The arterial fibrous rings were investigated in human embryos aged 7 and
8 weeks under light and scanning electron microscopes. In the present study it
was shown that the arrangement of collagen and formation of fibres changes
rapidly within one week. In the 7th week there are no collagen fibres and the
netlike fibrils extend between processes of fibroblasts. At the end of the
8th week the collagen fibres are formed and they have different arrangements
in the particular layers of the fibrous rings. (Folia Morphol 2010; 69, 3: 180-183

Bruska, M.

Rauhut-Klaban, M.

English

Via Medica Journals

Folia Morphol. Vol. 69, No. 3, pp. 180–183Copyright © 2010 Via MedicaISSN 0015–5659www.fm.viamedica.plO R I G I N A L   A R T I C L E180Address for correspondence: M. Rauhut-Klaban, MD, Department of Anatomy, University of Medical Sciences, Święcickiego 6,60–781 Poznań, Poland, tel: +48 61 854 65 54, e-mail: rauhut@wp.plScanning electron microscopic studyof the fibrous rings of the arterial orificesin embryos of the 7th and 8th weeksM. Rauhut-Klaban, M. BruskaDepartment of Anatomy, University of Medical Sciences, Poznań, Poland[Received 12 July 2010; Accepted 15 July 2010]The arterial fibrous rings were investigated in human embryos aged 7 and8 weeks under light and scanning electron microscopes. In the present study itwas shown that the arrangement of collagen and formation of fibres changesrapidly within one week. In the 7th week there are no collagen fibres and thenetlike fibrils extend between processes of fibroblasts. At the end of the8th week the collagen fibres are formed and they have different arrangementsin the particular layers of the fibrous rings. (Folia Morphol 2010; 69, 3: 180–183)Key words: human embryology, heart, arterial fibrous rings,scanning electron microscopeINTRODUCTIONEarly in the development of the heart, the singleheart tube consists of the inner and outer tubes,the endocardium, and myocardium, respectively,which are separated by an extracellular matrix se-creted by the myocardial cells and termed cardiacjelly. This extracellular matrix promotes the tubularlumen during contraction and acts as a site for thedeposition of inductive factors from the myocardialcells which can modify the differentiation of speci-fic endocardial cells [1]. The cardiac extracellularmatrix contains: a) structural proteins (collagen andelastin), b) cell adhesive molecules (fibronectin andlaminin), and c) proteoglycans [4]. This extracellularmatrix of the heart plays an important role in growthand development. The role of the extracellular ma-trix in heart development includes signalling neces-sary for cell migration, cell sorting, adhesion, differ-entiation, angiogenesis, and valve formation [3–5].During early embryogenesis, collagen is detected inthe atrioventricular region, which is associated withthe formation of valves.Alteration of collagen results in changes in themyocardial mechanical properties and ventricularfunction [8]. Cardiac collagen plays a vital role inthe maintenance of myofibrillogenesis [6]. The aimof the present study is to describe the arrangementof collagen fibres in the outflow tract of human em-bryos aged 7 and 8 weeks.MATERIAL AND METHODSInvestigations were performed on 7 embryos ofdevelopmental stages 19 and 23 (age 46 and 56 post-ovulatory days) from the Collection of the De-partment of Anatomy in Poznań. All embryos wereembedded in toto in paraplast, and serial sectionsin horizontal and sagittal planes were made (Table 1).Five embryos were intended for histological study.Sections of these embryos were stained with hae-matoxylin and eosin and with cresyl violet accord-ing to Nissl. Sections of two embryos were inspect-ed under scanning electron microscope (SEM). Sec-tions were rinsed in 96% alcohol, and after dryingat room temperature (20–25 degrees) all sections181M. Rauhut-Klaban, M. Bruska, Ultrastructure of embryonic fibrous ringswere coated with a 15 µm layer of gold and exami-ned under SEM Zeiss 435 VP at an accelerating volt-age of 15 KV.RESULTSIn embryos at stage 19 (46 postovulatory days)the arterial valves develop in the lower part of theconotruncal septum. Cells from this septum contri-bute to the formation of the valves (Fig. 1). The fibrousrings contain on their periphery concentrically ar-ranged connective tissue fibres. Collagen fibres in therings are arranged in the form of loose, netlike struc-tures with many fibroblasts (Figs. 2, 3). Collagen fibrilsextend between the processes of the fibroblasts (Fig. 4).The collagen fibrils are thin, elongated structures ofvariable diameter. They pass in various directions andsurround the fibroblasts and myocytes. In the lastweek of embryonic development the fibrous rings aremore compact annuli (Fig. 5). Under the SEM theserings consists of three layers. The outer and inner lay-ers have a loose arrangement. The middle layer isformed of densely packed collagen fibres which arebuilt of collagen fibrils (Figs. 6, 7).Table 1. Developmental stage, age, and plane of section of investigated embryosCatalogue No. Developmental stage Age in postovulatory days Plane of sectionB288 19 51 HorizontalB123 19 46 HorizontalBł1 20 49 SagittalZ9 21 51 HorizontalZ3 22 53 HorizontalBł9 23 56 HorizontalB293 23 56 SagittalFigure 1. Horizontal section of an embryo at stage 19; H+E;¥ 40; a — annulus fibrous of the aorta, b — lumen of the aorta,c — lumen of the pulmonary trunk, d — annulus fibrous of thepulmonary trunk.Figure 2. Horizontal section of an embryo at stage 19. Valve of theaorta; SEM; a — annulus fibrous of the aorta, b — cusp of the aorta.Figure 3. Horizontal section of an embryo at stage 19. Part ofannulus fibrous of aorta; SEM; a — fibroblast, b — network ofcollagen fibrils.182Folia Morphol., 2010, Vol. 69, No. 3DISCUSSIONIn the adult myocardium there are at least fivecollagen isoforms. The most abundant forms of col-lagen are collagen types I and III, which representmore than 90% of all collagen fibres in the myocar-dium [2, 8–12]. During development, collagen types Iand III are present in the valvular regions.Collagen fibres of the heart have been dividedinto epimysial, perimysial and endomysial compo-nents [7]. Modifications of the collagenous archi-tecture change during development and in heartdisease. The main sources of collagen synthesis arecardiac fibroblasts, which form the largest groupamong cardiac nonmyocyte cells.In the present study it was shown that the ar-rangement of collagen and the formation of fibreschanges rapidly within one week. In the 7th weekthere are no collagen fibres and the netlike fibrilsFigure 4. Horizontal section of an embryo at stage 19; Part ofvalve of the aorta; SEM; a — fibroblast, b — process of thefibroblast, c — collagen fibrils.Figure 5. Sagittal section of an embryo at stage 23; H+E; ¥ 100;a — ductus arteriosus, b — aorta, c — valve of pulmonary trunk,d — left ventricle, e — mitral valve, f — left fibrous trigone.Figure 6. Horizontal section of an embryo at stage 23; Valve ofpulmonary trunk; SEM; layers of annulus fibrous; a — innerlayer, b — middle layer, c — outer layer.Figure 7. Horizontal section of an embryo at stage 23; Valve ofpulmonary trunk; SEM; a — bands of collagen fibres.extend between processes of fibroblasts. At the endof the 8th week the collagen fibres are formed andthey have different arrangements in the particularlayers of the fibrous rings.REFERENCES1. Bolender DL, Markwald RR (1991) Endothelial forma-tion and transformation in early avian heart development:induction by proteins organized into adherans. In: Fein-berg RN, Sherer GK, Auerback R eds. The developmentof the vascular system. Karger, Basel, pp. 109–124.2. Bishop JE, Laurent GJ (1995) Collagen turnover and itsregulation in the normal and hypertrophying heart.Eur Heart J, 16C: 38–44.3. Damsky CH, Werb Z (1992) Signal transduction by in-tegrin receptors for extracellular matrix: cooperativeprocessing of extracellular information. Curr Opin CellBiol, 4: 772–781.4. Dixon IMC, Ju H (1997) The cardiac extracellular matrixduring development. In: Oštádal B, Nagano M, Takeda N,183M. Rauhut-Klaban, M. Bruska, Ultrastructure of embryonic fibrous ringsDolla NS eds. The developing heart. Lippincott, Raven,Philadelphia. New York, pp. 81–90.5. Duband JL, Dufours S, Thiery JP (1990) The instructiverole of fibronectins in cell migration during embryonicdevelopment. Ann NY Acad Sei, 588: 273–280.6. Fisher SA, Periascamy M (1994) Collagen synthesis in-hibitors disrupt embryonic cardiocyte myofibrilloge-nesis and alter the expression of cardiac specific genesin vitro. J Mol Cell Cardiol, 26: 721–731.7. Icardo JM, Colvee E (1998) Collagenous skeleton of thehuman mitral papillary muscle. Anat Rec, 252: 509–518.8. Janicki JS, Brower GL, Henegar JR, Wang L (1995) Ven-tricular remodeling in heart failure: the role of myocar-dial collagen. Adv Exp Med Biol, 382: 239–245.9. Lincoln J, Florer JB, Deutsch GH, Wenstrup RJ, Yutzey KE(2006) ColVa1 and ColXIa1 are required for myocar-dial morphogenesis and heart valve development. DevDyn, 235: 3295–3305.10. Pelouch V, Dixon JMC, Galfman L, Beamisk RE, Dhalla NS(1993) Role of extracellular matrix proteins in heartfunction. Moll Cell Biochem, 129: 101–120.11. Rao VU, Spinal FG (1999) Controlling myocardial ma-trix remodeling: implications for heart failure. CardiolRev, 7: 136–143.12. Tyagi SC (1997) Dynamic extracellular matrix remode-ling in the heart failure: cardiac hypertrophy, dilata-tion and fibrosis. Pathophysiology, 4: 227–234.

Scanning electron microscopic study of the fibrous rings of the arterial orifices in embryos of the 7th and 8th weeks

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Scanning electron microscopic study of the fibrous rings of the arterial orifices in embryos of the 7th and 8th weeks

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