the gut.
It is carried around the body
in the bloodstream and
eventually reaches the
kidneys.
Photo: http://www.worldofteaching.com/powerpoints/biology/ALCOHOL.ppt
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EFFECT OF DRUGS
ON KIDNEY

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The Kidneys and Drugs
• Alcohol is a diuretic, which makes you urinate
more. (Check the meaning of ‘diuretic’.)
• This means that the nephrons in the kidneys
are working much harder than normal to try to
maintain homeostasis. In fact, a person loses
far more water in his/her urine than is being
taken in the drink itself. This leads to
dehydration!
• Dehydration causes the brain to shrink away
from the skull slightly. This triggers pain
sensors on the outside surface of your brain.
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EFFECT OF DRUGS
ON KIDNEY

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Electrolyte Imbalance and Tiredness
• Vital electrolytes such as magnesium and
potassium are excreted from the body with the
urine, so excessive and prolonged drinking of
alcohol can cause an electrolyte imbalance.
• These electrolytes help keep the heart beating and
dangerous cardiac arrhythmias can occur after
heavy drinking and the resultant increased
urination, with loss of valuable electrolytes.
• As the heart no longer works efficiently, there is a
feeling of tiredness as cells are deprived of O2 and
CO2 poisons the body.
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EFFECT OF DRUGS
ON KIDNEY

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Long Term Effects on the Liver
• One of the most serious consequences of
alcohol abuse is for the liver. In response to
long-term alcohol exposure, it starts producing
more alcohol dehydrogenase, the enzyme
which it uses to break ethanol down.
• Long term drinking of alcohol causes the liver
to become over-active, cells die and the tissue
hardens. The result is cirrhosis of the liver. This
incurable condition can impede the liver’s
ability to carry out deamination.
Without regular deamination, what happens?
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EFFECT OF DRUGS
ON KIDNEY

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Summary
The nephron has the functions of:
• Ultrafiltration of water and solutes from the
blood occurring in the glomerulus.
• Tubular reabsorption and conservation of
water/needed substances back into the blood.
• Tubular secretion of ions and other waste
products from surrounding capillaries into the
distal tubule, thus forming urine.
• Excretion of urine into the ureters.
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Summary
• The work of the nephrons results in the
homeostatic regulation and
maintainance of the salts and water
balance of the body that accompanies
the process of urine formation.
• Without the work of the nephron, the
pH and osmotic balance of body fluids
would be upset beyond their ‘set point’
and toxic substances would accumulate,
poisoning body cells.
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Osmoregulation anyone?
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OSMOREGULATION
ext.sac.edu/.../mansfield_patricia/10intro.html
Module 3 Unit 8 Lesson 5

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Do Humans carry out Osmoregulation?
What do you think about that
comment in the previous cartoon?
Do humans ever practice
“osmoregulation channeling”?
If so… HOW?
Is it done by squirting out water to
prevent that feeling of being bloated
or water-logged?
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OSMOREGULATION

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Introduction
By the functions of nephrons in conserving
or excreting water, salts, glucose etc., the
kidneys regulate body fluid concentration
levels (osmoregulation) as a primary duty,
and remove harmful wastes as a
secondary one.
Osmoregulation is an example of a
negative feedback mechanism that causes
homeostasis.
What is a negative feedback mechanism?
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OSMOREGULATION

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What is a Hormone?
• A hormone is a chemical substance
produced in humans by endocrine or
ductless glands.
• Each hormone targets specific
cells/organs to influence growth,
development and various physiological
processes in the body and, in so doing,
maintain homeostasis.
• The Pituitary is the ‘master control
endocrine gland’; it secretes a wide
range of hormones, including ADH.
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OSMOREGULATION

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What is Osmoregulation?
• It is the homeostatic regulation and
maintainance of the salts and water
balance of an organism’s body.
• In humans, osmoregulation takes place
in the kidney units, and is under the
direct control of a hormone called Anti
Diuretic Hormone (or ADH).
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OSMOREGULATION

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Osmoregulation Control Centre
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Photo: www.umm.edu/.../articles/hypothalamus_000337.htm
OSMOREGULATION

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Osmoregulation
• If the blood gets too dilute, e.g. when
one drinks a lot of water,
osmoreceptors in the Hypothalamus of
the brain detect this.
• They send ‘messages’ to the Pituitary
gland causing it not to secrete any ADH.
• Because no ADH is secreted, Distal
tubules and Collecting ducts remain
impermeable to water, so much less or
no water at all is reabsorbed from the
filtrate resulting in a large amount of
dilute urine being produced.
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OSMOREGULATION

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Water content
of the blood normal
Water content
of the blood normal
Water content of
the blood HIGH
Water content of
the blood LOW
Too much
water drunk
Too much salt
or sweating
Brain produces
More ADH
Urine output
LOW
Brain produces
Less ADH
Urine output
HIGH
High volume of water
reabsorbed by kidney
Low volume of water
reabsorbed by kidney
(small volume of
Concentrated urine)
(large volume of
dilute urine)
Source: http://www.worldofteaching.com/powerpoints/biology/Intro%20to%20water%20and
%20ADH.ppt#264,9,Slide 9
Osmoregulation Explained
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OSMOREGULATION

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Osmoregulation
• If the blood is concentrated, the osmo-
receptors in the Hypothalamus detect
this.
• Hypothalamus sends a message to the
Pituitary gland to secrete more ADH.
• ADH gets to the kidneys via the blood.
The Distal Convoluted Tubule and
Collecting Duct become more
permeable to water, so the capillaries
reabsorb much water from the filtrate.
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OSMOREGULATION

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Osmoregulation
• Consequently, a small amount of
concentrated urine is produced.
• Anti Diuretic Hormone controls water
absorption in the Proximal Convoluted
Tubule and Collecting Duct of the
nephron in the kidneys.
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OSMOREGULATION

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Osmoregulatory Functions of the
Kidneys
• Maintain the volume of extracellular
fluid.
• Maintain ionic balance in extracellular
fluid.
• Maintain pH and osmotic concentration
of the extracellular fluid.
• Excrete toxic metabolic by-products
such as urea, ammonia, and uric acid.
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OSMOREGULATION

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Summary
Homeostasis is maintaining a stable internal
environment. Some examples in humans are:
• During the regulation of body temperature,
when sweating occurs, wastes are lost by the
skin.
• The control of blood glucose level is mainly
done by insulin secreted by the pancreas but
is also done when the neprons are functioning
to form urine.
• The major regulation of the amounts of water
and mineral salts, drugs and other wastes in
the body i.e. osmoregulation, happens in the
kidneys.
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OSMOREGULATION

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Credits
Dog urinating:
http://cdn2-
b.examiner.com/sites/default/files/styles/medium/hash/8e/5a/8e5a1
8943c7679e56c74f45064c76a2a.jpg
Earthworm feaces :
http://commons.wikimedia.org/wiki/File:Earthworm_faeces.jpg
Horse faeces, Dog feces:
http://photo.net/street-documentary-photography-forum/00EyEn
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