Cardiovascular System Flashcards
Describe the position, surfaces, borders, and landmarks of the heart.
The heart is located in the mediastinum of the thoracic cavity. The apex of the heart is located around the 5th intercostal space - the base of the heart is the back. The front sits behind the sternum and ribs.
The superior border of the heart is the top, where the great vessels emerge, the inferior border is the bottom, and there are right and left borders.
From the anterior aspect, the coronary sulcus, anterior interventricular sulcus, and auricles can be seen. The coronary sulcus marks the division between the atria and ventricles (fatty groove) - this continues around the back as well. The right coronary artery sits within the coronary sulcus. The anterior interventricuar sulcus separates the right and left ventricles. The left anterior descending artery sits within this fatty groove (a branch of the left coronary artery). Auricles are protrusions from the atria - these increase the capacity of the atria.
From the posterior aspect, the coronary sulcus and posterior interventricular sulcus can be seen (continuations from the anterior aspect). The coronary sinus sits within the coronary sulcus on the posterior side (large vein which stores all venous blood from the heart tissue). There is also a posterior descending artery within the posterior interventricuar sulcus, which can either stem from the right or left coronary artery.
Describe the layers of the heart.
The pericardium is a tough, fibrous sac which the heart sits within - it rests on, and is continuous with, the fibrous connective tissue of the diaphragm. A second layer of pericardium, called serous pericardium, lies beneath this. This layer is further subdivided into the parietal pericardium and visceral pericardium. The parietal pericardium is fused to the outer, fibrous layer, and the visceral is the outermost layer of the wall of the heart (is therefore also called the epicardium). These are divided by a pericardial cavity containing pericardial fluid.
The myocardium is a thick layer of cardiac muscle beneath the epicardium, and the endocardium is the innermost layer (the lining).
Describe the chambers and valves of the heart.
There are four chambers of the heart - the right and left atria and the right and left ventricles. The right atria receives de-ox blood via the inferior and superior vena cavae and coronary sinus, and delivers this to the right ventricle, which pumps this blood to the lungs via the pulmonary arteries. The oxygenated blood then arrives at the left atrium via the pulmonary veins, and delivers this to the left ventricle which supplies the entire body with blood via the aorta.
Atrioventricular valves separate the atria from the ventricles (right = tricuspid, left = bicuspid/mitral), and semilunar valves separate the ventricles from the great arteries (pulmonary and aortic valves). Chordae tendinae connect valve cusps to papillary muscles (protrusions of endocardium). As the ventricle fills, the papillary muscles pull on chordae tendinae, changing the configuration of the valve to prevent backflow.
Outline key differences between the left and right sides of the heart.
1) The right atrioventricular valve is tricuspid, whereas the left is bicuspid
2) Pectinate muscles (stripy in appearance) are a distinct feature of the right atrium
3) Fossa ovalis are also another distinct feature of the right atrium (a remanent of the ductus arteriosus)
4) On the left atrium, pulmonary veins will show distinct holes (if dissecting a heart)
5) The left ventricle is larger and more muscular compared to the right, as it must pump blood to the entire body
Describe the pathway of blood flow through systemic and pulmonary circulations.
The aorta carries blood from the left ventricle to the systemic circulation. The aortic arch has three main protrusions - the brachiocephalic trunk (which splits into two itself - the right subclavian and the right common carotid arteries), the left common carotid, and the left subclavian arteries.
Subclavian arteries supply the arms with blood, and common carotid arteries supply blood up the sides of your neck.
These initial arteries are large elastic arteries, and they branch into medium muscular (distribution) arteries, and then arterioles. Arterioles then branch further into capillary beds, which directly exchange molecules with the target tissues. Postcapillary venules then take up this deoxygenated blood, and converge to form muscular venules, then veins. Blood returns to the right atrium of the heart via the inferior and superior vena cavae, for the bottom and top halves of the body, respectively.
It is then pumped into the pulmonary circulation via the four pulmonary arteries, and this time gas exchange for oxygen occurs in lung alveoli. The blood is drained into the pulmonary venous circulation and returned to the left atrium via the four pulmonary veins.
Describe the pathway of blood flow in the coronary circulation.
In the coronary circulation, the heart supplies itself with oxygenated blood via the left and right coronary arteries. Once used, the deoxygenated blood is then taken up by the coronary veins (great cardiac, middle cardiac, and small cardiac veins), which drain into the coronary sinus, and subsequently, the right atrium. It then follows the pulmonary circulation until it reaches the left ventricle again.
Describe the main components of blood.
Blood is a connective tissue, and is therefore made up of resident cells within an extracellular matrix (plasma). Blood plasma is comprised of 92% water, as well albumin protein, and some glucose and electrolytes. Plasma comprises just over half the total volume of blood. There are 3 main resident cell types within blood - erythrocytes (RBCs), leukocytes (WBCs), and thrombocytes (platelets). Erythrocytes are produced in bone marrow, but erythropoetin (EPO), a hormone which stimulates their growth, is released from the kidneys. Haematocrit is the level of iron content in blood (should be 40-45%). Leukocytes can be subdivided into granulocytes and agranulocytes, and are associated with immune protection.
Thrombocytes are cell fragments which form fibrin clots to prevent haemorrhage (normal cound of platelets is 150-450K per ml blood)
Describe the structures and functions of each type of blood vessel.
Blood vessels all share the same fundamental structure - they are hollow, tube-like structures with a three-layered wall. The tunica interna/intima is the innermost, endothelial layer. The tunica media is a layer of smooth muscle and elastic tissue, and the outermost tunica externa/adventitia is a layer of connective tissue. Different types of vessel have different relative thicknesses of these layers, as well as different lumen sizes.
Large elastic (conducting) arteries have the largest diameter of all arteries (2nd largest overall). They have a very thick tunica media with lots of elastic fibres. The overall width of artery wall is <10% the total vessel diameter.
Medium muscular (distribution) arteries have thinner media layers with fewer elastic fibres (more smooth muscle). The wall thickness is roughly 25% total vessel diameter.
Arterioles (resistance vessels) are much thinner - the tunica media is just 2-3 cells thick of smooth muscle, and is still relatively thick compared to the other layers. Vessel diameter is roughly 50% wall.
Capillaries (exchange vessels) are the smallest of all vessels, and are the site of gas exchange. The walls of capillaries are a single layer of endothelium on a basement membrane, with no tunica media. Contunuous capillaries have a cohesive layer of endothelium, fenestrated capillaries have tiny holes, and sinusoid capillaries have large intercellular gaps and an incomplete basement membrane.
Postcapillary venules are the smallest veins - they have no tunica media and a sparse tunica externa. They are very poroud to allow for final exchange.
Muscular venules are microscopic, but have tunica media (1-2 layers of muscle cells), and a sparse tunica externa.
Veins are structurally similar to arteries, but they have larger lumen and thinner media layers. They also have bicuspid valves which are necessary to prevent backflow, and can have skeletal muscle pumps which use peristalsis to aid the pushing of blood against gravity.
Outline the stages of the cardiac cycle.
1) Diastole - 0.5sec @70bpm
AV valves are open and semilunar valves are closed (between two ECG signals). Filling of the ventricles is driven by venous pressure. As the ventricles expand, they exert pressure on the walls, and the atria contract to add 10-20% extra blood at rest. When the ventricular pressure exceeds the atrial pressure, the AV valves close.
2) Isovolumetric contraction - 0.05sec @ 70bpm
Both sets of valves are closed, and pressure builds up in the ventricles as they contract.
3) Systole - 0.3sec @70bpm
When the pressure of the ventricles exceeds the pressure of their respective arteries, the semilunar valves open. 75% of the total stroke volume is ejected within 0.15 seconds, and the other 25% over the next 0.15 seconds. Only 2/3 of the total volume within each ventricle is ejected (70/120mls).
4) Isovolumetric relaxation - 0.08sec @ 70bpm
When the pressure of the arteries exceeds the pressure of their respective ventricles, the semilunar valves close (all valves closed) until the arterial pressure drops below the ventricular pressure, and the AV valves open again to resume the cycle (atria were filling in the background).
Explain the heart’s own control of the cardiac cycle. How can this be altered by the sympathetic and parasympathetic nervous systems?
The heart will beat on its own (autonomously) at around 100bpm due to its SA node - a collection of cardiomyocytes that spontaneously depolarise themselves at regular intervals.
Within the body, the rate of depolarisation of cardiomyocytes is governed by the sympathetic and parasympathetic nervous systems.
Cardiac sympathetic fibres exit the spinal cord at T1-5, forming a sympathetic chain which splits into two branches which run along the great vessels - the right branch terminates at the atria and the left at the ventricles. These are noradrenalinergic fibres which act upon B1-adrenoreceptors, increasing AV conduction velocity (decreased 0.1 second delay caused by fibrotendonosis ring), increased rate of relaxation of myocytes, decreased myocyte action potential length, and increased contractile force of ventricles.
The parasympathetic nervous system will do the opposite by using acetylcholine as an inhibitory neurotransmitter, hyperpolarising the cardiomyocytes. At rest, the parasympathetic NS acts on the SA node via the vagal motor nuclei in the brainstem (gives rise to the vagus nerve). The right side of the vagus nerve terminates near the SA node, and the left side terminates near the AV node.
What is the Frank-Starling mechanism? Why is it important in the central control of hemodynamic funtion?
the Frank-Starling mechanism describes how the heart responds to pressure around the body - an increase in central venous pressure will result in greater contractile strength of the ventricle (due to faster filling - known as diastolic distension). This then results in increased stroke volume, and therefore increased pressure on the other circulation, increased rate of filling of the opposite ventricle (and thus diastolic distension again), and a proportionally increased stroke volume from the opposite ventricle. This means that central venous pressure and stroke volume are intrinsically linked.
Discuss the autonomic and metabolic pathways which mediate blood pressure and flow characteristics.
Peripheral control of haemodynamic function (as opposed to central control of the heart itself) relies on altering the “tone” of resistance vessels (arterioles). This can be considered to be mediated by autonomic or metabolic pathways:
1) Autoregulation inolves the baroreceptor reflex - baroreceptors are cells which measure pressure by sensing the degree of stretch in the aortic arch and carotid. This sensory information feeds back to the brainstem which restores blood pressure by manipulating HR, stroke volume, and blood vessel diameter (via smooth muscle). Carotid baroreceptors are for the brain, and they ensure the brain has sufficient blood supply at all times.
2) Metabolic control is determined by the local metabolic rate of the cardiac tissues (rate of oxygen consumption). Here, vascular tone is mediated in response to intrinsic or extrinsic factors.
Intrinsic control includes myogenic response (myocytes depolarise due to stretch - increase in arterial pressure = vasoconstriction, decrease = vasodilation); endothelial secretions (vasoconstrictors such as endothelin-1, or vasodilators such as NO), which are governed by shear stress; vasoactive metabolites (potassium, ATP, CO2, etc) which signify high rates of metabolism; and temperature (influences sympathetic vasoconstrictor fibres to regulate core body temperature).
Extrinsic control involves vasomotor nerves and vasoactive hormones: Vasomotor nerves can be sympathetic vasoconstrictors or parasympathetic vasodilators (vasodilation can be induced either by parasympathetic pathway, or just by lack of sympathetic stimulation).
Vasoactive hormones can induce dilation or constriction by acting on specific receptor proteins of vascular smooth muscle - adrenaline is excitatory (vasoconstriction), as are ADH and angiotensin; ANP and insulin are dilatory.
Discuss the pathology and risks of atherosclerosis.
Atherosclerosis is an inflammatory disease which can result from high cholesterol in the bloodstream. When this happens, cholesterol and other low-density lipids invade blood vessel walls occurs, as well as inflammatory cells (dendritic and T-cells). Macrophages in the blood vessel wall engulf lipid droplets and become lipid-laden foam cells. These then release MMPs which break downo the structure of the blood vessels, causing smooth muscle cells to migrate and forma fibrous cap over the foam cells. Over many years, this can cause narrowing of the blood vessels, causing an increase in blood pressure. These lesions can then rupture due to enzymatic activity or shear stress from the increased blood pressure, releasing foam cells and debris into the blood stream, and potentially leading to coagulation cascade (clotting). If full occlusion occurs in the heart - heart attack; in the brain - stroke; in the lung - pulmonary embolism; in the extremities - haemorrage. Partial occlusions can cause angina, transient ischaemic attack, and gangrene.
Discuss risk factors of cardiovascular diseases, with reference to original and modern studies.
Cardiovascular disease (CVD) are a group of disorders of the heart and circulatory system including coronary (ischaemic), cerebrovascular (stroke), peripheral arterial, rheumatic, congenital, and pulmonary.
Coronary heart disease is the number one cause of death in the UK, and cerebrovascular diseases are a major cause of death as well.
Risk factors for CVDs include diet/obesity, genetics, stress, T2D, inflammation, hypertension, sleep, smoking, metabolic syndrome, and physical activity.
Studies for these risk factors began in the early 50s, when Morris observed that bus drivers were more likely to suffer from CVD than bus conductors (and the same for postmen vs telephonists). He also found that of those who did suffer, more physically active individuals had lower mortalities. He found that moderate intensity exercise provides small reductions in mortality of CHD, but only in older cohorts (threshold effect on the intesntiy of exercise younger individuals are required to do). A finding in 2020 found that there was a dose response relationship between an individuals average walking pace and relative risk of stroke.
