4. Osmoregulation and Excretion
Chapter 44
Osmoregulation and Excretion

5. How does an albatross drink salt water without ill effect?
Figure 44.1 How does an albatross drink salt water without ill effect?

6. Osmoconformers vs. Osmoregulators What is the difference?

7. Osmotic Challenges
Osmoconformers, consisting only of some marine animals, are isoosmotic with their surroundings and do not regulate their osmolarity
Osmoregulators expend energy to control water uptake and loss in a hyperosmotic or hypoosmotic environment (stenohaline and euryhaline)
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8. Do I drink water?
Describe my pee.
Do I drink water?
Describe my pee.

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

11. Figure 44.4 Sockeye salmon (Oncorhynchus nerka), euryhaline osmoregulators

12. Water balance in a kangaroo rat (2 mL/day)
Figure 44.6
Water balance in a kangaroo rat (2 mL/day)
Water balance in a human (2,500 mL/day)
Ingested in food (0.2)
Ingested in food (750)
Ingested in liquid (1,500)
Water gain (mL)
Derived from metabolism (1.8)
Derived from metabolism (250)
Figure 44.6 Water balance in two terrestrial mammals.
Feces (0.09)
Feces (100)
Water loss (mL)
Urine (0.45)
Urine (1,500)
Evaporation (1.46)
Evaporation (900)

13. Figure 44.UN01
Animal
Inflow/Outflow
Urine
Freshwater fish. Lives in water less concentrated than body fluids; fish tends to gain water, lose salt
Does not drink water
Large volume of urine
Salt in (active trans- port by gills)
H2O in
Urine is less concentrated than body fluids
Salt out
Marine bony fish. Lives in water more concentrated than body fluids; fish tends to lose water, gain salt
Drinks water
Small volume of urine
Salt in
H2O out
Urine is slightly less concentrated than body fluids
Salt out (active transport by gills)
Figure 44.UN01 Summary figure, Concept 44.1
Terrestrial vertebrate. Terrestrial environment; tends to lose body water to air
Drinks water
Moderate volume of urine
Salt in (by mouth)
Urine is more concentrated than body fluids
H2O and salt out 13

14. Counter-current exchange in salt-excreting nasal glands
Counter-current exchange in salt-excreting nasal glands What else exhibits c-c e?
Secretory cell of transport epithelium
Lumen of secretory tubule
Vein
Artery
Nasal salt gland
Ducts
Nasal gland
Salt ions
Capillary
Secretory tubule
Transport epithelium
Nostril with salt secretions
(a)
Location of nasal glands in a marine bird
(b)
Secretory tubules
Blood flow
Salt secretion
Figure 44.7 Countercurrent exchange in salt-excreting nasal glands.
Key
(c)
Countercurrent exchange
Salt movement
Blood flow
Central duct

15. Most aquatic animals, including most bony fishes
Figure 44.8
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
Figure 44.8 Forms of nitrogenous waste.
Ammonia
Urea
Uric acid

16. Figure 44.9
Figure 44.9 Recycling nitrogenous waste.

17. Key steps of excretory system function: an overview.1
Filtration
Capillary
Filtrate
Excretory tubule 2
Reabsorption
Figure Key steps of excretory system function: an overview. 3
Secretion
Urine 4
Excretion

18. Components of a metanephridium:
Figure 44.12
Coelom
Capillary network
Components of a metanephridium:
Collecting tubule
Figure Metanephridia of an earthworm.
Internal opening
Bladder
External opening

19. Salt, water, and nitrogenous wastes
Figure 44.13
Digestive tract
Rectum
Hindgut
Intestine
Midgut (stomach)
Malpighian tubules
Salt, water, and nitrogenous wastes
Feces and urine
To anus
Malpighian tubule
Figure Malpighian tubules of insects.
Rectum
Reabsorption
HEMOLYMPH

20. Excretory Organs Kidney Structure Nephron Types Cortical nephron
Figure a
Excretory Organs
Kidney Structure
Nephron Types
Cortical nephron
Juxtamedullary
nephron
Renal cortex
Posterior vena cava
Renal medulla
Renal artery
Renal artery and vein
Kidney
Renal vein
Renal cortex
Aorta
Ureter
Figure Exploring: the Mammalian Excretory System
Ureter
Renal medulla
Urinary bladder
Urethra
Renal pelvis

21. Nephron Organization Afferent arteriole from renal artery Glomerulus
Figure b
Nephron Organization
Afferent arteriole from renal artery
Glomerulus
Bowman’s capsule
Proximal tubule
Peritubular capillaries
Distal tubule
Efferent arteriole from glomerulus
Branch of renal vein
Figure Exploring: the Mammalian Excretory System
Descending limb
Loop of Henle
Vasa recta
Collecting duct
200 m
Ascending limb
Blood vessels from a human kidney. Arterioles and peritubular capillaries appear pink; glomeruli appear yellow.

22. Animation: Bowman’s Capsule and Proximal Tubule
Right-click slide / select “Play”
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23. Proximal tubule Distal tubule Filtrate CORTEX Loop of Henle
Figure 44.15
Proximal tubule
Distal tubule
NaCl
Nutrients
H2O
HCO3
H2O K
NaCl
HCO3 H
NH3 K H
Filtrate
CORTEX
Loop of Henle
NaCl
H2O
OUTER MEDULLA
NaCl
Collecting duct
Figure The nephron and collecting duct: regional functions of the transport epithelium.
Key
Urea
Active transport
NaCl
H2O
Passive transport
INNER MEDULLA

24. Animation: Loop of Henle and Distal Tubule
Right-click slide / select “Play”
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25. Animation: Collecting Duct
Right-click slide / select “Play”
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26. Osmolarity of interstitial fluid (mOsm/L)
Figure
Osmolarity of interstitial fluid (mOsm/L)
300
300
300
300
H2O
CORTEX
400
400
H2O
H2O
OUTER MEDULLA
H2O
600
600
Figure How the human kidney concentrates urine: the two-solute model.
H2O
H2O
900
900
Key
H2O
INNER MEDULLA
Active transport
1,200
1,200
Passive transport

27. Osmolarity of interstitial fluid (mOsm/L)
Figure
Osmolarity of interstitial fluid (mOsm/L)
300
300
300
100
100
300
H2O
NaCl
CORTEX
400
200
400
H2O
NaCl
H2O
NaCl
OUTER MEDULLA
H2O
NaCl
600
400
600
Figure How the human kidney concentrates urine: the two-solute model.
H2O
NaCl
H2O
NaCl
900
700
900
Key
H2O
NaCl
INNER MEDULLA
Active transport
1,200
1,200
Passive transport

28. Osmolarity of interstitial fluid (mOsm/L)
Figure
Osmolarity of interstitial fluid (mOsm/L)
300
300
300
100
100
300
300
H2O
NaCl
H2O
CORTEX
400
200
400
400
H2O
NaCl
H2O
NaCl
H2O
NaCl
H2O
NaCl
OUTER MEDULLA
H2O
NaCl
H2O
600
400
600
600
Figure How the human kidney concentrates urine: the two-solute model.
H2O
NaCl
H2O
Urea
H2O
NaCl
H2O
900
700
900
Urea
Key
H2O
NaCl
H2O
INNER MEDULLA
Urea
Active transport
1,200
1,200
1,200
Passive transport

29. Loops of Henle quiz…
Who would have longer loops of Henle, a beaver or a desert hare?

30. Loops of Henle quiz…
Who would have longer loops of Henle, a beaver or a desert hare?
WHY?

31. Figure 44.18 A vampire bat (Desmodus rotundas), a mammal with a unique excretory situation.

32. How do we hold our pee (Micturition reflex video)

33. Antidiuretic Hormone
The osmolarity of the urine is regulated by nervous and hormonal control
Antidiuretic hormone (ADH) makes the collecting duct epithelium more permeable to water
An increase in osmolarity triggers the release of ADH, which helps to conserve water
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34. Animation: Effect of ADH
Right-click slide / select “Play”
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35. Osmoreceptors in hypothalamus trigger release of ADH.
Figure
Osmoreceptors in hypothalamus trigger release of ADH.
Thirst
Hypothalamus
ADH
Pituitary gland
STIMULUS: Increase in blood osmolarity (for instance, after sweating profusely)
Figure Regulation of fluid retention in the kidney by antidiuretic hormone (ADH).
Homeostasis: Blood osmolarity (300 mOsm/L)

36. Osmoreceptors in hypothalamus trigger release of ADH.
Figure
Osmoreceptors in hypothalamus trigger release of ADH.
Thirst
Hypothalamus
Drinking reduces blood osmolarity to set point.
ADH
Increased permeability
Pituitary gland
Distal tubule
STIMULUS: Increase in blood osmolarity (for instance, after sweating profusely)
Figure Regulation of fluid retention in the kidney by antidiuretic hormone (ADH).
H2O reab- sorption helps prevent further osmolarity increase.
Collecting duct
Homeostasis: Blood osmolarity (300 mOsm/L)

37. Second-messenger signaling molecule
Figure 44.20
ADH receptor
LUMEN
Collecting duct
COLLECTING DUCT CELL
ADH
cAMP
Second-messenger signaling molecule
Storage vesicle
Exocytosis
Figure ADH response pathway in the collecting duct.
Aquaporin water channel
H2O
H2O

38. How might alcohol affect your water balance?
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39. The Renin-Angiotensin-Aldosterone System
The renin-angiotensin-aldosterone system (RAAS) is part of a complex feedback circuit that functions in homeostasis
A drop in blood pressure near the glomerulus causes the juxtaglomerular apparatus (JGA) to release the enzyme renin
Renin triggers the formation of the peptide angiotensin II
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40. Angiotensin II
Raises blood pressure and decreases blood flow to the kidneys
Stimulates the release of the hormone aldosterone, which increases blood volume and pressure
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41. Homeostasis: Blood pressure, volume
Figure
JGA releases renin.
Distal tubule
Renin
Juxtaglomerular apparatus (JGA)
STIMULUS: Low blood volume or blood pressure (for example, due to dehydration or blood loss)
Figure Regulation of blood volume and blood pressure by the renin-angiotensin-aldosterone system (RAAS).
Homeostasis: Blood pressure, volume

42. Homeostasis: Blood pressure, volume
Figure
Liver
Angiotensinogen
JGA releases renin.
Distal tubule
Renin
Angiotensin I
ACE
Angiotensin II
Juxtaglomerular apparatus (JGA)
STIMULUS: Low blood volume or blood pressure (for example, due to dehydration or blood loss)
Figure Regulation of blood volume and blood pressure by the renin-angiotensin-aldosterone system (RAAS).
Homeostasis: Blood pressure, volume

43. Juxtaglomerular apparatus (JGA)
Figure
Liver
Angiotensinogen
JGA releases renin.
Distal tubule
Renin
Angiotensin I
ACE
Angiotensin II
Juxtaglomerular apparatus (JGA)
STIMULUS: Low blood volume or blood pressure (for example, due to dehydration or blood loss)
Adrenal gland
Figure Regulation of blood volume and blood pressure by the renin-angiotensin-aldosterone system (RAAS).
Aldosterone
Arterioles constrict, increasing blood pressure.
More Na and H2O are reabsorbed in distal tubules, increasing blood volume.
Homeostasis: Blood pressure, volume

44. Homeostatic Regulation of the Kidney
ADH and RAAS both increase water reabsorption, but only RAAS will respond to a decrease in blood volume
Another hormone, atrial natriuretic peptide (ANP), opposes the RAAS
ANP is released in response to an increase in blood volume and pressure and inhibits the release of renin
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45. Check out Bioflix, and Bozeman “Osmoregulation”

46. Test Your Understanding question 7
Figure 44.UN02 Appendix A: answer to Test Your Understanding, question 7