Transcript The Cardiovascular System

The Cardiovascular
System
Chapter 8
• http://www.youtube.com/watch?v=upctPU
a6RhA
Pump it Up!!!
• The heart is a pump for delivery of:
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Oxygen
Nutrients
Hormones
Antibodies
WBC’s
• Also removes wastes and antioxidants.
• All of these materials are propelled by the
heart through a closed system of tubes to
the tissues of the body.
– What are these tubes called?
Where is the heart located??
• Centrally located in the chest.
– Surrounded by lungs
– Protected by ribs
– Seems to be slightly shifted to left side of the
chest
– Heart lies in the mediastinum- space between
the pleural cavities that contain the lungs. Also
called the interpleural space.
• Trachea, esophagus, and other vascular
structures are also contained in the
mediastinum.
Basic Heart Terminology.
• Apex would be considered at the bottom of
the heart near the ventricles.
• Base is at the top of the heart, where
major blood vessels enter and exit.
External Structures of the heart
• Auricles- largest and most visible parts of the atria.
• Ventricles are separated by interventricular sulci.
• Atria do not have as thick of walls as the ventricles
do. Why??
• Remember that there are vessels that supply the
heart with blood itself as well. This is called
coronary circulation
• Highest pressure is found in aorta. Why???
• Brachiocephalic trunk and left subclavian artery
branch off aorta just after aortic valve.
Composition of the Heart Wall
• Primarily a muscle.
• Outer layer is called the pericardium.
– Consists of two layers with fluid filled cavity
between.
• 1. Outer fibrous pericardium
– Made of tough, fibrous connective tissue
that protects the heart and loosely
attaches to the diaphragm.
• 2. Inner serous pericardium
– Actually made up of two layers
» Inner visceral layer called the
epicardium.
» Outer parietal layer
Pericardial effusion and
Cardiac Tamponade
Composition of Heart Walls
continued…
• Inside the sac formed by the pericardium is the
myocardium- the thickest layer of the heart tissue.
• Between the myocardium and the heart chambers is a
thin membranous lining called the endocardium.
Internal Structures of the Heart
• The Valves of the heart
– Right Atrioventricular Valve (also called right AV
valve or tricuspid valve).
– Left atrioventricular Valve (also called the left
AV valve or mitral valve or bicuspid valve).
– Pulmonary valve (also called pulmonic valve is
a semilunar valve).
– Aortic valve (is a semilunar valve).
Valve Locations
What do the valves look like??
Valve Composition
• Have 2 or 3 leaflets (flaps) that originate from the
annulus of the valve which is a fibrous ring.
– These are the outer edges of the flaps
• Inner edges of flaps are attached to papillary
muscles by chordae tendinae.
• In right ventricle, there is a band of tissue that
originates at the interventricular septum but does
not attach to the flaps of the tricuspid valve; it is
called the Moderator band and connects to the
outside wall of the right ventricle.
So how does this all work??
Atrial Contraction/Ventricular
Relaxation
Ventricular Contraction/Atrial
Relaxation
• http://www.cardioconsult.com/Anatomy/
Blood Flow through the heart
• Let’s Review
– What do veins do?
– What do arteries?
Blood Flow through the heart continued….
• Blood only flows in one direction
in a healthy heart.
• Basic function is to receive
deoxygenated blood from the
tissues of the body, pumps it
through the lungs and then back
out through the body system.
Blood Flow Steps
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1. Caudal or cranial vena cava
2. Right atrium
3. Right Atrioventricular (AV) valve (tricuspid valve).
4. Right ventricle
5. Pulmonary valve
6. Pulmonary arteries
7. Lungs
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Exchange takes place at alveoli/capillaries
8. Pulmonary veins
9. Left atrium
10. Left Atrioventricular (AV) valve (mitral valve).
11. Left Ventricle
12. Aortic Valve
13. Aorta
14. Systemic capillaries
15. Tissue
16. Back to caudal or cranial vena cava
Phases of blood flow through the heart.
• Systole- mitral and tricuspid valves close
and ventricles pumps blood out pulmonic
valve and aortic valves.
• Diastole- Ventricles refill with blood with
tricuspid and mitral valves open and
pulmonic and aortic valves closed.
• http://www.sumanasinc.com/webcontent/a
nimations/content/human_heart.html
Heart Sounds…LUB DUB
• “Lub” sound of heart is also called S1.
– Closing of the AV valves
• “Dub” sound is also called S2.
– Closing of the semilunar valves.
Where do we listen for these sounds??
The Cardiac Cycle
• What causes the heart to actually pump?
– Electrical impulse for heartbeat comes from the
sinoatrial node (SA node) located in the right
atrium and known as the pacemaker for the
heart.
• SA node is a specialized area of cardiac
muscle cells that can generate automatically
the impulses that trigger the repeated
beating of the heart.
How is electrical impulse
generated?
• Remember Depolarization/Repolarization?
• Polarization: Cations (substances with a
positive charge) are pumped out of the
cell. This results in in outside of cell having
a more positive charge than inside cell.
• Depolorization: Gates open to allow
cations to flow back into cell to equalize
charge. This generates an electrical
current which causes the heart to contract.
• Depolarization= Systole
• Repolarization= Diastole
Electrical Activity Continued
• Electrical current is generated in SA node
and travels one of two paths from base of
heart to apex of heart.
– Speedy route-through cardiac muscle to AV
node and Purkinje fibers
– Scenic route- Through cardiac muscle fibers
alone.
– Cardiac muscle can generate electrical impulse
from one muscle cell to another, so electrical
impulses spread like a ripple through the heart.
Electrical Activity Continued
• Electrical Impulse is generated in SA node
and then spreads to atria.
• Atria contract pushing blood through AV
valves to ventricles.
• Impulse travels to AV node where it is
delayed until atrial systole is complete.
• After AV node, electrical impulse travels
through specialized fibers in ventricles
known as Bundle of His and the Purkinje
Fibers.
• Purkinje fibers carry impulse into
ventricular myocardium.
• 1 Sinoatrial node
(Pacemaker)
2 Atrioventricular node
3 Atrioventricular Bundle
(Bundle of His)
4 Left & Right Bundle
branches
5 Purkinje Fibers
• http://www.nhlbi.nih.gov/health/dci/Disease
s/hhw/hhw_electrical.html
The Electrocardiogram
• An electrocardiograph or EKG (most
correctly termed ECG) is used to detect
the electrical activity associated with the
heart cycle.
• The ECG is useful in detecting
abnormalites of the heart based on the
graphical appearance.
Interpreting an ECG
• P-wave- when the atria contract or
depolarize.
• QRS complex- when the ventricles
depolarize.
• T- wave- The repolarization of the
ventricles.
• www.nhlbi.nih.gov/health/dci/Diseases/hh
w/hhw_electrical.html
Blood Circulation in the Fetus
• Major difference in blood flow is that
newborn receives oxygen through its own
lungs while fetus receives oxygen from
blood of mother.
• Blood therefore bypasses the lungs during
the cardiac cycle in a fetus.
• Fetus receives oxygen through the
placenta.
• Blood from umbilical vein flows through
liver (some bypasses liver via ductus
venousus), into caudal vena cava, then
into right atrium.
Fetal Circulation Continued
• Two forms of bypass in the fetus.
– Foramen ovale- between right and left atria.
– Ductus arteriosis-if blood flows into right
ventricle, then will go from pulmonary artery to
aorta.
– Deoxygenated blood is sent back to placenta
via umbilical arteries to become oxygenated
from mother.
– At birth, lungs inflate and the newborn will
oxygenate its own blood. Normally all
bypasses will close at this point.
Heart Rate and Cardiac Output
• Cardiac output- the amount of blood that
leaves the heart.
– Must be sufficient for life sustaining activities.
– Is determined by 2 factors:
• Stroke volume
– Amount of blood ejected with each
cardiac contraction
• Heart rate
– How often the heart contracts.
– Is expressed:
• Cardiac Output (CO)=Stroke Volume (SV) x
Heart Rate (HR)
How to calculate Cardiac output.
• If a dog ejects 4 mls of blood with each
systolic contraction and Heart rate is 120
bpm.
• CO= 4x120
• CO=480 mls/min
How does this relate to large animals??
Cardiac output continued
• Vigorous exercise increases the demand
for oxygen in the tissues, so cardiac output
must increase to meet that demand.
– This process is called increased contractility or
positive inotropy. This in turn will increase
stroke volume.
– So basically during exercise, increased heart
rate, increased cardiac output will increase
stroke volume.
Starling’s Law
• States that increased filling of the heart
results in increased cardiac contraction.
– Causes the ventricular walls to stretch slightly,
which leads to more forceful contraction and
increased stroke volume.
Cardiac output continued
• Changes in blood pressure may affect
both stroke volume and heart rate.
– Animals in shock have rapid, weak pulses.
– Shock occurs when the blood pressure drops
substantially.
– Types of shock:
• Hypovolemic shock: occurs because of
blood loss
• Anaphylactic shock (allergic reactions) and
Septicemic shock (infection): blood pressure
drops because small blood vessels fo the
organs and tissues all dilate at the same
time.
Shock Continued
• Because of reduced blood
pressure, there is a
decreased preload to the
heart.
• This causes decreased stroke
volume which in turn caused
decreased cardiac output.
• Pulse will try to increase to
compensate.
Hormone and Drug Effects on
Blood Pressure
• Sympathetic nervous system: Fight or
flight-epinephrine is released and
increases stroke volume.
– Increases the strength of contractions.
• Parasympathetic system: stimulated by
general anesthesia-acetylcholine is
released and decreases stroke volume
and heart rate.
– Leads to decreased what??
Vascular Anatomy and
Physiology
• Arteries do what?
• Veins do what?
• Blood that is in the systemic circulation is
under higher pressure than blood in the
pulmonary or coronary circulation.
– Why?
Artery composition
• Aorta- Largest artery in body, largest
diameter and thickest vessel walls.
• Arterial walls are similar to the layers of
the heart.
– Tough outer fibrous layer
– Middle layer of smooth muscle and elastic
connective tissue.
– Smooth inner lining called endothelium
In aorta and pulmonary arteries, the middle layer
contains more elastic fibers- allows them to
stretch slightly as they receive the highpressure blood from the ventricles.
Vascular Anatomy
• Right and left subclavian arteries branch
from aorta and travel to forelimbs.
• Cartoid arteries branch off subclavian
arteries and supply blood to the head.
• Main trunk of aorta arches dorsally and
then travels caudally just below the spine.
– Numerous branches supply blood to abdominal
organs
• At hind limbs, aorta branches into right and
left iliac arteries which supply hindlimbs.
• Small coccygeal artery emerges to supply
blood to tail.
Vascular Anatomy Continued
• Smaller arteries branch off the aorta and
continue to become smaller and smaller
vessels.
• Turn from arterioles to capillaries which do
not have muscle in their walls.
– Capillaries are where oxygen and nutrients in
the blood are exchanged for carbon dioxide and
other waste products that are taken back
toward the heart.
Vascular Anatomy Continued
• After capillaries, blood starts journey back
to heart.
• Venules become veins.
• Due to lower pressure, veins have thinner
walls.
• Veins usually are located next to arteries.
• Veins in foreleg merge into larger vessels
and into left and right brachiocephalic
veins- these go to cranial vena cava.
• Veins in hind limb merge to right and left
iliac veins- these go to caudal vena cava.
• Jugular Vein-Drains blood from the head.
Vascular Anatomy Continued
• Smooth muscle in walls of most blood
vessels
• Constriction and relaxation allows vascular
system to direct blood to different regions
of the body under different circumstances
Venipuncture
• Cephalic vein: craniomedial aspect
of forelimb.
• Femoral Vein: medial aspect of hind limb.
• Saphenous: lateral aspect of hind limb.
• Jugular Vein: Ventral aspect of each side
of the neck.
• Milk Vein (superficial caudal epigastric
vein): found in lactating cows, not
generally used due to excessive bleeding.
• Coccygeal vein (tail vein): Found in
rodents and ruminants-runs along ventral
midline of the tail.
Heart/ Vascular System
Conditions
• Syncope: transient loss of consciousness
caused by insufficient delivery of oxygen to
the brain.
• Cardiac Murmurs: Described by time,
location and intensity.
• Heart Failure: Heart dysfunction.
– Right sided heart failure-leads to systemic
venous hypertension
– Left sided heart failure-pulomonary
hypertension, edema, coughing.
Conditions Continued
• Valvular Disease- shrunken, thickened valves
causes chordae tendinae to rupture which may
cause regurgitation which leads to dilation of atrium
and ventricle.
• Endocarditis- Infection involving the heart valves or
inner lining of the heart
• Dilated Cardiomyopathy- poor myocardial
contraction, causes are unknown. Causes
abnormally thin ventricular walls. Common in large
breeds (Boxers, Dobermans, and Great Danes).
• Hypertrophic Cardiomyopathy- Myocardium
thickens, leads to poor ventricular filling. More
common in cats.
Conditions continued
• Patent Ductus Arteriosis (PDA)- Most
common congenital defect in the dog. Is
the failure of the ductus arteriosis to close.
– Leads to blood shunt.
Drugs used for Cardiac Issues
• Diuretics-decrease venous congestion and fluid
accumulation.
– Lasix
• Vasodilators- relax arteriolar smooth muscle,
decreasing systemic vascular resistance.
– Enalapril
• Positive Inotropic Drugs- increase force of
myocardial contraction.
– Dopamine
• Calcium Channel Blockers- Block calcium which is
useful for improving ventricular filling and
decreasing heart rate.
– Diltiazem
• Antiarryhthmic drugs- Restore normal electrical
activity of heart.
– Lidocaine
• http://www.youtube.com/watch?v=upctPU
a6RhA