Cardiovascular System Esraa kiwan

Cardiovascular System The cardiovascular system consists of 3 main components: The heart: it functions as a pump that establishes pressure gradient necessary for the blood to flow to tissues. The blood vessels: they serve as passageways through which blood is distributed to the body parts. The blood: serves as the transport medium through which transported materials are dissolved or suspended.

Heart The heart is divided into right and left halves and have four chambers: The upper chambers, the atria (right and left) receive blood & passes it to the ventricles The lower chambers, the ventricles (right and left) pump the blood away from the heart

Blood Vessels The blood vessels: they serve as passageways through which blood is distributed to the body parts. The Heart → Large Artery → Smaller Arteries→ Arterioles → Capillaries→ venules → Veins→ and then to superior and inferior vena cava and then reach the right atrium.

Cardiovascular System Blood travels continuously through the circulatory system to and from the heart through two separated vascular loops: Pulmonary circulation: consists of a closed loop of vessels carrying blood between the hearts and lungs Systemic circulation: is a circuit of vessels carrying blood between the heart and other body systems

Cardiovascular System Pulmonary circulation: Right ventricle (deoxygenated blood) → pulmonary artery→ pulmonary capillaries (O2and CO2 exchange) → pulmonary veins (oxygenated blood)→ left atrium Systemic circulation: Left ventricle (oxygenated blood) → Aorta→ systemic capillaries (exchange) → systemic veins (deoxygenated blood)→ right atrium

Cardiovascular System In the pulmonary circulation ALL the blood flows to the lungs, on the contrary, the systemic circulation is a series of parallel pathways each one reaching a certain organ, so only PART of the blood pumped by the left ventricle reaches each organ system.

Cardiovascular System Both sides of the heart pump equal amounts of blood simultaneously.  The pulmonary circulation is a low pressure, low resistance system The systemic circulation is a high pressure, high resistance system So even the right & left sides of the heart pump equal amounts of blood, the left side still performs more work than the right side. Accordingly, the heart muscle on the left side is much thicker than on the right.

Cardiovascular System Heart valves: One way heart valves ensure the unidirectional flow of blood Open and close passively according to pressure difference

Cardiovascular System Heart valves: Right atrioventricular valve (tricuspid valve): this valve is located between the right atrium & ventricle. Left atrioventricular valve (mitral valve): this valve is located between the left atrium & ventricle. Aortic valve: this valve is located at the junction where the aorta leaves the left ventricle. Pulmonary valve: this valve is located at the junction where the pulmonary artery leaves the right ventricle.

Electrical Activity of The Heart Autorhythmicity: The heart beats or contracts as a result of action potentials generated by itself, without the need for nervous stimulation There are 2 specialized types of cardiac cells: Contractile cells: which perform the mechanical work of pumping. They can’t generate action potentials Autorhythmic cells: They are specialized for initiating and conducting action potentials

Electrical Activity of The Heart The cardiac autorhythmic cells display “pacemaker activity”, that is, their membrane depolarizes slowly between action potentials until it reaches a threshold at which firing occurs.

Electrical Activity of The Heart The specialized cardiac cells capable of autorhythmicity lie in the following specific sites: Sinoatrial node (SA node) Atrioventricular node (AV node) Bundle of His (AV bundle) Purkinje fibers

Electrical Activity of The Heart SA node has the fastest rate of autorythmicity So SA node leading the action potential in the heart (pacemaker)

The spread of cardiac excitation is coordinated to ensure efficient pumping The spread of excitation should satisfy three criteria: Atrial excitation and contraction should be complete before the onset of ventricular contraction 80% of ventricles filling occur passively 20 % of ventricles filling occur as result of atria contraction Excitation of cardiac muscle fibers should be coordinated to ensure that each heart chamber contract as a unit to pump efficiently The pair of atria and pair of ventricles should be functionally coordinated so that both members of the pair contract simultaneously

Atrial Excitation An action potential originating in the SA node first spreads throughout both atria: Gap junctions Interatrial pathway (rapidly transmits action potential from SA node to left atrium) → ensure that the both atrium depolarized to contract simultaneously Internodal pathway

Spread of Cardiac Excitation

Conduction Between the Atria and the Ventricles AV node is the only point of electrical contact between the atria and ventricles The action potential is conducted relatively slowly through the AV node AV node delay 100 msec (ensure that Atrial excitation and contraction occur and complete before the onset of ventricular excitation and contraction

Ventricular Excitation A network of ventricular conduction system is specialized for rapid propagation of action potential Bundle of His Purkinje fiber

Spread of Cardiac Excitation

Action potential of cardiac contractile cells

Excitation-contraction Coupling In Cardiac Contractile Cells

Excitation-contraction Coupling In Cardiac Contractile Cells

Relationship of an action potential and the refractory period to the duration of the contractile response in cardiac muscle Refractory period: this is a period of time during which a second AP cant be triggered until the end of the preceding action potential In skeletal muscles the refractory period is very short compared with the period of muscle contraction (fiber can restimulated before the end of 1st contraction) In cardiac muscle the refractory period is much longer than in skeletal muscles due to prolonged plateau phase Cardiac muscles cant be restimulated before the end of contraction

Electrocardiogram (ECG) Is a record of overall spread of electrical activity through heart Recording part of electrical activity induced in body fluids by cardiac impulse that reaches body surface Not direct recording of actual electrical activity of heart Recording of overall spread of activity throughout heart during depolarization and repolarization Not a recording of a single action potential in a single cell at a single point in time

Electrocardiogram (ECG)

Electrocardiogram (ECG)

Electrocardiogram (ECG)

Electrocardiogram (ECG) Wave = upwards or downwards deflection Segment = flat portion between waves Interval = often a wave plus a segment

Electrocardiogram (ECG)

Electrocardiogram (ECG)

Cardiac Cycle The cardiac cycle consists of alternate periods of: Systole: contraction and emptying Diastole: relaxation and filling

Cardiac Cycle

Cardiac Cycle

Cardiac Cycle Early Ventricular Diastole: Ventricle and Atrium in diastole Correspond to the TP interval Atrial pressure slightly exceeds ventricular pressure AV valve open Semilunar valves closed Ventricle passive filling (80%) Ventricular volume continues to elevate

Cardiac Cycle Late Ventricular Diastole: Ventricle in diastole and atrium in systole Correspond to the PR interval Atrial pressure exceeds ventricular pressure AV valve open Semilunar valves closed Ventricle active filling (20%) Ventricular volume continues to elevate

Cardiac Cycle Ventricular Filling:

Cardiac Cycle End Of Ventricular Diastole: Ventricular diastole ends at the onset of ventricular contraction Complete of atrium contraction and ventricular filling End diastolic volume (EDV) : volume of blood in the ventricle at the end of diastole 135 ml (maximum blood volume in this cycle)

Cardiac Cycle Onset Of Ventricular Systole: Ventricular contraction begins Ventricular pressure immediately exceeds that of atrium AV valve closed

Cardiac Cycle Isovolumetric Ventricular Contraction: Ventricular pressure more than atrium pressure (AV valve closed) , and less than aortic pressure (Aortic valve closed) Left ventricle is closed chamber (no blood entering or leaving constant volume and length of muscle fibers ) Ventricular pressure continues to increase but still less than aortic pressure

Cardiac Cycle Ventricular Ejection: Ventricular pressure more than Aortic pressure (Aortic valve open) (AV valve close) Aortic pressure rises as blood is forced into the aorta Decrease ventricular volume Stroke volume (SV): The volume of blood pumped of each ventricle with each contraction 70 ml

Cardiac Cycle End Of Ventricular Systole: Endsystolic volume (ESV):the amount of blood left in the ventricle at the end of systole when ejection is complete (65 ml) EDV-ESV=SV → 135-65=70 ml

Cardiac Cycle Onset Of Ventricular Diastole: Ventricle start to relax Ventricular pressure below aortic pressure Aortic valve closed No more blood leave ventricle

Cardiac Cycle Isovolumetric ventricular relaxation: Ventricular pressure more than atrium pressure (AV valve closed) , and less than aortic pressure (Aortic valve closed) Left ventricle is closed chamber (no blood entering or leaving constant volume and length of muscle fibers ) Ventricular pressure continues to decrease

Cardiac Cycle

Cardiac Cycle

Cardiac cycle (at rest) 800 msec Diastole 300 msec Systole

Heart Sound 1st heart sound (lub): 2nd heart sound (dub): Its associated with closure of AV valves Low pitched, soft and relatively long The onset of ventricular systole 2nd heart sound (dub): Its associated with closure of semilunar valves Higher pitched, sharper and shorter The onset of ventricular diastole

Blood normally flows in a laminar fashion (layer of fluid slide smoothly over each other, doesn't produce sound When blood flow become turbulent, a sound is produced, due to vibrations created in the surrounding structures

Cardiac Output Cardiac Output: is the volume of blood pumped by each ventricle per minute

Cardiac Output Cardiac output = Stroke Volume X Heart Rate CO = SV x HR Stroke Volume: volume of blood pumped by each ventricle per beat or stroke (averages 70 ml/beat) Heart Rate: heart beats/min (averages 70 beats/min)

CO= 70 ml/beat x 70 beats/min Cardiac Output Stroke Volume: volume of blood pumped per beat or stroke (averages 70 ml/beat) Heart Rate: heart beats/min (averages 70 beats/min) CO = SV x HR CO= 70 ml/beat x 70 beats/min = 4,900 ml/min ≈ 5 liters/min

Cardiac Output Resting cardiac output ≈ 5 L/min During exercise cardiac output can increase to 20 to 25 L/min Cardiac reserve: the difference between the cardiac output at rest and the maximum volume of blood the heart can pump per minute

Cardiac Output CO = SV x HR Cardiac output depends on heart rate and the stroke volume ( cardiac output increases or decreases in response to changes in heart rate or stroke volume . i.e. when one of them increase it will increase the cardiac out put) CO = SV x HR

The heart is innervated by both divisions of the autonomic nervous system (sympathetic & parasympathetic), which can modify the rate & strength of contraction. (not initiation of contraction)

Autonomic Regulation of HR

Stroke Volume Control Two types of controls influences stroke volume: Intrinsic control  The extent of venous return Extrinsic control  The extent of sympathetic stimulation of the heart Both factors increase stroke volume by increasing the strength of contraction of the heart

Stroke Volume Control Intrinsic control: Intrinsic ability to regulate SV (output) in response to changes in venous return (input)

Stroke Volume Control

Stroke Volume Control Extrinsic control: (sympathetic nervous system) Arterial muscle: increases contractility Ventricular muscle: increases contractility Adrenal medulla: increase epinephrine (augments the sympathetic actions on the heart) Veins: increase venous return

Effect Of Sympathetic Stimulation On SV

Shift of the frank starling curve to the left by sympathetic stimulation

Cardiac Output Regulation

Blood Pressure Blood pressure is the force exerted by the blood against a vessel wall Depends on: Volume of blood contained within the vessel Compliance or Distensability of the vessel wall

Blood Pressure During each heartbeat, Blood pressure varies between a maximum (systolic) and a minimum (diastolic) pressure Systolic pressure: The maximum pressure exerted in the arteries when the blood is ejected into them during ventricular systole  averages 120 mmHg Diastolic pressure: The minimum pressure within the arteries occurs when the blood is draining off into the rest of vessels during ventricular diastole  averages 80 mmHg

Blood Pressure Measurement Directly: inserting a needle (a canula) to blood vessel, which is linked to a device measure the blood pressure Indirectly: through the use of a sphygmomanometer

Blood Pressure Measurement

Blood Pressure Pulse pressure: is the difference between systolic and diastolic pressure (systolic – diastolic) Blood pressure = 120/80 Pulse pressure  40 mmHg Mean arterial pressure: is the average pressure responsible for driving blood forward MAP= diastolic pressure + 1/3 pulse pressure = 80 + (1/3 * 40) = 93 mmHg

Regulation of blood pressure Blood pressure is regulated by controlling: Cardiac output Total peripheral resistance Blood volume Blood pressure= cardiac output X peripheral resistance Cardiac output= HR X SV Total peripheral resistance depends on the radius of all arterioles as well as blood viscosity Resistance 1/r ( r: radius of the vessel)

Regulation of Blood Pressure Cardiac output= HR X SV HR SV

Regulation Of Blood Pressure Total peripheral resistance:

Regulation of Blood Pressure

Regulation of Blood Pressure Baroreceptor:

Regulation of Blood Pressure Baroreceptor:

Regulation of Blood Pressure Baroreceptor:

Regulation of Blood Pressure Blood volume: