Physiology of the Cardiovascular System - Week 4

Cardiac Conduction System

Self-excitable muscle fibers that act as a pacemaker and initiate action potentials.

P-Wave

Represents atrial depolarisation as the action potential moves through the atria.

QRS Complex

Represents ventricle depolarisation as the action potential moves through the ventricles.

T-Wave

Represents ventricle repolarisation as the ventricles start to relax.

First Heart Sound (Lubb)

Caused by blood hitting closed atrioventricular (AV) valves.

Second Heart Sound (Dupp)

Caused by blood hitting closed semilunar (SL) valves.

Cardiac Output Formula

CO = Stroke Volume (SV) multiplied by Heart Rate (HR).

Stroke Volume (SV)

The volume of blood ejected by the ventricle each contraction.

Factors Affecting Stroke Volume

Preload, contractility, and afterload.

What is preload in relation to the heart?

The amount the heart is stretched before it contracts.

What happens to stroke volume when preload increases?

It increases.

What is end-diastolic volume?

The volume of blood in the ventricles at the end of diastole.

What factors influence preload?

Duration of ventricular diastole and venous return.

What is afterload?

The pressure required to eject blood from ventricles.

How does an increase in afterload affect stroke volume?

↑ afterload = ↓ stroke volume.

What conditions can increase afterload?

Hypertension and atherosclerosis.

Cardiovascular Centre

Located in the medulla oblongata to regulate heart rate and blood pressure.

Blood Pressure Determinants

Determined by cardiac output, blood volume, and vascular resistance.

Baroreceptor Reflexes

Neural regulation stimulated by pressure-sensitive receptors detecting artery wall stretch.

Angiotensin II

increases BP by increasing vascular resistance

Aldosterone

increases BP by increasing blood volume

Epinephrine

increases BP by increasing vascular resistance

Antidiuretic Hormone

increases BP by increasing blood volume

Atrial Natriuretic Peptide

decreases BP by decreasing resistance and blood volume

Cardiovascular Centre Location

Located in the medulla oblongata.

Baroreceptor Reflexes Stimulus

Stimulated by pressure sensitive receptors which detect stretch of artery walls.

Chemoreceptor Reflexes

Stimulated by sensory receptors which monitor chemical composition of blood (O2, CO2, H+).

Vascular Resistance

Opposition to blood flow due to friction between blood and walls of blood vessels.

Factors Affecting Vascular Resistance

Size of lumen, blood viscosity, and total vessel length.

Vascular Resistance and Blood Pressure

Increased vascular resistance leads to increased blood pressure.

Blood Volume

Total volume of blood in the cardiovascular system.

Blood Volume and Blood Pressure

Increased blood volume leads to increased blood pressure.

Blood Volume Control

Controlled by urinary system (renin-angiotensin-aldosterone system).

Diuretics

Can be used to decrease blood pressure.

Cardiac Output Definition

Volume of blood ejected from the left ventricle each minute.

Cardiac Output and Blood Pressure

Increased cardiac output leads to increased blood pressure.

Systolic Blood Pressure

Highest pressure attained in arteries during systole

Diastolic Blood Pressure

Lowest pressure attained in arteries during diastole

Age

Resting heart rate decreases as we age.

Biological Sex

Females have a higher resting heart rate.

Physical Fitness

Resting heart rate decreased with improved fitness.

Body Temperature

Heart rate increases when hot, slows when cool.

Epinephrine and Norepinephrine

Increase heart rate.

Thyroid Hormone

Increases heart rate.

Cations (K+, Na+, Ca2+)

Needed for action potentials and muscle contraction.

Increased K+ or Na+

Can decrease heart rate.

Increased Ca2+

Can increase heart rate.

Higher Brain Centres Input

The cardiovascular centre receives input from the limbic system and cerebral cortex.

Sympathetic Stimulation Effects

Causes the release of norepinephrine and increases heart rate.

Parasympathetic Stimulation Effects

Delivered via the vagus nerve and decreases heart rate.

Contractility

Force of the contraction of ventricular muscle fibres

Contractility and Stroke Volume

↑ contractility = ↑ stroke volume

Factors Increasing Contractility

Sympathetic nervous stimulation and epinephrine

Factors Decreasing Contractility

Inhibition of sympathetic nervous

Cardiac Output Formula with Units

CO (mL/min) = SV (mL/beat) x HR (beats/min)

Heart Rate Definition

The number of beats per minute (beats/min).

Cardiac Diastole

Atria and ventricles relaxed, atria's filling, semilunar valves closed.

Atrial Systole

Atria contract, blood forces AV valves open, enters ventricles.

Ventricular Systole

Ventricles contract, AV valves close, blood forces SL valves open, enters arteries.