Thorax 3 - Mediastinum & Contents Flashcards
mediastinum; middle mediastinum; pericardium
what is the mediastinum?
part of the thoracic cavity - consists of all thoracic viscera except the lungs & associated pleural cavities
what are the anterior, posterior, superior, inferior & lateral borders of the mediastinum?
anterior - sternum & 1st-5th costal cartilages
posterior - T5-12 vertebral bodies
superior - superior thoracic aperture (jugular notch, clavicles, 1st rib, T1 vertebral body)
inferior - diaphragm
lateral - mediastinal parietal pleura
what divides the mediastinum into its superior & inferior subdivisions?
transverse thoracic plane - imaginary horizontal line at the level of the sternal angle (from 2nd rib to T4/5 IVD)
the transverse thoracic plane extends from WHAT anteriorly to WHAT posteriorly
from sternal angle
to T4/5
at what vertebral level the transverse thoracic plane?
T4/5
what are the divisions of the inferior mediastinum relative to WHAT structure?
anterior, middle, posterior - relative to the pericardial sac enclosing the heart
what part of the mediastinum holds the heart?
(inferior) middle mediastinum
structures within the (inferior) middle mediastinum? (5)
- heart & pericardial sac
- origins of the great vessels (ascending aorta, SVC, IVC, pulmonary vessels)
- phrenic nerve
- pericardiophrenic vessels
- main bronchi (left & right)
pericardiophrenic vessels are contained within what division of the mediastinum?
A: superior
B: anterior
C: middle
D: posterior
C: middle mediastinum
relationship of the middle mediastinum to the anterior mediastinum?
middle mediastinum is POSTERIOR to the anterior mediastinum
what is the pericardium?
double-walled, fibro-serous sac that encloses the heart and the roots of the great vessels
what are the pericardial layers of the heart?
- fibrous (outer)
- serous (inner) - consists of a visceral & parietal layer
what are the two layers of the serous pericardium?
visceral layer (epicardium)
parietal layer
which pericardial layer adheres closest to the heart?
A: fibrous pericardium
B: serous pericardium
C: visceral serous pericardium
D: parietal serous pericardium
C: visceral serous pericardium
between what two layers is the pericardial cavity located?
A: between the fibrous & parietal layer of serous pericardium
B: between the visceral & parietal layers of the serous pericardium
C: between the visceral layer of serous pericardium & heart wall
B: pericardial cavity is between the visceral & parietal layers of the serous pericardium
function of the fibrous pericardium?
prevents overdistension and excessive movement of the heart (as a tough dense connective layer)
how is the fibrous pericardium attached to surrounding structures? (anterior, superior, inferior, lateral attachments)
INFERIOR = attached to diaphragm’s central tendon via the pericardiophrenic ligament
SUPERIOR = fuses with tunica adventitia layer of the great vessels
ANTERIOR = connects to sternum via sternopericardial ligaments
LATERAL = in contact with the mediastinal pleura and phrenic nerves
inferior surface of the pericardium is attached to WHAT surface? what ligament aids with this?
inferior surface of the diaphragm is attached to the central tendon of diaphragm - via the pericardiophrenic ligament
what layer of the great vessels is the pericardium superiorly attached to?
tunica adventitia (outer) layer of the great vessels
how does the pericardium have attachments anteriorly?
attaches to sternum via sternopericardial ligaments
what is the pericardial cavity?
potential space between the parietal and visceral layers of the serous pericardium- contains serous pericardial fluid
what type of cells produce the serous pericardial fluid?
mesothelial cells
functions/purpose of the pericardial fluid?
- lubricates heart & reduces friction between heart and pericardium
- cushioning effect against external shocks
what nerve runs in close relation to the pericardium?
phrenic nerve - runs laterally along fibrous pericardium (provides sensory innervation)
what nerve provides sensory innervation to the fibrous pericardium?
phrenic nerve
describe the layers of the serous pericardium & the pericardial cavity
two layers - visceral layer & parietal layer
visceral layer adheres to the heart’s surface & reflects on itself at the roots of the great vessels to become the parietal layer, which is close to the fibrous pericardium
pericardial cavity in between the visceral & parietal layers, filled with 15-20ml of pericardial fluid
what is a pericardial effusion?
an accumulation of excess fluid in the pericardial cavity
common causes of a pericardial effusion? (3)
inflammation
infection
trauma/injury
which of these isn’t a symptom of a pericardial effusion?
A: disturbed heart rate
B: elevated blood pressure
C: heart compression
D: nausea & vomiting
D: nausea & vomiting
what serious complication can pericardial effusion lead to?
cardiac tamponade – compression of the heart restricting its function
what is cardiac tamponade?
excess fluid in the pericardial cavity compresses the heart, restricting its function
what is Beck’s triad?
classic set of three symptoms indicating cardiac tamponade:
1. hypotension
2. bulging neck veins
3. muffled heart sounds
why does hypotension occur in cardiac tamponade?
heart compression prevents proper heart filling - leads to reduced cardiac output & blood pressure
why do bulging neck veins occur in cardiac tamponade?
compressed heart cannot accept blood from the SVC - causes blood to back up into jugular veins
why do muffled heart sounds occur in cardiac tamponade?
fluid build-up in the pericardial cavity absorbs and dampens heart sounds
what sign/shape is commonly observed on a chest x-ray in patients with a large pericardial effusion?
‘water-bottle’ sign
what is pericarditis?
inflammation of the pericardium
common causes of pericarditis?
infection
autoimmune diseases
trauma
post-myocardial infarction
why does pericarditis cause referred shoulder pain?
phrenic nerve (C3-5) provides sensory innervation to pericardium - shares a dermatome with the shoulder
irritation of the pericardium can refer pain to the shoulder due to shared dermatomes
three layers of the heart wall (from outermost to innermost)?
- epicardium/ visceral layer of serous pericardium
- myocardium (cardiac muscle)
- endocardium
what are the two pericardial sinuses?
transverse sinus
oblique sinus
how are pericardial sinuses formed?
reflections of the serous pericardium around the roots of the great vessels
surgical significance of the transverse pericardial sinus?
identify transverse sinus by passing a finger through it - isolates the arterial & venous systems which can then be clamped during cardiac procedures
a surgeon passes their finger through the transverse sinus? where are the arterial & venous systems relative to the sinus?
arterial system posterior
venous system anterior
what is the oblique pericardial sinus?
blind-ended pouch posterior/behind the base of the heart
if you put your hands through the oblique sinus, what blood vessel will you encounter?
A: SVC
B: IVC
C: pulmonary artery
D: pulmonary veins
E: aorta
D: pulmonary veins
function of the oblique pericardial sinus?
provides space for the heart to expand during filling
which pericardial sinus has greater surgical significance?
transverse sinus is more surgically significant - allows for isolation of great vessels during cardiac procedures
