Cardio I Flashcards
Pulmonary and systemic circuits
Pulmonary- mean arterial pressure of 12 mm Hg
Systematic- mean arterial pressure of 90-100 mm Hg
pump equal amounts of blood over time-if left output falls, blood accumulates in the pulmonary circulation = CHF
Circulatory system: pressure
pressure: difference in pressure (~84 mm Hg) between arterial and venous sides drives arterial blood flow
return of venous blood to the heart relies on one way valves, muscular contraction, and changes in intrathoracic pressure
pressure difference between venules and heart is only 10 mm Hg
Circulatory system: blood volume
venous system acts as a blood reservoir
- 64% of blood in veins and venules
- constriction of veins shifts more blood to arterial circulation
Circulatory system blood flow
BF= change in pressure/ resistance
collective resistance is an part of circulation is the peripheral vascular resistance
normally laminar= plasma is adjacent to the vessel wall while WBC and platelets are more in center
Can become turbulent= vessel bifurcations or narrowing. Turbulence heard as a murmur buit
Turbulent flow increases risk of clotting
Atherosclerosis increases turbulence
Heart: pericardium
outer fibrous layer and inner serous layers
fibrous layer: resistance to distension and prevents acute dilation of heart chambers
serous layers: visceral layer (epicardium) covers the heart
Heart: valves
atrioventricular valves between the atria and ventricles
- tricupsid on the right sides of the heart
- bicupsid (mitral) on the left
Prevent blood in ventricles from reentering the atria
-semilunar valves at the start of pulmonary artery and aorta
prevent blood in these vessels from reentering the ventricles. Each valve composed if 3 tea-cup shaped leaflets. Coronary arteries exit aorta superior to leaflets (orifices)
Heart: cardiac cycle (diastole)
diastole:
ventricles relax and backward flow of blood in the large arteries closes the semilunar valves
AV valves open and blood flows into the ventricles by gravity
in the latter part of diastole, the atria contract to complete filling of ventricles
Heart: cardiac cycle (systole)
isovolumetric contraction period: contraction of the ventricles closes AV valves and increases ventricular pressure
ejection phase: ventricular pressure exceeds those in the aorta and pulmonary trunk and semilunar valves open
Heart: cardiac output
(CO)= SV x HR
-3 to 8 L/min
increased output depends on: preload or ventricular filling
afterload reistance to ejection of blood from the heart
cardiac contractility
heart rate- severe tachycardia may decrease CO by decreasing time for ventricular filling
Heart: preload
amount of blood that the heart must pump with each beat
Frank-starling mechanism: force of ventricular contraction depends on the degree to which muscle fibers are stretched just before contraction
Heart: afterload
the pressure required to move blood into the aorta
systemic arterial pressure is the main source of afterload
stenosis of the aortic valve also increases aferload
Heart: cardiac contractility
determined by the properties of myosin and actin, and influenced by calcium availability
Local control of blood flow: short term autoreguation
autoregulation of blood flow is the ability of tissues to regulate their own blood flow over a wide range of blood pressures
accomplished through changes in bv tone
Local control of blood flow: Hyperemia
hyperemia is an increase in local blood fow
-decreased smooth muscle tone of arterioles, venules, and precapillary sphincters
Local control blood flow: reactive hyperemia
increased BF to an area that suffered a transient occlusion of blood flow
-ex. transient redness seen on an arm after leaning on a hard surface
