The Cardiovascular System: The Heart

Define cardiac output and stroke volume. state the furmola.

CO is the volume of blood ejected from a ventricle each minute Stroke volume (SV) is the amount of blood pumped out of the ventricle in one beat CO= SV x HR 70mls x 75bpm= 5.25 L/min at rest

Describe the unique structural characteristics of cardiac muscle.

Striated, short, thick, branched cells

Explain how the SA node excites the myocardium.

by not having a stable resting potential

Describe the three layers of the heart wall.

- Epicardium - Myocardium - Endocardium

Explain what causes the sounds of the heartbeat.

- First heart sound (S1), louder and longer "lubb," occurs with closure of AV valves , turbulence in the bloodstream, and movements of the heart wall - Second heart sound (S2), softer and sharper "dupp," occurs with closure of semilunar valves , turbulence in the bloodstream, and movements of the heart wall - S3 and S4 are due to turbulence and not normally loud enough to be heard

Identify the factors that govern cardiac output.

- Heart rate: tachycardia( HR above 100 bpm), Bradycardia (HR less than 60 bpm) - Preload: affect of stretching, frank starling law of heart. the more muscle is stretched, greater force of contraction. -Contractility: Autonomic nerves, hormones, Ca+2 or K+ levels - After load: amount of pressure created by the blood in the way

Describe the general location, size, and shape of the heart.

- Located in mediastinum, between lungs Base: wide, superior portion of heart, blood vessels attach here Apex: inferior end, tilts to the left, tapers to point

Interpret a normal electrocardiogram.

- P wave - SA node fires, atrial depolarisation, systole - QRS complex - ventricular depolarisation (atrial repolarisation) - ST segment - ventricular systole - T waves - ventricular repolarisation

What is the cardiac output at rest and during vigorous excercize

At rest, entire blood volume passes through left ventricle in about 1 minute vigourus excersize CO is 21L/min for a fit person, for a world-class athlete 35L/min

Describe the arteries that nourish the myocardium and the veins that drain it.

Coronary arteries- ascending from aorta have left and right coronary arteries Coronary Veins- have branches coverage

Explain the nature and functional significance of the intercellular junctions between cardiac muscle cells.

Mechanical junctions: physically join cells - Prevents cells from pulling apart during contraction Electrical (gap) junctions: allow ions to flow between cells - Entire myocardium of either two atria or two ventricles acts like single, unified cell

Describe how changes in blood pressure operate the heart valves.

Pressure gradient, fluid travels down into low pressure. Resistance opposes flow

Trace the flow of blood through the four chambers and valves of the heart and adjacent blood vessels.

Right atrium, right ventricle, pulmonary veins, left atrium, left ventricle, aorta, body

Describe the nerve supply to the heart and explain its role.

Sympathetic nerves : increase heart rate and contraction strength - as high as 230 bpm Parasympathetic nerves (Cranial nerve X): reduces the heart rate - as low as 20 bpm

Describe the heart's pacemaker and internal electrical conduction system.

The auto rhythmic fibers in the SA node are the natural pacemaker of the heart because they initiate action potentials most often

Describe the pericardial sac that encloses the heart.

The pericardium is a double walled sac that encloses the heart and holds it in place.

Explain why the SA node fires spontaneously and rhythmically.

action potential form SA nodes cause the artria to depolarize and contract forcing blood into the ventricles

Define and distinguish between the pulmonary and systemic circuits.

systemic circulation: The routes through which oxygenated blood flows from the left ventricle through the aorta to all the organs of the body and deoxygenated blood returns to the right atrium. pulmonary circulation: The flow of deoxygenated blood from the right ventricle to the lungs and the return of oxygenated blood from the lungs to the left atrium.