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Class notes

  • Pulmonary circulation = circulation carrying blood from right ventricle out through pulmonary trunk to the lungs for gas exchange (O2 in, CO2 out)
    • Blood returns via the pulmonary veins (4, 2 on each side)
  • Systemic circulation = from left ventricle, through aorta, to capillary bodies throughout the body, then returns via vena cavae (sup and inf) to the right atrium, and the whole process continues again

Heart seen from the front

  • Pointy bit = apex, sitting down and to the right
  • Flat bit at the back of the patient
  • Heart sits in middle of chest
  • Surfaces of the heart:
    • Base (back)
    • Sternocostal surface (Rt side)
    • Diaphragmatic below
    • Left = pulmonary surface (to Lt lung)
  • Note aorta, pulmonary trunk, IVC and SVC
  • Vascular supply of the heart: right coronary artery (from the Rt coronary sinus on aorta) and (emerging behind the pulmonary trunk is the Lt coronary artery)
    • Coronary veins return blood to the right side of the heart (makes sense)

Shape, position and external features of the heart

  • Aortic arch
    • Brachiocephalic trunk
    • Left common carotid artery (Lt side of head and neck, and Lt brain)
    • Left subclavian artery (Lt upper limb)
  • Pulmonary trunk, carries deoxygenated blood from heart to lung
  • Ligamentum arteriosum is a small remnant of the ductus arteriosus (in foetal life, allowed blood getting into the pulmonary trunk into the arch of the aorta, bypassing the lungs, which weren't inflated). This bypass shunted blood from the right side of the heart into the systemic circulation without going through the lungs (between aortic arch and pulmonary trunk)
  • Right pulmonary veins
  • Left pulmonary veins (from respective lungs)
  • Grooves dividing heart into chambers: anterior interventricular sulcus, posterior interventricular sulcus, coronary sulcus (runs completely around the heart to between the Lt ventricle and atrium - this encircles the heart entirely, like a crown). Coronary arteries lie within the coronary sulcus
  • Apex of heart (sticks against the chest). Can feel the apex beat.
  • SVC
  • IVC
  • Pulmonary trunk and ascending aorta share a layer of pericardium wrapping them
  • Venous channels have another encircling layer of membrane (shared between all of them)
    • This separation is due to embryology: the heart used to be an inflow/outflow tract, hence it makes sense for this sac to wrap them separately.

Posterior view

  • Posterior interventricular sulcus
  • Coronary sulcus meets the interventricular sulcus and the interatrial sulcus; these 3 meet in a cross called the cardiac crux.
  • Coronary sinus = venous drainage to the right atrium from the coronary circulation, sitting in the coronary sulcus
  • IVC, SVC into right atrium
  • Pulmonary trunk (outflow tract from right side of heart)
  • Right pulmonary veins/Lt pulmonary veins back from lungs (into Lt atrium)
  • Aorta carries blood out of Lt ventricle to the body

View of heart from above

  • Valves protect the outflow path
  • These are the semilunar valves (pulmonary valve and aortic valve)
  • Auricles: ear-shaped appendages that push forward from the right and left atria to the front of the heart (these are embryological remnants of the early venous end of the heart)
  • Sulcus terminalis: groove that separates two distinct regions in the right atrium: pectinated part in the front and smooth part from the back
    • Front part has ridges on the inside (musculae pectinatae)
    • This ridge is a division between two distinct embryonic origins of the right atrium

The right atrium

  • IVC and SVC inflow
  • Strange circular depression: fossa ovalis - this is the wall between the Rt and Lt atria (in foetal life there was a communication between the Rt and Lt atrium (another shunt between Rt and Lt heart: the foramen ovale). In 3/4 of the population, the leaflets of the fossa ovale fuse and in 25% of the population they don't fuse (but pressure differences prevent a functional communication). In some people, there is an atrial septal defect.
  • Orifice of coronary sinus
  • Tricuspid valve orifice that passes into the right ventricle (can see one leaflet - the septal leaflet of the tricuspid valve)
  • Crista terminalis - the inside crest that is the inside manifestation of the sulcus terminalis on the outside
  • Musculi pectinati = muscular bands on the inside of the heart
  • Most of the Rt atrium = sinus venarum (the space of the right atrium receiving the veins)
  • Limbus fossa ovalis - the distinct ridge around the fossa ovalis (remnant of the edges of the leaflets forming the septum)
  • Sometimes there is a valve protecting the opening to the SVC

Right ventricle

  • Venous blood comes back to the right atrium, which only pumps about 30% of venous return into the right ventricle (most of it comes through simply via the pressure of blood being returned from various parts of the body)
  • V shaped movement of blood
  • Right atrioventricular valve (tricuspid): Three valve leaflet prevents regurgitation of blood when ventricle contracts
    • Anterior leaflet
    • Posterior leaflet
    • Septal leaflet
  • Chordae tendineae - fibrous cords that anchor the valve leaflet edges to little bulges of muscle on the inside of the ventricle; these muscles are the papillary muscles (of which there is an anterior, posterior and septal set)
    • Papillary muscles are active shortening/tensioning mechanisms
    • These hold the valve leaflets closed when the right ventricle is reducing in size
      • They contract WITH the right ventricle WHEN IT CONTRACTS (keeping it closed when blood pressure increases in the ventricle)
  • Septomarginal trabecula: runs between the interventricular septum, to the anterior papillary muscle. One of the bands of conducting pathway to reduce the time it takes for the electricity to cross this area - this makes sure the Rt ventricle contracts in synchrony with the rest of the heart
    • Bottom of interventricular septum is muscular, top is more membranous
  • Supraventricular crest separates the inflow tract from the outflow tract (making the V shape)
  • Blood flows out through infundibulum (conus arteriosus), through the pulmonary semilunar valve to the lungs via the pulmonary trunk

Left atrium and ventricle

Lt atrium

  • More simple in structure
  • Smooth walled structure, with the openings of the pulmonary veints (Lt and Rt)
  • Lt auricle (which has its own sneaky opening from the atrium into it)
  • Impression for fossa ovalis

Lt ventricle

  • Wall is very thick, for pumping at high systemic pressure (120mmHg at rest, compared to 25mmHg in the pulmonary circulation)
  • Anterior and posterior papillary muscles, valve leaflets and chordae tendinae = bicuspid valve
  • Trabeculae carneae: muscular ridges/bridges in the wall

Semilunar valves

  • Aortic (Lt) and pulmonary (Rt)
  • Designed to catch blood that wants to run backwards
  • Rims = lunules
  • Dense nodules at the centre of each cup give it mass so that there is momentum to shut the valve when blood flows back
  • Cusps, each of which has a lunule and a nodule
  • Lt and Rt coronary orifices just above the aortic semilunar valve
  • Names of cusps: pulmonary: Anterior, Lt and Rt; aortic = Lt, Rt, Posterior
    • Coronary arteries come out below Lt and Rt cusps of aortic semilunar valve
  • Shape of Lt ventricle different to Rt ventricle and wall 2x-3x thicker

Cardiac wall

  • A lot of muscle, arranged in spirals, which go in one direction at one level, and another direction at the other level
    • Spirals counter each other, so we don't get any rotation with contraction

Cardiac fibrous skeleton

  • Fibrous tissue forms an attachment point for muscle fibres, provides insulation between atrium and ventricles (so that atria contract before the ventricles -- communication between the two is the atriventricular bundle at the atrioventricular node), and strength at the valves
  • Pulmonary valve, cusp of pulmonary valve, aortic valve, cusp of aortic valve, mitral valve ring, tricuspid valve ring

Official notes

The heart

Introduction

General overview of the circulatory system

The heart is a muscular pump with 4 chambers (2 atria and 2 ventricles) and 4 major valves (tricuspid, pulmonary, mitral and aortic). Review the arrangement of the pulmonary and systemic circulations from the respiratory system lecture. Note that the right side of the heart (right atrium and ventricle) receives venous blood from the systemic circulation and passes it on to the pulmonary artery, while the left side of the heart (left atrium and ventricle) receives venous blood from the pulmonary circulation and passes it on to the aorta for distribution to the body via the systemic circulation. The valves between the atria and ventricles are known as atrioventricular valves (tricuspid on the right and mitral on the left). The valves at the outflow from the ventricles are known as the pulmonary valve (at the start of the pulmonary trunk) and the aortic valve (at the start of the aorta).

The shape and position of the heart

  • The heart lies in the mediastinum (the space between the pleural sacs) within the thoracic cavity. It lies at the level of the 6th to 9th thoracic vertebrae, and is related anteriorly to the body of the sternum (approximately 2nd to 6th costal cartilages).
  • The heart possesses an apex, which projects to the left and inferiorly, reaching the 5th left intercostal space in the midclavicular line; a base, where great vessels enter and leave the heart; three surfaces (anterior or sternocostal, inferior or diaphragmatic, and left or pulmonary) and finally, four borders (superior, inferior, left and right).
  • The cardiac chambers contribute to the borders and surfaces of the heart as follows:
    • Base: left atrium and posterior part of right atrium
    • Apex: left ventricle
    • Sternocostal surface: mainly right atrium and right ventricle, with some contributions from the left ventricle and auricle of the left atrium
    • Diaphragmatic surface: left and right ventricles
    • Pulmonary surface: left ventricle, with some contribution from the left atrium
    • Upper border: left and right atria
    • Right border: right atrium
    • Inferior border: right ventricle mainly, but left ventricle at apex
    • Left border: left ventricle and left auricle

1HMAAnatomy2.png

External features of the heart

  • Interventricular groove (sulcus): between the left and right ventricles
  • Coronary groove (sulcus): between the atria and ventricles
  • Sulcus terminalis: groove extending from the superior vena cava to the inferior vena cava down the anterolateral aspect of the right atrium

Internal features of the cardiac chambers

  1. Right atrium
    • This chamber has a smooth walled sinus venarum posteriorly, where the superior and inferior vena cavae enter. The sinus venarum is separated from the atrium proper by the crista terminalis, a muscular ridge which runs between the two caval openings on the lateral wall of the atrium. Musculi pectinati are muscular ridges which line the atrium proper (i.e. that part anterior to the crista terminalis) and auricle. The fossa ovalis is a depression which lies on the septal wall of the atrium. Its floor was originally part of a foetal septum between the atria. It has a prominent margin, known as the limbus fossa ovalis. In about 25% of individuals there is a small slit by which the left and right atria may communicate. This passage is kept closed by the higher pressures in the left atrium forcing the two leaflets together.
    • The opening of the coronary sinus (which drains the venous blood from much of the heart) lies between the inferior vena caval and atrioventricular orifices. It is protected by the valve of the coronary sinus, which prevents regurgitation of blood back into the coronary sinus during atrial contraction.
    • The right atrioventricular orifice is protected by the tricuspid valve. The tricuspid valve has three leaflets (anterior, posterior and septal).
    • 1HMAAnatomy5.png
  2. Right ventricle
    1. trabeculae carneae, which are ridges, bridges and papillary muscles, give the internal surfacea corrugated appearance
    2. papillary muscles, one for each of the tricuspid valve leaflets (anterior, posterior and septal) have chordae tendineae (collagenous bands) attached to their apices, and which in turn attach to the margins of the atrioventricular valve leaflets
    3. septomarginal trabecula (moderator band), a trabecula carnea, joins the septal wall to the base of the anterior papillary muscle. This carries the right atrioventricular bundle and ensures rapid depolarization of the right ventricular muscle.
    4. supraventricular crest separating the atrioventricular orifice from the outflow tract.
    5. the outflow tract of the right ventricle (conus arteriosus or infundibulum) extends towards the semilunar pulmonary valve
    6. the pulmonary valve has three cusps attached at their bases to a fibrous annulus. Nomina anatomica terminology calls them left, right and anterior. Each valve cusp has a lunule (thickened edge) and a nodule (at the apex of the cusp).
    • 1HMAAnatomy6.png
  3. Left atrium
    1. left auricle extends anteriorly left of the pulmonary trunk
    2. four pulmonary veins (two on each side) enter the left atrium
    3. valvule of the foramen ovale lies on the interatrial septal wall corresponding to the floor of the fossa ovalis on the other side
    4. left atrioventricular valve orifice with mitral valve leaflets
    5. musculi pectinati are fewer and smaller than in the right atrium
    6. in both atria there are foramina venarum minimarum, openings of the venae cordis minimarum which drain into the atrial lumen
  4. Left ventricle
    1. left atrioventricular orifice with mitral (bicuspid) valve leaflets (anterior and posterior)
    2. trabeculae carneae, chordea tendineae and papillary muscles as for the right ventricle, except that the left has two papillary muscles only (anterior and posterior) for corresponding mitral valve leaflets (anterior and posterior) for corresponding mitral valve leaflets
    3. aortic vestibule leading to the semilunar aortic valve
    4. aortic valve has three cusps, each with lunules and nodules as for the pulmonary valve. Nomina anatomica names the cusps left, right and posterior.
    5. interventricular septum has muscular (inferior) and membranous (superior) parts, the latter part lies towards the aortic valve and is partly confluent with the fibrous supports of the right and posterior cusps (see right atrium).
    6. the left ventricle wall is 2-3 times thicker than the right ventricle wall

General structure of the cardiac wall

  • The heart wall consists of three layers:
    • internal layer, the endocardium, continuous with the endothelium of the great vessels
    • muscular layer, the myocardium
    • subepicardial fat and connective tissue beneath the visceral layer of the serous pericardium (epicardium)

Myocardial architecture

  • Atrial fibres form two layers: superficial, common to both atria, and deep, confined to each.
  • Ventricular fibres also consist of superficial and deep layers, where the deep layers also contribute to the papillary muscles. Current thinking regards the ventricular myocardium as a series of nested spiral laminae. These fibre-pathways have varying obliquity so that the myocardium is capable of reducing all the dimensions of the ventricles simultaneously. (See the bottom plate in the previous image).

Cardiac fibrous skeleton

The intercellular spaces between the conducting and contractile elements of the heart are filled with connective tissue. Approximately along the plane of the coronary sinus, i.e. at the atrioventricular groove, and intimately related to the valve orifices of the atrioventricular and semilunar valves, is a complex framework of dense collagen, with membranous, tendinous and fribro-areolar extensions. This is known as the cardiac fibrous skeleton. The skeleton has several functions:

  1. to ensure electrophysiological discontinuity between the atria and ventricles (only connection is via the atrioventricular bundle; see next lecture)
  2. to provide mechanical attachment for the atrial and ventricular muscle
  3. to maintain the cardiac position within the pericardium
  4. to provide a stable but deformable base for the valvular fibrous cores

1HMAAnatomy9.png