Week 2

Question 1

What is the fibrous pericardium

Answer 1

The outer layer of connective tissue surrounding the heart - made of collagen bundles

Question 2

What is the serous pericardium

Answer 2

The inner membrane that folds under itself to form 2 layers

Question 3

What are the two layers of the serous pericardium and what is the pericardial cavity

Answer 3

1. Parietal layer: fused to the inner surface of the fibrous pericardium
2. 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

Question 4

What is the visceral pericardium (epicardium)

Answer 4

The outermost layer of the heart wall

Includes a thin layer of connective tissue containing fat deposits

Question 5

what is the myocardium

Answer 5

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

Question 6

what is the endocardium

Answer 6

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

Question 7

how many chambers does the heart consist of and what are they

Answer 7

the heart consists of 4 chambers - two atria and two ventricles

Question 8

what do the atria do

Answer 8

the atria receive blood from veins and pump blood into the ventricles through one-way valves

Question 9

what do the ventricles do

Answer 9

the ventricles eject blood into the arteries and carry blood through either systemic or pulmonary circuit

Question 10

what are veins

Answer 10

blood vessels that bring blood TO the heart

Question 11

what are arteries

Answer 11

blood vessels that carry blood AWAY from the heart

Question 12

briefly describe the steps of the pulmonary circuit

Answer 12

1. deoxygenated blood is pumped to the lungs by the right side of the heart
2. gas exchange occurs between air in the alveoli and blood in the pulmonary capillaries
3. oxygenated blood is returned to the left side of the heart

Question 13

briefly describe the steps of the systemic circuit

Answer 13

1. oxygenated blood is pumped to the body by the left side of the heart
2. gas exchange occurs between tissues and blood in the systemic capillaries
3. deoxygenated blood is returned to the right side of the heart

Question 14

what are the major system veins of the heart

Answer 14

• superior vena cava
• inferior vena cava

Question 15

what is the major systemic artery of the heart

Answer 15

aorta

Question 16

what are the major vessels of pulmonary circulation of the heart

Answer 16

• right and left pulmonary arteries
• right and left pulmonary veins

Question 17

what are the right and left ventricles separated by?

Answer 17

the interventricular septum

Question 18

are the ventricles or the atria larger

Answer 18

the ventricles are larger than the atria and have thicker walls. this results in stronger pumps

Question 19

compare the right and left ventricles

Answer 19

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

Question 19

which atrium is larger?

Answer 19

the right atrium is larger, thinner walled, and is more anterior

the left atrium is smaller, thicker walled, and more posterior

Question 20

what are the valves between the atria and ventricles called and what are the sub-categories

Answer 20

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)

Question 21

what are the valves between the ventricles and the pulmonary artery and aorta called and what are the sub-categories?

Answer 21

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

Question 22

what do valves do

Answer 22

valves keep blood flowing in one direction

Question 23

what does blood flow in response to?

Answer 23

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

Question 24

what are most cells in the myocardium?

Answer 24

most of the cells are myocytes (~99%) 1% are pacemaker cells

Question 25

describe myocytes in more detail

Answer 25

- 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

Question 26

describe pacemaker cells in more detail

Answer 26

- they generate spontaneous, rhythmic action potentials - the signal for myocyte contraction - these cells do not contribute to the contractile force of the heart

Question 27

what are intercalated discs?

Answer 27

intercalated discs are unique structures that join myocytes together and also connect pacemaker cells to contractile cells

Question 28

what are intercalated discs made up of?

Answer 28

- desmosomes: hold cells together - gap junctions: allow ions to pass rapidly from one cell to another

Question 29

what do pacemaker cells do?

Answer 29

they set the pace of the heart

Question 30

draw the pathway of the pacemaker cells and cardiac conduction

Question 31

describe the 4 steps of pacemaker cell action potentials

Answer 31

1. 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 2. full depolarization phase: at the threshold, voltage-gated Ca2+ channels open, and Ca2+ enters the cell, causing the membrane to fully depolarize 3. repolarization phase: Ca2+ channels close and voltage-gated K+ channels open, causing K+ outflow and membrane repolarization 4. minimum potential phase: K+ channels remain open, and the membrane hyperpolarizes. This opens HCN channels and the cycle repeats

Question 32

describe the 4 steps of cardiac electrophysiology - myocyte action potentials

Answer 32

1. rapid depolarization phase: voltage-gated Na+ channels activate and Na+ enter, rapidly depolarizing the membrane 2. initial repolarization phase: Na+ channels are inactivated and some K+ channels open; K+ leak out, causing a small initial repolarization 3. plateau phase: Ca2+ channels open and Ca2+ enter as K+ exit, prolonging the depolarization 4. repolarization phase: Na+ and Ca2+ channels close as K+ continue to exit, causing repolarization

Question 33

what are the 3 reasons for the perfect sequence and synchrony of each heartbeat?

Answer 33

1. the cardiac conduction system that focuses the electrical signal along a given path and allows for a delay at the AV node 2. gap junctions that allow the electrical signal to spread quickly through myocytes 3. the orientation of myocytes in the myocardium

Question 34

what is an ECG (electrocardiogram)

Answer 34

- 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

Question 35

draw out an ECG graph and annotate its specific components

Question 36

what is the cardiac cycle

Answer 36

- 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

Question 37

when do atrial and ventricular systoles and diastoles occur in relation to each other and why

Answer 37

atrial and ventricular systoles and diastoles occur at different times as a result of AV node delay

Question 38

what are the names of the 4 steps of the cardiac cycle

Answer 38

1. ventricular filling phase 2. isovolumetric contraction phase 3. ventricular ejection phase 4. isovolumetric relaxation phase

Question 39

describe step 1 of the cardiac cycle - the ventricular filling phase

Answer 39

1. the ventricles fill with blood and are in diastole 2. atrioventricular (tricuspid and mitral) valves are open 3. atrial systole occurs 4. 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)

Question 40

what is end-diastolic volume

Answer 40

the total amount of blood in the ventricles at the end of ventricular diastole

Question 41

describe step 2 of the cardiac cycle - isovolumetric contraction phase

Answer 41

1. ventricular systole begins 2. AV and semilunar (aortic and pulmonary) valves close when enough pressure builds up in the ventricles 3. 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

Question 42

describe step 3 of the cardiac cycle - ventricular ejection phase

Answer 42

1. ventricular systole continues 2. AV valves are still closed 3. atrial diastole continues 4. 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

Question 43

what is end-systolic volume

Answer 43

the amount of blood remaining in the ventricle at the end of ventricular ejection at rest, this is about 50 mL

Question 44

describe step 4 of the cardiac cycle - isovolumetric relaxation

Answer 44

1. ventricular diastole begins 2. AV valves are still closed 3. atrial diastole continues 4. 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.