Excretory System
Osmoregulation & Excretion
 Osmoregulation is important in homeostasis.
 Hyperosmotic
 Hyposmotic
 Isoosmotic
 Excretion helps in maintaining ionic & PH balance.
 The excretory system of all vertebrates have tubules
specialized in excretion called nephrons.
Excretion
 Simple organisms e.g Paramecium  contractile vacuole
 Invertebrate animals e.g earthworm metanephridia
 grasshoper  malphighian tubules
 N.B: Vertebrates have a backbone or a spinal column a.k.a
vertebral column (e.g mammals,reptiles, amphibians,
birds, sharks etc)
Invertebrates do not have a backbone or spine a.k.a vertebral
column (e.g insects, worms,snails, crabs)
The human Excretory System
Kidney & Urinary System
 Functions:
1- Maitain water content
2- Eliminate toxins & unwanted byproducts (ammonia)
3-Maintain proper body PH.
Questions-Activity
 Q1. Describe 2 main functions of the kidney.
 Answer:
-Elimination of wastes, regulation of PH and water
balance
 Q2. what deamination and why is it
important?
 Removal of amino group from an organic compound is
deamination. It is important because many humans
consume high protein diets which means the liver
needs to convert these proteins into carbohydrates
through deamination.
 Q3. How does formation of urea prevent poisoning?
 Answer:
Because deamination creates a byproduct ammonia
which is poisonous. 2 molecules of ammonia combine
with a carbon dioxide to form urea which is 100 000x
less toxic than ammonia. Animals can store urea for
short time in their body, which permits controlled
excretion in their urine.
 Q4. Fish are able to excrete ammonia continuously
from their gills. Explain why birds & mammals cannot
continuously remove toxic waste.
 The waste product is urine in humans and birds
instead of ammonia. Urine would have to be excreted
from body continuously with makes it difficult for land
animals to survive because fluids would have to be
continuously replaced in order to maintain
homeostasis.
Kidney & Urinary System
 When a.a are deaminated in liver it releases ammonia.
 Mammals convert ammonia to urea (2 ammonia+ 1
CO2)
 Goes into blood to kidney to be eliminated as urine.
Kidney ureter urinary bladder urethra
 Nephrons
 Blood is filtered by the kidney at a rate of 1.2 l/min
Urine formation depends on 3 things:
1- Filtration
2- Reabsorption
3- Secretion
Kidney
Urine Formation
 Activity
Pg.450-452
Nephron
Questions- Activity
 1- Why is it beneficial to have two kidneys rather than
one?
 2- Explain the function of a nephron
 3- Athletes undergo random urine testing for drugs.
Describe the pathway of substances such as drugs
through the urinary system from the time they enter
glomerulus to the time they excrete urine.