BIO 202 Lab: Section 2.3/3.1 - Cardiac Physiology

What are the two populations of cardiac myocytes (heart cells)

Nonpacemaker cells or regular contractile myocytes (makes up 99%) & Pacemaker cells (makes up 1%)

What are the unique property of pacemaker cells

Spontaneous depolarizing and generating action potentials

What do clusters of pacemaker cells made up

Cardiac conduction system that is throughout the heart

What are the main parts of the cardiac conduction system

Sinoatrial (SA) node, Atrioventricular (AV) node, Purkinje system

What is the function of the action potentials generated by pacemaker cells

The actions potential they initiate trigger action potentials of nonpacemaker cells, causing these cells to contract.

Where is the sinoatrial (SA) node located and what is its function

Upper right atrium. Acts as main pacemaker of heart, depolarizing spontaneously around 60 times per minute

Why is the heart rate generally higher than 60 beats per minute initiated by the SA node

Due to the influence of the autonomic nervous system

Where is the atrioventricular (AV) node located and what is its role

Lower right atrium just medial to tricuspid valve. It acts as a backup pacemaker and can pace the heart at about 40 beats per minute

What is the AV node delay and why is it important

It is a slow conduction through the AV node which allows for atria to depolarize and contract before the ventricles, allowing ventricles to fill with blood

What is the Purkinje system and what does it do

A group of pacemaker cells that transmit impulses from the AV node to the ventricle

How do myocytes of the Purkinje system pace

They pace the heart slowly but conduct impulses more rapidly than any part of the conduction system

What are the 3 components of the Purkinje system

Atrioventricular (AV) bundle or bundle of his, Right and left bundle branches, and Purkinje fibers

What is the atrioventricular (AV) bundle or bundle of his (1 of 3 components of purkinje system)

Small group of fibers in lower interatrial septum and upper interventricular septum that transmits impulses from AV node to ventricles

What is the function of right and left bundle branches in the cardiac conduction system (1 of 3 components of purkinje system)

They transmit impulses from AV bundle down either side of the interventricular septum by right/left bundle branches

How do the Purkinje fibers form

At the end of interventricular septum, the right/left bundle branches fan out through the myocardium as Purkinje fibers.

What is the role of the Purkinje fibers

The fibers extend 1/3 of the way into the heart muscle, blending with regular nonpacemaker cardiac myocytes.

What is an electrocardiogram (ECG or EKG)

A graph of the heart’s electrical activity expressed in millivolts (mV) over time

What instrument is used to obtain an ECG

Electrocardiograph

Where are electrodes placed to obtain an ECG

On arms and legs (limb leads) and along the chest (chest leads)

What is the purpose of an ECG

To detect if the electrical conduction pathway within the heart is normal and if any damage has been done to the heart

What are the 3 waves that appear in a typical lead II recording

P, QRS complex, and T

What do the waves represent in an ECG

Each wave represents an electrical event called a depolarization or a repolarization, which stimulate cardiac muscle within heart wall to contract or relax

What does P wave represent

Atrial depolarization - at the end of P wave, both atria have depolarized casing the atria to contract

What does QRS complex represent

Ventricular depolarization - at the end of QRS complex, both ventricles have depolarized causing ventricles to contract (atrial repolarization also occurs here but is masked by ventricular depolarization)

What does T wave represent

Ventricular repolarization - at the end of T wave, both ventricles have repolarized, causing ventricles to relax

What are 2 types of variations that may signal abnormalities

Variation in wave height (elevated or depressed) and variation in normal time intervals

What might a elevated P wave indicate

Atrial enlargement

What might a elevated QRS wave indicate

Ventricular enlargement

What might a tall and pointed T wave indicate

Myocardial ischemia

What is the P-R interval and its normal time interval

Time from beginning of P wave to start of QRS complex - 0.2 seconds

What is the S-T segment and its normal time interval

Time from end of S wave to beginning of T wave - 0.1 seconds

What is the Q-T segment and its normal time interval

Time from beginning of QRS complex to end of T wave - 0.4 seconds

What would a much longer P-Q interval indicate

A blockage in normal conduction pathway

What would a longer than normal Q-T segment indicate

Myocardial damage

What is blood pressure

The pressure exerted by the blood on the walls of the blood vessels

What 3 factors is blood pressure determined by

Cardiac output, peripheral resistance, blood volume

What is cardiac output (1 of 3 factors in BP)

Amount of blood each ventricle pumps in 1 minute. It is the product of stroke volume and heart rate

What is stroke volume (part of cardiac output)

The amount pumped with each beat

What is peripheral resistance (1 of 3 factors in BP)

Any impedance to blood flow encountered in blood vessels.

What is peripheral resistance determined by

Largely by the degree of vasoconstriction or vasodilation in the systemic circuit.
Vasoconstriction increases peripheral resistance.
Vasodilation decreases peripheral resistance
Other factors that influence resistance: obstructions in arteries

What is blood volume and what influences/controls it (1 of 3 factors in BP)

Amount of blood found in blood vessels at any given time. Greatly influenced by overall fluid volume and largely controlled by kidneys and endocrine system hormones

What factors can be altered quickly to change blood pressure and how fast does it occur

Cardiac output and peripheral resistance - alternations occur slowly and require 2/3 days to have noticeable effect

What instrument is used to measure atrial blood pressure

Sphygmomanometer and stethoscope

What is systolic pressure

Pressure in arteries during ventricular systole. The peak arterial BP attained during ventricular contraction. Averages between 100 and 120 mmHg (larger of the 2 readings)

What is diastolic pressure

Pressure in arteries during ventricular diastole and the minimum arterial BP occurring during ventricular relaxation between heart beats. Averages between 60 and 80 mmHg (smaller of the 2 readings)

What is sound of korotkoffW

When the cuff is inflated, it compresses brachial artery and cuts off blood flow. When pressure is released to level of systolic arterial pressure, blow flow continues but becomes turbulent. The result in sound is Sounds of Korotkoff

What is cardiac output (CO)

Amount of blood pumped out of a ventricle in 1 minute expressed in milliliters of blood per minute

How do you find cardiac output

CO = SV x HR (mL/min) → stroke volume times the heart rate

What is the value of a normal stroke volume

About 70 mL for an adult heart (it is the amount of blood pumped out of each ventricle in 1 beat)

What is preload (factors affecting stoke volume)

Amount of tension in ventricular cardiac muscle cells prior to contracting - The greater the tension on cells, the more forcefully they contract called Frank-Starling Law (ex: exercise increases stoke volume)

What is contractility (part of factors affecting stoke volume)

The degree to which cardiac muscle cells can shorten when stimulated by a specific chemical substance. (ex: abnormally low levels of calcium result in an irregular heartbeat, decreasing the stoke volume)

What is afterload (part of factors affecting stoke volume)

Amount of force needed from ventricular cardiac muscle cells to eject blood from the ventricles and past the semilunar valves. Anything that impedes blood flow can increase afterload. (ex: as afterload increases, the stoke volume decreases)

What are factors that affect heart rate

Age, sex, state of activity, endurance training, stress/anxiety

How do you maintain cardiac output

Primarily the job of cardiovascular (CV) center in medulla oblongata of brain. Hormones also help control cardiac activity

What are the 3 layers that make up the walls of arteries and veins and what type of cells are they made out of

Tunica interna/Tunica intima: innermost lining consisting of specialized simple squamous epithelium called endothelium
Tunica media: middle layer consisting of smooth muscle (controls diameter of vessel/perfusion/BP) and elastic fibers (allow vessel to expand and return to orginal shape/diameter)
Tunica externa/Tunica adventitia: outermost layer consisting of dense irregular collagenous connective tissue

Describe the tunica media in arteries, veins, and capillaries

Arteries have much thicker tunica media with prominent elastic fibers (branch into tiny capillary beds)
Veins have thin tunica media with few elastic fibers
Capillaries are extremely thin-walled and consist of only thin tunica interna

Describe the 3 major circuits of blood flow

Systemic circuit: delivers oxygenated blood in body
Coronary circuit: delivers oxygenated blood to heart
Pulmonary circuit: delivers deoxygenated blood to lungs