Surface anatomy of mediastinum and heart Flashcards
1
Q
What is the mediastinum?
A
- Central compartment or median septum between two pleural cavities within thoracic cavity
- Highly mobile region in living subjects because it consists of mainly hollow visceral structures (air or fl
- Extends from the superior thoracic aperture to diaphragm inferiorly
2
Q
Subdivisions of mediastinum
A
Superior and inferior (anterior, middle, posterior)
3
Q
Contents of mediastinum
A
Oesophagus, trachea, great vessels, heart, pericardium, nerves, sympathetic chain, lymphatic vessels, thoracic ducts, lymph nodes
4
Q
Why is thoracic duct vulnerable during thoracic oesophageal surgery?
A
Variable course and difficulty with identification
5
Q
What happens to thymus with age?
A
It shrinks
6
Q
What happens to thoracic contents in supine position?
A
- Arch of the aorta lies superior to transverse thoracic plane
- Bifurcation of trachea is transected by transverse thoracic plane
- Central tendon of diaphragm (diaphragmatic surface of heart) lies at level of xiphisternal junction and vertebra T9
7
Q
What happens to thoracic contents in standing position?
A
- Arch of aorta is transected by the transverse thoracic plane
- Tracheal bifurcation lies inferior to transverse thoracic plane
- Central tendon of diaphragm (diaphragmatic surface of heart) may fall to level of middle of xiphoid process and T9-T10 intervertebral discs
8
Q
Possible causes for widened mediastinum
A
- Haemorrhage into mediastinum from lacerated great vessels
- Enlargement of mediastinal lymph nodes due to malignant lymphoma
- Hypertrophy of heart due to congestive heart failure
9
Q
What is the pericardium?
A
- A fibrous membrane covering heart and parts of great vessels
- A closed sac made of fibrous and serous pericardium
- Serous pericardium is made of parietal and visceral layers
10
Q
What are the two pericardial sinuses?
A
Transverse and oblique
11
Q
Receiving chambers
A
Right atrium and auricle, left atrium and auricle
12
Q
Discharging chambers
A
Right and left ventricles
13
Q
What is wall of heart made from?
A
Endocardium, myocardium, epicardium (visceral pericardium)
14
Q
External features of heart
A
- Apex of heart formed by inferolateral part of L ventricle, lies in 5th intercostal space about 9 cm from median plane
- Base of heart: formed by L (mainly) and R atria, received pulmonary veins at left atrial portion, received superior and inferior venae cavae in its right atrial portion
- Four surfaces: anterior (sternocostal) - RV, diaphragmatic (inferior) - L/RV, right pulmonary - RA, left pulmonary - LV
- Four borders: right (RA, between SVC and IVC), inferior (right and left ventricle), left (LV and L auricle), superior (R and L atria and auricles)
15
Q
4 borders of heart
A
- Superior border: from inferior border of 2nd left costal cartilage to superior border of 3rd right costal cartilage, 1-2cm from margin of sternum on each side
- Right border: from 3rd right costal cartilage to 6th right costal cartilage - slightly convex to the right, 1-2cm from margin of sternum on each side
- Inferior border: from inferior end of right border to a point in the 5th intercostal space close to midclavicular line - apex of heart/apex beat
- Left border: line connects left ends of superior and inferior borders
16
Q
Benefits of fibrous skeleton in chest
A
- Collagen forms four rings around orifices of cardiac valves
- Structural foundation of heart valves - keeps patent and prevents overstretching
- Anchors myocardium
- Acts as electrical insulator between atria and ventricles
17
Q
Characteristics of right atrium
A
- Sinus venarum (smooth thin part, from right sinus horn, receives opening of SVC, IVC and coronary sinus)
- Rough part - pectinate muscles (from primitive atrium)
- Right atrioventricular orifice
- Crista terminalis (sulcus terminalis externally - separates between smooth and rough parts)
- Opening of coronary sinus
- Interatrial septum
- Oval fossa (fossa ovalis) - remnant of oval foramen
18
Q
Characteristics of right ventricle
A
- Conus arteriosus or cordis (infundibulum)
- Trabecular carneae - irregular muscular ridges from proximal bulbus cordis
- Supraventricular crest
- Separates the trabeculated and smooth wall parts, part of bulbus cordis
- Right atrioventricular (tricuspid) orifice
- Tricuspid valve - cusps of tricuspid valve (anterior, posterior and septal)
- Tendinous cords (chordae tendineae)
- Papillary muscles (anterior, posterior, septal)
- Interventricular septum
- Septomarginal trabecula (moderator band) - transverses right ventricular chamber, carries part of right branch of AV bundle of His
- Pulmonary valve - semilunar cusps (anterior, right, left)
19
Q
Autonomic innervation of heart
A
- Located in medulla oblongata are cardioacceleratory (pressor centre) - sympathetic and cardioinhibitory (depressor centre) - parasympathetic
- Sympathetic fibres through cardiac plexus to SA and AV nodes, cardiac muscles and coronary arteries, increases rate and force of contractions
- Parasympathetic fibres through carduac plexus to SA and AV nodes, cardiac muscles and coronary arteries - slows heart rate
- Afferent sympathetic fibres go to T1/2 - T4, referred pain across chest and upper limb
- Afferent parasympathetic fibres run with vagus nerve and are concerned with cardiac reflexes (baroreceptor, aortic arch and carotid sinus reflexes for BP homeostasis)
20
Q
Landmarks of valves and vessels
A
- Valves are located deep to sternum - sounds best heard superficial to chamber or vessel into which blood has passed and in direct line with the valve in the direction of blood flow
- Pulmonary area: sternal end of 1st or 2nd left intercostal space
- Aortic area: sternal end of 1st or 2nd right intercostal soace
- Mitral area: near apex of heart in 5th left intercostal space
- Tricuspid area: sternal edge at level of 4th or 5th intercostal space right or left of the sternum
