Mediastinum and Heart Flashcards
What is the mediastinum?
it forms a mobile midline between the two lungs and their pleural cavities
All structures within the mediastinum are held together by what?
held loosely together by connective tissue
How is the mediastinum divided into superior and inferior divisions?
A line drawn from the junction of the manubrium and body of the sternum (sternal angle) posteriorly between the bodies of T4 and T5
The inferior mediastinum is further divided into what?
3 more divisions; anterior, middle, and posterior
What is the defining structure of the divisions of the inferior mediastinum?
the heart and its pericardial sac, as it lies within the middle division (can be seen from a lateral view)
Anterior mediastinum is between what?
the pericardial sac of the heart posteriorly and the posterior aspect of the sternum anteriorly
What does the anterior mediastinum containt?
- only fat, connective tissue and a few vessels in the adult
- before puberty it contained the thymus
Thymus funtion
T-Cell maturation
Posterior mediastinum is between what?
the posterior aspect of the pericardial sac and the anterior aspect of the vertebral column
All 3 portions of the inferior mediastinum are bounded inferiorly by the
diaphragm
Other important structures in the middle mediastinum besides the heart and pericardial sac?
-the ascending aorta(first part from the heart)
-pulmonary trunk (and its division into rt. and lt. pulmonary aa.),
-portions of the superior vena cava,
-pulmonary vv. as they enter the heart
-the termination of the azygos vein,
-the phrenic nn.
-the bifurcation of the trachea into lt. and rt. main
bronchi
What is the pericardium?
also called the pericardial sac, as two layers: outer tough fibrous and inner serous (slippery) layers
What is the fibrous pericardium
tough fibrous layer that restrains the heart during beating from
moving violently around the mediastinum
What does the fibrous pericardium fuse with
- superiorly: fuses with the adventitia (outer CT layers) of the great vessels leaving the heart and entering the superior mediastinum
inferiorly: with the central tendon of the diaphragm
The phrenic nerve is sandwiched between what
the mediastinal pleura and the outer aspect of the fibrous pericardium - along the lateral borders of the pericardial sac
Phrenic n. on both sides of the heart are accompanied by what?
tiny vessels -the pericardiophrenic br. of the internal thoracic a.
How does the fibrous pericardium prevent cardiac tamponade?
due to its unstretchable nature that prevents the accumulation of fluid from inflammation and bleeding from a rupture vessel/chamber letting blood flow into the pericardial sac
What is cardiac tamponade?
when extra fluid builds up in the space around the heart which impedes filling of the heart
What is the serous pericardium?
Separates the fibrous pericardium from the epicardium (surface of the heart)
Serous pericardium is also called what
The serous layer covering the posterior side of the fibrous pericardium is
referred to as the PARIETAL SEROUS PERICARDIUM
What is the visceral pericardium?
That portion reflected out onto the surface of the heart, at the roots of the great vessels
- also called the epicardium
- lies directly on surface of the heart
What is the pericardial cavity?
a potential space between the parietal serous pericardium and the visceral serous pericardium; it is filled with pericardial fluid
Removal of fluid from the sac is referred to as?
pericardial aspiration
What are the two pericardial sinuses?
transverse pericardial sinus and oblique pericardial sinus
transverse pericardial sinus
the serous pericardium extends up as separate sleeves over the superior vena cava on the right side, and the aorta and pulmonary trunk on the left which leaves a communication of the pericardial cavity between the two sleeves
oblique pericardial sinus
With the heart removed, you can also see that the sleeve of serous pericardium that enclosed the superior vena cava also encloses the openings of the inferior vena cava and the pulmonary veins; this irregular outline forms a blind-ending serous-lined cavity
What is the transverse pericardial sinus important for?
clinically important being used commonly for vessel ligation in heart surgery
How many circulatory systems and what are their names?
4; pulmonary circulation, coronary circulation, systemic circulation, hepatic portal system
What is pulmonary circulation?
-right ventricle pumps deoxygenated blood returned from the body to the right atrium to the lungs for oxygenation
The ___ and ___ of the lungs are a filter between right and left hearts
arteries and capillaries
What is coronary circulation?
The right. and left. coronary aa. arising from the aorta supply the myocardium of the heart with freshly oxygenated blood just returned from the lungs to
the left atrium and pumped out into the aorta via the left ventricle
The ___ and ___ of the body are a filter between left. and right hearts
arteries and capillaries
What is systemic circulation?
-Freshly oxygenated blood enters the aorta from the left ventricle under great
pressure to be pumped to all tissues of the body (including the tissue of the
lungs via the bronchial aa.)
-It is returned to the right atrium from the top and bottom portions of the body via the superior and inferior vena cava.
What do the superior and inferior vena cava do?
collect all the deoxygenated blood from the body, including lymphatic drainage and return it to the rt. atrium for reoxygenation via the pulmonary system
What is the hepatic portal system?
collects all venous blood returning from the tubular gastrointestinal tract (filled with ingested nutrients, etc.) and takes it to the liver (via the hepatic portal vein) for screening/metabolism prior to its entry back into the systemic system through the hepatic vein
While the heart looks like a single organ, it functions as what?
a pair of muscle pumps linked to each other by the pulmonary circulation
- The right pump is fed by venous return (superior and inferior vena cavae).
- The left pump empties into the aorta.
The vertical plane between left and right sides of the heart lies _____
in the body
obliquely
What is the result of the oblique orientation of the vertical plane of the heart?
the anterior (sternocostal) surface of the heart is composed almost entirely of the right ventricle while the posterior surface is mostly the left ventricle and atrium
What are the chambers of the heart?
- right side: right atrium and right ventricle
- left side: left atrium and left ventricle
The right atrium receives blow flow from where?
venous return from the body
Are there valves that restrict blood flow into or out of the right atrium?
No
Features of the right atrium include:
pectinate muscles, crista terminalis, interatrial septum, fossa ovalis, limbus of the fossa ovalis, opening of the coronary sinus, location of the atrioventricular node
What is the fossa ovalis?
represents the remnant of an embryonic valve connecting the 2 atria allowing blood to bypass the right ventricle (as it did not need to go to the lungs
while the fetus was in utero)
-This valve remains patent (open) to some degree in about 25% of adults but generally causes no significant problem
What is the right atrioventricular valve?
- also called the tricuspid valve;
- Blood flows from the right atrium into the right ventricle
Features of the right ventricle include:
a much thicker muscular wall than the atrium, irregular muscular ridges/projections - trabeculae carnae, septomarginal (moderator) band, supraventricular crest above which is the smooth infundibulum, papillary muscles and chordae tendineae attached to the 3 cusps of the right A-V valve
How does blood leave the right ventricle?
by passing by the right semilunar (pulmonary) valve into the pulmonary trunk
What is the ligamentum arteriosum?
-remnant of the fetal circulation - the ductus arteriosus
Describe fetal circulation
- the majority of oxygenated blood comes to the rt. atrium via the IVC from the
placenta. It bypasses the right ventricle via the foramen ovale (fossa ovalis is the closed opening found in the adult) and is pumped out the aorta to the body
-Deoxygenated blood returning from the head and neck however, falls down into the right ventricle. Ventricular contraction pumps it out into the pulmonary trunk where the majority enters the ductus arteriosus - which joins the aorta after the 3 main branches have been given off the aortic arch
At birth, how is the foramen ovale closed?
by a relative increase in left atrial pressure forcing the valve against the septum; in most cases is fuses shut forming the fossa ovalis
At birth, how is the ligamentum arteriosus formed?
the ductus arteriosus contracts and eventually obliterates leaving the cord-like ligamentum arteriosus
Failure of the formation of the ligamentum arteriosus to form results in what?
surgical intervention
The left atrium receives blood through what?
2-4 pulmonary veins, blood returning from the lungs
Pectinate muscles are present where in the left atrium?
only out in the auricle
How does the blood flow from the left atrium into the left ventricle?
by passing through the left A-V oriface which is guarded by the left
A-V valve
The left AV valve is also called what
bicuspid or mitral valve
The left ventricle does not have what structures that the right ventricle does?
- moderator band
- supraventricular crest
Why are the walls twice as thick in the left ventricle compared to the right?
due to the pressure generated to pump to the systemic circulation (body)
How is blood pumped out of the left ventricle?
it is pumped into the aorta passing over the left semilunar (aortic) valve
Semilunar valves separate?
ventricles from outflow vessels
Atrio-ventricular valves separate?
atria from ventricles
What is the fibrous skeleton of the heart?
The myocardium (cardiac muscle) around each of the valves of the heart contains a region of fibrous thickening used to anchor the valves into the myocardium- this forms the skeleton
The fibrous rings of the AV valves appear was what structure?
ring like structure
The fibrous rings of the semilunar valves appear like what structure?
cuff-like appearance
What is the inter-ventricular septum?
septum between the right and left hearts; has 3 parts
- thicker, muscular part between the ventricles
- thinner, fibrous parts between where the valves attach
- -> interatrial septum and interventricular septum
The rate and force of the heartbeat is controlled by what?
the autonomic nervous system
the sympathetic division sends what kind of fibers to the heart?
post-ganglionic fibers
Where do the post-ganglionic fibers come from?
via the cervical cardiac rami from as high as the superior cervical ganglion, but mostly the primarily the sympathetic ganglion of T1-T5 into the cardiopulmonary plexus
What do the sympathetic postganglionic fibers do for the heart?
accelerate heat beat and increase the strength of its contractions
Parasympathetic innervation to the heart?
The vagus nerve contributes parasympathetic preganglionics via the cervical cardiac br. to the cardiopulmonary plexus
What does parasympathetic innervation do for the heart?
slow the heat beat and weaken the strength of the contractions
What is the cardiopulmonary plexus?
aggregation of postganglionic fibers from the sympathetic division and preganglionics from the parasympathetic division of the ANS
How is the cariopulmonary plexus distributed?
over the tracheal bifurcation and extends out to the hilus of the lung. It is also found covering the pericardial sac of the heart.
The fibers from the cardiopulmonary plexus stimulate or inhibit what of the heart?
The SA node, which is the pacemaker of the heart
Why do cardiac muscle fibers need an SA node?
Because they beat intrinsically, so they require a pacemaker to coordinate their contraction
Where is the SA node located?
on the external surface of the heart (inside the pericardial sac) - referred to as being subepicardial
-found where the upper end of the sulcus terminalis reaches the base of the
superior vena cava
How are impulses spread from the SA node?
impulse to contract is spread over the atrial wall in groups of fibers referred to as the internodal fibers
The internodal fibers of the atrium transmit the impulses where?
to the atrioventricular (A-V) node
Where is the AV node located?
located subendocardially on the floor of the right atrium between the opening of the coronary sinus and the tricuspid valve
How does the electrical impulse leave the AV node?
via the atrio-ventricular (A-V) bundle, which contains modified cardiac muscle cells referred to as Purkinje fibers
How do purkinje fibers differ from regular muscle cells?
10-20X larger than musclecells, lose their ability to contract and gain the ability to conduct electrical impulses efficiently
Once the bundle of His reaches the interventricular septum, it breaks up into what?
bundles of His, or right and left bundle branches that continue on down to the apex of the heart and then up around the surface walls of the heart
Each group of papillary muscles receives what?
a group of purkinje fibers
The moderator band of the right side of the heart always contains what
a tract of purkinje fibers
The moderator band passes where?
from the septal wall to the base of the anterior papillary muscle and is thought to represent a short-cut for these fibers
Location of the right and left coronary arteries?
open as orifices from the vessel wall in the right and left coronary cusps of the aortic semilunar valve
-These openings are functionally related to the cusps
What happens during ventricular systole?
(contraction) blood is ejected from the left ventricle into the aorta and the cusps are forced back again the vessel wall, closing off the orifices of the coronary arteries - preventing backflow of blood from the myocardium (under contraction) back into the aorta
What happens during ventricular diastole?
(relaxation) blood from the aorta falls back into the aortic semilunar cusps, filling them to functionally occlude the aortic opening, and freshly oxygenated blood flows freely our into the coronary vessels and into the myocardium which is now relaxed
During the next ventricular systole following diastole what happens?
the atria are relaxed (low pressure) so that the high pressure
within the contracting ventricles forces blood through the cardiac veins, into the coronary sinus and into the right atrium
What maintains a one-way flow of blood through the myocardium of the heart
the relation of the orifices of the coronary arteries to the aortic semilunar valve cusps
Where does the RCA arise from?
the right coronary cusp of the aortic semilunar valve
What is the first branch off the RCA?
SA node branch, which supplies the SA node about 60-70% of the time (with the rest of the supply coming from a branch of the LCA on the posterior aspect of the heart)
The RCA extends along the heart in the
right anterior A-V groove
What is the next branch the RCA gives rise to?
the marginal artery that extends along the inferior (acute) margin of the heart
The RCA then passes onto the posterior surface of the heart and runs along what
the right posterior A-V groove
The RCA terminates how?
by dividing into the posterior interventricular branch and a continuation of
variable size that anastomoses with the circumflex br. of the LCA
The posterior interventricular branch of the RCA continues along the?
posterior interventricular groove
The posterior interventricular branch of the RCA anastomoses with what?
anterior interventricular branch of the LCA
The LCA is a short branch that terminates into what?
terminates at the tip of the left auricle into the circumflex branch
and the anterior interventricular branch (left anterior descending)
The anterior interventricular branch of the LCA continues along the heart in the what?
anterior interventricular groove to the apex of the heart where it passes posteriorly and continues in the posterior interventricular groove to anastomose with the posterior interventricular br. of the RCA
The circumflex branch of the LCA extends where?
wraps around the obtuse margin of the heart in the left A-V groove to terminate by anastomosing with the terminal br. of the RCA
Both anastomotic sites are located where?
on the posterior surface of the heart
The anastomotic sites are classified as what and why?
insufficient anastomoses because their size is insufficient to protect the heart from damage due to blockage of one of the coronary aa
Both interventricular branches are sending what into the heart?
penetrating br. into the muscular interventricular septum
The venous return of the heart is said to be indirect why?
because the individual veins returning blood to the heart do not actually drain into the right atrium individually, they instead drain into the coronary sinus which then drains into the right atrium
Location of the great cardiac vein?
-begins at the apex of the heart and accompanies the anterior interventricular br. of the LCA
When does the great cardiac vein become the coronary sinus?
Once it rounds the obtuse margin of the heart and accepts the posterior vein of the left ventricle
What other veins does the coronary sinus accept?
oblique vein of the left atrium, the middle cardiac vein and the small cardiac vein
Aside from a small amount of blood returned from the myocardium directly
by small veins opening into all four chambers of the heart (the venae cordis minimae), the only other direct venous drains are?
inconsistent anterior cardiac veins that drain the right ventricle into the rt. atrium
Anterior cardiac veins drain where?
drain the right ventricle in to the right atrium, but they are inconsistent
All cardiac veins have a valve that prevents backflow where they terminate at the coronary sinus, except for the
oblique vein
Does the coronary sinus have a valve?
Yes, where it terminates in the right atrium
