In the

anatomy Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having i ...

of the

heart The heart is a muscular Organ (biology), organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as ca ...

, the smallest cardiac veins, also known as the Thebesian veins (for

Adam Christian Thebesius Adam Christian Thebesius (January 12, 1686 – November 10, 1732) was a German anatomist who was a native of Sandenwalde, Silesia. He studied medicine in Jena, Leipzig and Leiden, receiving his doctorate from the University of Leiden in 170 ...

), are small valveless

vein Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated ...

s in the walls of all four heart chambers.

Structure

Course

The smallest cardiac veins are most abundant in the right atrium and least in the

left ventricle A ventricle is one of two large chambers toward the bottom of the heart that collect and expel blood towards the peripheral beds within the body and lungs. The blood pumped by a ventricle is supplied by an atrium, an adjacent chamber in the uppe ...

. They drain the

myocardium Cardiac muscle (also called heart muscle, myocardium, cardiomyocytes and cardiac myocytes) is one of three types of vertebrate muscle tissues, with the other two being skeletal muscle and smooth muscle. It is an involuntary, striated muscle tha ...

. They run a perpendicular course to the endocardial surface, directly connecting the heart chambers to the medium-sized, and larger coronary veins. The smallest cardiac veins have been successfully identified by following the route of contrast flow - during catheterization procedures - from the subendocardium, through the smallest cardiac veins, into larger veins, and into the

coronary sinus In anatomy, the coronary sinus () is a collection of veins joined together to form a large vessel that collects blood from the heart muscle (myocardium). It delivers deoxygenated blood to the right atrium, as do the superior and inferior vena ...

. The

empties into the right atrium.

Openings

The ''openings of the smallest cardiac veins'' are located in the

endocardium The endocardium is the innermost layer of tissue that lines the chambers of the heart. Its cells are embryologically and biologically similar to the endothelial cells that line blood vessels. The endocardium also provides protection to the va ...

. Here the smallest cardiac veins return

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...

into the heart chambers from the

capillary bed A capillary is a small blood vessel from 5 to 10 micrometres (μm) in diameter. Capillaries are composed of only the tunica intima, consisting of a thin wall of simple squamous endothelial cells. They are the smallest blood vessels in the body: ...

in the muscular cardiac wall, enabling a form of collateral circulation unique to the heart. Not every endocardial opening connects to the smallest cardiac veins, as some connect to the vessels of Wearn, which are arteries. Therefore, the endocardial opening must be traced to a vein before it is definitely called an opening of the smallest cardiac veins.

Function

The small cardiac venous network is considered an alternative venous drainage of the

. The smallest cardiac veins draining into the left heart, along with deoxygenated blood originating from the bronchial veins draining into the pulmonary veins, contribute to normal physiologic

shunting Shunting may refer to: * Ribosome shunting, a mechanism in protein biosynthesis * Shunting (rail), a rail transport operation * Shunting (neurophysiology), a concept in neurophysiology * Shunting (sailing), a maneuver for sailing upwind See a ...

of blood. As a consequence of the input of these vessels, blood in the left heart is less oxygenated than the blood found at the pulmonary capillary beds, usually to a very small degree.

History

Etymology

The smallest cardiac veins are also known as the Thebesian veins. They are named after the German

anatomist Anatomy () is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having it ...

, who described them in a 1708 treatise called ''Disputatio medica inauguralis de circulo sanguinis in corde''.

Mislabelling

The smallest cardiac veins are sometimes accurately referred to as vessels, but they are frequently confused with a distinct set of

artery An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pu ...

connections, eponymously referred to as the "vessels of Wearn". In his 1928 publication, Wearn himself referred to the arterio-cameral connections (vessels of Wearn) as Thebesian, but later, after additional research, provided disambiguation and strictly used the term Thebesian for coronary vein-heart chamber connections.

References

External links

GPnotebook - "venae cordis minimae"
{{Authority control Cardiac anatomy