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 contract 2. Diastole - atria and ventricles relax Pulse: arteries expand and contract with the heartbeat

Fig. 13.5

Control of the Heartbeat Intrinsic: controls within the heart itself Extrinsic: controlled by factors outside the heart (the nervous system)

Intrinsic Control Specialized muscle fibers within the heart cause contractions of the chambers: SA node  AV node  Purkinje fibers

SA Node Sinoatrial node (pace maker) In upper wall of R atrium Nerve impulse initiates heartbeat Stimulates atria to contract at regular intervals

AV Node Atrioventricular node In base of R atrium Receives signal from SA node Sends message to Purkinje fibers Signals ventricles to contract after atria

Purkinje Fibres Special muscle fibres in ventricles Receive impulse from AV node Stimulate contraction of ventricles

Extrinsic Control Autonomic nervous system (involuntary) Cardiac control centre in medulla oblongata of the brain controls heart rate Inactivity(parasympathetic nervous system): SA and AV node activity decreases Activity / excitement (sympathetic nervous sytem): SA and AV node activity increases

Fight or Flight Response Adrenal medulla produces hormones epinephrine (adrenaline) and norepinephrine Cause increase in heart rate

Blood Pressure Blood pressure is greater in arteries than in veins BP 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 pressure Can cause excessive stress on the arteries and heart can be caused by: Increase in heart rate Increase in blood volume Narrowing of blood vessels Genetic and lifestyle factors play a role

Hypotension Lower than normal blood pressure Can result in the heart and other parts of the body not receiving enough blood Many causes including heart problems or other illness Can 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: Salt Stress Dehydration High fat diet