Heart: Location, Size, Orientation, and Pericardial Anatomy (Lecture 2)

The heart is located in the mediastinum, the central compartment of the thoracic cavity (the middle chest).
It lies between the sternum anteriorly and the spine posteriorly, with the esophagus nearby.
The mediastinum is the central region of the thorax; the heart is slightly offset to the left of the midline.
Orientation: the apex is the pointed, inferior tip; the base is the broad, superior part; the margin sits above the diaphragm.
Relative position in the chest:
- The heart sits between the $2^{\text{nd}}$ and $5^{\text{th}}$ intercostal spaces.
- It is just behind the sternum and in front of the bodies of the vertebrae and the esophagus.
Apparent tilt: the heart is slightly tilted/leaning toward the left; the apex points downward and to the left, giving the left chest a slight curve.
The sternum is anterior, the vertebral column posterior, and the esophagus lies posterior and slightly to the left of the heart.
The heart is surrounded by serous membranes and has its own serous membranes that create a protective space around it (the pericardial sac).

The heart is about the size of a clenched fist.
It is a busy, durable muscle: it beats about $100{,}000$ times per day.
It pumps about $8{,}000$ liters of blood per day.
Pathology can lead to enlargement: autopsies sometimes show a bigger heart when it has been working overtime for a long time.
Core function: move blood around in the vessels, providing circulation to all body systems.
If the heart stops, nearly everything else stops; the brain can stop, but the heart helps keep circulation going for other tissues (the speaker notes this as part of the heart’s critical role).
The heart is described as busy and almost miraculous in its endurance; a reminder that it outpaces other muscles in continuous activity.

The heart sits within its own serous membrane pouch, the pericardial sac, which is part of the serous membranes surrounding the heart.
The pericardial sac prevents the heart from sticking to surrounding tissues during its continuous beating by providing lubrication and a contained space.
This arrangement supports smooth, uninterrupted contraction and reduces friction during daily cardiac cycles.

Apex: the pointed, inferior end of the heart, located toward the left side.
Base: the broad, superior part of the heart.
Margin: the side of the heart that rests above the diaphragm.
The heart is located between the $2^{\text{nd}}$ and $5^{\text{th}}$ intercostal spaces.
It lies just behind the sternum and in front of the vertebral bodies and the esophagus.
The heart is slightly offset to the left of the midline and is not perfectly centered in the thorax.

This session begins the heart unit, focusing on overall characteristics and key anatomical features before discussing action potentials.
The instructor mentions that APs of pacemaker cells and contractile cells (the conduction system) will be explored later.
The class is covering objectives 12 through 19 (with 12a addressing location) for this lecture, using the slides that map to these objectives.
The cardiovascular sequence in the course is: blood, then the heart, then the blood vessels.
The slides are described as exceptional and helpful for understanding the material, including objective numbers on the slides.

Terminology note: the term mediastinum is used frequently; some speakers may spell or pronounce it slightly differently (mediastinum vs. mediastinum) but both refer to the same region.
The instructor uses a conversational, occasionally humorous tone to emphasize concepts, such as the heart’s busy nature and the importance of getting rest when needed.
Practical takeaway: the heart’s location, size, orientation, and protective coverings are foundational for understanding broader cardiovascular anatomy and subsequent topics like electrical activity and blood vessel dynamics.