The smallest cardiac veins (also known as the Thebesian veins (named 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 the circulatory system of 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 those of the pulmonary and feta ...

s in the walls of all four

heart chambers The heart is a muscular organ found in humans and other animals. This organ pumps blood through the blood vessels. The heart and blood vessels together make the circulatory system. The pumped blood carries oxygen and nutrients to the tissue ...

that drain venous blood from the

myocardium Cardiac muscle (also called heart muscle or myocardium) is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. It is an involuntary, striated muscle that constitutes the main tissue of the wall o ...

directly into any of the heart chambers. They are most abundant in the

right atrium The atrium (; : atria) is one of the two upper chambers in the heart that receives blood from the circulatory system. The blood in the atria is pumped into the heart ventricles through the atrioventricular mitral and tricuspid heart valves. ...

, and least abundant in the

left ventricle A ventricle is one of two large chambers located 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 t ...

Structure

The smallest cardiac veins vary greatly in size and number. Those draining the right atrium have a lumen of up to 2 mm in diameter, whereas those draining the right ventricle have lumens as small as 0.5 mm in diameter.

Course

They run a perpendicular course to the endocardial surface, directly connecting the heart chambers to the medium-sized, and larger coronary veins.

Openings

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

endocardium The endocardium (: endocardia) 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 prot ...

. 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 is com ...

into the

heart chamber The heart is a muscular organ found in humans and other animals. This organ pumps blood through the blood vessels. The heart and blood vessels together make the circulatory system. The pumped blood carries oxygen and nutrients to the tissue ...

s from the

capillary bed A capillary is a small blood vessel, from 5 to 10 micrometres in diameter, and is part of the microcirculation system. Capillaries are microvessels and the smallest blood vessels in the body. They are composed of only the tunica intima (the inn ...

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 veins are responsible for venous return of 10% of the coronary blood supply. 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 The bronchial veins are small vessels that return blood from the larger bronchi and structures at the roots of the lungs. The right side drains into the azygos vein, while the left side drains into the left superior intercostal vein or the acce ...

draining into the

pulmonary veins The pulmonary veins are the veins that transfer oxygenated blood from the lungs to the heart. The largest pulmonary veins are the four ''main pulmonary veins'', two from each lung that drain into the left atrium of the heart. The pulmonary ve ...

, contribute to normal physiologic shunting 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 morphology concerned with the study of the internal 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 scien ...

, 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 () is a blood vessel in humans and most other animals that takes oxygenated blood away from the heart in the systemic circulation to one or more parts of the body. Exceptions that carry deoxygenated blood are the pulmonary arteries in ...

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 C