Cardiac Structure Flashcards
What is the innermost layer of the heart ?
- endocardium
- lines heart chambers + is coninuous with blood vessels
What is the middle layer of the heart ?
- myocardium
- thick + muscular layer = responsible for pumping blood
What is another name for the epicardium + where is it located ?
- epicardium is also called visceral pericardium
- outermost layer of the heart + part of serous membrane
What is the pericardial cavity ?
- space between the visceral + parietal pericardium
- fluid-filled to reduce friction
What are the 2 layers of the serous pericardium + what are there roles ?
- visceral pericardium (epicardium) = lines surface of the heart
- parietal pericardium = lines internal surface of fibrous pericardium
What does it mean that the heart tissue is “continuous with blood vessels”?
- endocardium (inner heart lining) is directly connected to the lining of the blood vessels
- ensuring smooth blood flow
Why is the myocardium of the left ventricle much thicker than the right ?
- left pumps blood to rest of the body
What supplies blood to the heart ?
- the coronary artery supplies oxygenated blood to the heart
Where do the coronary arteries branch off from ?
- coronary arteries branch off from aorta
- they branch into smaller vessels
How does coronary artery disease arise ?
- when coronary artery cannot deliver blood adequately often due to plaque in arterial walls
What is myocardial infarction ?
- blood supply to heart is completely blocked off so muscle dies
What are the functions of the pericardium ?
- protects and anchors the heart
- prevents overfilling of blood in heart
- allows for heart to work in friction-free environment
What is the pericardium + what 2 things is it composed of ?
- pericardium is double-walled sac around heart
Made of : - superficial fibrous pericardium
- deep two-layer serous pericardium (visceral + parietal )
What are the 2 circuits of the heart + what are there functions ?
- pulmonary circuit - blood to and from lungs
- systemic circuit - blood to and from rest of the body
Why are arteries considered as pressure vessels ?
- maintain high pressure to carry blood away from heart
Why are veins considered capacitance vessels ?
- can distend (expand) to match various blood volumes
What is the cardiac cycle ?
- electrical, pressure and volume changes that occur in functional heart between two heart beats
What is the diastolic phase ?
- myocardium is relaxing
- allows chambers to fill with blood
What is the systolic phase ?
- myocardium contracting
- pumps blood out the chambers
- systole = sounds like squeezing
What happens during atrial diastole ?
- atria are relaxed
• Blood flows passively from veins into the atria and into the ventricles (80% of blood flow).
• AV valves are open.
What happens during atrial systole ?
• Atria contract, increasing pressure.
• 20% of blood is pumped into ventricles.
• AV valves remain open.
What occurs during ventricular filling ?
• 80% of blood flows passively into ventricles.
• Atrial systole pumps the remaining 20% into the ventricles.
• AV valves remain open.
What occurs during ventricular systole ?
- AV valves close due to increased ventricular pressure, producing the “lubb” sound.
- Isovolumetric contraction phase = volume stays the same (see separate flashcard)
What is the 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
What occurs during ventricular diastole ?
- Ventricles relax; blood backflow, closes semilunar valves (“dubb”)
- Blood once again flowing into relaxed atria and passively into ventricles
What causes the ‘lub’ sound + where is it loudest ?
- closure of AV valves
- loudest at the cardiac apex
What causes the ‘dub’ sound + where is it the loudest ?
- closing of the SLV
- Loudest at the base of the heart
Where is the tricuspid valve located ?
- between right atrium + right ventricle
- has 3 cusps
Where is the bicuspid valve located ?
- between left atrium + left ventricles
- has 2 cusps
blood flow through the heart
deoxygenated blood:
- superior + inferior vena cava
- right atrium through
- tricuspid valve
- right ventricles
- pulmonary SLV
- pulmonary artery
- lungs
Oxygenated blood:
- pulmonary vein
- left atrium
- bicuspid valve
- left ventricle
- aortic SLV
- aorta
- body
Where is the aortic SLV located ?
- between left ventricle and aorta
Where is the pulmonary SLV located ?
- between right ventricle and pulmonary artery
What is the pulse ?
- surge of pressure in artery
What is tachycardia ?
- resting heart rate more than 100 bpm
- caused by stress, drugs, heart disease
What is bradycardia ?
- heart rate less than 60 bpm
- in sleep and endurance trained athelets
What are premature atrial contractions ?
- Occasional shortened intervals between one contraction and next (frequently occurs in healthy people)
What is the stroke volume ?
- volume of blood pumped by a ventricle per beat
What is the equation for calculating stroke volume ?
SV= end diastolic volume (EDV) - end systolic volume (ESV)
What is end diastolic volume (EDV) ?
- amount of blood in a ventricle at end of diastole
What is end systolic volume (ESV) ?
- amount of blood remaining in a ventricle after contraction
What is ejection fraction ?
% of EDV pumped by the ventricle
What is cardiac output + equation ?
- amount of blood pumped by each ventricle in one minute
CO = HR x SV
(ml/min) = (beats/min) x (ml/beat)
What factors affect heart rate ?
- autonomic innervation - ANS
- hormones eg. Adrenaline
What factors stroke volume ?
- EDV + ESV
What is blood pressure ?
- force exerted by blood against blood vessel walls
What role do baroreceptors play in blood pressure regulation?
- Baroreceptors detect changes in blood pressure
- increased pressure stretches the receptors - activating the vagus nerve
- triggers the parasympathetic system to lower blood pressure.
When is blood pressure highest and lowest during the cardiac cycle?
- Highest during ventricular systole (when the ventricles contract).
• Lowest during ventricular diastole (when the ventricles relax).
What factors increase blood pressure ?
- increased blood volume
- increased heart rate
- increased stroke volume
- increased blood viscosity
- increased peripheral resistance
What is preload ?
- tension applied before the muscle performs any work
- equal to EDV
- increasing in filling pressure (more blood entering the heart) = increased preload
What is afterload ?
- load that preloaded muscle has to work against
- resistance ventricles must overcome to circulate blood into arteries/aorta
- associated with ventricular wall stress after systolic ejection
- estimated using VWS = Pressure x radius / 2 (wall thickness)
How does preload affect cardiac output ?
- increased preload (more blood in ventricles) = increased cardiac output
What is the Frank-Starling mechanism ?
- increased venous return (blood returning to heart) increases EDV which increases preload
- preload is initial stretching of cardiac myocytes prior to contraction
- as myocytes stretch they generate more force so increased stroke volume (pump out more blood)
How does afterload affect cardiac output ?
- increased afterload = decreased cardiac output
- increased afterload (e.g., higher blood pressure or narrowed arteries) makes it harder for the heart to pump blood.
How does contractility affect cardiac output ?
- increased contractility = increased cardiac output
What is hypertension ?
- arterial pressure too high
- heart has to work harder
- left ventricle enlarges
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
What is renin and when is it secreted ?
- secreted by the kidney in response to reduced blood pressure or blood volume
What is angiotensin and how is it formed ?
- Renin converts Angiotensinogen —> Angiotensin I
What is role of Angiotensin Converting-Enzyme (ACE) ?
- converts Angiotensin I —> Angiotensin II
What are the actions of angiotensin II in regulating blood pressure ?
-
Intense vasoconstriction —> increases blood pressure
• release of Aldosterone from adrenal cortex -> promotes Na+ and H2O reabsorption in kidney —> cause increased blood volume
• Regulatory negative feedback on the release of Renin.
• CNS: Stimulate thirst in hypothalamus, stimulate sympathetic outflow - increases ADH secretion from pituitary gland more H20 absorption
What do ACE inhibitors do to RAAS pathway ?
- inhibit formation of angiotensin II
- decrease release of aldosterone
- so less Na+ + H20 reabsorbed
- so decreased blood volume = decreased blood pressure
What do ACE receptor blockers do ?
- Block angiotensin receptors on blood vessels and adrenal cortex
• Produce vasodilation and decrease the activity of aldosterone
