Chapter 19.3: The Circulatory System - Heart

What type of muscle is found in the heart?

Cardiac muscle

What is the average resting heart rate?

About 75 beats per minute (bpm; beats per minute)

What does myogenic mean?

The heartbeat originates within the heart itself

What does autorhythmic mean?

The heart beats independently of the nervous system due to its internal pacemaker

What are cardiomyocytes?

Short, thick, branched muscle cells of the heart

How long and wide are cardiomyocytes?

50–100 micrometers (μm; micrometers) long and 10–20 micrometers (μm; micrometers) wide

What is the role of the sarcoplasmic reticulum (SR; Sarcoplasmic Reticulum) in cardiac muscle?

Stores and releases calcium ions (Ca²⁺; Calcium Ions) for muscle contraction; less developed than in skeletal muscle

How do transverse tubules (T tubules; Transverse Tubules) in cardiac muscle compare to skeletal muscle?

They are larger and admit extracellular calcium ions (Ca²⁺; Calcium Ions) to trigger contraction

What are intercalated discs?

Junctions connecting cardiomyocytes that aid electrical and mechanical coupling

What are interdigitating folds?

Plasma membrane folds that interlock to increase contact surface area

What are fascia adherens?

Mechanical junctions that anchor actin filaments between cells

What are desmosomes?

Patches that prevent cardiomyocytes from pulling apart

What are gap junctions?

Electrical junctions that allow ion flow between cardiomyocytes

What is the function of gap junctions in the heart?

Enable unified contraction; atria and ventricles function as single units

How does cardiac muscle repair itself?

Mainly by fibrosis (scar tissue formation)

What type of respiration does cardiac muscle use?

Aerobic respiration

What three components are abundant in cardiac muscle?

Myoglobin, glycogen, mitochondria

What percentage of the cell do mitochondria occupy in cardiac muscle?

About 25%

Where does cardiac muscle get most of its fuel from?

60% fatty acids, 35% glucose, 5% ketones/lactate/amino acids

Why is cardiac muscle fatigue

resistant?

What is the function of the sinuatrial node (SA node; Sinuatrial Node)?

Acts as the pacemaker; initiates heartbeat and sets the heart rate

Where is the sinuatrial node (SA node; Sinuatrial Node) located?

Right atrium, near the superior vena cava (SVC; Superior Vena Cava)

What is the role of the atrioventricular node (AV node; Atrioventricular Node)?

Electrical gateway to the ventricles; delays signal so atria can contract first

Where is the atrioventricular node (AV node; Atrioventricular Node) located?

Lower interatrial septum, near the right atrioventricular valve (Right AV Valve; Right Atrioventricular Valve, also called Tricuspid Valve)

What is the atrioventricular bundle (AV bundle; Atrioventricular Bundle, also called Bundle of His)?

Carries signals from the atrioventricular node (AV node; Atrioventricular Node) to the ventricles

Where do the right and left bundle branches go?

Into the interventricular septum

What are Purkinje fibers (Purkinje Fibers, also called Subendocardial Branches)?

Fibers that spread electrical signals through the ventricles

Where are Purkinje fibers (Purkinje Fibers) more elaborate?

In the left ventricle

How do cardiomyocytes propagate electrical signals?

Through gap junctions