Describe the size, shape and location of the heart
Size
Closed fist
Shape
Apex is a blunt rounded point of cone Base is flat part at opposite of end of cone
Location
Thoracic cavity, mediastinum
Describe what pericardium is and what it does
Membrane that surrounds the heart
Keeps the heart in place and limits its motion
Prevents it from over expanding and acts as an anchor
What are the two layers of the pericardium called?
Outer layer fibrous pericardium
Inner layer serous pericardium
Name and describe the two layers of the serous pericardium?
Parietal layer Lines the fibrous pericardium
Visceral layer Covers the heart surface
The two are continuous and have a pericardial cavity in between that reduces friction as the heart beats
Name and describe the three layers of the heart
Epicardium Smooth outer surface of heart
Myocardium Composed of cardiac muscle cell, responsible for heart contracting
Endocardium Smooth inner surface of heart chambers
Name and describe the four chambers of the heart and the two septums
Right atrium Receives deoxygenated blood from the superior and inferior vena cava and the coronary sinus
Left atrium Receives oxygenated blood from pulmonary veins
Right ventricle Pumps deoxygenated blood to pulmonary trunk/artery
Left ventricle Pumps oxygenated blood to aorta
Inter-atrial septum Wall between the atria
Inter-ventricular septum Wall between the two ventricles
What is the primary function of heart valves?
Prevents back flow of blood
Where do the atrioventricular (AV) valves lie?
Between atria and ventricles are the tricuspid valve on the right side of the heart and bicuspid valve on the left
What are the valves attached to?
Each valve has leaf like cusps that are attached to cone shaped papillary muscles by tendons
What and where are the two semilunar valves?
Aortic valve - base of the aorta
Pulmonary valve - base of the pulmonary trunk
Outline the route of blood flow within the body
What are the three parts of the body's circulatory system?
Pulmonary
Coronary
Systemic
Describe systemic circulation
The left side of the heart is the pump for the systemic circulation
It pumps oxygenated blood from the lungs out into the vessels of the body
Describe pulmonary circulation
The right side of the heart is the pump for the pulmonary circulation
It receives deoxygenated blood from the body and sends it to the lungs for oxygenation
What is the blood volume distribution?
Pulmonary circulation - 18% Coronary - 12% Systemic - 70%
Describe coronary circulation
Provides blood flow to the myocardium
coronary artery disease
How is the myocardium specialised?
Has intercalated discs with gap junctions to allow muscle action potentials to conduct from one muscle fibre to its neighbours
Describe what is meant by autorythmic cells
Cells can spontaneously depolarise and generate action potentials
Cells act as a pacemaker to set the rhythm for the entire heart
Form their own conduction system
How do cardiac muscle cells contract?
Action potential initiated in the conduction system is propagated across the sarcolemma of cardiac muscle cells
Thin filaments and sarcomeres shorten within cardiac muscle cells
What does the conduction system do?
Heart regulates the rate and strength of contraction through an intrinsic conduction system, modified by external sympathetic and parasympathetic pathways
Describe the function of the SA node in relation to the conduction system
mass of auto-rhythmic cells in the right atrial wall near the entrance of the superior vena cava
generates impulses about 100x per minute and sets pace for entire heart
Describe the function of the AV node in relation to the conduction system
mass of auto-rhythmic cells located in the inferior portion of the inter-atrial septum above the tricuspid valve
each impulse is delayed briefly here, allowing atria to contract before ventricles
Describe the function of the bundle of His in relation to the conduction system
Auto-rhythmic cells located in the inter-ventricular septum
Only electrical connection between atria and ventricles
Describe the function of the Purkinje fibres in relation to the conduction system
Run through the inter-ventricular septum, penetrate the heart apex, then turn upwards through the ventricular myocardium triggering ventricular contraction and pushes blood through the semilunar valves.
Define ECG
Electrocardiogram
A recording device for the heart's electrical events during each cardiac cycle
What does the P wave represent on the ECG?
Depolarisation of atrial myocardium
Signals onset of atrial contraction
What does the QRS complex represent on the ECG?
Ventricular depolarisation and signals onset of ventricular contraction
Repolarisation of atria simultaneously
What does the T wave represent on the ECG?
Repolarisation of ventricles
Precedes ventricular relaxation
What does the PQ interval represent on the ECG?
Atria contract and begin to relax
Ventricles begin to contract
What does the QT interval represent on the ECG?
Ventricles contract and begin to relax
Label the waves on an ECG
What is the cardiac cycle made up of?
Sequence of events that make up a heartbeat
Consists of systole and diastole of both atria, rapidly followed by systole and diastole of both ventricles
How long does a complete cardiac cycle take?
75 beats/min = 0.8 secs
Define auscultation
Act of listening to heart sounds within the body
What is the 'lub' and 'dup' caused by?
'Lub' - blood turbulence associated with tricuspid and bicuspid valves closing
'Dup' - blood turbulence associated with pulmonary and aortic valves closing
Define cardiac output?
Amount of blood pumped out by each ventricle in one minute
Volume of blood ejected from the left ventricle into the aorta each minute
heart rate x stroke volume
Define stroke volume
Volume of blood pumped out by a ventricle with each contraction/heart beat
Usually 70ml
What is stroke volume affected by?
Venous return
Force of contraction of heart regulated by
hormones sympathetic nervous system
Define heart rate
Number of times the heart beats in one minute
What is the heart rate regulated by?
Parasympathetic nervous system - acts on SA node to decrease heart rate
Sympathetic nervous system - acts on SA node to increase heart rate
Hormones, age, exercise, body temperature
Define tachycardia
Heart rate greater than 100bpm
Define bradycardia
Heart rate slower than 60bpm
Define venous return
Amount of blood which returns to the heart
What is venous return regulated by?
Blood volume - increases with exercise and decreases in event of a haemorrhage
Skeletal muscle and respiratory pumps - muscles contracting around blood vessels aid venous return to the heart
State the formula for mean arterial pressure?
(1/3 x Systolic BP) + (2/3 x Diastole BP)