Chapter 20: The heart Flashcards
Location of the heart
located in the mediastinum
What does the pericardium consist of
- superficial fibrous pericardium
- deeper serous pericardium
Fibrous pericardium
- has one layer
- composed of tough, inelastic dense irregular connective tissue
Fibrous pericardium function
- prevents overstretching of the heart
- provides protection
- anchors the heart to the mediastinum
- Apex of the heart is anchored to the diaphragm
Serous pericardium
- has 2 layers
- parietal pericardium
- visceral pericardium
The parietal and visceral pericardium is separated by
the pericardial cavity, a fluid filled space
- reduces friction between the layers when the heart moves
Layers of the heart wall
- epicardium (visceral layer)
- myocardium (muscle layer)
- endocardium (inner most layer)
Pericarditis
- inflammation of the pericardium
- Acute pericarditis: sudden, no known cause, may be linked to viral infection
- Chronic pericarditis: build up of fluid around the pericardium
Myocarditis
- inflammation of the myocardium, usually complication of viral infection
Endocarditis
- inflammation of the endocardium
- typically due to bacteria and involves heart valves
Chambers of the heart
- 2 atria (single is atrium)
- 2 ventricles
Coronary sinus
major coronary vein located in the rear section of the heart
Right atrium
receives blood from the superior and inferior vena cava and the coronary sinus
Right ventricle
receives blood from the right atrium and sends blood to the lungs through the pulmonary valve –> pulmonary trunk –> pulmonary artery
Left atrium
receives blood from the pulmonary veins
- brings oxygenated blood from the lungs
Left ventricle
receives blood from the left atrium through the left atrioventricular valve
- sends blood all over the body
The left ventricle is much thicker than that if the right ventricle because…
the left ventricle has to pump blood to the rest of the body
Fibrous skeleton of the heart
- 4 dense connective tissue rings that surround the valves of the heart
- forms the foundation in which the heart valves attach
- serves as a point of insertion for cardiac muscle bundles
- prevents overstretching of the heart as blood passes through them
- acts as an electrical insulator between the atria and ventricles
What do the valves of the heart prevent
- they open and close in response to pressure changes as the heart contracts and relaxes
- right and left atrioventricular valves prevent backflow from ventricles into the atria
- right and left semilunar valves prevent backflow from the arteries to the ventricles
Chordae tendineae
- heart strings
- connect valves to papillary muscles
- relaxed when valves are open
- when the valves close heart strings become taught
Damage to the chordae tendineae can lead to
heart problems
Coronary circulation
- blood flows through coronary arteries to deliver oxygenated blood to the myocardium
- the arteries branch from the ascending aorta
- coronary veins remove CO2 and waste
- coronary vein branches converge to the coronary sinus
Myocardial ischemia
- reduced blood flow to the myocardium
- can cause hypoxia and angina pectoris, and pain in the neck, chin, left arm and elbow
Myocardial infarction
- heart attack
- death of tissues due to interrupted oxygen supply
Intercalated discs show
borders of cardiac muscle cells
What type of cardiac cells are self excitable
- autorythmic fibers are self excitable
- not all cardiac myocytes are self excitable
The heart does not need…
nerve impulses however the brain can still send impulses to slow down or speed up the heart
What do autorhythmic fibers do
repeatedly generate spontaneous action potentials that then trigger heart contractions
Originating heart rhythm comes from
SA node
- natural pacemaker
SA node and AV node
SA node:
- generates an electrical signal that causes the atria (upper chambers) to contract
AV node:
- the electrical signal then passes through the AV node causing the ventricles to contract
What is considered the pacemaker of the heart
SA node
The AV node has less
gap junctions therefore the electrical signal is delayed
Artificial pacemakers
- device that sends out small electrical currents to stimulate the heart to contract
- connected to 1-2 flexible leads threaded through superior vena cava and champers of the heart
What can influence the heart rate and force of contraction
signals from the nervous system and hormones like epinephrine can modify heart rate but they do not set the fundamental rhythm
What happens after a heart transplant
you no longer have nerve control over the heart but still have hormonal control
- the vagus nerve of the nervous system helps to slow the heart down when needed normally but after a heart transplant the heart rate remains the same as the SA node sets it
Action potential in a ventricular fiber
- rapid depolarization: influx of na
- Plateau: maintained depolarization
- Repolarization
Cardiac muscle generates ATP via
anaerobic cellular respiration and creatine phosphate
Cardiac muscle cannot do
wave summation because we dont need stronger contractions, we need the same rate
ECG
recording of the electrical changes that accompany each heart beat
What does the cardiac cycle consist of
contraction (systole) and relaxation (diastole) of both atria rapidly followed by systole and diastole of the ventricles
Events of one heart beat
- electrical events: PQRST wave
- Pressure changes: BP
- Heart Sounds
- Volume changes
- Mechanical events
Electrical events of a heart beat explained
- P wave: precedes atrial systole and the electrical signal travels towards the ventricles
- QRS wave: directly precedes and turns on muscles of ventricles (before ventricular systole)
T wave: precedes relaxation of ventricles and atria
Which wave is depolarization and which wave is repolarization
P wave is depolarization
T wave is repolarization
Repolarization meaning
resetting the electrochemical gradients of the cell to prepare for a new action potential
why is there a delay in ventricular contraction
AV node has less fibers and gap junctions
Heart sounds
S1: Av valves slam shut
S2: semilunar valves slam shut
S3: ventricular filling: turbulence
S4: sound of blood turbulence due to atrial contraction and blood going from atria to ventricles
Volume changes: isometric volume
volume doesn’t change because the 4 valves are closed for a brief second
Volume changes: ventricular systole
volume decreases during ventricular systole
In the relaxation period the volume starts to go…
up as the atria fill up
Mechanical events of a heart beat
- atrial contraction
- isovolumetric contraction
- ventricular ejection
- isovolumetric relaxation
- ventricular filling
What happens during isovolumetric relaxation:
pressure in the ventricles goes down as the heart relaxaes.
- All 4 valves close; as the heart relaxes, the negative pressure causes the valves to close. Eventually the AV valves open with the pressure.
In order to fill the ventricles we dont need
atrial systole however it helps to further push the blood into the ventricles
Dicrotic wave:
second upstroke upon closing of the aortic valve
Ventricular pressure rises during
atrial and ventricular systole
atrial pressure rises
slightly during atrial systole and then slightly during ventricular systole to close the AV valve shut
Cardiac output
volume of blood ejected from the left or right ventricle into the aorta or pulmonary trunk each minute
Stroke volume
amount of blood pumped out of the ventricle in one beat
Athletes have a higher stroke volume which leads to
decreased hr
What 3 factors regulate stroke volume
- Preload
- Contractility
- Afterload
Preload
- how much the ventricles can fill
- the more the ventricles, the higher the stroke volume
Who would have a higher preload and stroke volume
people with a low resting hr because they have a longer duration of ventricular diastole
Contractility
- affected by Ca+
- it is the strength of the contraction at any given preload
- contractility is increased or decreased by positive inotropic agents
Afterload
- pressure in the aorta and the pulmonary trunk
- the pressure in the aorta and pulmonary trunk to open the semilunar valves
The lower the afterload
the higher the stroke volume
What conditions can increase afterload and therefore decrease stroke volume
- hypertension, atherosclerosis
Intra-aortic balloon pump
- catheter inserted through groin
- balloon inflates and pushes blood both towards heart and peripheral tissues
- the balloon is then deflated rapidly before next ventricular systole
Ventricular assist device
- mechanical pump helps a weakened ventricle pump
- may be used while waiting for heart transplant
- creates a detour
Some people with VADs dont have
pulses
Both ventricles ventricle assist pump is called
biventricular device
Cardiomyoplasty
- a large piece of the patients own skeletal muscle (left latissmus dorsi) is partially freed from connective tissue attachments and wrapped around the heart. this leaves the blood and nerve supply intact
Skeletal muscle assist device
a piece of patients own skeletal muscle is used to fashion a pouch inserted between the heart and the aorta.
- the functions as a booster heart. this stimulates the muscles motor neurons to elicit contraction
fetal blood flow
- 2 umbilical arteries carry deoxygenated blood from the fetus to placenta
- 1 umbilical vein carries oxygen and nutrients rich blood from the placenta to the fetus
- the blood passes from the right atrium to the left via the foramen ovale
- some blood enters the right ventricle and foes straight to the aorta via the ductus arteriosus
