1. Osmoregulation and Excretion
Chapter 44
Osmoregulation and Excretion

2. Figure 44.1 Salvin’s albatrosses (Diomeda cauta salvini), birds that can drink seawater with no ill effects

3. Figure 44.2 Largemouth tilapia (Tilapia mossambica), an extreme euryhaline osmoregulator

4. Figure 44.3 Osmoregulation in marine and freshwater bony fishes: a comparison
Gain of water and
salt ions from food
and by drinking
seawater
Osmotic water loss
through gills and other parts
of body surface
Excretion of
salt ions
from gills
Excretion of salt ions
and small amounts
of water in scanty
urine from kidneys
Uptake of
water and some
ions in food
Osmotic water gain
by gills
large amounts of
water in dilute
(a) Osmoregulation in a saltwater fish
(b) Osmoregulation in a freshwater fish

5. (a) Hydrated tardigrade
Figure 44.4 Anhydrobiosis
(a) Hydrated tardigrade
(b) Dehydrated tardigrade
100 µm

6. Figure 44.5 Water balance in two terrestrial mammals
a human
(2,500 mL/day
= 100%)
balance in a
kangaroo rat
(2 mL/day
Ingested
in food (0.2)
in food (750)
in liquid
(1,500)
Derived from
metabolism (250)
metabolism (1.8)
gain
Feces (0.9)
Urine
(0.45)
Evaporation (1.46)
Feces (100)
Evaporation (900)
loss

7. Figure 44.6 What role does fur play in water conservation by camels?
The fur of camels plays a critical role in their conserving water in the hot desert environments
where they live.
Knut and Bodil Schmidt-Nielsen and their colleagues from Duke University observed that the
fur of camels exposed to full sun in the Sahara Desert could reach temperatures of over 70°C, while the
animals’ skin remained more than 30°C cooler. The Schmidt-Nielsens reasoned that insulation of the skin
by fur may substantially reduce the need for evaporative cooling by sweating. To test this hypothesis, they
compared the water loss rates of unclipped and clipped camels.
RESULTS
CONCLUSION
Control group
(Unclipped fur)
Experimental group
(Clipped fur) 4 3 2 1
(L/100 kg body mass)
Water lost per day
EXPERIMENT
Removing the fur of a camel increased the rate of water loss through sweating by up to 50%.

8. Figure 44.7 Salt-excreting glands in birds
An albatross’s salt glands empty via a duct into the
nostrils, and the salty solution either drips off the tip of the beak or is exhaled in a fine mist.
(a)
The secretory cells actively transport salt from the blood into the tubules. Blood flows counter to the flow of salt secretion. By maintaining a concentration gradient of salt in the tubule (aqua), this countercurrent system enhances salt transfer from the blood to the lumen of the tubule.
(c)
Nasal salt gland
Nostril
with salt
secretions
Lumen of
secretory tubule
NaCl
Blood
flow
Central
duct
Direction
of salt
movement
Transport
epithelium
Secretory
tubule
Capillary
Vein
Artery
Secretory cell
of transport
One of several thousand secretory tubules in a salt-excreting gland. Each tubule is lined by a transport epithelium surrounded by capillaries, and drains into a central duct.
(b)

9. Figure 44.8 Nitrogenous wastes
Proteins
Nucleic acids
Amino acids
Nitrogenous bases
–NH2
Amino groups
Most aquatic
animals, including
most bony fishes
Mammals, most
amphibians, sharks,
some bony fishes
Many reptiles
(including
birds), insects,
land snails
Ammonia
Urea
Uric acid
NH3
NH2 O C N H HN

10. Figure 44.9 Key functions of excretory systems: an overview
Filtration. The excretory tubule collects a filtrate from the blood.
Water and solutes are forced by blood pressure across the
selectively permeable membranes of a cluster of capillaries and
into the excretory tubule.
Reabsorption. The transport epithelium reclaims valuable substances
from the filtrate and returns them to the body fluids.
Secretion. Other substances, such as toxins and excess ions, are
extracted from body fluids and added to the contents of the excretory
tubule.
Excretion. The filtrate leaves the system and the body.
Capillary
Excretory
tubule
Filtrate
Urine 1 2 3 4

11. Figure 44.10 Protonephridia: the flame-bulb system of a planarian
Nucleus
of cap cell
Cilia
Interstitial fluid
filters through
membrane where
cap cell and tubule
cell interdigitate
(interlock)
Tubule cell
Flame
bulb
Nephridiopore
in body wall
Tubule
Protonephridia
(tubules)

12. Figure 44.11 Metanephridia of an earthworm
Nephrostome
Metanephridia
Nephridio-
pore
Collecting
tubule
Bladder
Capillary
network
Coelom

13. Figure 44.12 Malpighian tubules of insects
Digestive tract
Midgut
(stomach)
Malpighian
tubules
Rectum
Intestine
Hindgut
Salt, water, and
nitrogenous
wastes
Feces and urine
Anus
tubule
Reabsorption of H2O,
ions, and valuable
organic molecules
HEMOLYMPH

14. Figure 44.13 The mammalian excretory system
Posterior vena cava
Renal artery and vein
Aorta
Ureter
Urinary bladder
Urethra
(a) Excretory organs and major
associated blood vessels
Juxta-
medullary
nephron
Cortical
Collecting
duct To
renal
pelvis
Renal
cortex
medulla
20 µm
(b) Kidney structure
Kidney
Section of kidney from a rat
Afferent
arteriole
from renal
artery
Glomerulus
Bowman’s capsule
Proximal tubule
Peritubular capillaries
SEM
Efferent
arteriole from
glomerulus
Branch of
renal vein
Descending
limb
Ascending
Loop of
Henle
Vasa
recta
Distal
tubule
(d) Filtrate and
blood flow
(c) Nephron

15. Figure 44.14 The nephron and collecting duct: regional functions of the transport epithelium
Proximal tubule
Filtrate
H2O
Salts (NaCl and others)
HCO3– H+
Urea
Glucose; amino acids
Some drugs
Key
Active transport
Passive transport
CORTEX
OUTER
MEDULLA
INNER
Descending limb
of loop of
Henle
Thick segment
of ascending
limb
Thin segment
limbs
Collecting
duct
NaCl
Distal tubule
Nutrients
HCO3 K+
NH3 1 4 3 2 5

16. Paired Activity
Explain how nephrons function to filter the blood. Be sure to discuss the structure of nephrons in your explanation.
Generate a standards list if this was an essay on the AP exam
Create multiple sections and list exactly what would be needed to earn each point

17. Osmolarity of interstitial fluid (mosm/L)
Figure 44.15 How the human kidney concentrates urine: the two-solute model (layer 1)
H2O
300
100
400
600
900
1200
700
200
Active transport
Passive transport
OUTER MEDULLA
INNER MEDULLA
CORTEX
Osmolarity of interstitial fluid (mosm/L)

18. Osmolarity of interstitial fluid (mosm/L)
Figure 44.15 How the human kidney concentrates urine: the two-solute model (layer 2)
H2O
Nacl
300
100
400
600
900
1200
700
200
Active transport
Passive transport
OUTER MEDULLA
INNER MEDULLA
CORTEX
Osmolarity of interstitial fluid (mosm/L)

19. Osmolarity of interstitial fluid (mosm/L)
Figure 44.15 How the human kidney concentrates urine: the two-solute model (layer 3)
H2O
Nacl
300
100
400
600
900
1200
700
200
Active transport
Passive transport
OUTER MEDULLA
INNER MEDULLA
CORTEX
Urea
Osmolarity of interstitial fluid (mosm/L)

20. Figure 44.16 Hormonal control of the kidney by negative feedback circuits
Osmoreceptors
in hypothalamus
Drinking reduces
blood osmolarity
to set point
Increased Na+
and H2O reab-
sorption in
distal tubules
Homeostasis:
Blood pressure,
volume
STIMULUS:
The juxtaglomerular
apparatus (JGA) responds
to low blood volume or
blood pressure (such as due
to dehydration or loss of
blood)
H2O reab-
sorption helps
prevent further
osmolarity
increase
The release of ADH is
triggered when osmo-
receptor cells in the
hypothalamus detect an
increase in the osmolarity
of the blood
Blood osmolarity
Hypothalamus
ADH
Pituitary
gland
Increased
permeability
Thirst
Aldosterone
Adrenal gland
Angiotensin II
Angiotensinogen
Renin
production
Collecting duct
Distal
tubule
Arteriole
constriction
JGA
Antidiuretic hormone (ADH) enhances fluid retention by making
the kidneys reclaim more water.
The renin-angiotensin-aldosterone system (RAAS) leads to an increase
in blood volume and pressure.
(a)
(b)

21. Figure 44.17 A vampire bat (Desmodus rotundas), a mammal with a unique excretory situation

22. Figure 44.18 Environmental Adaptations of the Vertebrate Kidney
MAMMALS
Bannertail Kangaroo rat
(Dipodomys spectabilis)
Beaver (Castor canadensis)
FRESHWATER FISHES AND AMPHIBIANS
Rainbow trout
(Oncorrhynchus mykiss)
Frog (Rana temporaria)
BIRDS AND OTHER REPTILES
Roadrunner
(Geococcyx californianus)
Desert iguana
(Dipsosaurus dorsalis)
MARINE BONY FISHES
Northern bluefin tuna (Thunnus thynnus)