Describe the structure and function of the pericardium.
- A fibroserous sac
- Encloses the heart and roots of the great vessels
- Two layers:
I. Strong outer fibrous layer
II. Inner serosal layer - adheres to the external wall of the heart and is called the visceral pericardium. The visceral pericardium reflects back on itself and lines the outer fibrous layer, forming the parietal pericardium.
II. Space between visceral and parietal layers consists of pericardial fluid which reduces friction.
- Attached to the sternum and mediastinal portions of the right and left pleural.
- The aorta, the pulmonary artery, and the superior vena cava emanate from the pericardium superiorly.
- The inferior vena cava projects through the pericardium inferiorly.
Outline the surface anatomy of the heart.
- The apex is formed by the tip of the left ventricle, which points inferiorly, anteriorly, and to the left.
- The base or posterior surface of the heart is formed by the atria, mainly the left, and lies between the lung hila.
- The anterior surface of the heart is shaped by the right atrium and ventricle.
- The inferior surface of the heart is formed by both ventricles, primarily the left. This surface of the heart lies along the diaphragm; (diaphragmatic surface).
Identify the four major valves in the normal heart that direct blood flow in a forward direction and prevent backward leakage.
- Atrioventricular valves
I. Tricuspid valve
II. Mitral valve
- Semilunar valves
I. Aortic valve
II. Pulmonic valve
What is the endocardium?
- The single layer of endothelial cells that line the surface of the heart valves and interior surface of the chambers.
- The subendocardial tissue contains fibroblasts, elastic and collagenous fibres, veins, nerves and branches of the conducting system.
What is the myocardium?
- The myocardium is the thickest layer of the heart and consists of bundles of cardiac muscle cells.
- External to the myocardium is a layer of connective tissue and adipose tissue through which pass the larger blood vessels and nerves that supply the heart muscle.
What is the epicardium?
The epicardium is the outermost layer of the heart and is identical to, and just another term for, the visceral pericardium.
Outline the structure and components of the right atrium.
- Opening into the right atrium are the superior and inferior venae cavae and the coronary sinus.
- The venae cavae return deoxygenated blood from the systemic veins into the right atrium
- The coronary sinus carries venous return from the coronary arteries.
- The interatrial septum forms the posteromedial wall of the right atrium and separates it from the left atrium.
- The tricuspid valve is located in the floor of the atrium and opens into the right ventricle.
Outline the structure and components of the right ventricle.
- The ventricle is covered by a number of irregular bridges (termed trabeculae carneae) that give the right ventricular wall a sponge-like appearance.
- The right ventricle contains three papillary muscles, which project into the chamber and via their thin, string-like chordae tendineae attach to the edges of the tricuspid valve leaflets. The contraction of these muscles prevents the back-flow of blood.
- At the apex of the right ventricular outflow tract is the pulmonic valve, which leads to the pulmonary artery. During ventricular relaxation, elastic recoil of the pulmonary arteries closes the pulmonic valve.
Outline the structure and components of the left atrium.
- Entering the posterior half of the left atrium are the four pulmonary veins.
- The wall of the left atrium is about 2 mm thick, being slightly greater than that of the right atrium.
- The mitral valve opens into the left ventricle through the inferior wall of the left atrium.
Outline the structure and components of the left ventricle.
- The cavity of the left ventricle is approximately cone shaped and longer than that of the right ventricle.
- In a healthy adult heart, the wall thickness is 9 to 11 mm, roughly three times that of the right ventricle.
- The aortic vestibule is a smooth-walled part of the left ventricular cavity located just inferior to the aortic valve. Inferior to this region, most of the ventricle is covered by trabeculae carneae, which are finer and more numerous than those in the right ventricle.
- The left ventricular chamber contains two large papillary muscles. These are larger than their counterparts in the right ventricle, and their chordae tendineae are thicker but less numerous.
- The chordae tendineae of each papillary muscle distribute to both leaflets of the mitral valve.
- Surrounding the aortic valve opening is a fibrous ring to which is attached the three cusps of the valve. Just above the right and left aortic valve cusps in the aortic wall are the origins of the right and left coronary arteries.
Outline the structure and function of the coronary veins.
- The coronary veins follow a distribution similar to that of the major coronary arteries.
- These vessels return blood from the myocardial capillaries to the right atrium predominantly via the coronary sinus.
- The major veins lie in the epicardial fat, usually superficial to their arterial counterparts.
- The thebesian veins, provide an additional potential route for a small amount of direct blood return to the cardiac chambers.
Outline the structure and function of the left main coronary arteries.
- The large left main coronary artery passes between the left atrium and the pulmonary trunk to reach the AV groove.
- There it divides into the left anterior descending (LAD) coronary artery and the circumflex artery.
I. The LAD travels within the anterior interventricular groove toward the cardiac apex.
II. During its descent on the anterior surface, the LAD gives off septal branches that supply the anterior two thirds of the interventricular septum and the apical portion of the anterior papillary muscle.
III. The LAD also gives off diagonal branches that supply the anterior surface of the left ventricle.
- The circumflex artery
I. The circumflex artery continues within the left AV groove and passes around the left border of the heart to reach the posterior surface.
II. It gives off large obtuse marginal branches that supply the lateral and posterior wall of the left ventricle.
Outline the structure and function of the right coronary artery.
- The right coronary artery (RCA) travels in the right AV groove, passing posteriorly between the right atrium and ventricle. It supplies blood to the right ventricle via acute marginal branches.
- In most people (85%), the distal RCA gives rise to a large branch, the posterior descending artery.
I. This vessel travels from the inferoposterior aspect of the heart to the apex and supplies blood to the inferior and posterior walls of the ventricles and the posterior one third of the interventricular septum.
II. Just before giving off the posterior descending branch, the RCA usually gives off the AV nodal artery.
- The blood supply to the SA node is also most often (70% of the time) derived from the RCA.
I. However, in 25% of normal hearts, the SA nodal artery arises from the circumflex artery
II. In 5% of cases, both the RCA and the circumflex artery contribute to this vessel.
Infarction: death of cells (yellow tissue - dead cells)
Outline the blood flow to different tissues of the body.
- Brain needs high, constant flow
- Heart muscle needs high flow which increases during exercise
- Kidneys need high, constant flow
- Blood flow to skeletal muscle can be very high during exercise and gut blood flow is high after a meal
Outline the control of blood flow.
- Blood flow must adjust to meet the tissue’s metabolic needs. The cardiovascular system must supply between 5 and 25 l.min-1 of blood to the tissues whilst at all times maintaining perfusion to vital organs such as the brain, heart and kidneys.
- The higher the rate of metabolism, the greater the demand for O2 and nutrients. Increases in metabolism must be met by increases in blood flow. The rate of blood flow is known as the perfusion rate.
I. At rest, total blood flow is about 5 l.min-1
II. In exercise, this can rise to 25 l.min-1
State the factors that affect the rate of diffusion.
- Area available for exchange
- Diffusion ‘resistance’ – nature of the molecule, the barrier, the path length
- Concentration gradient
Outline the factors affecting the rate of diffusion in the capillaries.
1. Area available for exchange
- Area for exchange between capillaries and tissues is generally very large – it depends on capillary density
- A tissue which is more metabolically active will have more capillaries – higher capillary density
2. Concentration gradient
- A substance which is used by the tissues will have a lower concentration in capillary blood than arterial blood
- How much lower depends on:
I.The rate of use by the tissue
II. The rate of blood flow through the capillary bed
- The lower the blood flow, the lower the capillary concentration.
- Blood flow must be high enough to maintain a sufficient concentration gradient.
- The rate of blood flow determines the concentration gradient driving O2 diffusion into the cells
What is pericardial effusion?
- Normally only a very thin film of fluid.
- If excess fluid builds up relatively rapidly this can compress the heart due to the inextensible fibrous pericardial layer.
- Compression of the heart can lead to cardiac tamponade. As the heart cannot fill during diastole.
- Through a procedure called pericardiocentesis, fluid may need to be removed for testing or to relieve compression.
What is coronary circulation?
Coronary circulation: the circulation of blood in the blood vessels of the heart muscle (myocardium).
- The vessels that deliver oxygen-rich blood to the myocardium are known as coronary arteries.
- The vessels that remove the deoxygenated blood from the heart muscle are known as cardiac veins.
- The left and right coronary arteries originate at the base of the aorta from openings called the coronary ostia located behind the aortic valve leaflets.
- The left and right coronary arteries and their branches lie on the surface of the heart, and therefore are sometimes referred to as the epicardial coronary vessels.
Outline some of the problems associated with coronary arteries.
- Coronary arteries are prone to atheroma. A thrombus can form which blocks the artery.
- Coronary arteries are vital to supply well oxygenated blood to the myocardium.
- Right coronary artery rises in the right aortic sinus. Left coronary artery rises in the left aortic sinus.
- The anterior interventricular artery is often the artery that is blocked during a myocardial infarction. It supplies the apex of the heart, the septum and the left ventricle and a bit of right ventricle with blood.
Discuss the relationship between pathology in the atrioventricular valves.
The aortic and mitral valve are closely associated. Hence, if a disease affects one it will likely affect the other.
What is serum?
Serum: plasma minus the clotting factors. The main clotting factor is fibrinogen.
What is buffy coat?
Buffy coat: contains white blood cells and a few platelets
Differentiate between the different types of fluid collected from blood.
- The fluid collected from unclotted blood = plasma
- The fluid collected from clotted blood = serum
Discuss factors affecting whole blood viscosity.
What is the significance of minor changes in plasma viscosity?
- Minor changes in plasma viscosity can result from raised levels of acute phase plasma proteins (e.g. Fibrinogen, Complement factors and C-reactive protein).
- Acute phase proteins increase in response to inflammation. Therefore, minor changes in plasma viscosity can be used to ‘measure’ the inflammatory response.
- In recent years, we have been able to measure C-reactive protein (CRP) and this is more commonly used to ‘measure inflammation’.
What is haemodynamics?
- Haemodynamics: how pressure affects flow in blood vessels
- Although blood is a mixture of cells and plasma, it is considered a fluid for practical purposes.
- Fluids move from regions of high pressure to regions of low pressure.
Explain the difference between flow and velocity of blood.
- Retrograde flow in the arterial system can occur and is greatest when the peripheral resistance is high – ‘blood bounces back’. Hence the blood meets resistance and returns.
- In the case of blood flowing in a vessel, velocity is often expressed in the units of cm/sec.
- In contrast, flow is the volume of a liquid (/gas) that is moving per unit of time.
Understand the difference between laminar and turbulent flow.
- Laminar flow: blood usually flows in streamlines with each layer of blood remaining the same distance from the wall. When laminar flow occurs, the velocity of blood in the centre of the vessel is greater than that toward the outer edge creating a parabolic profile.
- Turbulent flow:
I. Blood flowing in all directions in the vessel and continually mixing within the vessel.
II. When the rate of blood flow becomes too great
III. When it passes by an obstruction in a vessel
IV. When it makes a sharp turn
V. When it passes over a rough surface
VI. Increased resistance to blood flow
What is peripheral resistance?
- Peripheral resistance: the totality of the resistance being posed to the blood pumped from the heart.
- Low peripheral resistance lowers diastolic pressure and therefore increases pulse pressure. E.g. hot bath, exercise, pregnancy (Vasodilation of arterioles)
What is a pulse?
What are the factors affecting the volume of a pulse?
Which conditions can increase/decrease pulse volume?
- Pulse: a rhythmical throbbing of the arteries as blood is propelled through them, typically as felt in the wrists or neck. What we feel is a shock wave that arrives slightly before the blood itself.
- A weak pulse is often described as “thready”.
- A strong pulse is often described as “bounding”.
- The strength or what is also called the volume of the pulse is determined primarily by two factors:
I. The force with which the left ventricle is able to eject blood into the arterial system and thus develop a normal shock wave.
II. The pulse pressure. The greater the pulse pressure the stronger the pulse.
- Reduced pulse volume can result from left ventricular failure, aortic valve stenosis, hypovolaemia (severe dehydration, bleeding).
- Bradycardia, such as heart block, increases pulse pressure and leads to a stronger pulse.
Outline the principles of the measurement of blood pressure.
- Phase 1 – the point at which the first sound appears
- Phase 5 – the point at which the sounds disappear
Define pulse pressure.
Pulse pressure: (Peak systolic pressure – end diastolic pressure), which because of the way we measure BP with a sphygomanometer means that: Pulse pressure = (systolic pressure – diastolic pressure). Therefore, most commonly, pulse pressure is (120mm Hg – 80 mm Hg) = 40mm Hg
Define mean arterial pressure.
Mean arterial pressure: estimated as (diastolic pressure + 1/3 of the pulse pressure). Therefore, most commonly, mean arterial pressure is (80 mmHg + 13 mmHg) = 93 mm Hg. If mean arterial pressure falls below 70 mm Hg then organ perfusion is impaired.
What is the mediastinum?
- The heart lies in the middle mediastinum; the mediastinum is the intervening region in the thoracic cavity between the right and left pleural cavities which are occupied by the lungs.
- The middle mediastinum consists of the pericardial sac containing the heart and its blood vessels (coronary vessels) and the roots of the aorta, superior and inferior vena cava and the pulmonary vessels.
Identify the structures visible from the anterior surface of the heart
Identify the structures visible from the posterior surface of the heart
Describe the anatomy of the heart and its position in situ.
Identify the cardiac veins in the anterior and posterior surface of the heart.
Identify the coronary arteries in the posterior and anterior surface of the heart.
Outline the structure of the leaflets/cusps in the different heart valves.
- The aortic valve has three cusps:
I. Left coronary cusp (LCC)
II. Right coronary cusp (RCC)
II. Non coronary cusp (NCC)
- The mitral valve has an alphanumeric nomenclature that number from the anterior to the posterior, with respect to the heart. (A1-A3), (P1-P3)
- The pulmonary valve has three cusps:
I. The anterior cusps (AC)
II. The left cusp (LC)
III. The right cusp (RC)
- The tricuspid valve has three leaflets:
I. Anterior (A)
II. Septal (S)
III. Posterior (P)
Identify and name the major arteries comprising the vascular system.
- The head and neck
I. Brachiocephalic trunk
II. Common Carotid
III. External Carotid & its branches
IV. Facial artery
V. Maxillary artery
VI. Superficial temporal artery
VII. Internal Carotid
- The abdomen
I. Abdominal Aorta & its paired branches
II. Suprarenal arteries
III. Renal arteries
IV. Ovarian/Testicular arteries & its unpaired branches
V. Celiac artery
VI. Superior Mesenteric artery
VII. Inferior Mesenteric artery
- The thorax
Thoracic (Descending) Aorta & its
- The pelvis
I. Common Iliac artery
II. External Iliac artery
III. Internal Iliac artery
- The upper limb
I. Subclavian artery
II. Axillary artery
III. Brachial artery
IV. Radial artery
V. Ulnar artery
- Lower limb
II. Popliteal artery
III. Anterior and Posterior Tibial arteries
Identify and name the major veins in the vascular system.
- The head and neck
I. External jugular vein
II. Internal jugular vein
III. Right and left brachiocephalic vein
- The abdomen
I. Inferior Vena cava
II. Right and left renal veins
III.Left and right testicular vein
- The thorax
Superior Vena cava
- The pelvis
I. Common Iliac vein
II. External Iliac vein
III. Internal Iliac vein
- Upper Limb
I. Subclavian vein
II. Cephalic vein
III. Basilic vein
IV. Median cubital vein
- Lower Limb
I. Femoral vein
II. Long Saphenous vein
III. Short Saphenous vein
IV. Popliteal veins