Cardiovascular System Anatomy Lecture Notes PDF

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Cardiac Anatomy (Lectures 1-3)Lecture One: Blood Circuits and the Heart (Anatomy of the CardiovascularSystem)Overview of the Cardiovascular System Cardiovascular System Courier body (delivery and removal system) of the body as tissues/cell immobile Heart, blood vessels and the blood Blood is the med...

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Cardiac Anatomy (Lectures 1-3) Lecture One: Blood Circuits and the Heart (Anatomy of the Cardiovascular System) Overview of the Cardiovascular System Cardiovascular System Courier body (delivery and removal system) of the body as tissues/cell immobile Heart, blood vessels and the blood Blood is the medium of the transport, and the heart is the driver of this Supplies cells with what they need (oxygen) and remove waste products (carbon dioxide) Heart Human heart is 12cm long, 9cm wide at broadest point and 6cm thick Human heart weighs around 300g ILO. 1 Compare the systemic and pulmonary blood circuits, and briefly describe unusual features of venous drainage from the gut Heart pumps blood in two closed circuits, output each circuit becomes input of the other

Hepatic Portal Vein

5L 9%

7%

84%

5L/min

Pulmonary Circuit Pump is the right ventricle Supplies capillaries in alveoli of lungs 9% of total blood volume contained in pulmonary circuit Smaller circuit (less blood vessels) so medium resistance so medium pressure to propel smaller volume of blood

Pathway of Pulmonary Circulation Right atrium receives deoxygenated blood returning from systemic circulation -> Right ventricle ejects blood into the pulmonary trunk -> left and right pulmonary arteries (2) -> pulmonary capillaries right/left lungs -> pulmonary veins (4) -> left atrium -> left ventricle ejects blood into the aorta to enter systemic circulation Systemic Circuit Pump left ventricle Supplies capillaries of all systems except alveoli of the lungs supplied by pulmonary circulation 84% of total blood volume is contained in the systemic circuit; 75% of this amount is contained in systemic veins Larger circuit (more blood vessels) so higher resistance and so higher pressure required to propel large volume of blood Pathway of the Systemic Circuit Left atrium receives oxygenated blood from the lungs -> left ventricle ejects blood into the aorta -> progressively smaller systemic arteries carry oxygenated blood to organs throughout body -> arterioles (smaller diameter) lead to beds of systemic capillaries (exchange nutrients/gases across thin capillary walls) -> systemic venule -> venules merge to form larger systemic veins -> systemic veins merge to form the vena cava -> right atrium Portal system Venous system/veins from organ capillary beds -> organ capillary bed (not heart) Venous Drainage from Gut Liver detoxifies blood and ‘packages’ nutrients absorbed through digestion Hepatic portal vein drains blood from the capillary beds gut and passes this to the capillary beds of the liver Provides liver dual supply of blood, poorly oxygenated nutrient rich blood from the gut and highly oxygenated blood from the systemic arteries Pumps Heart has two hard-working pumps (the left ventricle and right ventricle) Ventricles pump blood out into high pressure arteries which supply capillary beds 7% of total blood volume is contained in the pumps (and cells) If pumps cease significant consequences, heart stoppage causes unconsciousness after 10 seconds and irreversible damage to tissues/death after 4 minutes due to lack of oxygen and glucose to the brain First hour after the onset of a heart attack is regarded as the golden hour, appropriate action of restarting the heart (e.g CPR, defibrilation) in this time dramatically increases survival chances

ILO. 2 Describe or label the chambers and great vessels of the heart Anterior/Ventral View of Heart Heart not as often represented in posterior view as in cardiac surgery it is accessed most often through the sternum (anterior aspect). Cardiac surgery is rarely done via the posterior aspect to avoid spinal column and its nerves (and hence paralysis) you would have to transcend to access heart from back If the heart is being viewed anteriorly, name the structures from the owner’s perspective

Chambers of the Heart Four chambers Atria two superior receiving chambers, receive blood from blood vessels returning blood to heart Ventricles two inferior pumping chambers, eject blood from the heart into blood vessels called arteries Right Atrium

Right Ventricle

Left Atrium

Receives blood from three veins: superior vena cava, inferior vena cava and coronary sinus Inside posterior wall smooth, inside anterior wall rough due to pectinate muscles (extend into auricle) Venous blood collects here during ejection phase Right Auricle is an extension Venous blood flows from the right atrium to the right ventricle Muscular structure able to change volume Contains series of ridges called trabeculae carneae Pressurizes blood and injects it into the pulmonary trunk Receives blood from the lungs through four pulmonary veins Inside posterior and anterior wall is smooth (pectinate muscle confined to left auricle) Arterial blood collects here during ejection phase Blood flows into left ventricle from here Less visible as orientated on the back of the heart

Left Ventricle

Thickest chamber of the heart Contains an abundance of trabeculae carneae Injects blood into the aorta

Superior Vena Cava

Vein draining venous blood from superior aspect of the body (above heart) to the right atrium Largest veins in the body Vein draining venous blood from the inferior aspect of the body (below heart) to the right atrium Short so not that visible Largest veins in the body Large artery that divides into the left and right pulmonary arteries Carries blood to the lungs Important landmark Not visible as entering from behind the heart Drain oxygenated blood from the pulmonary circuit to the left atrium Left and right pulmonary vein exist Bring oxygenated blood from pulmonary circuit back to heart to be sent out to the tissues Large elastic artery that takes blood to the systemic circuit Some of the blood that enters the ascending aorta can flow into the coronary arteries, the remainder passes into the arch of the aorta and descending aorta which carry blood throughout the body Branch from ascending aorta and carry blood to the heart wall 2-4mm in diameter

Inferior Vena Cava

Pulmonary Trunk

Pulmonary Veins

Aorta

Coronary Arteries

Sulci Grooves located on the surface of the heart Contain coronary blood vessels and a variable amount of fat Marks external boundary between two chambers of heart Anterior Interventricular Sulcus Posterior Interventricular Sulcus Coronary Sulcus

Groove on anterior surface of heart Defines the left and right ventricles on anterior aspect of heat Continuous posterior interventricular sulcus Groove on posterior surface of heart Defines the left and right ventricles on posterior aspect of heat Continuous anterior interventricular sulcus Encircles most of the heart and marks the boundary between the atria and ventricles

Trabeculae Carneae Series of ridges formed by raised bundles of cardiac muscle fibres Some of these participate in the conduction system of the heart Located inside the left and right ventricles Posterior View of Heart

Right Lateral View of Heart

Coronal ‘Four Chamber’ View of Heart Diagram of Ventricular Filling Divide heart into anterior and posterior half Retain the posterior heart and view the cut surface

Orientation of the Atria (Blood Flow through the Heart) The atria are orientated by the way that they drain The systemic circuit (involves the left ventricle and right atrium) drains above heart (superior vena cava) and below the heart (inferior vena cava) Right atrium therefore has a vertical orientation relative to the circuit that it drains The pulmonary circuit (involves the right ventricle and left atrium) drains either side from lateral left and right pulmonary veins Left atrium therefore has a vertical orientation as this is where the pulmonary circuit sits in relation to it

ILO.3 Explain and/or draw the ventricular inlet and outlet valves in their open and closed states Ventricle (ventricular pump) is represented as a box with thick muscular walls Venous inlet on left side Arterial outlet on right hand side Filling Phase Ventricle/chamber is filling with blood (from venous end) Increase volume/decrease pressure of chamber No energy required (passive phase) as can rely on elastic coil of chamber Arterial outlet valves essential to prevent high pressure arterial blood from returning back the pump/chamber Venous inlet valves are in the opened state

Ejection Phase Ventricle empties blood from arterial end Decrease volume of chamber Venous inlet valves close to prevent high-pressure blood in pumping chamber returning to veins Arterial outlet valves in opened state Energy required (active phase) to retract the chamber

In the filling phase venous inlet valves are pushed out by blood flow into the chamber, and in the ejection phase arterial outlet valves are pushed out by blood flow out of the chamber

Model Modification #1 Atrium is reservoir upstream of the pump When the inlet valve is closed during the ejection phase the atrium accumulates venous blood that quickly enters the ventricle during the filling phase Atrium is the ‘collecting area’ for venous blood

Model Modification #2 Venous inlet and arterial outlet valves are located close to one another to increase the area of the walls (an extra wall can contribute to the ejection phase)

This means that the walls of the chamber can shorten in length and width Results in a ‘V-shaped blood flow in heart Auricle or appendage is an extension of the atrium that increases it’s storage capacity Both of these modifications increase the efficiency of the pump Auricle Left and right auricles exist Appendage Extension/continuation of atrium on its side (auricle and the atrium are continuous) Slightly increases storage capacity of an atrium so it can hold a greater volume of blood For a pump to be effective it must have: - An inlet valve - Volume adjusting chamber (muscularized) - An outlet valve

Pump in its anatomical configuration Two of these make up the human heart Inlet valve and outlet valve

Atria and Inlet Vessels The inlet vessel to the right atrium is the superior vena cava and the inferior vena cava The inlet vessel to the left atrium is the left and right pulmonary veins There are no inlet valves in these inlet vessels, this affects the atria’s ability to be a good pump (no valves between the vena cavae/right atrium or the pulmonary veins/left atrium) When the atria contract a small amount of blood flows backwards from the atria into the vessels Backflow prevented instead by contraction of atrial muscles compressing and nearly collapsing the weak walls of the venous blood entry points Valves Function of heart is dependent on valves Open ends on superior ends of ventricles are subdivided into inlet and outlet valves Valves open and close in response to pressure changes as the heart contracts or relaxes Four valves in the heart Each valve ensures the one-way flow of blood by opening to let it through and then closing to prevent its backflow Soft and plaint, yet tough enough to withstand 100,000 closures every day for 70-80 years The heart has four values; mitral, tricuspid, aortic and pulmonic valve Valves of the heart are composed of dense connective tissue covered by endocardium

Ventricular Inlet Valves (Atrioventricular Valves) Valves located between atrium and ventricles One-way valves that allow blood to flow only in one direction (into the chamber/ventricle) The ventricular inlet valve on the LHS of the heart is the bicuspid/mitral valve The ventricular inlet valve on the RHS of the heart is the tricuspid valve Closed during ventricular ejection phase and open during filling phase (passive process, cusps pushed out of the way by blood flow)

Applies to the left and right ventricle

Structure of Atrioventricular Valves The inlet valves are constructed from either two or three flat flaps of fibrous connective tissue The free edge of each flap is tethered by the chordae tendineae (tendinous cords) which prevent inversion of the valves (bursting upwards into atrium) during systole.

The chordae tendineae are attached to papillary muscles (cone shaped trabeculae carneae) that contract to allow the valves to seal off during systole. Bicuspid/Mitral Valve Contains two cusps/leaflets Inlet valve on the left-hand side Large and strong to resist pressure Tricuspid Valve Consists of three cusps/leaflets Inlet valve on the right-hand side Ventricular Outlet Valves (Semilunar Valves) Valves located between the ventricle and artery Allow ejection of blood from the heart into arteries but prevent backflow of blood into the ventricles Made up of three crescent moon shaped cusps Each cusp attaches to the arterial wall by its convex outer margin, the free borders of the cusps project into the lumen of the artery The cusps are shaped like a small pocket and gain strength from their 3D shape when inflated with blood Lack chordae tendineae and papillary muscles as this would impede flow due to their smaller diameter as well as when the valves close the cusps remain stable because of their cup-shape and smaller diameter (inversion will not occur)

Mechanism of Ventricular Outlet Valves/Semilunar Valves When ventricles contract, pressure builds up in the chambers Semilunar valves open when pressure in the ventricles exceeds the pressure in the arteries, allowing ejection of blood from the ventricles to the pulmonary trunk (pulmonary valve) and aorta (aortic valve)

During ventricular filling free edges of cups are forced together As the ventricles relax blood begins to flow back into heart Backflowing blood fills the valve cusps, causing their free edges to contact one another tightly and close the opening between ventricle and artery

Aortic Semilunar Valve The ventricular outlet valve on the LHS Blood passes through the aortic valve from the left ventricle into the ascending aorta

Pulmonary Semilunar Valve The ventricular outlet valve on the RHS of the heart Blood passes through the pulmonary valve from the right ventricle into the pulmonary trunk ILO. 4 Relate the shape and wall thickness of the four chambers to the maximum blood pressure within them

The left ventricle forms a central cone that defines the shape of the rest of the heart. The right ventricle forms a crescent shaped hole that sits to the side of the left (pocket on pair of jeans) Size of Inlet and Outlet Valves

The diameter of the inlet and outlet holes determine the amount of inflow/outflow of blood into the chambers Inlet valves have a large diameter so blood can enter the low-pressure ventricle during the filling phase. Outlet valves have a small diameter as blood leaves the high-pressure ventricle during the ejection phase. Relate the shape and wall thickness of the four chambers to the maximum blood pressure in them Peak Pressures (not average pressure) Right ventricle: 27mmHg Left ventricle: 120mmHg Left atrium: 8mmHg Right atrium: 5mmHg Why is there a difference in thickness between the left and right ventricle? Left ventricle has thick muscular walls and a significantly higher peak pressure than right ventricle (despite pumping the same volume of blood) as it pumps blood over great distances to all other parts of the body (systemic circuit) at higher pressure and resistance to blood flow is larger. Right ventricle has thinner walls and a small peak pressure than the left ventricle as it pumps blood over short distances to the lungs at a lower pressure (pulmonary circuit) and the resistance to blood flow is smaller.

Why is there a much larger drop between the peak pressures in the left ventricle and right atria and the right ventricle and left atria? Right atrium retains less of the initial pressure as it is being pumped to by the left ventricle via the long, high resistance systemic circuit so by the time the blood reaches the pressure has dropped significantly from the initial pressure (120mmHg to 5mmHg) Left atrium retains more of the initial pressure as it is being pumped to by the right ventricle via the short and medium resistance pulmonary circuit (27mmHg to 8mmHg) Why is there a difference in thickness between the ventricles and atria? Thickness of myocardium of four chambers varies according to the function of each chamber. Right and left ventricles act as two separate pumps that eject equal volumes of blood Right ventricle has much smaller workload; pumps blood shorter distance to lungs at lower pressure, resistance to blood flow is small Left ventricle has a higher workload; pumps blood great distance to all parts of the body at higher pressure, resistance to blood flow is larger Left ventricle therefore must work much harder to maintain the same rate of flow as the right ventricle. Anatomy of two ventricles confirms this functional difference.

Atria are thin walled as they deliver blood under less pressure to the adjacent ventricle Ventricles pump blood under higher pressure over greater distances so have thicker walls Peak Pressure Ratio LV:RV is 5:1 Wall Thickness Ratio LV:RV is 3:1 Left and Right Atrium (and auricles) Inefficient Pumps Ventricles in transverse section Not pressurized so blood flows out easily Thin walled muscular structure so is a weak chamber Generates less pressure (smaller peak pressure) No inlet valves between junctions of veins and atria so blood flows out Left and Right Ventricles Main pumping chamber Large, thick, muscular walls Generates a lot of pressure (higher peak pressure) Contain inlet and outlet valves Only two chambers (ventricles) contribute to two pumps of the heart

Lecture Two: Heart (continued) Describe the orientation and borders of the heart The heart rests on the diaphragm near the midline of the thoracic cavity located behind the sternum and between the lungs The heart lies in the mediastinum (anatomical region that extends from the sternum to the verterbral column) One third of heart mass lies to the right of the midline of the body and two thirds to the left

Cardiopulmonary resuscitation (CPR) is made possible because the heart lies between two rigid structures (the sternum and veterbral column) so pressure on the chest can be used to compress blood out of the heart and into circulation

Apex (Purple dot) Right Border

Where the left and right ventricle join Formed by the tip of the left ventricle Points inferiorly (down), anteriorly (backwards) and to the left Formed mainly by the right atrium Faces the right lung

(Pink) Inferior Border (Yellow) Left Border (Purple) Superior Border (Blue)

Formed mainly by the right ventricle, sits mostly on the diaphragm

Formed mainly by the left ventricle (and partly the left atrium and auricle) Faces the left lung The site of entry of the great vessels (superior/anterior vena cava, pulmonary artery, pulmonary vein, aorta) of the heart. Formed mainly by the left atrium and partly the right atrium. The base (widest part of an organ) Base of the heart is superior and posterior The heart is connected to the body by the blood vessels at the base. The rest of the heart moves around while beating.

Cardiothoracic ratio: Heart should not exceed over 50% of the ribcage The orientation and position of the heart in the ribcage can be used to diagnose various conditions

Rheumatic Fever Bacterial infection treatable with antibiotics Creates antibodies that attack and inflame tissues rich in collagen (heart valves) Valves become damage and scarred New fibers placed down resulted in thick and stiff valve and stenosis (narrowing of the heart valve) This leads to increased resistance to blood flow

Hypertrophy Thicker left ventricle Lumen decreased in size so ability to fill is compromised Coronary arteries supplying the heart with blood are no longer able to supply the increased amount of cardiac muscle tissue, eventually not enough can be supplied and heart failure results

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