Higher Human Biology Subtopic 14 The Heart Physiology and Health Higher Human Biology Subtopic 14 The Heart

Learning Intentions To discuss the structure of the heart To calculate cardiac output To describe the nervous control of the heart To describe how to measure blood pressure

blockbusters

The Heart

Structure of the heart 4 chambers Right and left atria Right and left ventricle Valves Atrioventricular valves (tricuspid and bicuspid) Semilunar valves The valves prevent backflow

Right semi-lunar valve Left atrio-ventricular valve Right atrio-ventricular valve Left semi-lunar valve

Right AV valve Left AV valve

Calculating Cardiac Output Heart Rate (HR) Number of beats per minute Stroke Volume (SV) Volume of blood expelled by each ventricle when contracting Cardiac Output (CO) Volume of blood pumped out of a ventricle per minute

Calculating Cardiac Output Heart rate (bpm) CO = HR × SV Cardiac output (litres) Stroke volume (ml / min)

What is the CO of this individual? CO = 72 x 70 = 5040 ml/min a) At rest: HR = 72bpm SV = 70ml What is the CO of this individual? CO = 72 x 70 = 5040 ml/min = 5 litres/min b) During exercise: HR = 200bpm SV = 150ml CO = 200 x 150 = 30000ml/min = 30 litres/min

Factors Affecting Cardiac Output CO can very depending on level of exercise and level of fitness More intense exercise = higher cardiac output Increased physical fitness level improves cardiac output

Cardiac cycle Systole – contraction Diastole – relaxation The atria contract first – 0.1s Then the ventricles contract –0.3s Then the heart rests – diastole - 0.4s

Cardiac Cycle - 3 stages ATRIAL SYSTOLE VENTRICULAR SYSTOLE AND ATRIAL DIASTOLE VENTRICULAR DIASTOLE

ATRIAL SYSTOLE 2 Atria contract simultaneously Sends blood through open AV Valves into the ventricles SL valves closed, ventricles fill up First 0.1 seconds

At this point the ventricles are relaxed and in a state of diastole VENTRICULAR DIASTOLE At this point the ventricles are relaxed and in a state of diastole

VENTRICULAR SYSTOLE AND ATRIAL DIASTOLE ATRIAL SYSTOLE VENTRICULAR SYSTOLE AND ATRIAL DIASTOLE VENTRICULAR DIASTOLE 18

VENTRICULAR SYSTOLE AV valves close, ventricles contract Pressure inside ventricles > arteries Forces SL valves open and blood leaves heart Takes 0.3 seconds

VENTRICULAR SYSTOLE AND ATRIAL DIASTOLE ATRIAL SYSTOLE VENTRICULAR SYSTOLE AND ATRIAL DIASTOLE VENTRICULAR DIASTOLE 20

ATRIAL AND VENTRICULAR DIASTOLE Blood returns from Vena Cava and Pulmonary Vein Blood pressure in the atria increases Begins to force AV valves open, next ATRIAL SYSTOLE begins Takes 0.4 seconds

State of Ventricular Wall Summary Table Atrial Systole Ventricular Systole State of Atrial Wall State of Ventricular Wall State of AV Valves State of SL Valves Contracted Relaxed Relaxed Contracted Open Closed Closed Open

Heart Sounds Start of v diastole (closing of SL) Start of v systole (closing of AV)

Conduction of the Heart Heart beat is regulated by the nervous system and hormones

Sino-atrial (SA) node Atrio-ventricular (AV) node Bundle of His Right & left bundle branches Purkinje fibres

The Pacemaker Called the sinoatrial node Found in right atrial wall Initiates the heartbeat Exhibits spontaneous excitation Causes atria to contract

The steps in contraction…… Waves from SA node pass across the atria causes contraction Signal passes to AV node Down bundle of His Divides into left and right bundles Is conducted up through the pirkinje fibres Ventricles contract (from bottom up)

Nervous Control The heart is controlled by the autonomic nervous system. There are 2 pathways that are antagonistic to one another (work in opposites).

Control Centre CAC - cardioaccelaratory centre Medulla of the brain contains 2 groups of neurones which control heart rate CAC - cardioaccelaratory centre CIC - cardioinhibitory centre CAC has sympathetic fibres which when stimulated increase heart rate CIC has parasympathetic fibres that innervate the heart, stimulation of these nerves slow heart rate

Control Centre

Cardiac accelerator nerves – sympathetic fibres CAC in medulla Cardiac accelerator nerves – sympathetic fibres Noradrenaline released Innervates SA node/AV node/Myocardium Increased Heart rate and strength of contraction

CIC in medulla Parasympathetic fibres Acetylcholine released This innervates SA node/AV node Decreased Heart rate and strength of contraction

Hormonal Regulation of the Heart Stress / exercise causes the adrenal glands to produce adrenaline This travels in the blood to the SA node and causes an increase in HR

Electrocardiogram (ECG) ECG’s measure the electrical activity of the heart 3 waves: P QRS T

Electrocardiogram (ECG) P wave – electrical excitation over the atria QRS wave - electrical excitation over the ventricles T wave – electrical recovery at end of ventricular systole

ABNORMAL ECG’S Atrial flutter Rapid contraction of the atria Atria contract 3 times for every ventricular contraction

ABNORMAL ECG Ventricular tachycardia Ventricles beat rapidly and independently of the atria SOLUTION – artificial pacemaker

ABNORMAL ECG’S Ventricular fibrillation Unco-ordinated electrical activity Pumping cannot take place Fatal if not corrected Defibrillation

Blood Pressure Blood pressure is the pressure exerted on the wall of a blood vessel Measured in mmHg Highest in large elastic arteries

How do we measure BP? Using a sphygmomanometer Systolic pressure Maximum pressure during ventricular contraction - 120mmHg Diastolic pressure Minimum pressure during ventricular relaxation - 80mmHg

Pressure decreases as blood flows round the body Narrow vessels cause friction and resistance that decrease pressure

Measuring Blood Pressure

Hypertension Hypertension – prolonged elevation of blood pressure Major risk factor for many diseases including coronary heart disease.

Hypertension Factors Overwieght Lack of exercise Fatty diet High salt diet Excess alcohol Stress

Learning Intentions To discuss the structure of the heart To calculate cardiac output To describe the nervous control of the heart To describe how to measure blood pressure