The Cardiovascular System PDF

Body Structure and Function The Cardiovascular System Learning Outcomes Describe the passage of blood through venules to capillaries and arterioles Learning Outcomes Describe the function of the heart muscles and valves Explain the heart ‘sounds’ Describe systole and diastole Describe the nerv...

Body Structure and Function The Cardiovascular System Learning Outcomes Describe the passage of blood through venules to capillaries and arterioles Learning Outcomes Describe the function of the heart muscles and valves Explain the heart ‘sounds’ Describe systole and diastole Describe the nervous control of the heart beat by describing the sequence of events Describe a wave of depolarisation as described by an electrocardiograph Account for P, QRS and T functions Learning Outcomes Describe the function of the heart muscles and valves Heart Structure – Muscle Walls The wall of the heart contains three distinct layers: outer epicardium - serous membrane consists of an exposed epithelium and an underlying layer of areolar tissue. middle myocardium - cardiac muscle tissue, blood vessels, and nerves. inner endocardium - simple squamous epithelium and underlying areolar tissue. Sample header set Lincoln Blue Sample text in here for body copy – set at 18pt  Heart Structure – Muscle Walls Cardiac Muscle Cells Are short, branched, striated - contain a single, centrally located nucleus. Cells connected by Intercalated discs Contains myofibrils - individual sarcomeres shorten during contraction Almost totally dependent on aerobic metabolism for the energy needed to continue contracting (many mitochondria and abundant myoglobin) Cardiac Muscle  Contractile unit I-band - actin filaments, A-band - myosin filaments which may overlap with actin filaments, H-band - zone of myosin filaments only (no overlap with actin filaments) within the A-band, Z-line - anchoring of actin filaments belonging to two neighbouring sarcomeres (mediated by a protein called alpha-actinin), M-line - band of connections between myosin filaments (mediated by proteins, e.g. myomesin, M-protein). Dark A bands and light I bands repeat along myofibrils, and the alignment of myofibrils in the cell causes the entire cell to appear striated or banded.  Sarcomere The sarcomere is the basic structural and functional unit of the myofibril. It is bordered by a Z-band on each end with adjacent I-bands, and there is a central M-line with adjacent H- bands and partially overlapping A-bands.  Cardiac muscle Highly coordinated contractions of cardiac muscle pump blood into the vessels of the circulatory system. Like skeletal muscle, cardiac muscle is striated and organized into sarcomeres, possessing the same banding organization as skeletal muscle Intercalated discs Intercalated disks (or lines of Eberth) are specialised junctions between cardiac muscle fibres (myocytes) that allow for rapid electric (action potential) and nutrient exchange. They occur at the Z line of the sarcomere and can be visualized easily when observing a longitudinal section of the tissue. The disks join the cells together by both mechanical attachment and protein channels. Intercalated discs are complex structures that connect adjacent cardiac muscle cells. The three types of cell junction recognised as making up an intercalated disc are: Desmosomes, Fascia adherens junctions, Gap junctions. Gap junctions connect the cytoplasms of neighboring cells electrically by forming channels , allowing cardiac action potentials to spread between cardiac cells by permitting the passage of ions between cells, allow the depolarizing current to flow from one cardiac muscle cell to the next - allows the quick transmission of action potentials and the coordinated contraction of the entire heart. This network of electrically connected cardiac muscle cells creates a functional unit of contraction called a syncytium. Learning Outcomes Explain the heart ‘sounds’ Heart Sounds There are four heart sounds, named S1 through S4. “lubb” - AV valves close and the semilunar valves open. “dupp” - Semilunar valves close. Sample header set Lincoln Blue Sample text in here for body copy – set at 18pt Sample header set Lincoln Blue Sample text in here for body copy – set at 18pt Heart Sounds – S1 The first heart sound results from the closing of the mitral and tricuspid valves. Heart Sounds – S2 The second heart sound is produced by the closure of the aortic and pulmonary valves. Heart Sounds – S3 The third heart sound, also known as the “ventricular gallop,” occurs just after S2 when the mitral valve opens, allowing passive filling of the left ventricle. The S3 sound is actually produced by the large amount of blood striking a very compliant LV. Heart Sounds – S4 The fourth heart sound, also known as the “atrial gallop,” occurs just before S1 when the atria contract to force blood into the LV. If the LV is noncompliant, and atrial contraction forces blood through the atrioventricular valves, a S4 is produced by the blood striking the LV. Heart Sounds – S3 vs S4 S3 – Ventricular gallop S4 – Atrial gallop Occurs in early diastole Occurs in late diastole Occurs during active LV filling Occurs during passive LV filling Almost always abnormal May be normal at times Requires a noncompliant LV Requires a very compliant LV (left ventricle becomes stiff and unable to fill properly) Can be a sign of systolic Can be a sign of diastolic congestive HF congestive HF Diastolic heart failure, also known as heart failure with preserved ejection fraction (HFpEF), is a condition in which your heart's main pumping chamber (left ventricle) becomes stiff and unable to fill properly. Systolic congestive heart failure occurs when the heart does not pump blood effectively. Heart Sounds S3 https://www.youtube.com/watch?v=_i2D1KZkN1w S4 https://www.youtube.com/watch?v=KcMF8rJDTIk Learning Outcomes Describe systole and diastole Phases of the cardiac cycle At the beginning of the cardiac cycle, both the atria and ventricles are relaxed (diastole). Blood is flowing into the right atrium from the superior and inferior venae cavae and the coronary sinus. Blood flows into the left atrium from the four pulmonary veins. The two atrioventricular valves are both open. The two semilunar valves are closed. Atrial systole and diastole Contraction of the atria follows depolarization, represented by the P wave of the ECG. Atrial systole lasts approximately 100 ms and ends prior to ventricular systole, as the atrial muscle returns to diastole. Ventricular systole Ventricular systole follows the depolarization of the ventricles and is represented by the QRS complex in the ECG. Initially, as the muscles in the ventricle contract, the pressure of the blood within the chamber rises, but it is not yet high enough to open the semilunar (pulmonary and aortic) valves and be ejected from the heart. Ventricular systole This increase in pressure causes blood to flow back toward the atria, closing the tricuspid and mitral valves. In the second phase of ventricular systole, the ventricular ejection phase, the contraction of the ventricular muscle has raised the pressure within the ventricle to the point that it is greater than the pressures in the pulmonary trunk and the aorta. Blood is pumped out of the heart, pushing open the pulmonary and aortic semilunar valves. Ventricular diastole Ventricular relaxation, or diastole, follows repolarization of the ventricles and is represented by the T wave of the ECG. During the early phase of ventricular diastole, as the ventricular muscle relaxes, pressure on the remaining blood within the ventricle begins to fall. When pressure within the ventricles drops below pressure in both the pulmonary trunk and aorta, blood flows back toward the heart, producing the dicrotic notch (small dip) seen in blood pressure tracings. Ventricular diastole In the second phase of ventricular diastole, called late ventricular diastole, as the ventricular muscle relaxes, pressure on the blood within the ventricles drops even further. Eventually, it drops below the pressure in the atria. When this occurs, blood flows from the atria into the ventricles, pushing open the tricuspid and mitral valves. Cardiac cycle - Wiggers diagram