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排序方式: 共有793条查询结果,搜索用时 296 毫秒
1.
V. G. Borkhvardt 《Russian Journal of Developmental Biology》2000,31(3):154-161
The development of the fin and limb buds involves a balance of centrifugal (active) and centripetal (passive) mechanical forces,
the first of which acts to move the walls of these structures away from each other and the second of which holds them together.
When the volume of the mesodermal core increases, the generated force meets with the resistance of the basal membrane, and
as a result, the limb bud has a tendency to acquire a cylindrical shape. Collagen fibers, individual mesenchymal cells, and
their groups hold together the dorsal and the ventral wall of the limb bud, prevent the movement of these walls away from
each other, and in this way direct bud growth along the proximodistal and the anteroposterior axes. The balance of the forces
which stretch the ectodermal layer and those which constrain it has also been observed in the development of other body parts. 相似文献
2.
3.
Gender difference in the relationship of performance in the handgrip and standing long jump tests to lean limb volume in young adults 总被引:1,自引:0,他引:1
B. N. Davies Elizabeth J. Greenwood S. R. Jones 《European journal of applied physiology and occupational physiology》1988,58(3):315-320
Groups of young, adult males and females performed the handgrip and standing long jump tests. Their total forearm and leg volumes were calculated from a series of circumference and length measurements, and the lean volumes (bone + muscle) calculated by taking the skinfold thickness into consideration. In the handgrip, the mean female performance was 298 N compared with 496 N for the males. In the standing long jump, mean performance expressed as distance x body mass was 87.3 kg.m for females compared with 137.7 kg.m for males. These superior performances of males could simply reflect their greater muscle mass, as the mean lean volumes of female and male limbs respectively were 0.54 l and 0.89 l for forearms, and 11.82 l and 14.82 l for the two legs. However, when the performances of males and females were grouped by lean limb volume, it was found that while in both tests there were linear relationships, males and females did not share a common line. In both tests the male relationship was at a higher level than the female; therefore, for a given lean volume, the male performance was significantly superior to that of the female. The gender difference found in this study has not been seen in other studies in which the performance of skeletal muscle has been related to the cross-sectional area of the active muscles and the possible reasons for the differences are considered. 相似文献
4.
Summary In order to study mitogenic control during axolotl limb regeneration, we have developed a primary blastema cell culture as a very sensitive bioassay for blastema mitogens. Transferrin, an iron-binding glycoprotein which has been shown to be the neurotrophic factor for muscle cells, is the mitogen which has been analysed in the present report. Addition of approximately 2 g human transferrin/ ml of serum-free culture medium enhances blastema cell proliferation 11-fold over control levels and 2-fold over that produced by the addition of nerve extracts or purified growth factors extracted from nerve tissues (basic and acidic fetal growth factor, FGF). At a higher concentration (20 g/ml), transferrin alone has no mitogenic effect unless the medium is also supplemented with FeCl3 (100 M). The results are discussed with regard to the sensitivity of the blastema cell culture bioassay and in the context of the neurotrophic theory of urodele limb regeneration. 相似文献
5.
Fully adult partial skeletons attributed to Australopithecus afarensis (AL 288-1, “Lucy”) and to Homo habilis (OH 62, “Lucy's child”), respectively, both include remains from upper and lower limbs. Relationships between various limb bone dimensions of these skeletons are compared to those of modern African apes and humans. Surprisingly, it emerges that OH 62 displays closer similarities to African apes than does AL 288-1. Yet A. afarensis, whose skeleton is dated more than 1 million years earlier, is commonly supposed to be the ancestor of Homo habilis. If OH 62, classified as Homo habilis by its discoverers, does indeed represent a stage intermediate between A. afarensis and later Homo, a revised interpretation of the course of human evolution would be necessary. 相似文献
6.
Shingo Kurabuchi 《Development genes and evolution》1992,201(6):376-382
Summary The relationship between the size and shape of regenerative outgrowth and the quantity of innervation was studied in adult Xenopus laevis. The forelimbs, of which the nerve supply was artificially altered, were amputated midway through the stylopodium and were kept for 1 year. The regenerative outgrowths that formed in normal limbs with an intact nerve supply were mainly spike-shaped and occasionally rod-shaped. However, when the nerve supply to the distal part of the forelimb was augmented by surgically diverting ipsilateral sciatic nerve bundles, the quantity of innervation was increased to about two and a half times that of the normal limb. These hyperinnervated outgrowths were somewhat larger than those of the normally innervated outgrowths and the majority of them were oar-shaped, a type hardly ever encountered in normal regeneration. In contrast, when partial denervation was performed concomitantly with limb amputation, by ablation of the N. radialis at the shoulder joint, the quantity of innervation decreased to about one half that of the normal limb. The outgrowths obtained were spike-shaped in all cases, with their size being about half that of the normally innervated outgrowths. Furthermore, when both the N. radialis and N. ulnaris were ablated in the same way, the amputated limbs were mostly non-regenerative, but some of them regenerated small conical outgrowths. Based on these results, a discussion is presented concerning the relationship between a regenerative outgrowth and the innervation of the forelimb in Xenopus. 相似文献
7.
Summary Cellular impalements were used in combination with standard transepithelial electrical measurements to evaluate some of the determinants of the spontaneous lumen-positive voltage,V
e
, which attends net Cl– absorption,J
Cl
net
, and to assess how ADH might augment bothJ
Cl
met
andV
e
in the mouse medullary thick ascending limb of Henle microperfusedin vitro. Substituting luminal 5mm Ba++ for 5mm K+ resulted in a tenfold increase in the apical-to-basal membrane resistance ratio,R
c
/R
bl
, and increasing luminal K+ from 5 to 50mm in the presence of luminal 10–4
m furosemide resulted in a 53-mV depolarization of apical membrane voltage,V
a
. Thus K+ accounted for at least 85% of apical membrane conductance. Either with or without ADH. 10–4
m luminal furosemide reducedV
e
andJ
Cl
net
to near zero values and hyperpolarized bothV
a
andV
bl
, the voltage across basolateral membranes; however, the depolarization ofV
bl
was greater in the presence than in the absence of hormone while the hormone had no significant effect on the depolarization ofV
a
, Thus ADH-dependent increases inV
b
were referable to greater depolarizations ofV
bl
in the presence of ADH than in the absence of ADH 68% of the furosemide-induced hyperpolarization ofV
a
was referable to a decrease in the K+ current across apical membranes, but, at a minimum, only 19% of the hyperpolarization ofV
bl
could be accounted for by a furosemide-induced reduction in basolateral membrane Cl– current. Thus an increase in intracellular Cl– activity may have contributed to the depolarization ofV
bl
during net Cl– absorption, and the intracellular Cl– activity was likely greater with ADH than without hormone. Since ADH increases apical K+ conductance and since the chemical driving force for electroneutral Na+,K+,2Cl– cotransport from lumen to cell may have been less in the presence of ADH than in the absence of hormone, the cardinal effects of ADH may have been to increase the functional number of both Ba++-sensitive conductance K+ channels and electroneutral Na+,K+,2Cl– cotransport units in apical plasma membranes. 相似文献
8.
Summary The present studies examined some of the properties of Cl– channels in renal outer medullary membrane vesicles incorporated into planar lipid bilayers. The predominant channel was anion selective having aP
Cl/P
K ratio of 10 and a unit conductance of 93 pS in symmetric 320mm KCl. In asymmetric KCl solutions, theI-V relations conformed to the Goldman-Hodgkin-Katz equation. Channel activity was voltage-dependent with a gating charge of unity. This voltage dependence of channel activity may account, at least in part, for the striking voltage dependence of the basolateral membrane Cl– conductance of isolated medullary thick ascending limb segments. The Cl– channels incorporated into the planar bilayers were asymmetrical: thetrans surface was sensitive to changes in ionized Ca2+ concentrations and insensitive to reducing KCl concentrations to 10mm, while thecis side was insensitive to changes in ionized Ca2+ concentrations, but was inactivated by reducing KCl concentrations to 50mm. 相似文献
9.
H. Preuschoft 《Human Evolution》1989,4(2-3):145-156
The variation of body shape among prosimians is reviewed. Special emphasis is placed on the selective advantages, that is
the mechanical reasons, to which variants of the locomotor apparatus can be traced back.
There are differences found in the cheiridia, but at present they cannot be explained in terms of mechanics; there is nearly
no knowledge about the mechanical meaning of their diversity. Myological characteristics of taxa can be explained mechanically,
but this has not yet been done.
Well known are variations of body proportions. These discriminate higher taxa, and are largely coincident with the often-used
locomotor categories. In spite of this, there are only few sound arguments about the real biomechanic value of characteristic
proportions for a given locomotor mode. What is known on this field, is reviewed. Progress can be made only, if the mechanical
conditions, set by postural behavior and locomotion, are understood completely.
The subtle distinctions between lower taxonomic units can normally be identified only on the basis of detailed and quantified
analyses of movements on one hand, and of biometrics on the other. In the few cases in which such studies have been made,
the differences of morphology fit to the mechanical requirements of locomotion which also differ only in quantitative details. 相似文献
10.
Satoshi Muraki Masahiro Yamasaki Yoshito Ehara Kunio Kikuchi Kunihiro Seki 《European journal of applied physiology and occupational physiology》1996,74(5):481-483
The purpose of the present study was to examine the effect of maximal arm exercise on the skin blood circulation of the paralyzed
lower limbs in persons with spinal cord injury (PSCI). Eight male PSCI with complete lesions located between T3 and L1 performed
graded maximal arm-cranking exercise (MACE) to exhaustion. The skin blood flux at the thigh (SBFT) and that at the calf (SBFC)
were monitored using laser-Doppler flowmeter at rest and for 15 s immediately after the MACE. The subject's mean peak oxygen
uptake and peak heart rate was 1.41 ± 0.22 1·min−1 and 171.6 ± 19.2 beats·min−1, respectively. No PSCI showed any increase in either SBFT or SBFC after the MACE, when compared with the values at rest.
These results suggest that the blood circulation of the skin in the paralyzed lower limbs in PSCI is unaffected by the MACE. 相似文献