Clinical anatomy of the cardiovascular system

Describe some features of coronary blood flow

- Coronary blood flow increases with increased myocardial activity and oxygen consumption through metabolic (active or functional) hyperaemia. Adenosine, a by-product of ATP metabolism, is thought to be the main metabolic vasodilator. - Its regulation through adrenoceptor-mediated vasoconstriction and vasodilation. - Its pulsatile pattern, with the majority of flow occurring during diastole. - It's susceptibility to disruption through the development of coronary artery atherosclerosis.

What are the three main branches from the aortic arch?

1. Brachiocephalic artery- divides into the right sub-clavian artery and the right common carotid artery. 2. Left common carotid artery 3. Left sub-clavian

Describe the heart chambers

Atria= thin-walled structures which act as the initial collecting duct for blood entering the heart. Right atrium= forms part of the right heart border and receives the superior and inferior venae cavae. Left atrium= lies posterior to the right atrium and receives the four pulmonary veins. Ventricle= thick-walled structures comprising mainly of muscle tissue. They make up the main bulk of the heart mass. Right ventricle= lies anterior to the left ventricle and forms the mid-anterior surface of the heart. Left ventricle= forms the posterolateral, lateral and anterolateral surface of the heart, and its apex.

Describe how coronary blood flow is regulated by nervous innervation

Basal tone in the arterioles is maintained by sympathetic vasoconstrictor nerves, which release norepinephrine (noradrenaline) onto alpha-adrenoceptors. During exercise, however, circulating levels of epinephrine (adrenaline) increase, which acts preferentially on beta-2-adrenoceptors to produce vasodilation that reinforces the metabolic vasodilation.

What is the neurogenic theory of auto-regulation?

Cerebral arterioles respond to perivascular nerve stimulation. This effect is thought to be small.

What is the myogenic theory of auto-regulation?

Cerebral blood flow is regulated by the degree of stretch in the walls of the cerebral arteries.

Which artery is the dominant coronary artery?

Coronary artery anatomy varies between individuals. The dominant coronary artery is the one which gives rise to the posterior descending branch, which supplies blood to the inferior wall of the left ventricle. In about 90% of individuals, the right coronary artery is dominant, and in about 10% of people the circumflex artery is dominant.

What is capillary (or vascular) recruitment?

For example, at rest, not all skeletal muscle capillaries are perfused, but when oxygen requirements increase, the number of perfused capillaries increases. This is known as capillary or vascular recruitment.

Describe the murmur heard in aortic regurgitation

In aortic regurgitation, blood flows backwards through the aortic valve immediately after its closure. The murmur is therefore an early diastolic murmur. It is a high pitched noise which is best heard over the left sternal border during held expiration.

Describe the murmur heard in aortic stenosis

In aortic stenosis, turbulent blood flow occurs during the ventricular ejection (systolic) phase as blood passes through the restricted valve. The murmur is therefore called an ejection systolic which occurs between S1 and S2. Maximal flow, and therefore the peak intensity of the murmur occurs in mid-systole. It is best heard in the aortic area or at the left sternal edge and it radiates to the carotid arteries..

Vasa vasorum

In large vessels, the adventitia contains a network of blood vessels called the vasa vasorum (vessel of vessels) supplying the smooth muscle.

Describe the murmur heard in mitral regurgitation

In mitral regurgitation, the back flow of blood into the left atrium during ventricular systole produces a long murmur that lasts throughout systole, called a pan-systolic murmur. It is loudest at the apex and radiates to the axilla.

What is an innocent murmur and who may have one?

Innocent murmurs are usually ejection murmurs due to turbulent blood flow across normal semilunar valves. They are common in the young, during pregnancy or fever, and in anaemic patients.

Describe how local factors produced as a consequence of hypoxia increase blood flow

Local factors produces as a consequence of tissue hypoxia, including K+, CO2, H+ (from lactic acid) and adenosine, increase blood flow through metabolic hyperaemia. Sympathetic stimulation produces vasoconstriction. The local factors override sympathetic effects during exercise.

Describe the murmur heard in mitral stenosis

Mitral stenosis produces a mid-diastolic murmur, the turbulent blood flow arising as blood flows forward through the restricted mitral valve. In sinus rhythm, pre-systolic accentuation of the murmur may be noticed during atrial systole. The murmur is low pitched and heard best at the apex with the patient lying on their left side.

What causes a murmur?

Murmurs are sounds caused by turbulent blood flow. Murmurs may be physiological or "innocent" or pathological.

Describe the innervation of the intercostal muscles

Pairs of intercostal arteries branch out from the posterior aspect of the thoracic aorta to supply the intercostal muscle.

What are pathological murmurs caused by?

Pathological murmurs are caused by valve disease or congenital heart defects.

Describe how hypoxia affects the arterioles

Reduced tissue oxygen concentration (hypoxia) generally leads to vasodilation in response to tissue need for oxygen, a form of metabolic hyperaemia (action or functional hyper-aemia). Pulmonary arteries, however, constrict in response to hypoxia, reducing blood flow to poorly ventilated lung tissue. Well-ventilated alveoli can then be perfused better, which facilitates oxygen up-take into the blood.

Describe murmurs heard in pulmonary valve disease

Right-sided valve pathology produces the same type of murmur as the equivalent left sided lesion but the location of the murmur is different. Pulmonary stenosis produces an ejection systolic murmur and pulmonary regurgitation produces an early diastolic murmur, both heard best in the pulmonary area. Tricuspid stenosis causes a mid-diastolic murmur and tricuspid regurgitation causes a pan-systolic murmur at the left sternal edge.

Where should the heart valves be auscultated?

Sounds related to particular valves are heard best at different sites on the chest wall, which are give the names of the relevant valve. These locations do not correspond with the positions of the valves, but rather to where the sounds are transmitted most distinctly. Aortic: right second intercostal space Pulmonary: left second intercostal space Tricuspid: fourth intercostal space at the left sternal border Mitral: heart apex

What are the two main types of valvular heart disease?

Stenosis- in which the valve opening is restricted, producing an obstruction to blood flow. Incompetence/ regurgitation- in which the valve does not close properly and blood leaks backwards through the valve.

Describe the progression of the ascending aorta to the common iliac arteries

The ascending aorta curves upwards ad back-wards as the arch of the aorta (aortic arch), before turning downwards as the thoracic (or descending) aorta at the level of T4. Below the diaphragm (at T12), the thoracic aorta becomes the abdominal aorta, which bifurcated at about the levels of L4 into the right and left common iliac arteries.

What is auto-regulation?

The brain's capacity to regulate its own blood supply. There is a constant cerebral blood flow over a wide range of mean arterial pressures (60-160 mmHg).

What causes the dominant heart sounds in a healthy adult?

The dominant sounds in healthy adults are the first and second heart sounds which are produced by the closing of the AV and semilunar valves respectively. These "lubb" and "dubb" sounds mark the beginning and end of systole. The flow of blood through the heart and the opening of normal heart valves are usually silent.

What is the function of the fibrous pericardium?

The fibrous outer layer of the pericardium, fibrous pericardium, anchors the heart in the mediastinum and protects the heart from trauma, the spread of infection from adjacent organs such as the lungs, and from over-expansion should the intra-cardiac volume increase.

What is the pericardium?

The heart is covered by the pericardium. This is made up of three layers of connective tissue. Two layers closest to the heart are composed of a serous membrane which folds back on itself where the great vessels emerge from the heart. The innermost layer is the visceral pericardium (or epicardium) and the second layer is called the parietal pericardium. The space enclosed between these two layers forms the pericardial cavity.

What is the anatomical location of the heart?

The heart is located in the middle mediastinum, between the lungs. It is protected by the sternum anteriorly, by the vertebral column posterioly, and by the ribs.

What is dextrocardia?

The heart's apex normally points left. Rarely (1 in 12,000) it points to the right. This condition is known as dextrocardia and it may be associated with other congenital abnormalities.

What are the components of the cardiovascular system?

The heart- a muscular pump. Blood vessels which are organized into two circuits which operate in series (the systemic circulation and pulmonary circulation). The blood and its constituents.

What is the jugular venous pressure (JVP) and how is it used clinically?

The jugular venous pulse is assessed with the patient lying at 45 degrees. The height of the venous pressure wave in the internal jugular veins measured in centimetres vertically from the sternal angle is the jugular venous pressure is used clinically to assess right atrial pressure. The JVP is normally <4 cm above the sternal angle.

What is the difference between the left and right ventricle?

The left and right ventricles generate the force required to propel the blood around the systemic circulation and the pulmonary circulation, respectively. The left ventricle has a thicker myocardium because it is required to generate a much higher pressure than the right ventricle.

Describe the course of the left coronary artery, and the functions of its branches

The left coronary artery arises in the left aortic sinus as the left main stem, before it divides into two branches, the circumflex artery, which passes down the back of the heart in the left atrioventricular grove, and the anterior descending (or anterior inter-ventricular) artery, which runs down the anterior inter-ventricular groove. They supply both atria, the rest of the inter-ventricular septum and most of the ventricle, the circumflex artery supplying the posterior and posterolateral aspects of the left ventricle and the anterior descending artery supplying the anterior wall, anterolateral wall and apex.

Arterial supply of the brain

The main arterial supply of the brain comes from the internal carotid arteries, which supply the anterior brain, and the vertebral basilar arteries (vertebrobasilar system), which provide the posterior circulation. The anterior and middle cerebral arteries supply the frontal and parietal lobes. The posterior cerebral artery supplies the occipital lobe. The vertebral and basilar arteries perfuse the brain stem, mid-brain and cerebellum. Communicating arteries provide connections between the anterior and posterior circulations and between the left and right hemispheres, creating protective anastomotic connections that form the circle of Willis.

Which valves are the atrioventricular valves, and how are they connected to the ventricles?

The mitral valve is located between the left atrium and the left ventricle. The tricuspid valve is located between the right atrium and the right ventricle. Their positions denote these structures as the atrioventricular (AV) valves. The AV valves are attached to the papillary muscle on the inner wall of the ventricles via cord-like connective tissue and elastin tendons called cordae tendineae.

What is the apex beat?

The most inferior and lateral position at which the cardiac impulse can be palpated. It is normally found in the fifth left intercostal space in the mid-clavicular line

What are the layers surrounding the heart?

The outer layer of connective tissue is known as the epicardium/ visceral pericardium. The middle layer is known as the myocardium, which is composed of cardiac muscle and connective tissue. This is the contractile part of the heart. The inner layer, endocardium, is in contact with the blood, covers the heart and is continuous with the inner lining of the blood vessels, the vascular endothelium. It comprises a thin layer of connective tissue and endothelium.

What is the function of the papillary muscles?

The papillary muscles maintain closure of the AV valves and prevent regurgitation of blood back into the atria during ventricular contraction.

What is the function of the pericardial cavity?

The pericardial cavity contains pericardial fluid which serves as lubricant to allow the two layers to slide over each other.

Describe the course of the right coronary artery, and its function.

The right coronary artery raised in the right aortic sinus before coursing down the right atria-ventricular groove. It provides the main arterial supply to the right ventricle, and also supplies blood to part of the inter-ventricular septum, and to both atria.

What is the annulus fibrosus cordis and what is its function?

The valves and the base of the aorta and pulmonary artery are surrounded by four fibrous rings of dense collagenous connective tissue known as the annulus fibrosus cordis. These rings bolster the structure of the heart, providing support to the heart valves. The muscle fibres of the atria and ventricles are attached to it as the fixed point about which muscular contraction takes place, and it provides electrical separation of the atria from the ventricles.

Blood vessel walls

The walls of larger blood vessels comprise three layers: an inner intima (tunica intima) consisting of a thin layer of endothelial cells, a thick media (tunica media) containing smooth muscle and elastin filaments that provide elastic properties, and an outer adventitia (tunica adventitia) consisting of fibroblasts and nerves embedded in a collagenous tissue. The layers are separated by inner and outer elastic lamina. Veins have a thinner media than arteries, and contain less smooth muscle. All three layers contain fibrous collagen, which acts as a framework to which cells are anchored.

What is the humeral theory of auto-regulation?

The waste products of metabolism regulate cerebral blood flow. Hypercapnia causes cerebral vasodilation, and hypocapnia causes vasoconstriction. The effect of increased pCO2 decreases with age. The effect of oxygen is less marked. Low pO2 produces modest vasodilation.

What is the importance of the collaterals within the coronary arteries?

There are extensive anastomoses between the left and right coronary arterial circulations. These are functionally closed in their healthy state. However, should one of the major arteries become blocked, these anastomoses may pen to become functionally useful as collaterals which allow blood to flow from the open artery to the blocked one. The maintenance of blood flow through the collaterals may limit the size of myocardial infarction or, in some cases, prevent infarction altogether.

What are the names of the four heart valves?

There are four heart valves within the heart which, when functioning normally, ensure that the flow of blood through the heart is unidirectional. All of the valves have three cusps except for the mitral valve, which is a bicuspid valve.

What is the function of the coronary sinus?

This drains deoxygenated blood from heart. The major veins of the heart coalesce to form the coronary sinus on the posterior aspect of the heart. It drains directly into the right atrium, close to the tricuspid valve annulus.

What does infero-lateral displacement of the heart suggest?

This usually indicates left ventricular dilation, due to, for example, ischaemic heart disease, dilated cardiomyopathy or a volume overloaded left ventricle due to aortic or mitral regurgitation.

Endothelium vasodilators and vasoconstrictors

Vasodilators - NO (synthesis is increased by factors that elevate intracellular Ca2+, such as bradykinin, histamine and serotonin, and some neurotransmitters such as Substance P) - Prostacyclin - Endothelium-derived relaxing factor (EDRF) Vasoconstrictors - Endothelin-1 - Angiotensin II - ADH - Noradrenaline

Describe how the aortic and pulmonary valves open

When the ventricles contract and ventricular pressure exceeds the pressure in the aorta and pulmonary artery, the valve cusps open flat against the arterial walls and blood flows out of the ventricles.

Describe how the aortic and pulmonary valves close

When the ventricles relax and the pressure in the great arteries exceeds that in the ventricles, the valve cusps come together in apposition and prevent back-flow of blood into the heart.