Esraa kiwan

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.

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

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.

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 lungsSystemic circulation: is a circuit of vessels carrying blood between the heart and other body systems

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

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.

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.

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

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.

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

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.

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

SA node has the fastest rate of autorythmicity

So SA node leading the action potential in the heart (pacemaker)

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

An action potential originating in the SA node first spreads throughout both atria:Gap junctionsInteratrial pathway (rapidly

transmits action potential from SA node to left atrium) → ensure that the both atrium depolarized to contract simultaneously

Internodal pathway

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

A network of ventricular conduction system is specialized for rapid propagation of action potentialBundle of HisPurkinje fiber

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

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

Wave = upwards or downwards deflectionSegment = flat portion between wavesInterval = often a wave plus a segment

The cardiac cycle consists of alternate periods of:Systole: contraction and emptyingDiastole: relaxation and filling

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

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

Ventricular Filling:

End Of Ventricular Diastole: Ventricular diastole ends at the onset of ventricular Ventricular diastole ends at the onset of ventricular

contractioncontraction Complete of atrium contraction and ventricular fillingComplete of atrium contraction and ventricular filling End diastolic volume (EDV) : End diastolic volume (EDV) : volume of blood in the volume of blood in the

ventricle at the end of diastole 135 ml (maximum ventricle at the end of diastole 135 ml (maximum blood volume in this cycle)blood volume in this cycle)

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

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

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

End Of Ventricular Systole: Endsystolic volume (ESV):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

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

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

11stst heart sound (lub): heart sound (lub): Its associated with closure of AV valvesLow pitched, soft and relatively longThe onset of ventricular systole

22ndnd heart sound (dub): heart sound (dub): Its associated with closure of semilunar valvesHigher pitched, sharper and shorterThe 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

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)

Cardiac output = Stroke Volume X Heart Rate

CO = SV x HR

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 HRCO= 70 ml/beat x 70

beats/min = 4,900 ml/min ≈ 5

liters/min

Resting cardiac output ≈ 5 L/minDuring 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 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

Extrinsic control: (sympathetic nervous (sympathetic nervous system)system)

Arterial muscle: increases contractilityVentricular muscle: increases contractilityAdrenal medulla: increase epinephrine (augments the sympathetic actions on the heart)Veins: increase venous return

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

Blood PressureBlood pressure is the force exerted by the

blood against a vessel wall Depends on:

Volume of blood contained within the vesselCompliance or Distensability of the vessel wall

Blood PressureDuring 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 PressurePulse 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 outputTotal peripheral resistanceBlood volume

Blood pressure= cardiac output X peripheral resistance

Cardiac output= HR X SVTotal 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 PressureCardiac output= HR X SVHR

SV

Regulation Of Blood Pressure

Total peripheral resistance:

Regulation of Blood Pressure

Regulation of Blood Pressure

Baroreceptor:

Regulation of Blood PressureBaroreceptor:

Regulation of Blood PressureBaroreceptor:

Regulation of Blood PressureBlood volume: