The Heart 1 Cardiovascular System, pt. 1 (Chapter 9)

The cardiovascular system includes: Heart Blood vessels Blood Blood circulation 2

What is the heart? Also called the cardiac muscle A hollow cone-shaped muscular organ divided into four chambers Straddles the midline within the thoracic cavity just dorsal to the sternum 3

What is the heart? 4 The heart is a pump that circulates blood throughout the body to nourish and remove waste from the tissues.

What is the heart? 5 The base of the heart is located craniodorsally and the apex points ventrally and to the left. The apex is free within the pericardium.

6 The Structure of the Heart Covered by a saclike membrane with 3 layers: Pericardium - tough external layer Parietal – Lines the pericardium Visceral - Covers the surface of the heart The pericardial space lies between the inner layers & contains pericardial fluid

7 The Walls of the Heart The heart is composed of three layers: The outer layer (epicardium) The middle layer (myocardium) The innermost layer (endocardium) Lines the chambers and covers the valves

8 The Walls of the Heart

9 The Chambers of the Heart The heart is divided into a right and left side. The hollow of the heart is divided into four chambers. Atrium - Cranial chambers Ventricle - Ventral chambers

10 The Chambers of the Heart

11 The Chambers of the Heart Interatrial septum – Wall that divides atria into right and left sides Interventricular septum – Wall divides ventricles into right and left sides No communication between the two sides

The atria have thin walls and are receiving chambers. The ventricles do the pumping and have thick walls. Because the left ventricle pumps blood to the whole body, its walls are much thicker. 12 The Chambers of the Heart

The right side of the heart receives deoxygenated blood from the body and sends it to the lungs to be oxygenated. 13 The left side receives oxygenated blood from the lungs and sends it to the tissues.

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15 Heart Valves Primary valves in the heart: Tricuspid – Divides right atrium & ventricle Bicuspid (mitral) – Divides left atrium & ventricle Semilunar – Prevent backflow from arteries back into the ventricles Located at the bases of the pulmonary artery & aorta

16 Valves within the heart ensure blood flows in only one direction.

17 Cardiac Conduction System The heart begins pumping in utero. Conduction consists of: Sinoatrial node (SA node): The “pacemaker” This impulse contracts the atrium and forces blood into the ventricles.

The atrioventricular node (AV node) This consists of cells that conduct the electrical impulses down to the next area… 18

The atrioventricular bundle (bundle of his) This continues on as the Purkinje fibers which stimulate ventricular contraction. 19 After a brief rest, the cycle repeats…

Purkinje fibers 20

Cardiac Nerve Function The autonomic nervous system has two divisions with opposite actions within the heart. 21

22 The Parasympathetic Division Supplies the SA and AV nodes “Rest & digest” Slows the heart rate Reduces impulse conduction Constricts the coronary arteries

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24 The Sympathetic Division Acts through the same nodes to: “Fight or flight” Increase heart rate Increase impulse conduction Dilate coronary arteries

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26 The Cardiac Cycle Includes the contraction (systole) and relaxation (diastole) of the atria and ventricles The two atria contract in unison and as they relax the two ventricles contract

27 The Cardiac Cycle Atrial contraction (systole) forces blood through the bicuspid and tricuspid valves into the ventricles The semilunar valves close to prevent blood from entering the arteries

28 The Cardiac Cycle Atrial relaxation (asystole) moves blood into the atrial chambers from the pulmonary veins (left) and the vena cava (right) while the ventricles contract. When the ventricles contract, the bicuspid and tricuspid valves close to prevent backflow of blood into the atria.

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30 Blood Vessels Animals have three major types of blood vessels: Arteries Capillaries Veins

31 Arteries Arteries carry oxygenated blood to all structures of the body. Arteries are elastic tubes with thick walls composed of three layers: Tunica intima (inner) - endothelium Tunica media (middle) - muscle Tunica adventitia (outer) - fibrous

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33 Arterioles, Capillaries and Venules Arteries become smaller and smaller, becoming arterioles. Arterioles feed the blood into capillaries, which distribute blood to all tissues. Blood returns to the venules, where it passes into veins and returns to the heart.

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35 Veins Similar to arteries but have thinner and less elastic walls These transport deoxygenated blood back to the heart. Smallest veins (venules) collect blood from the capillaries before connecting to larger veins and finally joining the vena cava to return to the heart.

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37 Next up…