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The Cardiovascular SystemTask 1
Describe size, weight and location of heart within the thorax:
o located within thoracic cavity, medially b/t lungs in space called mediastinum
(Inferior).
o Average size of your fist: 12 cm in length, 8 cm wide, 6 cm in thickness.
o Average weight is less than a pound
Describe orientation of heart within thorax with regards to axis of heart, base, and apex
o Base points towards right shoulder and is beneath second rib. The apex is directed
towards left hip and rests on diaphragm, approximately at the level of the fifth
intercostal space.
The heart is enclosed in a fibrous sac of connective tissue - the PERICARDIUM. The
pericardium is composed of 2 distinct layers – the fibrous pericardium and the serous
pericardium. The most outer layer is the fibrous pericardium. Deep to the fibrous pericardium is
the double-layered serous pericardium – consisting of both the parietal & visceral layers. The
outer layer of the serous pericardium, known as the parietal layer lines the internal aspect of the
fibrous pericardium. At the superior aspect of the heart the parietal layer folds back on itself to
form the visceral pericardium. The visceral pericardium lies directly on top of the myocardium –
becoming in fact an integral component of the heart wall and is often referred to as the
epicardium.
Task 2
From which important muscle does the pericardium take attachment inferiorly? Does this
explain why the heart looks long and thin in lung conditions typified by hyperinflation
e.g. COPD? Diaphragm
Outline the structure of the fibrous pericardium. How does this relate to its function?
made of dense, irregular connective tissue and is relatively non-distensible. Its rigid
structure prevents excessive distension, rapid overfilling of the heart, and provides
protection
What exists between the parietal and visceral layers of the serous pericardium?
Pericardial cavity with serous fluid
State the function of the serous pericardium. To lubricate heart and prevent friction,
allows heart to beat easily in relatively frictionless environment as the serous pericardial
layers slide smoothly across each other.
Outline how inflammation can affect pericardial function (Pericarditis). Inflammation
results in decrease in already small amount of serous fluid. This causes pericardial layers
to rub, bind and stick to each other which forms adhesions and interferes with heart
movements.
,Myocardium (cardiac muscle): thickest section of heart wall and contains cardiomyocytes;
contractile cells of heart.
Endocardium: inner most layer, continuous with the endothelium of all blood vessels in the
body. This layer is composed of squamous epithelial cells which just like those of blood vessel
endothelium provides a friction free interface between the walls of the chambers and the blood
contained within them / moving through them. This layer – just like endothelial cells lining blood
vessels also secretes prostacyclin in order to repel platelets / prevent platelet adhesion to the
walls of the cardiac chambers / vessels.
4 chambers:
The heart consists of 4 chambers; left and right atria (atrium) – left and right ventricles. All
chambers are separated by part fibrous / part muscle septae (septum). The presence of septae
basically separate the left and right sides of the heart – or the oxygenated and deoxygenated
blood. In some individuals the septae are not fully completed at birth resulting in an abnormal
connection between the left and right atria (atrial septal defect – ASD) or between the left and
right ventricles (VSD) or a larger hole affecting the atrial & ventricular portion of the septum
(AVSD).
Right Atria
The RA receives venous return (VR) from the systemic circulation via the “Great Veins”
and also from the coronary sinus.
o State the names of these vessels and from which regions of the body they convey
blood
superior vena cava and inferior vena cava- receive oxygen poor blood
from the veins of the body through SVC and IVCand then pump it out
through pulmonary trunk
pulmonary artery- carries blood to lungs where oxygen picked up and
CO2 unloaded
pulmonary vein- oxygen rich blood drains from lungs and returned to left
side of heart through four pulmonary veins
aorta- oxygen rich blood returned to left atrium flows in to left ventricle
and is pumped out in to arota from which systemic arteties branch to
supply all body tissues
after oxygen is delivered to tissues, oxygen poor blood circulates from
tissues back to RA which empty in to SVC or IVC
o Are these entry vessels associated with any particular valves? Atrioventricular
valves are located between atria and ventricles on each side and prevent backflow.
Left AV valve is called bicuspid/mitral valve and right AV valve is called
tricuspid valve and has tiny white cords called chordae tendinae. There are also
semilunar valves which guard the bases of the two large arteries leaving
ventricular chambers, called pulmonary semilunar valve and aortic semilunar
valve.
, Coronary sinus also delivers deoxygenated blood to RA. Which organ has this blood
come from? From Myocardium of heart which is drained by cardiac veins that empty in
to coronary sinus.
Name AV valve located between RA and RV- tricuspid valve
Right Ventricle
In which vessels is deoxygenated blood conveyed to the lungs- oxygen poor blood goes
from superior vena cava and inferior vena cava and pumps through pulmonary trunk.
Pulmonary trunk splits in to right and left pulmonary arteries.
This pathway is associated with pulmonary semilunar valve
Left Atria
Oxygenated blood returns from lungs to left side of heart via four pulmonary veins
Left Ventricle
Blood flows from left atrium to left ventricle and on contraction of the heart (SYSTOLE)
the LV ejects blood into aorta from which systemic arteries branch to supply body
tissues, The oxygen poor blood circulates from tissues back to RA via systemic veins
which empty in to SVC and IVC.
This pathway is associated with the aortic semilunar valve
Atrioventricular valves:
How are the structures of the chordae tendinae and papillary muscles related to their
function- Papillary muscles are muscle sin ventricles that attach to cusps of AV valves
via chordae tendinae and contract to prevent inversion or prolapse of valves. Chordae
tendinae are like tiny white cords that anchor cusps to walls of ventricles. If cusps were
unanchored, they would blow upward in to atria like umbrella.
, Coronary Arteries
At rest, ~ 5 – 6 litres of blood passes through the cardiac chambers per minute but the cardiac
muscle wall is so thick that diffusion is not a feasible option. So just like other tissues of the
body, must receive blood directly via its own specific blood supply – i.e. coronary circulation.
In total there are two coronary arteries - the left and right coronary arteries, which arise from
the root of the aorta and encircle the base of the heart travelling in the atrio-ventricular groove.
The left coronary artery: runs towards the left side of the heart where it divides into its 2 main
branches:
The anterior descending branch (anterior interventricular artery) – supplying the
interventricular septum and the anterior walls of both ventricles.
The more minor circumflex artery – which supplies the left atrium and the posterior
aspect of the left ventricle.
The Right Coronary Artery: supplies blood to the wall of the RV and part of the posterior LV.
The right Coronary artery also supplies the SAN, AVN, Bundle of His.
In health there are no / very few anastomoses ( small interconnecting vessels) between coronary
arteries. This means that if there is a sudden occlusion of a coronary artery all the myocardial
fibres distal to the occlusion and dependent on the blocked vessel may potentially die (MI). In
people who suffer repeated bouts of myocardial ischemia due to angina, anastomes may form
The coronary arteries lie in epicardium of heart, but give off smaller branches that
perpendicularly penetrate myocardial muscle mass travelling towards the endocardium. As the
arteries penetrate the mass of the heart they sub-divide into arterioles, capillaries. The numerous
coronary capillaries lie in extremely close proximity to the cardiac myocytes. A high capillary-
to-cardiac fibre ratio and short diffusion distances ensure efficient oxygen delivery to the
myocytes and removal of metabolic waste products from the cells.
After passing through myocardium in rich capillary networks, the now venous blood is
transported via the coronary veins, (following roughly the same routes as the arteries), most of
these veins join to form the coronary sinus, which empties venous blood directly into RA
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