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PBL 8 > Heart anatomy and conduction > Flashcards

Heart anatomy and conduction Flashcards

1
Q

Label this diragram of the heart

A
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2
Q

What does the heart sit on?

A

Diraphragm - with 2/3s lying to the left of the midline

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3
Q

In what structure does the heart lie?

A

Mediastinum

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4
Q

What is the ‘pericardium’ and what does it do?

A

Membrane that surrounts and protects the heart

Confines heart to its position in mediastinum but allows movement for vigorous and rapid contraction

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5
Q

What are the 2 parts that the pericardium consist of?

A

Fibrous pericardium (superficial)

Serous pericardium (deep)

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6
Q

What does fibrous pericardium consist of?

A

tough, inelastic, dense irregular connective tissue

Its open end is fused to the connective tissues of the blood vessels entering and leaving the heart

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7
Q

What is the fucntion of the fibrous pericardium?

A

Prevents overstretching of the heart, provides protection, and anchors the heart in the mediastinum

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8
Q

What is the fibrous pericardium attached to?

A

Partially fused to the central tendon of the diaphragm

◦ Movement of the diaphragm, as in deep breathing, facilitates the movement of blood by the heart.

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9
Q

What is the Serous epicardium?

A

is a thinner, more delicate and forms a double layer around the heart.

‣ The outer parietal layer of the serous pericardium is fused to the fibrous pericardium.

‣ The inner visceral layer of the serous pericardium, also called the epicardium, adheres to the surface of the heart.

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10
Q

What is the function of the serous pericardium?

A

Between the parietal and visceral layers of the serous pericardium is a thin film of pericardial fluid in the pericardial cavity

◦ reduces friction between the layers of the serous pericardium as the heart moves.

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11
Q

What are the layers of the heart wall?

A

The wall of the heart consists of three layers:

Epicardium (external layer)

Myocardium (middle layer)

Endocardium (inner layer)

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12
Q

What is the epicardium?

A

Composed of two tissue layers.

‣ Visceral layer of the serous pericardium (outermost)

‣ Delicate fibroelastic tissue and adipose tissue.

◦ The adipose tissue predominates and becomes thickest over the ventricular surfaces, where it houses the major coronary and cardiac vessels of the heart.

Imparts a smooth, slippery texture to the outermost surface of the heart.

Contains blood vessels, lymphatics, and vessels that supply the myocardium.

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13
Q

What is the myocardium responsible for?

A

Responsible for the pumping action of the heart

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14
Q

What is the myocardium composed of?

A

Composed of cardiac muscle tissue.

It makes up approximately 95% of the heart

wall.

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15
Q

How are the cardiac muscle fibres organised?

A

The cardiac muscle fibres are organised in bundles that swirl diagonally around the heart and generate the strong pumping actions of the heart

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16
Q

What is the endocardium?

A

Thin layer of endothelium overlying a thin layer of connective tissue.

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17
Q

What is the purprose of the endocardium?

A

Provides a smooth lining for the chambers of the heart and covers the valves of the heart

The smooth endothelial lining minimises the surface friction as blood passes through the heart

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18
Q

What is the endocardium continuous with?

A

The endocardium is continuous with the endothelial lining of the large blood vessels attached to the heart

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19
Q

Name the chambers of the heart

A

The heart has four chambers.

‣ Atria (superior)

‣ Ventricles ( inferior)

Atria receive blood from veins

Ventricles eject the blood from the heart into arteries.

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20
Q

What is an auricle and where is it found?

A

On the anterior surface of each atrium is a wrinkled pouch-like structure called an auricle.

Each auricle slightly increases the capacity of an atrium so that it can hold a greater volume of blood.

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21
Q

What are sulci?

A

grooves on the surface of the heart that contain coronary blood vessels and variable amound of fat

Each sulcus marks the external boundary between two chambers of the heart

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22
Q

What marks the external boundary between the atria and ventricles?

A

The deep coronary sulcus encircles most of the heart and marks the external boundary between the atria and ventricles

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23
Q

What marks the marks the external boundary between the right and left ventricles?

A

The anterior interventricular sulcus is a shallow groove on the anterior surface of the heart that marks the external boundary between the right and left ventricles.

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24
Q

What marks the external boundary between the ventricles on the posterior aspect of the heart

A

posterior interventricular sulcus, which marks the external boundary between the ventricles on the posterior aspect of the heart.

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25
Q

What are the valves composed of?

A

dense connective tissue covered by endocardium

26
Q

Where does the right atrium receive blood from?

A

Receives blood from three veins:

Superior vena cava

Inferior vena cava

Coronary sinus

27
Q

Describe the structure of the right atrium?

A

The inside of the posterior wall is smooth

The inside of the anterior wall is rough

due to the presence of muscular ridges called pectinate muscles (also extend into the auricle)

28
Q

What is the partition between the right and left atrium called?

A

Between the right atrium and left atrium is a thin partition called the interatrial septum.

29
Q

What is the fossa ovalis?

A

the remnant of the foramen ovale (an opening in the interatrial septum of the foetal heart that normally closes soon after birth).

30
Q

What does the inside of the right ventricle contain?

A

series of ridges formed by raised bundles of cardiac muscle fibres called trabeculae carneae

31
Q

What are the cusps of valves connected to?

A

chordae tendineae

which are connected to cone-shaped trabeculae carneae called papillary muscles.

32
Q

where does the blood from the right ventricle go?

A

Blood passes from the right ventricle through the pulmonary valve into the pulmonary trunk, which divides intoright and left pulmonary arteries and carries blood to the lungs

33
Q

Where does the left atrium receive blood from?

A

It receives blood from the lungs through four pulmonary veins

34
Q

What is the texture of the inside of the left atrium?

A

The inside of the left atrium has a smooth posterior wall.

Because pectinate muscles are confined to the auricle of the left atrium, the anterior wall of the left atrium also is smooth.

35
Q

Where does the blood from the left ventricle go?

A

Blood passes from the left ventricle through the aortic valve (aortic semilunar valve) into the ascending aorta

36
Q

Where does some of the blood from the aorta go?

A

Some of the blood in the aorta flows into the coronary arteries, which

branch from the ascending aorta and carry blood to the heart wall.

37
Q

Describe the passage of blood through the aorta?

A

The remainder of the blood passes into the arch of the aorta and

descending aorta to the rest of the body.

38
Q

What is the ductus arteriosus?

A

During foetal life, a temporary blood vessel, called the ductus arteriosus, shunts blood from the pulmonary trunk into the aorta. Hence, only a small amount of blood enters the nonfunctioning foetal lungs.

‣ The ductus arteriosus normally closes shortly after birth, leaving a remnant known as the ligamentum arteriosum, which connects the arch of the aorta and pulmonary trunk.

39
Q

Why does the myocardium have its own supply of blood vessels?

A

Nutrients are not able to diffuse quickly enough from blood in the chambers of the heart to supply all the layers of cells that make up the heart wall

40
Q

How does blood flow work in the coronary arteries?

A

Coronary arteries branch from the ascending aorta and encircle the heart.

While the heart is contracting, little blood flows in the coronary arteries because they are squeezed shut.

When the heart relaxes, however, the high pressure of blood in the aorta propels blood through the coronary arteries, into capillaries, and then into coronary veins

41
Q

Where do the 2 coronary arteries branch from and what is their function?

A

The ascending aorta

Supply oxygenated blood to the heart to the myocardium

42
Q

Which coronary artery is inferior to the left auricle and what does it split into?

A

left coronary artery

divides into the anterior interventricular and
circumflex branches

43
Q

What does the anterior interventricular branch supply?

A

supplies both ventricles

44
Q

What does the circumflex branch supply?

A

supplies the left ventricle and the left atrium

45
Q

What does the right coronory artery supply?

A

supplies small branches to the right atrium

46
Q

What does the right coronary artery divide into?

A

divides into the posterior interventricular and marginal branches

47
Q

What does the posterior interventricular branch supply?

A

Both walls of the ventricles

48
Q

What does the marginal branch supply?

A

runs along the right margin of the heart - supplies the right ventricle.

49
Q

Define the term ‘anastomoses’

A

connections between 2 or more arteries that supply the same region

50
Q

Define the term ‘collateral circulation’

A

alternative roots for blood to reach destination as a result of anatomoses

51
Q

Where does most of the deoxygenated blood from the myocardium drain?

A

coronary sinus

52
Q

Where does the deoxygenated blood in the coronary sinus empty?

A

Right atrium

53
Q

Which vessels carry blood into the coronary sinus?

A

Great cardiac vein

middle cardiac vein

small cardiac vein

anterior cardiac veins

54
Q
A
55
Q

Describe the histology of Cardiac Muscle tissue in terms of: nucleus location, connection of fibres and mitochondria

A
  1. One centrally located nucleus
  2. Cardiac muscle fibres connect to beighbouring fibres by irregualr thickenings of the sarcolemma = intercalated discs
    • contain desmosomes - hold fibres together
    • gap junctions - alllow APs to conduct from one musce fibre to neighbour
      • Allows entire myocardium of atra or ventricles to contact as a single, coordinated unit
  3. Mitochondria are larger and more numerous
56
Q

What is the source of electrical activity for cardiac muscle fibres?

A

Autorhythmic fibres

57
Q

What are the 2 most important functions of these rare fibres?

A
  • Form the cardiac conduction system
  • Pacemaker
58
Q

Explain the sequence of the conduction system in the heart?

A
  1. Sinoatrial (SA) node cells trigger an action potential
  2. The action potential reaches the atrioventricular (AV) node. At the AV node, the action potential slows considerably as a result of various differences in cell structure in the AV node. This delay provides time for the atria to empty their blood into the ventricles.
  3. From the AV node, the action potential enters the atrioventricular (AV) bundle (bundle of His).
  4. After propagating along the AV bundle, the action potential enters both the right and left bundle branches. The bundle branches extend through the interventricular septum toward the apex of the heart.
  5. Finally, Purkinje fibres conduct the action potential beginning at the apex of the heart upward to the remainder of the ventricular myocardium. 

59
Q

What acts as the natural pacemaker of the heart?

A

SA node

60
Q

How does an action potential occur in a contractile fibre?

A
  1. Depolarisation

‣ Unlike autorhythmic fibres, contractile fibres have a stable resting membrane potential that is close to -90 mV.

‣ When an action potential causes sodium ion channels to open the Na+ flow down the electrochemical gradient, causing depolarisation.

‣ Na+ channels then close

  1. Plateau

‣ A period of maintained depolarisation.

‣ It is due in part to opening of voltage-gated slow Ca2+ channels

in the sarcolemma.

When these channels open, Ca2+ move from the interstitial fluid into the cytosol.

This inflow of Ca2+ causes even more Ca2+ to pour out of the sarcoplasmic reticulum into the cytosol.

‣ Several different types of voltage-gated K+ channels are also found in the sarcolemma of a contractile fibre.

◦ Just before the plateau phase begins, some of these K+ channels open, allowing potassium ions to leave the contractile fibre.

• Therefore, depolarisation is sustained during the plateau phase because Ca2+ inflow just balances K+ outflow.

  1. Repolarisation

‣ After a delay, additional voltage-gated K+ channels open.

‣ Outflow of K+ restores the negative resting membrane potential

(-90 mV).

‣ At the same time, the Ca2+ channels in the sarcolemma and the

sarcoplasmic reticulum close

61
Q
A

PBL 8 (3 decks)

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