1. Homeostasis
Osmosis & Diffusion 1

2. Homeostasis
Homeostasis refers to maintaining internal stability within an organism and returning to a particular stable state after a fluctuation. 2

3. Homeostasis Changes to the internal environment come from:
Metabolic activities require a supply of materials (oxygen, nutrients, salts, etc) that must be replenished.
Waste products are produced that must be expelled. 3

4. Homeostasis
Systems within an organism function in an integrated way to maintain a constant internal environment. 4

5. Osmosis
Cells require a balance between osmotic gain and loss of water.
Water uptake and loss are balanced by various mechanisms of osmoregulation in different environments. 5

6. Osmoregulation regulates solute concentrations and balances the gain and loss of water.
The tendency of living organisms to control or regulate changes in their internal environment.
Osmoregulation in bony fish. Bony fish are osmoregulators. An organism that regulates its internal concentration of salts.
Osmoregulation

7. Osmosis
Osmosis is the movement of water across a selectively permeable membrane.
If two solutions that are separated by a membrane differ in their osmolarity, water will cross the membrane to bring the osmolarity into balance (equal solute concentrations on both sides). 7

8. Osmotic Challenges
Osmoconformers, which are only 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.
Osmoregulation = biological processes involved in controlling the levels of water and salt in the body fluids and cells. 8

9. Osmotic Regulation
Most marine invertebrates are osmotic conformers – their bodies have the same salt concentration as the seawater.
The sea is highly stable, so most marine invertebrates are not exposed to osmotic fluctuations.
These organisms are restricted to a narrow range of salinity – stenohaline.
Marine spider crab 9

10. Osmotic Regulation
Conditions along the coasts and in estuaries are often more variable than the open ocean.
Animals must be able to handle large, often abrupt changes in salinity.
Euryhaline animals can survive a wide range of salinity changes by using osmotic regulation.
Hyperosmotic regulator (body fluids saltier than water)
Shore crab. 10

11. Osmotic Regulation
The problem of dilution is solved by pumping out the excess water as dilute urine.
The problem of salt loss is compensated for by salt secreting cells in the gills the actively remove ions from the water and move them into the blood.
Requires energy. 11

12. Osmotic Regulation - Freshwater
Freshwater animals face an even more extreme osmotic difference than those that inhabit estuaries. 12

13. Osmotic Regulation - Freshwater
Freshwater fishes have skin covered with scales and mucous to keep excess water out.
Water that enters the body is pumped out by the kidney as very dilute urine.
Salt absorbing cells in the gills transport salt ions into the blood.

14. Osmotic Regulation - Freshwater
Invertebrates and amphibians also solve these problems in a similar way.
Amphibians actively absorb salt from the water through their skin.

15. Living in freshwater: SUMMARY
Freshwater is 100% H2O
Fish cells are 98.6% H2O
Freshwater fish are hyperosmotic (less water)
Problem:
1. lose salt
2. gains too much H2O by
osmosis.
Solution:
1. does not drink
2. salt absorbed by gills
3. large volume of
dilute urine

16. Osmotic Regulation – Marine
Marine bony fishes are hypoosmotic regulators.
Maintain salt concentration at 1/3 that of seawater.
Marine fishes drink seawater to replace water lost by diffusion.
Excess salt is carried to the gills where salt-secreting cells transport it out to the sea.
More ions voided in feces or urine. 16

17. Osmotic Regulation – Marine
Sharks and rays retain urea (a metabolic waste usually excreted in the urine) in their tissues and blood.
This makes osmolarity of the shark’s blood equal to that of seawater, so water balance is not a problem.
Kidneys- The shark has two kidneys on either side of the midline. The shark osmoregulates in a unique way compared to most other vertebrates. The shark kidney extracts urea from urine and returns the urea to the blood, whereby it concentrates urea in the blood. In this way the osmotic pressure of the sharks body fluids are maintained as high as that of sea water. With this system the shark does not lose water or gain salts through osmosis.
Rectal glands- This is a tube-like extensions of the rectum. This gland helps the kidney control the salt (NaCl) concentration within the body. Excess salt is released into the rectum for expulsion 17

18. Living in saltwater:
Alternative #1 = Osmoconformers - organism that allows internal salt concentration to change with the salinity of the water (conform to the environment). Cells are isosmotic. Total salts in body balance salts in sea water (3.5% or 35 0/00 marine algae and most invertebrates). 18

19. Alternative #2 = Osmoregulator - an organism that controls internal salt concentration different from the environment. In fish, mammals, birds and reptiles blood is hypoosmotic so they tend to lose water. (sharks save urea). May expend 5-30% of energy maintaining osmotic balance. 19

20. Living in the Ocean: SUMMARY Seawater is 96.5% H2O
Fish cells are 98.6% H2O
Marine fish cells are hypo-osmotic (more H2O)
Problem:
1. Loses H2O by osmosis
2. gains too much salt.
Solution:
1. drink lots of water
2. secrete salt through gills
3. excrete small amount of concentrated salty urine 20

21. Air breathing marine vertebrates:
Mammals and some birds use their kidneys to remove salt from blood then release in urine.
Some birds and reptiles salt is removed by glands under the eyes, salty tears. 21

23. Salt Excreting Glands
Birds, although they have loops of Henle, cannot make a very concentrated urine - their loops are fairly short.
Marine birds and reptiles (which cannot make a concentrated urine) have evolved extrarenal routes of salt excretion.
Birds use nasal glands that release salt excretions into the nasal passages.
Sea turtles have modified tear ducts that secrete salt into the orbit of the eye.

24. Osmoregulation Advantages Disadvantages
Osmoregulators can live in a wide variety of habitats: marine, estuaries, freshwater, land.
Disadvantages
Osmoregulation is energetically costly, depending on how different the animal’s internal osmolarity is from the environment, how permeable the animal’s surfaces are to water and ion movement, and how costly it is to pump ions across membranes.

25. Osmoregulation in marine fish
Marine fish face two problems: they tend to lose water and gain ions.

26. Osmoregulation in freshwater fish
Freshwater fish face two problems: they tend to lose ions and gain water. 26

27. Osmoconformers: some marine animals
Animals whose body fluids are isotonic to their
environment. They do not actively adjust the internal
osmolarity.
Osmoregulators: terrestrial animal, freshwater animals,
many marine animals
Animals whose body fluids are hypotonic. They will
gain water from the environment and must continuously
eliminate excess water.
Animals whose body fluids are hypertonic. They will
lose water to the environment and must continuously
take in excess water.
Osmoregulators must expend energy to maintain osmotic
balance (5% to 30% of metabolic rate). 27

28. Marine Animals:
1. Osmoconformers – most
marine invertebrates
May still need to regulate
internal composition of
specific ions. Usually slight,
but may be significant.
The external environment determines the mechanism of
maintaining water balance:
2. Osmoregulators – most marine vertebrates
a. Cartilagenous fish (ex, sharks)
b. Bony fish

29. Cartilagenous fish (ex. shark)
Maintain a lower osmolarity for salt
than seawater.
Salt diffuses through gills.
Excrete salt
a. kidneys excrete some salt
b. rectal glands (salt excretory glands) excrete NaCl.
Animal fluids still slightly hypertonic to seawater
Due to accumulation of urea
Water slowly enters body by osmosis.
Excretory organs (kidneys) eliminate excess water as urine.

30. Osmotic Regulation – Terrestrial
Marine birds and turtles have a salt gland capable of excreting highly concentrated salt solution.

31. Solute Gradients and Water Conservation
The collecting duct, permeable to water but not salt conducts the filtrate through the kidney’s osmolarity gradient, and more water exits the filtrate by osmosis.

32. Solute Gradients and Water Conservation
Urea diffuses out of the collecting duct as it traverses the inner medulla.
Urea and NaCl form the osmotic gradient that enables the kidney to produce urine that is hyperosmotic to the blood. 32

33. Regulation of Kidney Function
The osmolarity of the urine is regulated by nervous and hormonal control of water and salt reabsorption in the kidneys. 33

34. Regulation of Kidney Function
Antidiuretic hormone (ADH) increases water reabsorption in the distal tubules and collecting ducts of the kidney.

35. Temperature Regulation
Animals must keep their bodies within a range of temperatures that allows for normal cell function.
Each enzyme has an optimum temperature.
Too low and metabolism slows.
Too high and metabolic reactions become unbalanced. Enzymes may be destroyed. 35

36. Temperature Regulation
Poikilothermic animals’ body temperatures fluctuate with environmental temperatures.
Homeothermic animals’ body temperatures are constant. 36

37. Temperature Regulation
All animals produce heat from cellular metabolism, but in most this heat is lost quickly.
Ectotherms – lose metabolic heat quickly, so body temperature is determined by the environment.
Body temp may be regulated environmentally.
Endotherms – retain metabolic heat and can maintain a constant internal body temperature. 37

38. Ectothermic Temperature Regulation
Many ectotherms regulate body temperature behaviorally.
Basking to increase temperature.
Shelter in shade or coolness of a burrow to decrease temperature. 38

39. Ectothermic Temperature Regulation
Most ectotherms can also adjust their metabolic rates to the environmental temperature.
Activity levels can remain unchanged over a wider range of temperatures.

40. Endothermic Temperature Regulation
Constant temperature in endotherms is maintained by a delicate balance between heat production and heat loss.
Heat is produced by the animal’s metabolism.
Producing heat requires energy – supplied by food.
Endotherms must eat more in cold weather.

41. Endothermic Temperature Regulation
If an animal is too cool, it can generate heat by increasing muscular activity (exercise or shivering). Heat is retained through insulation.
If an animal is too warm it decreases heat production and increases heat loss.

42. Adaptations for Hot Environments
Small desert mammals are mostly fossorial (living underground) or nocturnal.
Burrows are cool and moist.
Adaptations to derive water from metabolism and produce concentrated urine & dry feces. 42

43. Adaptations for Hot Environments
Larger desert mammals (camels, desert antelopes) have different adaptations.
Glossy, pallid color reflects sunlight.
Fat tissue is concentrated in a hump, rather than being evenly distributed in an insulating layer.
Sweating and panting are ways of dumping heat. 43

44. Adaptations for Cold Environments
In cold environments, mammals reduce heat loss by having a thick insulating layer of fat, fur, or both.
Heat production is increased.
Extremities are allowed to cool.
Heat loss is prevented through countercurrent heat exchange. 44

45. Adaptations for Cold Environments
Small mammals are not as well insulated.
Many avoid direct exposure to the cold by living in tunnels under the snow.
Subnivean environment.
This is where food is located. 45

46. Adaptive Hypothermia Endothermy is energetically expensive.
Ectotherms can survive weeks without eating.
Endotherms must always have energy supplies. 46

47. Adaptive Hypothermia
Some very small mammals & birds (bats or hummingbirds) maintain high body temperatures when active, but allow temperatures to drop when sleeping.
Daily torpor 47

48. Adaptive Hypothermia
Hibernation is a way to solve the problem of low temperatures and the scarcity of food.
True hibernators store fat, then enter hibernation gradually.
Metabolism & body slows to a fraction of normal.
Body temperature decreases.
Shivering helps increase temperatures when they are waking up. 48

49. Adaptive Hypothermia
Other mammals, such as bears, badgers, raccoons and opossums enter a state of prolonged sleep, but body temperature does not decrease. 49

50. Adaptive Hypothermia
Adverse conditions can also occur during the summer.
Drought, high temperatures.
Some animals enter a state of dormancy called estivation.
Breathing rates and metabolism decrease.
African lungfish, desert tortoise, pigmy mouse, ground squirrels. 50