1522 



HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



cytosis" (286) and "cytopempsis" (270), the latter 

 being preferred since it does not imply actual utiliza- 

 tion of the transported substances by the endothelial 

 cell. 



Myocardial I 'etm 



There are twice the number of venous as arterial 

 channels in the heart, their density in the left ventricle 

 greatly exceeding that of the right (191), and they 

 have been subdivided into superficial and deep cir- 

 cuits (153, 365, 366). The superficial left ventricular 

 veins parallel the arterial branches and course toward 

 the base of the heart to empty into the great cardiac 

 vein anteriorly, and its continuation in the left auric- 

 uloventricular groove, the coronary sinus, poste- 

 riorly. The latter empties into the right atrium in the 

 posterior-inferior interatrial septum located between 

 the medial end of the inferior vena cava and A-V 

 ring, and receives subsidiary trunks up to its orifice 

 (183). The anterior cardiac veins drain the right 

 ventricle and are smaller, frequently solitary, trunks 

 which empty individually into the right atrium just 

 above the A-V valves (153). 



The deeper venous circuit has communications 

 with both atrial and ventricular cavities via Thebesian 

 and sinusoidal channels (153). Myocardial sinusoids 

 or trabeculae are especially rich in the ventricular 

 walls and maintain communications with arterioles, 

 capillaries, venules, and the heart cavities (64, 153, 

 189, 191, 365, 366) These sinusoids are lined by a 

 single layer of endothelium and range from 40 to 75 ji 

 in dogs, and 60 to 90 jx in newborn humans in the 

 septal myocardium. In dogs and pigs there is a mas- 

 sive formation of sinuses in the left ventricular wall 

 communicating with the cavity (64). 



Collateral Circulation 



As noted earlier (vide supra), intercoronary anasto- 

 moses were first demonstrated by Lower using a 

 watery injection of dye, and in 1803 von Haller re- 

 ported on the extracardiac communications of the 

 coronary arteries, utilizing the same techniques (153, 

 382). The latter were principally channels from the 

 base of the pulmonary artery and veins, root of the 

 aorta and venae cavae, and other basal (usually 

 atrial) vessels, to vessels in the intrapericardial re- 

 flections. These vessels are largely from the internal 

 mammary artery via the pericardiacophrenic branch, 

 but communications also exist with the bronchial 

 arteries. 



In lower vertebrates the blood supply to the heart 



is nearly all extracardiac in origin, whereas the rat 

 maintains a dual supply of both intracardiac and 

 extracardiac origin. In normal mammalian hearts the 

 extracardiac communications are of the order of small 

 arterioles and capillaries and are anatomically and 

 physiologically insignificant. 



Intracardiac coronary anastomoses in human 

 hearts and those of various laboratory animals have 

 been the subject of numerous pathologic and experi- 

 mental investigations during the past decade. Col- 

 lateral arterial communications in normal hearts have 

 been anatomically divided into those stemming from 

 the same major coronary artery, i.e., intracoronary, 

 and those between the right and left coronary- 

 branches, i.e., intercoronary (18, 258). All mammalian 

 species show some intercoronary anastomoses, espe- 

 cially over the anterior left ventricle, while inter- 

 coronary anastomoses vary appreciably between 

 species, the dog's being fairly vvell developed, the 

 pig's poorly, and man's quite variable; the greater 

 proportion occurring in the muscular interventricular 

 septum (18, 189). 



Functional collateral channels, as opposed to 

 anatomic communications, have been defined for 

 mammalian hearts as those above 40 tx in diameter, 

 i.e., those which do not traverse a capillary bed (37, 

 38, 338). High viscosity fluids do not penetrate vessels 

 below 40 /x and, utilizing this technique or those with 

 graduate spheres above 35 tx, 6 to g per cent of normal 

 human hearts have adequate collateral channels (38, 

 2gi, 411). Conversely, latex casts have shown lux- 

 uriant anastomoses ranging from 20 to 350 /x in all 

 normal hearts and in all myocardial areas below the 

 subepicardial layer of muscle (18). Thus, while the 

 experimental and pathophysiological approaches to 

 this problem will be more fully discussed in a later 

 section, the disparity between the functional state, 

 i.e., its physiologic competency, and the nonfunctional 

 state, i.e., its anatomic patency, becomes more obvious 

 and the reason for the designation of the coronary 

 arteries as "end arteries" more apparent (153, 404). 



While the above discussion has dealt mainly with 

 arterial collaterals, venous collateral channels freely 

 communicate over the surface of the heart (153), in- 

 cluding those between the anterior cardiac veins of 

 the right ventricle and the left ventricular coronary 

 sinus system. Extracardiac communications of the 

 cardiac veins are not uncommon especially in lower 

 mammals, and are usually related to the persistence 

 of the left caval or cardinal veins. In the pig, large 

 communications may exist between the hemizygous 

 vein and the great cardiac vein, the latter also having 

 substantial epicardial connections with the anterior 



