The Cardiovascular System: The Heart Chapter 21 Lecture Chapter 21 The Cardiovascular System: The Heart Frederic Martini Michael Timmons Robert Tallitsch

The blood must stay in motion to maintain homeostasis. Introduction The blood must stay in motion to maintain homeostasis. The heart keeps blood moving. The volume of blood pumped by the heart can vary widely, between 5 and 30 liters per minute.

An Overview of the Cardiovascular System The heart is a small organ; it is roughly the size of a clenched fist. The heart has four muscular chambers: Right and left atria Right and left ventricles

Fig 21.6

An Overview of the Cardiovascular System [Insert fig 21.1] Figure 21.1 The Pulmonary and Systemic Circuits

Orientation of the Heart Figure 21.4 Position of the Heart

The Pericardium Figure 21.2a,b The Location of the Heart in the Thoracic Cavity

The Pericardium Figure 21.2c The Location of the Heart in the Thoracic Cavity

The Pericardium Figure 21.2d The Location of the Heart in the Thoracic Cavity

Epicardium/visceral pericardium The heart wall Parietal pericardium Epicardium/visceral pericardium Myocardium-cardiac muscle tissue Endocardium- epithelia tissue Fig 21.3

Intercalated discs & gap junctions Intercalated discs hold adjacent cardiac muscle cells together Cells work together during contraction Mechanically links cells together Gap junctions allow ions to pass from cell to cell Electrical stimulation in one cell can pass directly into other cells Electrically/chemically links cells together Cardiac muscle cells work as a well organized unit

Structure of the Heart Wall Figure 21.3c-e Cardiac Muscle Tissue

Fig 21.5

Fig 21.5

Fig 21.6

Internal Anatomy and Organization of the Heart Figure 21.6d Horizontal Section of Heart

Heart valves allow blood to flow only in one direction thru the heart Atrioventricular valves (AV)-between an atrium and ventricle rt. atrium>Rt. AV (tricuspid) valve>rt. ventricle lt. atrium>Lt. AV (bicuspid/mitral) valve>lt. ventricle

The Structure and Function of Heart Valves Figure 21.7a Valves with Ventricles Relaxed

Semilunar valves-between the ventricle & an artery lt. ventricle>Aortic semilunar valve>aorta rt. ventricle>Pulmonary semilunar valve>pulmonary artery

The Structure and Function of Heart Valves Figure 21.7b Valves with Ventricles Contracted

Coronary Circulation Figure 21.9a Anterior Heart Figure 21.9b Posterior Heart

Pulmonary circuit Systemic circuit - from heart to lungs back to heart to body back to heart

Atria vs. ventricles Blood enters the heart via atria Atria have thinner walls than ventricles Atria pump blood to the ventricles Ventricles pump blood thru the pulmonary and the systemic circuit

Right vs. Left ventricle Fig 21.6 The left Ventricle has a much thicker myocardium

Heart sounds The two heart sounds are: “Lub”-AV valves closing “Dub”-semilunar valves closing Aortic-2nd intercostals space (Right side) Pulmonary- 2nd ICS (Left side) Right AV valve- 5th ICS (Right of sternum) Left AV valve- 5th ICS (inferior to left nipple)

Heart Valves and Heart Sounds Closure of the AV valves create the 1st heart sound (‘lub’). Closure of the semilunar valves create the 2nd heart sound (‘dub’). Placement of a stethoscope varies depending on which heart sounds and valves are of interest.

The cardiac cycle A chamber of the heart can be in one of two phases: Systole-contraction of the muscle, ejecting blood out of the chamber Diastole-relaxation of the muscle, the chamber fills with blood The heart pumps by using cycles of systole and diastole

Systole: contraction phase Diastole: relaxation phase Cardiac Cycle Systole: contraction phase Diastole: relaxation phase Mid-to-late diastole . dub lub Cardiac cycle is a complete heartbeat. Consists of 2 phases: systole and diastole, defined as whether the ventricles are contracting or relaxing. During the cycle, valves open and close, producing the familiar “lub-dub” sound. Go to Cardiac Cycle layered slide Diastole: ventricles relax, blood passively moves in and contraction of atria “tops off” the ventricles. Systole: ventricles contract-increasing pressure in ventricle closes the atrioventricular valves (lub), and opens the pulmonary and aortic valves. Ventricles begin to relax: pressure decreases and pul. and aortic valves close (dub). Pressure in aorta increase during systole, and falls somewhat during diastole: aorta elastically recoils, causing backpressure that closes the aortic valve. Valve video? Early diastole Ventricular systole

Nodal cells spontaneously depolarize causing an action potential Two groups of nodal cells: Sinoatrial (SA) node-makes 80-100 AP/min Primary pacemaker Posterior wall of the rt. atrium Atrioventricular AV node-slower than SA node Secondary pacemeker Inferior region of the rt. Atrium wall

Figure 49.7 The Heartbeat From AV node, action potentials are conducted to ventricles down through fibers called Bundle of His. The fibers branch to tips of left and right ventricles and spread throughout the ventricles as Purkinje fibers. Purkinje fibers spread the action potential rapidly and evenly throughout the ventricles. The AV fires after a short delay to ensure that the atria contract first, so that blood passes progressively from the atria to the ventricles to the arteries.

Electrical Conduction System 1. Sino Atrial (SA) Node 2. Atrial Ventricular (AV) Node 3. AV Bundle (Bundle of His) 4. L and R Bundle Branches 5. Purkinje Fibers

The Cardiac Cycle Figure 21.11 The Cardiac Cycle

Fig 21.12 The electrical signal stimulates contraction of the chambers

Figure 49.4 The Cardiac Cycle Right atrium Left atrium Left ventricle Right ventricle Ventricle contracting Ventricle relaxing P (mm Hg) V (ml) Pressure in left ventricle Left ventricular volume Pressure in aorta

EKG-electrocardiogram Surface electrodes can monitor the depolarization of the nodal and conducting fibers EKG graph gives electrical and mechanical diagnostic information

Figure 21.13 The ECG

The Autonomic Innervation of the Heart The stimulus for contraction is generated by pacemaker cells of the SA node. Modified by the ANS Modified by Hormones

Autonomic Control of Heart Rate Basic rate established by pacemaker cells that inside the heart (myocardium) – called “intrinsic myogenic control” Modified by ANS Parasympathetic: ACh decreases rate and contraction force via the Vagus nerve X Sympathetic: NE increases heart rate and force of contraction via nerve.

Cardioaccelatory center Cardiac Centers in CNS Cardioaccelatory center Medulla oblongata (Activates sympathetic neurons) Cardioinhibitory center Medulla oblongata (Parasympathetic neurons) Centers receive input from Higher centers (cerebrum) Receptors monitoring blood pressure Receptors monitoring dissolved gases

Superior/Inferior Vena Cava Rt. Atrium Rt. Atrioventricular valve Rt. Ventricle Pulmonary Semilunar valve Pulmonary Arteries Lungs Pulmonary Veins Lt. Atrium Lt. Atrioventricular valve Lt. Ventricle Aortic Semilunar valve Ascending Aorta

Normal Functional Heart Anatomy

Congenital Heart Defects

Congenital Heart Defects