Goals:

-Review macro/external anatomy of the heart

-What is the internal/micro anatomy of the heart

-What are the phases of the cardiac cycle

-How do muscles contract

-Apply muscular contraction to the heart

-How is electrical activity propagated through the heart

Blood travels from the systemic system to:

The right atrium ----> the right ventricle ----> pulmonary system ----> the left atrium -----> the left ventricle

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Transverse section near superior border of the heart demonstrates the paricardial cavity

The heart has 3 layers

-Endocardium: inner/deep layer

-Myocardium: middle (muscular) layer

-Epicardium: outer/superficial layer

The right ventricle is more powerful than the left

Internal anatomy controls the direction of blood flow

-Valves block “regurgitation” (Atrioventricular and Semilunar valves)

-AV valves are tethered to the papillary muscles of the ventricle walls via chordae tendineae (tricuspid or bicuspid)

-SL valves are more rigid, not tethered

Ventricles relaxed

Ventricle contraction closes AV valves

Valves are supported by the cardiac “skeleton”

The atria contract together, as do the ventricles during the cardiac cycle

- Increasing heart rate shortens diastole more than systole

The atria contract together, as do the ventricles during the cardiac cycle

1 cardiac cycle at 75 bpm

A heart characteristically beats in a “lubb” “dubb” pattern. The “lubb is from the AV valves closing, and the “dubb” is from the SL valves closing. During which phase of the cardiac cycle is each sound generated?

Lubb - ventricle systole - isovolumetric phase/early phase

Dubb - ventricle diastole - early

The microstructure of the myocardium allows for a coordinated heart beat

Cardiac muscle characteristics:

-Small cells

-Single nucleus

-Branching, specialized connections between cells

-Aerobic, have rich oxygen supply and store oxygen via myoglobin

Chapter 9! Skeletal muscle: 1 functional unit = a sarcomere

- Myofilaments are surrounded by a sacroplasmic reticulum

An electric “potential” exists across muscle cell membranes

-T tubules connect the sarcoplasmic reticulum to the outside of the cell

-The sarcoplasmic reticulum stores Ca+

-Electric impulses (provided by nerves) travel along muscle cell membranes and induce Ca+ release into the cell

Myofilaments are overlapping in a sarcomere and slide past each other during muscle contraction

The sliding filament model of muscle contraction

-Calcium is required to expose actin binding sites

-ATP is required to reset the myosin head

Chapter 18 - The microstructure of the myocardium allows for a coordinated heart beat

Cardiac muscle characteristics:

-Small cells

-Single nucleus

-Branching, specialized connections between cells

-Aerobic, have rich oxygen supply and store oxygen via myoglobin

The conducting system of the heart coordinates contraction

The sino atrial node (SA) acts as a pace maker - cells spontaneously depolarize

The internodal pathways loop around both atria, trigger contraction in multiple places simultaneously

Internodal pathways converge at the atrioventricular node (AV), which conducts to the ventricles (and can also function as a pacemaker)

The stimulus is delivered to the apex of the heart, where contractions begin in the ventricles, and are passed to other locations in the ventricles

Cardiac “skeleton” between atria and ventricles prevents signal propagation from the atria to the ventricle except through the SA

The relative timing of signal propagation along the conducting system and contraction in the atria and ventricles

Skeletal muscles can be over stimulated and undergo tetanus seiziure…….

….Long recovery (refractory) in the SA node pacemakers avoids this

Cardiac output (amount of blood moved by the left ventricle/minute) fluctuates to meet demand

-Can increase heart rate by 250%

-Can double stroke volume