HEART RATE AND BLOOD PRESSURE
Learning Outcomes
C4 – Analyze the relationship between heart rate and blood pressure
describe the location and functions of the sinoatrial (SA) node,atrioventricular (AV) node, and Purkinje fibres
describe how the autonomic nervous system increases and decreases heart rate and blood pressure
differentiate between systolic and diastolic pressures
describe hypertension and hypotension and their causes
demonstrate the measurement of blood pressure
Heartbeat
Beats when heart muscles contract and relax
Sounds are valves closing (“lub-dup”) a.v. valves, then semilunar valves
Cardiac Cycle
One complete heartbeat:1. Systole - atria and ventricles contract2. Diastole - atria and ventricles relax
Pulse: arteries expand and contract with the heartbeat
Fig. 13.5
Control of the HeartbeatIntrinsic: controls within the heart itselfExtrinsic: controlled by factors outside the
heart (the nervous system)
Intrinsic ControlSpecialized muscle
fibers within the heart cause contractions of the chambers:
SA node
AV node
Purkinje fibers
SA NodeSinoatrial node (pace maker)In upper wall of R atriumNerve impulse initiates heartbeat Stimulates atria to contract at regular
intervals
AV NodeAtrioventricular nodeIn base of R atriumReceives signal from SA nodeSends message to Purkinje fibersSignals ventricles to contract after atria
Purkinje FibresSpecial muscle fibres in ventriclesReceive impulse from AV nodeStimulate contraction of ventricles
Extrinsic ControlAutonomic nervous system (involuntary)Cardiac control centre in medulla oblongata
of the brain controls heart rateInactivity(parasympathetic nervous
system): SA and AV node activity decreasesActivity / excitement (sympathetic nervous
sytem): SA and AV node activity increases
Fight or Flight ResponseAdrenal medulla produces
hormones epinephrine (adrenaline) and norepinephrine
Cause increase in heart rate
Blood PressureBlood pressure is greater in arteries than in
veinsBP is greater closer to the heart
BP and velocity decrease as blood flows from arteries into arterioles (cross-sectional area increases)
BP and velocity are lowest in capillaries (greatest cross-sectional area)
As blood moves into venules and veins, velocity increases but BP does not (decreasing cross-sectional area, increased distance from heart)
Measurement of BP
Blood pressure is measured with a sphygmomanometer
Systolic (contracting) / Diastolic (relaxing)Normal: 120 / 80
Hypertension Higher than normal blood pressureCan cause excessive stress on the arteries
and heartcan be caused by:
Increase in heart rateIncrease in blood volumeNarrowing of blood vessels
Genetic and lifestyle factors play a role
HypotensionLower than normal blood pressureCan result in the heart and other parts of
the body not receiving enough bloodMany causes including heart problems or
other illnessCan be caused by dehydration, shock, or
blood loss (temporary)
Review:1. List the steps in one “heartbeat” cycle
naming all the parts involved.2. Explain the effect of each of the following
on blood pressure:SaltStressDehydrationHigh fat diet
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