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Journal of the Anatomical Society of India

Effect of Tangential Pressure of Pulsation on Tunica Media of Human Arteries

Author(s): Kumar, Keshaw

Vol. 51, No. 1 (2002-01 - 2002-06)

Department of Anatomy, Institute of Medical Sciences, B. H. U., Varanasi, INDIA

Abstract

During autopsy 10mm. long arterial segments were obtained from ascending aorta, pulmonary trunk and femoral artery immediately distal to their commencements to be preserved in 10% formalin from 300 human adults not suffering from any cardiovascular disease. Lumen of each arterial segment was opened by cutting its wall longitudinally to measure lumen circumference and wall thickness. Paraffin sections of 10 micron thickness were cut and stained with orcein and counterstained with haematoxylin and eosin to observe densities of elastic fibres and smooth muscle fibres per magnified field in tunica media of each artery.Number of elastic/smooth muscle fibres in ascending aorta, pulmonary trunk and femoral artery was calculated by multiplying arterial wall areas with tunica medial densities of these fibres in the arteries. Wall thickness of an artery is directly proportional to pulsatory power of that artery. Arterial segments having equal length and equal pulsatory power have equal number of smooth muscle fibres in their tunica media.

Key words: Tunica Media, Human arteries, Tangential Pressure

Introduction :

Effect of ageing in the tunica medial elastic fibres of aorta was studied by Foster (1909), Hass (1943), Saxton (1942) and Smith et al. (1951). Gray et al (1953) reported the effect of ageing in tunica medial elastic fibres of aorta as well as pulmonary artery. Ahmed (1967) described the age and sex differences in tunica medial structure of human aorta. Laitinen (1963) noticed the effect of experimental atherosclerosis in the elemental structure of aorta. Fischer (1971) showed the effect of oestrogen on collagen and elastin dynamic in arterial wall. Present study is conducted to observe the effect of pulsatory power on tunica medial elastic fibres and smooth muscle fibres of human arteries which is not available in the literature as yet.

Material and Method:

10mm. long arterial segments were obtained from ascending aorta, pulmonary trunk and femoral artery immediately distal to their commencements from 300 human adults immediately after their death due to accidents after knowing history from their relatives that they were not suffering from any cardiovascular disease. Arterial segments were preserved in 10% formalin. Lumen of each arterial segment was opened by cutting its wall longitudinally to measure lumen circumference and wall thickness. Mean of the wall thickness and mean of the lumen circumference were calculated separately for ascending aorta,pulmonary trunk and femoral artery.

Paraffin sections of 10 micron thickness were cut to be stained with orcein and counter stained with haemotoxylin and eosin. Each layer of arteries was graded for fibres + , ++, +++,++++ according to density of elastic fibres as well as smooth muscle fibres with + representing the minimum and ++++ representing the maximum density of fibres. Results were obtained as visual assessments by a single observer to record tunica medial densities of elastic fibres and smooth muscle fibres per magnified field in each artery.

Number of elastic fibres and smooth muscle fibres in tunica media of ascending aorta, pulmonary trunk and femoral artery was calculated by multiplying arterial wall areas with tunica medial densities of these fibres in the arteries. Arterial wall area was obtained by multiplying arterial length, arterial wall thickness and arterial lumen circumference with one another. (Kumar, 1998). Pulsatory power of above arteries was calculated by the formula 'Pulsatory power of an artery is directly proportional to wall thickness of that artery having 1mm wall thickness is reported as 2000 joule per heart beat (Kumar 1993)'.

Observations:

Mean wall thickness of ascending aorta was 1.5mm while in case of pulmonary trunk and femoral artery it was 0.5mm (Table 1). Mean lumen circumference of femoral artery was 15mm while in case of ascending aorta and pulmonary trunk it was 60mm (Table 1).

Density of elastic fibres was ++++ in tunica media of ascending aorta (Fig. 1) as well as pulmonary trunk (Fig. 2) but in tunica media of femoral artery (Fig. 3) density of elastic fibres was + (Table 2).

Table-1 Arterial wall area of arterial segments having equal length

Arterial
segment
Arterial
wall
thickness
Lumen
circumference
Length of
arterial
segment
Arterial
wall area
Ascending aorta 1.5mm 60mm 10mm 900 mm3
Pulmonary Trunk 0.5mm 60mm 10mm 300 mm3
Femoral artery 0.5mm 15mm 10mm 75 mm3

 

Table-2: Densities of elastic fibres and smooth muscle fibres in tunica media of different arteries

Arteries Elastic fibres Smooth muscle fibres
Ascending aorta ++++ +
Pulmonary Trunk ++++ +
Femoral artery + ++++

Density of smooth fibres was + in tunica media of ascending aorta (Fig. 1) as well as pulmonary trunk (Fig. 2) but in tunica media of femoral artery (Fig. 3) density of smooth muscle fibres was ++++ (Table 2).

Arterial wall area of pulmonary trunk segment was four times greater than the arterial wall area of femoral arterial segment and arterial wall area of ascending aorta segment was thrice more than the arterial wall area of pulmonary trunk segment (Table 1).

Ratio of 3 :1 (Table 6) between number of elastic fibres (Table 3) as well as smooth muscle fibres (Table 4) equalled with ratio between pulsatory powers of these arteries (Table 5). Pulmonary trunk segment and femoral arterial segment had equal number of smooth muscle fibres (Table 4, 7 & 8) and equal pulsatory powers (Table 5 & 8) but in the number of elastic fibres a ratio of 16:1 was existing between pulmonary trunk segment and femoral arterial segment (Table 7). Therefore, it is concluded that pulsatory power of an artery has its effects only on the number of smooth muscle fibres in tunica media of that artery. Arterial segments having equal length and equal pulsatory powers have equal number of smooth muscle fibres in their tunica media (table 8).

Table-3 Number of tunica medial elastic fibres in arterial segments having equal length

Arterial Segments Aterial Wall
area (mm3)
Density of
elastic
fibres
Number of
elastic
fibres
Ascending aorta 900 ++++ 900 x 4 ‘+’ = 3600 +
Pulmonary trunk 300 ++++ 300 x 4 ‘+’ = 1200 +
Femoral artery 75 + 75 x 1‘+’ = 75 +

Pulsatory power of ascending aorta was 3000 joule per heart beat while in case of pulmonary trunk and femoral artery it was 1000 joule per heart beat (Table 5).

Table-4 Number of tunica medial smooth muscle fibres in arterial segments having equal length

Arterial
segments
Arterial
wall area
(mm3)
Density
of smooth
muscle
fibres
Number
of smooth
muscle
fibres
Ascending aorta 900 + 900 x 1 ‘+’ = 900 +
Pulmonary trunk 300 + 300 x 1 ‘+’ = 300 +
Femoral Artery 75 ++++ 75x4 ‘+’ = 300 +

Table-5 Pulsatory power and number of the tunica medial elastic fibres & smooth muscle fibres in arterial segments having equal length.

Arterial
segments
Pulsatory
power
Joule/Heart Beat
Number
of elastic
fibres
Number
of smooth
muscle
fibres
Ascending aorta 3000 3600 + 900+
Pulmonary trunk 1000 1200 + 300+
Femoral artery 1000 75 + 300 +

Table- 6: Ratio between number of tunica medial elastic fibres/smooth muscle fibres in ascending aorta and pulmonary trunk segments having equal length

Fibres Ascending aorta Pulmonary Trunk Ratio
Number of elastic fibres 3600+ 1200 + 3 : 1
Number of smooth muscle fibres 900+ 300+ 3 : 1

Table- 7 Ratio between number of tunica medial elastic fibres/smooth muscle fibres in pulmonary trunk and femoral arterial segments having equal length.

Fibres Pulmonary
Trunk
Femoral
artery
Ratio
Number of elastic fibres 1200+ 75+ 16 : 1
Number of smooth Muscle fibres 300+ 300+ 1 : 1

Table-8 Ratio between pulsatory powers and number of tunica medial smooth muscle fibres in pulmonary trunk and femoral arterial segments having equal length

  Pulmonary
Trunk
Femoral
artery
Ratio
Pulsatory power in Joule/heart beat 1000 1000 1 : 1
Number of tunica medial smooth muscle fibres 300 + 300+ 1 : 1

Discussion:

Wehn (1957) pointed that in embryos and in lower organisms the peripheral vessels contract rhythmically and are responsible for the circulation of blood. Even when the heart develops it does so as a specialized type of arterial segment, so there is nothing inherently impossible about the concept that muscular arteries may be contracting rhythmically with each heart beat and that this contraction is controlled and serves some purpose.

Kumar (2001) described that heart beat per minute corresponds with the arterial pulsation per minute and arterial pulsation consists of arterial expansion followed by arterial contraction. Elasticity of an artery depends upon the density of elastic fibres in its tunica media and muscularity of an artery depends upon the density of smooth muscle fibres in its tunica media. During systole of heart arterial expansion occurs according to arterial elasticity and during diastole of heart arterial contraction occurs according to arterial muscularity.

Because elastic fibres and smooth muscle fibres are the only components related to pulsation in arterial tunica media, therefore, arterial pulsatory power must effect either both or one of these components. Answer of this question was not available in the literature as yet that whether the arterial pulsatory power effected only the arterial contraction or arterial expansion as well as arterial contraction both. Present study clarified that arterial pulsatory power effected only the arterial contraction. Arterial expansion is not effected by the arterial pulsatory power at all because pulsatory power did not effect number of tunica medial elastic fibres in the arteries. Only the number of tunica medial smooth muscle fibres was effected by the arterial pulsatory power.

Findings obtained in the present work revealed + density of smooth muscle fibres and ++++ density of elastic fibres in the tunica media of ascending aorta which resembled with the observations made by Foster (1909), Hass (1943), Saxton (1942), Smith et al. (1951) and Fischer (1971) who reported maximum distribution of elastic fibres and minimum distribution of smooth muscle fibres in tunica media of ascending aorta.

In the Present study ++++ density of elastic fibres and + density of smooth muscle fibres noticed in the tunica media of pulmonary trunk support the results obtained by Gray et al (1953) where they found maximum distribution of elastic fibres and minimum distribution of smooth muscle fibres in tunica media of pulmonary artery as well as aorta.

References

  1. Fischer, G. M. (1971): Effect of oestrogen on collagen and elastin dynamic in arterial wall. Circulation, 44,(Sup.11): 21. J. Anat. Soc. India 51(1) 35-38 (2002)
  2. Foster, L. L. (1909): Changes occuring in the elastic fibres of the aorta with advancing age. Journal of Medical Reserach 2 : 297-311
  3. Gray, S.H.; Hardler, F. P.; Blache, J.O.; Zuckner, J. and Blumenthal, H.T. (1953): Ageing process of aorta and pulmonary artery in negro and white races. Archives of Pathology. 56 : 238-253.
  4. Hass, G. M. (1943): Elastic tissue. Relation between the structure of the ageing aorta and the properties of the isolated aortic elastic tissue. Archives of Pathology, 35 : 29-45.
  5. Kumar Keshaw (1993): Pulsatory power of human arteries. Vijnana Parishad Anusandhan Patrika 36, (2) : 115-120.
  6. Kumar Keshaw (1998): Area of arterial wall. Vijnana Parished Anusandhan Patrika. 41, (3) : 211-215.
  7. Kumar Keshaw (2001): Microstructure of human arteries. Journal of Anatomical society of India. 50 (2) : 127-130
  8. Laitinen, E. (1963): Changes in the elemental structure of the aorta in human and experimental atherosclerosis. Acta. Pathologica microbiologica scandenevia 167:
  9. Ahmed M. Mumtazuddin (1967): Age and Sex differences in the structure of the tunica media of the human aorta. Acta. Anatomica 66 : 45 - 58.
  10. Saxton, J. A. (1942) Elastic properties of the rabbit aorta in relation to age. Archives of Pathology 34 : 262-274.
  11. Smith,C.; Seitner, M. M. and Wang, H. P. (1951): Ageing changes in the tunica media of aorta. Anatomical Record. 109: 13-39.
  12. When, P. S. (1957) Pulsatory activities of peripheral arteries. Scandenevian Journal of Clinical Laboratory Investigation I.Suppl. 30 : 1

Missing Image

Fig-1. Transverse section of Human ascending aorta showing ++++ density of elastic fibres (EF) and + density of smooth muscle fibres (SMF) in tunica media. (TM) (Orcein X 100)

Missing Image

Fig-2. Transverse section of human pulmonary trunk showing ++++ density of elastic fibres (EF) and + density of smooth muscle fibres (SMF) in tunica media. (TM) (Orcein X 100)

Missing Image

Fig-3. Transverse section of human femoral artery showing + density of elastic fibres (EF) and ++++ density of smooth muscle fibres (SMF) in tunica media. (TM) [Internal elastic lamina - IEL] (Orcein X 100)

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