Cardiac System: Structure and Function Flashcards
State the structures of the cardiac tissue.
- Serous membrane
- Pericardial cavity
- Parietal pericardium
- Fibrous pericardium
- Coronary blood vessel
- Endocardium
- Myocardium
- Epicardium
Describe the myocardium
Cardiac muscle fibres arranged into 4 chambers: 2 atria, 2 ventricles
Describe the conduction system
Specialised tissue which conducts nerve impulses through heart, SA and AV node, bundle of His, bundle branches and purkyne fibres
Describe the nerve supply
Nerve branches from both sympathetic and parasympathetic divisions of the ANS - regulates heart rate and force of contraction
Describe the thickness of cardiac walls
Myocardium of left ventricle is much thicker than the right.
Describe blood supply to the heart.
- Coronary artery and vein system
- Right and left coronary arteries branch off from aorta and into smaller vessels
- Cardiac veins deliver blood to coronary sinus and back to the right atrium
How does coronary artery disease occur?
When coronary arteries cannot deliver blood adequately: plaques in arterial walls
How does a myocardial infarction occur?
When blood supply to heart is completely blocked; muscle dies
Describe the structure of the pericardium.
Double-walled sac around the heart composed of:
- superficial fibrous pericardium
- deep two-layer serous pericardium
- parietal layer lines the internal surface of the fibrous pericardium
- visceral layer lines the surface of the heart
- Separated by the fluid-filled pericardial cavity
Describe the function of the pericardium.
- Protects and anchors the heart
- Prevents overfilling of the heart with blood
- Allows for the heart to work in a relatively friction-free environment
State the functions of the heart.
- Regulates blood supply: changes in contraction rate and force to match changing metabolic needs
- Generating blood pressure
- Ensuring one-way blood flow: valves
State and describe the two circuits of the heart.
- Pulmonary circuit: blood to and from the lungs - eliminates CO2 via the lungs and oxygenates the blood
- Systemic circuit: blood to and from the rest of the body - delivers oxygen to all body cells and carries away wastes
Describe the movement of blood in the heart.
- Venous return into the heart via the vena cava, into the right atrium and then the right ventricle
- Venous blood pumped to the lungs via pulmonary arteries
- Oxygenated blood (red blood) returns to heart via pulmonary veins, into the left atrium and then the left ventricle
- Red blood then pumped to all body tissues via aorta
Define cardiac cycle
Electrical, pressure and volume changes that occur in functional heart between two heart beats
State and describe the two phases of the cardiac cycle
Diastolic phase: When myocardium is relaxing
Systolic phase: myocardium is contracting
Name the valve between the right atrium and right ventricle?
Tricuspid valve
Name the valve between the right ventricle and pulmonary trunk.
pulmonary semilunar valves
Name the valve between the left atrium and left ventricle.
bicuspid valve
Name the valve between the left ventricle and aorta.
Aortic semi-lunar valves
Describe atrial diastole and systole
- Blood flows into and passively out of atria (80% of total); AV valves open
- Atrial systole pumps only about 20% of blood into ventricles
Describe ventricular filling: mid-to-late diastole
- Heart blood pressure is low as blood enters atria and flows into ventricles
- 80% blood enters ventricles passively; atrial systole occurs pumping other 20%
Describe ventricular systole
- Atria relax; rising ventricular pressure closes AV valves (‘lubb’)
- Isovolumetric contraction phase
– Ventricles contract, no blood leaving (Pressure too low to open semilunar valves)
– Ventricular ejection phase opens semilunar valves - Ventricular pressure»_space; pressure in arteries (aorta and pulmonary trunk)
Describe ventricular diastole
Ventricles relax; blood backflow, closes semilunar valves (“dubb”)
- Blood once again flowing into relaxed atria and passively into ventricles
Describe ‘lubb’ and ‘dubb’
Lubb - when the atrioventricular valves - tricuspid and bicuspid - close i.e atrial diastole
Dubb - when the semi-lunar valves - pulmonary and aortic - close i.e ventricular diastole
What is the avg bpm for young adult females?
72-80
What is the avg bpm for young adult males?
64-72 bpm
State the resting heart rate in those with tachycardia
in excess of 100 bpm due to stress, anxiety, drugs, heart disease or increased body temp.
State the heart rate of those with bradycardia
less than 60 bpm - in sleep and endurance trained athletes
What is meant by premature atrial contractions?
Occasional shortened intervals between one contraction and next - occurs in healthy people
Define cardiac output.
amount of blood pumped by each ventricle in one minute
CO = Heart Rate (beats/min) x Stroke Volume (ml/beat)
What are the factors affecting cardiac output?
heart rate - autonomic innervation and hormones
stroke volume - end-diastolic volume and end-systolic volume
What is stroke volume?
the volume of blood pumped by a ventricle per beat
SV - end diastolic volume (EDV) - end systolic volume (ESV)
what is EDV?
amount of blood in a ventricle at the end of diastole
what is ESV?
amount of blood remaining in a ventricle after contraction
What does ejection fraction mean?
% of EDV pumped by the ventricle
Define blood pressure.
Force exerted by blood against blood vessel walls
Which receptors detect changes in blood pressure?
Baroreceptors - rising pressure stretches receptors - vagus nerve which in the parasympathetic system.
Where and when is blood pressure the highest?
- In large arteries
- Highest with ventricular systole
When is blood pressure the lowest?
- Lowest with ventricular diastole
How to calculate blood pressure?
Peak pressure divided by minimum pressure.
Describe how blood pressure increases.
- Blood volume increases
- Heart rate increases
- Stroke volume increases
- Blood viscosity increases
- Peripheral resistance increases
Describe reducing blood pressure.
- Cardiac output increases
- Blood pressure rises
- Baroreceptors in aortic arch and carotid sinuses are stimulated
- Sensory impulses to cardiac centre
- Parasympathetic impulses to heart
- S-A node inhibited
- Heart rate decreases
- Blood pressure returns toward normal
What is meant by preload?
- Tension applied before the muscle performs any work = end diastolic volume
- INCREASE IN FILLING PRESSURE=INCREASED PRELOAD
What is meant by afterload?
- Load that preloaded muscle has to work against
- aortic pressure present at the instant that the aortic valve opens.
- Higher aortic diastolic pressure- greater work to pump blood into heart.
- Afterload = Ventricular Wall Stress that develops during systolic ejection.
Estimated using Laplace’s Law: VWS = Pressure x radius / 2 (wall thickness)
How does preload affect cardiac output?
Increased preload = increased cardiac output
Describe Frank-Starling mechanism.
- Increased venous return increases ventricular filling and thus preload
- Myocyte stretching causes an increase in force generation
- This enables the heart to eject the additional venous return, thereby increasing stroke volume
How does after load affect cardiac output?
Increased after load decreases cardiac output
How does contractility affect cardiac output?
- Increased contractility leads to increased cardiac output
What is meant by hypertension?
- When arterial pressure is too high
- The heart has to work harder
- The left ventricle enlarges
- Atherosclerosis can affect coronary arteries - leads to heart disease
- Deficient blood supply to other parts of the body as damage to blood vessels increases - leads to heart heart failure
What is renin?
Secreted by the kidney in response to reduced blood pressure or blood volume
What is the treatment for hypertension?
- Change lifestyle factors
- Drug therapy to reduce heart rate
- Ca2+ channel blockers; reduce calcium flow into heart muscle and thus heart rate
- Beta blockers (reduce stimulation by sympathetic nervous system)
- Diuretics reduce blood volume
- ACE inhibitors interfere with renin- angiotensin pathway
- Vasodilators (such as nitroglycerin) open up blood vessels (reduce resistance)
What is the role of renin?
converts Angiotensinogen into Angiotensin I
What is the role of ACE?
converts Angiotensin I into Angiotensin II
What are the actions of angiotensin 2?
- Intense vasoconstriction - increase total peripheral resistance
- Causes release of Aldosterone from adrenal gland - promotes Na+ and
H2 O reabsorption in kidney - cause increased blood volume. - Regulatory negative feedback on the release of Renin.
- CNS: Stimulate thirst in hypothalamus, stimulate sympathetic outflow.
- Designed to bring arterial blood pressure back up to normal set-point
State the role of ACE inhibitors.
- Inhibit formation of angiotensin
- Decrease release of aldosterone, retaining sodium and water
State the role of ACE receptor blockers
- Block angiotensin receptors on blood vessels and adrenal cortex
- Produce vasodilation and decrease the activity of aldosterone
What happens as a result of systolic heart failure?
- Less blood pumped out of ventricles
- Weakened heart muscle can’t squeeze as well
What happens as a result of diastolic heart failure?
- Less blood fills the ventricles
- Stiff heart muscle can’t relax normally
