Bio 3302 Lec 2 Mechanisms of oxygen delivery and co2 removal is based upon 2

systems circulatory system and respiratory system Oxygen moves around in cells by the use of diffusion

o The time for diffusion depends on how far the oxygen has to travel

o Time required= distance2 As distance gets larger time required to increases fairly

quicklyo Larger animals need a system to enhance the rate of delivery of

oxygen Metabolic rate also come into play in terms of oxygen delivery

o The higher the metabolic rate the more oxygen needed Ex large animals with very low metabolic rates may not

really need a circulatory system Ex 2 small animals with very high met rates may need a

circ system in order for faster O2 deliveryo Once animal that is an exception to this rule of having a high

met rate= having a circ system These are insects. They have the highest known met rates

but don’t use their circ system for oxygen delivery This is b/c they have a tracheal system which circulates

gas until it is very close to the tissues and then oxygen diffuses from the end of the tracheal system into the mitochondria

Circ system can also be used foro Waste excretiono Nutrient deliveryo Cell to cell communicationo Hormone transporto Thermoregulation

Circ syst will transport anything that can move in a fluid but it can also transport heat

o Generates force Animals with hydrostatic skeletons rely on fluid force

generated by the circ systemo Animals that need to enlarge or extend an organ also uses the

circ system to do so. Ex monarch butterfly

Monarch caterpillars and they use the circ system to move

Once they are done feeding off milkweed they will form into a crystal

And they emerge from the crystals with their wings folded up the force that unfurls their wings is hydrostatic force provided by a circ system

Circ system has 3 key elementso A pump

Usually a heart but not always The pumps work by generating force and pushing the fluid

a head of them(+pressure) 3 basic types of pumps

Peristaltic pumpo Ex type of heart found in insects and

crustaceanso It’s a tube with muscular walls and a wave of

contractions passes along the tube pushing the blood in front of it

o This heart has force generation and direction built into one

Direction in which contraction moves determines the direction in which the blood moves

Chamber pump with contractile walls Ex Human heart

o muscle chamber and when muscle contracts it squeezes the blood pushing it out

o in order for blood to move in the right direction a series of valves are needed to direct the flow

chambered pump with non-muscular walls; but is surrounded by external factor(muscle) that compresses

o this also needs valves to direct flowo the external muscle will contract squeezing

the chamber and then the valves determines where the fluid flows

o ex of this type of pump in humans The large veins in the leg act as

chambers to collect blood and when one moves their legs muscle contraction squeeze those veins to return blood to the heart.

o Network of vessels(vascular system) 3 types of tubes

Arterieso Take blood from heart to the periphery of the

animal

Capillarieso Specialized for exchange of material

Veinso Collect blood from periphery and take it back

to the heart Not all 3 are present in all animals Collectively known as vascular system or peripheral

systemo Circulating fluid

This can be blood or haemolymph Open vs closed system shows where you see the presence or absence

of the diff types of blood vessels(bv’s) Open Circulatory System

o Animals with open circ system do not have capillarieso Blood will be pump by the heart into a set of arteries form there

it goes to the tissues directly The blood bathes the tissues directly; there is only

exchange between the circulating fluid and the tissues themselves

o Circulating fluid is then collected up and returned back to the heart and this may/may not involve some type of venous system

o It is quite difficult to direct flow with an open system Tend to be low flow, low pressure, low resistance systems

o If the system of vessels is open one cannot distinguish between the circulating fluid and the fluid that is bathing the tissues directly

o Animals with open circ systems have haemolymph instead of ‘blood’

Makes up 30% of animals body mass Closed Circulatory system

o The blood is in vessels the entire way; from leaving the heart to returning to the heart

Animals with higher met rates tend to have closed circ systems

This is a evolutionary trendo Reason for this trend is the ability to better

control the rate of blood flow and hence the rate of O2 delivery with a closed separated system

As met rate increases you tend to see the trend of closed circ system

Within these animals a second trend can be seen As met rate goes up there tends to be more

separating of blood flow to the gas exchange

organs(resp circ) and blood flow to the rest of the tissues(systemic circ)

o As met rate goes up there is an increased separation between the respiratory and systemic circulatory systems

o The animals with higher metabolic rates are air breathers and along with this there is a shift to separating out the respiratory and systemic circulation

Basic fish plan; o Closed implies that there is a complete set of vessels

Blood leaves the heart and arteries exchange between the tissue and blood occurs in the capillaries and blood returns to the heart in veins

It is a continuous circuit of vessels with an exchange between the circulating fluid and the tissues happening at the capillaries

o These circulatory systems are found in all vertebrates(fish, amphibians, reptiles, mammals, birds) and in a number of invertebrates particularly ones that have a high metabolic rate(cephalopods-squid and octopus; or in animals that use the circ system for a hydrostatic skeleton-earth worm)

o b/c blood is circulating in vessels all the time the circ system provides quite a bit of resistance to flow and so higher pressures must be generated in order to move the blood through the closed systems of vessels

these are often considered to be high pressure/high resistance systems

more force must be generated to move the fluid around but they are able to direct and control the speed of the

flowo In this case one can distinguished between the circulating

fluid(blood) and the fluid that bathes the tissue’s (interstitial fluid ISF)

Blood contains red blood cells and proteins in the palms ISF lacks both rbc’s and proteins Keeping blood and ISF separate is quite important

Plasma proteins that escape from the blood and into the ISF have to be collected up and returned to the blood

o The is a function of the lymphatic systemo Together the blood and ISF make up the ECF(in both closed and

open systems) ECF accounts for about 30% of body mass

But in this case blood is only about 5% of that total with the remaining amount being the ISF

Fisho The circulatory plan in the fish is fairly simple

Blood is pumped by the heart, goes to the gills and is oxygenated, the oxygenated blood is carried to the systemic tissues where it gives up its oxygen and the blood returns to the heart

o The problem with this circ sys is that the heart has to pump blood to the gills and the systemic circulation both of which are sites of resistance

Heart must generate relatively high pressures The gills as the first point of the system are going to see

relatively high points of pressure They are able to withstand this because there is

water on the other side of the gill to counter balance this pressure

Pressure of the system as a whole is limited to the pressure that the gills can withstand

o Fish heart has 4 chambers in a series Blood enters the sinus venoses the atrium

ventriclebulbous or conus arteriosis The ventricle is where the main force generation

occurs Bulbous and conus arteriosis are structurally

different but share the same purpose functionally which is to maintain blood flow when the heart relaxes

o Same function as the aorta in a mammalo Sinus venosus is only found in fish; it disappears it land living

organisms Mammals and birth

o Essential there are 2 two chambered hearts They are physically together in the same organ however

when broken down you have 2, 2 chambered heartso The left side of the heart and a right side.

Left side Always on the right when looking at a diagram and right side is the left in the diagram

o The left side of the hear takes blood returning from the lungs and pumps it out to the systemic circulation

o The right side of the heart takes blood returning from systemic circulation(deoxygenated) and it pumps it to the lungs to be oxygenated

o Each side of the heart both have an atrium and a ventricle Left for systemic; right for pulmonary

o Low pressure is needed in the pulmonary circuit and high pressure in the systemic circulation

This is possible because in effect they have 2 hearts The left/right sides are operating independently So the left ventricle can generate high pressure to send

blood to the systemic circulation The right ventricle generates lower pressure to send blood

to the pulmonary circuito The only problem with this circulatory design is that blood flow

always has to go to both parts As it comes back from the systemic circulation it has to go

back to the pulmonary circuit There is no way to stop blood flow to the lungs (like when

you hold your breath...doesn’t happen bud) Intermittent air breathers- amphibians; reptiles+ air breathing fish

o Typically have lower metabolic rate o Heart has 2 atria; one for blood collection from the lungs and

one that is collecting blood from the systemic circulationo Typically has one ventricle- that directs the flow of blood to the

tissues In reptiles its partially separated into a left and right

ventricle In amphibians there is only one ventricle

So deoxygenated blood from the tissues and oxygenated blood from the lungs come into the same ventricle and are pumped out to the lungs and tissue

o Even though there is a single ventricle the oxygenated and deoxygenated blood is relatively separated

The mechs for this are not well understoodo Blood pressure in this animal as a whole is fairly low

Having a high bp will destroy its lung Bp is limited by what the lungs can withstand Low bp and low met rate animals

o The advantage of this is that when the animal is under water/ holding its breath the lungs become useless

So the system reduces blood flow to the lungs and redistributes it to the skin where it can still take up oxygen

o When it resurfaces it redistributes the blood back to the blood It has the capacity to shunt blood to diff organs depending

on its require The presence of a single ventricle makes this possible

o Same idea is seen in reptiles though there is as light separation in ventricles

o Same plan in air breathing fish

lung fisho These fish can drowno Obligate air breathing fish without any access to air they will

drowno They have a set out gills, a lung and a hearto They have low met rateso Tend to breath once every five minutes

During the rime spent underwater the animal is depleting the oxygen in its lung

o There is a single 4 chambered heart (like a standard fish heart) As the blood leaves the heart it is directed to the gills The gills are separated into anterior gills which are not

used for O2 uptake and posterior gills which are used for O2 uptake

From the posterior gills the blood moves up either to the lung-if there is usable oxygen here- or if there is no useable O2 in the lung the ductus opens up and directs the blood from the gills to the systemic tissues

Oxygenated blood is directed by anterior gills to the tissues

Deoxygenate blood is directed to posterior gills which direct to lungs if there is air there or it its directed to the tissues

The state of the ductus determines whether the blood goes to the tissues or to the lungs

o The ventricle generates pressure for the lungs, gills, systemic tissues. Systemic circuit as a whole

Must be a low pressure pump so the lungs are blown These are low met rate animals

Lecture 3Mammalian heart

Systemic half on the left has much thicker walls which allows for higher levels of pressure

Blood returning from lung enters the left atrium and from there goes into the left ventricle and is pumped out to the systemic tissue where it is deoxygenated

o The deoxygenated blood is pumped into the right atrium and then into the right ventricle and is pumped out to the lung

This heart is a chambered heart with contractile walls and based on this there are valves that direct blood flow

In the mammalian heart there are vales between the atria and the ventricles to control blood flow

Heart is made of cardiac muscleo It is similar to skeletal muscle

o These are considered to be striated because they contain sarcomeres

o They are quite short and are connected end to end by intercalated discs

In these discs one will find gap junctions Which are communicating junctions that allow

electrical communication between the different cells of the heart so they can contract as a unit

o The heart is innervated by the ANS Within the ANS; there are 2 divisions

Sympathetico Responsible for fight/flight alarm type

situationso Neurotransmitter of choice is noradrenaline

Interact with receptor in the tissues that are adrenergic receptors

o B-1 receptors are more important for the heart Parasympathetic

o Responsible for housekeeping or vegetative functions

o ‘the rest and digest system’o Responsible for functions outside of alarm

situationso Neurotransmitter of choice is acetylcholine

Interacts with muscular genic receptors in the effector organ

Main one for the heart is the m2 receptor

Both sympathetic and parasympathetic divisions are active and in most tissues you can find innervation from both

Heart is innervated by both but they have opposite affects

o Sympathetic will increase heart rate to allow for response in emergency situation

o Parasympathetic will slow it down They have antagonistic effects

ANS allows good control of internal functions without any conscious control

Most of the heart is made of cardiac muscle cells and these come in two types

o 99% is made up of strongly contractile muscle cells Packed full of sarcomeres; responsible for generating

force o Other 1% are the cells of the conducting system

Pacemaker cells

They do not have a lot of contractile apparatus’ They are specialized for controlling and coordinating

heart beat Include the cells of the sinoatrial node, the atrial

ventricular node and the other cells forming the conducting system that direct electrical activity over the heart as a whole

The pacemaker cells have a resting potential that is quite unstableo They have arresting potential that changes over time-pacemaker

potential and the presence of this changing resting potential is the key characteristic of a pacemaker cell

o The pacemaker cells slowly depolarize because of the changing membrane potential and when they reach a certain threshold they trigger an action potential which the trigger a heartbeat/ contraction of heart

Initiate heart beat+ control ito The pacemaker potential reflects the presence of the ‘funny

channel’ It is considered to be funny because it is open and then

slowly closes and it functions as a Na+ leak channel Allows Na+ to leak into the cell causing a gradual

depolarizationo Also present in the cell are voltage gated Ca2+ channels(t-

types) when the membrane potential depolarizes to the

threshold these channels open and it creates an action potential

o this is what initiates the heart beat in a vertebrate heart and because it is a muscle cell for the initiation of this heart beat; vertebrates hearts are considered to be myogenic

neurogenic: nervous activity activate heart beat gap junctions allow electrical communication between cells

o once an action potential is fired within a cell that is then spread to the other cells in their heart

o spreads from one heart cell to another by the gap junctionso the heart rate is then set by the cells that depolarize most

quickly and these happen to be the cell of the sinuses venoses in fish or sinoatrial node in mammals

pacemaker cells set the heart rate the pacemaker cells in human sinoatrial node fire at rate of 100 time

per minuteo 100 depolarization’s a minuteo This means the heart rate should be 100beats/mino Heart beat is controlled by other mechanisms

There is input from the parasympathetic nervous system that regulates heart rate

Sinoatrial node is in the atrium of the mammalian heart and it fires its action potential first and this spreads across the atria real quick

o It slows down when it gets to the atrial ventricular nodeo There is a layer of connective tissue between the two atria and

the two ventricleo The cells of the atria re connected by gap junctions and the cells

of the ventricle are connected by gap junctions But the atria and the ventricles do not communicate This layer of connective tissue means there is no electrical

communication between the atria and ventricles except through the atrial ventricular node

Conduction though this part of the system is quite slow Once it gets through this system it speeds up

tremendously and shoots up through the ventricles at a rate of 4or 5 m/s

ECGo Measures the consequence of all the action potentials in the bod

fluid as a whole It is the sum effect of all the action potentials happening

togethero Measured by placing electrodes upon the body’s surface not by

trying to impale a single heart cell to measure membrane potential of that cell

o In the standard mammalian EKG there is a small wave called the p wave

This shows the atria depolarizingo There is a larger wave(QRS): this is the ventricles depolarizingo Small t wave- this is the ventricular repolarizationo The repolarizing of the atrium is not seen because it occurs at

the same time that the ventricles depolarize and so it is masked by this

o Value of the EKG tries to figure out what is going on in the heart The heart as a pump

o Electrical activity in the conducting system has to be converted into muscle contractions in 99% contractile part of the heart

To get these cells to contract the heart first has to be depolarized

A strong action potential is needed in the muscle contractile cells (an ex can be found in slide 22/23)

There is stable resting potential; there is a strong depolarization, then there is a plateau phase

Slide 22 Action potential f contractile cells

o Stable resting potential and when it is triggered it undergoes depolarization and a voltage gated Na+ channel opens allowing Na+ to pour into the cell and this gives you a strong depolarization

There is also a voltage gated Ca2+ channel that opens a little bit later and this calcium channel stays open for a while and that is how one gets the plateau region

This is an L-type gates calcium channel; in pacemaker there is a t-type calcium channel

The flow of calcium into the cell triggers calcium release from stores within the cell

o Not only have calcium moving into the cell through the voltage gated channels you also have calcium being released from stores inside the cell

o The release of these stored calcium the triggers the contraction of the cell

Calcium inflow + calcium released=occurrence of muscle contraction

o The cell then repolarizes and this represents a K+ channel that is opened which allows K+ ions to flow out.

o Note in the diagram there is a prolonged plateau phase and a refractory period

This is long refractory period is important because the heart has to relax and refill with blood before it can contract again

So the refractory period allows for the cells to rest and reset as well as gives time for the heart to relax and be refilled with blood

The long plateau in the action potential is necessary because it allows all the muscle cells to contract at the same time

This also makes sure that the heart cannot go into a tetanic contraction-no muscle cramp in the heart

Refractory period: period where the cell is resting before another AP can occur

Slide 23 Systolic

o When heart is contracting Diastolic

o When the heart is relaxing Stroke volume

o Volume of blood pumped b the heart

o When heart contracts it ejects a volume of blood called the SV and this is the difference in volume of the heart when it is full(end diastolic volume) and after it contracts(end systolic volume)

Most of the filling of the ventricles is due to venous pressure o The valves between the atria and ventricle sis open and so the

blood flow through the valves to the ventricle from the atria o This is driven by venous pressure; the atrial contraction helps

but it is only responsible for 1/3 of the volume in the ventricle Venous pressure does all the work

For the heart to function properly output from the heart must match the need for oxygen delivery

o This can be achieved by increasing heart rate or stroke volume o Regulation of stroke volume is referred to as inotropic control

and its caused by both a mechanical relationship and neural and hormonal control

The mechanical relationship is the frank-starling relationship

See in slide 23 It shows that as end diastolic volume increases(as

heart if filled) SV also increaseso The fuller the heart the more forceful the

contraction and this ejects more blood It is ;mechanical b/c as you fill the heart fuller it

stretches out muscle and this result in a more forceful contraction

Very important because you always want to empty the heart to the same point so by filling the heart fuller you need more blood out of it to get back to the same empty point

As heart rate goes higher there is less time needed to fill it with blood and so the SV gets smaller there hormonal and neural; mechanisms to accompany the mechanical relationship and these mechs work to stoop stroke volume from falling

o Neural/hormonal control of the heart The sympathetic nerves innervate the ventricles and

strongly contractile muscle cells they release noradrenaline which acts on ß1 androgenic receptors and this increases the force of contraction

As you increase sympathetic activity at any given volume more blood is released from the heart; vice versa for decreased sympathetic activity

Frank Starling relationship describes the change in SV for a change in filling

o For any given level of sympathetic stimulation there is a spec frank starling curve

o (only sympathetic control over SV)o Circulating catecholamine’s

Sympathetic cells release noradrenaline The cell that you find in the centre of the adrenal

gland are sympathetic neurons but instead of releasing neurotransmitter onto the nerve it releases the NTM into the blood and it circulates as a hormone

Which is responsible for the fight or flight response This too can regulate strong volume by acting on the

ß1 adrenergic receptors heart rate

o controlling heart rate is the chonotropic effect o the pacemaker is innervated by both the sympathetic and

parasympathetic systems contains ß1andrenrgic receptors activated by sympathetic

system or by circulating catecholamine’s also contains m2 muscarinic receptors activate by ACh

which are activated by the parasympathetic system sympathetic leads to an increase; parasympathetic causes

it to decreaseo Sympathetic nervous system

When the ß1 receptor is activated by adrenaline or noradrenaline it acts to open the sodium channels more to get a faster depolarization(faster pacemaker potential)

o parasympathetic When ACh acts on the m2 receptors it has the effect of

opening up potassium channels which allows positively charged ions escape from the cell and there for it depolarizes more slowly

The consequence of this is as low heart rateo At rest both the sympathetic and parasympathetic systems are

activeo Sympathetic tone which helps set the resting heart rateo Parasympathetic tone

Parasympathetic nerve that goes to heart is the vagus nerve(can also be called vagal tone)

This also helps set the resting heart rate.o Chonotropic effects only affects the pacemaker potential