Exercise 27

Gross Anatomy of the HeartBI 232

Mediastinum The heart and

pericardial cavity are located within the mediastinum, a centrally located area within the thoracic cavity.

The Pericardium Membranous sac 2 parts: outer fibrous

pericardium that is fused to adjacent structures and an inner serous pericardium which is a delicate serous membrane that forms a double-layered sac around the heart.

The serous pericardium consists of parietal and visceral layers.

The heart Two-sided, double-

pumping organ. The left side controls

the flow of blood to all tissues and cells in the body, where oxygen and nutrients are delivered and wastes are taken away.

The right side sends blood to the lungs, where oxygen stored in RBCs is replenished and CO2 is released

External Anatomy of the Heart

External Anatomy of the Heart

Internal Anatomy of the Heart

Coronary Circulation

Coronary Circulation On the posterior

surface of the heart, the coronary artery branches to become the posterior interventricular artery

Near the apex of the heart the anterior and posterior interventricular arteries form an anastomosis (connection)

Coronary Circulation On the posterior

surface of the heart, the coronary sinus runs along the coronary sulcus and empties into the right atrium.

Great cardiac vein found in the anterior interventricular sulcus

Middle cardiac vein ascends along the posterior interventricular groove

Blood flow Through the Heart Pulmonary

Circulation- Blood from the right side of the heart flows to and from the lungs

Systemic Circulation- Blood from the left side of the heart flows from and to all body tissues.

Position of Heart Base of the heart

extends from the inferior border of the second costal cartilage on the left side to the superior border of the third costal cartilage on the right.

Apex of the heart is located in the left fifth intercostal space, left of the median plane

Heart: muscular pump Actually 2 pumps

acting in unison Systole is

contraction of heart muscle Atrial systole Ventricular systole

Diastole is relaxation of heart muscle Atrial diastole Ventricular diastole

Conduction system of the Heart (Exercise 32) Electrical activity of the

heart stimulates the heart muscle to contract.

Sinoatrial (SA) node = pacemaker of the heart

Atrioventricular (AV) node: there is a slight delay (0.10 second)

Atrioventricular bundle (bundle of His)

Right and left bundle branches

Purkinje fibers: stimulate cardiac muscle of the ventricles to contract

http://youtu.be/te_SY3MeWys

Electrical activity of the Heart Heart produces low-voltage

electrochemical impulses The average potential

difference is -90 millivolts These impulses can travel

through the saline medium of the body and be picked up by sensors attached to the skin

The collective action potentials generated by the atria and ventricles depolarizing and repolarizing can be recorded using an electrocardiograph machine

EKG Waveform

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P wave

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The P wave indicates the depolarization of the atria just prior to the beginning of atrial contraction or systole

QRS complex (QRS interval) Represents the depolarization of the

ventricles which precedes ventricular systole.

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T wave Results from ventricular repolarization, which

occurs before ventricular relaxation or diastole.

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Analysis of the ECG Irregularities in Heart

rate: Tachycardia: Above

100 in adults (in small children this may be normal)

Bradycardia: in young adults below 60 beats per minute (unless person is highly trained aerobic athlete)

Heart Blocks PR intervals are normally

about 0.16 second. Time between the beginning

of atrial depolarization and the beginning of ventricular depolarization.

Long PR might indicate a heart block (reduced conduction between atria and ventricles)

Longer than 0.2 second Complete heart block the

atria do not stimulate ventricular depolarization at all, so atria fire independently of ventricles

Heart Blocks Normal QRS is 0.08 to

0.10 second on average.

Longer than 0.12 may indicate a right or left bundle branch block

QT interval is normally about 0.3 second

This is shorter as the heart rate increases and longer as heart rate slows.

Cardiac Arrhythmias A major diagnostic use is to

detect arrhythmias, abnormal rhythms of the heart

Atrial fibrillation: electrical activity of the heart is uncoordinated causing the upper chambers to quiver.

Ventricular fibrillation: where electrical signals in the ventricles fire in a very fast

uncontrolled manner. Premature ventricular

contraction (PVC): electrical signal causes an early heartbeat that usually goes unnoticed

Today’s lab Dissect sheep heart ID structures on the heart models We will also be doing EKGs (We will be using

the Vernier EKGs rather than the BIOPAC machines mentioned in the lab manual)

After performing your EKG follow the instructions in your lab manual and calculate the mean electrical axis of your heart

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The End