Chapter 20 (Heart) PDF

Preview

Summary

Required learning for BIOL 235 Chapter 20...

Description

Chapter 20: Cardiovascular System: Heart

20.1 Anatomy of the Heart Location of the Heart Heart   

Roughly same size as closed fist. 250 g (Females), 300 g (males). Rests on the diaphragm, near midline of thoracic cavity.

Heart Surfaces (7): 1. Mediastinum  Anatomical region from sternum to vertebral column, from 1 st rib to diaphragm, and between lungs. 2. Apex  Tip of the left ventricle (lower left chamber of heart), and rests on diaphragm. 3. Base  Opposite of the apex and posterior. Formed by atria (upper chambers), mostly the left atrium. 4. Anterior Surface  Deep to sternum and ribs. 5. Inferior Surface  Between apex and right surface; rests on the diaphragm. 6. Right Surface  Faces right lung, from inferior surface to base. 7. Left Surface  Faces left lung, from base to apex.

Pericardium Pericardium   

Membrane that surrounds and protects the heart. Confines the heart in position of mediastinum, while allowing movement for contraction. Two main parts: (1) Fibrous pericardium, (2) Serous pericardium.

Fibrous Pericardium   

Superficial part Inelastic, dense irregular tissue. Prevents overstretching, protection, and anchors heart to mediastinum.

Serous Pericardium  

Deeper, thinner, more delicate membrane that forms a double layer around the heart. Two layers: o Parietal layer: fused to fibrous pericardium. o Visceral layer (epicardium): one of the layers of heart wall, and adheres to the surface o o

of heart. Pericardial Cavity: the space between parietal and visceral layer. Pericardial fluid: thin film of lubricating fluid by pericardial cells.

Layers of the Heart Wall Epicardium (External)   

Contains two tissue layers: visceral layer of serous pericardium and fibroelastic/adipose tissue layer. Smooth, slippery texture of outer surface of heart. Contains blood vessels that supply the myocardium.

Myocardium (Middle)  

Composed of cardiac muscle tissue; makes up 99% of the heart wall. Responsible for pumping action of the heart.

Endocardium (Inner)   

Thin layer of endothelium and connective tissue. Provides smooth lining for chambers of the heart. Covers valves of heart.

Chambers of the Heart 1. Atria: two superior receiving chambers. 2. Ventricles: Two inferior pumping chambers. Auricle – anterior surface of each atrium, which increases the atria’s volume for blood. Coronary Sulcus – encircles the heart and marks boundary between superior atria and inferior ventricles.

Right Atrium (2-3 mm thickness) Right Atrium  

Receives blood from three veins: superior vena cava, inferior vena cava, coronary sinus. Inside of posterior wall is smooth; inside of anterior wall is rough.

Pectinate Muscles 

Inside of anterior wall, which are muscular ridges and extends into auricle.

Interatrial Septum 

Thin partition of left and right atrium.

Fossa Ovalis (foramen ovale) 

Oval depression, which closes after birth.

Tricuspid Valve (atrioventricular valve) 

Blood passes from the right atrium to right ventricle through this valve.

Right Ventricle (4-5 mm thickness) Right Ventricle 

Most of the anterior surface of heart.

Trabeculae Carneae 

Raised bundles of cardiac muscles. Convey part of conduction system.

Chordae Tendineae 

Tendon-like cords that are connected to cusps of tricuspid valve.

Papillary Muscles 

Cone-shaped trabeculae carneae.

Interventricular Septum 

Separates the right and left ventricle.

Pulmonary Valve 

Blood passes through the valve to the pulmonary arteries to the lungs.

Left Atrium (2-3 mm thickness) Left Atrium  

Forms most of the base of heart. Receives blood from lungs through pulmonary veins.

Bicuspid (mitral) valve (left atrioventricular valve) 

Blood passes from left atrium to left ventricle through this valve.

Left Ventricle (10-15 mm thickness) Left Ventricle  

Forms the apex of heart. Also contains trabeculae carneae and chordae tendineae.

Aortic Valve 

Blood passes from left ventricle through the aortic valve and into ascending aorta (then to descending aorta).

Ligamentum Arteriosum 

Is a remnant of ductus arteriosus (which closes after birth), and connects the arch of aorta to pulmonary trunk.

Myocardial Thickness and Function   

Walls of the atria are thinner because it pumps blood only to adjacent ventricles (short distance). Walls of the ventricles are thick because it pumps blood at great distances. The ventricles pump equal amounts of blood. However, the left works harder because it brings blood to the entire body.

Fibrous Skeleton of the Heart   

Dense connective tissue of the heart forms the Fibrous skeleton. Four rings. Four functions: o Structural foundation of valves o Prevents overstretching of valves o Point of insertion for cardiac muscle fibers o Electrical insulator between atria and ventricles

20.2 Heart Valves and Circulation of Blood Operation of the Atrioventricular (AV) Valves   

AV valve open, rounded end of cusps project into ventricle. Relaxed ventricles; papillary muscles, chordae tendineae slacked, blood moves from high pressure (atria) to low pressure (ventricle). Ventricle contract; pressure of blood moves cusps upwards, closing the AV valve.

Operation of Semiulnar (SL) Valves  

Contraction of ventricles; pressure builds up in chamber, SL valves open when ventricle pressure is greater than arteries. Relaxation of ventricles; blood flows back to heart, and fills valve cusps, closing opening between ventricle and artery.

Systemic and Pulmonary Circulations Systemic Circulation (left side of heart)     

Receives oxygenated blood from lungs. Left ventricle ejects blood into aorta. Aorta to separate stream entering systemic arteries throughout the body. Systemic capillaries are the site of O2 drop off, CO2 pick up. Systemic venule carry deoxygenated blood and merge with systemic veins.

Lungs -> left ventricle -> aorta -> systemic arteries -> systemic capillaries -> systemic venule -> systemic veins

Pulmonary Circulation (Right side of heart)     

Deoxygenated blood from systemic circulation. Right ventricle to pulmonary trunk which branch into pulmonary arteries. Pulmonary arteries to right and left lungs. Pulmonary capillaries unload CO 2 and loads O2. Oxygenated blood flows into pulmonary veins and left atrium.

Systemic circulation -> Right Ventricle -> Pulmonary Trunk -> Pulmonary Arteries -> Right and Left Lungs -> Pulmonary Capillaries -> Pulmonary Veins -> Left Atrium

Coronary Circulation Coronary Circulation/Cardiac Circulation  

Network of blood vessels that supply the myocardium of the heart. Composed of the coronary arteries and coronary veins.

Coronary Arteries 

Left and right coronary arteries supply oxygenated blood to the myocardium.

Anastomoses  

Connection or extension of branches to other coronary arteries. Provide detours for blood if a route becomes obstructed.

Collateral Circulation 

Alternate routes for oxygenated blood to reach the heart muscles.

Coronary Veins 

Carries deoxygenated blood away from the heart.

Coronary Sinus 

Large vascular sinus in which deoxygenated blood drains into, which then goes to the right atrium.

20.3 Cardiac Muscle Tissue and the Cardiac Conduction System Histology of Cardiac Muscle Tissue   

Intercalated discs – ends of cardiac muscle fibers that connect neighboring fibers; thickening of the sarcolemma. Desmosomes – inside the discs, and holds the fibers together. Gap Junctions – allows action potential to conduct from one muscle fiber to its neighbors. Allows the contraction of a single, coordinated unit.

Autorhythmic Fibers: The Conduction System Autorhythmic Fibers  

Specialized cardiac muscles which repeatedly generated action potentials for contraction. Two important functions: 1. Pacemaker: sets the rhythm of electrical excitation for contraction. 2. Cardiac Conduction System: provide path for cardiac excitation to progress through the heart.

Cardiac Conduction System Pathway 

Sinoatrial (SA) Node – Depolarize spontaneously. Action potential propagates through gap junctions. Sets rhythm for contraction (natural pacemaker). o Pacemaker Potential: spontaneous depolarization of the SA node.



Atrioventricular (AV) Node – Action potential slows down allowing the atria to empty blood into ventricles. Atrioventricular (AV) Bundle (Bundle of His) – ONLY site to conduct from atria to ventricles. Right/Left Bundle Branches – from interventricular septum to apex of heart. Purkinje Fibers – Action potential from apex to remainder of ventricular myocardium.

  

Artificial Pacemaker – sends small electric currents to stimulate heart contraction if the SA node is damaged.

Action Potential and Contraction of Contractile Fibers Contractile Fibers 

Atrial and ventricular fibers in which action potentials travel along.

Action Potential Stages (4) 1. Depolarization – have a stable resting membrane potential of -90 mV.  Voltage-gated fast Na+ channels open rapidly to allow Na+ to enter, causing a rapid depolarization. 2. Plateau – a period of maintained depolarization due to Ca 2+ and K+ channels.  Voltage-gated slow Ca2+ channels opens allowing Ca2+ to enter.  Voltage – gated K+ channels open allowing K+ to leave.  Balance of Ca2+ inflow and K+ outflow maintains plateau. 3. Repolarization – Recovery of resting membrane potential due to closing of inflow channels.  K+ outflow remains, while Ca2+ inflow closes. 4. Refractory Period – lasts longer than contraction; maintained contraction (tetanus) cannot occur.

Electrocardiogram Electrocardiogram (ECG/EKG): recording of electrical signals produced by the heart. Electrocardiograph: instrument used to record the signals. Three Waves: 1. P Wave – upward deflection, and represents atrial depolarization. o Atrial Depolarization: action potential from SA Node to contractile fibers in atria (2). 2. QRS Complex – down, up, down; Triangular deflection; represents rapid ventricular depolarization. o Rapid Ventricular Depolarization: action potential in ventricular contractile fibers. 3. T Wave – dome-shaped upward deflection; represents ventricular repolarization. o Ventricle Depolarization: relaxing of ventricles; ECG is flat during plateau period. Correlation of ECG Waves with Atrial and Ventricular Systole Systole – the phase of contraction. Diastole – the phase of relaxation.

20.4 The Cardiac Cycle Cardiac Cycle  

All the events associated with one heartbeat Consists of systole and diastole of atria, and systole/diastole of ventricles.

Pressure and Volume Changes during Cardiac Cycle 

Blood moves from area of high pressure to lower pressure.

Atrial Systole (0.1 sec)  

Atria are contracting while ventricles are relaxed. 4 Steps: 1. SA node and atrial depolarization (P Wave) 2. Atrial systole; blood pushed to open AV valves into ventricles. 3. Each ventricle contains 130 mL of blood at the relaxation (diastole) period. This is called end-diastolic volume (EDV). 4. Ventricular depolarization (QRS).

Ventricular Systole (0.3 sec)  

Ventricles are contracting while atria are relaxed (atrial diastole). 4 steps: 1. Isovolumetric Contraction: AV and SL valves are closed, isometric muscle contraction. 2. Ejection of blood from heart. Ventricular ejection is the period where SL valves are open. 3. Left ejects 70 mL into aorta, and right to the pulmonary trunk. End-systolic volume (ESV) is 60 mL remaining in each ventricle. Stroke volume is the amount ejected per beat which is 70 mL. 4. Ventricular repolarization (T Wave).

Relaxation Period (0.4 sec)  

Atria and ventricles are relaxed. 2 steps: 1. Ventricular diastole (repolarization). Rebound of blood off closed cups of aortic valve produces dicrotic wave. Isovolumetric relaxation is a period in which ventricular blood volume does not change. 2. Ventricular filling occurs when AV valves open, blood flows from atrium to ventricle. P wave appears.

Heart Sounds Heart Sounds – four sounds during each cardiac cycle, but only first and second can be heard. Lubb (S1) – caused by blood turbulence with closure of AV valves. Dupp (S2) – caused by closure of SL valves. Heart murmur 

Abnormal sound consisting of clicking, rushing, or gurgling noise after normal heart sounds. Indicate valve disorder in adults.

20.5 Cardiac Output Cardiac Output (CO)   

Volume of blood ejected from left (or right) ventricle to the aorta (or pulmonary trunk) per minute. Stroke Volume – volume of blood ejected by ventricle each contraction. CO = Stroke volume (SV) x Heart Rate (HR).

Cardiac Reserve 

The difference between maximum cardiac output and cardiac output at rest.

Regulation of Stroke Volume Three factors regulate stroke volume: 1. Preload – degree of stretch on heart before contraction. 2. Contractility – forcefulness of contraction of ventricular muscle fibers. 3. Afterload – pressure that must be exceeded to eject blood from ventricles.

Preload: Effect of Stretching    

Greater preload stretch = greater contraction. Frank-Starling Law of the heart – preload is proportional to end-diastolic volume (EDV); greater EDV = greater contraction. Venous return – blood returning to right ventricle. Frank-Starling Law of heart equalizes the left and right ventricles by keeping blood flow equal. The venous return increases on one side if the contraction becomes unequal.

Contractility   

Contractility is the strength of contraction at any given preload. Positive inotropic agents – increase contractility. Negative inotropic agents – decrease contractility.

Afterload  

Pressure that must be overcome before a semilunar valve can open is called an afterload. Increase afterload = decrease stroke volume to fill up the ventricles.

Regulation of Heart Rate 

Two controls: (1) ANS, (2) Adrenal Medulla (epinephrine and NE).

Autonomic Regulation of Heart Rate Cardiovascular Center 

Is the regulating center for the heart; directs appropriate output in both sympathetic and parasympathetic divisions.

Proprioceptors 

Muscles and limbs input is a major stimulus for the cardiovascular center. Increased physical activity = rapid increase in heart rate.

Chemoreceptors 

Monitor chemical changes in blood.

Baroreceptors 

Monitor stretching of arteries and veins; detect changes in blood pressure.

Cardiac Accelerator Nerves   

Sympathetic nerves from the spinal cord to the SA, AV nodes, and myocardium. Impulses of cardiac accelerator nerves triggers release of NE which binds to beta-1 (b 1) receptors. Two effects of NE: o Speeds rate of spontaneous depolarization in SA and AV nodes, thus increase heart rate. o Enhances Ca2+ entry, thus increasing contractility.

Vagus (X) Nerves   

Parasympathetic nerve impulses reach the heart via vagus (x) nerves. Releases ACh, which slows spontaneous depolarization, thus slower heart rate. Little effect on contractility.

Chemical Regulation of Heart Rate 1. Hormones  Epinephrine/NE, Thyroid hormones increase heart rate and contractility.  Tachycardia is an elevated resting heart rate; major sign of hyperthyroidism. 2. Cations  Increased K+ or Na+ = decrease heart rate and contractility.

  

Excess Na+ blocks Ca2+inflow, thus decreasing contractility. Excess K+ blocks generation of action potential. Moderate increase in Ca2+ increases heart rate and heartbeat strength.

Other Factors in Heart Rate Regulation Bradycardia – resting heart rate under 50 beats/min; more energy efficient for endurance. Hypothermia – cooling of a person’s body; beneficial for surgical repair of heart, allowing short periods of interrupted or reduced blood flow.

20.6 Exercise and the Heart Exercising results in the following:   

Increased maximal cardiac output, thus increasing oxygen to tissues. Oxygen delivery rises because skeletal muscles develop more capillary networks. Hypertrophy (enlargement) of the heart

Disorders Arteriosclerosis 

Thickening of walls and loss of elasticity of arteries.

Atherosclerosis 

Progressive arteriosclerosis; formation of walls of large or medium-sized plaques.

Ventricular Fibrillation (VF)  

Deadly arrhythmia; ventricular fiber contraction are not synchronized causing quivering of ventricles. Ventricular pumping stops, blood ejection ceases, and ultimately death.

Medical Terms Cardiac Arrest – Stopping of heart or in ventricular fibrillation. Palpitation – Abnormal rate or rhythm of heart....