Define respiratory pigments and understand their function in gas transport
Interpret O2 and CO2 equilibrium curves
Explain what the P50 index means
Explain how pH relates to both O2 and CO2 transport, including both the Bohr effect and the Haldane effect
Respiration involves convection of O2 in to the lungs or CO2 out of the lungs. Convection is done to maintain the partial
pressure of O2 and CO2 at appropriate levels so that diffusion can happen in tissues.
Respiratory pigments are proteins that can reversibly bind to O2. This helps to facilitate O2 transport, because when a gas
molecule is bound to another molecule, it does not contribute to partial pressure of that gas in that volume. It means that
as your blood soaks up O2, if it binds to the respiratory pigments in blood, O2 PP is not changing although the O2
concentration is changing. In this way, you can maintain the O2 cascade and keep the PP on the levels you want while still
shuttling O2 throughout the circulatory system.
Example: hemoglobin molecule with disclike structure with Fe atom in the center. The heme group is where the O2
At the quaternary level, in hemoglobin, a tetramer is formed, and when O2 binds at one heme, it alters the shape of the
tetramer, altering the affinity for O2 of the other heme sites.
Myoglobin is a respiratory pigment that exists in muscles. It helps the muscles to have a high O2 concentration while still
maintaining a PP.
If the binding of one O2 molecule affects the binding of others, what is this an example of? – homotropic cooperativity.
This is because we have a single type of molecule that affects the binding of the same types of molecule. It is a form of
cooperativity because it is ultimately the substrate of a protein binding to a protein.
Other type of respiratory pigment is hemocyanin. It uses copper to bind O2, and floats freely in blood. It exists in insect
blood. Hemoglobin is contained in RBC, while hemocyanin floats freely in blood
The Fe in hemoglobin is red, while copper in hemocyanin makes it blue, hence the term respiratory pigments. It does so based on the PP at different sites. There’s a particular PP in the lungs, near the lungs, in the PP, etc. Depending
on the PP, there’s more or less O2 bound to the hemoglobin. As the hemoglobin pass by your lungs, it soaks up O2. As it
moves away from the lungs, it releases O2 to the systemic tissues and so PP decreases. When you exercise, you don’t
change the O2 cascade because your body works hard to maintain it. But sometimes, if you exercise hard, you notice a
drop of PP in systemic tissue. If that happens, the hemoglobin helps to compensate by dumping more O2 in systemic
tissues because of the lower PP.
P50 index – halfmax PP of O2. PP of O2 at which you get halfmax of saturation of hemoglobin with O2 in your blood.
How does affinity relate to P50? – As P50 goes up, affinity goes down.
Hemoglobin unbinds O2 at a higher PP than no cooperativity. As the hemoglobin passes through the lungs, it will pick up
the same amount of O2 as if there’s no cooperativity. But as it goes through your systemic tissues, it will drop more O2 in
there. The more cooperativity, the more extreme the curve is, and the more hemoglobin will actively load and unload O2
at various sites. Given the law of mass action, and Henry’s law, what would happen if the PP of CO2 increased? – pH would decrease
We can regulate pH in our blood by exhaling CO2.
If you provide more X, you can soak up more and more H+, or alternatively, if you have less and less X, you release
more and more H+. Imidazole acts as a buffer.
When the H+ bind to the hemoglobin, they change the shape of the hemoglobin and they thereby alter the affinity of the
hemoglobin for O2.
Bohr effect – blood’s pH alters the equilibrium curve for your blood.
Low pH = affinity is reduced; shifted to the right
High pH = affinity is increased; shifted to the left
This helps to regulate hemoglobin’s function when you are engaged in strenuous exercise.
The higher the CO2 PP, the more acidic it’s gonna be and the more the curve shifts to the right. This allows hemoglobin to
“sense” the metabolic demands of the animal and respond appropriately. If O2 is bound to hemoglobin and its affinity is
reduced, O2 is released. This is a way for the hemoglobin to act as a store for extra oxygen in cases where CO2 rises. CO2
will rise when you engage in strenuous activities
As [CO2] increases, you have lower affinity for O2 in your hemoglobin. As you change from fully deoxygenated to fully oxygenated, you alter the CO2 equilibrium curve – how much CO2 can
be soaked up by blood.
When you have a lot of O2 in your blood, the amount of CO2 your blood can take up is lower, as a result, your blood is
not soaking as much CO2. But when you’re exercising and O2 levels go down and you need to transport more CO2, you
get a shift on the curve so that more CO2 can be soaked up.
Describe what hearts do and how they fit into different types of circulatory systems.
Understand the difference between open and closed circulatory systems
Define total fluid energy
Explain how blood convection is affected by blood pressure and vascular constriction/dilation.
The job of your heart is to provide the mechanical energy necessary for blood convection (via pumping). The muscles in
your heart contract, and the mechanical energy creates a pressure differential – a form of potential energy which moves
blood through the circulatory system. Muscles (including heart muscles) contract as a result of changes in the muscle cells’ electrochemical gradients. This
generates a measurable electrical signal known as the electrocardiogram (ECG). Various ions and minerals flow across the
cell, and they change the electrochemical gradient and the voltage of the cell. The change in voltage can be measured by
attaching electrodes to the body (or the heart).
P – initial atrial depolarization of the left atrium
QRS spike – result of the ventricular depolarization; very strong pumping action that occurs in the ventricles
T – ventricular repolarization (no need to know the details of these ~__~) Closed system – mammals, birds, and some invertebrates
Open system – invertebrates
In many invertebrates, their heart just pumps blood to the arteries, go throughout their body, then goes back to the heart
through the gills via infrabrachial sinus to pick up oxygen.
Notice the SKIN of amphibians, turtles, lizards, and snakes. What is always required to move blood through your circulatory system? – energy
**kinetic energy of momentum of blood
As blood comes down to the body towards the feet, there is greater and greater pressure. As a result, if it’s only pressure
differences that moves blood through the system, blood will always move from your feet up. But it doesn’t. It also moves
down. The reason for that is because blood literally falls into your legs because of the gravitational pull.
The gravity pulls your blood down, but the pressure produced by the heart pulls the blood up.
When we’re lying down (or if blood is moving against gravity) most of the movement of our blood has to come from
pressure differences created by our heart.
The pressure differential in the equation is important. There should be a good amount of pressure in the blood coming in
compared to the one exiting.
As we change the radius of the tube, the effect of the flow also changes.
The capillaries have very small radius so as a result, the blood moves very slowly through them. Another reason is
because they have a higher crosssectional area. As the area increases, pressure decreases. That is good though because
capillaries is where we exchange stuff so slow movement is needed there.
Your body dynamically regulates the speed of the blood flow throughout your body using smooth muscles.
Systolic pressure – pressure when your heart is actually pumping and creating potential energy using mechanical energy
of constriction of muscles.
Diastolic pressure – pressure when heart is not beating and blood is just flowing through the system using kinetic energy
and gravitational energy.
High BP = high BP in the exit of the tubes so the flow rate is hampered. The heart has to create an even higher pressure in
the entrance. The heart is working too hard and may cause a heart attack.
High BP is not always bad = for athletes.
The exchange of water between your blood and systemic tissues is a result of a combination of two pressures: osmotic
pressure, and the hydrostatic pressure created by your heart beating. The two pressures combine to determine the direction
of the flow of water from your capillaries to the tissues.
As the blood comes in, there’s a high HS pressure which outcompetes O pressure (typically the O pressure of your blood
is greater than the rest of the tissues because of the presence of the proteins in the blood). So water wants to move into the
blood but the pressure created by the heart will drive water out and the difference between those determines the direction
which it flows. Lecture 15
Differentiate between osmotic, ionic, and volume regulation.
Understand why water is lost through evaporation and urine and how this relates to metabolism
Define the U/P ratio for urine
Identify the major challenges for water and salt regulation in aquatic and terrestrial animals
There are 3 distinct, yet related aspects of water and salt in the body that animals regulate:
1.) Osmotic pressure
2.) Ion concentration
3.) Water volume
Each concept can be applied to the fluid of the body as a whole, compared to the external environment, or to the
intracellular fluid compared to the extracellular fluid.
Osmotic pressure helps us to determine which direction the water will flow via osmosis.
Remember that in osmosis, water moves from low [ ] to high [ ]. In (A), if you just let the water move through osmosis, it
will result to (B). The water moves to the ▯and the barrier moves .▯ However, if force is applied on the piston, it would
create hydrostatic pressure. It causes the water to move ▯(from the area of solution to the area of pure water). At some
point, the water movement by osmosis will be counteracted by the water movement caused by hydrostatic pressure = that
is the osmotic pressure of the solution.
Water moves from area of low osmotic pressure to high osmotic pressure.
What is the relationship between ion concentration and osmotic pressure? – high [ions] = high osmotic pressure
The greater the [ions], the higher hydrostatic pressure necessary to counteract osmosis, and therefore, higher the osmotic
pressure. Salt – a molecule with a charge.
Salts vs. nonsalts (organic solutes) = molecules with charge vs. molecules without a charge.
As we raise the amount of organic solute molecules, we raise the osmotic pressure. Notice that the number of inorganic
ion is constant. In this way, although the number of inorganic ions helps to determine the osmotic pressure, it can be
decoupled from osmotic pressure using organic molecules like amino acids. Many animals maintain osmotic pressure
while also separately regulating concentration of various salts in the cell using these various salts like amino acid.
The osmotic pressure is indicated by the darkness of blue. Cell (1) has the same osmotic pressure as the extracellular fluid
around it. If you move the cell to a dilute solution, water will enter the cell via osmosis, which will lead to cell swelling.
The volume of the cell will be altered as a result of the osmotic pressure relationships of the cell and its environment.
Likewise, if you move the cell to a more concentrated solution, it will result to cell shrinking and cell volume decrease. In
order for the cell to maintain its volume, what it has to do is to have an osmotic pressure that is the same as its
surrounding fluid. If we move the cell to a dilute solution, it has to decrease its osmotic pressure to retain its volume, and
if we move the cell to a concentrated solution, it has to increase its osmotic pressure to retain its volume.
What do all animals have to regulate with respect to their blood (not their intracellular fluid)? – volume
Animals can’t fill up like a balloon. They will die if you can’t regulate your volume. You will shrink or will burst.
In order for a crab to get out of its shell to change it, it stops regulating its volume and it expands to force itself out of the
shell. Not all animals engage in osmotic regulation.
An osmotic regulator always maintains the same osmotic pressure in their blood no matter what the osmotic pressure of
the surrounding area is. Terrestrial animals like us are regulators.
Some animals are conformers. If you place them in saltier and saltier water, they get saltier and saltier blood.
The mussel is a conformer. The shrimp is an osmotic regulator. There are certain animals that act as regulators at certain
levels of osmotic regulator in the water, and act as conformer otherwise. The green crab regulates its osmotic pressure so
that it doesn’t drop to a certain level but at higher levels of ambient osmotic pressure, it just lets itself go along.
Animals need a constant source of new water, why?
Evaporation can be good if we’re trying to get rid of heat, otherwise it’s bad because we’re losing water in our body.
Water vapor is water in gaseous form. It moves from an area of high partial pressure (PP) to low partial pressure. If you
have both water in the form of gas and its liquid state, we can still talk about the partial pressure of water vapor in the
water. It’s defined as the PP that would be created in the air if we would enclose that water in a close system with the gas.
If you put water in a container and the rate of gas ▯liquid, and liquid ▯gas are the same, we have equilibrium, you would
have the PP that we speak of when we talk about the water vapor in solution for water.
Note that it is temperaturesensitive. As the temperature increases, the water vapor pressure for the water increases
because more and more water vapor would go into the air. The flow of WV in from a solution (evaporation) into a gas is determined by the equation where WVPs and WVPa are the
water vapor pressure of the solution and the air, respectively. X = distance between the two factors.
Our mouth and nasal passages are moist and full of water, therefore they have a high WVP. That high WVP leads to faster
evaporation in the air. That can be used to advantage by some animals like dogs. When dogs pant, they’re using the
evaporation from their mouth in order to cool themselves. But if they’re not overly hot, it’s a bad thing to do. Lungs are
designed to promote gas diffusion. They have thin epithelium in alveoli, and that means that it’s even easier for water to
diffuse from the alveoli into the air within your lungs. As a result, you a lot of water from your lungs when you breath.
Nasal passages help to prevent evaporative water loss via countercurrent cooling. They cool the air as they come out.
So as we breathe in, the air gets warmed up as it travels down to our lungs. That heat helps more and more water to be
evaporated. But as we breathe out, it starts to get cooled off again, and as it cools water comes out of air and into the
solution (the lining in our throats and mouths) so we get to keep some water that would have otherwise been lost. The
reason it’s countercurrent is that you have the coldest areas of your nasal cavity (nose) and the warmest down there
(throat), so there’s a gradient of cool to hot in this direction .▯ And as you breathe out, it goes hot to cool to this direction .▯
If you don’t pee, you won’t get rid of the waste from your cells, especially excess nitrogen from proteins.
U/P ratio = how much water is used in the urine. **blood plasma; that’s why it’s U/P
If you have a high U/P, the OsmP of urine is higher than of the blood (urine is concentrated)
If you have a low U/P, the OsmP of urine is higher than of the blood (urine is watery) If your U/P = 1, you are peeing urine that has the same OsmP as your blood
What is your U/P ratio if you drink 8 glasses of water/day? – U/P 1. Some desert animals can’t afford to lose water so they
produce a very concentrated urine.
What sorts of environments would necessitate a U/P ratio > 1. – dry environment
The loop of Henle is a structure in the nephron is where mammals and birds create urine that is hyperosmotic to blood.
The loop of Henle of desert animals are very long compared to those who live in wet environments.
The loops of Henle create urine with high OsmP using two mechanisms:
1.) The single effect 2.) Ccountercurrent multiplication
There is an active transport of NaCl out of the ascending limb into the interstitial fluid, and it leads to a high OsmP in the
interstitial fluid between the two tubes. Through diffusion and osmosis, there is a high OsmP in the descending tubule.
The single effect lowers the OsmP in the ascending tubule, and increases it in the descending tubule.
In countercurrent multiplication, the OsmP increases as you go down the interstitial fluid.
Diagram: (2) shows single effect; (3) shows countercurrent multiplication
In countercurrent multiplication, the current moves in opposite directions from each other; it’s called multiplication
because you increase the OsmP as you go down.
The longer the loop of Henle, the more countercurrent multiplication you get.
The ascending limb is ascending more and more dilute fluid to the ureters and to the bladder.
Why is a high OsmP in the bottom of the loop? It’s because the collecting duct must pass through the interstitial fluid
before it heads to the bladder and urethra. If the collecting duct has a high number of aquaporins in it, then it will lead to
osmotic equilibrium with the interstitial fluid, which will produce a high OsmP in the fluid that heads towards the renal
pelvis of the kidney (will ultimately pee out). How does the N from amino acids get removed from the body? It depends on what species you are.
Ammonotelic – uses ammonia to get rid of nitrogen
Ureotelic – uses urea to get rid of nitrogen
Uricotelic – uses purines to get rid of nitrogen like uric acid or guanine
Two problems with urea:
1.) It’s still toxic to some extent
2.) It’s energy expensive Advantage: it’s a good strategy for preserving water
Disadvantage: it’s very energy expensive
Explain the neuron doctrine.
Describe how the cell membrane of neurons function as a capacitanceresistance circuit
Understand how the current flows passively in dendrites
Understand how ion concentrations and currents determine neurons’ resting and reversal potentials
Explain how neurons signal down their axons using Na+ and K+ based action potentials
To survive, animals must rapidly coordinate millions, or even trillions or cells in their body in an intelligent manner.
Not all animals place quite so much emphasis on massive computing power, but they still use neural circuits to control the
rest of the cells in their bodies in order to maximize the chances of their survival. Example is an earthworm. It has ganglia
throughout its body so even if you cut it, it can still coordinate its movements. How can a cell (a bag of fat and protein filled with salty water) electrically integrate signals?
The more ion channels open, the less resistance there is for the ions to flow down the electrochemical gradient.
The resistance has a direct effect on the current that flows across a circuit. Inverse relationship = as the resistance goes up,
current flow goes down; as resistance go down, current flow goes up.
What happens to the amount of ionic current flowing across the membrane when ion channels open? If we inject positive current in, the (+) current will displace some of the () ions that lines up the cell membrane
previously, which will lead to the change in voltage across the membrane. As current flows into the cell, the voltage across
the membrane will change as well.
The way in which the voltage in the CM changes, depends on how easily current can flow in the cell. There are two
resistances: for the internal solution, and for the cell membrane. If we inject current in a particular location in the dendrite,
it’s going to spread like an exponential decay along the dendrite, such that at some point we can hit 37% (lambda – length
Length constant – ratio of the two resistances. As internal resistance goes down (Ri), lambda goes up. We get less decay
throughout the dendrite = current flow easier. As the resistance of the membrane (Rm) go down, lambda goes down
because more and more current can flow out through the ion channels.
The speed on which the voltage changes depends on T = RmC (time constant).
Time constant – product of the resistance of the membrane and the capacitance. The lower the T, the faster the neuron
response is = faster voltage changes.
So, the voltage of any part of a neuron is determined by what currents are flowing across the membrane, and down the
dendrites. If we don’t change the ion channels that are open, does the voltage ever stabilize? YES.
Because of the active transport of K+ into the cell, we have a high [K+] inside. The ion channels will allow K+ to leave
the cell. As it flows out of the cell, A are also going to try to flow out of the cell because they are attracted to the K+ flowing out of the cell. However, because of selective permeability, the A build up along the CM. that buildup along the
CM creates the voltage. Also, because of the buildup, the K+ will be attracted back into the cell because it’s gonna create
an electrical gradient that favors the movement of K+ into the cell.
Electrical gradient = causes K+ to flow into the cell
Chemical gradient = causes K+ to flow out of the cell
Eventually, we will reach a point where the two counterbalances each other. Inflow and outflow of K+ will be in equal
extents. It is known as the reversal potential for K+. When you get equal flow in and out of the cell because of balanced
electrical and chemical gradients = reversal potential.
The axons of neurons are equipped with a high density of a special type of ion channel: voltagegated ion channels (they
open and close depending on the voltage of the cell). These channels help axons to “actively” propagate voltage changes
over long distances – these signals are called action potentials. The voltage sensors are made up of alpha helices with positive charges such that they are normally attracted in the cell. If
they get pulled down, the gate closes. If it gets pulled up, the gate opens.
Current flows into the axon, depolarizing it and increasing the voltage, which then leads to new Na+ channels next to that
channel to open. In that way, you get a constant propagation of depolarization down the axon. It doesn’t travel backwards
though because of the inactivation of Na+ channels.
Correction: ***increase Rm (increase the membrane resistance) The larger the diameter of the axon, the faster the flow of current because of lower resistance.
Describe the difference between chemical and electrical synapses
Understand how synapses enable presynaptic AP to cause postsynaptic currents
Explain how inputs from multiple presynaptic cells leads to spatial and temporal summation
Understand how synaptic plasticity is the basis of learning and memory The difference is whether or not the voltage change is transmitted electrically, or chemically.
In electrical synapse, the presynapti