The Cardiovascular System

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The Cardiovascular System

• Chapter 8

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• http//www.youtube.com/watch?vupctPUa6RhA

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Pump it Up!!!

• The heart is a pump for delivery of
• Oxygen
• Nutrients
• Hormones
• Antibodies
• WBCs
• 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?

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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.

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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.

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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.

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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

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Pericardial effusion and Cardiac Tamponade
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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.

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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).

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Valve Locations
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What do the valves look like??
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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.

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So how does this all work??Atrial
Contraction/Ventricular Relaxation
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Ventricular Contraction/Atrial Relaxation
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• http//www.cardioconsult.com/Anatomy/

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Blood Flow through the heart

• Lets Review
• What do veins do?
• What do arteries?

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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.

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Blood Flow Steps

• 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
• 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

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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.

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• http//www.sumanasinc.com/webcontent/animations/co
  ntent/human_heart.html

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Heart SoundsLUB 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??

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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.

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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

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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.

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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.

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• 1 Sinoatrial node (Pacemaker)2 Atrioventricular
  node3 Atrioventricular Bundle (Bundle of His)4
  Left Right Bundle branches5 Purkinje Fibers

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• http//www.nhlbi.nih.gov/health/dci/Diseases/hhw/h
  hw_electrical.html

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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.

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Interpreting an ECG

• P-wave- when the atria contract or depolarize.
• QRS complex- when the ventricles depolarize.
• T- wave- The repolarization of the ventricles.

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• www.nhlbi.nih.gov/health/dci/Diseases/hhw/hhw_elec
  trical.html

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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.

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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.

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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)

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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
• CO480 mls/min
• How does this relate to large animals??

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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.

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Starlings 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.

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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.

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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.

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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??

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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?

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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
  high-pressure blood from the ventricles.

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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.

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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.

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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.

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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

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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.

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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.

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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.

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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.

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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

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• http//www.youtube.com/watch?vupctPUa6RhA