BIOL233 - Outline 5 (Circulation and Gas Exchange)

8/6/2019 BIOL233 - Outline 5 (Circulation and Gas Exchange)

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Circulation and Gas Exchange:

Readings:

Russell et al:

Chapter 37 pp. 891-896, 899-906

Chapter 42 pp. 1039-1053


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Main Topics:

Circulation:Open and closed circulatory systems

Cardiac cycle

Vasculature

Gas Exchange:Terminology: volume% and partial pressures

Ficks diffusion law

Water breathing

Air breathing

Gas transport (transport of O2 and CO2)


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Animals need to supply oxygen to the

mitochondria of the cells for oxidativemetabolismand remove waste product of

metabolism CO2.

Circulatory system provides the avenue fortransport of these gases


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Or, they have an extensive tracheal network which

allows gases to penetrate deep within body example:insects

They still have a cardiovascular

system, but its hardly used.


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Most animals, however, rely on a circulatory

system to transport gases.

Two types: closed and opened

Closed Circulating fluid (blood) is completely enclosed

within a series of blood vessels. At no time does theblood directly contact other body fluids.

Open circulating fluid (hemolymph) is allowed to enter

the body cavity and come into contact with other bodyfluids or tissue s themselves.


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Evolution of the closed circulatory system:

Given the colours (red and blue) refer to oxy- and

deoxygenated blood, what do you notice about fish heart

vs. the hearts of other vertebrates?


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Fish single circuit

one atrium- one ventricle:

They pump deoxygenated blood into

the gill. In the gil, there is exchange of

O2 and CO2 Blood becomes oxygenated as it travels

through the gill

Oxygenated blood is transported to

tissues exchange of O2 and CO2 at

tissues, which deoxygenated the blood,

which returns to the heart.

Known as in-series circulatory system.


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Amphibians (frog) dual circuits:

Two atria one ventricle

(Air breathers)

Known as in-parallel circulatory system.

Two atria one for deoxygenated blood, and

one for oxygenated blood.

Single ventricle pumps both oxygenated and

deoxygenated blood.


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Birds, reptiles and mammals dual circuits:

Two atria-two ventricles

Turtles, lizards

The ventricle has some

septa that are

beginning to divide theventricle into two sides.

Crocdiles septum is

more apparent.

Birds/Mammals total

sepration of R and L

ventricles

Purple vessel = Shunt

Shunt of blood away from lungs during

a dive to reduce blood thats not being

ventilated.


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Birds, reptiles and mammals dual circuits:

Two atria-two ventricles *Note: separation of

these two circuits.

Pulmonary circuit

- Low resistance- Low pressure

Systemic circuit

- High resistance

- High pressure

- Many more and more

extensive blood

vessels.


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Cardiac cycle: filling and emptying of the heart

Open circulatory system: Example crayfish or lobster:

Blood (hemolymph) flows into pericardial cavity

(surrounding heart) via openings in cavity

Hemolymph enter the ostia of heart during filling(diastole)

Heart muscle contracts (systole) ostia close and

blood is ejected out the arteries.

Heart is filledbysuctionValved ostia artery

^ Suspensory ^

ligament

Paricardial sac (rigid)

Paricardial cavity


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Open circulatory system: Example crayfish or lobster:

Suspensory ligaments stretch

Ostia close

Contraction forces blood out the arteries.

(Ostia is valved to prevent backflow)


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Steps in the cardiac cycle of vertebrate heart: example humanFilling occurs under pressure

rather than suction.

Diastole: pressure in atria is

greater than pressure in

ventricles get filling of

ventricles.

AV valves between atria

and ventricles which opento allow blood to fill

ventricle.

Then AV valves close to

empty ventricle.

diastole


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Steps in the cardiac cycle of vertebrate heart: example human

Systole -- Blood is ejected out

of ventricles into:

Pulmonary artery (right

side of heart) Or Aorta (left side of heart)


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Control of cardiac cycle:

Neurogenic vs. myogenic hearts

Example of neurogenic heart crustacean heart

Control is via a nerve ganglion (cardiac ganglion) that sits on

top of the heart.

It is not muscle tissue! It is nerve tissue.

This sets the pace of the heart.

Removal of cardiac ganglion heart will not beat.


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Neurogenic vs. myogenic hearts

Example of myogenic heart all vertebratehearts

The pace is set by modified muscle cells called pacemakers.

This includes SA node (primary pacemaker) and AV node

(secondary)

Heart will still beat on its own even if all neural

connections are removed.


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Pacemakers of myogenic hearts

Brown area = electrical excitation, starting at SA node. Excites

all the atria, which stimulates the AV node which excites theventricles.

AV node delay in wave of excitation so that the ventricle

doesnt contract at the same time as atria (ventricle wouldnt

have enough time to fill)


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Vasculature:

Closed system Composed of: Aorta,

arteries, arterioles,

capillaries, venules, veins


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Vessels in cross-section :

In systemic circuit:


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Surface area is

greatest at level ofcapillaries area of

nutrient and gas

exchange

Velocity of flow

slowest in capillaries

facilitates nutrient and

gas exchange

Artery Vein

ArteriolesCapillaries


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Control of flow to various capillary beds controlled by:

Vasodilation or vasoconstriction of arteriolar smoothmuscle

Opening or closing of pre-capillary sphincters


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Agents that cause arterioles and capillaries to open:

Increase in tissue fluid lactic acid Decrease in tissue fluid oxygen pressure

Increase in tissue fluid CO2 pressure

Decrease in tissue fluid pH

Ex. In a runner, more oxygenated blood goes to the limbs that

need it the most (legs) because of the above agents.


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Gas exchange O2 and CO2

Main Topics:

Terminology: volume% and partial pressuresFicks diffusion law

Water breathing

Air breathing

Gas transport (transport of O2 and CO2)


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Concepts and terms

Volume % - fraction of a gas in an atmosphere dry air

is 21% oxygen, 79% nitrogen, 0.03% CO2 (same

regardless of altitude)

Partial pressure that part of the atmospheric

pressure attributed to a particular gas

Is found by multiplying the atmospheric pressure bythe fraction of gas in the atmosphere


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Concepts and terms

For example:

the atmospheric press. at sea level is 760 mmHg

therefore the partial pressure of oxygen in theatmosphere is 0.21 x 760 = 160 mm Hg;

partial pressure of CO2 is 0.23 mm Hg;

partial pressure of nitrogen is 600 mm Hg


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In Calgary; atmospheric press. = 670 mmHg

PO2 = 141 mmHgPCO2 = 0.20 mmHg

Atmospheric press. at top ofMt. Everest = 250 mmHgPO2 = 53 mm Hg

All gas exchange in the simply gases diffusing down aconcentration gradient.

P = partial pressure


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All gas exchange occurs across a moist surface (whether aquatic or

terrestrial) and depends on Ficks Law of diffusion

Rate of diffusion depends on:mLO2/unit time

Or

mLCO2/unit time

To facilitate rate of diffusion:

1. Large surface area for gas

exchange

2. Reducing thickness of membrane

across which gas is going tomove (ex. Flatworms have very

thin skin, gases just diffuse through

membrane)

3. Keep difference between partial pressure to favour

movement of gas in that direction

Surface area^

of gas exchange

surface


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Organisms one or two cell-layers thick (like cnidarians)

do not need special respiratory organs gases simplydiffuse across cell membranes..

but multi-layered animals have to have a respiratory

organ of some sort.


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Breathing in aquatic environments:

Gills may be external (stick out into environment) or

internal (enclosed by some sort of covering)External: no energy is wasted trying to pump water over surface of

gill when water just glides over gills. But gills become exposed to

damage or predation.

Internal: gills are not as subject to damage, however, there needsto be a device to pump water over the gills.


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Internal gills have to be ventilated.

Cavity containing gills is ventilated by drawing or forcingwater over gills.

Gill bailer sits at the front of the gill chamber and acts like a

paddle so that water is sucked up over surface of the gills, and

water is collected and forced out through the front of theanimal. A current is created by moving the little gill bailer at

the front of the animal.

Gills are protected.

But a lot of energy is required


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For example: In crayfish, scaphognathite (gill bailer)

creates a negative pressure in gill chamber thus drawing

water over gills.


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In fish, operculum and mouth are used to move water

over gillsGreen bar = floor of mouth which can move up

and down. Flaps allow water to come in and outof mouth.

Suction phase lower floor of mouth, opens

mouth and water flows into gill.

Force pump floor of mouth moves up, squeeze

fluid out the operculum and mouth closes.


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Anatomy of fish gill:

Gill arch composed of stack of gillfilaments each gill filament has

secondary lamellae


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Countercurrent flow of water over gill:

advantage: allows for continuous diffusion gradient all along

surface of secondary lamellae.

% saturation with O2

% saturation with O2


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Breathing in terrestrial environment:

Advantages over breathing water

1. There is more O2/unit volume in air than in water at the

same temperature. Three times more O2 available in air than

in water.

2.Air is less dense, and therefore less energy is

required to move air over gas exchange surface

Problem with breathing air : desiccation (losing vapor)

Solution : Internal the gas exchange surface.

Humidify the air as it enters the animal.


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Air breathing: positive pressure ventilation of the lungs

Example: frogsInhalation:

1. Open nostrils and lower floor of

buccal cavity air moves into

buccal cavity. Glottis is closed.

2. Close nostrils and raise floor of

buccal cavity air is forced intolung. Glottis is open

(Buccal cavity is like the floor of the

mouth)


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Exhalation: elastic recoil of lung wall

forces air out of lung and through

mouth and nostrils


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Air breathing: negative pressure ventilation of the lungs

Negative pressure ventilation examples mammals and

birds ..


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Pressure more

negative than

atmosphere


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Negative pressure ventilation: in mammals

Inhalation:

1. Outward movement of rib cage (by contraction of

intercostals muscles) and diaphragm contraction expands

thorax and lung creating sub-atmospheric press. in lung

2. Air flows into lung via nasal passages and mouth because

pressure in expanding lung is less than atmospheric

3. Eventually air flow stops at point of max expansionbecause as the lung fills with air, pressure diff. between

lung and atmosphere becomes zero.


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Negative pressure ventilation: in mammals

Exhalation:

1. Intercostal muscles relax and lung recoils.

2. Air is forced out because lung pressure exceeds

atmospheric pressure.

In mammals tidal flow of air means some exhaled air is

always mixed with fresh air

Old dead air is mixed with fresh air, so air found in lung has a

lower partial pressure than in the atmosphere.

Rapid, shallow breathing is not as good as deep, slow

breathing.


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Negative pressure ventilation: in birds

Lung is a series of parallel rigid

tubes (parabronchi) connected

to air sacs on either end.

Air sacs expand and contract

with each ventilation cycle.

Air continually moves across

the lung

The lung does not expand orcontract! It stays the same size.

The air sacs are what expand

and contract.


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Inhalation:

1. Outward movement of thorax (by contraction of

intercostals muscles) expands air sacs creating sub-

atmospheric pressure in air sacs.

2. Fresh air flows into posterior air sacs via nasal passages

and trachea.

3. Air in lungs is sucked into anterior air sacs.


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Exhalation:

1. Fresh air (high in oxygen) from posterior air sacs moves

through the lung

2. Air in anterior air sacs is forced out of trachea and nasal

passages


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It takes two cycles (i.e.

two inspirations and

two expirations) for anair molecule to move

though both air sacs

and lung.Red = fresh air

When we breathe in, fresh air

goes to posterior sacs.

On the next expiration, air is

forced over the parabronchi

(parallel lines).On the next inspiration, the

air that has gone over

oxygenation, it gets sucked

into anterior sacs.


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Insects - dont have lungs or gills - use trachea to breath

Trachea series of blind-ended tubes that lead from the surface of

the abdomen to muscle tissue deep within the insect.

The opening is guarded by a spiracle which can be open or closed

when desired.

No circulatory system is necessary to deliver oxygen to tissuebecause trachea terminate right in the tissue.

Ventilation of gas exchange surface in Insects:


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Ventilation of gas exchange surface in Insects:

Tube opens up, and oxygen simplydiffuses through tube and directly

to the cells that need the oxygen

supply.


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Larger insects can increase ventilation by contracting and relaxing

abdominal muscles which squeeze the tracheal system and force air

through it.

Flight muscles increase tracheal ventilation in flying insects during

flight.

Contracting and

relaxing wing

muscles facilitates

squeezing the

trachea andincreases

ventilation. The

air moves faster.


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Gas transport:

Except for the insects that use a tracheal system to supplyoxygen to their tissues, most animals transport gases using a

circulatory system and have a respiratory pigment in the

circulating fluid that allows them to transport more gas than can

simply dissolve in the fluid.

Gas transport in animals with no resp. pigment gases are

dissolved in circulating fluid


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Gas transport:

Gas transport in animals with respiratory pigment gases aredissolved in circulating fluid, but much larger % of gas transport

via resp. pigment.

example: human blood carries about 3 mL O2

/L dissolved in

blood plasma

but as much as 200 mL of oxygen can be carried by

hemoglobin/L of blood.

therefore 1.5% of oxygen is dissolved in blood plasma and 98.5

% is carried bound to hemoglobin


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Gas transport:

Respiratory pigments include

hemoglobin, hemerythrin, hemocyanin, chlorocruorin

All vertebrates use hemoglobin as their resp.

Dont memorize all these. Just know that hemoglobin is the

most common pigment, and that there are more than one type

of respiratory pigment.

^red ^purple ^blue ^green

when oxygenated


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Gas transport:

Hemoglobin structure: made up of four protein subunits calledglobulins (alpha and beta) each with a porphyrin ring containing

iron

Four porphyrin rings each containing Fe+2 that binds a

molecule of oxygen

porphyrin ring = green thing

Curly blue and red things are

proteins.

Iron binds oxygen.


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Gas transport:

Oxygen binding:

Somewhere from 30-60 Po2, % saturation of hemoglobin

increases rapidly.


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Gas transport:

Oxygen binding:

Between

30-60


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Gas transport:

Oxygen binds cooperatively to hemoglobin (Hb) i.e. binding ofone molecule facilitates the binding of more to the Hb hence

the rapid increase in binding between 20 and 60 mm Hg.

In lung:PO2 = 100mmHg


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Gas transport:

At level of gas exchange surface (where the PO2 is 100 mmHg) Hb quickly becomes saturated with oxygen;


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Gas transport:

Bohr shift helps unload even more oxygen Increased acidity = lower pH in tissue = lower pH in blood.Red line = normal arterial blood pH

Blue line = pH of blood after picking up acid from tissues (Venus blood)

Venus blood picks up CO2, lactic acid, and other organic acids from

the tissue, which lowers the blood pH.

Increased blood CO2 =

decreased blood pH

% saturation ofhemoglobin at the

lung is not affected by

the Bohr shift.


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Gas transport:

CO2 is also carried by Hb (and is also dissolved in plasma or asHCO3

-) from tissues to gas exchange surface.

CO2 diffuses into red blood cell. Inside

the red blood cell,

CO2 + H2O H2CO3H2CO3 H+ + HCO3-

HCO3- diffuses into blood plasma.

At the lung, this whole processes is

reversed.

BIOL233 - Outline 5 (Circulation and Gas Exchange)

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