Session 1 - Dissection of ze Heart

Question 1

Where does the heart lie in situ?

Answer 1

The heart lies in the middle mediastinum

Question 2

What is the middle mediastinum?

Answer 2

The intervening region in the thoracic cavity between the right and left pleural cavities which are occupied by the lungs

Question 3

What does the middle mediastinum consist of?

Answer 3

The heart, it’s blood vessels and the roots of the aorta, superior and inferior vena cava and pulmonary vessels

Question 4

Give a more detailed description of where the heart sits in the chester

Answer 4

Posterior to the sternum and the lungs, anterior to the verterbral column, oesohphagus and trachea

Question 5

What are the two components of the pericardium?

Answer 5

Fibrous pericardium

Serous pericardium

Question 6

What is the structure of the pericardium?

Answer 6

A tough connective tissue outerlayer

Question 7

What is the function of the pericardium?

Answer 7

Helps to retain heart in position, due to its attachment to diaphragm and sternum

Tough sac limits cardiac distension

Question 8

What is the structure of the serosa?

Answer 8

Parietal layer: lines the inner surface of the fibrous pericardium
Visceral layer: adheres to the heart and forms its outer covering

Question 9

What is the function of the serosa?

Answer 9

Space between the parietal and visceral layer lubricates the heart and allows for the relatively uninhibited movement of the heart

Question 10

What is the clincal relevance of the the pericardium?

Answer 10

reflections of serous pericardium create the oblique and transverse pericardial sinuses. During a coronary bypass, a finger can be placed into the transverse sinus in order to separate arteries from the veins.

Question 11

What is the function of the phrenic nerve? Where does it originate?

Answer 11

The phrenic nerves, which innervate the diaphragm and originate from C3, C4 and C5, pass through the pericardium and also innervates it.

Question 12

What is the clinical relevance of the phrenic nerve?

Answer 12

C3 and C4 also innervate the shoulder, pain carried from the pericardium (pericarditis) can cause shoulder pain.

Question 13

Whip out a diagram of the heart and label the coronary arteries

Answer 13

Do it!

Question 14

Describe the course of blood in and out of the heart

Answer 14

IN

1. Blood enters the right atrium via the superior and inferior vena cavae as well as via the coronary sinus, which returns blood from the walls of the heart itself.
2. The left atrium receives blood from the four pulmonary veins

OUT

1. The aorta (ascending, arch and thoracic) receives oxygenated blood from the left ventricle for systemic circulation.
2. The pulmonary artery receives deoxygenated blood from the right ventricle for pulmonary circulation.

Question 15

Where is the heart situated on a subject?

Answer 15

Upper margin of the heart is level with the 3rd costal cartilage on the RHS of the sternum, and the 2nd intercostal space on the LHS of the sternum.
Lower margin of the heart is level with the 6th costal carilage on the RHS of the sternum and the 5th intercostal space on the LHS of the sternum.

Question 16

What does the right coronary artery do?

Answer 16

supplies the right atrium and ventricle and the SAN and AVN

Question 17

What does the left coronary artery do?

Answer 17

supplies the left atrium and ventricles and the septum, bundle of his and purkinje fibres.

Question 18

When do the coronary arteries fill?

Answer 18

Filled during diastole as semi-lunar valves are closed

Question 19

What does increased heart rate mean for coronary arteries and why?

Answer 19

Filled during diastole so increased heart rate > decreased blood flow to coronary arteries.

Question 20

What does accumulation of fluid in pericardial sac cause?

Answer 20

Compression of heart and decreased cardiac output

Question 21

Where does the right coronary artery originate from?

Answer 21

the right aortic sinus of the ascending aorta

Question 22

What is the path of the right coronary artery?

Answer 22

Moves anteriorly to the right and descends vertically in the coronary sulcus between the right atrium and ventricle

Question 23

What happens to right coronary artery at inferior margin of the heart?

Answer 23

it turns posteriorly and continues in the base of the heart where it divides to give several branches

Question 24

Where does the left coronary artery originate from?

Answer 24

Originates from the left aortic sinus of the ascending aorta

Question 25

What happens to left coronary artery?

Answer 25

While posterior to the pulmonary trunk it divides into two terminal branches

Question 26

What happens to the Left Anterior Descending branch of the coronary artery?

Answer 26

descends towards to the apex of the heart in the anterior interventricular sulcus

Question 27

What happens to the circumflex branch of the left coronary artery?

Answer 27

1.courses to the left in the coronary sulcus.
A large branch, the left marginal artery, usually arises from it and continues across the rounded obtuse margin of the heart.

Question 28

Where do the coronary arteries drain into?

Answer 28

The great cardiac vein and the coronary sinus

Question 29

Give process of muscle contraction

Answer 29

Stage 1 of contraction – Attachment
Rigor configuration: myosin head is tightly bound to actin molecule. In death, lack of ATP perpetuates this binding (rigor mortis).
Stage 2 of contraction – Release
ATP binds the myosin head causing it to uncouple from the actin filament.
Stage 3 of contraction – Bending
Hydrolysis of ATP causes the uncoupled myosin head to bend & advance a short distance (5nm)
Stage 4 of contraction – Force Generation
The myosin head binds weakly to the actin filament causing release of inorganic phosphate, which strengthens binding, and causes the ‘power stroke’ in which the myosin head returns to its former position.
Stage 5 of contraction – Reattachment
The myosin head binds tightly again and the cycle can repeat. Individual myosin heads attach and flex at different times causing movement.

Question 30

Give six features of cardiac muscle

Answer 30

Striations
Branching of muscle fibres
Centrally positioned nuclei (1 or 2 per cell)
Intercalated discs between muscle fibres for electrical and mechanical coupling
Gap junctions (for electrical coupling)
T tubules inline with Z line

Question 31

Give five features of skeletal muscle

Answer 31

Striated
T tubles in line with A-I  band junction
Multinucleated at periphery of cells
Voluntary control
Rapid, forceful

Question 32

Give five features of smooth muscle

Answer 32

Not striated, no sarcomeres, no t tubules
Cells are spindle shaped
Contraction is slower and more sustained
Responds to stimuli in form of never signals, hormones, drugs and blood gasses
Thick and thin filaments arranged diagonally in cell
Capable of being stretched

Question 33

Can cardiac muscle repair themselves? What occurs after damage?

Answer 33

Incapable of regeneration

Following damage, fibroblasts invade, divide and lay down scar tissue.

Question 34

What do purkinje fibres do?

Answer 34

transmit action potentials to the ventricles

Question 35

Describe structure of purkinje fibres

Answer 35

arge cells with:
Abundant glycogen
Sparse myofilaments
Extensive gap junction sites

Question 36

Why are purkinje fibres important?

Answer 36

They conduct action potentials rapidly compared to regular cardiac muscle. This rapid conduction enables the ventricles to contract in a synchronous manner.