BIO3302 Lec 7
Lec 6 recap Baroreceptor reflex is one of the really important
neural pathways for the acute regulation of blood pressure But its
not the only neural pathway There are chemoreceptors that detect
blood and CO2 levels that help regulate blood pressure
Baroreceptors are still the key mechanism for the adjustment of
blood pressure on a moment to moment basis Going from lying down to
standing up They are sensory receptors in the all of the aorta and
carotid sinuses and are activated by stretch Have a resting firing
rate and as pressure goes up they fire more, as pressure falls they
fires less This degree of firing is integrated by the
cardiovascular center in the medulla and appropriate output is sent
to the effector organs(heart and smooth muscle in blood vessel
walls) and they adjust pressure To adjust pressure heart rate and
vasoconstriction of the arterioles are adjusted and this occurs in
a negative feedback fashion Slide 52 Arterial blood pressure has
increased Could happen if one quickly drink a large volume of water
Or going from standing up to lying down Increase in bp and want to
bring down to the normal value This increase is detected by the
baroreceptors Causes the firing to increase Firing is detected and
integrated by the cardiovascular center in the brain stem It adjust
the sympathetic and parasympathetic activity in the heart and blood
vessels Heart If blood pressure increased, decrease cardiac output
must occur to bring heart rate down Parasympathetic control So
heart rate has to slow down by increasing the parasympathetic
activity through the vagus nerve and m2 receptors Need to increase
vagal tone The increase in parasympathetic activity will in turn
decrease heart rate and decrease cardiac output Sympathetic control
Decrease in sympathetic activity will lower heart rate and stroke
volume 1 receptor activation allows for this all of these process
will lower heart rate and in turn lower blood pressure the
vasomotor center in order to reduce bp vasodilation is needed in
this center vasodilation is achieved by decreasing sympathetic
activity which decreases tonic activity in the arteries and veins
and this will cause them to dilate which lowers resistance and
reduces bp 1 receptors are involved when baroreceptors are at the
normal resting value, then everything is in the tonic/background
level of activity and there is no need to change activity as soon
as activity changes and any minor changes in bp are immediately
corrected through this pathway problem with baroreceptors is that
they adapt to the change of pressure over time if one has
consistently high bp(hypertension) the baroreceptors reset so that
the high bp becomes the new norm same thing for hypotension the
adjustment of vasodilation/constriction arterials cause an
immediate effect on pressure b/c such activity affects resistance
on the other hand the adjustment of vasomotor tone to the venous
system, venous return is affected which affects cardiac output
which affects blood pressureExercise increases met rate an in turn
increase O2 consumption by 5-10x this mean that increased oxygen
delivery to the exercising tissues in part this oxygen delivery is
the responsibility of the circ system to meet the high O2demand
caused by exercise an increased cardiac output is needed so more o2
can get to the tissues there is also a redistribution of cardiac
output some tissues are not used very much where other are heavily
used the blood is redistributed to meet the needs of the tissues
slide 54 the blood flow priorities during rest+ exercise Large
increase in cardiac out put Significant changes where the blood is
going to But these changes occur with only small consequences on
blood pressure P=QR P remains the same Increase in Q R would
decreaseCirculatory responses to exercise Hyperemia Exercising
muscles need increased blood flow Active hyperemia is one method of
achieving such It is a local metabolic effect Even before you start
exercising there is an increase in sympathetic activity in
anticipation of exercise This causes dilation of some of the blood
vessels in skeletal muscles b/c some of the sympathetic neurons can
release ACh As the sympathetic system is activated there is some
vasodilation to the skeletal muscle As soon as the muscle starts
exercising active hyperemia takes over and massive blood flow to
exercising muscle can occur Increases Cardiac Output This increase
in blood flow has to be met with increasing cardiac output The
increased sympathetic activity increases heart rate and the force
of contraction of the heart Peripheral Vasoconstriction This will
be achieved through the1 receptors Blood flow going to abdominal
organs will be reduced It could cause vasoconstriction in muscle
fibers but active hyperemia takes over Does cause constriction of
the veins; this is a benefit because it increases venous return and
this helps to increase cardiac output As you exercise the skeletal
muscle pumps in the legs also promote venous return and this helps
cardiac output An increase in cardiac output tends to increase bp,
however at the same time there is an increase in cardiac output
there is an overall fall in peripheral resistance The fall in
peripheral resistance is driven primarily by vasodilation in
skeletal muscles There is vasoconstriction to abdominal muscles but
this constriction is offset by the vasodilation in the skeletal
muscle So over all resistance falls and cardiac out increases and
pressure stays the same
Gas Exchange
Basic Principles Large animals, with high met rates need a
circulatory system to deliver oxygen to the tissues b/c diffusion
isnt fast enough to keep up They also have a dedicated gas exchange
system This is the point at which O2 enters the animal and CO2
leaves the animal Regardless of looking at a small animal w/ a
small met rate or a larger complex animal what drives oxygen
movement is the same He partial pressure difference between the
environment and the tissues Cells use O2 meaning there is a partial
pressure gradient between the external environment and the cell O2
moves down that partial pressure gradient from out of the cell in
CO2 moves from the cell other external environment The Oxygen
Cascade What drives o2 into an animal is diffusion along its
partial pressure gradient And this o2 movement can be thought of as
a series of steps called the O2 Cascade High O2 levels in the
external environment Low O2 in the mitochondria where o2 is being
used for metabolism This difference of partial pressure between the
environment and the tissue site of o2 use that allows for o2
movement in other tissues Depending the complexity of the animal
there will be a series of steps Oxygen is delivered to the exchange
surface by some type of ventilation Transfer of respiratory gases
is Done in 4 steps in vertebrates Ventilation Brings o2 to gas
exchange surface Diffusion Across the respiratory epithelium
Carrying of O2 in the blood to the tissues Diffusion from the blood
into the tissues When this is broken down one ca see 2 steps where
diffusion is involved At the gas exchange surface At the tissues
And there are 2 steps where o2 is being carried by the bulk flow of
fluid Ventilation of air and water Blood flow These are convective
steps Diffusion This is the movement of molecules by random
Brownian motion Movement of gas by diffusion is driven by the
diffusion gradient which in the case of gases is the partial
pressure gradient pgas Diffusion depends on permeability
Kgas=estimate of permeability Diffusion of gas is much faster in
are than it is in water and this reflects the permeability
Permeability in part depends on how readily the gas dissolves into
the medium(air, water or blood) Gases are more mobile in air than
in water b/c they are more mobile in air Depends on surface area
Large the surface area the greater diffusion can occur And
diffusion is inversely proportional to thickness For fast gas
diffusion, a thin barrier is preferred Fick equation: Mgas = Pgas
Kgas SA/T Diffusion depends on P, not C Convection The gas is being
moved by the bulk flow of the medium and this medium can be air
water or blood The individual o2 molecules are carried by the
medium This is a much faster transport pathway allows higher rats
of gas transfer In terms of o2 delivery; the movement/flow of
medium and the conc of gas in the medium So how much o2 is present
the medium The flow of the medium times the concentration
difference tells you how much gas is being delivered Mgas = Vmedium
Cgas Convection plays a role in boundary layers Boundary layers are
regions next to the gas exchange surface that becomes depleted in
o2 Area where o2 has diffused from and is now low inn o2 b/c they
can become depleted in o2 they slow down diffusion convection
eliminates boundary layers by delivering o2 directly to the gas
exchange site/tissues how are partial pressure and convection are
related for gases partial pressure determines movement in terms of
metabolism what really matters is how much gas is present i.e. the
conc of gas these two variable are related see graph in slide 6
capacitance is a way of relating concentration to partial pressure
(slide 6) Capacitance = C/ P if pressure and capacitance is known,
one could calculate conc Capacitance of Air and liquids need to
considered separately Air looking at o2 and co2 in air they have
exactly the same capacitance b/c in air they follow the ideal gas
law when the ideal gas law equation is rearranges on can find the
slope of the relationship= 1/rt so ALL gases have the same
capacitance in air Fluid(blood/water) If air is put overtop of a
fluid where initially there is no o2 O2 will move into the fluid
according to its partial pressure gradient until the partial
pressures are the same in the fluid and the air This will occur by
diffusion Partial pressure of o2 in the fluid is going to
equilibrate with the partial pressure of o2 in the air over top so
there is the same partial pressure in both locations The
concentration of o2 in the gas vs the liquid will be different b/c
the conc of gas in the liquid will depend on the solubility of the
liquid for oxygen for o2 and whether there is anything in the
liquid to which o2 can bind Gas will physically dissolve in the
liquid and this is determined by solubility Knowing solubility you
can calculate the conc of gas in the liquid There is a chance that
o2 will react with the liquid and this will increase the conc of o2
in the liquid 2 cases O2 physically dissolves in the liquid Amount
hat physically dissolves is determined by the solubility
coefficient= depends on the particular gas, temperature and
salinity as temp goes up solubility goes down from we can calculate
the physically dissolved o2 C= P O2 is involved with additional
chemical binding Chemical biding of the gas The gas for o2 in blood
and for CO2 in water and in blood
Lec 8
When water is air equilibrated the CO2 concentration is water
and air is equal but the concentration of O2 in water and air
differ Conc of o2 is water depends on how much o2 can be physically
dissolved in the water and this is given by the following equation:
[O2]dissolved= PO2 x When going beyond water you end up with
binding of o2 to respiratory pigments like hemoglobin If the gas
chemically reacts with something in the solution then physically
dissolved gas no longer describes all the gas that is present You
will have to add in a term to described the amount of chemically
bound gas that is present Ex blood contains hemoglobin and oxygen
binds to hemoglobin therefore the conc of o2 in blood is the amount
of oxygen that physically dissolves in the plasma plus the amount
of o2 chemically bound to hemoglobin CO2 chemically reacts with
water They react to form carbonic acid which then dissociates in
bicarbonate and then this further dissociates to carbonate ions So
the conc of co2 is not only the physically dissolved CO2 but on top
of that you have to add the amount of co2 that has chemically
reacted with the water This includes the bicarbonate ions, and the
carbonate ions Note: the pH of a physiological system is one in
which we are only worrying about the bicarbonate It dominates b/c
the carbonate ions are pretty small and can be considered
negligible most of the time Co2 in blood It is physically dissolved
Co2 reacts with the water in blood and so the conc of bicarbonate
and carbonate ions are included Co2 chemically reacts with
respiratory pigments such as hemoglobin and co2 that is bound to
hemoglobin is called carbamino co2 Carbamino co2 describes the
amount of co2 that is bound to hemoglobin When there is more than
just physically dissolved as, capacitance is especially useful If
there is only dissolved gas then one can rely on the solubility
coefficient to give the conc of gas present Beyond that(^^) the
value of capacitance describes all of the different ways the gas
can be carried in the liquid It includes things like O2 bound to
hemoglobin, or co2 that is chemically reacted with water is a
functional measure of solubility it will tell you how much gas is
in the liquid whereas the solubility coefficient will only tell you
the amount of gas that physically dissolved in the liquid movement
of o2 into animal can be divided into 4 steps oxygen is brought to
the gas exchange surface this involves ventilation so it involves
air or water moving across the gas exchange surface this is a
convective step the o2 has to move across the respiratory surface
this is a diffusive step and so it relies on the Fick equation o2
is carried in the circulatory system to the tissues sites of use
another convective step b/c the gas is being carried by the blood
o2 moves from the blood into the tissue site of use this is a
diffusive step relying on the Ficks equation can use this exact
same model for co2 however its in reverse for any convective step,
the amount of gas that Is moved Mgas=flow of medium carry it (air,
water or blood) X the concentration mgas= amount of gas that is
movedGas transfer revisited MO2 = Vm (CiO2-CeO2) i=inspired
E=expired How much air youre breathing multiplied by the difference
between your expired and inspired are in the amount of o2 that is
present Or it's the amount of water a fish is breathing multiplies
by the difference between inspired water and expired water in the
o2 content Sometimes its difficult to measure concentration and its
often easier to measure pressure Because we have a relationship
between concentration and capacitance, concentration can be
replaced with capacitance Vm mO2 (PiO2-PeO2) This tells how much O2
is being carried to the gas exchange surface by the flow of
air/water V=flow(ml/min) MO2 = Vb (CaO2-CvO2) = Vb bO2 (PaO2-PvO2)
Here we can calculate amount of O2 in the blood Here we use blood
flow so Vb As well as arterial(a)and venous(v) content Or Pressure
The flow of blood multiplied by the difference between the arterial
venous blood in terms of how much blood is being carried Arterial
blood brings O2 to the tissue and the Venous blood flows away from
the tissue The difference between tells how much o2 the tissue has
acquired In a well-designed gas exchange system, the amount of O2
moving through the system will be the same the whole way So at each
step we can look at a calculation for mO2 but if our calculate the
amount of oxygen that is being carried to the gas exchange surface
we should also note the amount of o2 that is diffusing into the
tissue(in s4) The amount of O2 moving should be constant within the
system The end game is to get o2 to the tissues. Everything
preceding that is just moving it into the system this is a handy
property b/c it means we can use things that are easy to calculate
such as the amount of o2 being delivered to the lungs in the air as
a proxy for things can are really difficult to calculate like the
amount of o2 being delivered to the tissues by diffusion its quite
difficult to calculate movement by diffusion even when given the
Fick equation b/c parts of the Fick equation are quite difficult to
calculate MO2 constant across system so can rearrange equations to
solve for unknown variables. MO2 = DPO2 KO2 SA/T Here is a eq of o2
consumption as a function of blood flow and blood o2 content If you
want to calculate blood flow; the rearrangement of the eq will
allow itBlood O2 transport O2 is carried in the blood both as
physically dissolved gas and gas that is bound to a respiratory
pigment(i.e. hemoglobin but there is a ton) Hemoglobin increases
the amount of o2 the blood can carry See slide 14 The amount of
just physically dissolved o2 in the blood is about 0.3 vol % The
amount of o2 present in the blood when you have a respiratory
pigment is 20 vol% Vastly more oxygen available b/c f chemical bind
fo2 to the resp pigment Hgb is an awesome o2 carrier Without Hgb in
order to deliver the necessary amount of o2 blood flow must
increase Ex crustacean + fish Crusts have to have a higher blood
flow b/c their hemoglobin holds less o2 How high does blood flow
need to be in anemic human beings in order for the human to meet
the normal o2 consumption of 1mmO2/g/hr. See There is a fish that
lacks Hgb The ice fish see the blood in slide 16 Its clear w/out
any Hgb This fish can survive without any Hgb by relying on
dissolved o2 only This means that the fishes cardiac output will be
very high This means the heart of an ice fish is fairly large The
heart is actually 3x larger than the hearts of similar red blooded
fish to accommodate for the need of a higher cardiac output It is
an ectothermic living in very cold temperatures Has a low met rate
Though the water is old and the solubility of o2 is really
highRespiratory Pigments Hemoglobin is not the only respiratory
pigment but it is the most common It is the respiratory pigment of
vertebrates; also found in a lot of invertebrates Called a
respiratory pigment because it changes colour depending on whether
o2 is bound to it or not. Hgb where O2 is bound(Hb-O2) is bright
red Deoxygenated blood deoxy-Hb is a blue-red (so purple...) In
crustaceans there is hemocyanin This hemocyanin is copper based
meaning when oxygenated their blood is blue Clear when deoxygenated
In annelids they have chlorocruorins which are green when
oxygenated and clear when deoxygenated Worms have hemerythrins and
this is violet color when oxygenated and clear when its not. The
Hgb molecule is a tetrameric molecule, so there are 4 subunits 2
alpha and 2 beta subunits And associated with each globin is an
iron based prosthetic group called the heme group This is where o2
binds 1 molecule of hemoglobin can bind 4 molecules of o2 Due to
the subunits each with their own heme group
