ANATOMY: 1.5 - monitoring the circulatory system

Explanation of how the heart beats

Your heart contains specialized cells that conduct electrical impulses. These impulses stimulate your heart cells and cause them to contract; in other words, this is what makes your heart beat!

Order of electrical signal passage through the heart

1. Sinoatrial (SA) node → 2. Atrioventricular (AV) node → 3. Bundle of His → 4. Bundle Branches → 5. Purkinje Fibers

Sinoatrial (SA) node

Also known as the “pacemaker,” this structure initiates a heartbeat

Atrioventricular (AV) node

This structure delays the nerve impulse, allowing the ventricles to fill up with blood

Bundle of His

This structure carries the electrical signal from the AV node to the Purkinje fibers

Purkinje Fibers

These structures cause the cells of the ventricles to contract almost simultaneously

What is responsible for the first heart sound (“lub”)?

The closing of the atrioventricular (AV) valves as blood is pumped from the atria to the ventricles

What is responsible for the second heart sound (“DUB”)?

The closing of the semilunar valves as blood is pumped from the ventricles to the arteries

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Name one cause for heart murmurs

Stenosis causing heart murmurs

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Definition of ECG

The electrical signals that cause your heart to beat can be measured using electrodes. These voltage measurements produce a printout called an electrocardiogram (ECG).

P wave?

SA node fires and the atria contract

Q?

Impulse is delayed at AV node; ventricles fill

QRS Complex?

AV node stimulates the ventricles to contract and the atrioventricular valves close

T wave?

It occurs when the ventricles relax and semilunar valves close

Definition of blood pressure

The force that blood exerts against the walls of blood vessels

Definition of systole

When the ventricles contract, they force blood out of the pulmonary arteries and aorta, increasing pressure in these vessels. This phase is known as systole.

Definition of diastole

After pumping blood out of these vessels, the ventricles relax, decreasing pressure in these vessels. This phase is known as diastole.

Definition of sphygmomanometer

Blood pressure readings can tell medical professionals about the health of the heart and vessels. It is measured using a device called a sphygmomanometer.

Blood pressure is recorded as a fraction, and the units used to measure it are millimeters of mercury (mmHg).

Units of blood pressure measurement

Systolic pressure

120

Diastolic pressure

80

Explanation of how the heart beats

Your heart contains specialized cells that conduct electrical impulses. These impulses stimulate your heart cells and cause them to contract; in other words, this is what makes your heart beat!

Heart rate

The number of heartbeats per minute

Stroke volume

The volume of blood pumped out of the heart with each heartbeat

Cardiac output

The volume of blood pumped out by the heart in mL/min

Formula for cardiac output

Cardiac Output = Heart Rate x Stroke Volume

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