1. The Heart

2. Location Heart Rests on diaphragm situated in mediastinum
Two thirds lies to left of midline

3. Pericardium Heart enclosed and held in place by pericardium
Two layers:
Outer fibrous layer
Attached to diaphragm
Prevents overstretching
Inner serous layer
Outer parietal layer
Fused to fibrous pericardium
visceral layer (epicardium)
Attached to surface of heart
Pericardial cavity filled with fluid
reduces friction.

4. Heart wall Heart wall has three layers:
epicardium (visceral layer of serous pericardium)
myocardium (cardiac muscle tissue)
Bulk of heart tissue
Provides pumping action
Endocardium
Continuous with endothelial lining of blood vessels

5. Heart chambers - Atria Right atrium receives blood from
Superior vena cava
Inferior vena cava
Coronary sinus
passes blood into right ventricle via tricuspid valve
Left atrium receives blood from:
pulmonary veins
passes blood into right ventricle via bicuspid valve

6. Heart chambers - ventricles
Right ventricle
Passes blood through pulmonary valve into pulmonary trunk
Left ventricle
Passes blood through aortic valve into ascending aorta

7. Myocardial function
Thickness of myocardium varies between chambers according to function
Atria
deliver blood to ventricles
thin walled
Right ventricle
pumps blood short distance to lungs against low resistance
Relatively thin wall
Left ventricle
Pumps blood to all tissues except lungs against high resistance
Thick wall

8. Atrio-ventricular valves
tricuspid valve
right side
bicuspid valve
left side
Valve eversion prevented by:
Chordae tendinae
Papillary muscles

9. Semilunar valves Semilunar valves
prevent blood flow back into ventricles
Made up of three crescent-moon shaped cusps
right ventricle
pulmonary semilunar valve
left ventricle
aortic semilunar valve

10. Systemic circulation Systemic circulation
Oxygen-rich blood enters ascending aorta from left ventricle
Divides into progressively smaller arteries
Arterioles
Capillaries
EXCHANGE IN TISSUES
Venules
Veins
Empty into right atrium

11. Pulmonary circulation
Blood enters pulmonary trunk
Branches into right and left pulmonary arteries
Arterioles
Capillaries
GAS EXCHANGE
Venules
Pulmonary veins
Empty into left atrium

12. Coronary circulation Coronary arteries branch from ascending aorta
carry oxygenated blood to the myocardium
Pulsatile blood flow
Little flow during systole
deoxygenated blood returns to the right atrium primarily via the coronary sinus
Thin walled vein with no smooth muscle to alter diameter

13. Histology of cardiac tissue
Cardiac muscle fibres
connected via intercalated discs
Contain desmosomes and gap junctions
large mitochondrial content
same arrangement of contractile protein as skeletal muscle
small sarcoplasmic reticulum
Small intracellular Ca2+ reserve
Contract according to sliding filament mechanism

14. Conduction system
Cardiac muscle can contract without extrinsic stimulation
Autorhythmic fibres
Act as pacemaker
Form conduction system

15. Conduction system Components of the hearts conduction system are:
sinoatrial node (pacemaker)
Spontaneously depolarise (100 times/min)
Rate of depolarisation modified by neurotransmitters from ANS
atrioventricular node
Spontaneous depolarisation times/min
Conduction slows at AV node
Delay allows atria time to contract
bundle of HIS
right and left bundle branches
conduction myofibers (Purkinje fibers)

16. Cardiac action potential
Action potential occurs in three phases:
Depolarisation
Resting membrane potential –90mV
Moves toward firing threshold
Opens voltage-gated sodium channels
Close rapidly
Plateau
Voltage-gated slow Ca2+ channels open in sarcolemma and sarcoplasmic reticulum
Balances slow K+ outflow
Repolarisation
Voltage-gated K+ channels open
Voltage-gated slow Ca2+ channels close

17. Electrocardiogram Electrocardiogram (ECG)
Composite record of action potentials produced by all heart fibres during one beat
P wave - atrial depolarisation
QRS complex - ventricular depolarisation
atrial repolarisation hidden by QRS complex
T wave - ventricular repolarisation

18. Cardiac cycle Cardiac cycle All events associated with one heartbeat
Atrial systole
Atria contract
Contributes ~25ml to ventricles
Most blood enters ventricles during ventricular diastole
Ventricular systole
Ventricles contract
Isovolumetric contraction until pressures in pulmonary trunk and aorta overcome
Both ventricles eject same volume of blood
Relaxation period
Atria and ventricles relaxed
As ventricular pressure falls below atrial pressure AV valves open and ventricular filling commences
With increasing HR
relaxation period shortens considerably
atrial and ventricular systole only shorten slightly

19. Cardiac output Cardiac output
volume of blood ejected by left or right ventricle per minute
CO = stroke volume (mL/beat) x heart rate (beats/min)
Average CO approx 5.25 L/min (70 mL/beat x 75 beats/min)
Similar to total blood volume of ~5 litres (male)
Cardiac reserve
maximal CO – resting CO

20. Stroke volume Stroke volume (SV) depends on:
volume of blood ejected by a ventricle during systole
depends on:
Preload
Degree of stretch prior to contraction
Contractility
Forcefulness of contraction
Afterload
Pressure that must be exceeded before ejection of blood from ventricles can occur

21. Stroke volume Preload Contractility Afterload
Frank-Starling law of the heart
Greater stretch (preload) increases force of contraction
Preload proportional to end-diastolic volume (EDV)
EDV determined by:
Duration of ventricular diastole (filling time)
Venous return
Frank-Starling law equalises output from both ventricles
Contractility
Forcefulness of contraction
Positive inotropic agents usually increase contractility by promoting Ca2+ inflow
Negative inotropic agents usually reduce contractility by blocking Ca2+ channels
Afterload
Pressure that must be exceeded before ejection of blood from ventricles can occur

22. Heart rate Several factors contribute to regulation of heart rate:
(1) Autonomic regulation (medullary CV centre)
Receives input from higher brain centres and variety of sensory receptors
Proprioceptors
Chemoreceptors
Baroreceptors
Sympathetic output increases heart rate and contractility
Parasympathetic impulses decrease heart rate
Little effect on contractility
does not innervate ventricular myocardioum

23. Heart rate Several factors contribute to regulation of heart rate:
(2) Chemical regulation
Cardiac activity depressed by
Hypoxia
Acidosis
Alkalosis
Hormones
Catecholamines and thyroid hormones increase HR and contractility
Cations
Alterations in balance of K+, Na+ and Ca2+ alter HR and contractility

24. Heart rate Several factors contribute to regulation of heart rate:
(3) Other factors
Age
U shaped curve
Gender
Female HR higher
Physical fitness
Resting bradycardia
Body temperature
Increase causes SA node to discharge more rapidly