1. The Heart

2. Functions of the Heart
The heart works in conjunction with cardiovascular centers and peripheral blood vessels to achieve this goal
The function of the heart
Generates blood pressure to produce a gradient that pushes blood through the vascular system
Regulates blood supply - changes in contraction rate & force match blood delivery to metabolic needs
Routes blood, ensuring one-way blood flow, separates pulmonary and systemic circulations

3. The Heart Heart – typically weighs 250–350 grams (healthy heart)
A muscular double pump
Pulmonary circuit – takes blood to and from the lungs
Systemic circuit – vessels transport blood to and from body tissues

4. Location and Orientation within the Thorax
Largest organ of the mediastinum
Located between the lungs
Apex lies to the left of the midline
Base is the broad posterior surface
Figure 18.2

5. Structure of the Heart
Right and left atria - Superior chambers, receive blood from the pulmonary and systemic circuits
Right and left ventricles - Inferior chambers, the pumping chambers of the heart
External markings
Left/right auricles
Apex
Internal Structures
Interventricular septa
Fossa ovalis

6. Chambers Right Atrium Right Ventricle Forms right border of heart
Receives blood from systemic circuit
Fossa ovalis - depression in interatrial septum, remnant of foramen ovale
Right Ventricle
Receives blood from right atrium through the tricuspid valve (right atrioventricular valve)
Pumps blood into pulmonary circuit via the pulmonary semilunar valve into pulmonary trunk
Internal walls of right ventricle
Trabeculae carneae
Papillary muscles
Chordae tendineae

7. Chambers Left atrium Left Ventricle Makes up heart’s posterior surface
Receives oxygen-rich blood from lungs
Opens into the left ventricle through the Mitral valve (left atrioventricular valve)
Left Ventricle
Forms apex of the heart
Internal walls of left ventricle
Trabeculae carneae
Papillary muscles
Chordae tendineae
Pumps blood through systemic circuit via the Aortic semilunar valve (aortic valve)

8. Heart Valves – Valve Structure
Each valve composed of - endocardium with connective tissue core
Atrioventricular (AV) valves between atria and ventricles
Aortic and pulmonary valves at junction of ventricles and great arteries

9. Function of the Atrioventricular Valves
Figure 18.9a

10. Function of the Semilunar Valves
Figure 18.10a, b

11. Structure of the Heart – Coverings
Pericardium – two primary layers
Fibrous pericardium - strong layer of dense connective tissue
Serous pericardium -formed from two layers
Parietal pericardium
Visceral pericardium
Pericardial cavity

12. Structure of the Heart – Layers of the Heart Wall
Epicardium - Visceral layer of the serous pericardium
Myocardium
Consists of cardiac muscle
Muscle arranged in circular and spiral patterns
Endocardium
Endothelium resting on a layer of connective tissue
Lines the internal walls of the heart

13. Structure of Heart Wall
Walls differ in thickness
Atria – thin walls
Ventricles – thick walls
Left ventricle – three times thicker than right
Exerts more pumping force
Flattens right ventricle into a crescent shape
Systemic circuit
Longer than pulmonary circuit
Offers greater resistance to blood flow

14. Blood Flow Through the Heart
Beginning with oxygen-poor blood in the superior and inferior venae cavae
Go through pulmonary and systemic circuits
A blood drop passes through all structures sequentially
Figure 18.6

15. Cardiac Muscle Tissue Forms a thick layer called myocardium
Striated like skeletal muscle
Contractions pump blood through the heart and into blood vessels
Contracts by sliding filament mechanism
Cardiac muscle cells
Short
Branching
Have one or two nuclei

16. Cardiac Muscle Tissue Cells join at intercalated discs
Complex junctions
Form cellular networks
Cells are separated by delicate endomysium
Binds adjacent cardiac fibers
Contains blood vessels and nerves

17. Electrical Activity of Heart
Heart beats rhythmically as result of action potentials it generates by itself (autorhythmicity)
Two specialized types of cardiac muscle cells
Contractile cells
99% of cardiac muscle cells
Do mechanical work of pumping
Normally do not initiate own action potentials
Autorhythmic cells
Do not contract
Specialized for initiating and conducting action potentials responsible for contraction of working cells

18. Cardiac Conduction System
SA node ~ 75 bpm - sets the pace of the heartbeat
AV node ~ 50 bpm - delays the transmission of action potentials
Purkinje fibers ~ 30 bpm - can act as pacemakers under some conditions
70-80/min
40-60/min
20-40/min
Approximately 1% of the cardiac muscle cells are autorhythmic rather than contractile. * These specialized cardiac cells don’t contract but are specialized to initiate and conduct impulses through the heart to coordinate its activity. * These constitute the intrinsic cardiac conduction system. These autorhythmic cells constitute the following components of the intrinsic conduction system:
* the sinoatrial (SA) node, just inferior to the entrance of the superior vena cava into the right atrium,
* the atrioventricular node (AV) node, located just above the tricuspid valve in the lower part of the right atrium,
* the atrioventricular bundle (bundle of HIS), located in the lower part of the interatrial septum and which extends into the interventricular septum where it splits into right and left bundle branches * which continue toward the apex of the heart and the purkinje fibers * which branch off of the bundle branches to complete the pathway into the apex of the heart and turn upward to carry conduction impulses to the papillary muscles and the rest of the myocardium.
Although all of these are autorhythmic, they have different rates of depolarization. * For instance, the SA node * depolarizes at a rate of 75/min. * The AV node depolarizes at a rate of 40 to 60 beats per minute, * while the rest have an intrinsic rate of around 30 depolarizations/ minute. * Because the SA node has the fastest rate, it serves as the pacemaker for the heart. *