Flashcards in The Heart Deck (120):
Describe the location of the heart
Lies in the thoracic cavity in the mediastrium, lies a little more to the left than the right (obliquely). Base above and apex below, apex about 9cm to the left of the midline at the 5th intercostal space, base extends to the level of the 2nd rib.
What are the 3 layers that of tissue that compose the heart wall.
Pericardium, myocardium and endocardium.
Which is the outer most layer made up of 2 sacs?
What does the outer sac of the pericardium consist of?
What does the inner layer of the pericardium consist of?
Continuous double layer of serous membrane
What about the pericardium prevents over distension of the heart?
It's in elastic, fibrous nature
What is the outer layer of the serous membrane of the pericardium called?
What is the inner layer of serous membrane of the pericardium called?
Visceral pericardium or epicardium
What cells does the serous membrane consist of?
Flattened epithelial cells
When someone is healthy how do the two layers of serous membrane lie together?
Lie closely together with only the thin film of serous fluid between them.
What divides the heart into the right and left side?
What is each side of the heart divided by?
Atrioventricular valve into the upper atrium and ventricle below.
What is the name of the right atrioventricular valve?
How many cusps does the tricuspid valve have?
What is the name of the left atrioventricular valve?
How many cusps does the mitral valve have?
Which 2 veins enter their contents into the right atrium?
The superior and inferior venae cavae
Where is the blood pumped after it passes through the right atrioventricular valve into the right ventricle?
Pulmonary artery or trunk
What is the opening of the pulmonary artery guarded by?
The pulmonary valve
Now many semilunar cusps form the pulmonary valve?
What does the pulmonary valve do?
Prevents the back flow of blood into the right ventricle when the ventricular muscle relaxes.
After leaving the heart where does the pulmonary artery carry the blood?
Splits into right and left, carries blood to lungs where exchange of gases takes place. CO2 is excreted and O2 is absorbed.
Where do the two pulmonary veins from the lungs carry oxygenated blood back to?
After the lungs and the left atrium where does the blood go?
Through the left atrioventricular valve into the left ventricle, then pumped into the aorta.
What guards the aorta?
The aortic valve
How many cusps form the aortic valve?
3 semilunar cusps
How does the foetus obtain oxygen, nutrients and excrete waste?
Via the mothers circulation
What is the function of the placenta?
Provides an interface between mother and foetus, allows exchange of substances between their circulatory systems.
What does most blood bypass in the foetus?
What is the name of the continuation of the umbilical vein that returns blood directly into the foetal inferior venae cavae?
What is the ductus arteriosus?
Small vessel that connects the pulmonary artery to the descending throracic aorta. Diverting more blood into the systemic circulation meaning that very little blood passes through the fetal lungs.
What does the foremen ovale form?
Valve-like opening allowing blood to flow between the right and left atria, so that blood bypasses the non-functional foetal lungs.
What happens when the baby tales it's first breath?
The lungs inflate for the first time increasing pulmonary blood flow. Foramen ovale is closed preventing blood flow through the atria, blood is therefore diverted into the pulmonary circulation. Blood oxygen increases causing constriction of the ductus arteriosus.
What happens to the ductus venosus and umbilical arteries soon after birth?
Describe the structure of cardiac muscle.
Forms a branching network of cells
Cells are interconnected by intercalated discs which contain gap junctions allowing ion transport promoting coordinated contraction
Cardiac cells act as functional syncitium
Cardiac muscle is autorhythmic
Is myocardium under voluntary control?
What is myocardium composed of?
Specialised cardiac muscle only found in the heart
What gives the myocardium the appearance of being a sheet of muscle?
Cells close with adjacent cells, intercalated discs
Why do the fibres in myocardium not need separate nerve supplies?
Because of the end to end continuity of the fibres
What happens in the myocardium when am impulse is initiated?
Spreads from cell to cell over the whole sheet of muscle causing a contraction.
What else is running through the myocardium?
Network of specialised conducting fibres responsible for transmitting the hearts electrical signals.
Where is the myocardium the thickest?
At the Apex of the left ventricle
What does autorhythmicity mean?
Generates it's own electrical impulses and beats independently of nervous or hormonal control.
Which nerve fibres supply the heart?
Sympathetic and parasympathetic
Which hormones do the heart respond to?
Adrenaline and thyroxine
What do small groups of specialised neuromuscular cells in the myocardium initiate?
Impulses, causing coordinated and synchronised contraction of the heart muscle
Describe the sinoatrial node?
Small mass of specialised cells which lie in the wall of the right atrium near the opening of the superior venae cavae
Why do the sinoatrial cells generate regular impulses?
Because they are electrically unstable leading them to discharge (depolarise) regularly
How many times a minute do the sinoatrial cells depolarise?
What is depolarisation followed by?
Recovery (repolarisation) - instability leads them to discharge again immediately.
Describe the atrioventricular node
Small mass of neuromuscular tissue situated in the wall of the atrial septum near the atrioventricular valves.
What are the functions of the AV node?
Transmits the electrical signals - secondary pacemaker function if there is a problem with the SA
What is the intrinsic firing rate of the AV node?
40-60 beats per min
What is the bundle of his?
Mass of specialised fibres that originate from the AV node
Describe the structure of the bundle of his
AV bundle crosses fibrous ring that separates atria and ventricles, upper end of ventricular septum it divides into R and L bundle branches, within ventricular myocardium branches break up into fine fibres called the purkinje fibres.
What do the AV bundle, bundle branches and Purkinje fibres do?
Transmit electrical impulses from the AV node to the apex of the myocardium, where ventricular contraction begins, then sweeps upwards and outwards pumping blood into pulmonary artery and the aorta.
Which nervous system is the heart rate regulated by?
The autonomic nervous system
Which nerves supply the SA and AV nodes and atrial muscle?
What is the effect of parasympathetic stimulation on the heart beat?
Reduced the rate in which impulses are produced and decreases rate and force of heart beat.
What do the sympathetic nerves supply?
SA and AV nodes, myocardium of atria and ventricles.
What does sympathetic stimulation do the heart rate?
Increases rate and force of the heartbeat
At rest what is the adult heart rate?
60-80bpm, during each heartbeat
What is systole
What 3 things does the cardiac cycle involve?
- atriole systole - contraction of the atria
- ventricular systole - contraction of the ventricles
- complete cardiac diastole - relaxation of the atria and ventricles
Which side of the heart does deoxygenated blood go into?
Which side of he heart does oxygenated blood go into?
What is the P wave on an ECG?
Impulse from SA node sweeps over the atria (atrial depolarisation)
What is the QRS wave on the ECG?
Rapid spread of impulse from AV node to AV bundle, purkinje fibres and electrical activity of the ventricular muscle (ventricular depolarisation)
What is the T wave on the ECG?
Relaxation of ventricular muscle (ventricular repolarisation)
What is the arterial supply to the heart?
Right and left coronary arteries branch from the aorta
What is the venous drainage of the heart?
Cardiac veins join to form coronary sinus, opens into right atrium, remainder passes through venous channels into the heart chamber.
What is the systemic circulation?
Blood is pumped out from the left ventricle carried by the branches of the aorta around the body and return to the right atrium of the heart by the superior and inferior venae cavae.
What do the walls of arteries and arterioles consist of?
3 layers of tissue
What are the three layers of tissue in the arteries and arterioles?
Tunica adventitia - outer layer of fibrous tissue, tunica media - middle layer of smooth muscle and elastic tissue, tunica intima - lining of squamous epithelium called endothelium.
In large elastic arteries what does the tunica media consist of more and less of?
More elastic tissue and less smooth muscle - allowing vessel wall to stretch
In the smallest arterioles what does the tunica media consist almost entirely of?
Smooth muscle - enables control of diameter and regulates pressure.
Do arteries or veins have thicker walls?
What are anastomoses?
Arteries forming a link between main arteries supplying an area, provide collateral circulation.
What is an end artery and give 2 examples of them?
Have no anastomoses eg branches from circulus arteriosus in the brain or central artery to the retina of the eye
What are capillaries?
The smallest arterioles
What are veins?
Blood vessels that return blood at low pressure to the heart.
What is there less of in the tunica media of veins?
Less muscle and elastic tissue
What does infarction mean?
Death of tissue
What is the commonest cause of an MI
Atheromatus plaque complicated by thrombosis
What are the complications of MI?
Severe arrhythmias, acute failure or carcinogenic shock, rupture of ventricle wall, pulmonary or cerebral embolism, pericarditis, angina pectoris, recurrence
When is the pressure of the blood highest?
When is pressure of blood lowest?
What is mean arterioles blood pressure?
Average blood pressure in an individual. Determined by cardiac output, systematic vascular resistance and central venous pressure.
(CO x SVR) + CVP
What is stroke volume?
Volume of blood in the ventricles immediately before they contract
What is end diastolic volume
Volume of blood contained by the ventricles at the end of diastole when the chambers are full
What is end systolic volume?
Volume of blood that remains in the ventricles after systole when the heart is fully contracted
What is cardiac output determined by?
Stroke volume and heart rate.
What is total peripheral resistance?
Overall resistance to blood flow through systemic blood vessels
What is hear tp rate determined by?
ANS, circulating chemicals (hormones), position, exercise, emotion, gender, age, temperature and baroreceptor reflex
What are the 3 main factors determining blood pressure?
- Cardiac output
- peripheral or arteriole resistance
- auto regulation - levels of activity, organs capable of adjusting bp in local vessels eg kidneys, brain
What are baroreceptors?
Nerve endings sensitive to pressure changes within the vessel
Where are baroreceptors situated?
Arch if the aorta and in the carotid sinuses
How do the Baroreceptors react to high BP?
Increase PNS nerve activity, slow heart down
Decrease in SNS causing vasodilation
How do the Baroreceptors react to low BP?
Increase SNS drive speed up heart, vasoconstriction.
Where do interconnected neurones receive, integrate and coordinate inputs from the Baroreceptors, chemoreceptors and higher centres in the brain?
Medulla and pons of the brain stem
What are chemoreceptors and where are they situated?
Nerve endings in the carotid and aortic bodies
What are chemoreceptors involved in?
Levels of O2 and CO2 in the blood and PH balance
What do chemoreceptors do when blood oxygen is low or CO2 is high?
Send signals to CVC, increase SNS drive, pushes up BP, improves tissue blood supply, respiratory effort increases blood oxygen.
When would chemoreceptors input to the CVC?
When arterial BP falls to less than 80mmHg
Where are chemoreceptors found in the brain that detect changes in CSF?
What influences CVC from the higher centres of the brain?
Emotional states, fear, anxiety, pain, anger.
Hypothalamus - temp change, CVC adjusting diameter of blood vessels.
What sort of space exists between the visceral and parietal pericardium?
What surrounds the heart
Describe the pericardeum
Fibrous outside layer - in elastic to prevent overfilling
Serous pericardium - 2 layers visceral and parietal, separated by parietal cavity containing serous fluid - prevents friction
How many layers does the heart wall have?
Describe the 3 layers of the heart wall
Endocardium - inner layer, endothelium
Myocardium - middle layer, cardiac muscle
Epicardium - outer layer, visceral pericardium
What is preload determined by?
End diastolic volume
What is end diastolic volume determined by?
What is venous return determined by?
Volume of circulating blood
What can contractility be increased by?
Norepinephrine and epinephrine
What can contractility be deceased by?
Where is the cardiac centre and what does it do?
Modifies heart rate - medulla oblongata