Week 2 Flashcards
What is the fibrous pericardium
The outer layer of connective tissue surrounding the heart - made of collagen bundles
What is the serous pericardium
The inner membrane that folds under itself to form 2 layers
What are the two layers of the serous pericardium and what is the pericardial cavity
- Parietal layer: fused to the inner surface of the fibrous pericardium
- Visceral layer (epicardium): the inner layer closest to the heart wall
The pericardial cavity is found between the two layers and is filled with serous fluid (pericardial fluid) - it is a lubricant to decrease friction as the heart beats
What is the visceral pericardium (epicardium)
The outermost layer of the heart wall
Includes a thin layer of connective tissue containing fat deposits
what is the myocardium
it is the main component that makes up the wall of the heart
mostly cardiac muscle cells (myocytes). also contains specialized pacemaker cells and connective tissue
what is the endocardium
the innermost layer of the heart wall - faces the lumen of the heart chambers
made up of simple squamous epithelium and layers of connective tissue containing collage and elastic fibers
how many chambers does the heart consist of and what are they
the heart consists of 4 chambers - two atria and two ventricles
what do the atria do
the atria receive blood from veins and pump blood into the ventricles through one-way valves
what do the ventricles do
the ventricles eject blood into the arteries and carry blood through either systemic or pulmonary circuit
what are veins
blood vessels that bring blood TO the heart
what are arteries
blood vessels that carry blood AWAY from the heart
briefly describe the steps of the pulmonary circuit
- deoxygenated blood is pumped to the lungs by the right side of the heart
- gas exchange occurs between air in the alveoli and blood in the pulmonary capillaries
- oxygenated blood is returned to the left side of the heart
briefly describe the steps of the systemic circuit
- oxygenated blood is pumped to the body by the left side of the heart
- gas exchange occurs between tissues and blood in the systemic capillaries
- deoxygenated blood is returned to the right side of the heart
what are the major system veins of the heart
- superior vena cava
- inferior vena cava
what is the major systemic artery of the heart
aorta
what are the major vessels of pulmonary circulation of the heart
- right and left pulmonary arteries
- right and left pulmonary veins
what are the right and left ventricles separated by?
the interventricular septum
are the ventricles or the atria larger
the ventricles are larger than the atria and have thicker walls. this results in stronger pumps
compare the right and left ventricles
the right ventricle has a thin wall, and its chamber is crescent-shaped
the left ventricle has a thick wall, and its chamber is circular
which atrium is larger?
the right atrium is larger, thinner walled, and is more anterior
the left atrium is smaller, thicker walled, and more posterior
what are the valves between the atria and ventricles called and what are the sub-categories
the valves between the atria and ventricles are called the atrioventricular (AV) valves
this consists of:
- the tricuspid valve - between right atrium and right ventricle (contains 3 cusps)
- the bicuspid (mitral) valve - between left atrium and left ventricle (contains 2 cusps)
what are the valves between the ventricles and the pulmonary artery and aorta called and what are the sub-categories?
the valves between the ventricles and the pulmonary artery and aorta are called the semilunar valves
this consists of:
- the pulmonary valve - between right ventricle and pulmonary trunk
- the aortic valve - between the left ventricle and aorta
what do valves do
valves keep blood flowing in one direction
what does blood flow in response to?
blood flows in response to pressure gradients. as ventricles contract and relax, pressure in chambers changes, causing blood to push on valves and open or close them
what are most cells in the myocardium?
most of the cells are myocytes (~99%)
1% are pacemaker cells
describe myocytes in more detail
- contain contractile proteins (actin and myosin) that are organized in the same way as skeletal muscle fibers, producing striations
- they are branched muscle fibers with only 1 nucleus and fibers are are shorter + wider than skeletal muscle fibers
- each myocyte contains many mitochondria - high energy demands
- myocytes generate action potentials when membrane is depolarized to threshold
- they are the source of force-production (contraction) of the heart muscle
describe pacemaker cells in more detail
- they generate spontaneous, rhythmic action potentials
- the signal for myocyte contraction
- these cells do not contribute to the contractile force of the heart
what are intercalated discs?
intercalated discs are unique structures that join myocytes together and also connect pacemaker cells to contractile cells
what are intercalated discs made up of?
- desmosomes: hold cells together
- gap junctions: allow ions to pass rapidly from one cell to another
what do pacemaker cells do?
they set the pace of the heart
draw the pathway of the pacemaker cells and cardiac conduction
describe the 4 steps of pacemaker cell action potentials
- slow initial depolarization phase: more cations leak in than leak out through HCN channels in the plasma membrane, causing the membrane to slowly depolarize to threshold
- full depolarization phase: at the threshold, voltage-gated Ca2+ channels open, and Ca2+ enters the cell, causing the membrane to fully depolarize
- repolarization phase: Ca2+ channels close and voltage-gated K+ channels open, causing K+ outflow and membrane repolarization
- minimum potential phase: K+ channels remain open, and the membrane hyperpolarizes. This opens HCN channels and the cycle repeats
describe the 4 steps of cardiac electrophysiology - myocyte action potentials
- rapid depolarization phase: voltage-gated Na+ channels activate and Na+ enter, rapidly depolarizing the membrane
- initial repolarization phase: Na+ channels are inactivated and some K+ channels open; K+ leak out, causing a small initial repolarization
- plateau phase: Ca2+ channels open and Ca2+ enter as K+ exit, prolonging the depolarization
- repolarization phase: Na+ and Ca2+ channels close as K+ continue to exit, causing repolarization
what are the 3 reasons for the perfect sequence and synchrony of each heartbeat?
- the cardiac conduction system that focuses the electrical signal along a given path and allows for a delay at the AV node
- gap junctions that allow the electrical signal to spread quickly through myocytes
- the orientation of myocytes in the myocardium
what is an ECG (electrocardiogram)
- an important clinical tool for examining the function of the heart - gives us a picture of the electrical activity occurring in all cardiac muscle cells over a period of time
- recorded by placing electrodes on the surface of your skin
- electrical changes that are shown on the ECG reflect the depolarization and repolarization of cells in different areas of the heart
draw out an ECG graph and annotate its specific components
what is the cardiac cycle
- it is a cycle that describes the mechanical events of the heart
- each cardiac cycle consists of one period of contraction (systole) and one period of relaxation (diastole) for each chamber of the heart
when do atrial and ventricular systoles and diastoles occur in relation to each other and why
atrial and ventricular systoles and diastoles occur at different times as a result of AV node delay
what are the names of the 4 steps of the cardiac cycle
- ventricular filling phase
- isovolumetric contraction phase
- ventricular ejection phase
- isovolumetric relaxation phase
describe step 1 of the cardiac cycle - the ventricular filling phase
- the ventricles fill with blood and are in diastole
- atrioventricular (tricuspid and mitral) valves are open
- atrial systole occurs
- semilunar valves are closed
- blood flows down its pressure gradient from the atria into the ventricles
- most of the blood passively drains into the ventricles and then the atria contract to eject the remaining blood (atrial systole)
what is end-diastolic volume
the total amount of blood in the ventricles at the end of ventricular diastole
describe step 2 of the cardiac cycle - isovolumetric contraction phase
- ventricular systole begins
- AV and semilunar (aortic and pulmonary) valves close when enough pressure builds up in the ventricles
- atrial diastole begins
- isovolumetric because the pressure in the ventricles is not yet high enough to push open the semilunar valves
- ALL VALVES CLOSED DURING THIS PHASE
describe step 3 of the cardiac cycle - ventricular ejection phase
- ventricular systole continues
- AV valves are still closed
- atrial diastole continues
- pressure opens SL valves, and blood is ejected into the pulmonary artery and aorta
- at rest, approx 70 mL of blood is pumped for each ventricle
what is end-systolic volume
the amount of blood remaining in the ventricle at the end of ventricular ejection
at rest, this is about 50 mL
describe step 4 of the cardiac cycle - isovolumetric relaxation
- ventricular diastole begins
- AV valves are still closed
- atrial diastole continues
- SL valves close
- isovolumetric because blood is neither being ejected from nor entering into the ventricles
- volume briefly remains constant in the ventricles
- the pressure in the ventricles is still somewhat higher than in the atria, so AV valves remain closed at this point.
