The Cardiovascular System: The Heart 18 P A R T A The Cardiovascular System: The Heart

Approximately the size of your fist Location Heart Anatomy Approximately the size of your fist Location Superior surface of diaphragm Left of the midline Anterior to the vertebral column, posterior to the sternum

Heart Anatomy Figure 18.1

Pericardium – a double-walled sac around the heart Coverings of the Heart Pericardium – a double-walled sac around the heart Visceral layer (covers the heart) Parietal layer (attached to the body wall) Protects and anchors the heart Prevents overfilling of the heart with blood Pericardial cavity Filled with serous fluid (pericardial fluid) Allows for the heart to work in a relatively friction-free environment

Pericardial Layers of the Heart Figure 18.2

Cardiac Muscle Bundles Myocardium: Forms the bulk of the heart wall Figure 18.3

External Heart: Major Vessels of the Heart (Anterior View) Vessels returning blood to the heart include: Superior and inferior venae cavae Right and left pulmonary veins Vessels conveying blood away from the heart: Pulmonary trunk, which splits into right and left pulmonary arteries Ascending aorta (three branches) – brachiocephalic, left common carotid, and subclavian arteries

interventricular artery (in anterior interventricular sulcus) Inferior Left common carotid artery Brachiocephalic trunk Left subclavian artery Superior vena cava Aortic arch Right pulmonary artery Ligamentum arteriosum Ascending aorta Left pulmonary artery Left pulmonary veins Pulmonary trunk Left atrium Right pulmonary veins Auricle Right atrium Circumflex artery Right coronary artery (in coronary sulcus) Left coronary artery (in coronary sulcus) Anterior cardiac vein Left ventricle Right ventricle Great cardiac vein Marginal artery Small cardiac vein Anterior interventricular artery (in anterior interventricular sulcus) Inferior vena cava (b) Apex Figure 18.4b

External Heart: Major Vessels of the Heart (Posterior View) Vessels returning blood to the heart include: Right and left pulmonary veins Superior and inferior venae cavae Vessels conveying blood away from the heart include: Aorta Right and left pulmonary arteries

interventricular artery (in posterior interventricular sulcus) (d) Superior vena cava Right pulmonary artery pulmonary veins Right atrium Right coronary artery (in coronary sulcus) Right ventricle Coronary sinus Middle cardiac vein Left Left atrium Auricle of left atrium Left ventricle Posterior vein of left ventricle Posterior interventricular artery (in posterior interventricular sulcus) Great cardiac vein Apex Inferior Aorta Figure 18.4d

Left anterior coronary artery – widow maker Coronary Circulation Coronary circulation is the functional blood supply to the heart muscle itself Collateral routes ensure blood delivery to heart even if major vessels are occluded (blocked) Left anterior coronary artery – widow maker Damage to the left ventricle is most serious Cardiac muscle is amitotic; cell death is repaired by noncontractile scar tissue

interventricular artery (in anterior interventricular sulcus) Inferior Left common carotid artery Brachiocephalic trunk Left subclavian artery Superior vena cava Aortic arch Right pulmonary artery Ligamentum arteriosum Ascending aorta Left pulmonary artery Left pulmonary veins Pulmonary trunk Left atrium Right pulmonary veins Auricle Right atrium Circumflex artery Right coronary artery (in coronary sulcus) Left coronary← artery (in coronary sulcus) Anterior cardiac vein Left ventricle Right ventricle Great cardiac vein Marginal artery Small cardiac vein Anterior interventricular artery (in anterior interventricular sulcus) Inferior vena cava (b) Apex Figure 18.4b

Coronary Circulation: Arterial Supply Figure 18.7a

Coronary Circulation: Venous Supply Figure 18.7b

Aorta Superior vena cava Left Right pulmonary artery pulmonary artery Left atrium Pulmonary trunk Left pulmonary veins Right atrium Right pulmonary veins Mitral (bicuspid) valve Fossa ovalis Aortic valve Pectinate muscles Pulmonary valve Tricuspid valve Left ventricle Papillary muscle Right ventricle Chordae tendineae Interventricular septum Myocardium Trabeculae carneae Visceral pericardium Inferior vena cava Endocardium (e) Figure 18.4e

Atria of the Heart Atria are the receiving chambers of the heart Each atrium has a protruding auricle Blood enters right atrium from superior and inferior venae cavae and coronary sinus Blood enters left atrium from pulmonary veins

Ventricles of the Heart Ventricles are the discharging chambers (pumps) of the heart Right ventricle pumps blood into the pulmonary trunk Left ventricle pumps blood into the aorta Left ventricle wall is thicker – does more work

Right and Left Ventricles Note the thickness Figure 18.6

Pathway of Blood Through the Heart and Lungs Inferior and superior vena cavae →Right atrium  tricuspid valve  right ventricle Right ventricle  pulmonary semilunar valve  pulmonary arteries  lungs Lungs  pulmonary veins  left atrium Left atrium  bicuspid valve  left ventricle Left ventricle  aortic semilunar valve  aorta Aorta  systemic circulation

Figure 18.5

Damage to Left Side of the Heart Left ventricle is too weak to pump blood to the aorta so fluid accumulates in lungs. Symptoms: dyspnea (shortness of breath) on exertion and in severe cases, dyspnea at rest. Easily fatigued and intolerant to exercise. "Cardiac asthma" or wheezing may occur. Treatment: Elevate head with pillows or sleep while sitting up. Also best to sleep on the right side.

Damage to Right Side of Heart Right ventricle too weak to pump blood to the lungs so fluid accumulates in the body causing swelling (edema) in the feet, ankles, legs, liver, and abdomen. Where the fluid accumulates depends on the amount of excess fluid and the effects of gravity. Fluid accumulation in the liver or stomach can cause nausea and loss of appetite. Treatment: Elevate legs

Heart Valves Heart valves ensure unidirectional blood flow through the heart Atrioventricular (AV) valves lie between the atria and the ventricles AV valves prevent backflow into the atria when ventricles contract Chordae tendineae anchor AV valves to papillary muscles

Heart Valves Figure 18.8c, d

Atrioventricular Valve Function Figure 18.9

Heart Valves Aortic semilunar (SL)valve lies between the left ventricle and the aorta Pulmonary semilunar valve lies between the right ventricle and pulmonary trunk Semilunar valves prevent backflow of blood into the ventricles

Heart Valves No chordae tendineae Figure 18.8a, b

Semilunar Valve Function Figure 18.10

Microscopic Anatomy of Heart Muscle Cardiac muscle is striated, short, fat, branched, uninucleate and interconnected Actin and myosin very greatly in diameter and are branched 25-35% of volume is mitochondria Less extensive Ca++ ion delivery system: fewer and wider T tubules Sarcoplasmic reticulum is simpler and lacks large terminal cisternae Intercalated discs anchor cardiac cells together and allow free passage of electricity and ions between cells Desmosomes act as door hinges Gap junctions allow passage of electricity and ions

Cardiac Muscle Tissue Contraction Contracts by the sliding filament mechanism Absolute refractory period is 250 ms – nearly as long as the contraction to avoid tetany Muscle cells are stimulated by the nervous system but some cells are self-excitable and can contract on their own (autorhythmicity): to keep a rhythm Heart muscle behaves as a functional syncytium The heart either contracts as a unit or not at all

Microscopic Anatomy of Cardiac Muscle Figure 18.11

Microscopic Anatomy of Skeletal Muscle Striated Long, cylindrical, multinucleate muscle fibers 2% of the volume is mitochondria Thin actin and thick myosin fibers uniform in size and not branched Very extensive Ca++ delivery via T tubules Sarcoplasmic reticulum contains lg. terminal cisternae

Skeletal Muscle Contraction Contracts by the sliding filament mechanism Absolute refractory period is 1-2 ms; contraction lasts 15 – 100 ms Muscle fibers act independently of one another (not interconnected) Contract as a motor unit; not of an entire muscle Each muscle fiber is stimulated by a nerve ending; not self-excitable

Microscopic Anatomy of Skeletal Muscle: Motor Unit

Microscopic Anatomy of Skeletal Muscle