Cardiovascular system structure and function Flashcards
Describe the flow of blood within the heart
Blood flows into the heart (right atria) via the superior and inferior Vena Cava from the whole body. It is then moves into the right ventricle by passing through the valve artioventicluar valve tricuspid valve preventing black flow of blood. The blood then passes through the pulmonary valve (semi lunar valve) into the left and right pulmonary arteries. This then travels to the lungs where the blood becomes oxygenated and releases C02. Blood then re-enters the heart into the left atrium via the pulmonary veins then into the left ventricle passed the mitral (atria ventricular valve/ bicuspided) valve. From the left ventricle the blood passes the aortic valve (aortic semi-lunar valve) and out of the heart to the systemic system via the aorta.
About 2/3 of the blood from the atria passively goes into the ventricle via an open valve. The remaining 1/3 enters the ventricle due to contraction of the atria forcing the blood into the ventricle through the valve. This is called the atrial kick.
Then the volume is decreased during the ventricle twist increasing the pressure. Causing the tricuspid and mitral value to close and the aortic and pulmonary artery to open. So changes in pressure cause opening and closing of valves. Ensuring one way flow. The Lub sound occurs when the tricuspid and mitral valves close. And the Dub noise when the artial semi-lunar values close.
Describe the anatomy of the heart
The left ventricle pumps blood to the systemic system so needs to generate a large pumping power and so it has a thick muscle mass compared to the right ventricle that pumps blood into the lungs.
The atria have a much thinner muscular wall
Chrondae tendi- tendonous chords holds the valve to prevent then flapping black (over expand) to insure that there is no back flow of blood. Rooted into the wall of the heart via specialise muscles called papillary muscles.
There is a fibrous sack around the heart for protection of the heart and stops the heart over expanding, and reduces friction during the heart beat.
The pericardium is the tissue around the heart lined with parietal pericardium. The sac is filled with around 15-20ml of pericardial fluid and has viceral pericardium on the other side next to the myocardium.
Tissue next to the heart is made up of squamous vascular endothelial cells. Allows for smooth blood flow. Know as the endocardium. The think bands of cardiac muscle striated muscle called the myocardium makes up the muscular wall.
The cardiac septum separates the left and the right side of the heart. The left is the body pump and the right the lung pump.
The base of the heart is at the top where the main veins and arteries of the heart are and the tip of the heart is called the apex.
Explain the electrical system of the heart.
The impulse to stimulate cardiac contraction is intrinsic. In the right atrium there is an area of specialised myocardium tissue cells called the sinoatrial SA node. Generates the rhythm of the heart. It depolarises spontaneously about 90 times a minute generating a new electrical activity. There is also the AV node between the atria and the ventricles. There are conducting pathways from the SA node. There are 3 preferential pathways (posterior, middle and anterior pathway). These signals depolarise the atrial myocardial cells which caused contraction of the atria.
These pathways (intra-nodal tracts) converge at the AV node, (collecting node). There is fibrous tissue in the valvular plane, producing a ring, separating the atria from the ventricles. This tissue does not conduct electricity so acts as an insulator. There is a delay in the AV node signal to allow time for the blood to pass from the atria to the ventricles. There is a AV bundle of tissue in the septum of the heart that will conduct the electrical signal, dividing into two separate bundles down to the cardiac apex. Smaller fibres take the signal into the myocardium called purkinjie fibres, taking signal to contractile myocardial myocytes causing depolarisation and contraction. Impulse then carries up to all parts of the ventricular myocardium. The septum also contracts and shortens.
The parasympathetic innovation of the vagus nerve leads to a reduction in heart rate by inhibition. There is also sympathetic fibres to the SA node will increase the strength and rate of contraction. The heart can also be affected by hormones such as adrenaline.
The cells of the SA node have no steady resting potential but show a slow change in potential known as the pacemaker potential. The conduction of the cardiac impulse through the atria occurs via normal atrial myocytes. In the ventricles, the specialized conducting cells are the bundle cells and the Purkinje fibers, which transmit their action potentials to the ventricular myocytes via gap junctions. The speed of conduction is slowed as the cardiac action potential passes through the AV node.
The conduction of the cardiac impulse through the atria occurs preferentially via certain fibre bundles, which are formed of normal atrial myocytes. In the ventricles, however, the specialized conducting cells are the bundle cells and the Purkinje fibres.
What are the main functions of the blood within the cardiovascular system?
Regulation of pH and ion concentration.
Control of body temperature
Body defence against pathogens via leukocytes action.
Clotting properties via platelet action in the presents of injury.
Transport of oxygen nutrients and hormones, removal of metabolic wastes (carbon dioxide, nitrogenous wastes).
Describe the structure and function of the blood vessels.
Arteries: carries blood away from the heart. Arteries do not have values.
Veins: carries blood towards the heart. Veins do have valves. Stopping the blood regurgitating backwards. Many valves seen in veins in the legs and the arms.
There is a lumen which is the inside hollow part of the artery surrounded by a layer of vascular endothelium, that allows a smooth flow of blood.
Layers called tunica.
Middle layer : Tunica interna
Smooth muscle and elastic tissue: Tunica media
Outside layer: Tunica Externan or adventitia (made up of elastic tissue and collagen). In larger arteries there is also some small vessels and nerves.
The elasitc lamina is found in larger arteries around the tunica media.
Walls in veins are thinner. Tunica media is smooth muscle and some elastic fibres. Do not have elastic lamina like the large arteries do.
Pressure is higher in arteries than in veins. About 120/80 systemic arterial pressure. 25/12 vein pressure.
Talk about Haemoglobin and its role
Hb is found in RBCs. Each Hb has a complex quaternary shape. The Hb molecule has two alpha chains and two beta chains of polypeptides. Each individual chain is a globular protein subunit like myoglobin. Each Hb molecule contains a heme group each heme group holds an iron ion in such as way that the iron can hold oxygen. This forms oxyhaemoglobin Hb02. This blood in bright red. The interaction between iron and oxygen is very weak so that oxygen can readily be given out to the bodies tissues, and the heme unit and oxygen are not damaged in the process. Hb without 02 is called deoxyhaemoglobin. Normal oxygen saturation of the blood is 95-100%.
Oxygen saturation in the veins is normally around 70-80%.
Discuss arterioles
The arterioles are mainly under the control of sympathetic vasoconstrictor fibres but are also regulated by circulating hormones and local factors (especially the terminal arterioles).
Discuss the coronary arteries
The coronary arteries supply blood to the cardiac muscle which requires a continuous supply of oxygen and nutrients. During maximum exertion the demand for oxygen rises considerably, blood flow may increase up to nine times.
The left and right coronary arteries originate from the base of the ascending aorta at the aortic sinuses goes round the cornoary sulcus.
Right coronary artery then the right marginal or right acute marginal artery down the front of the right side of the heart along the margin, and then there is the posterior descending artery. This supplies blood to the interventricular septum (myocardium between the left and right ventricles) and so this artery maybe also known as the posterior interventricular artery. It runs towards the apex within the posterior interventricular sulcus. At the crux an artery goes to the AV node.
The LCA is only a few cm long it then branches into the LAD and the LCX (left circumflex). The LCX branches into the left marginal artery or left obtuse marginal artery.
Coronary dominance refers to which right or left coronary artery gives rise to the posterior descending artery. 60-80% it is right dominance. In very small % of times the PDA can come from both the LCA and the RCA this is called co-dominance.
Cardiac veins:
Great cardiac vein arises from the appex moves on the anterior of the heart superiorly around the coronary sulcus to the coronary sinus. Is parallel to the LAD and drains the LCA.
Middle cardiac vein: moves up the posterior interventricular septum and drains into the coronary sinus.
Small cardiac vein: moves across the margin of the heart drains into the coronary sinus.
Regulation of blood flow in the coronary system is primarily control by local metabolites. adenosine can result in vasodilation. Symathetic
What does the P,Q,R,S wave of the electrocardiogram show?
P wave: is the depolarisation of the artia. The artia begin to contract 100msecs after the begining pof the P wave.
QRS: Is the depolarisation of the ventricle and the repolarisation of the atria (which is masked by the contraction of the ventricle). the ventricle begins to contract just after the peak of the R wave. This is a strong electrical signal.
T: is the repolarisation of the ventricle.
Properties of blood
Red blood cells will maintain their integrity and live about 120 days. About one-third of the volume of an erythrocyte is hemoglobin.
AB is the rarest blood type. O is the most common.
Who is at risk for developing a fatal Rh incompatibility?Second Rh+ fetus of Rh- mother.
Vitamin K is necessary for the synthesis of prothrombin a coagulant.
Plasmin can dissolve a blood clot.
Fibrin is the active molecule that forms the network of fibrin threads in the clot that will entrap cells forming a blood clot.
Thrombin acts as an enzyme to cleave fibrinogen into active fibrin molecules
Thrombin arises from the first steps of clotting and requires a prothrombin activator and calcium to become active.
Collagen promotes the appearance of the platelet plug
The high density lipoproteins (HDL) contain high concentrations of protein and lesser amounts of lipid.The low density lipoproteins transport most of the cholesterol to places of deposition such as the walls of coronary arteries.
Although the majority of the osmotic molecules are the electrolytes and proteins, only the proteins are not free to cross capillary membranes and therefore exert a constant osmotic pressure; albumin is the most common blood protein. Proteins comprise about 7% of the total plasma volume.
