狗冠状动脉的生物力学特性：Ⅰ.一维载荷下力学特性的实验研究

本文报道采用6例狗的左冠状动脉前室间支、旋支,右冠状动脉、胸廓内动脉,大隐静脉以及股静脉在生物软组织力学试验台上,进行离体的压力-直径关系和一维载荷下的应力-应变关系实验。上述血管的各向同性增量弹性模量(E_(inc)、容积弹性模量(E_v)和压力-应变模量(E_p)随血管内压力(P)的上升而增大;这些血管的dT/dλ随张应力T的增加而增大,其一维载荷下的应力-应变关系为指数函数。讨论了上述血管的显微结构成份含量与力学特性的关系,以及冠状动脉旁路移植实验研究中的力学问题,认为动脉的C/E值可以反映动脉弹性的大小;胸廓内动脉的力学特性比静脉更接近于冠状动脉,冠状动脉旁路移植时可优先选用该动脉。     

微观吸引作用对DNA膜弹性性质的影响

目的研究高价盐下微观吸引作用对DNA膜弹性性质的影响。方法采用Kornyshev静电拉链模型描述高价盐下DNA链间的相互作用势能;采用思想实验法和宏观连续介质弹性杆模型,预测单向应力状态下DNA膜的应力-应变关系、预应力和弹性模量。结果在给定封装条件下,DNA膜具有拉伸预应力和负的弹性模量,预应力为-1.52～1.17 MPa,弹性模量为-4.2～64 MPa。结论与单价盐下的情形不同,随着封装密度和盐浓度的变化,高价盐作用下微观吸引作用使得DNA膜弹性性能展现出非单调的变化,而且拉压弹性性能明显不同,拉伸预应力和压缩预应力以及正负弹性模量会出现转换。研究结果有助于进一步理解病毒复制的机制,并为基因检测和基因治疗提供参考。     

ACL和MCL拉伸力学性质实验研究

目的 研究了10具新鲜成人尸体膝关节前交叉韧带和内侧副韧带的拉伸力学性质,为临床提供生物力学参数.方法 取正常国人新鲜尸体前交叉韧带和内侧副韧带各20个试样进行单向拉伸实验,得出了破坏载荷、强度极限、最大应变、弹性模量.对实验数据以多项式进行拟合,得出了应力-应变曲线和应力-应变关系表达式.结果 前交叉韧带的拉伸强度极限最大应变弹性模量大于内侧副韧带.     

人股前区全厚、中厚和刃厚皮片垂直轴向本构关系及其意义

本文通过对股前区全厚、中厚和刃厚皮片垂直轴向拉伸试验，实验结果表明：它们的应力－应变关系为指数函数关系，材常数C（量纲）组间的比较依次为：全厚＜中厚＜刃厚，而材常数α（无量钢）组间的比较依次为：全厚＞中厚＞刃厚，并经t检验，刃厚支片的材料常数C和α与中厚或全厚去片相应的材料常之间的比较均有显著性差异（P＜0．01）。从一定应变时增量弹性模量的组间比较结果依次为：全厚＜中厚＜刃厚，刃厚片的增量弹性模量与其它两组比较均有显著性差异，这说明表皮抵抗变形的能力最强，乳头层次之，网状层最弱。     

材料参数与镍钛形状记忆合金的本构关系

在Ｔａｎａｋａ模型基础上，我们讨论了形状记忆合金热力学特性的本构关系。特别注意了桓温拉伸过程和强迫回复过程。本构方程的材料参数，即弹性模量Ｄ，变化张量Ω，热力弹性张量均以镍钛合金实验测试值来确定。在不同的应力－应变－温度关系试验中发现Ｄ和Ω与温度之间有很强的相关性。     

人体四肢正常动、静脉纵向残余应变与应力-应变关系

目的：探讨人体四肢正常动,静脉的纵向残余应变特性和应力－应变关系,以及对临床修复血管损伤时方法选择的影响。方法;以人体正常血管标本为研究对象,通过血管拉伸试验及检测血血管纵向伸长率,获取四肢正常的,动,静脉纵向残余应变及应力－应变变化规律。     

人眼巩膜归一化松弛函数探讨

本文对软组织材料——巩膜的力学性能进行描述.在单项拉伸状态下,测量了其拟弹性模量、破坏应力及相应的应变值.给出了单向拉伸状态下的应力应变曲线.同时做了常温下的应力松弛实验.测定了巩膜应力和时间相关的不同效应,给出了巩膜的归一化松弛函数和有关参数.     

人气管软骨的拉伸力学特性

背景:气管损伤缝合与新型人工气管的研制都需要了解气管软骨的拉伸力学特性以修复、重建气管功能。以往的国内外研究对人工气管的生物力学报道较多,而对人气管软骨生物力学的报道较少。目的:以一维拉伸实验方法观察气管软骨的力学性质。方法:正常人新鲜尸体气管标本2个,标本获取征得家属同意。取出标本,在常温下解冻,以手术刀切取气管软骨试样标本加工成试样长度25mm,宽度5mm,厚度1.8～2.2mm试样20个,在日本岛津电子万能试验机上对20个气管软骨试样进行一维拉伸实验,拉伸实验速度为5mm/min。观察试件拉伸最大载荷、最大位移、最大应力、最大应变、弹性模量、应力-应变曲线。结果与结论:人尸体气管软骨最大载荷为(60.946±10.377)N,最大位移为(1.973±0.159)mm,最大应力为(6.229±1.125)MPa,最大应变为(32.825±2.776)%。气管软骨的应力-应变曲线为指数关系变化的,曲线最初的低坡部分是由于施加拉力的方向与胶原蛋白结构的排列一致,曲线的陡峭部分代表胶原蛋白本身的拉伸刚度。为描述气管软骨一维拉伸中的应力-应变关系,对气管软骨实验数据各取15个点应力-应变数据采用多项式,以最小二乘法进行拟合,得出应力(δ)-应变(ε)关系σ(ε)=-0.1113e5+1.6021e4-7.8216e3+17.9951e2+3.624e式:。实验结果显示,气管软骨具有较强的承受载荷和抵抗变形能力,反映其具有黏性又有弹性的黏弹性力学特性,支持软骨的力学性质与软骨胶原含量呈正相关的观点。     

关节软骨压缩特性的实验研究

目的 探讨正常关节软骨的压缩特性。方法 将人的股骨头软骨制成圆柱形标本,分A、B、C、D四组。应用两种不同力学实验装置分别对A、B组标本加载,测定标本在受压后1秒末的应力和应变值,作出应力-应变曲线图。C组标本在恒定压力下受载,测量标本在受压后不同时间应变值的变化。D组标本受压后并保持一定的应变值,观察关节软骨受压后不同时间压力的变化。结果(1)正常关节软骨的瞬时应力-应变曲线呈非线性关系,应力越大,弹性模量值越高;两种装置的实验结果具有明显差异性。(2)关节软骨在恒定应力作用下,应变随时间的延长而增大,     

兔眼角膜生物力学特性的年龄相关性

目的 利用兔眼角膜条的单轴拉伸实验数据,研究角膜生物力学特性与年龄的相关性。 方法 分别取3月龄和7~8月龄兔眼角膜条,实施单轴拉伸实验,获得实验数据;用指数模型和幂模型对应力 应变数据进行分析;用黏弹性力学模型对应力松弛数据进行分析。结果 兔眼角膜条呈现非线性黏弹性特征。在实验误差允许的范围内,不同月龄兔眼角膜条的非线性应力-应变关系差别不明显,7~8月龄兔眼角膜的切线模量略偏大,但其应力衰减得明显快。不同的拉伸速率对3月龄兔眼角膜条非线性应力-应变关系的影响不明显,但快速拉伸后的角膜条应力衰减明显变快。结论 兔眼角膜随月龄增加会轻微变硬,而角膜的松弛特性随月龄变化明显。     

Age-related human small intestine methylation: evidence for stem cell niches

Background

The small intestine is constructed of many crypts and villi, and mouse studies suggest that each crypt contains multiple stem cells. Very little is known about human small intestines because mouse fate mapping strategies are impractical in humans. However, it is theoretically possible that stem cell histories are inherently written within their genomes. Genomes appear to record histories (as exemplified by use of molecular clocks), and therefore it may be possible to reconstruct somatic cell dynamics from somatic cell errors. Recent human colon studies suggest that random somatic epigenetic errors record stem cell histories (ancestry and total numbers of divisions). Potentially age-related methylation also occurs in human small intestines, which would allow characterization of their stem cells and comparisons with the colon.

Methods

Methylation patterns in individual crypts from 13 small intestines (17 to 78 years old) were measured by bisulfite sequencing. The methylation patterns were analyzed by a quantitative model to distinguish between immortal or niche stem cell lineages.

Results

Age-related methylation was observed in the human small intestines. Crypt methylation patterns were more consistent with stem cell niches than immortal stem cell lineages. Human large and small intestine crypt niches appeared to have similar stem cell dynamics, but relatively less methylation accumulated with age in the small intestines. There were no apparent stem cell differences between the duodenum and ileum, and stem cell survival did not appear to decline with aging.

Conclusion

Crypt niches containing multiple stem cells appear to maintain human small intestines. Crypt niches appear similar in the colon and small intestine, and the small intestinal stem cell mitotic rate is the same as or perhaps slower than that of the colon. Although further studies are needed, age-related methylation appears to record somatic cell histories, and a somatic epigenetic molecular clock strategy may potentially be applied to other human tissues to reconstruct otherwise occult stem cell histories.     

Differences in Intraepithelial Lymphocytes in the Proximal,Middle, Distal Parts of Small Intestine,Cecum, and Colon of Mice

We have previously reported the regional differences in the intraepithelial lymphocytes (IELs) present in the small intestine of mice. In this study, we further investigated these differences on the basis of our previous findings and studied the entire intestine, including the cecum and colon. Most of the significant differences in phenotypic compositions were found between the small and large intestines, although some differences were found among the different parts of the small and large intestines. In particular, the composition of the subsets in αβ T cells and γδ T cells clearly differed between the small and large intestines. For example, in αβ T cells, the percentages of double negative (DN) and CD8αα⁺ cells were higher in the large intestine, that of CD8αβ⁺ cells was higher in the small intestine, and those of CD4⁺ and CD4⁺ CD8αα⁺ double positive (DP) cells were higher in the distal part of the small intestine. In γδ T cells, the percentage of CD8αα⁺ cells was higher in the small intestine and that of DN cells was higher in the large intestine. These results indicate that the differences between IELs in the small and large intestines are discontinuous.     

Immunohistochemical characterization of the lymphocyte and the immunoglobulin-containing cell in the epithelium and the lamina propria of normal human intestines

In order to clarify difference of the mucosal immunity in various sites of normal large and small intestines, we studied the population of lymphocyte subsets and immunoglobulin (Ig)-containing cells in situ in biopsy specimens taken from various sites (ascending colon, sigmoid colon and rectum) of the large intestine and from the duodenum using an immunohistochemical method. Monoclonal antibodies against pan-T (Leu 1), cytotoxic/suppressor T (Leu2a), helper/inducer T (Leu3a), suppressor T (Leu15) and natural killer/K (Leu7) cells, and polyclonal antibodies to human IgG, IgA and IgM were used. In the duodenum, intraepithelial lymphocytes (IELs) were more prominent than in the large intestine. Immunoelectron microscopic observation revealed that some Leu2a+ IELs possessed pseudopods extending into intestinal epithelial cells, indicating that some IELs belong to the cytotoxic T cell subset. Leu7+ IELs were scarcely observed and Leu7+/Leu1+ ratio was higher in the large intestine than in the duodenum. Furthermore, the number of Leu7+ cells were more in the distal than the proximal colon. In the lamina propria Ig-containing cells tended to be fewer in the rectum than in the duodenum and the proximal colon. Our findings may suggest the variation of local immune responses and the difference of assigned immunological functions among the various sites of the intestines.     

P-选择素对ApcMin/+小鼠肠道肿瘤的作用

目的: 研究P-选择素(P-selectin)在Apc^Min/+小鼠肠道肿瘤中的作用。方法: 采用P-selectin 基因缺失的基因工程小鼠和肠道肿瘤模型Apc^Min/+小鼠杂交,计数Apc^Min/+小鼠与Apc^Min/+ P-selectin ^-/-杂交小鼠小肠及大肠肿瘤的数目,并测量其肿瘤体积,研究P-selectin对Apc^Min/+小鼠肠道肿瘤的作用。结果: 与Apc^Min/+小鼠相比,Apc^Min/+P-selectin^-/-杂交小鼠在9周龄时肠道肿瘤数目与总负荷明显减少。结论: P-selectin 缺失能够显著抑制Apc^Min/+小鼠肠道肿瘤的生长。     

Epithelial and subepithelial resistance of rat large intestine: segmental differences,effect of stripping,time course,and action of aldosterone

Epithelial and subepithelial electrical resistances of rat large intestine were measured by means of a 4-electrode AC impedance technique in three segments, colon ascendens, colon descendens and rectum. Epithelial resistance of colon ascendens and colon descendens was about 35 omega X cm2 and not different between these two segments. It was, however, about 3 times higher in rectum (99 omega X cm2). This finding is in accord with our previous observation of about 3-fold higher net fluxes of ions and water in colon ascendens and colon descendens than in rectum. It confirms the concept of a main functional difference between the terminal part of the large intestine (rectum) and the more proximal segments (colon). The acutely (within hours) varied level of aldosterone by keeping the rats for 7 h in anaesthesia caused in the rectum a more than 10-fold increase in short circuit current (Isc) and transepithelial voltage but no significant decrease in resistance. Similarly, the decline in Isc, as regularly observed in the early phase of in vitro measurements on partially stripped large intestine, was paralleled by voltage changes but not by changes in resistance. We conclude that the wide range of resistance values published so far was caused to a great extent by including various portions of colon or rectum. By comparing intact (not stripped) and partially stripped preparations (muscularis propria removed) of the rectum it was shown that partial stripping did not alter the epithelial resistance but reduced the subepithelial resistance in this segment from 26 to 8 omega X cm2, or by 68%.(ABSTRACT TRUNCATED AT 250 WORDS)     

Helicobacter hepaticus infection promotes colon tumorigenesis in the BALB/c-Rag2(-/-) Apc(Min/+) mouse

Adenomatous polyposis coli (APC) mutations are linked to human and mouse colorectal cancers. The Apc multiple intestinal neoplasia (Min) mouse mutation causes adenomas to develop throughout the small and large intestines. The BALB-Min (C.B6-Apc(Min/+)) congenic strain was generated by backcrossing into BALB/c the Apc(Min) allele from C57BL/6J-Apc(Min/+) mice. BALB-Min mice have a low tumor multiplicity (27.4 small intestine tumors/mouse) and a relatively long life span (>1 year) that makes them amenable to long-term studies. To investigate the interplay of the adaptive immune system and intestinal tumorigenesis, the immunodeficient compound mutant strain BALB-RagMin (C.Cg-Rag2(-/-) Apc(Min/+)) was generated. BALB-RagMin mice had a significant increase in tumors in the small, but not large, intestine relative to their BALB-Min counterparts (43.0 versus 24.0 tumors/mouse, respectively). The results suggest that the adaptive immune system plays a role in either the elimination or the equilibrium phase of cancer immunoediting in the small intestine in this model. We investigated the effect of the enterohepatic bacterial pathogen Helicobacter hepaticus on liver and intestine tumorigenesis in BALB-RagMin mice. H. hepaticus-infected BALB-RagMin mice developed moderate hepatitis, moderate typhlitis, and mild colitis. There were no differences in small intestine and cecal tumor multiplicity, regionality, or size relative to that in uninfected mice. However, H. hepaticus-infected BALB-RagMin mice had a significant increase in colon tumor incidence relative to uninfected BALB-RagMin mice (23.5% versus 1.7%, respectively). The data suggest that H. hepaticus, which is present in many research colonies, promotes colon tumorigenesis in the BALB-RagMin mouse and that it has the potential to confound colon tumorigenesis studies.     

Staphylococcus aureus MnhF Mediates Cholate Efflux and Facilitates Survival under Human Colonic Conditions

Resistance to the innate defenses of the intestine is crucial for the survival and carriage of Staphylococcus aureus, a common colonizer of the human gut. Bile salts produced by the liver and secreted into the intestines are one such group of molecules with potent antimicrobial activity. The mechanisms by which S. aureus is able to resist such defenses in order to colonize and survive in the human gut are unknown. Here we show that mnhF confers resistance to bile salts, which can be abrogated by efflux pump inhibitors. MnhF mediates the efflux of radiolabeled cholic acid both in S. aureus and when heterologously expressed in Escherichia coli, rendering them resistant. Deletion of mnhF attenuated the survival of S. aureus in an anaerobic three-stage continuous-culture model of the human colon (gut model), which represents different anatomical areas of the large intestine.     

The effect of vitamin C on the absorption of glycine and chlorides by the intestine

Summary The effect of ascorbic acid on the regulation of absorption of glycine was studied in experiments on 3 dogs with chronic fistulae of the intestine and colon. It was established that ascorbic acid, administered in definite doses, improved absorption of glycine in the intestine and of sodium chloride in the colon. 32 and 22 are the optimal ratios of glycine and sodium chloride to the vitamin. In the presence of the above ratio absorption of glycine in the intestines increases by 24–28%, while absorption of chlorides in the colon increases by 18%.Presented by Active Member Acad. Med. Sci. USSR P. S. Kupalov     

Specific gamma-glutamyl transpeptidase inhibitor from human and animal intestines.

An inhibitor of gamma-glutamyl transpeptidase in human and animal intestines was assayed by means of a new method. In mice fed with LSM fodder, accumulation of the inhibitor in the mucous membrane of the small intestine was observed. Purified gamma-glutamyl transpeptidase inhibitor from mouse and human intestines was identified as L-serine. Neither this amino acid nor purifed inhibitor acted on other intestinal peptidases. Presumably, one of the ingredients of LSM feed influences accumulation of the inhibitor, and consequently diminishes absorption of gamma-glutamyl substrates in the intestine.     

Gut formation after transection of the midgut loop in the chick embryo

The primitive gut in vertebrates can be divided into the foregut, midgut, and hindgut. The midgut forms the midgut loop or the intestinal loop, which rotates as it develops the small and large intestines. We examined the effects of transection of the midgut loop on the subsequent development of the intestine in chick embryos by their out-of-the-shell incubation. The development of the embryo and the intestines out of the shell was nearly identical to that usual in-the-shell incubation. The rotation of the midgut loop began in stage 27 (5 days of incubation) and was completed in stage 36 (10 days of incubation) after counterclockwise rotation through 180 degrees. In experimental groups, the midgut loop was transected immediately before or in the early stages of rotation (stages 27-33) proximally or distally to the apex of the loop. Transecting of the midgut loop caused little effects on its subsequent rotation regardless of the time or the site of transection although the secondary loop formation of intestine was poor in some cases. The stumps of the transected intestine were repaired and closed. After closure of the stumps, the proximal segment of the intestine was dilated in some cases. The secondary loop formation, or convolution of the intestine didn't occur in some dilated cases.