Significance of the cranial venous system in
anthropogenesis in the light of contemporary clinical
and experimental data
Jaroslaw Wysocki
AbstractT he m anner o f th e appearance o f the Hominidae fam ily is still a very controversial issue, since there is no general agreem ent am ong the authors upon w hether it w as an isolated and extraordinary event in th e natural history or rather a necessary consequence o f the evolution process. R apid augm entation o f the cranium capacity w hich occurred in this group had been probably preceded by the developm ent o f the erect body posture. Elevation o f the head created new, better conditions for th e outflow o f th e venous blood from th e cranium due to the involvem ent o f the gravitation force into this m echanism . A new m odel o f venous outflow from the cranium m u st have been developed.
Jaroslaw W ysocki, 1997; Anthropological Review, vol. 60, Poznan 1997, pp. 9 7 -1 0 1 , ISB N 83-86969-18-0, ISSN 0033-2003
According to the classical views, having originated as long ago as in the previous century, blood within venous sinuses o f cranial dura m ater was to flow from the anterior and upper part towards the posterior and lower part o f the cra nium, heading towards jugular foramina and flowing out through emissaries. However, due to the lack o f valves
[BOCHENEK, REICHER 1993] this prevail ing direction o f the blood stream could change depending on momentary differ ences in the blood pressure. Based on these views, cranial emissaries are con sidered to have a very important function in the generation o f collateral circulation bypassing the jugular foramen forms as a Department o f Anatomy
Institute o f Biostructure Medical Academy in Warsaw Chałubińskiego 5, 02-004 Warszawa
result o f a uni- or bilateral ligation o f the internal jugular vein [A h n , SlNDELAR
1989, BOCHENEK, REICHER 1993, SCHEL-
LING 1978], Undoubtedly, cranial emis saries play also an important role in the spread o f intracranial inflammatory com plications originating in the head and
neck organs [DANZIGER, PRICE, SCHE-
CHTER 1980].
Contemporary studies in the field o f anatomy, physiology as well as clinical observations prove that the mechanisms o f blood circulation within the head are far more complex than previously be lieved. The directions o f the blood flow in intracranial blood vessels, in the large sinuses o f the dura m ater in particular, depend also on factors other than the pressure gradients. Any changes o f these directions enforced by a surgical inter vention always lead to the dysfunction o f
98 Jarosław W ysocki
the central nervous system. Hence, in spite o f undeniable progress in anaes thesiology and intensive medical care in
recent times [Ah n, SlNDELAR 1989,
SHELLING 1978], a relatively high mor tality rate is still observed following the operations o f the uni- or bilateral ligation o f internal jugu lar vein, especially if perform ed at the same procedure, This is in opposition to the established view supported by numerous clinicians on relatively easy generation o f collateral circulation following this type o f opera tion. Furthermore, it should be empha sised that the radiological intravital tests o f the arterial and venous vessels o f the cranium seem to indicate that in some com pletely healthy people venous blood does not enter but leaves the cranium through ophthalmic veins, and that di rection o f this flow depends on an indi vidually variable configuration o f large tributaries to the cavernous sinus. This causes the changes o f the pressure be tween this sinus and orbital veins
[SERVO 1981]. Experimental function tests conducted on healthy volunteers indicate that the direction o f the blood flow in ophthalmic veins may vary for the same individual. It depends on the therm ic situation o f the system in a given moment, which is probably o f signifi cance for the therm oregulation mecha nism o f the brain [CAPUTA 1982]. Other experimental studies indicate that blood
enters the cranium [TYCHMANOWICZ
1992] also through other emissaries. It seems that the intracranial direction o f the blood flow indicated by the very position, and in particular by the angle at which some important emissaries per m eate the cranium wall [PIASECKI, WY SOCKI, S k a r ż y ń s k i, R e y m o n d 1995], The m echanism s regulating the direc
tions o f the blood flow within the head are without doubt very precise and effi cient, since they make it possible to maintain constant pressure in the supe rior sagittal and sigmoid sinuses in spite o f serious and long-lasting disturbances in venous outflow. This is a trait acting to the advantage o f the organism, since these sinuses are the zones o f the most intensive absorption o f the cerebrospinal
fluid [TYCHMANOWICZ 1992], These
mechanisms are probably based on the existence o f extremely rich autonomous innervation o f the sinus walls, o f the cavernous sinus in particular, with nu merous baroreceptive endings, as well as on the presence o f valves in the openings o f large venous emissaries to sinuses
[A u er , J o h a n s s o n 1981, C a p u ta 1982,
K ę d z ia 1987, T y c h m a n o w ic z 1992], There are two phenomena, very im portant for the understanding o f the principles o f blood circulation in the head, which nevertheless have been ne glected by majority o f the authors o f clinical papers. These are latéralisation and sexual dimorphism. Latéralisation o f the cranial venous system consists in directing the main stream o f blood through a single jugular foramen and further through a single internal jugular vein. This probably promotes faster out flow, since, according to the Bernoulli principle, a stream o f liquid loses energy in each branching point. As a result, al most always one o f the jugular foramina, usually the right-hand one, is larger than the opposite foramen. Foramina o f simi lar size are found extremely rarely
[SCHELLING 1978]. The latéralisation phenomenon seems to be a universal feature, characteristic o f the vertebrates with the erect body posture, which is suggested by its occurrence also among
99
birds [KRASNIKOV 1988]. The latéra lisation o f the jugular foramina o f the cranium is not observed in the majority o f quadruped m am mals [HEGEDUS, S h a c k e l f o r d 1965]. The fact that among humans latéralisation is stronger in female individuals seem s to suggest that also sexual dimorphism should be taken into consideration in the study o f the venous system o f the cranium [BAUER
1971]. The occurrence o f easily iden tifiable latéralisation and sexual dimor phism w as ascertained recently also by Polish authors, also by the author o f the present paper [PIASECKI, WYSOCKI, S k a r ż y ń s k i, R e y m o n d 1995], Ana tomical studies on the mastoid em issaries o f the cranium indicate that all metric characteristics o f these em issaries show significant statistical differences depend ing on the sex o f the individual and the side o f his/ her body. Clinicians som e times fail to observe the described phe nomena. Some clinical studies, however, devoted to intracranial inflammatory complications deserve attention. Materi als covering large groups o f patients prove that the male individuals suffer from com plications much more often than fem ales (from 1.5 to 3.5 times more often). So far the phenomenon has not been explained [DANZIGER, PRICE, SCHECHTER 1980]. This is a confirma tion o f sexual differences in the structure o f the cranial venous system observed in anatomic studies which so far have not been sufficiently supported with basic physiological studies.
Certain new data widening the scope o f our knowledge on the structure and functions o f the cranial venous system have been contributed by the studies in the field o f comparative anatomy and anthropology. The development o f the
model o f the venous blood outflow from the cranium observed in contemporary people extended over several m illion o f years o f the H o m in id a e fam ily evolution [FALK 1986]. In this fam ily o f primates a rapid augmentation o f the brain capacity took place [LOVEJOY 1981]. In the course o f this process the original system underwent thorough transformation. In
the original system the main stream o f the venous blood left the cranium through the great foramen o f the cranium and through em issaries located at the cranial basis and subsequently flow ed into vertebral venous plexuses and deep jugular veins. A s a consequence o f the transformations, in certain H o m in id a e
forms [FALK 1986] a considerable devel opment o f marginal and occipital sinuses, o f condyloid em issaries and sublingual canals w as possible. The changes were probably generated by other physical m odifications o f the organism, especially by the developm ent o f the erection body posture, which created new conditions for the venous outflow promoting the jugular foramina as the ones located at the low est points [FALK 1986]. In the course o f the evolution other foramina located within the cranial basis, such as foramen ovale or postglenoid foramen which are the m ost important venous outlets [H e g e d u s, S h a c k e l f o r d 1965,
KĘDZIA 1987] for the majority o f quad ruped mammals were losing significance. From the point o f v iew o f the fluid m e chanics laws these foramina, even when they occur in man, w hich is rare in the case o f the postglenoid foramen, play a minor role in the venous blood outflow [SCHELLING 1978]. In the contemporary man approximately 95% o f the venous blood volum e leaves the cranium through the jugular foramina [TYCHMANOWICZ
100 Jarosław W ysocki
1992], From : among numerous venous emissaries only the mastoid and condy loid emissaries [SCHELLING 1978, SO L-
TER, PALJAN 1973] seem to be o f great
hem odynam ic significance. The trans form ations described m ust have been beneficial if they were preserved in the course o f the evolution. These were not m inor changes, since, for instance, in contem porary birds the relationship be tween the m orphology o f the cranial venous system and the anim al’s life style
[K RASNIK O V 1988] is evident. The modi
fication o f the m anner o f venous blood outflow from the cranium was probably one o f the leading mechanisms in the process o f the brain development, since it facilitated cooling o f this organ generat ing so large quantities o f heat [C APUTA 1982, Ku j a w a 1993, M A RIAK 1996]. The capacity and, as a result, the mass o f the brain were growing in proportion to the sphere radius raised to the third power, while the surface o f the organ and surrounding cranium, acting as the me dium in the heat exchange - only pro portionally to the second power o f this radius. Improvement o f the flow blood to and from the cranium interior was pro bably one o f the basic problems to be solved in the second stage o f evolution
[KUJAWA 1993], A close relationship
between the brain capacity and the cross section o f the venous sinuses o f the dura m ater was proved recently following the study o f human corpses [SEKELES, Gi t- LIN 1981]. Similarly, a close relationship between the size o f the jugular foramina and the size o f the two most important venous emissaries: mastoid and condy
loid one [SOLTER, PALJAN 1973] was
proved.
In the light o f the above listed obser vations it seems clear that also cranial
venous emissaries must have played a significant role in the process o f anthro- pogenesis. The fact that there are no scientific publications to support this intuitive presumption shared by many authors from various fields o f science is very surprising.
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Streszczenie
D okonano przeglądu najw ażniejszych pozycji piśm iennictw a dotyczącego anatom ii i fizjologii układu żylnego głowy u człow ieka i zw ierząt w aspekcie przekształceń zachodzących w procesie antropogenezy. Stw ierdzono, Ze pionizacja ciała była praw dopodobnie jed n y m z czynników decydujących o szybkim tem pie ew olucji Hominidae.
N owe, korzystniejsze w arunki odpływ u żylnego z w nętrza czaszki, pow stałe n a sk u tek dołączenia siły graw itacji do dotychczas funkcjonujących m echanizm ów rządzących ruchem krwi żylnej, spow odow ały praw dopodobnie uspraw nienie procesów term oregulacji ośrodkow ego układu nerw ow ego i stw orzyły podstaw y dla skokow ego zw iększenia jeg o m asy. Z punktu w idzenia podstaw ow ych praw fizyki i m atem atyki oczyw isty w ydaje się fakt, że w m iarę w zra stania w ielkości obiektu o kształcie zbliżonym do kulistego, stosunek je g o pow ierzchni do objętości m aleje. M ózgo wie, będąc narządem bardzo aktyw nym fizjologicznie i w ytw arzającym znaczne ilości ciepła (u człow ieka do 15% ciepła ustrojow ego) w ym aga w ydajnego i niezaw odnego m echanizm u chłodzenia, zapobiegającego przegrzaniu. Z badań czynnościow ych prow adzonych tak na zw ierzętach, ja k i n a ludziach w iadom o, że d ecy d u jącą rolę w tych procesach odgryw a napływ chłodnej krwi żylnej: u zw ierząt ze śluzów ki ja m y nosow ej - u ludzi zaś z pozbaw ionej ow łosienia twarzy. W ydaje się, że siłą spraw czą tego napływ u je s t złożony system u m ożliw iający spraw ny odpływ żylny z ja m y czaszki, stw arzający adekw atne siły ssące. W ydaje się także, że pow szechna u ludzi (także u ptaków ), a nieobecna u zw ierząt czw oronożnych lateralizacja głów nych otw orów żylnych czaszki, sprzyja tym m echanizm om . Z praw a B em oulliego w ynika bow iem , że prąd cieczy traci znacznie w ięcej energii w przypadkach, gdy rozdziela się on n a strum ienie rów norzędnej w ielkości, niż w sytuacjach, w których uchodzi jed n y m , dom inującym otworem. W św ietle powyższych rozw ażań asym etria układu żylnego czaszki pow inna być uw ażana za zjaw isko progresywne.
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