Middle Mediastinum Functions

What are the three layers of the pericardial sac

Fibrous pericardium, parietal layer of serous pericardium, visceral layer of serous pericadium

Fibrous pericardium

Resists stretching and prevents heart from over-filling with blood during times of high venous return

Parietal layer of serous pericardium

One of two layers in direct contact with pericardial fluid and contains lymph vessels that are crucial for draining pericardial fluid

Visceral layer of serous pericardium

One of two layers in direct contact with pericardial fluid and contains the capillaries that are responsible for producing pericardial fluid via the process of ultrafiltration

Right atrium

Houses key electrical structures such as SA and AV nodes

Right/Left atrium

Pass through for blood returning to heart

How much blood moves through atria passively and flows directly into ventricles below

80%

How much blood enters ventricles due to atrial contraction (at rest)

20%

Right/left auricles

Holding chamber during high venous return

Pectinate muscles

Stretch to increase internal volume of aruicle and helps blood drain from auricle into chamber of atria

Tricuspid valve

Opens and allows blood flow when right atrial pressure is greater than right ventricular pressure, closes when ventricular pressure increases

Right/left ventricle

Receive blood from atria above, pressurizes blood, ejects into great vessels

Where do the great vessels emerge from

Base of the heart

Interventricular septum

Houses important electrical fibers called right and left bundle branches that conduct action potentials from AV node and Bundle of His above the Purkinje fibers below

Trabbeculae Carneae

Prevent ventricular walls from sticking together during contraction due to suction, ensuring ventricles can open and receive blood during relaxation

Papillary muscles

Contract with ventricular walls and shorten which puts tension on chordae tendineae

Chordae Tendineae

Conduct tension created by papillary muscles below to AV valves above, preventing inversion of valves during ventricular contraction

Do the Chordae Tendineae contract themselves

No

Pulmonary semilunar valve

When pressure in right ventricle is greater than that in the pulmonary trunk, flaps open and permit ejection of blood from right ventricle to pulmonary trunk. The reverse happens when right ventricle relaxes and pressure falls so prevents back flow of blood from pulmonary trunk into the ventricle

Ligamentum arteriosum

Fetal remanent (ductus arteriosus) structure which serves no purpose after fetal development but being a landmark, shunts blood from pulmonary arteries to the aorta

Pulmonary trunk

Receives deoxygenated blood from right ventricular outlfow tract through the pulmonary semilunar valve

Left and right arteries

Carry deoxygenated blood from the right side of the heart to the lungs

Pulmonary veins

Carry oxygenated blood under very low pressure back to left atrium

Bicuspid valve

Opens and allows blood flow into ventricle when left atrial pressure is greater than left ventricular pressure. Reverse happens when ventricular pressure increases so no additional blood enters ventricle

Aortic semilunar valve

Flaps open and permit ejection of blood from left ventricle into aorta when pressure in left ventricle is greater than that in the aorta. Reverse happens when left ventricle relaxes and pressure falls, the valve prevents the back flow of blood from aorta into ventricle