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

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

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 (heart rate x stroke volume; L/min) > 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

Using a Sphygmomanometer Blood Pressure Using a Sphygmomanometer

Arterial Blood Pressure Blood pressure is measured using an instrument called a sphygmomanometer Measures the amount of air pressure equal to the blood pressure in an artery Unit: mm Hg (millimeters of mercury) original instruments measured how high air pressure could raise a column of mercury in a glass tube

What do those Number Mean Anyway? The blood pressure cuff is wrapped around the upper arm and exerts pressure on the brachial artery Systolic pressure: force with which blood is pushing against artery walls when the ventricles are contracting Harder since the left ventricle is contracting Diastolic pressure: force of the blood when the ventricles are relaxed Just from the resistance of blood vessels

How To Take Blood Pressure 1. Bag is inflated to a pressure above the systolic pressure (do NOT go above 200mmHg!) flow of blood is stopped and the artery is silent 2. Slowly release the valve letting air out of the bag there are now 5 phases based on the loudness and quality of the sounds.

The Sounds of Korotkoff The Five Phases 1. A loud, clear tapping (or snapping) 2. Succession of murmurs 3. A loud, thumping sound, similar to phase 1 but less clear. 4. A muffled sound 5. All sounds disappear. (this phase is absent in some people)

What You Should Listen For 1. When you hear the first sound Read the pressure gage. = Systolic Pressure (needle jumps) 2. At the end of the muffled sounds or when there is no longer any sound (Needle smoothes out) Read the pressure gage = Diastolic pressure

Chart of Age-Appropriate Blood Pressure Ranges Systolic Diastolic 6-9 91-120 53-81 10-12 97-137 58-91 16-18 115-120 73-81 Adults 112-137 79-87

Fluctuations in blood pressure the time of day Fluctuations occur during waking hours, and are lower during sleep. physical activity Usually higher during and immediately after exercise, and lower at rest. emotional moods Feelings (such as fear, anger, or happiness) can affect blood pressure.

stress Physical or emotional stress can elevate blood pressure. age, height, weight, and gender Blood pressure varies for each person. other illnesses Other illnesses a person may have (such as kidney or heart disease) affect blood pressure.