BIOL364 Final - Ion and Water Balance

Lecs Ion & Water Bal 1-5

3 meanings of environment in a physiology context (3)

1. External world for the whole animal

2. extracellular fluid (eg. plasma and interstitial fluid) for a cell

3. cytoplasm/intracellular fluid for intracellular enzymes

Agree or Disagree: animals use ONE type of tissue to control ion and water balance in internal environments only. (2 - explain why or why not)

Disagree.

Animals use different combinations of tissues (1) in various internal and external environments (1) to control ion and water balance.

3 homeostatic processes (3)

1. osmotic regulation

2. ionic regulation

3. nitrogenous waste excretion

osmotic regulation refers to:

osmotic pressure of body fluids

ionic regulation refers to ____. give 1 example.

concentration of specific ions
example: sodium & potassium ion gradients

nitrogenous waste excretion refers to:

excretion of end products of protein metabolism

what is homeostasis? why is it important?

• state of internal constancy state maintained as a

  result of active regulatory processes

• control over the internal environment allows life to survive in different external environments

Solutes move through water by what process?

diffusion

What does the rate of diffusion depend on? (3) Hint: think of the Fick’s equation in the context of ions.

1. Diffusion coefficient (D_s) - includes size of molecule plus its hydration shell

2. Diffusion area (A)

3. Size of concentration gradient (dC/dX) - X is distance

For ion and water balance, the direction of diffusion depends on:

the concentration gradient

Concerning osmotic pressure, describe what’s happening in panels a)-d). (3)

a) water randomly moves back and forth the two sides of the semipermeable membrane

b) and c) salt added, water now wants to move to the side with salt (from high water activity/low solute to low water activity/high solute)

d) height difference set when eqilibrium or homeostasis is met

Define osmosis

The movement of water across a membrane from an area with a high activity of water (aka low solute) to an area with low activity of water (aka high solute).

higher osmolarity / osmolality (same for this course, only units differ) = ____ solutes in water

more

consider 2 solutions seperated by a semi-permeable membrane. A is hyperosmotic, and B is hyposmotic. How does water diffuse between A and B?

water diffuses from B to A

if osmolarities are the same, 2 solutions are

isosmotic

tonicity

the effect of a solution outside the cell on cell volume

cells ___ in hypertonic solution, water ___ cell by osmosis.

cells ___ in hypotonic solution, water ___ cell by osmosis.

shrink, leave, swell, enter

Agree or Disagree: if a cell is isotonic with its environment, water doesn’t need to move across membranes and the cell doesn’t shrink or swell. (2 - explain why or why not)

disagree (no marks, marks for correct explanation only)

• water still constantly moving across membranes, just no NET osmosis (1)

• cell doesn’t shrink or swell is correct (1)

agree or disagree: hyperosmotic is always hypertonic. explain why or why not.

disagree because osmotic is about num of solutes compared to a solution, while tonicity is about cell volume, which includes num of solutes and the permeability of cell membranes.

eg. something can be hyperosmotic but isotonic if the solutes aren’t permeable and cell doesn’t swell up!

Describe the tonicity of solutions relative to the 3 RBCs. For the last 2, give a physiological consequence of each. (5 marks total)

• iso, hypo, hyper solns

• hypo = cannot fit RBC in a capillary (one cell thick)

• hyper = crystallization occurs within RBCs from collapse

Why is it important to regulate cell osmolarity? (2)

1. increased intracellular activity can directly interfere with cellular processes (e.g. protein-protein interactions, cellular fluidity for diffusion)

2. changes in osmolarity means water will move across membranes, changing cell volume

In the context of osmolarity regulation, what is the consequence of moderate cell swelling? excessive cell swelling? excessive cell shrinkage? (3)

1. moderate swelling = disruption of membrane

2. excessive swelling = cell lysis

3. shrinkage = macromolecules are crowded

how does a cell control cell volume? what process does it rely on?

• by transporting solutes in and out of extracellular fluid (ECF)

• relies on osmosis: water follows solutes

why do animals modify the composition of ECF?

modification provides cells with the appropriate external soln which allows them to maintain proper cell volume

consider these 4 major ions: Na+, K+, Cl-, Ca2+. what is Na+ regulated by? (2)

• Na+/K+ ATPase

• Na + /H + exchanger

consider these 4 major ions: Na+, K+, Cl-, Ca2+. what is K+ regulated by? (1)

Na+/K+ ATPase

consider these 4 major ions: Na+, K+, Cl-, Ca2+. what is Cl-regulated by? (1)

it’s distributed passively (think Goldman equation of resting membrane potential) usually via co-transporters

consider these 4 major ions: Na+, K+, Cl-, Ca2+. what is Ca2+ regulated by? (2)

• Na+/Ca+ antiporter

• Ca2+ ATPase

Describe how cells perform regulatory volume increase (RVI) to swell up. What is the main channel/transporter used? What alternative channels/transporters may be opened? (4)

• cells actively import ions

• water follows ions passively

• main: NKCC (Na K Cl cotransporter)

• alternatives: Na+ channels, Cl- channels, Na+ H+ exchangers (note that exchanger is a subtype of transporter)

note: different types of ion transporters exist that are species and tissue specific in driving water transport

Describe how cells perform regulatory volume decrease (RVD) to shrink. What is the main channel/transporter used? Give an example. (4)

• cells actively export ions

• water then follows passively (in response to changes in ions and osmolality)

• main: opening K+ channels

• eg: K+ leaves cell down its electrochemical gradient, water follows passively, K+ leaving quickly causes hyperpolarized effect, so Cl- channels also open and Cl- also leaves to counter it.

what specialized structure does water move through?

aquaporins

(note that porins are for larger molecules compared to ion channels)

Consider ionic and osmotic challenges.

1) marine animals tend to ___ salts and ___ water.

2) freshwater animals tend to ___ salts and ___ water.

3) terrestrial animals tend to ___ water.

4) T or F: many animals move between environments and must be able to alter their homeostatic mechanisms (think of a frog that moves btwn water and land)

1) gain, lose

2) lose, gain

3) lose

4) T

Define ionoconformer. What animals are ionoconformers? (2)

• have little control over the ion profile within the extracellular space

• only found in marine animals eg invertebrates, hagfish

Define ionoregulator. What animals are ionoregulators? (2)

• control the ion profile of the extracellular space

• most vertebrates

osmoconformer vs osmoregulator. examples of each.

• conformer = internal and external osmolarities are similar. eg. marine invertebrates.

• regulator = osmolarity is constant regardless of external environment. eg. most vertebrates

stenohaline and euryhaline refer to the ability to cope with what? define each.

• cope with external salinities

• steno = narrow range of tolerance

• eury = wide range (think eurkaryotes = multicellular)

looking at this graph, compare hagfish to bony fish using the terms listed. explain each term used.

• hagfish = ionoconformer + osmoconformer

  • hagfish ion profiles CONFORM to seawater (their env) and their internal and external osmolarities are similar (internal CONFORMS to external)

• bony fish = ionoregulator + osmoregulator

  • bony fish CONTROL internal ion profiles (NOT conformed to seawater) and their osmolarity is constant regardless of external osmolarity

similarity between 1 and 2? difference?

similarity: both osmoconformers. shown by starting osmolarity (•) differing from ending osmolarity.

difference:

1. euryhaline osmoconformer, LONGER range before death, lets osmolarity decrease in parallel with water until death.

2. stenohaline osmoconformer, SHORT survival range, dies after minor osmotic disruption

similarity between 3 and 4? difference?

similarity: both osmoregulators. shown by starting osmolarity being similar to osmolarity at death.

difference:

3. WIDE range of nearly constant internal state before eventual death (see long orange line)

4. NARROW range of nearly constant internal osmolarity before death (see short green line)

explain the 3 graphs here in terms of hagfish capacity to osmoregulate during 48h exposure to a range of salinities. (Regular SW is 32 g l-1)

osmolality inc as salinity inc

lost body weight as salinity inc

muscle water content inc as salnity inc
So, no signification osmoregulation as it’s all changing with the salinities !!

3 ways to classify solutes, explain each, give examples

1. perturbing - DISRUPTS macromolecular function. eg. Na+, K+, Cl–, SO4+, charged amino acids

2. compatible - LITTLE EFFECT on macromolecular function. eg. glycerol, glucose, and uncharged amino acids

3. counteracting - disrupts function on their own, but effects COUNTERACT when used in conjunction eg. urea + TMAO

how do animals compensate for passive ion and water movements?

by active transport of ions across osmoregulatory epithelia

3 primary osmoregulatory epithelia of vertebrates

1. kidney

2. gills

3. digestive system

What is special about birds and mammals in terms of how they produce urine?

only ones who produce a CONCENTRATED urine (hyperosmotic compared to blood) at the KIDNEYS

Looking at this diagram, what are 4 epithelial properties for ion movement?

Hint: 1 of these are not directly on the diagram.

1. membrane transporters are assymetrically distributed (see the 3 cells with various # of transporters)

2. cells are interconnected to form an impenetrable sheet of tissue (see tight junctions in orange)

3. abundant mitochondria → provides ATP for ion transporter

4. high cell diversity within tissues

2 main routes of transport used by epithelial cells (2)

1. transcellular transport - movement through cell

2. paracellular transport - movement between cells

4 types of transporters for solute movement (4)

1. Na+K+ATPase (NKA)

2. ion channels (Cl-, K+, Na+)

3. electroneutral cotransporters

4. electroneutral exchangers

osmoregulation in fish: freshwater fish (5)

• Passively gains __1__ and loses __2__ across gill and gut

• Produces __3__ urine in kidney to __4__ water

• Actively ___5___ ions at gill

1. water

2. ions

3. dilute

4. remove / excrete

5. absorbs

osmoregulation in fish: seawater fish (5)

• Passively gains __1__ and loses __2__ across gill and gut

• Cannot produce __3__ urine to __4__ water

• Actively ___5___ ions at gill

1. ions (think salt)

2. water

3. concentrated (remember that only birds/mammals can make hyperosmotic urine relative to blood!)

4. conserve

5. secretes

what are fish ionocytes? what do they have a lot of? (3)

• ion transporters on fish filaments (and sometimes lamellae)

• have a lot of mitochondria

• have a lot of NKA activity to drive ion movement

T or F: the Na+K+ATPase is the driving force of ion regulation in seawater fish but not freshwater fish.

F, it’s the driving force in both

mechanism of salt secretion in hyperosmotic env: describe the image.

START ANSWERING HERE CARD 52!!!

mechanism of salt secretion in hypoosmotic env: describe the image.

diadromous

fish that move between fresh and seawater throughout life cycle

2 types of diadromous fish. define each.

1. catadromous: adults in freshwater, breed in sea. eg. eel!

2. anadromous: adults in seawater, breed in fresh. eg. salmon!

NOTE: ana means up (think like anabolism or building up muscle), and anadromous fish swim UPRIVER (aka towards freshwater to spawn). cata means down.

what is smolting? why is it needed? consider it in the context of salmon.

• psychologically preparing for seawater (SW) when still residing in freshwater (FW)

• needed bc most animals die when going from FW to SW or back

graph 1 showing metabolic stuff w/ hormones. explain it.

graph 2 w/ the colourfully tagged gills. explain it.

what do salt glands do in reptiles and birds (show the pic as well)

salt glands in marine birds

rectal gland in shark/elasmobranch. explain the diagram.

ion and water bal in terriestrial

in humans, 60% of water gain comes from drinking it. what are some other ways ?

mechanism of water conservation in humans while breathing

desert animals needs way better water conservation than human. name 3 ways they achieve this. (6 answers listed, any 3 of the 6 are valid!)

what parts of the body excrete nitrogenous wastes? hint: this isn’t their only function, name the other thing that they do as well.

how ammonia made in the body and why does it have to be excreted?

3 forms of ammonia excretion, examples of animals that excrete each form (6 - 1 mark for each example given despite answer having many examples)

How is the type of nitrogen excreted related to an animal’s environment?

Advantages of ammonia excretion? Disadvantages?

Advantages of uric acid excretion? Disadvantages?

Advantages of urea excretion? Disadvantages?

smth on slide 23, probably NH4+/ammonium

explain fish ammonia excretion diagram

what do sharks use urea for? why do sharks excrete urea instead of ammonia? think about their ionic and osmo type.

ION WATER QS OVER ANS TMR