Mammalian Circulatory system

Topic: Mammalian Circulatory System

Class Reporter: Elino, M. M. H.

Class Instructor: Geonyzl Lepiten-Alviola, MSBio

Animal Physiology: Mammalian Circulatory System Class Reporter: Elino, M. M. H.

REPORT OUTLINE:

I- Brief Introduction of the Mammalian Heart

II- Pumps: Mechanical Events of the Mammalian Cardiac Cycle

III- Pumps: Cardiac Output and Its Control

IV-Pumps: Nourishing the Vertebrate Heart Muscle (Coronary Circulation)

VI- Circulatory Pathways and Vessels

VII- Vessels: Flow Regulation and Hemodynamics

VIII-Pathways: Open Circulation

IX- Pathways: Closed Circulation


Brief Introduction on Mammalian Heart and Circulation

The Mammalian Heart has four chambers:

Right Atrium, Left Atrium, Right Ventricle, Left Ventricle

1) The Right Atrium and Left Atrium are reservoirs for blood (to be sent
to Right Ventricle and Left Ventricle)

2) The Right Ventricle and Left Ventricle are the main pumping
chambers of the heart




Right Atrium Left Atrium

Left Ventricle
Right Ventricle



The Mammalian Heart has four valves:
two Atrioventricular Valves (AV) and two Semilunar Valves (SV)

1) Tricuspid Valve – an AV valve between Right Atrium - Right Ventricle

2) Bicuspid Valve – an AV valve, also called “Mitral Valve” between Left
Atrium and Left Ventricle

3) Pulmonary Valve – a SV valve between the Right Ventricle and
Pulmonary artery

4) Aortic Valve – a SV valve between Left Ventricle and Aorta

Valves act as one-way doors to keep blood moving forward




Pulmonary Valve Aortic Valve

Tricuspid Valve Bicuspid Valve



Other Parts
Aorta

Superior Vena Cava Pulmonary Artery

Sinoatrial Node
Pulmonary Vein

Atrioventricular Node
Septum
Bundle of His
Purkinjie Fibers

Inferior Vena Cava Myocardium



The Circulation (Brief Diagram):

Deoxygenated blood from the body returns to the heart via:

Superior and Inferior Vena Cava Right Atrium Tricuspid Valve

Right Ventricle Pulmonary Valve Pulmonary Artery Lungs

(the blood now comes oxygenated)

Oxygenated blood from the lungs returns to the heart via:

Pulmonary Vein Left Atrium Bicuspid Valve Left Ventricle

Aortic Valve Aorta Body (the blood now comes deoxygenated)


Pumps: Mechanical Events of the Mammalian Cardiac Cycle

The cardiac cycle consists of alternate periods of

Systole – the contraction and emptying

Diastole – relaxation and filling

In vertebrates, the atria and ventricles go through separate cycles of
systole and diastole.



Hearts alternately contract to empty and relax to fill.

Contraction – occurs as a result of the spread of excitation
across the heart; depolarization of the muscles of the heart follows the
contraction.

Relaxation – follows the subsequent repolarization of the
cardiac musculature.



ECG – Electrocardiogram

The electrical currents generated by cardiac muscle during
polarization and repolarization spread into tissues surrounding the
heart and are conducted through body fluids.

A small portion of this electrical activity reaches the body
surface, where it can be detected using recording electrodes on skin.
The record produce is an electrocardiogram.



Electrocardiogram

- it is a recording of that portion of the electrical activity induced by the
body fluids by the cardiac impulse that reaches the surface of the body.

- is a complex recording representing the over-all spread of activity
throughout the heart during depolarization and repolarization.



Electrocardiogram



Electrocardiogram

P wave represents atrial
depolarization

QRS complex represents ventricular
depolarization.

T wave represents ventricular
repolarization



Depolarization – a change in a cell's membrane
potential, making it more positive, or less negative.

Repolarization – reestablishment of polarity, especially the
return of cell membrane potential to resting potential

Action Potential – is a short-lasting event in which the electrical
membrane potential of a cell rapidly rises and fall, following a
consistent trajectory; whenever there’s large depolarization among
cells

Resting Potential – resting event, opposite to action
potential, comes after action potential, whenever there’s a large
repolarization among cells



Excitation/Activation of heart by Sino-Atrial Node (especialized auto-
rhythmic cells).

(animation / presentation)
File name: conduction_ct.swf
Download my file at:
http://www.4shared.com/rar/13zOoh6I/animal_physio_reports_ppt.html



The Full Cardiac Cycle:

1) Early Ventricular Diastole
2) Late Ventricular Diastole
3) End of Ventricular Diastole
4) Ventricular Excitation and Onset of Ventricular Systole
5) Isovolumetric Ventricular Contraction
6) Ventricular Ejection
7)End of Ventricular Systole
8) Ventricular Repolarization and Onset of Ventricular Diastole
9) Isovolumetric Ventricular Relaxation
10) Ventricular Filling



1st : Early Ventricular Diastole

During early ventricular diastole, the atrium is still also in
diastole. This stage corresponds to the TP interval (on the ECG) – the
resting stage.

The AV valve is open.



2nd : Late Ventricular Diastole

SA node reaches threshold and fires.

Impulse spreads through out the atria and is recorded on the
ECG as P wave.

Atrial depolarization brings about atrial contraction which
squeezes more blood into the ventricle, causing a rise in the atrial
pressure curve.



3rd : End Ventricular Diastole

Ventricular Diastole ends at the onset of ventricular
contraction. By this time, atrial contraction and ventricular filling are
completed.

The volume of the blood in the ventricle at the end of diastole
is known as “end-diastolic volume” (EDV), which averages about
135mL in humans.

No more blood is added to the ventricle during this cycle.



4th: Ventricular Excitation and Onset of Ventricular Systole

Following atrial excitation, the impulse passes through the AV
node and specialized conduction system to excite the ventricle.

QRS complex represents this ventricular excitation which
induce ventricular contraction.



5th: Isovolumetric Ventricular Contraction

After ventricular pressure exceeds atrial pressure and AV valve
has closed, the ventricular pressure must continue to increase before it
can open the aortic valve.

Between closure of the AV valve and opening of Aortic
valve, there is a brief period of time when the ventricle remains a
closed chamber. During this time, no blood can enter or leave the
ventricles.



6th: Ventricular Ejection

It is when ventricular pressure exceeds aortic pressure. The
aortic valve is forced open and ejection of the blood begins.

The ventricular volume decreases substantially as blood
rapidly pumped out.

 Ventricular systole includes both the period of isovolumetric
contraction and the ventricular ejection phase.



7th : End of Ventricular Systole

After ventricular pressure exceeds atrial pressure and AV valve
has closed, the ventricular pressure must continue to increase before it
can open the aortic valve.

Between closure of the AV valve and opening of Aortic
valve, there is a brief period of time when the ventricle remains a
closed chamber. During this time, no blood can enter or leave the
ventricles.



8th : Ventricular Repolarization and Onset of Ventricular Diastole

It is signified by T wave, occurring at the end of ventricular
systole. As the ventricles starts to relax on repolarization, ventricular
pressure falls below aortic pressure and the aortic valves closes.

Closure of the aortic valve produces a disturbance as notch on
the aortic pressure curve known as the “discrotic notch”.

No more blood leaves the ventricle during this
cycle/phase, because the aortic valve has closed.



9th : Isovolumetric Ventricular Relaxation

When the aortic valve closes, the AV valve is not yet
open, because ventricular pressure still exceeds atrial pressure, so no
blood can enter the ventricle from the atrium. Therefore, all valves are
once again closed for a brief period of time.

The muscle fiber length and chamber volume remain constant.
No blood moves as the ventricle continues to relax; pressure steadily
falls.



10th : Ventricular Filling

When the ventricular pressure falls below the atrial
pressure, the AV valve opens and ventricular filling occurs once again.

 Ventricular Diastole includes both the period of isovolumetric
ventricular relaxation and the ventricular filling phase.



(Points to Ponder)

 Atrial repolarization and Ventricular depolarization occur
simultaneously, so the atria are in diastole throughout ventricular
systole.

 Blood continues to flow from the pulmonary veins into the left atrium.
As this incoming blood pools in the atrium, atrial pressure rises
continuously.

 When the AV Valve opens at the end of ventricular systole, the
blood that accumulated in the atrium during ventricular systole pours
rapidly in the ventricle.



(Points to Ponder)

 Ventricular filling thus occurs rapidly at first because of the increased
atrial pressure resulting from the accumulation of blood in the atria.
Then ventricular filling slows down and atrial pressure starts to fall.

 During the period of ventricular filling, the blood continues to flow
from the pulmonary veins into the left atrium and through the open
AV valve into the left ventricle.

 During late ventricular diastole, when ventricular filling is proceeding
slowly, the SA node fires again and the cardiac cycle starts over.


Pumps: Cardiac Output and Its Control

Cardiac Output

It is the volume of blood per minute pumped by a heart to the
body, and is the most important physiological parameter of a circulatory
pump.

It depends on the heart rate and the stroke volume. Thus, the
key formula is:

Cardiac Output = Heart Rate x Stroke Volume
(volume per minute) (beats per minute) (volume per pumped
per beat of stroke)



Cardiac Output depends on the heart rate and the stroke volume.

 Heart rates vary tremendously with activity state of an individual and
across the animal kingdom.

 Larger animals tend to have slower heart rates. Ex: 6 beats/min for
whales and 300 beats/min in a rat.

 During any period of time, the volume of blood flowing through
pulmonary circulation is equivalent to the volume flowing through
systemic circulation.

 Cardiac output from each ventricle is normally identical, minor
variations may occur.




CARDIAC OUTPUT = Heart Rate x Stroke Volume

Horse 13, 500 mL/min = 30 beats/min x 450 mL/beat

Human 4, 900 mL/min = 70 beats/min x 70 mL/beat

Pigeon 195.5 mL/min = 115 beats/min x 1.7 mL/beat

Trout 17.4 mL/min = 37.8 beats/min x 0.46 mL/beat




Cardiac Output changes with development. In young broiler
chicks, stroke volume almost doubles in a two-week period:

CARDIAC OUTPUT = Heart Rate x Stroke Volume

4 weeks old 253 mL/min = 362 beats/min x 0.70 mL/beat

6 weeks old 434 mL/min = 328 beats/min x 1.33 mL/beat




Cardiac Output also Thorough Bred Horse 300, 000 mL/min
changes with activity,
often by large amounts.
Human (untrained) 25, 000 mL/min

The following are Human (athlete) 40, 000 mL/min
some values that have
been measured at high
Pigeon 1, 072 mL/min
activity levels ( running,
flying, swimming)
Trout 53 mL/min



Heart rate is determined primarily by antagonistic regulation of
autonomic influences on the SA node.

The vertebrate heart is innervated by both division of the
ANS, which is the sympathetic and parasympathetic Nervous
System, which can modify the rate ( as well as strength) of
contraction, even though nervous stimulation is not required to initiate
contraction.

The parasympathetic nerve to the mammalian heart, the vagus
nerve, primarily supplies the atrium especially the SA and AV nodes.
Parasympathetic innervation of the ventricles is sparse.

The cardiac sympathetic nerves also supply the atria, including
SA and AV nodes, and richly innervates the ventricles as well.




Both parasympathetic and sympathetic nervous system affect
the heart by altering the activity of the cyclic AMP (second messenger
system in the innervated cells.




Both parasympathetic and sympathetic affect the heart through
the release of:

1) Acetylcholine (Ach) – released from the vagus nerve binds to
muscarinic receptors that are coupled to an inhibitory G protein, which
reduces the cyclic AMP pathway. cAMP in turn increases the
permeability of the SA node to K+ by slowing the closure of EAG K+
channel.




the release of:

2) Norepinephrine (NE) – sympathetic neurotransmitter binds with a B-
adrenergic receptor that is coupled to a stimulatory G protein, which
accelerates cAMP pathway. In turn, cAMP appears to decrease K+
permeability by accelerating inactivation of EAG channels.




the release of:

3) Ach and NE that both affects Ca++ conduction.



Effect of Parasympathetic Stimulation on the Mammalian Heart

Parasympathetic stimulation reduces cardiac output through
these effects:

1) It decreases heart rate.
2) It decreases excitability of the AV node.
3) It shortens the action potential of the atrial contractile cells.



Effect of Sympathetic Stimulation on the Mammalian Heart

Sympathetic stimulation increases cardiac output through
these effects:

1) It increases heart rate through its effect on pacemaker tissue.
2) It reduces AV nodal delay at the node by increasing conduction
velocity.
3) It speeds up the spread of the action potential throughout the
specialized conduction pathway.
4) It increases contractile strength of the atrial and ventricular
contractile cells.



Control of the Heart Rate

Thus, as typical of the ANS, parasympathetic and sympathetic
effects on heart rate are example of antagonistic relation. At any given
moment, the heart rate is determined largely by the existing balance
between the inhibitory effects of vagus nerve and the stimulatory
effects of the cardiac sympathetic nerves.

The relative level of activity in these two branches in turn is
primarily coordinated by the cardiovascular control center located at
the brain stem.



Control of the Heart Rate

Although autonomic innervation is the primary means by which
heart rate is regulated, other factors affect it as well. The most
important is epinephrine, a hormone that is secreted into the blood
from the adrenal medulla on sympathetic stimulation and the acts in a
manner similar to norepinephrine to increase the heart rate.



Stroke Volume is determined by the extent of venous return and by
sympathetic activity.

The other component that determines the cardiac output is
stroke volume, the amount of blood pumped out by each ventricle
during each beat. Two types of controls influence stroke volume:

1) Intrinsic Control – related to the extent of venous return
2) Extrinsic Control – related to the extent of sympathetic stimulation
of the heart.



Increased end-diastolic volume results in increased stroke volume

As more blood is returned to the vertebrate heart, the heart
pumps out more blood, but the heart does not eject all the blood it
contains. The direct correlation between end-diastolic volume and
stroke volume constitutes the intrinsic control of stoke volume, which
refers to the heart’s inherent ability to vary the stroke volume.



Frank-Starling Law of the Heart

states that:
“ Heart normally pumps all the blood returned to it”

This effect is not unique to invertebrates; for example, mollusk hearts
also respond in this way to increased filling (they also beat faster in
response)



Frank-Starling Law of the Heart

The built-in relationship matching stroke volume with venous
return has two important advantages:

1) It is for equalization of output between the right and left sides of the
avian and mammalian hearts, so that the blood pumped out by the
heart is equally distributed between pulmonary and systemic
circulation.

2) When larger cardiac output is needed in any vertebrate, venous
return is increased through action of the sympathetic nervous
system.



The contractility of the heart and venous return are increased by
sympathetic stimulation.

In addition to intrinsic control, stroke volume is also subject to
extrinsic control by factors originating outside the heart, the most
important of which are actions of the cardiac sympathetic nerves and
epinephrine. Sympathetic stimulation and epinephrine act into two
ways:
1) The heart contracts more forcefully and squeezes out a greater
percentage of the blood it contains on sympathetic stimulation.

2) Sympathetic stimulation increases stroke volume also by
enhancing venous return.



The contractility of the heart and venous return are increased by
sympathetic stimulation.

The strength of cardiac muscle contraction and
accordingly, the stroke volume can thus be graded by

1) Varying the initial length of the muscle fibers, which turn depends
on the degree of ventricular filling before contraction and;

2) Varying the extentof sympathetic stimulation (extrinsic control).


Pumps: Nourishing the Vertebrate Heart Muscle

The heart receives most of its own blood supply through the coronary
circulation.

Coronary circulation is the circulation of blood in the blood
vessels of the heart muscle (the myocardium). The vessels that deliver
oxygen-rich blood to the myocardium are known as coronary arteries.
The vessels that remove the deoxygenated blood from the heart
muscle are known as cardiac veins.



The heart receives most of its own blood supply through the coronary
circulation.

Although the blood passes though the heart, the heart muscle
cannot extract O2 or nutrients from the blood within its chamber, in part
because the walls are too thick to permit diffusion of O2 and other
supplies from the blood in the chamber to all the cardiac cells.

Therefore, like other tissues of the body, heart muscle must
receive blood through blood vessels, specifically by means of the
coronary circulation (which first evolved in fishes). The coronary
arteries branch in fishes from the branchial arteries leaving the
gills, and in mammals from the aorta just beyond the aortic valve.



Coronary Circulation




 During locomotory activity, the rate of coronary blood flow increases
several-fold above its resting state. Increased delivery of blood to the
cardiac cells is accomplished primarily by vasodilation, or
enlargement, of the coronary vessels, which allows more blood to
flow through them.

 Coronary blood flow is adjusted primarily in response to changes in
the heart’s O2 requirements.

 The major link that coordinates coronary blood flow with myocardial
O2 needs is adenosine (which is formed from ATP).




Increased formation and release of adenosine from cardiac cells occur:
1) When there is cardiac O2 deficit or
2) When cardiac activity is increased and the heart accordingly
requires more O2 for ATP production.

The heart primarily uses free fatty acids, glucose, lactate as fuel
sources. Note: depending on their availability and it can shift metabolic
pathways to use whatever nutrient is available.

The primary danger of insufficient coronary blood flow is not fuel
shortage but O2 deficiency.




Reduced O2 in cardiac adenosine release

vasodilation of coronary vessels

increased blood flow and O2 delivery to myocytes


Circulatory Pathways and Vessels

Circulatory fluids transport materials in a parallel manner, especially in
closed systems.

Most animals have either open (hemolymph) or a closed
(blood) system.

 Blood moves through closed vessels.
 Hemolymph moves more randomly through open spaces “lacunae”
among organs.



Circulatory fluids transport materials in a parallel manner, especially in
closed systems.

There are two important design features in closed ( and often
in open system)

1) Closed systems always have initial parallel branching in
arteries, and many open system do as well. Parallel plumbing
allows individual organs or body regions to obtain fresh blood (or
hemolymph).
2) There can be muscular valves on some of the branching parallel
vessels. These appear universally in closed system and occur in
some open ones.



Circulatory fluids are driven by pressure and can transmit useful force.

Directing fluid flow in parallel manner can serve another
purpose – force of transmission to specific organs. To move from one
point to another it needs pressure ( is created by a pump, and is the
driving force for fluid movement).

But it can be used to exert a force for other functions:

1) Movement
2) Ultrafiltration
3) Erection




1) Movement – hemolymph pressure (rather then skeletal muscle) is
used to extend the legs in arachnids such as spiders. Arteries
branch to the legs and flow to them controlled. Hemolymph
entering into bent leg at high pressure (from an open artery) makes
the leg straighten out.

2) Ultrafiltration – Blood pressure can force water and
small, dissolved solutes out of pores in capillary linings. This is
usedin the initial process of urine formation in the kidney and for
interactions with the ECF in many tissues.




3) Erection – Blood can enter a flaccid organ under high
pressure, and if exiting blood is restricted, the force of the
pressure will inflate that organ. This occurs during arousal of
erectile genitalia (penis, clitoris) Scientist also think it inflates the
sensitive snout of the echidna ( a monotreme) which pokes its
snout into termite and ant nests to feed.


Vessels: Flow Regulation and Hemodynamics

Blood flow through vessels depends on the pressure gradient and
vascular resistance.

Flow of fluid obeys certain physical law called the hemodynamic law.
The Flow rate of blood (volume of blood passing through per unit of
time) is directly proportional to the pressure gradient and inversely
proportional to vascular resistance. Expressed in Hemodynamic Flow
Law.
F= P/R or F = (P1 - P2) / R

where F = flow rate of fluid through a vessel
P = (P1 - P2) , P1 =pressure at the inflow end of a vessel
P2 =pressure at the end flow end of a vessel
R = resistance of blood vessels




Factors affecting flow rate:

1) Pressure Gradient
2) Resistance




1) Pressure Gradient – the difference in pressure between the
beginning and end of a vessel – is the main driving force for flow
through the vessel; that is,
The blood flows from an area of higher pressure to an area of lower
pressure down a pressure gradient.

The greater the pressure gradient for forcing of blood through a
vessel, the greater the rate of flow through that vessel.

Gravity is another major factor in establishing the pressure
gradient. This is particularly important in terrestrial animals such as
human and giraffe.




2) Resistance – is a measure of the hindrance to blood flow through a
vessel caused by friction between the moving fluid and the
stationary vascular walls.

As resistance to flow increases, it is more difficult for blood to
pass through the vessel, so flow decreases ( as long as the pressure
gradient remains unchanged).

When resistance increases, the pressure gradient must increase
correspondingly to maintain the same flow rate.




2) Resistance – is a measure of the hindrance to blood flow through a
vessel caused by friction between the moving fluid and the
stationary vascular walls.

Resistance to blood flow depends on several factors. (Laminar
flow is the term for smooth flow). Three key factors are:

- Viscosity of the blood (the greater the viscosity , the greater the R)
- Vessel Length (the longer the vessel, the greater the R)
- Vessel Radius ( the smaller the radius, the greater the R)


Pathways: Open Circulation

In an open circulatory system, blood is pumped from the heart
through blood vessels but then it leaves the blood vessels and enters
body cavities (hemocoel), where the organs are bathed in blood, or
sinuses (spaces) within the organs.

Blood flows slowly in an open circulatory system because there is no
blood pressure after the blood leaves the blood vessels. The animal
must move its muscles to move the blood within the spaces.

The most widely studied animals with open circulations are
dominated by a single hemolymph space. Wide group of animals that
have open circulatory system are: Mollusks (decapods except snails
and octopuses) Insects, Crustaceans


Mollusks


Insects


Crustaceans
The heart is a muscular sac, situated dorsally, beneath the
carapace, and it gives origin to six arterial trunks, which convey the
aerated blood to all parts of the body. The terminations of the arteries
open into a series of irregular venous sinuses, whence the blood is
collected into a principal ventral sinus, and distributed to the
branchiae, where it undergoes aeration.
From the gills the now aerated blood is carried by a series of branchial
vessels to a large sac, which is badly termed the "pericardium," and
which envelops and surrounds the heart. The arterial blood gains
access to the cavity of the heart by means of six pairs of valvular
fissures, which allow of the ingress of the blood, but prevent
regurgitation. A portion of the venous blood, however, is not sent to the
branchiae, but is returned directly, without aeration, to the pericardium;
so that the heart finally distributes to the body a mixture of venous and
arterial blood.



Diagram of the circulation of the Lobster. The systemic arteries are
shaded longitudinally, the veins are dotted, and the branchial
vessels are black. h Heart; a a Systemic arteries; b b Branchial
vessels; c c Venous sinuses; g g Branchiae; p Pericardium.


Pathways: Closed Circulation

In a closed circulatory system, blood is not free in a cavity; it is
contained within blood vessels. Valves prevent the backflow of blood
within the blood vessels.

Wide group of animals that have closed circulatory system are
Nemerteans, Annelids, Fish, Reptiles, Amphibians, Birds, Mammals.



Fish

Fish have a two-chambered heart
with one atrium (A) and one ventricle
(V).

The gills contain many capillaries for
gas exchange, so the blood
pressure is low after going through
the gills. Low-pressure blood from
the gills then goes directly to the
body, which also has a large number
of capillaries. The activity level of
fish is limited due to the low rate of
blood flow to the body.



Amphibians

Amphibians have a 3-chambered
heart with two atria and one
ventricle.

Blood from the lungs (pulmonary
flow) goes to the left atrium. Blood
from the body (systemic flow) goes
to the right atrium. Both atria empty
into the ventricle where some mixing
occurs.

The advantage of this system is that
there is high pressure in vessels that
lead to both the lungs and body.



Reptiles

In most reptiles, the ventricle is
partially divided.

This reduces mixing of oxygenated
and unoxygenated blood in the
ventricle. The partial division of the
ventricle is represented by a dashed
line.



Birds, Mammals, Crocodilians

Birds and mammals
(also crocodilians) have a four-
chambered heart which acts as two
separate pumps.

After passing through the
body, blood is pumped under high
pressure to the lungs. Upon
returning from the lungs, it is
pumped under high pressure to the
body. The high rate of oxygen-rich
blood flow through the body enables
birds and mammals to maintain high
activity levels.


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And also visit the site

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Mammalian Circulatory system

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