AICE Biology, Chapter 9 The Mammalian Heart

The Heart Location – Thorax between the lungs in the inferior mediastinum Orientation – Pointed apex directed toward left hip – Base points toward right shoulder About the size of your fist

The Heart Figure 11.1a–b

The Heart Figure 11.1c

The Heart Figure 11.2a

The Heart: Coverings Pericardium—a double-walled sac – Fibrous pericardium is loose and superficial – Serous membrane is deep to the fibrous pericardium and composed of two layers Visceral pericardium – Next to heart; also known as the epicardium Parietal pericardium – Outside layer that lines the inner surface of the fibrous pericardium – Serous fluid fills the space between the layers of pericardium

The Heart: Heart Wall Figure 11.2b

The Heart: Heart Wall Three layers – Epicardium Outside layer This layer is the visceral pericardium Connective tissue layer – Myocardium Middle layer Mostly cardiac muscle – Endocardium Inner layer Endothelium

The Heart: Heart Wall Figure 11.2b

The Heart: Heart Wall Figure 11.2c

The Heart: Chambers Right and left side act as separate pumps Four chambers – Atria Receiving chambers – Right atrium – Left atrium – Ventricles Discharging chambers – Right ventricle – Left ventricle

The Heart: Chambers Figure 11.2c

Differences in Right and Left Ventricles Figure 11.4

The Heart: Septa Interventricular septum – Separates the two ventricles Interatrial septum – Separates the two atria

The Heart: The Great Vessles Figure 11.2c

The Heart: Valves Allow blood to flow in only one direction to prevent backflow Four valves – Atrioventricular (AV) valves—between atria and ventricles Bicuspid (mitral) valve (left side of heart) Tricuspid valve (right side of heart) – Semilunar valves—between ventricle and artery Pulmonary semilunar valve Aortic semilunar valve

The Heart: Valves Figure 11.2c

The Heart: Valves AV valves – Anchored in place by chordae tendineae (“heart strings”) – Open during heart relaxation and closed during ventricular contraction Semilunar valves – Closed during heart relaxation but open during ventricular contraction Notice these valves operate opposite of one another to force a one-way path of blood through the heart

Figure 11.5a, step 1 Blood returning to the atria, puts pressure against AV valves; the AV valves are forced open Ventricles Operation of the AV valves AV valves open (a)

Figure 11.5a, step 2 Blood returning to the atria, puts pressure against AV valves; the AV valves are forced open As the ventricles fill, AV valve flaps hang limply into ventricles Ventricles Operation of the AV valves AV valves open (a)

Figure 11.5a, step 3 Blood returning to the atria, puts pressure against AV valves; the AV valves are forced open As the ventricles fill, AV valve flaps hang limply into ventricles Atria contract, forcing additional blood into ventricles Ventricles Operation of the AV valves AV valves open (a)

Figure 11.5a, step 4 Ventricles contract, forcing blood against AV valve flaps (a)

Figure 11.5a, step 5 Ventricles contract, forcing blood against AV valve flaps AV valves close AV valves closed (a)

Figure 11.5a, step 6 Ventricles contract, forcing blood against AV valve flaps AV valves close Chordae tendineae tighten, preventing valve flaps from everting into atria AV valves closed (a)

The Heart: Valves PLAY Figure 11.5b, step 1 As ventricles contract and intraventricular pressure rises, blood is pushed up against semilunar valves, forcing them open Aorta Pulmonary trunk Semilunar valve open Operation of the semilunar valves (b)

Figure 11.5b, step 2 As ventricles contract and intraventricular pressure rises, blood is pushed up against semilunar valves, forcing them open Aorta Pulmonary trunk Semilunar valve open Semilunar valve closed As ventricles relax, and intraventricular pressure falls, blood flows back from arteries, filling the leaflets of semilunar valves and forcing them to close Operation of the semilunar valves (b)

The Heart: Cardiac Cycle Cardiac cycle—events of one complete heart beat – Atrial Systole: Atria contract simultaneously – Ventricular Systole: Atria relax, then ventricles contract – Diastole: relaxation

Filling Heart Chambers: Cardiac Cycle Figure 11.7, step 1a Mid-to-late diastole (ventricular filling) Ventricular filling Left atrium Right atrium Left ventricle Right ventricle

Filling Heart Chambers: Cardiac Cycle Figure 11.7, step 1b Atrial contraction Mid-to-late diastole (ventricular filling) Ventricular filling Left atrium Right atrium Left ventricle Right ventricle

Filling Heart Chambers: Cardiac Cycle Figure 11.7, step 2a Atrial contraction Mid-to-late diastole (ventricular filling) Ventricular systole (atria in diastole) Isovolumetric contraction phase Ventricular filling Left atrium Right atrium Left ventricle Right ventricle

Filling Heart Chambers: Cardiac Cycle Figure 11.7, step 2b Atrial contraction Mid-to-late diastole (ventricular filling) Ventricular systole (atria in diastole) Isovolumetric contraction phase Ventricular ejection phase Ventricular filling Left atrium Right atrium Left ventricle Right ventricle

Filling Heart Chambers: Cardiac Cycle Figure 11.7, step 3 Atrial contraction Mid-to-late diastole (ventricular filling) Ventricular systole (atria in diastole) Early diastole Isovolumetric contraction phase Ventricular ejection phase Isovolumetric relaxation Ventricular filling Left atrium Right atrium Left ventricle Right ventricle

Measuring Blood Pressure A typical blood pressure for a healthy young adult is about 120/70. Blood pressure is commonly measured using a sphygmomanometer. Hypertension is a serious cardiovascular problem in which blood pressure is persistent at or above – 140 systolic and/or – 90 diastolic. © 2012 Pearson Education, Inc.

Typical blood pressure: 120 systolic 70 diastolic Rubber cuff inflated with air Artery Artery closed 21 Pressure in the cuff above

Typical blood pressure: 120 systolic 70 diastolic Rubber cuff inflated with air Artery Artery closed Pressure in the cuff above 120 Pressure in the cuff at 120 Sounds audible in the stethoscope

Typical blood pressure: 120 systolic 70 diastolic Rubber cuff inflated with air Artery Artery closed Pressure in the cuff above 120 Pressure in the cuff at 120 Pressure in the cuff at 70 Sounds audible in the stethoscope Sounds stop 2134

Hypertension causes – the heart to work harder, weakening the heart over time, – increased plaque formation from tiny ruptures, and – increased risk of blood clot formation. Hypertension can contribute to – heart attacks, – strokes, and/or – kidney failure. © 2012 Pearson Education, Inc.

The Heart: Conduction System Intrinsic conduction system (myogenic heart) – Heart muscle cells contract, without nerve impulses, in a regular, continuous way

The Heart: Conduction System Special tissue sets the pace Sinoatrial node = SA node (“pacemaker”), is in the right atrium Atrioventricular node = AV node, is at the junction of the atria and ventricles Atrioventricular bundle = AV bundle (bundle of His), is in the interventricular septum Bundle branches are in the interventricular septum Purkinje fibers (Purkyne fibers) spread within the ventricle wall muscles

Heart Contractions Figure 11.6

Heart Contractions Contraction is initiated by the sinoatrial node (SA node) Sequential stimulation occurs at other autorhythmic cells Force cardiac muscle depolarization in one direction—from atria to ventricles

Heart Contractions Once SA node starts the heartbeat – Impulse spreads to the AV node – Then the atria contract At the AV node, the impulse passes through the AV bundle, bundle branches, and Purkinje fibers Blood is ejected from the ventricles to the aorta and pulmonary trunk as the ventricles contract

Heart Contractions Figure 11.6

Problems with Control & Conduction Heart block—failure of a part of the conduction system, usually due to ischemia or infarction Ischemia – low oxygenation of heart tissue, often resulting from arterial disease Arrhythmia—an abnormal rhythm, often the result of a damage to the SA node Tachycardia—rapid heart rate over 100 beats per minute Bradycardia—slow heart rate less than 60 beats per minutes Fibrillation—uncoordinated, unproductive contraction of heart muscle

Coronary Circulation Blood in the heart chambers does not nourish the myocardium The heart has its own nourishing circulatory system consisting of – Coronary arteries—branch from the aorta to supply the heart muscle with oxygenated blood – Cardiac veins—drain the myocardium of blood – Coronary sinus—a large vein on the posterior of the heart, receives blood from cardiac veins Blood empties into the right atrium via the coronary sinus

Electrocardiograms ECG measures electrical activity associated with conduction and contraction. Parts of the wave correspond to events of the Cardiac Cycle: – P wave – atrial contraction – QRS complex – ventricular contraction – T wave – ventricular repolarization during diastole

Figure 23.5A_1 2 ECG Right atrium SA node (pacemaker) AV node Signals from the SA node spread through the atria. Signals are delayed at the AV node. 1

Figure 23.5A_2 34 Apex Specialized muscle fibers Specialized muscle fibers pass signals to the heart apex. Signals spread throughout the ventricles.