Chapter 18 The heart (Part 2)

• Microscopic Anatomy of Cardiac Muscle

• Heart cells

• Electrocardiography (ECG)

• Stroke volume and cardiac output

Microscopic Anatomy of Cardiac Muscle:

Characteristics

Intercalated discs (unique)BranchesStriationUninucleate

Microscopic Anatomy of Cardiac Muscle:

Characteristics

Intercalated discs (unique)BranchesStriationUninucleate

Microscopic Anatomy of Cardiac Muscle

Gap junctions

Microscopic Anatomy of Cardiac Muscle:Intercalated discs

Desmosomes

Microscopic Anatomy of Cardiac Muscle:Intercalated discs

• Junctions between cells

Gap junctions: allow ions to pass from cell to cell, which makes heart to be functional syncytium

Microscopic Anatomy of Cardiac Muscle:Intercalated discs

• Junctions between cells

Gap junctions: allow ions to pass from cell to cell, which makes heart to be functional syncytium

Desmosomes: prevent cells from separating during contraction

Microscopic Anatomy of Cardiac Muscle:

Characteristics

Intercalated discs (unique)BranchesStriationUninucleate

Microscopic Anatomy of Cardiac Muscle:Striation

A band

Chapter 18 The heart (Part 2)

• Microscopic Anatomy of Cardiac Muscle

• Heart cells

• Electrocardiography (ECG)

• Stroke volume and cardiac output

Heart cells

Heart cells

• Pace maker cells (1%)

• Cardiac muscle cells (99%)

Heart cells

• Pace maker cells (1%)

• Cardiac muscle cells (99%)

Pace maker cells

Sinoatrial (SA) node

Pace maker cells: SA node

1% of cells: modified cardiomyocytes

Only exist in right atrium of heart

Automaticity (sinus rythm):

Do not need nervous system stimulation

Can depolarize entire heart

Intrinsic cardiac conduction system

Intrinsic cardiac conduction system

1, SA node in right atrium2, AV node3, AV bundle4, Bundle of His5, Purkinje fibers

Modified cardiomyocytesArrhythmia

Intrinsic cardiac conduction system

Chapter 18 The heart (Part 2)

• Microscopic Anatomy of Cardiac Muscle

• Heart cells

• Electrocardiography (ECG)

• Stroke volume and cardiac output

ECG

Electrocardiography (ECG)

Electrocardiography (ECG)

P

QRS complex

T

ECG waves

P wave – Atrial depolarization

QRS complex - ventricular depolarization and atrial repolarization

T wave - ventricular repolarization

ECG intervals and segments

P-R interval

S-T segment

Q-T interval

ECG intervals and segments

P-R interval

S-T segment

Q-T interval

ECG intervals: P-R interval

Beginning of atrial excitation to beginning of ventricular excitation

P-R

ECG intervals and segments

P-R interval

S-T segment

Q-T interval

ECG intervals: S-T segment

Entire ventricular myocardium depolarized

S-T

ECG intervals and segments

P-R interval

S-T segment

Q-T interval

ECG intervals: Q-T interval

Beginning of ventricular depolarization through ventricular repolarization

Q - T

Normal sinus rhythm.

Junctional rhythm. The SA node is nonfunctional, P waves areabsent, and the AV node paces the heart at 40 –60 beats/min.

Second-degree heart block. Some P waves are not conductedthrough the AV node; hence more P than QRS waves are seen. Inthis tracing, the ratio of P waves to QRS waves is mostly 2:1.

Ventricular fibrillation. These chaotic, grossly irregular ECGdeflections are seen in acute heart attack and electrical shock.

ECG

31

Chapter 18 The heart (Part 2)

• Microscopic Anatomy of Cardiac Muscle

• Heart cells

• Electrocardiography (ECG)

• Stroke volume and cardiac output

Stroke volume (SV)

• volume of blood pumped out by one ventricle with each beat.

• 70ml/beat

Cardiac Output (CO)

• Volume of blood pumped by each ventricle in one minute

• CO (ml/min) = HR (75 beats/min) SV (70 ml/beat) = 5.25 L/min

• Normal – 5.25 L/min

Regulation of SV and CO

Sympathetic

Parasympathetic

SA node

Regulation of SV and CO

By autonomic nervous system via medulla oblongata

Sympathetic rate and force

Parasympathetic rate and force