The Card System 2 Flashcards
Cardiac Muscle
The myocardium consists of cardiac muscle fibers and is responsible for the hearts pumping action
Cardiac muscle fibers are:
- amitotic( do not regenerate)
- striated(sliding filament model of contraction)
- branched
The heart acts
As 1 functional syncytium through;
- structural connections at intercalated discs
- electrical connections are facilitated by gap junctions
The 2 types of cardiac muscle fibres
Contractile cells generate the contraction
Pacemaker cells don’t contract but spontaneously depolarize
Contractile cells
Make up the majority of the heart
The action potential is made up of 3 phases:
Depolarization: Na* channels open; Nat enters cell
• Plateau: both K+ and Ca2+ channels open; Ca2+ enters cells while K+ leaves cells
• Repolarization: Ca2+ channels close; K* channels remain open
True or False
Cardiac muscle have more mitochondria and depends less on a continual supply of oxygen than skeletal muscle
Cardiac muscle has more mitochondria (25-35% of cell volume) that afford resistance to fatigue.
Cardiac muscle depends more on a continual oxygen supply than skeletal muscle. Aerobic respiration requires oxygen, and the heart cannot function long without oxygen.
Pacemaker cells
Are autorhymic
- initiates the depolarization of the heart without the nervous system
/ enables the heart to contract in a sequential manner
How are pacemaker dells autorhythmic?
Due to unstable resting membrane potentials called pacemaker potentials
The 3 stages in a pacemaker action potential:
Pacemaker potential: unstable Nat channels open and lead to spontaneous depolarization
• Depolarization: Ca?+ channels open
• Repolarization: K* channels oper
Pacemaker cells cells are found in the myocardium
- Sinoatrial(SA) node depolarized at around 100 beats per minute
- found in the right atrium
- determines the heart rate - Atruoventicular(AV) node depolarizes at around 50 bpm
Cardiac Output(CO)
Is the blood volume pumped by the left or right ventricle each minute
Defined by:
Stroke volume(amount of blood per beat) or
Heart rate
Stroke volume
Stroke volume=End diastolic volume(EDV) - End Systolic Volume(ESV)
- EDV: blood collected in a ventricle during relaxation
- ESV: blood remaining in a ventricle after contraction
Stroke volume is influenced by
- Preload
- After load
- Contractility
Preload
Is the stretch of cardiac muscle before contraction
- the more blood returns to the heart, the greater preload, like filling up a water balloon
How does preload affect stroke volume?
the more the cardiac muscle is stretched (greater preload), more blood can be pumped out (greater stroke volume), to a certain extent.
• this is known as the Frank-Starling law
After load
Is the pressure to overcome by the ventricles to eject blood
- the higher the pressure in the aorta and pulmonary trunk, the higher the afterload
- it is the barrier to overcome
How does asteroid affect stroke volume?
A greater afterload makes it harder for the heart to pump out blood( lower stroke volume)
True or False
An increase in afterload can be caused by conditions such as hypertension (high blood pressure) and aortic stenosis (narrowing of the aortic valve).
True
Contractility
Is the force of a heart contraction
- determined by calcium availability and cross bridge formation
How does cobtractility affect stroke volume
increase in contractility increases stroke volume
If blood volume drops significantly from severe bleeding, the autonomic nervous system increases heart rate to maintain cardiac output
True
Heart rate(HR)
Is the number of cardiac cycles(beats) per minute
- normal resting heart rate in an adult is 60-100 beats per minute
- brachycardia<60 beats per min
- tachycardia>100 bpm
Heart rate is regulated extrinsicaly by
- the Autonomic nervous system
- hormones
What is the instrinsic regulator of the heart?
Pacemaker cells
Heart Rate:
The cardiac centers in the medulla have
Extrinsic control over heart rate:
Parasympathetic stimulation decreases heart rate
– dominates during the resting state
Sympathetic stimulation increases the heart rate and contraction factors
What is the expected heart rate immediately after being removed from a living body
100 bpm
What would happen if the vagus nerves to the heart were cut?
The heart rate would increase by about 25 bpm
Which hormones from the endoctine system have you learned about that affect heart rate?
- catecholamines increase heart rate and contractility.
• thyroid hormones from the thyroid gland increase heart rate.
• cortisol from the adrenal cortex during stress elevates heart rate and blood pressure.
Sthethoscope
Is a medical instrument for auscultating sounds produced by the body
- ranges from 20Hz-2000Hz
There are 2 sides of the fat piece
Bell: used for low freq sounds
Diaphragm: better for high freq sounds
What physiological sounds can we ausculate?
Blood pressure, lungs and the digestive system
Which heart sound(s) are the loudest/strongest of the 4 positions and why
The mitral valve as that has the highest blood pressure
