Introduction to Cardiac Physiology

VMED 5161

Give an overview of the parts of the cardiovascular system

heart, blood vessels, blood, nervous system, lymphatics

Describe the characteristics of the cardiovascular system

a closed circle

elastic

filled with liquid at a positive mean pressure that is independent of the pumping of the heart

Does the heart pump actively or passively?

passively rather than sucking

What regulates circulation rate since the filling of the heart is passive?

peripheral-vascular factors vs cardiac variables

Flow from the heart is ??, while flow to the heart is ??

intermediate, continuous

how does the heart use energy?

excess expenditure to maintain normal circulation, aka pump energy excess

what is normal in ventricular capacity?

excess diastolic filling volume, aka pump capacity excess

What is blood flow dependent on?

vascular resistance and the compliance of the system

What is cardiovascular physiology?

the study of the function of the heart, blood vessels, and blood

What is the primary function of the CVS?

the transport of substances that are essential for life

Who is credited with the proof of the heart propelling blood in a circulatory pattern? What year?

William Harvey, 1628

What are primary cardiovascular dysfunctions?

fundamental disturbances of the CVS directly, such as hemorrhage and myocarditis

What are secondary cardiovascular dysfunctions?

CV complications developed even when the CVS isn’t the primary target of the disease

severe burns, persistent V/D causing CV complications

CVS dysfunction can be present in what two ways?

congenital (present at birth) or acquired (developing after birth)

In what species are congenital cardiac defects common?

dogs and horses

What are common causes of acquired CV defects?

parasites (heartworm), colic, aanesthetic overdose

Is the distinction between primary and secondary CV dysfunction clear cut?

no

How is the heart grossly divided? (will disrupt previous teaching)

right heart (r atrium and ventricle)

left heart (L atrium and ventricle)

What is the role of the “right heart” (right atrium and ventricle)?

receives deoxy blood from the body through the vena cava into the right atrium. Blood enters right ventricle via tricuspid valve. During a ventricular contraction, blood is ejected out through the pulmonary artery to the lungs

What is the path of the “left heart”?

receives purified blood from the lung through the pulmonary vein (oxy blood) into the left atrium. Blood moves to the left ventricle via the mitral/ bicuspid valve. During a ventricular contraction, blood is ejected from the L. ventricle into the aorta and oxy blood is distributed through the body

What % of body weight (typically) makes up the heart?

0\.75

Give a general description of the location of the heart

thoracic cavity, mediastinum

conical in shape and placed asymmetrically within the thorax with the linger part lying on the left side of the median plane'

base is dorsal and reaches the horizontal plane that bisects the first rib

apex is placed close to the sternum opposite of the 6th costal cartilage

What is myocardium?

cardiac muscle fibers arranged into 4 chambers (2 atria and 2 ventricles)

What is the conduction system?

specialized tissue that conducts nerve impulses through the heart

SA and AV node, bundle of His, bundle branches, Purkinje fibers

What is the nerve supply?

nerve branches from both the sympathetic and parasympathetic divisions of the autonomic nervous system, regulate heart rate and force of contraction

does the nervous system actively make the heart beat?

NO, done by conduction system! The heart can beat without nervous impulse

What is the action of the sympathetic nervous system on the heart?

increase firing (SA)

increase conduction velocity (AV)

increased force of contraction of muscle

increased Ca and Na permiability

What is the function of the parasympathetic nervous system on the heart?

decrease firing (SA)

decrease conduction velocity (AV)

increase K permeability to hyperpolarize the membrane

What % of cardiac muscle cells are autorhythmic rather than contractile?

1%

What are the parts of the intrinsic cardiac conduction system?

sinoatrial node (SA)

Atrioventricular node (AV)

Atrioventricular bundle (Bundle of His)

Bundle branches

Purkinje fibers

How many times per minute does the SA node fire?

75

How many times per minute do the AV node, bundles of His, and bundle branches fire?

40-60

How many times per minute do Purkinje fibers fire?

30

What is the function of the intrinsic conduction system?

initiate and distribute impulses so heart depolarizes and contracts in an orderly manner from atria to ventricles

What are the 5 parts of a normal electrocardiogram at rest?

P, Q, R, S, T

What is the pacemaker of the heart?

SA node

What does the P wave represent? What is it controlled by?

atrial depolarization, SA node

What does Q-R represent? What is it controlled by?

atrial repolarization, AV node

What does R-S represent? What is it controlled by?

Ventricular depolarization, AV node

What does T represent? What is it controlled by?

Ventricular repolarization, SA node

On average, how long should a single beat of the heart last?

0\.8seconds

What indicates a 1st degree heart block on an ECG

P-Q interval longer than 0.2 seconds

What is Frank Starling’s Law of the Heart?

the more cardiac muscle is stretched withing physiological limits, the more forcibly the heart will contract expressed with a rubber band analogy

increasing volumes of blood in ventricles increase the stretch and thus the force generated by ventricular wall contraction

Greater stretch means what?

more blood volume is pumped out within physical limits

What is meant by saying that the pulmonary and systemic circulation are arranged in a series?

blood must pass through the pulmonary vessels between each passage through the systemic circuits

How does blood interact with capillary beds in one normal pass?

Will encounter only one capillary bed before being collected in the veins and return to the heart

What circulations are the exceptions to capillary interaction rules?

splanchnic, renal, and certain brain circulations

What is splanchnic circulation?

a portal system for the blood supply to digestive system?

What is renal circulation?

blood enters kidney via the renal artery and passes through two sets of capillaries (glomerular and tubular) before returning to the veinous side of systemic circulation

What portal system does the brain have and what does it control?

hyothalamo-hypophyseal portal system, control of hormone secretion from pituitary gland

While pulmonary and systemic circulations are arranged in series, how are the various organs arranged?

parallel

Describe the general path of the systemic circulation

L. atrium → L. ventricle → systemic arteries → systemic capillaries → systemic veins → R. atrium → R. ventricle

What is the function of systemic circulation?

carried oxy blood from the left side of the heart through systemic arteries to all the organs and tissues. Return deoxy blood through systemic veins to right atrium where pulmonary circulation begins

What is the range of normal mean systemic arterial pressure?

70-105mm Hg

How is systemic blood pressure measured?

blood pressure cuffs, more invasively telemetry and catheters

What is the path of pulmonary circulation?

Right atrium, right ventricle, pulmonary arteries, pulmonary capillaries, pulmonary veins, left atrium, left ventricle

What is the function of pulmonary circulation?

carries deoxy blood from the r side of the heart through pulmonary arteries to the lungs. After receiving oxy and delivering CO2 in pulmonary capillaries, returns oxy blood through pulmonary veins to the L atrium where systemic circulation begins

What is the pressure of pulmonary circulation?

low pressure system, 10-22 mm Hg

How is the pressure of the pulmonary circulation measured?

pulmonary artery catheters

What % of blood sits in central circulation (meaning the heart, pulmonary vessels, and lungs)

25%

What % of blood is in systemic circulation outside of the heart?

75%

What % of systemic blood lies in arteries and arterioles?

15%

What % of systemic blood lies in capillaries?

5%

What % of systemic blood is kept in venules and veins?

80%

What substances are transported by blood?

oxygen, glucose, amino acids, fatty acids, and lipids

hormones!!

What does blood remove from organs for disposal?

CO2, lactic acid, nitrogenous wastes of protein metabolism

What are the two forms of transport in the CVS?

bulk flow and diffusion

What is bulk flow and its characteristics?

movement of blood from the heart to the distant parts of the body such as the head and limbs

rapid and requires energy

achieved by the difference in pressure between two points on the blood vessels known as perfusion pressure

What is CVS diffusion and its characteristics?

dissolved substances move across the blood vessels from the bloodstream into the interstitial fluid and vice versa

slow, passive, requires energy for the passive diffusion of a substance across the capillary wall

The source of energy is the concentration difference of substances between the capillary and interstitial spaces

What is cardiac output?

the volume of blood pumped per minute by right or left ventricle

What is the normal cardiac output in a resting dog?

3L/min/m^2

How is perfusion pressure calculated?

P(inlet) - P(outlet)

What is Transmural pressure?

pressure “across the wall”, difference in the pressure inside the blood vessel and the fluid pressure in the tissue immediately outside the vessel

will cause blood to flow out of vessels to exchange nutrients

P(inside)- P(outside)

What does it mean if transmural pressure is negative?

vein is collapsed

What is the composition of blood?

suspension of cells in liquid (RBC/Platelets, WBC, plasma)

How is blood responsible for distribution?

carries Oxy from lungs to cells

supplies nutrients from digestive system to cells

transports metabolic wastes from cells to disposal sites

transports hormones to target tissues/organs

How does blood function in regulation?

regulates body temperature, pH, and blood volume to support efficient circulation to cells, tissues, organs, and systems

What are the protective functions of the blood

prevents blood loss via clotting factors

prevents infection through the activity of WBCs, complement and antibodies

What is plasma?

acellular or extracellular liquid in the blood

What is the composition of plasma?

93% water, 7% plasma proteins

proteins include globulin, albumin, fibrinogen

gases such as oxygen, CO2, nitrogen

electrolytes (mainly Na and Cl), bicarbonate, potassium, calcium, magnesium, phosphates, sulfates

glucose, AA, vitamins, lipids

urea, creatinine, uric acid, bilirubin

hormones in small quantities

What is the order of plasma protein concentration??

Albumin (60%), globulins (36%), clotting proteins fibrinogen (4%)

What is serum?

liquid part of blood WITHOUT clotting proteins

What is hematocrit?

percent of formed elements (cells vs fluid)

\

What is normal hematocrit in dogs?

40-59%

What is normal hematocrit for cats?

29-50%

What makes blood appear red?

hemoglobin in RBC

What is another name for WBC

leukocytes

What do leukocytes include?

neutrophils, lymphocytes, monocytes, eosinophilsm and basophils

What is another term for platelets?

thrombocytes

What are thrombocytes?

fragments of megakaryocytes found in bone marrow

play a role in the control of bleeding through coagulation and clotting

What is involved in coagulation and clotting?

coagulation cascade

key step is the formation of thrombin, an enzyme that catalyzes the transformation of fibrinogen and fibrin

What are platelet factors?

react with Ca2++ and other clotting factors to initiate clot formation

What is thromboplastnin

a lipid tissue factor released from injured cell membranes which accelerates the clotting process

What are prostaglandins

lipids released from damaged cell membranes such as thromboplastin having localized effect

What is converted into thrombin? how?

prothrombin via prothrombin activator

What is the role of thrombin?

converts fibrinogen into fibrin (insoluble)

What is the role of fibrin in clot formation?

forms a mesh that glues the platelets and RBCs together

What role does vitamin K play in clot formation?

required by liver to produce prothrombin and several other clotting factors

What is the role of calcium in clot formation?

necessary for prothrombin → thrombin and fibrinogen → fibrin conversion

What is the role of thromboplastin in clot formation?

speeds up clot formation from 3-6 minutes to 15 seconds