NOTES: UNIT 6- The Circulatory System part 4 Blood Pressure

Remember: Blood vessels form a closed circuit of tubes that carry blood from the heart to body cells and back again. *composed of arteries, arterioles, capillaries, venules, & veins

ARTERIES -carry blood away from heart -largest artery = AORTA ARTERIOLES CAPILLARIES -walls are only 1 cell thick VENULES VEINS -carry blood to the heart -thinner walls -are less muscular than arteries

BLOOD PRESSURE: Blood pressure is the force blood exerts against the inner walls of blood vessels. *force occurs throughout system but “blood pressure” commonly refers to pressure in arteries supplied by branches of the aorta

BLOOD PRESSURE: Arterial blood pressure rises & falls in relation to the cardiac cycle –Contracting ventricles squeeze blood out into the aorta and pulmonary arteries which increases arterial pressure Ventricular contraction causes the elastic arterial walls to distend –Relaxed ventricles lead to a drop in blood pressure & a recoiling of arterial walls –Felt as a pulse

BLOOD PRESSURE: ● SYSTOLIC PRESSURE: pressure produced in the arteries when the ventricles contract; highest pressure ● DIASTOLIC PRESSURE: pressure in the arteries when the ventricles are relaxed

BLOOD PRESSURE: Arterial blood pressure depends upon: > cardiac output (volume of blood pumped from each ventricle in 1 min.) CO= HR x SV > blood volume (increase vol. = inc. press.) > peripheral resistance (friction between the blood & vessel walls; contracting artery walls slows blood & inc. press.) > blood viscosity (thickness)

REGULATION OF BLOOD PRESSURE: Baroreceptors in the walls of the aorta & carotid arteries sense changes in blood pressure –Changes in pressure causes baroreceptors to send nerve impulses to medulla oblongata –Medulla oblongata sends nerve impulses to S-A node to increase or decrease heart rate

VENOUS BLOOD PRESSURE: is much lower…how does blood flow through veins (in some cases, against gravity?)  skeletal muscle contraction squeezes blood from one segment to the next  breathing movements change pressure in thoracic and abdominal cavities pulling/pushing blood upward toward the heart  VALVES prevent blood from flowing backward into a previous segment