Chapter 46 Osmoregulation + waste disposal
• Water!!!!!
Is important to all critters!!
• Homeostasis: maintaining a constant
internal environment
- Metabolic wastes also need to be
controlled (excretion)
•CO 2
Nitrogenous wastes:
Proteins
AA
A
A
N (Nitrogen-containing amino group)
•Water
•Nitrogenous wastes
How do critters deal with this problem?
• Fish eliminate Ammonia -
TOXIC
Ammonia
Osmosis: The movement of water across
a semi-permeable membrane
dilution is the solution
• Mammals and Amphibians - Urea in water
Hypertonic:
membrane
High conc. solutes
• Birds - Uric Acid
(Crystalline Paste)
Hypotonic:
Low conc. solutes
- protonephridia w/ flame cells
• Proto - nephridial, flame cells
(closed tubules)
• Metanephridia
• Malpighian tubules
• Green glands
• Kidneys
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Fig. 46.4
- metanephridia (opened tubules)
Fig. 46.5
Solution for fresh H2O fishes :
Vertebrates
• Kidney (osmoregulation and excretion)
- Cleans blood of wastes and maintains
water balance
Fish??? Fresh water and salt water fishes
- Drink no water
- Salts leave by diffusion/Active uptake
of salts by gills
- excrete large quantities of dilute urine
Fresh H2O fish body fluids are Hypertonic
- i.e., Body fluids have high solutes (salt conc.)
- H2O will enter osmotically
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Salt H2O fishes
Osmoregulation in Freshwater Fish
- Body fluids are hypotonic
(body fluids has low solute conc. (salt conc.)
- water tends to leave the fish by osmosis
Solution:
- drink lots of water
- excrete the salt (through gills)
- small volumes of isotonic urine
Fresh H 2O fish body fluids are Hypertonic
Mammalian Kidney
Marine Types
- Body fluids are
hypotonic
• The mammalian kidney helps maintain
homeostasis
– Excretes the majority of the nitrogenous wastes and
helps maintain fluid balance
• Other excretory organs are the lungs, skin, and
digestive system
- Kidney reabsorbs
urea – tissue is
hypertonic
Excretory Functions and Organs
The Urinary System
• The kidneys, urinary bladder, and their
ducts make up the urinary system
• The ureters carry urine to the urinary
bladder, which is a distensible, muscular
sac
• During urination, urine flows through the
urethra
• In males, the urethra also carries semen
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Human Urinary System
Mammalian
Kidney
Human Urinary System
Mammalian kidneys have nephrons
• The outer portion of the
kidney is the cortex; the
inner is the medulla
• The medulla is composed
of 8-10 pyramids, each
with nephrons, the ends
of which are the
collecting ducts
• The urine flows from a
collectting ducts to renal
pelvis
- 4 parts
1) Bowman’s capsule (which houses
the glomerulus)
2) Proximal tube
3) Loop of Henle
4) Distal tube
- Many nephrons empty into a single
Collecting duct then to ureter
Filtration, Secretion,
and Reabsorption
Proximal tubule
Bowman’s capsule
Distal tubule
Glomerulus
Fluid
Solutes:
Glucose
A.A.
Na
K+
Urea
No to:
Blood cells
proteins
H2O
Collecting
duct
H2
O
Na Cl
H2 O
NaCl
NaCl
NaCl
NaCl
U
r
e
a
H2
O
Loop of Henle
Fig. 46.13
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• Water balance controlled by brain and
hormones.
- e.g.
Water stress
Blood pressure decreases
Hormones released by Pituitary
(antidiuretic hormone) (ADH)
Collecting duct becomes
more permeable to H 2O
(i.e., water is reabsorbed)
Additionally when under water stress
• Decrease in BP causes Adrenal Glands to
release Aldosterone
• Aldosterone stimulates sodium
reabsorption across the nephron walls
• This causes increased osmosis out of
nephron into the kidney tissue of water
• Too much water Pituitary and Adrenals
stop release of hormones
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