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LU 3: EXCRETION by (51494 & 54020) (Objective (A) Maintain…
LU 3
:
EXCRETION
by
(51494 & 54020)
Objective
A) Maintain
Homeostasis
B) Maintain:
i)
concentration of ions
ii)
body volume
iii)
osmotic concentration
C) Remove:
i)
metabolic end products
(urea, uric acids)
ii)
foreign substances
Excretory Organs
Coelenterates & Echinoderm
-
DO NOT have
excretory organ
excretes through
cell membrane
->
body cavity
->
environment
Types
of excretory organs
A)
Epithelial excretory surfaces
i)
Fish
-
Chloride cells
ii)
Brine shrimp
-
salt pumps
B)
Tubular excretory organs
i)
Vetebrates
-
nephrons in kidney
ii)
Insects
-
malpighian tubules
iii)
Flatworms
-
flame cells
iv)
Earthworms
-
nephridia
Excretory Products
Amino groups are excreted from body in three forms:
i)
Ammonia
ii)
Urea
iii)
Uric acid
A)
Ammonotelic
-
excrete Ammonia
i)
most toxic
ii) needs
large amount
of
water
for removal
iii)
highly soluble
in water
iv) released through
body surface
/
gill membranes
e.g.
:
Aquatic invertebrates & bony fishes
B)
Ureotelic
-
excrete Urea
i)
Ammonia is
converted into
urea
ii)
less toxic
iii)
water soluble
iv) excreted in
urine
form
e.g.
:
mammals & amphibians
C)
Uricotelic
-
excrete Uric acid
i) Largely
insoluble
ii) Secreted as a
paste
+
little
water loss
e.g.
:
birds, reptiles, land snails & terrestial insects
Excretory System
Process
i)
Filtration
ii)
Reabsorption
iii)
Secretion
iv)
Excretion
Types of
Animals
A)
Flatworm
i)
Flame-bulb
system
ii)
Protonephridium
Opening
: Nephridio
pore
Dead Ends
:
flame cells
(have
cilia
)
Cilia
allow
* entry of water & solutes from interstitial fluid
Beating of cilia
Filtrate
flows down the
tubule
towards
nephridiopore
Water & solutes
reabsorbed
as filtrate flows
1 more item...
B)
Earthworm
i)
Meta
nephridia
ii)
Pressure
from
closed circulatory system
**
water & solutes are pushed from blood
into
coelomic fluid
excreted as dilute
urine
iii)
NaCl
reabsorbed by
active transport
Urine
-
more dilute
than body fluids
C)
Insects & terrestrial arthropods
i)
Malpighian tubules
Reabsorption of salt, water & nitrogeneous wastes
Diuretic hormones
-
urine production
ii)
Hindgut
Rectum - Presence of papillae
Reabsorption of
ions & water
(
Antidiuretic hormones
)
iii)
Chloride cells
In
gills
(
mayfly
) /
rectum
(
dragonfly
) for
salts retrieval
D)
Fish
i)
Freshwater
fish
Chloride cells -
Absorb Cl
Little fresh water enters
Gills
- Active
NaCl absorption
+ Osmotic water enters
Kidney
- Active
NaCl reabsorption
Diluted urine excretion
Water
gained
via
skin
ii)
Saltwater / marine
fish
Chloride cells -
Extrude Cl
Plenty of sea water
enters
Gills
- Active
NaCl secretion
Kidney
- Active
MgSO4 secretion
Concentrated urine excretion
Kidneys: -
Major role for Excretion of Mg & SO4 of marine fish
Water
loss
via
skin
E)
Amphibians
Frog kidney
- Urea is eliminated by
glomerular filtration & tubular secretion
Mangrove Frog
lives in
salt water
carries
high urea
in blood - achieve osmotic equilibrium -
retain low [salt] in tissues
urea loss is decreased (very low urine flow rate & cessation of urea secretion)
F)
Reptiles
i)
Freshwater
reptiles
Excrete
dilute
urine
ii)
Marine
reptiles
Excess salt is
eliminated by
salt glands, not via kidneys
iii)
Dry land
reptiles
Waste form:
Semisolid uric acid
- requires very little water
Na & K salts of uric acid - eliminated
without
additional expense of water
G)
Mammals
Main excretory organ =
Kidney
(
elimination of metabolic waste products
)
H)
Birds
lack
urinary bladder
Wastes are eliminated as
uric acid
(
allows water retention
)
Marine
birds
Nasal salt glands
-
Excrete excess salt
(
sneeze / shake off salt droplets
)
Kidney
Steps
Step 1
:
Filtration
-
glomerular capsule
Blood flows through
-
glomerular capillaries
-
plasma
(
water, nutrients, waste, salts
)
& enters
Bowman's capsule
via
filtration pressure
Step 2
:
Tubular reabsorption
of filtrate
-
Proximal tubule
-
Loop of Henle
-
Distal tubule
Na, glucose & amino acids
are
reabsorbed
Na-K ATPase pump
supplies energy
Step 3
:
Tubular secretion
-
Distal tubule
K+ & NaC
l concentrations of body fluids are
regulated
Collecting duct
-
Urea & water
are
reabsorbed
Principal site of:
water balance & salt regulation
(
osmoregulation
)
Functional Unit:
-
Nephron
Process of
removing metabolic waste products
from the body
