Cardiovascular Physiology

Blood Pressure  =force exerted by the blood against the walls of the blood vessel; Changes throughout cardiac cycle –Systolic Blood pressure=maximal pressure achieved by ventricular contraction –Diastolic Blood pressure=lowest pressure remaining in blood vessels after ventricle contracts

 Blood flow - amount of blood flowing at any given time. Dependent on Cardiac output (CO).  Blood pressure - force per unit area exerted on wall of blood vessel  Autonomic Nervous System –Sympathetic – causes vasoconstriction of arterioles  Increases blood pressure –Parasympathetic – causes vasodilation  Decreases blood pressure Blood Pressure

 Systolic pressure  Diastolic pressure  Pulse pressure = systolic - diastolic  MAP = Diastolic + (Pulse pressure/3)  Hypotension - Low blood pressure (Nutritional, anesthesia)  Hypertension - High blood pressure (increased peripheral resistance, high blood viscosity) Blood Pressure

Pressure  Systemic circulation-high hydraulic pressure required to overcome gravitational forces and resistance  Arteriole-vessels with high resistance to reduce pressure before reaching capillary beds  Pulmonary Circulation-low pressure, due to low resistance to blood flow

Effects of High Blood Pressure  Abnormally high blood pressure within veins-can cause leaking of fluid from blood vessels –Result-edema –Congestive heart failure  Right heart failure-leaking of fluid from vena cava –Pleural effusion  Left heart failure-leaking of fluid within lungs –Pulmonary edema

Distribution of Blood Flow  Pulmonary Circulation – 15%  Systemic Circulation – 80% –65% in veins –10% in arteries and arterioles –5% in capillary beds  Heart – 5%

Functions of the CV System  Maintain blood pressure within the arteries  Maintain blood flow to the tissues  Maintain normal blood pressures within the capillaries and veins =Perfusion

Perfusion  Allows delivery of oxygen and nutrients (i.e. glucose)  Removal of waste products –Carbon dioxide  Transport of hormonal messages from one part of the body to another

Forces  Heart must adjust contractility (inotropic state) based on forces working on the heart. –Preload –Afterload

Afterload  =Sum of forces the ventricles must contract against to make blood flow forward  Increased systemic blood pressure –Increases or Decreases Afterload???? –Chronic blood pressure-increases the work of the heart-heart enlarges!

Preload  =Amount of blood in the heart just prior to contraction of the ventricle  =Venous Return or amount of blood returning to the heart –Leaky valves-regurgitate blood back into the atrium  Increases or Decreases Preload??

Inotropic State  Adjustments in contractility based on Calcium and contractile protein interactions –Sympathetic tone (norepinephrine- neurotransmitter) –Increases heart rate and contractility by increasing Calcium availability –Starling’s law-increased contractility with stretching of sarcomere

The Cardiac Cycle  “Pacemakers” of the heart-send electrical signal through heart –Systole-ventricular contraction –Diastole-Heart is relaxed allowing filling of the heart **Based on Ventricle, although atria also contract and relax

The Cardiac Cycle  End of Diastole-maximal ventricular filling  Electrical signal-triggers ventricular contraction.  Pressure in Ventricle > Atria = closes AV valves; semilunar valves not open yet

The Cardiac Cycle  First Heart Sound =closure of AV valves  Semilunar Valves open once pressure in ventricle is greater than aorta or pulmonary artery  Stroke Volume = amount of blood ejected (end diastolic volume-end systolic volume)  Second Heart Sound= Closure of the Semilunar valves

The Cardiac Cycle  Semilunar Valve-open  AV valves-closed  Ventricle Relaxes  Once pressure in the ventricle is less than the atrium-AV valves open allowing filling of ventricle  Third heart sound =passive filling of the ventricle –Normal to hear in horses and ruminants-not carnivores

Ventricular Filling  Initial, rapid filling phase-passive  Slow-filling phase-atrial contraction  Fourth heart sound =atrial contraction –Normal in ruminants and equine, not in carnivores

Cardiac Muscle  Striated muscle  Impulse from cell to cell  Automaticity-cells can become self- excitable –Small portion of the muscle cells

Activation of cell  Depolarization=Opening of fast sodium channels  Wave of depolarizations travels down myocardium-Ca++ channels open in sarcoplasmic reticulum –Crosslink of myocardium  Refractory Period-resting between depolarization, unable to contract

Cardiac Impulse Propagation  Automatic Tissues-generate action potentials  Sequence of activation –Sinoatrial (SA) node-fastest rate!  Atrial Contraction –AV node –Bundle of His –Rt. And Lt. Bundle Branch to v. apex –Purkinje fibers to myocardium

Conduction Propagation

Action Potential 

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THE WHOLE PICTURE CHARGE INSIDE CELL TIME Na + influx creates (+) internal charge Resting cell Depolarization Repolarization K+ leaves cell and cell returns to it’s resting or repolarized state **Purple numbers indicate phase numbers

Action Potential  0-Sodium enters cell via fast channels  1-fast sodium channels close  2-Ca and Na enter cell via slow channels  3-K exits cells  4- Na and K equilibrium

Intrinsic Rate  SA node-fastest  AV note bpm  Sympathetic and Parasympathetic Nervous System-alter the intrinsic rate –SNS-increase rate of depolarization –PNS-decrease rate of depolarization

Heart Rate Regulation  Baroreceptors-in blood vessels and heart chamber –If blood pressure decreases  Brain>>Increased Sympathetic nervous system  Increases Heart rate and vasoconstricts to increase blood pressure –If blood pressure increases?

Excitation-Contraction Coupling  See muscle physiology!!  Ca++ influx  Myofibrils couple via troponin/tropomysin complex

The Electrocardiogram (ECG)  Recording of electrical activity of the heart  Waves-positive vs. negative depending on the direction the impulse is traveling

 P wave- –Atrial depolarization  QRS complex –Ventricular depolarization  T wave-ventricular repolarization ECG

Conduction

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