Middle Mediastinum

Question 1

Boundaries

Answer 1

anterior: anterior pericardium
posterior: posterior pericardium
lateral: mediastinal pleura
inferior: diaphragm
superior: transverse thoracic plane T4/5

Question 2

External features of the heart

Answer 2

right and left auricle

atrioventricular groove and interventricular groove

Question 3

Atria

Answer 3

Right: 2 regions - sinus venarum (smooth walled) and pectinate muscle
blood enters from superior and inferior vena cava, and the coronary sinus
Left: oxygenated blood from superior and inferior pulmonary veins (2 veins from each side)

Question 4

Valves

Answer 4

semi-lunar: pulmonary - left, right, anterior; aortic - left, right, posterior
atrio-ventricular: bicuspid/mitral - anterior and posterior cusp; tricuspid - anterior, posterior and septal cusp

Question 5

Pericardium

Answer 5

3 layers: serous (parietal and visceral layer) and fibrous pericardium (external). Pericardial cavity located between parietal and visceral layer.
Influenced by movement of great vessels, sternum and diaphragm.
Protects heart from overfilling (cardiac distension) and retains heart in position (pericardio-sternal ligaments).

Question 6

Pericardial Sinuses

Answer 6

where parietal and visceral layers meet
Transverse sinus: located between outflow vessels of heart, and inflow vessels
Oblique sinus: located between pulmonary veins

Question 7

Anastamoses

Answer 7

functional (potential) anastamoses exist between the coronary artery branches
e.g. end branches of anterior interventricular artery with posterior interventricular artery.
these do not maintain substantial collateral circulation if major branch is occluded suddenly

Question 8

Coronary Artery Dominance

Answer 8

dominance defined by CA which gives rise to Posterior IV artery.
67% RCA dominant, 15% LCA dominant.
Posterior IV artery branches from circumflex artery

Question 9

Conduction of Nerve Impulses

Answer 9

SA node: close to crista terminalis at junction between SVC and right atrium.
AV node: interatrial septum close to coronary sinus opening

Question 10

Fibrous Skeleton

Answer 10

framework of 4 fibrous rings of dense connective tissue.
provides attachment for AV and semilunar valves.
forms electrical insulator between atria and ventricles.

Question 11

Regulation of Conducting System

Answer 11

Parasympathetic fibres from Vagal nerve enter cardiac plexus and travel to SA node.
Sympathetic fibres from sympathetic trunk levels T1-5 enter cardiac plexus, then travel to SA node.