Lecture 10 - Cardiovascular 3 The Heart Flashcards
Where is heart located
In mediastinum
How does heart sit in chest
2/3rds to the left
What is approximately size of heart
Vary with body size
About 310g male and 225g female
About two fist clench together
What is a survivable birth defect re: location of heart
Right sided heart - 1 per 200 rats
Where is Apex of heart
Bottom left side
What are 2 types of pericardium
Fibrous and serous
What is structure is fibrous pericardium
Tough, loose fitting inextensible sac
What is structure of serous pericardium
- Parietal layer lies inside the fibrous pericardium
- visceral layer (epicardium) adheres to the outside of the heart
- pericardial space with pericardial fluid separates the two
What to heart covering protect against
Friction
What are the three layer distinct layers that make up wall of the heart
Epicardium
Myocardium
Endocardium
What is epicardium
Outer layer of heart
Visceral layer of serous pericardium
What is myocardium
Thick, contractile middle layer of heart wall
- compresses the heart cavities and the blood within them with great force
What is endocardium
Delicate inner layer of endothelial tissue
How is heart divided into right and left
By the septum ( ventricles separated by inter ventricular septum)
How many chambers are there
4
What are receiving chambers
Atria because they receive blood from veins
Where are atria
Top of heart superior to the ventricles
How to stir receive and push blood
Relax to receive and contract to push
Is myocardial wall of atria thick and why
No because they dont have to move blood far ; just sending into ventricles
What is article of heart
Earlike flap protruding from each atrium
What are the pumping chambers
Two lower chambers which are the ventricles that push blood into larger networks of vessels
Describe ventricle myocardium
It is thicker than atria’s because great force must be generated to pump blood a large distance;
- myocardium of left ventricle thicker than right as must pump blood much farther
What are the valves of the heart
Mechanical devices that permit the flow of blood in one direction only
What do atrioventricular (AV) valves do
- prevent blood from flowing back into the atrium from the ventricles when the ventricle contract
What is tricuspid valve
Its is atrioventricular valve of R side of the heart
- has 3 flaps of endocardium that are attached to papillary muscles by chordae tendineae
What is bicuspid valve
Also called mitral valve
- L side of heart
- only two flaps that attach to papillary muscles by chordae tendineae
What are semi lunar valves
Half moon shaped flaps growing out from lining of the pulmonary artery and aorta
- prevent blood from flowing back into ventricles from aorta or pulmonary artery
What is pulmonary valve
The pulmonary semi lunar valve at entrance of pulmonary artery
What is aortic valve
Valve at entrance of the aorta
- aortic semi lunar valve
What is skeletal structure of heart
Set of connecting rings that serve as a semi rigid support for the heart valves and the attachment of cardiac muscle of myocardium
- serves as electrical barrier between myocardium of the atrium and that of ventricles
What is coronary circulation
The blood flow to supply the cardiac tissue of the heart with nutrients and remove waste
Where do ventricles receive blood from
From left LCA and right RCA coronary arteries
Where do atria receive blood from
Small branch of coronary artery
Where does majority of coronary blood flow go
To left ventricle
What % of people have a dominant RCA, LCA or neither
RBC 50%
LCA 20%
NEITHER 30%
What are anastomosis
They are extra branches arteries make so they can bypass blocks if needed to keep blood flowing
Do coronary arteries anastomose
Yes
Where do coronary veins drain into
Coronary sinus into right atrium
Veins follow arteries side by side
Structure of cardiac muscle
Striated muscle cells, ratified, involuntary contractions
What links cardiac muscle cells
Intercalated discs which have:
Desmosomes (link cells together
Gap junctions ( permit muscle action potential or electrical signal to pass from 1 myocyte to another inside the motor unit)
Why are cardiac myocytes and skeletal myocytes similar
They have same mechanism of contraction
- actin and myosin
Function of cardiac muscles
Intercalsted discs form a solid connection so that contraction generated acts as if it came from a single source
- called functional syncytium
How are units electrically isolated
Through CT
What are main components of the conduction system of the heart (5)
- Sinoatrial (SA) node
- Atrioventricular (AV) node
- Atrioventricular (AV) bundle (bundle of His)
- R & L Bundle branches
- Subendocardial branches (Purkinje fibres)
What is special about conduction system structures
More highly specialized then ordinary cardiac muscle tissue and permit only rapid conduction of an action potential through the heart
Another name for SA node
Pacemaker
What is function of SA node
Initiates each heart beat and sets its pace
How does SA node work
Specialized pacemaker cells in the node possess an intrinsic rhythm
- after being generated by the SA node, each impulse travels through the muscle fibers of both atria, which begin to contract
What happens after atria begin to contract
- as action potential enters the AV node from the right atrium its conduction slows to allow complete contraction of both atrial chambers before the impulses reach the ventricles
Where do the impulses go after the AV node
Conduction velocity increases as the impulse is relayed through the AV bundle into the ventricles
Where do impulses go after AV bundle
Right and left branches of the bundle fibers and subendocardial branches (purkinje fibers) conduct the impulses throughout the muscles of both ventricles, stimulating them to contract almost simultaneously
What is autonomic nervous system influence on conduction system of the heart
Composed of modified cardiac muscle, it generates and distributes the heart’s own rhythmic contractions
- can be regulated by afferent nerves
What is autonomic nervous system influence on cardiac plexuses
Located near the arch of the aorta
composed of sympathetic and parasympathetic fibers
- fibers from cardiac plexus accompany R and L coronary arteries to enter the heart
- most fibers end in SA node but some in AV node and atrial myocardium (the nodes are hearts pacemaker)
What is autonomic nervous system influence on sympathetic nerves
Accelerator nerves
What is autonomic nervous system influence on vagus fibers
Inhibitory, or depressor nerves
What does autonomic nervous system do
Innervates the heart, modifies activites
Where can sympathetic nervous system impulses come from
Medulla (cardioacceleration)
Sympathetic neurons
What is sympathetic nervous system hormonal mechanism to increase cardiac frequency
The release of noradrenaline
Where can parasympathetic nervous system send impulses from
Medulla (cardioihibitory neurons )
Vagus nerve
What is parasympathetic nervous system hormonal mechanism to decrease cardiac frequency
Release acetylcholine
What is autorhythm
Heart beats at 75 beats / min in an autonomic fashion without any nerve impulses
What is action potential
Essentially a nerve impulse or electrical signal traveling through a cell
Why do cells need to receive action potential do contract
As it causes them to depolorize
What is resting membrane potential for most cells
-70mV
What happens when get a signal from nerve
Protein “gates” on cell membrane open allowing ions into cell
- effectively change electrical charge inside and outside the cell (depolarization)
What is repolarization phase of action potential
After all Na+ ions from outside go into cell the K+ ions that were in cell go out
- charge will rebalance = repolarization
Do cells always overshoot action potential repolarization
Yes but balance back out
Depolarization
Contraction
- influx of Na+ ions
- rapidly increasing membrane potential
- cell has been depolarized and the nerve impulse is propagated forward
Repolarization
Relaxation
- movement of K+ ions out of the cell
- rapidly decreasing membrane potential
- cell has been repolarized and the nerve impulse finished
Hyperpolarization
- overshoot during the movement of K+ out and Na+ back in using sodium potassium pump
What is ECG /EKG
Electrocardiograms
- recording of the electric current during the cardiac cycle
- does not record function of heart just the electrical impulses in heart
How is ECG done
Use electrodes placed at various sites: legs, arms, chest
What is 4 lead
Limb leads
- used to gather basic info regarding electrical conduction as it travels through the heart
What is 12 lead
- used to assist with identification of myocardial infarctions and their possible location within the heart
What are the 3 distinguishable waves of ECG
P- wave
QRS complex
T-wave
What occurs in P wave
Lasts about 0.08s
- atrial depolarization that goes from the sinoatrial node and throughout the atria
- 0.1s after the beginning of P wave the atria contracts
What happens in P-R interval
Lasts about 0.16s
- delay between the start of the atrial contractions and the start of ventricular contractions
- measures time necessary for the action potential to go throughout the atrioventricular node, atrioventricular bundle and the rest of the conduction system
What happens in QRS complex
Lasts about 0.08s
- ventricular depolarization that goes throughout the ventricles
- then ventricles start to contract at the beginning of the QRS complex
What is the T wave
Lasts about 0.16s
- ventricular repolarization; produced immediately before the ventricular fibers relax
- it is possible to perceive the repolarization of the atria but it is ordinarily INVISIBLE because of the superimposed QRS complex
What is S-T segment
End of s wave and the start of T wave
- period where the fibers of the ventricles are depolarized
What is Q-T interval
Lasts about 0.38s
-period from ventricular depolarization up to ventricular repolarization
When does arterial pressure vary
As ventricle is contracting or relaxing
Is the arterial pressure in left and right ventricles and atria the same
No
- right ventricle has the lowest pressure because it has thinnest walls (even though right atrium is smaller)
What is systole
Phase of contraction
What is diastole
Phase of relaxation
There is both a _______ and a ______ for the atria and ventricles
Systole and diastole
How long is cardiac cycle normally and how many bpm approx
0.8s or 75bpm
Breakdown the 0.8s of cardiac cycle
Contraction
• atrial systole 0.1s
• ventricular systole 0.3s
Relaxation
• atrial systole 0.3s
• ventricular diastole 0.1s
What is isovolumetric diastole
Early diastole
- short phase following T wave
- ventricles relaxes; decrease in ventricular pressure
- blood of aorta and pulmonary trunk backflow towards the ventricles closing their semilunar valves
- ventricles are entirely closed (all 4 valves closed)
What is phase of ventricular filling
Mid to late diastole
- low pressure in atria and ventricles, then increases in atria
- circulating blood passively flows into atria and ventricles through open atrioventricular valves
- aortic and pulmonary valves are closed during the relaxation period
- when ventricles about 70% full cusps of atrioventricular valves begin to close
- depolarization (systole) of atria (p-wave) results in contraction and blood is compressed
- pressure in atria increases and residual blood (30% left over) is ejected into the ventricles
What is ventricular systole
- atria relaxes (atrial diastole)& ventricles depolarize (systole) ( QRS complex)
- pressure in ventricles increases leading to AV closure
- phase of isovolumetric contraction: during a fraction of a second, all valves are closed and the blood volume is constant
- pressure in the ventricles continues to increase until it exceeds the pressure of the large arteries of ventricles
- aortic and pulmonary valves open; the blood is exposed: ventricular ejection phase
What produces heart sounds
Principally produced by the closure of valves
What are the 2 normal heart sounds
1st Lub is loud and long
- from closure of AV valves and is start of ventricular systole
2nd dup is sharp and short
- from closure of aortic and pulmonary valves and is start of ventricular diastole
What is refractory period
It is the PAUSE after the last sound
Making fundamental rhythm
Lub-dub, pause, lub-dub, pause
