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