Osmoregulation

Question 1

Define Physiology

Answer 1

The study of an organism’s vital functions

Question 2

What are Common Principles in Animal Physiology?

Answer 2

Physiological processes obey the laws of physics and are usually regulated.

Question 3

What is meant by the obligatory exchange for osmoregulation and ion regulation?

Answer 3

Through integument (skin), feeding, excretion, and respiration, there is an obligatory exchange of water and ions. All animals have input and output methods, as they cannot live without the exchange of water.

Question 4

What is the fundamental problem of osmoregulation and ion regulation?

Answer 4

The concentration of solute in the intracellular environment affects the functions of organic molecules (proteins), and changes the functions of the organism.

Question 5

There is an _____ _____ of inorganic ion concentration for protein function.

Answer 5

An optimal range, often very narrow. The inorganic ion concentration affects the catalytic rate and affinity of enzymes.

Question 6

True or false: The effects of changing the ion concentration have a linear relationship, with productivity of the enzyme decreasing or increasing in accordance to the change in concentration.

Answer 6

False, the relationship is not linear. For example, doubling the concentration of an ion around an enzyme could cause productivity to drop by 60% (NaAcetate example).

Question 7

Solutes interact with proteins, affecting the ____ and _____.

Answer 7

Stability and function. Hofmeister series; Chlorine, Potassium, Sodium, Hydrogen, and Calcium are all mid-range solutes.

Question 8

What do weakly hydrated cations or strongly hydrated anions cause?

Answer 8

They are the most protein stabilizing, and cause a decrease in the solubility of proteins, salting out (aggregate), and decrease in protein denaturation.

Question 9

What do weakly hydrated anions or strongly hydrated cations cause?

Answer 9

They are the most protein destabilizing, and they cause an increase in the solubility of proteins, salting in (solubilize), and increase in protein denaturation.

Question 10

What is important about the Potassium ion?

Answer 10

It is, in general, less inhibitory. Eukaryotic cells maintain concentrations of 100-150 mM, and potassium levels greater than 180 mM inhibit protein synthesis.

Question 11

What is the fundamental limitation of animals?

Answer 11

To maintain their functions, there is a very narrow range of suitable organic (and inorganic) molecules.

Question 12

What do most cells use to regulate intracellular ion composition?

Answer 12

ATP is used to pump ions into and out of a cell.

Question 13

True or False: Water does not use ATP to enter or leave a cell.

Answer 13

True. Water cannot be pumped, it follows osmotic pressure to enter or leave a cell. Most animal cells are water permeable.

Question 14

What does it mean to be a water permeable cell?

Answer 14

It means that the cell is able to maintain an ionic difference across the membrane but not an osmotic difference. Water is allowed to move freely. Only some epithelial cells are capable of maintaining osmotic difference.

Question 15

What is the Osmotic Gradient?

Answer 15

Water moves from a low solute concentration to areas of high solute concentration.

Question 16

What is Aquaporin?

Answer 16

A water channel that allows water to move into and out of a cell. Most cells cannot prevent water from moving between cells.

Question 17

What do changes in osmolarity cause?

Answer 17

Changes in osmolarity cause a transmembrane osmotic gradient, therefore water moves across the membrane and the cell volume is affected.

Question 18

Define Osmolarity.

Answer 18

The measure of solute concentration; the number of osmoles per litre. Dissolution.

Question 19

How many osmols are in 1 mole of glucose?

Answer 19

1 osmol. It separates into one ion.

Question 20

How many osmols are in 1 mole of NaCl?

Answer 20

2 osmol, because it separates into two ions.

Question 21

What does it mean to be isotonic?

Answer 21

It means that the osmotic and solute concentrations are equal on either side of the membrane and that there is no net movement of water or change in cell volume.

Question 22

How do most cells respond to shrinking or swelling?

Answer 22

By activating specific membrane transport and/or metabolic processes that serve to return cell volume to its normal resting state. Volume sensing mechanisms are extremely sensitive; cells can sense and respond to volume changes of >3%.

Question 23

Volume (perturbations) changes activate:

Answer 23

Volume regulatory mechanisms.

Question 24

What is a problem with the gain or loss of inorganic ions?

Answer 24

Large changes in the levels of inorganic ions are incompatible with long-term normal protein function.

Question 25

What is an organic osmolyte?

Answer 25

Any organic molecule in the intracellular environment; found in high concentrations in the cytosol of all animals. They are used tom maintain cell volume.

Question 26

What are the three types of organic osmolytes?

Answer 26

1. Carbohydrates (e.g. sorbitol)
2. Amino acids and their derivative (e.g. proline)
3. Methylamines (e.g. trimethylamine-N-oxide, TMAO)

Question 27

What is a perturbing osmolyte?

Answer 27

One the disrupts metabolism when found in high concentrations or when large shifts in their concentration occur; urea is an example.

Question 28

What is a compatible (non-perturbing) osmolyte?

Answer 28

An osmolyte that does not affect protein function, this is the more common osmolyte. Examples: glycine, proline, inositol, sorbital. Compatible osmolyte use is widespread.

Question 29

What happens with a loss of organic osmolytes?

Answer 29

There is a volume reduction. A transporter in the cell membrane is opened and the osmolytes leave.

Question 30

What happens with a gain of organic osmolytes?

Answer 30

There is a volume increase, occurring because of changes in rates of synthesis and degradation of osmolytes or obtaining more from the environment (through Na-coupled transporters).

Question 31

True or False: Accumulating compatible osmolytes allow cells to survive in enviroments with varying osmotic concentrations.

Answer 31

True, for example some cells in the loop of Henle are exposed to environments ranging from 600 to 1200 mOsm.

Question 32

What are Osmoconformers?

Answer 32

Organisms whose bodily fluids and cells are equal in osmotic pressure to the environment. These organisms are mainly found in the oceans, where osmolarity is about 1000 mOsm.
They do not actively control the osmotic conditions of the extracellular environment, but may control extracellular osmolytes. Many osmoconformers will die if put in an unfamiliar environment.

Question 33

What are Osmoregulators?

Answer 33

Organisms whose osmotic pressure of bodily fluids is homeostatically regulated and usually different from the external environment.

Question 34

What do Osmoregulators do?

Answer 34

Maintain extracellular osmolarity and keep ion composition constant. They are strict with extracellular osmotic homeostasis, and cells and tissues are not able to cope with changes in extracellular osmolarity and ion concentration. There can be large external fluctuations, but because of control systems there are small internal extracellular fluctuations.

Question 35

What do Osmoconformers do?

Answer 35

They do not actively control the osmotic conditions of the extracellular environment, but they may control extracellular osmolytes. There is a high degree of cellular osmotic tolerance. Cells and tissues can cope with high extracellular osmolarities by increasing osmolarities with compatible osmolytes in order to maintain cell volume. Large external fluctuations lead to large internal fluctuations in the internal extracellular environment.

Question 36

Cells regulate __ ____ and __ in order to deal with intracellular aqueous environment affecting protein function.

Answer 36

Ion composition and pH levels.

Question 37

What are the two main evolution strategies to deal with maintaining osmotic homeostasis?

Answer 37

Osmoconformation and osmoregulation.

Question 38

What animals usually use osmoconformation?

Answer 38

Marine invertebrates.

Question 39

Is osmoconformation or osmoregulation more energetically expensive?

Answer 39

Osmoconformation is less energetically expensive. The external cellular fluid is similar to seawater (1000 mOsm), and this is dominated by NaCl. The internal cellular fluid has the same osmotic pressure as the external cellular fluid due to universal solutes (like Potassium, 400 mOsm) and organic osmolytes (600 mOsm).

Question 40

Most organic osmolytes:

Answer 40

Do not disturb macromolecules and some stabilize macromolecules against denaturing forces.

Question 41

What is the strategy of osmoconformers?

Answer 41

To maintain the extracellular body fluid isomostic with environtment, and to keep intracellular inorganic levels within a range compatible with protein function (compatible osmolytes).

Question 42

What are the types of osmoconformers?

Answer 42

Stenohaline and euryhaline.

Question 43

What are stenohaline osmoconformers?

Answer 43

They are restricted to a narrow range of salinity, and cannot regulate their osmolytes to compensate.

Question 44

What are euryhaline osmoconformers?

Answer 44

They are tolerant of changes in salinity, successful in intertidal zones (tidal pools), and regulate organic osmolytes in their cells.

Question 45

Who conserves compatible osmolytes?

Answer 45

Osmoconformers, bacteria, unicellular algae, vascular plants, invertebrates, and vertebrates. Convergent evolution is evident, organisms have strong selective pressures in conserving compatible osmolytes.

Question 46

What organism has an alternative to compatible osmolytes?

Answer 46

The Halobacterium. It lives in areas of high salinity (>1 M NaCl), and accumulates intracellular KCl (7 M). This strategy requires massive amino acid substitution in thousands of proteins, and is stenohaline. They can only survive in that one environment.

Question 47

What is an advantage of compatible osmolytes?

Answer 47

They are euryhaline, they can tolerate a wide range of salinities.

Question 48

What are Dunaliella?

Answer 48

Euryhaline micro-algae that grow in saturated brine or very dilute solutions by regulating the level of intracellular compatible osmolytes. They are genetically simple, and temporally flexible with adaptive mechanisms in the face of syclic water stress.

Question 49

What is important to remember about osmoconformation?

Answer 49

It is not the lack of regulation; it is a strategy that may be well regulated and use ATP. Animals can be osmoconformers in one range and osmoregulators in another.

Question 50

How does the Culex Tarsalis (mosquito) osmoconform?

Answer 50

It increases intracellular and haemolymph proline concentration in response to changes in osmotic pressure in the environment. It sense the haemolymph NaCl content, not the osmotic pressure.

Question 51

What are Sharks different?

Answer 51

There are stenohaline (tolerate narrow range of salinities) sharks that osmoconform and have no compatible osmolytes. They maintain high concentrations of urea, a perturbing osmolyte. The effect of urea is counteracted by trimethylamine-N-oxide (TMAO).

Question 52

What shark species can penetrate fresh waters?

Answer 52

Euryhaline sharks, they must have osmoregulatory strategies. Very energetically expensive, taxing on bodies (no reproduction in fresh water). They have less NaCl and Urea than salt water fish, double the osmolarity than normal freshwater fish, and go through more water/urine.

Question 53

What are some examples of osmoregulatory organs?

Answer 53

They depends on transporting epithelia and contain active ion transport, but the fundamental mechanisms are the same in all animal groups. On the external surface there may be gills, or skin. Salt glands and guts. Specialized internal organs: kidneys, protonephrones, metanephrones, malpighian tubules.

Question 54

What is important about gills?

Answer 54

The gills of vertebrate and invertebrate animals are involved in ion transport and the excretion of nitrogenous waste. In teleost fish (marine fish?) there are chloride cells.

Question 55

Marine Osmoregulators:

Answer 55

Are usually hypo-osmotic, lose water to the environment, live in oceans, environment is 1000 mOsm, remove water via chloride cells in gills, gain water/salt though seawater/food, lose salt in feces/urine, and have bodily fluids = 400 mOsm.

Question 56

Freshwater Osmoregulators:

Answer 56

Are hypersomotic, gain water from the environment, live in an environment of <5mOsm, absorb water though gills and skin, obtain salts though chloride cells and food, lose salts via feces/dilute urine, bodily fluids = 300 mOsm.