A&P Chapter 19 Heart

Question 1

The only thing that moves blood is?

Answer 1

A Change in Pressure, blood moves from a high pressure to a low pressure. The heart plays a role in changing pressures.

Question 2

What are the two Circuits of the cardiopulmonary system?

Answer 2

The Pulmonary Circuit where CO2 filled blood leaves the heart and enters the lungs returning to the heart with O2.

The Systemic Circuit where O2 filled blood leaving the heart travels to every part of the body to deposit O2 and pick up CO2.

Question 3

Describe the Heart

Answer 3

It is a pump, approx. 250-300grams.

It is located in the MEDIASTINUM.

It is anterior to vertebrae and posterior to the sternum. The base of the heart begins at about the 2nd rib and the apex ends at about the 6th rib.

The heart is superior to the diaphragm and is surrounded by the lungs.

ALL VESSELS, NERVES, Ect…enter and leave the heart at the BASE.

Question 4

From Inner to Outer what are the layers of the heart?

Answer 4

Endocardium: a thin simple squamous epithelia.
Myocardium: the THICK layer of cardiac muscle.
Epicardium: the thin layer of dense irregular connective tissue.

Question 5

Which layer of the heart is the only one to contract?

Answer 5

The Myocardium

Question 6

Describe a Myocardiocyte

Answer 6

The are striated muscle cells with usually one nucleus but they can have two. They are much shorter than skeletal muscle cells and they are attached to one another by INTERCALATED DISCS which are made of SUPER STRONG DESMOSOME connections which hold the cells together tightly and GAP JUNCTIONS which allow ions and cell signaling molecules to travel between cells very quickly.

Question 7

What is the layer that surrounds the heart?

Answer 7

The Pericardium

Question 8

Describe the Serous Pericardium:

Answer 8

It is a double layer of connective tissue that helps to hold the heart in place and allows the heart to rotate at the apex with very little to no friction.

There is a VISCERAL layer which is the EPICARDIUM and surrounds the heart directly.

There is a PARIETAL layer which remains still when the heart beats and is attached to the structures around the heart.

The space between the layers is the PERICARDIAL CAVITY filled with a serous fluid comprised of phospholipids.

Question 9

Describe the Fibrous Pericardium

Answer 9

It is a much thicker layer of dense irregular connective tissue that surrounds the Serous Pericardium. It is very strong and if blood or something fills the pericardial cavity it can limit the ability of the heart to beat, expand and contract. This is the case with a Cardiac Tamponade

Question 10

What layer of the heart do the Coronary Arteries and the Cardiac Veins run in?

Answer 10

The Epicardium/Visceral Layer of the Serous Pericardium.

Question 11

What is an Anastomosis? What function do they serve? Why are they potentially important?

Answer 11

They are locations where two arteries or veins combine and flow into each other. This allows blood to flow back around to the other side of a blockage thus perfusing tissue, potentially preventing an MI.

Question 12

Where do the branches of the coronary arteries and cardiac veins travel?

Answer 12

They travel deep to the Epicardium into the Myocardium to supply capillary beds in the cardiac muscle tissue.

Question 13

How much Serous fluid is in the Pericardial Cavity at a given time?

Answer 13

3-5ml’s

Question 14

Where does the Coronary Sinus empty?

Answer 14

The Right Atrium

Question 15

What chamber of the heart pumps the largest volume of blood?

Answer 15

None: they all pump the same volume of blood.

Question 16

What is a Ventricular Septal Defect?

Answer 16

A hole most likely located in the thinnest part of the interventricular septum between the right and left ventricles.

Question 17

Where are there no valves controlling the flow of blood?

Answer 17

From the superior and inferior vena cavae in the Right Atrium.

From the pulmonary veins flowing into the Left atrium.

Question 18

What prevents the atrioventricular valves from inverting into the atria?

Answer 18

The cordae tendonae connected to the papillary muscles.

Question 19

Which valve in most older men leaks? What does leaky valves lead to?

Answer 19

The Left Atrioventricular Valve, it can lead to heart failure.

Question 20

Describe the cardiac conduction system starting with the SA Node through the Purkunjie fibers

Answer 20

The Sinoatrial Node depolarizes resulting in the depolarization of the Atria. The specialized cells in the SA node spontaneously depolarize and with the gap junctions between the cardiomyocytes will propagate the action potential to all the other cells in the atria.

The Atrioventricular Node has a slight delay before firing, once it does it sends the signal down the Atrioventricular Bundle (of His), from the Bundle of His it splits into the Bundle Branches before travelling down to the Purkunjie fibers. The depolarization of the Ventricles begins at the apex from the action potential generated by the Perkunjie fibers.

Question 21

Where is the only place where there are gap junctions in the cardiomyocytes between the atria and ventricles?

Answer 21

The atrioventricular bundle.

Question 22

Why does the action potential traveling down the Bundle branches NOT depolarize cardiomyocytes until it travels all the way to the Purkunjie fibers?

Answer 22

Because there are NO gap junctions between the cardiomyocytes that make the Bundle of His or the bundle branches, it is only down at the apex of the heart in the Purkunjie fibers do the cardiomyocytes of the Purkunjie fibers form gap junctions with the rest of the surrounding cardiomyocytes which allows the action potential to spread UP the heart towards the base pushing blood UP and into the Aorta and the Pulmonary Trunk.

Question 23

Where are there NO Gap junctions between cardiomyocytes in the heart?

Answer 23

Between the Atria and Ventricles EXCEPT at the Atrioventricular Bundle and along the Interventricular septum.

Question 24

Where would a block in the cardiac conduction system be fatal?

Answer 24

In the Atrioventricular Bundle

Question 25

If the Sinoatrial Node did not fire would you die? What would happen?

Answer 25

No this is known as a Nodal rhythm where the Atrioventricular node will fire on it's own. It isn't as efficient as when the Sinoatrial Node triggers the Atrioventricular node. If this happens the ventricals will contract but the Atria will NOT. This isn't fatal because the negative pressure in the ventricles will pull the blood from the atria into the ventricles.

Question 26

Give a brief description of how the flow of ions results in an action potential and a contraction in cardiac muscle.

Answer 26

Na+ ions flow into the cell until threshold is reached at which point the K+ channels open and begin allowing K+ out of the cell to begin repolarization. The action potential generated by the membrane voltage change travels across the sarcolemma down the T-Tubles to the Terminal Cisternae resulting in VOLTAGE gated Ca2+ channels on the Sarcoplasmic reticulum being opened flooding the inside of the cell with Ca2+. The Ca2+ binds with troponin which changes it's conformation resulting in the movement of the tropomyosin from the active sites on the actin myofilaments. This allows cross bridges to be formed and a contraction to occur.

Question 27

Contraction of the heart (or anyone of its chambers) is known as?

Answer 27

Systole

Question 28

Relaxation of the heart (or anyone of its chambers) is known as?

Answer 28

Diastole

Question 29

One systole followed by one diastole is one what?

Answer 29

Cardiac Cycle

Question 30

If someone refers to a systole or diastole of the heart and they don't specify any specific area of the heart where are they referring to?

Answer 30

The Left Ventricle

Question 31

Describe an EKG wave form, give the names of the waves and what is happening to the heart during each phase.

Answer 31

Step 1: Forms the P wave, the atria begin depolarizing. Step 2: Atrial depolarization is complete, the P wave is complete this is followed by a short flat line. Step 3: Ventricular depolarization begins at the apex and progresses superiorly WHILE the atria are repolarizing, this is the QRS complex. Step 4. Ventricular Depolarization is complete, this completes the QRS complex and is followed by a flat line. Step 5. Forms the T wave, the Ventricular Repolarization begins at the apex and progresses superiorly. Step 6. The T wave is complete and the Ventricles have repolarized and the cardiac cycle is complete.

Question 32

Why do you not see a P wave on a Nodal Rhythm?

Answer 32

The Sinoatrial node does not fire and thus the Atria do NOT contract so NO P wave is recorded on the ECG. The AV node takes over and the ventricles depolarize, contract and relax.

Question 33

What happens in Fibrillation? What does a Defibrillator do in this situation?

Answer 33

In Fibrillation the electrical signals are spreading in a random pattern all over the heart. No coordinated contraction occurs and the heart does not beat. A Defibrillator shocks the heart with enough voltage to reset ALL of the cardiac myocytes at once allowing the proper distribution of electrical signals to begin again.

Question 34

What is missing on the ECG in a heart block? Where is the problem at in the cardiac conduction system?

Answer 34

The QRS Complex and the T wave are absent from an ECG reading. The problem occurs at the Atrioventricular Bundle (of His) in which damage to the bundle is not allowing the electrical signal to flow down to the Purkunjie fibers and depolarize the Ventricles.

Question 35

The flow of blood through the heart is controlled by what?

Answer 35

Changes in pressure. The open and closing of valves depends entirely on the difference in pressure from one side to the other. Higher pressure will push a valve open or closed.

Question 36

What is Heart rate?

Answer 36

The Number of beats/min.

Question 37

What is Stroke Volume?

Answer 37

The volume of blood ejected from a ventricle during a single systole. Assume the Left ventricle unless specially told otherwise. Average stroke volume is approx. 70ml's.

Question 38

What is Cardiac Output? How do you calculate it?

Answer 38

Cardiac output is the volume of blood ejected by a ventricle in one minute. CO=HR X Stroke Volume.

Question 39

What is Cardiac Index?

Answer 39

The volume of blood pumped by a ventricle per minute per square meter of body surface.

Question 40

How can you change your cardiac output?

Answer 40

By increasing/decreasing the heart rate or the stroke volume. In reality increases/decreases in both occur at the same time.

Question 41

What is the Frank-Starling Law of Cardiac Contraction?

Answer 41

That your ventricles modify both heart rate and stroke volume on a beat by beat basis and that this depends on how much the cardiac muscle cells are stretched during the preceding diastole, which itself depends on the volume of blood in the chamber.