middle mediastinum

Question 1

What are the boundaries of the middle mediastinum

Answer 1

Anterior – anterior pericardium
Posterior – posterior mediastinum
Lateral – mediastinal pleura
Inferior – diaphragm
Superior - transverse thoracic plane (T4/5)
It’s the broadest part of the interpleural space

Question 2

what are the contents of the middle mediastinum

Answer 2

Heart and pericardium 
Ascending aorta
Pulmonary trunk and arteries 
Pulmonary veins 
Nerves

Question 3

what are the external features of the heart

Answer 3

Right and Left auricles (for extra blood to enter atrium)
atrioventricular groove (below right atrium)
inter ventricular groove

Question 4

what great vessels are in the middle mediastinum

Answer 4

ascending aorta
pulmonary trunk
pulmonary veins
vena cava

Question 5

how does blood leave the heart via the ascending aorta

Answer 5

via ascending aorta, aortic arch, descending thoracic aorta (posterior mediastinum) and descending abdominal aorta

Question 6

how does blood leave the heart via the pulmonary trunk

Answer 6

pulmonary trunk, branches into l and r pulmonary arteries and enter hilum/ root of lungs

Question 7

what makes up the right atrium

Answer 7

2 regions – sinus verarum (smooth walled) and pectinate muscle
SVC, IVC and coronary sinus feed into it
fossa ovalis
crista terminalis (division between two muscle types)

Question 8

what makes up the right atrium

Answer 8

fossa ovalis
auricle
openings of pulmonary veins

Question 9

what is seen in both ventricles

Answer 9

chord tendineae
papillary muscle
trabecular carneae (uneven to stop blood adhering to walls and aid contraction)
moderator band
outflow smooth walled for smooth blood flow

Question 10

what are the valves of the heart

Answer 10

Semilunar (pulmonary and aortic)

Atrioventricular (tricuspid and bicuspid)

Question 11

what makes up the bicuspid valve

Answer 11

an anterior and posterior cusp

Question 12

what makes up the tricuspid valve

Answer 12

an anterior, posterior and septal cusp

Question 13

what are cusps

Answer 13

leaflets attaching to chordae tendineae to attach to papillary muscles

Question 14

what cusps do semi lunar valves have

Answer 14

Pulmonary valve cusp
Left
Right 
anterior
Aortic valve cusp
Left 
Right 
Posterior

Question 15

what aortic cusps feed into which arteries (blood pockets)

Answer 15

Right coronary artery from right cusp and left to left

Question 16

what is the pericardium

Answer 16

3 layered sac which heart is suspended in
Attached to great vessels superiorly and diaphragm inferiorly
Influenced by movement of the great vessels, sternum and diaphragm
Phrenic nerve travels over pericardium

Question 17

what are the functions of the pericardium

Answer 17

Protect heart from overfilling (cardiac distension)

Retains heart in positions (pericardio-sternal ligaments)

Question 18

what are the layers of the pericardium

Answer 18

Serous (internal) with parietal and visceral (or epicardium) layers
Fibrous (external)
Pericardial cavity located between parietal and visceral pericardium, contains a small amount of serous fluid to allow for uninhibited movement

Question 19

what are pericardial sinuses

Answer 19

Where parietal and visceral layers of serous pericardium meet, the reflections form 2 sinuses

Question 20

what is the transverse sinus

Answer 20

located between outflow vessels of the heart and inflow vessels – can be used in surgery to clamp the outflow of blood from the heart

Question 21

what is the oblique sinus

Answer 21

located between pulmonary veins

A sinus is a sac/cavity in an organ or tissue

Question 22

where are the coronary arteries located

Answer 22

Coronary vessels located in the atrioventricular and interventricular grooves
Two main coronary arteries are right and left (from ascending aorta)

Question 23

what anastomoses are found in the coronary arteries

Answer 23

Functional (potential) anastomoses exist between the coronary artery branches
Eg end branches of anterior interventricular artery and posterior interventricular artery
These do not maintain substantial collateral circulation if major branches suddenly occluded

Question 24

what is coronary artery dominance

Answer 24

Dominance is defined by the coronary artery which gives rise to the posterior IV artery
67% right dominant and 15% left (where posterior IV artery branches from the circumflex artery)

Question 25

what is coronary artery variation

Answer 25

Variation in the coronary circulation is common
4% have an accessory CA (3rd artery from ascending aorta)
40% population the SA nodal branch comes of the circumflex

Question 26

what is the SA node

Answer 26

SA node location – close to crista terminalis at junction between SVC and right atrium
SA node initiates contraction, impulses spread through atrial wall to AV node via internodal tracts

Question 27

what is the AV node

Answer 27

AV node location – interatrial septum close to coronary sinus opening
Av node continues into AV bundle (of His) and divides in the interventricular septum to travel to left and right ventricles to conduct the impulse to the left and right purkinje fibres

Question 28

what is the fibrous skeleton

Answer 28

Framework of 4 fibrous rings of dense connective tissue
Provides attachment for AV and SL valves
Forms an electrical insulator between atria and ventricles

Question 29

how is the conducting system regulated

Answer 29

Innervation of the myocardium is regulated by the ANS
Nerves from the ANS destined for the heart enter the cardiac plexus
Parasympathetic fibres from the vagus nerve enter the cardiac plexus and travel to the SA node
Sympathetic fibres from the sympathetic trunk (levels T1-5) enter the cardiac plexus then travel to the SA node

Question 30

where is the cardiac plexi

Answer 30

superficial cardiac plexus on aorta above foramen ovale

deep cardiac plexus on bottom of trachea before it branches into each lung