Heart Structure And Function Flashcards
What is the heart?
A four chambered organ, supplied by the coronary circulation, that pumps oxygen-poor blood to the lungs and oxygen-rich blood to the rest of the body
What are the 4 chambers of the heart?
Left and right atria and ventricles
Where is the heart located?
Located posterior to the sternum, level with the 3rd costal cartilage, down to the 5th costal space, approximately 7.5cm to the left of midline
What is the mediastinum?
An area in the chest this is between the lungs and it contains the heart, trachea, oesophagus and major blood vessels
What is the heart surrounded by?
The heart is surrounded by the pericardium with about 15-20ml of pericardial fluid in between
What are the two layers of the pericardium?
Visceral/epicardial -> a serous membrane that covers the heart, it is in direct contact with the heart
Parietal -> covering over the top of the visceral layer
What are the 4 chambers of the heart separated by?
Intratrial and intraventricular septum’s
Name the atrioventricular valves
Tricuspid (on right side of heart)
Bicuspid/mitral (on the left side if the heart)
What are the valves of the heart tethered down by?
Chordae tendineae which are fibrous connective tissue
Where do the fibres of the chordae tendineae originate from?
Parts of the muscle walls of the heart by capillary muscles
Name the semilunar valves
Pulmonary valve
Aortic valve
What is the trabecular Carneae of the heart?
It is muscular ridges
What is the moderator band of the heart?
It is a larger version of a trabeculae carneae but it is heavily involved with the transmission of an impulse to make your heart contract
What are cardiac muscles cells connected by?
Intercalated discs
What is the importance of intercalated discs in the heart?
At these discs is where two cardiac cells are bound together, this connection means that it stabilises all the cardiac cells. It allows for ions to be transferred and molecules to move from one muscle cell to another
What is a syncytium?
A multinucleate mass of cytoplasm resulting from fusion of cells
How many syncytiums does the heart have and what is each one composed of?
It has 2
The atria are considered as one syncytium and the ventricles as the other
What is the resting potential of cardiac muscle?
It is the same as skeletal muscle (-90mV)
What does the action potential in cardiac muscle pass via?
Gap junctions/intercalated discs
How long does cardiac muscle action potential last in comparison to skeletal muscle?
0.3 sec (cardiac muscle)
0.001 sec (skeletal muscle)
What is the refractory period of contraction of cardiac muscle?
It is the time interval before another contraction can take place
What is the purpose of the refractory period?
It means fibres are in relaxation before next contraction can occur
It allows the pumping action of cardiac muscle
Why does the action potential need to be coordinated in the heart?
So the heart can act as an effective pump
What slows down the rate of APs per minute in the SAN?
Vagus nerve
What is the cardiac cycle?
All events associated with one heartbeat
What is contraction of the heart called?
Systole
What is relaxation of the heart called?
Diastole
When the atria contract how much blood do they force into the ventricles?
20-25 mL (30% of ventricles volume as already holding 70%)
What is end diastolic volume?
It is the amount of blood the ventricle is holding at the end of its relaxation/before it contracts
What is the EDV of the ventricles?
130mL
What is isometric contraction in the heart?
An event occurring in early systole during which the ventricles contract with no corresponding volume change
What is stroke volume?
The amount of blood that is ejected
What is end systolic volume?
The amount of blood left in the ventricles after contraction
What is the ESV?
50mL
How long does ventricular diastole last?
430msec
What is isovolumetric relaxation?
The part of the cardiac cycle between the time of aortic valve closure and mitral opening
What is cardiac output?
The total blood volume passing through the lungs and systemic circulation in one minute
What is the cardiac output equation?
Cardiac output = stroke volume x heart rate
What is stroke volume?
Volume of blood ejected during ventricular systole
What 3 factors govern stroke volume?
Preload
Contractility
After load
What is preload?
The stretch on your heart prior to it contracting
What is contractility
The strength of the contraction
What is afterload?
The pressure that you need before blood will be pushed out into vessels
What is the Frank-Starling law of the heart?
The more the heart is filled in diastole, the greater the stretch and the greater the force of systole
What are positive inotropic substances?
Certain things that can promote contractility of the heart -> could be drugs or our own internal system
What are negative inotropic substances?
Certain things that will decrease contractility of the heart -> drugs like beta blockers, Ca ion channel blockers, stimulation of parasympathetic nervous system, lack of oxygen
What does increased afterload result in?
It results in reduced stroke volume because more blood remains in ventricle at end of systole
What are the major coronary arteries?
Right coronary
Left coronary
Left anterior descending
Left circumflex
What effect does the parasympathetic nervous system have on the heart?
It slows heart rate
What effect does the sympathetic nervous system have on the heart?
It increases heart rate
What do adrenaline and noradrenaline do to heart rate and contractility?
Increases both
What does hyperthyroidism do to the heart?
It gives tachycardia
What does increase potassium and sodium ions do to heart rate and contractility?
It decreases both
What does a moderate increase of calcium ions do to heart rate and contractility?
Increases both
What will happen in the event of SAN disease or damage?
AVN can take over at 40-60bpm
What will happen to the heart if both the AVN and SAN are suppressed?
Ventricles will beat at 20-30 bpm from Purkinje fibres
What is an electrocardiogram?
A measure of the hearts rhythm and rate through the detection of its electrical activity
What causes the P wave on an ECG?
Atrial depolarisation, initiated by the SAN
What causes the QRS complex of an ECG?
Ventricular depolarisation which begins at the apex
What causes the T wave?
Ventricular repolarisation
