mediastinum Flashcards
1
Q
mediastinum
A
the region in the middle of the thorax that includes all contents of the thoracic cavity except the lungs and pleura
2
Q
mediastinum boundaries
A
thoracic inlet, superiorly
diaphram, inferiorly
3
Q
superior mediastinum
A
lies above the transverse thoracic plane
4
Q
inferior mediastinum
A
lies below this plane and is subdivided into 3 regions - anterior, middle, and posterior mediastina
5
Q
middle mediastinum
A
centrally located within the thoracic cavity and contains the pericardium, phrenic nerves, heart and roots of the great vessels
6
Q
pericardium
A
consists of a fibrous portion and a serous portion
7
Q
fibrous pericardium
A
tough and anchors the heart and great vessels by a number of attachments
anteriorly - attached to the posterior surface of the sternum by small sternopericardial ligaments
inferiorly - it is fused to the central tendon of the diaphragm
superiorly - it is continuous with the adventitia of the great vessels
8
Q
serous pericardium (parieta pericardium)
A
thin layers that lines the fibrous portion on the deep (inner surface)
9
Q
heart muscle
A
myocardium
10
Q
visceral pericardium/epicardium
A
a thin layer of serous pericardium that lines the mycocardium
11
Q
pericardial cavity
A
between parietal and visceral layers of serous pericardium
the space contains only a thin film of fluid that allows the 2 layers of serous pericardium to slide easily on each other when the heart contracts
12
Q
anatomical position of the pericardium
A
pericardium (and therefore the heart_ lies posterior to the sternum and the 2nd-6th costal cartilages; approximately 1/3 lies to the right of the midsternal line and 2/3 lies to the left
13
Q
oblique pericardial sinus
A
area if reflection between the veins and the base of the heart forms a cul-de-sac of the pericardial cavity
a hand placed under the heart’s apex and moved superiorly slips into the oblique pericardial sinus
14
Q
transverse pericardial sinus
A
the slit-like passageway of the pericardial cavity between the 2 sites of reflected serous pericardium
the sinus lies anterior to the superior vena cava and posterior to the aorta and pulmonary trunk so a finger placed in the transverse sinus separates the arteries and veins
15
Q
pericardial sinus development
A
during development, the longitudinal embryonic heart tube invaginates the double-layered pericardial sac (some-what like placing a hot dog in a hot dog bun); the primordial heart tube then “loops” ventrally, bringing the primordial arterial and venous ends of the heart together and creating the primordial transverse pericardial sinus between them; with the growth of the embryo, the veins expand and spread apart, inferiorly and laterally; the pericardium reflected around them forms the boundaries of the oblique pericardial sinus
16
Q
what supplies most arterial blood to the fibrous and parietal pericardia
A
pericardiacophrenic arteries
17
Q
pericardiacophrenic arteries
A
branches of the internal thoracic arteries
run with the phrenic nerves anterior to the roots of the lungs
18
Q
visceral pericardium (epicardium)
A
shares its arterial blood supply with the myocardium via the coronary arteries
19
Q
phrenic nerves
A
carry sensory fibers from the fibrous and parietal percardia
20
Q
anterior (sternocostal) heart surface
A
right ventricle
21
Q
left heart surface
A
left ventricle
22
Q
right heart surface
A
right atrium
23
Q
posterior heart surface (base)
A
left atrium
24
Q
inferir (diaphragamatic_ heart surface
A
left ventricle and a portion of the right ventricle
25
arterial supply of the heart
myocardium (heart muscle) receives its arterial blood supply from the most oxygenated blood in the body directly from the first 2 branches of the aorta, the right and left coronary arteries
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right coronary artery
passes between the right auricle and the pulmonary trunk to run along the coronary sulcus (atrioventricular sulcus)
gives off the sinuatrial nodal artery which supplies the SA node (part of the heart's conduction system)
gives off a small right marginal artery, which runs along the surface of the right ventricle
continues along the coronary sulcus providing blood to the right atrium
when it reaches the posterior interventricular sulcus it descends towards the apex of the heart as the posterior interventricular artery
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coronary sulcus
the groove between the atria and ventricles that encircles the entire heart
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posterior interventricular artery
gives off the atrioventricular (AV) nodal artery which supplies the AV node (part of the heart's conduction system)
also supplies both ventricles, posterior 1/3 of interventricular septum, and the atiroventricular (AV) bundle (part of the heart's conduction system)
29
left coronary artery
very short and upond entering the coronary sulcus, bifurcates into the anterior interventricular artery and the circumflex branch
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anterior interventricular artery (left anterior descending of LAD)
runs along the anterior interventricular sulcus between the two ventricles, providing blood to both ventricles (anteriorly) and the anterior /3 of the interventricular septum
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circumflex artery
runs along the coronary sulcus between the left ventricle and atrium, giving off a left marginal branch that supplies the left atrium and posterior aspect of left ventricle
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when does most blood flow into the coronary arteries
during ventricular relaxation (diastole)
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myocardial bridge
a band of heart muscle that lies superficial to a coronary artery, istead of deep to it; with a mycocardial bridge, part of a caronary artery dips into and partially deep to the heart muscle and then comes back out again
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coronary sinus
a wide venous channel running from left to right in the psterior part of the coronary sulcus; it empties directly into the right atrium
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great cardiac vein
accompanies the anterior interventricular artery and drains the apex, left aspect of the right ventricle and the interventricular septum; the great cardiac vein becomes continuous with the coronary sinus (where the oblique vein of the left atrium enters it)
36
left marginal and left posterior ventricular veins
drain the areas supplied by left marginal and circumflex arteries (all supplied by left coronary artery); the left marginal and left posterior ventricular veins drain into the coronary sinus
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middle cardiac vein
runs in the posterior interventricular sulcus; the small cardiac vein accompanies the right marginal artery and then runs along the coronary sulcus with the right coronary artery;both veins drain areas supplied by the right coronary artery and empty into the coronary sinus
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60-70% of the venous blood drained is returned to the heart via
coronary sinus
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remaining 30-40% of venous blood from the myocardium either drains into
the right atrium or other heart chambers
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anterior cardiac veins
from the anterior surface of the right ventricle cross over the coronary sulcus and enter the right atrium
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least cardiac veins (or Thebesian veins, or venae cordis minimae)
are small (not visible) veins in the wall of the heart that drain diredctly int thee right atrium or any chamber.
42
arteriosclerosis
any hardening and loss of elasticity of medium or large arteries
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atherosclerosis
a type of arteriosclerosis but names are someitmes used interchangeably; hardeningof theartery is specifically due to a buildup of fats and cholesterol in and on artery walls, forming plaques that may restrict blood flow
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cardiac ischema
a reduction in blood supply to myocardium usually resulting from atherosclerosis; it may be asymptomacticor may cause chest pain (angina pectoralis)
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myocardial infaction
commonly called a heart attack - death of cardiomyocytes is due to obstruction of myocardium's blood supply and usually occurs as a result of blockage of a coronary artery or ruptureof an atheroscleoritc plaque
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right atrium
low pressure chamber receiving venous (poorly oxygenated) blood from the SVC, IVC, and coronary sinus
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pectinate muscle
ridges of myocardium in the atrium and auricle
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crista terminalis
band of tissue extending from roof of right atrium to inferior vena cava; is the demarcation between the ridged portion (more anterior and has pectinate muscles) and the sinus venarum (more posterior and smooth)
its superiorend marks the lcoation of the sinuatrial (SA) node
49
coronary sinus
small opening on the inner wall; lies just inferior to the location of the atrioventricular (AV) node
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valve of the IVC (valve of the coronary sinus)
remnants of the valve of the sinus venosus in the embryo
51
fossa ovalis
depression in the interatrial septum (between left and right atria)
marks the locationof the foramen ovale, which permit oxygenated blood to flow from the right atrium to the left atrium
closure of membranous portion at birth is due to increased pressure in the left atrium
sometimes still patent in adult (congenital atrial septal defect)
52
right ventricle
deoxygenated blood fills the right ventricle during ventricular diastole passing through the right AV valve (tricuspid valve - 3 cusps, or "leaflets); most blood passes into the ventricle passively; the reamining blood is forced in by atrium contraction
53
trabeculae carneae
elevated ridges of myocardium on the inflow part of the ventricle
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papillary muscles
present in both ventricles, their contraction maintains tension on the chordae tenineae; usually 3 in the right ventricle: anterior (most prominent), septal (small could be absent), and posterior (several small ones, or even absent0
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chordae tenineae
attach to the cusps of the tricuspid valve (bicuspid in left ventricle) to prevent prolapse (eversion) of the valve into the atria during ventricular contraction
56
conus arteriosus
smooth outflow tract of right ventricle
57
interventricular septum
small upper portion in membranous and larger lower portion is muscular
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septomarginal trabecula (moderator band)
elevation of trabeculae carnae that forms a bridge betwen the interventricular septum and the anterior papullary muscle; only in the right ventricle; bridges conducting system
59
left atrium
receives oxygenated blood from the lungs via the 4 pulmonary veins; like the right atrium, it has a smooth part and a ridged part with pectinate muscle
60
left ventricle
high pressure chamber receiving highly oxygenated blood from the left atrium as it passes through the left AV valve; similar arrangement ot he right ventricle except that the myocardium is thicker and the left AV valve has 2 cusps (bicuspid or mitral valve); two papillary muscles - anterior and posterior; trabeculae carnae are present on the inflow part of the ventricle
61
blood flow through the heart
1. blood enters the right atrium from the SVC, IVC, and coronary sinus.
2. blood in the right atrium flows through the right AV valve into the right ventricle.
3. contraction of the right ventricle forces the pulmonary valve open.
4. blood flows through the pulmonary valve into the the pulmonary trunk
5. blood is distributed by the right and left pulmonary arteries to the lungs, where it unloads CO2, and loads O2
6. blood retruns from the lungs via the pulmonary veins to left atrium.
7. blood in the left atrium flows through the left AV valve into the left ventricle
8. contraction of the left ventricle (simultaneous with step 3 above) forces the aortic valve open
9. blood flows through the aortic valve into the ascending aorta
10. blood in the aorta is distributed to every organ in the body, where it unloads O2 and loads CO2
1. . blood returns to the heart via the SVC, IVC, and coronary sinus
62
pulmonary and aortic (semilunar) valves
each valce has 3 thin, concave cusps that oppose each other at closure
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aortic valve
has posterior, right and left cusps; coronary arteries arise from the right and left aortic sinuses between the cusps and wall of the ascending aorta
64
pulmonary valve
has anterior, right and left cusps
closure of these valves depends on backflow of blood after ventricular ejection
65
normal heart sounds
first heard sound "lubb" occurs when the atrioventricular valves close. the second heart sound "dubb" occurs when the aortic and pulmonary semilunar valves close
66
auscultation sites
to distinguish an individual valve sounds, listen at a site where the sound is projected by the direction of blood flow:
aortic semilunar valve = right 2nd intercostal space
pulmonary semilunar valve = left 2nd intercostal space
tricuspid valve = left or inferior end of sternum at 5th intervostal space
bicuspid valve = at heart apex in 5th intercostal space
67
conducting system
SA node --> AV node --> right and left bundle branches --> purkinje fibers
68
initiation of contraction occurs
in the sinuatrial (SA) node (at junction of SVC and right atrium wall); specialized cells have a lower threshold for depolarization and normally depolarize at a rate of ~70 times/min
69
what causes atrial contraction
impulse is transmited along muscle fibers of right and left atria
70
what happens after atrial contraction
impulse is transmitted to the atroventricular (AV) node located in the interatrial septum, superior to the coronary sinus opening
71
what happens after AV node receives impulse
impulse from AV nodes passes through the AV bundle in the membranous part of interventricular septum; AV bundle splits into right and left bundle branches once it reaches the muscular part of the septum
72
how do bundle branches run
both bundle branches run inferiorly within the interventricular septum beneath the endocardium to first reach the papillary muscles of each respective ventricle
right bundle branch runs through the septomarginal trabecula (moderator band), to the papillary muscles
left bundle branch runs directly to anterior and poterior papillary muscles
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what happens with each bundle
each bundle divides into a plexus of purkine fibers to direct impulses through the muscular walls of each ventricle for contraction of myocardial cells
74
myocaridal muscle fibers
are arranges within the walls of chambers in a swirling manner so contraction occurs in a manner similar to wringing water out of a wash cloth
75
problems resulting from decreasing coronary blood supply to the areas of the conducting system
compromise of the coronary artery serving AV node, resulting in anoxia to this region and damage to this node will not permit transmittal of impulses from the atria ("hear block") - ventricles will contract independently at slower rate than atria
what might happen if areas served by left coronary artery are compromised? left coronary artery will supply the anterior 2/3 of the interventricular septum with bundle branches possibly being affected - asynchronous contraction
76
sympathetic innervation
increases heart rate and force of contraction, cuases dilation of coronary arteries
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parasympathetic innervation
decreases heart rate
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superior mediastinum
is bounded superiorly by the thoracic inlet, inferiorly by the transverse thoracic plane, anteriorly by the manubrium of the sternum and posteriorly by vertebral bodies T1-T4
79
from anterior to posterior structure of the superior mediastinum
1. endocrine layer - thymus
2. vascular layer - veins - brachiocephallic veins and superior part of the SVC; arteries (posterior to veins) - aoritc arch and roots of its major branches (bacriocephalic trunk, left common carotid artery, and left subclavian artery)
3. respiratory layer - trachea
4. digestive layer - esophagus
5. lymphatic layer - thoracic duct
the nervous system does not have its own layer but it is integrated with the vascular, respiratory, and digestive layers; nerves within these layers are th vagus nerves, phreni nerves, and the cardiac plexus
80
thymus
a lymphoid gland located posterior to the manubrium; secretes hormones that stimulate the development of T cells; continues to grown until about 5 years of age and then progressively atrophies/involutes
81
brachiocephalic vein
are formed in the neck posterior to sternoclavicular joints by union of internal jugular and subclavian veins; left braciocephalic v. - runs obliquely down and behind the manubrium; crosses roots of 3 branches of aortic arch; right brachiocephalic vein unites with the left brachicephalic cein to form the superior vena cava (SVC)
82
superior vena cava (SVC)
is formed by union of the right and left brachicephalic veins posterior to the right 1st costal cartilage
returns blood to heart from all structures above diaphragm except for the heart and lungs
descends vertically and ends in the right atrium
lies to the right of the ascending aorta and to the left of right phrenic nerve
receives the azygos vein before piercing the fibrous pericardium
83
aortic arch
the continuation of the ascending aorta at the sternal angle; gives off 3 arteries superiorly (brachiocephalic trunk, left common carotid artery, and the left subclavian artery); lies superior to the right pulmonary artery and anterior to the tracheal bifurcation; ligamentum arteriosum (a remnant of ductus arteriosus in the fetus) is between its inferior surface and the left pulmonary artery; during fetal life, the ductus arteriosus shunts blood from the pulmonary trunk directly into the aortic arch, thus bypassing the lungs; passes over the root of th eleft lung; its distal portion lies to the left of the trachea and esophagus; ends as the thoracic (descending) aorta at the sternal angle
84
vagus nerve
provide parasympathetic innervation to all thoraci and most abdominal viscera
85
right vagus nerve
enters superior mediastinum anterior to right subclavian artery; descends on the right side of the trachea; passes posterior to the right braciocephalic vein and the SVC; enter the middle mediastinum posterior to the root of the right lung
86
left vagus nerve
enters superior mediastinum between the left common carotid and left subclavian arteries; descends to left side of aoritc arch; gives off the left recurrent laryngeal nerves just below the aortic arch; enters the middle mediastinum posterior ot the root of the left lung
87
left recurrent laryngeal nerve
loops around the aortic arch; ascends in the tracheoesophageal groove between the trachea and esophagus to reach the layrnx in the neck; note that the right recurrent laryngeal nerve is not located in the mediastinum; it is formed as the right vagus nerve passes anterior to the right subclavian artery in the neck
88
phrenic nerves
ventral rami of C3-C5 spinal cord segments
89
right phrenic nerve
enters superior mediastinum lateral to the right brachiocephalic vein; lies on the right side of SVC; enters middle mediastinum on pericardial surface of right atrium and runs anterior to the root of the right lung
90
left phrenic nerve
enters superior mediastinum adjacent to the left subclavian artery; lies posterior to the left brachiocephalic vein; crosses the left side of the aortic arch, anterior to vagus nerve; enters the middle mediastinum anterior to the root of the left lung and runs on the pericardial surface of the left ventricle
91
superficial and deep plexuses
are autonomic and both receive fibers from the vagus nerves and sympathetic trunks
92
superficial plexus
lies on the concave inferior surface of the aortic arch and is the smaller of the 2 plexuses
93
deep plexus
lies on the anterior surface of the tracheal bifurcation
94
components of the cardiac plexus
parasympathetic from vagus nerve are preganglionic fibers, which synapse with postganglionic cells bodies in the heart; visceral afferents from chemo- and baroreceptors in aortic arch follow parasympathics of the vagus nerve (CN X) back to the brain
sympathetic from cervical and thoracic cardia nerves are postganglionic fibers; preganglionics are from 4 upper thoracic spinal segments; synapse occurs with postganglionic neurons in the sympathetic trunk (superior cervical through T4 chain ganglia); visceral afferents carrying pain sensation from the heart follow sympagthetics back to T1-T4 spinal cord levels; pain is referred by the CNS to somatic regions innervated by the same spinal cord levels
95
trachea
lies anterior to the esophagus
bifurcates into right and left main bronchi at the sternal angle; proximal part of aortic arch lies anterior to trachea, but distal part lies to left; brachiocephalic trunk crosses the trachea anteriorly to the right and the left common carotid crosses to the left, forming a V-shape
96
esophagus
enters superior mediastinum posterior to the trachea and anterior to the vertebral bodies; left surface is related to the aortic arch; thoracic duct lies at its left posterior surface
97
thoracic duct
lies posteriorly and to left of the esophagus; begins in abdomen as the cisterna chyli; drains lymph from the body regions below the diaphragm and the left side of body above the diaphragm; ends in the neck at the venous angle between the left internal jugular vein and the left subclavian vein.
