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EXCRETION
The removal of cellular
wastes (Metabolic Waste)
from the body.
Major Metabolic Wastes
 Carbon Dioxide (CO2)
 Produced as a result of cellular respiration.
 Water (H2O)
 An end product of many chemical reactions
including cell respiration and dehydration
synthesis.
 Nitrogen Wastes
 An end product of the breakdown of protein.
 Ammonia – most toxic
 Urea – mildly toxic
 Salts
 Produced as a result of chemical reaction
Organs of Excretion:
 Lungs  Removes carbon dioxide and
water
 Liver  Urea is formed which resulted
from break down of amino acids and
breakdown of RBCs
 Skin  Sweat Glands -Removes excess
water and salts, urea and heat.
 Kidneys  Remove water, salts and
urea
Liver
Removal and detoxification of
harmful substances from the
blood (bacteria, drugs,
hormones, alcohol)
Liver
Removal of broken down RBC’s
Liver
Deamination
Ammonia (NH3) is
formed by the
breakdown of amino
acids
Liver
 ammonia is converted
into a less toxic
substance, urea,
which enters the
bloodstream to the
kidneys for excretion
The Skin
The Skin
 Sweat comes out of pores in your skin.
 Mixture of three metabolic wastes:
 Water
 Salts
 Urea
The Skin
 As you sweat, your body
accomplishes two things:
 1) It has a cooling effect on the body.
 2) metabolic wastes are excreted
The Lungs
The Lungs
 Cellular respiration produces carbon dioxide as a
waste product.
The Kidneys
 The major excretory organ in the human body
 Filtering of the blood helps regulate its chemical
composition.
 Water soluble materials are absorbed from blood by
diffusion into the kidney.
 Needed materials are reabsorbed
 Wastes: Urea, salts and excess water are excreted
Organs of the Urinary System
Organs of the Urinary System
 Kidneys
 Two kidneys are located on either side of the spinal
column near lower back.
 Ureter
 Two tubes that leaves each kidney carrying urine
to the urinary bladder.
 Urinary Bladder
 Muscular sac that stores liquid wastes before
excretion.
 Urethra
 Carries the urine from the bladder to the outside of
the body – controlled by a sphincter muscle.
The Functions of the Kidney
1. Filtration of blood:
 water, urea, amino acids, salts,
glucose pass out of the blood into
the Kidneys by diffusion
 Proteins (enzymes, hormones,
antibodies) and blood cells remain
behind in the blood
The Functions of the Kidney
2. Reabsorption:
Important substances are returned to
the blood (water, glucose, amino acids,
salts) by active transport and diffusion
The Functions of the Kidney
3. Formation of urine: (urea, excess
water, salts)
The Kidneys
 There are three major
areas in the kidney
 Outer portion is the
cortex
 Middle portion is the
medulla
 Inner portion is the
renal pelvis
The Kidneys
 Bean-shaped about
10 cm long each.
 Nephron:
The functional unit of
the kidney
 Renal artery and
Renal vein leading to
and from the kidneys
Parts of the Nephron
 Glomerulus
 Ball of capillaries
surrounded by
the Bowman’s Capsule.
 Bowman’s Capsule
 Cup-shaped structure
that filters the materials out
of the blood.
Parts of the Nephron
Filtration of the Blood
 Filtration occurs as blood pressure forces fluid
from the blood in the glomerulus into the
lumen of Bowman’s capsule
 Filtration of small molecules is nonselective
 RBC’s and Protein don’t get filtered
 The filtrate contains salts, glucose, and
nitrogen wastes
Pathway of the Filtrate
 From Bowman’s capsule, the filtrate passes
through three regions of the nephron: the
proximal tubule, the loop of Henle, and the
distal tubule
 Fluid from several nephrons flows into a
collecting duct, all of which lead to the
renal pelvis, which is drained by the ureter
From Blood Filtrate to Urine: A
Closer Look
Proximal Tubule
 Reabsorption of Salts , Glucose . Nutrients
 Takes place by Active and Passive Trasport
Distal Tubule
 Regulates the K+ and NaCl concentrations
of body fluids
 Helps in pH regulation
Collecting Duct
 The collecting duct carries filtrate through
the medulla to the renal pelvis
 This is where the filtrate becomes more
concentrated.
Flow through Kidney:
Renal Artery
Glomerulus
Bowman’s Capsule
Loop of Henle
Collecting Tubule( Duct )
Ureter
Bladder
Urethra
Malfunctions of the Excretory
System
 Urinary Tract Infection
(UTI)-
 Bacterial infection that
can affect any part of
the urinary system.
Nephritis:
Bacterial infection of the
kidney.
Malfunctions of the Excretory
System
 Kidney Stones –
 Caused by
accumulation of a
crystallized solid
such as calcium
Treatment:
 Sound waves
 Surgery
Gout:
Disease associated with abnormal uric acid
production and excretion - causing
deposits in the joints (toes) resulting in
severe pain.
Gout:
Kidney (Renal) Failure
•Prolonged Blockage
•Prolonged infection- Untreated
•Polycystic Kidney Disease
•Diabetes
•High Blood Pressure
•Illegal Drug Use
•Prescription Drugs
Treatment:
Dialysis
Kidney Transplant
Review Questions…
1. Which is the correct pathway for the elimination
of urine?
a) urethra, ureter, bladder, kidney
b) kidneys, urethra, bladder, ureter
c) bladder, ureters, kidney, urethra
d) kidneys, ureters, bladder, urethra
Review Questions…
2. In humans, for carbon dioxide to be excreted, it
must pass from the blood into:
a) nephrons
b) alveoli
c) sweat glands
d) the liver
Review Questions…
3. A blockage in a ureter would interfere with:
a) urine entering the kidney
b) urine entering the bladder
c) urine leaving the body
d) urea entering the kidney
Review Questions…
4. Which is NOT a metabolic waste in humans?
a) carbon dioxide
b) oxygen
c) salt
d) urea
e) water
Review Questions…
5. In which form are nitrogenous wastes excreted in
humans?
a) ammonia
b) uric acid
c) urea
d) amino acids
Review Questions…
6. Nitrogenous wastes are the result of metabolism
involving:
a) lipids
b) carboohydrates
c) inorganic compounds
d) proteins
Review Questions…
7. In addition to water, the principal components of
urine are:
a) amino acids & fatty acids
b) urea & salts
c) ammonia & bile
d) hydrochloric acid & urea
Review Questions…
8. Name a malfunction of the excretory system
and explain how it can upset the homeostasis of
an organism.