The Circulatory System – The Heart

Part 4: Regulation & Maintenance

The Heart

The Heart: The pump that supplies force critical to move blood through the circulatory system. Located in the thoracic cavity.10 ounces total, 12 cm long, 9 cm wide.Great vessels attach at superior end, inferior

end tapers off. Mediastinum: Mass of tissue that extends

from sternum to vertebral column between the lungs. Contains the heart!

The Heart

Pericardium: The double-walled membrane surrounding the heart. Fibrous Pericardium: Outer membrane made of

tough connective tissue providing protection & preventing overstretching of the muscle.

Serous Pericardium: Inner membrane. Parietal Layer: Outer layer Pericardial Cavity: Small gap that is filled with lubricating

paricardial fluid. Visceral Pericardium aka Epicardium: Inner layer

The Heart

Heart Wall: Made up of 3 layers!Epicardium: The outer layer (and layer of the

serous epicardium). Composed of mesothelium & connective tissue.

Provides smooth & slippery texture. Myocardium: Middle layer.

Cardiac muscle that makes up the bulk of the heart & provide contraction force.

Endocardium: Smooth lining inside the chambers & valves; composed of endothelium.

The Heart

Chambers: 4 chambers total, 2 upper & 2 lower. Atria: Upper chambers, both right & left.

Receive blood! Auricle: A slight extension to each atria that increases the

total volume. Ventricles: Lower chambers, both right & left.

Pump blood out to the body.

Interatrial Septum: Separates the right & left atria.

Interventricular Septum: Separates the right & left ventricles.

The Heart

Valves: Control the one-way flow of blood through the chambers. 4 total: Right Atrioventricular (A-V) Valve aka Tricuspid Valve:

Regulates blood flow into the right ventricle. Left Atrioventricular (A-V) Valve aka Bicuspid Valve aka

Mitral Valve: Regulates blood flow into the left ventricle. Aortic Valve: Regulates flow from the left ventricle to the aorta. Pulmonary Valve aka Semi-lunar Valve: Regulates flow from

the right ventricle to the pulmonary trunk. Chordae Tendineae: Connects the Right & Left A-V

Valves to the papillary muscles.

The Heart Flow of Blood through the Heart:

Deoxygenated blood flows into the heart at the right atrium.

Blood passes from the right atrium to the right ventricle via the Right A-V valve.

Blood flows from the right ventricle through the pulmonary valve into the pulmonary trunk (and off to the lungs!).

Oxygenated blood re-enters the heart through the left atrium.

Blood passes from the left atrium through the left A-V valve to the left ventricle.

Blood flows from the left ventricle through the aortic valve into the aorta (and out to the body!).

The Heart

Flow of Blood Simplified: Pulmonary Circuit: Right side of the heart

pumps blood to the lungs only. Systemic Circuit: Left side of the heart

pumps blood to the rest of the body.

Disorders of the Heart Valves

Stenosis: Failure of a heart valve to fully open.

Insufficiency: Failure of a heart valve to fully close.

Mitral Valve Prolapse (MVP): Blood leaks back into the left atrium from the left ventricle.

Coronary Circulation

Left & Right Coronary Arteries: The first branches off the aorta that supply the left & right halves of the heart with blood.

Great & Middle Cardiac Veins: Return blood from the heart muscle itself to the coronary sinus & right atrium.

Anastomoses: The point where two or more branches of an artery serving the same area meet.

Cardiac Muscle Contraction Cardiac Muscle: Striated, involuntary muscle

specifically found in the heart. Rhythmicity: Property of beating on a regular basis

even without electrical stimulation. This is unique to cardiac muscle!

Myocytes: Ends of cardiac muscle cells joined together by intercalated discs.

Gap junctions between the discs allow for action potentials (for communication) & desmosomes (to hold the fibers together).

Endomysium: Surrounds the myocytes and supplies access to capillaries. 10X as many mitochondria as skeletal muscles.

Autorhythmic Conduction Cardiac Conduction System: The electrical

conduction system that triggers cardiac muscle contractions. Composed of nodal tissue (special conductive tissue).

Sinoatrial (SA) Node: The pacemaker of the heart – sets the heart rhythm at appx. 72 beats per minute at rest.

Eptopic Pacemaker: Occurs when the heart rhythm is set by some other site than the SA node.

Arrhythmia: The term used for any abnormal cardiac rhythm.

Autorhythmic Conduction

Steps of Autorhythmic Conduction: SA nodes send signals to the

atrioventricular node. Atrioventricular node sends signals through

the atrioventricular bundle aka bundle of his to the ventricles.

Signal travels from the atrioventricular bundle to the remainder of the heart via Perkinje fibers.

Autorhythmic Conduction

Cardiovascular Center: Located in the medulla oblongata – receives sensory input from limbic system, cerebral cortex & sensory systems & interprets the need to decrease or increase heart rate. Cardioacceleratory Center: Speeds the

heart up. Cardioinhibitory Center: Slow the heart

down.

Measuring Cardiac Output Electrocardiogram aka EKG: Records the

electrical activity of the heart. Electrocardiograph: The registered read out of the

heart rhythm. Only shows the depolarization, not contraction of the muscle.

Three Deflections of the EKG: P-Wave: Corresponds to the depolarization of the

atria (Atrial contraction). QRS-Wave: Corresponds to the depolarization of the

ventricles (Ventricle contraction). T-Wave: Corresponds to the ventricular

repolarization.

Cardiac Cycle

Cardiac Cycle: Consists of one complete heartbeat. Systole: The contraction phase. Diastole: The relaxation phase.

Cardiac Cycle 6 Phases of the Cardiac Cycle:

Rest: Atria are filling with blood; A-V valves open. Atrial Systole: Atrial depolarization prompted by depolarization of the

SA node. Forces blood into the ventricles (25 mL) over 0.1 seconds. Ventricular Systole: Rising blood pressure in the ventricle triggers

isovolumetric contraction, which leaves the volume the same but raises pressure.

Ventricular Ejection: When ventricular pressure is greater than aortal pressure, the semi-lunar valves open.

Stroke Volume: Total amount of blood moving into the pulmonary trunk & aorta (typically 70 mL).

Relaxation Period: Ventricular repolarization causes ventricular diastole – all 4 valves close for isovolumetric relaxation.

Ventricular Filling: A-V valve opens when ventricular pressure drops back below atrial pressure, allowing the ventricles to fill again. Lasts 250 msec.

Heart Sounds

Heart Sounds: The sounds made by the opening & closing of the valves & the rush of blood.

First Heart Sounds (S1): The closing of the A-V valves, usually louder & longer lasting.

Second Heart Sounds (S2): The closing of the semi-lunar valves, usually quieter & quicker.

Heart Rhythm Disorders

Heart Murmer: Any abnormal clicking, gurgling, or rushing noise accompanying the heartbeat.

Tachycardia: Persistent resting heart rate of 100 BPM or higher. Can be caused by stress, heart diseases, drugs,

medications, or hyperthermia. Bradycardia: Persistent resting heart rate of 60

BPM or less. Can be caused by hypothermia; may be normal in

athletes.

Cardiac Output Cardiac Output: The amount of blood volume pumped

by each ventricle per minute. Cardiac Reserve: The difference between a resting

cardiac output & the maximum potential cardiac output. Heart Rate: The number of times the heart goes through

one complete cardiac cycle per minute. Adult males: 64-72 BPM resting. Adult females: 72-80 BPM resting. Infants: 120 BPM or more resting.

Cronotropic Agents: Anything that raises or lowers the rate of contraction.

Inotropic Agents: Alters the stroke volume of the ventricles. Dopamine, epinephrine, & noreopinephine

Cardiac Output

Cardiac Output: Stroke volume X heart rate CO (mL/min). SV (mL/beat) X HR (beats/min)

Chemicals Impacting Heart Rate

Sympathetic neurotransmitters & some hormones of the adrenal glands can accelerate the heart rate.

Hypernatremia: Excessive amounts of sodium - can lower the heart rate.

Hyperkalemia: Excessive amounts of potassium – can lower the heart rate and lead to death.

Hypercalcaemia: Excessive amounts of calcium – slows the heart rate.

Hypocalcaemia: Lowered amounts of calcium – speeds the heart rate up.

Stroke Volume

Stroke Volume: The amount of blood ejected by the ventricle during each contraction. Mostly determined by the amount of tension generated in the ventricles.

Stroke Volume

Regulated by 3 factors: Preload: The greater the tension of the cardiac

muscle prior to contraction, the greater the force of the contraction & the more blood that is expelled. Known as the Frank-Starling Law of the Heart.

Contractility: Strength of the contraction is enhanced by positive inotropic factors and decreased by negative inotropic agents. (Anything that stimulates or inhibits the sympathetic nervous system).

Afterload: The amount of pressure in the semi-lunar valves in the ventricles. The higher the pressure in the arteries, the less stroke volume.

Blood Pressure

Blood Pressure: The pressure in the heart and blood vessels. The left side of the heart has higher blood

pressure than the right, but both have the same volume of blood.

Pressure Gradient: The difference in pressure of the two sides of the heart & causes the valves to stay open.

Sphygmomanometer: The device used to measure the blood pressure.

Exercise & The Heart

Aerobic Exercise: Exercise that gets your heart pumping!Can be good for the heart. Increases cardiac reserve.