Cardiovascular System

Heart Actions A. The cardiac cycle consists of the atria beating in unison (atrial systole) followed by the contraction of both ventricles, (ventricular systole) then the entire heart relaxes for a brief moment (diastole).

B. Cardiac Cycle 1. During the cardiac cycle,

pressure within the heart chambers rises and falls with the contraction and relaxation of atria and ventricles.

2. When the atria fill, pressure in the atria is greater than that of the ventricles, which forces the A-V valves open.

3. Pressure inside atria rises further as they contract, forcing the remaining blood into the ventricles.

4. When ventricles contract, pressure inside them increases sharply, causing A-V valves to close and the aortic and pulmonary valves to open.

a. As the ventricles contract, papillary muscles

contract, pulling on chordae tendinae and preventing the backflow of blood through the A-V valves.

C. Heart Sounds1. Heart sounds are due to

vibrations in heart tissues as blood rapidly changes velocity within the heart.

2. Heart sounds can be described as a "lubb-dupp" sound.

3. The first sound (lubb) occurs as ventricles contract and A-V valves are closing.

4. The second sound (dupp) occurs as ventricles relax and aortic and pulmonary valves are closing.

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D. Cardiac Conduction System 1. Specialized cardiac muscle tissue

conducts impulses throughout the myocardium and comprises the

cardiac conduction system.2. A self-exciting mass of

specialized cardiac muscle called the sinoatrial node (S-A node or pacemaker), located on the posterior right atrium, generates the impulses for the heartbeat.

3. Impulses spread next to the atrial syncytium, it contracts, and impulses travel to the junctional fibers leading to the atrioventricular node (A-V node) located in the septum.

a. Junctional fibers are small, allowing the atria to

contract before the impulse spreads rapidly over the ventricles.

4. Branches of the A-V bundle give rise to Purkinje fibers leading to papillary muscles; these fibers stimulate contraction of the papillary muscles

at the same time the ventricles contract.

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F. Electrocardiogram1. An electrocardiogram is a recording of the electrical changes that occur during a cardiac cycle.2. The first wave, the P wave, corresponds to the depolarization (contraction) of the atria.3. The QRS complex corresponds to the depolarization of ventricles (contraction) and hides the repolarization (relaxation) of atria.

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4. The T waves end the ECG pattern and corresponds to ventricular repolarization (relaxation).

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1. Atria begin depolarize2. Atria depolarize.

3. Ventricles depolarize at apex; atria repolarize4. Ventricles depolarize

5. Ventricles begin repolarization at apex.6. Ventricles repolarize.

How to read one?

• Watch the movie and find out.

Diagnostic Value of ECG

• Abnormalities in conduction pathway

• Myocardial infarction (heart attack)

• Heart enlargement

• Electrolyte and hormone imbalance

• Ischemia-blood supply restriction

Fast heart; chest pain, Shortness of breath, abnormal pacemaker

Heart rate is less than 60 beats

Blood pressure

• Systolic (pressure in arteries when ventricles contract) over diastolic (pressure in arteries when ventricles are filling up with blood) pressure

• 120/80 is normal

• Pulse (normal is 60 to 100 beats)-expanding and recoiling of arteries

• Many factors influence blood pressure

Factor 1: Heart action• Stroke volume-blood leaving the LV with each

contraction– 70 milliliters

• Cardiac output-how much volume pumped from LV in one minute (stroke volume x heart rate)

• Decrease stroke volume-cardiac output and blood pressure decrease

• Increase stroke volume-cardiac output and bp increase

• An average person has a resting heart rate of 70 beats/minute and a resting stroke volume of 70 mL/beat. The cardiac output for this person at rest is:

Cardiac Output = 70 (beats/min) X 70 (mL/beat) = 4900 mL/minute.

• Average person cycles his/her 5 L of blood each minute at rest.

• Important for heart abnormalities

Blood volume

• Sum of formed elements and plasma volumes in the vascular system

• Blood pressure is directly proportional to blood volume

• Can change due to dehydration, blood transfusion, hemorrhage

Peripheral Resistance and blood viscosity

• Peripheral resistance-Force caused by friction between blood and vessel walls

• Blood viscosity-ease of fluid movement– Greater viscosity, harder it is to flow (more

resistance to flow)– More force is needed to push blood through– Factors=temperature (higher temp lower viscosity),

anemia, chronic low oxygen levels so increase in RBC formation

Control of Blood Pressure• Controlled by cardiac output and peripheral

resistance

• More blood that enters the heart, the stronger the ventricle contracts, greater stroke volume, greater cardiac output

• Factors that control these items– Autonomic nervous system responses – Peripheral resistance

Basoreceptors

• Located in aortic arch• Arterial blood increases, basoreceptors send nerve

impulse to medulla oblongata• Sends impulse to SA node

– Cause heart rate to decrease– Blood pressure return to normal

• Arterial blood decreases, sends signal to SA node to increase heart work– Exercise, rise in temp, emotions

Peripheral Resistance• Change in arterioles control this

• Vasoconstriction-increase resistance; blood pressure decreases; constricts and increase resistance– Epinephrine and norepinephrine

• Vasodialation-decrease resistance; blood pressure rises, dialate and decrease resistance– Exercise, increase in carbon dioxide and decrease

in oxygen

Hypertension

• Hypertension-high blood pressure in arteries– Caused by kidney disease, high sodium intake,

obesity, stress, arteriosclerosis– Lead to enlarged heart due to increase pumping

action of LV– Cause embolism, thrombosis, stroke

Vein Control

• Skeletal muscles-pushes blood to the heart

• Breathing movements

• Vasoconstriction-low pressure causes muscles to contract