Cardiac Biology - Summary of notes taken from lectures for this module. PDF

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Cardiac BiologyLecture 1: Heart IHeart has 4 chambers, 2 sides  Lift and right atriums and ventricles  left side pumps blood around body  right side receives deoxygenated blood  if we have a cardiac output at rest of 5L/ min we must also have a venous return of 5L/ min -if venous return is chang...

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Cardiac Biology Lecture 1: Heart I Heart has 4 chambers, 2 sides  Lift and right atriums and ventricles  left side pumps blood around body  right side receives deoxygenated blood  if we have a cardiac output at rest of 5L/ min we must also have a venous return of 5L/ min -if venous return is changed in any way it will have an effect on blood flow Heart viewed from the front (recommended to practice drawing it to learn)  superior vena cava and inferior vena cava (rather short)  right atrium  right ventricle -most of what is in front is the right ventricle -stab wounds most likely effect right ventricle  left ventricle -only small bit showing  base of pulmonary artery is anterior to the aorta

Mediastinum  heart is located in the mediastinum which can be divided into two major parts -superior and inferior  inferior has 3 parts

Surface anatomy  manubriosternal joint = “angle of louis” = sternal angle  they are the synarthrotic joint formed by articulation of the manubrium (top of sternum) and the body of the sternum  located at 2nd costal cartilage  palpable clinical landmark -you can feel the angle of louis and while examining a patient you can know that this is the start of the second intercostal space -you can then count down to the 5th and this is the location of the apex of the heart

Angle of Louis

The pericardium  tough fibrous sac  filled with fluid which helps with lubrication  encases the heart with a number of layers each made of a single sheet of epithelial cells 1. outermost layer of pericardium: fibrous layer o cant be stretched : non complient, inextensible sac 2. parietal layer of serous pericardium o lines the internal surface of the fibrous pericardium

3. layer of serous fluid 4. visceral layer of serous pericardium (epicardium) o outer layer of the chamber of the heart

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ligaments of pericardium to stabilise heart and minimise jolts as if you apply a mechanical force to the heart it can interfere with rhythm (can stop rhythm in healthy beating heart but can initiate in cardiac arrest) 1. phreno-pericardial ligaments: tethers heart to the diagphragm 2. superior sterno-pericardial ligaments: attaches pericardium to surface of the sternum 3. xipho-pericardial ligaments: attaches right ventricle to xiphoid process 4. vertebro- pericardial ligaments

Sinuses  Transverse Pericardial Sinus -formed as a result of folding of the heart tube in an embryo -separates the arterial vessels and the venous vessels o located posteriorly to the ascending aorta and anteriorly to the SVC o superior to the left atrium -surgical significance: with one motion can pass finger through and locate and ligate (tie off) coronary arteries during coronary artery bypass o in an emergency can rapidly put person on a bypass circuit o if you can control these two vessels can control the whole circuit of blood

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oblique sinus -found on posterior surface -J shaped surrounding the SVC, IVC and pulmonary veins -a hand placed under the apex and moved superiorly slips into oblique sinus

Cardiac tamponade  if heart fills with blood or fluid the pericardial sac will not stretch to accommodate this -causes are varied including haemopericardium (blood in pericardium which is expected from trauma) and pericarditis  rigidity mean that the heart is subject to resulting increased pressure  can compress blood vessels entering and leaving heart compromising cardiac output  serious life threatening -increasingly common to carry ultrasound probes to see if there is a lot of fluid in the pericardial sac making it easier to diagnose  Becks triad describes the signs -low BP -muffled heart sounds when listening with stethoscope -distension of jugular vein  Chest x-ray for this can show the “water bottle sign” -shape shown from x-ray looks like a water bottle shape: not showing shape of the heart but of the pericardium with the heart in the fluid somewhere  Emergency treatment is to make a drain

Pericarditis  Inflammation of the pericardium  Conditions can cause the serous fluid to increase -linked with bacterial infection and myocardial infarction  Painful condition linked with a distinctive posture (classic sign) -sat up leaned over their knees which makes the pain less by minimising load of the tendons of pericardium -most painful position is to lie out flat as it stretches ligaments due to gravity of the heart Orientation of the heart  1/3 on right side of the body, 2/3 on the left  long axis lies parallel to the interventricular septum  short axis is perpendicular to the long axis at the level of the atrioventricular valve Heart broken down  described as a pyramid that has fallen on its side  apex -tip of the left ventricle located approx. directly down from mid clavical o 5th left intercostal space at the mid-clavicular line -when contracting the heart rotates a little bit and the apex hits off the chest wall -this is what you can feel when feeling chest for heart beat -if the heart is enlarged the apex beat could be much further over  base -mainly left atrium -anterior to the oesophagus o to monitor activity of left atrium can often be done through the oesophagus  Surfaces (3D concept) -Right pulmonary surface: mainly RA -Left pulmonary surface: LV o leaves cardiac impression on left lung -Anterior/ sternocostal surface: RV -Inferor/ diaphragmatic surface: mainy LV o rests above central tendon of diaphragm

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4 borders (2D concept) -left: mainly left ventricle (LV) -right: right atrium (RA) between superior vena cava (SVC) and inferior vena cava (IVC) -superior: RA, LA, auricles and great vessels -inferior: mainly RV plus some LV

Transverse section through atria

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pulmonary vessels enter at this level there is a right and left auricle -atrium= upper heart chambers but auricle= ear like conical muscular pouch that arise from each atrium

-auricles consist of pectinate muscles o pectinate muscles are parallel ridges in the walls of the atria of the heart o in ventricles there are trabeculae carneae which are irregular rather than parallel -between pectinate muscles and smooth muscle is crista terminalis, a smooth muscular ridge between the two layers

Features in chambers of the heart  Right Atrium -opening of IVC -annulus fossae ovalis: ring shape structure o Prominent rounded margin of fossa ovalis -fossa ovalis: oval shaped depression o during development there is no point of using lungs as they are full of fluid o body develops ways to bypass lungs by moving blood straight from left to right ventricle o before birth this closes up and we are left with fossa ovalis in the interatrial septum o Patent Foramen Ovale >congenital defect resulting in hole not closing and then called patent foramen ovale >results in potential for right-to-left shunt between the two atria -opening of coronary sinus o coronary sinus is a collection of veins joined together to form a large vessel that collects blood from the heart muscle and delivers it to the right artrium -tricuspid valve o 3 cusp valve allowing flow from RA to RV -preferential streaming of blood from the SVC and IVC into right atrium o SVC blood towards tricuspid o IVC blood toward the fossa ovalis

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Right Ventricle -attached to cusps of tricuspid valve are the chordae tendinae o Attach to papillary muscles o The three right ventricular papillary muscles originate in ventricular wall and attach to anterior, posterior and septal cusps of the tricuspid valve vie chordae tendinae -moderator band o A band of muscle which carries part of the conducting system of the right bundle branch to the anterior papillary muscle

o Right bundle branch is a division of the atrioventricular bundle (bundle of His) from the conducting system of the heart - trabeculae carneae: rounded irregular muscular columns which project from the inner surface of the left and right ventricles of the heart -pulmonary valve o Valve between RV and pulmonary artery o 3 cusps o semilunar valve (1 of 2) -conus arteriosus o extension of the right ventricle in the heart from which pulmonary artery originates

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Left Atrium -fossa ovalis -left atrial appendage o Extension of the left atrium that pumps oxygenated blood from the lungs to the left ventricle -mitral valve (bicuspid valve) o Valve between left atrium and LV allowing filling of LV o 2 cusps -pulmonary vein ostia o Right and left pulmonary veins enter the posterior left atrial wall transporting oxygenated blood from the lungs to LA

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Left Ventricle -much thicker than right V in an adult o About 2-3x thicker than RV o Allows for high pressure to send blood around the body o Important for RV to not be too strong as is getting sent to really tiny alveoli in the lungs which are fragile: pressure needs to be strong enough to drive flow but not to damage the small structures -aortic valve o Between left ventricle and aorta allowing blood to be ejected from LV into aorta o Semilunar valve (2 of 2) o 3 cusps

Work of heart  Pressure x volume = work of the heart  To increase work of the heart you increase pressure or volume  If there is long standing high blood pressure the heart will be “pressure loaded” -ventricle gets much thicker inwards -the work the heart is doing will be much greater which can result in heart failure  Can have a mixture of pressure and volume load in the heart

Lecture 2: Heart II (Heart Valves and Conducting Tissues) Heart valves  2 valves to allow blood to pass from atria to respective ventricles = atrioventricular valve -mitral and tricuspid valve o mitral valve: between left atrium and left ventricle o tricuspid valve: between right atrium and right ventricle  2 semilunar valves that allow blood to pass from ventricles to 1)lungs 2)rest of body 1. pulmonary valve: between right ventricle and pulmonary artery 2. aortic valve: between left ventricle and aorta Aortic Valve  ventricular contraction= valve open  Semilunar valve -the other is pulmonary valve  3 half moon shaped cusps -open silently, closure of valves is reason for heart sounds  allows blood flow into aorta during ventricular contraction , prevents blood flow moving back in the opposite direction during ventricular relaxation -cusps are forced to close with recoil of blood from aorta after ventricle contracts filling the sinuses of the cusps o think of a dropper when you squeeze it first it expels liquid but when you let it relax it pulls liquid back in  Sometimes can be bicuspid

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Calcification – valve starts to accumulate calcific deposits called aortic stenosis -thought to be genetic -narrowing of the aortic valve opening restricting blood flow from the left ventricle to the aorta

Atrioventricular valves  Ventricular contraction= valve closed  In general the design is the cups with tendons connecting to the papillary muscles -tendons to ensure that when the valves contracts that it closes properly  When ventricles are filling the valves are open -contraction of papillary muscles attached to cusps by chordae tendinae keeps valves closed during ventricular contraction and ensures the blood doesn’t push the cusps up and fill the atria  Opening and closing of these valves is passive – based on pressure -when blood pressure in atrium is greater than in ventricle the valve is pushed open and blood flows from atrium  ventricle -when ventricle is contracting and creates a stronger internal pressure it forces the valve closed  Right ventricle= tricuspid valve -anterior, inferior and septal cusps  Left ventricle = bicuspid = mitral valve -anteromedial cusp and posterolateral cusp

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On this diagram you can also see anterior and posterior grooves -anterior and posterior interventricular sulcus o Groove separates ventricles of the heart -coronary sulcus (not seen on this) o Atria separated from ventricles by coronary sulcus More inferior into the RV you can see the moderator band -carries important impulse through side wall of RV

Right Atrioventricular Valve = Tricuspid Valve  Cusps of the right atrioventricular valve (tricuspid valve) attach to chordae tendinae  chordae tendinae extend to papillary muscles -chordae tendinae from 2 paillary muscle attach to each cusp preventing separation of cusps during ventricular contraction  the inferior papillary muscle, anterior muscle and septal muscle

Left Atrioventricular Valve = Mitral valve  cusps are continuous with each other near their bases at sites called commissures in atrioventricular valves  myocardial infarction = lack of blood supply causing tissue damage -when near the mitral valve can cause ripping of the papillary muscles o usually seen as a systolic murmur Surface anatomy for cardiac valves  Aortic valve sends pulse to 3rd intercostal space -right ventricle relaxing  Pulmonary valve pulse at other side of the sternum at 3rd intercostal space -left ventricle relaxing  Mitral valve sends pulse to apex of heart -left ventricle contracting  Tricuspid valve sends pulse to -right ventricle contracting

Heart sounds 

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M1T1 ---- A2P2 -Lub ---- Dub -Mitral1,Tricuspid1 --- Aortic1Pulmonary1 Valves of left heart close first by a very small amount -left heart is activated first -bigger and conducting tissue is bigger Normal heartbeat= simple lub dub

Heart Murmurs  Aortic stenosis  Didn’t finish Fibrous skeleton  Dense connective tissue  Electrical insulator -Insulates atria from ventricles  Structure and support -Scaffolding present for cusps of valves  In cardiac cells they’re connected through gap junctions  Reason for pause between atria and ventricles contracting is that they are electrically insulated due to fibrous skeleton

Conducting system  Made of cardiac cells that have specialised features for heart excitation -network of cells= conducting system -in electrical contact with cardiac muscle cells via gap junctions  Initiates heartbeat and helps spread rapid impulse throughout the heart  Contraction of cardiac muscle is triggered by depolarisation of the plasma membrane

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-initial excitation of one cell spreads rapidly due to gap junctions o Gap junctions allow action potentials to jump from one cell to another Initial depolarisation arises in a small group of conducting system cells: Sinoatrial (SA) node -SA node= pacemaker of the heart -located in right atrium near entrance to SVC -AP generated here spreads throughout the atria then into and throughout the ventricles -SA node discharge rate determines the heart rate o Heart rate= number of times heart contracts per minute Spread of depolarisation is rapid enough that the two atria contract at the same time Spread of the action potential to the ventricles is more complicated Link between atrial and ventricular conducting system= Atrioventricular (AV) node -located at base of RA at Koch’s c o Koch’s Triangle= anatomical area of which its angles are 1. Coronary sinus orifice 2. Tendon of Todaro 3. AV node -spreading of AP through RA causes depolarisation of the AV node -this node as a very important characteristic: the propagation of APs through the AV node is relatively slow

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o Delay allows atrial contraction to be completed before ventricular excitation occurs After leaving AV node AP propagates down interventricular (IV) septum -this pathway of conducting fibres= Bundle of His -AV node + Bundle of His= only connection of conducting system between atria and ventricles Bundle of His branches into right and left bundle branches in IV septum -at apex of heart these branches enter walls of left and right ventricles -fibres make contact with purkinje fibres o Large conducting cells o Rapidly distribute impulse through much of the ventricles -purkinje fibres make contact with ventricular myocardial cells which spread the impulse through rest of ventricles Rapid conduction along fibres cause depolarisation to happen nearly simultaneously  single coordinated contraction -apex contracts slightly earlier causing the blood to move upwards towards the valve for an efficient contraction

moderator band (aka septomarginal band) = muscular band that carries part of right bundle branch to the anterior papillary muscle -extends from inferior septum

Cardiac Action Potentials

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mechanism by which APs are conducted in membranes of heart cells is similar to other excitable tissues different types of heart cells express unique combinations of ion channels that produce different AP shapes -allows for specialisation of different roles in the spread of excitation through heart cardiac action potential takes a different form in different cardiac cells -SA nodal cells, atrial muscle cells, AV nodal cells, Purkinje fibres, ventricular muscle cells Cardiac ventricular AP shape shows rapid depolarisation and repolarisation -rapid upstroke (phase 0) caused by rapid opening of Na+ channels – depolarisation -followed by partial repolarisation (phase 1) caused by closing of the fast channels opening K+ channel -membrane potential enters plateau phase (phase 2) due to inward Ca2+ currents -repolarisation phase (phase 3) occurs as Ca2+ channels inactivate and more K+ channels open and Na+ channels revert to closed state

SA node= most excitable cells in the heart -has an unstable resting potential so instead undergoes a slow depolarisation o Gradual depolarisation = pacemaker potential -3 mechanisms contribute to pacemaker potential 1. Progressive reduction in K+ permeability: K+ channels gradually close due to membrane’s return to negative potentials

2. Unique set of pacemaker channels called “funny” or F-type channels: open when the membrane potential is at negative values conducting a depolarising Na+ current 3. T-type Ca2+ channels: Ca2+ channel that opens briefly but contributes to Ca2+ current and an important final depolarising boost to pacemaker potential

Lecture 3: Heart III (Nutritive circulation to the heart itself)

Coronary ostia (right and left)  Aortic cusp has 2 small opening  Sinus of Valsalva -anatomic dilations between the wall of the aorta and each of the 3 cusps of the aortic valve (the pouch-like section of the valve) -Imagine aorta is simple cylinder o problem with this is that when the valve opens the ostia (openings) will be covered

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o so there is a sinus that creates a vortex when the blood flows in, stopping the ostia from always being covered so that blood enters the coronary system coronary ostia are located in the aortic sinuses (sinus of Valsalva) -left coronary ostia is in left aortic sinus and right coronary ostia is in the right aortic sinus -non-coronary sinus of Valsalva has no ostia and lies to the left and posteriorly at the origin of the ascending aorta

Coronary arteries  Marginal branch comes off the right coronary artery  LAD= left anterior descending branch -branch of the left coronary artery : anterior interventricular branch  Coronary arterial system -aortic valve with 3 sinuses -right coronary artery (RCA) emerges from right anterior aortic sinus o Descends through the atrioventricular groove then curves posteriorly o It turns towards posterior side of the heart and continues downward in the posterior interventricular sulcus -posterior descending artery o Where it begins to run posteriorly it branches anteriorly to form the right marginal artery o Continues to the apex of the heart -left coronary artery (LCA) emerges from left posterior aortic sinus o LCA passes between left side of pulmonary trunk and left auricle o It divides into the left circumflex and left anterior descending (or interventricular) arteries o The left circumflex artery follows the coronary sulcus onto posterior of the heart and gives rise to the marginal artery branch which fol...