医学院校开设数学实验课程的认识与思考

开设数学实验课程,可以提高学生应用数学的意识和创新能力。本文论述了开设数学实验课的必要性,介绍了数学实验课程教学的指导思想、基本原则和应当具备的条件。     

Growth and renal function after steroid-free tacrolimus-based immunosuppression in children with renal transplants

Steroid withdrawal after renal transplantation and cyclosporine-based immunosuppression enhances growth in children, but this practice is not widely employed because of a 50%–60% rate of rejection, graft dysfunction, or graft loss. The current study evaluates growth and renal function after withdrawal and discontinuation of steroids within 1 year of transplantation in 52 children receiving tacrolimus (FK-506)-based immunosuppression. Height Z-score, weight-for-height index (WHI), and body mass index (BMI), as well as graft loss and calculated creatinine clearance as a measure of glomerular filtration rate (GFR), were assessed. Children were divided into three groups according to age at transplantation: group I, 16 children aged 0–5 years; group II, 17 children aged 6–12 years; group III, 19 children aged 13–16 years. Significant and sustained improvement in height occurred in groups I and III, with Z-scores increasing by 1.51 and 1.57 standard deviations at 3 years after transplantation compared with the Z-score at transplantation (P<0.02). Mean WHI values remained near 100% in groups I and III, and significantly increased above 100% only in group II at 2 years after transplantation. Although actual BMI scores improved significantly in groups II and III at both 2 and 3 years post transplantation (P<0.05), when BMI scores were adjusted for height age, none of these groups had values >95% denoting obesity. Failure of steroid withdrawal, defined as reinstitution of steroids, graft dysfunction, or graft loss, occurred in 9 of 68 (13%) children who underwent steroid withdrawal at any time after transplantation, and resulted in graft dysfunction or graft loss in 5 (7%). Over a 3-year period, rates of renal dysfunction, as manifested by >50% rise in the serum creatinine level above baseline, or graft loss were lower in these 68 children compared with 8 children who never had steroid withdrawal (P<0.05). Mean GFR at 3 years after transplantation ranged from 96 to 102 ml/min per 1.73 m² in all three steroid withdrawal groups, and remained stable during the 3 years of follow-up. These data indicate that steroid withdrawal enables normalization of growth without obesity, and without imposing an excessive risk for graft dysfunction or graft loss. Received: 29 March 1999 / Revised: 23 December 1999 / Accepted: 2 January 2000     

The growth hormone/insulin-like growth factor-I system: implications for organ growth and development

Growth hormone (GH) and insulin-like growth factors (IGFs) are essential for normal growth and development during embryonic stages as well as postnatally. While GH has little effect on these processes prenatally, the IGFs are important during these stages. On the other hand the GH-IGF-I axis is important for pubertal growth. To determine whether postnatal growth and development are dependent on circulating or locally produced IGF-I, we deleted the IGF-I gene in the liver using the cre/LoxP system used for tissue-specific gene deletion. These animals demonstrated approximately 75%–80% reduction in circulating IGF-I and an approximate fourfold increase in circulating GH. Despite the marked reductions in circulating IGF-I, growth and development was apparently normal. Thus the original somatomedin hypothesis needs to be re-evaluated in the light of these new findings. Received: 5 September 1999 / Revised: 11 December 1999 / Accepted: 18 December 1999     

Does bone design intend to minimize fatigue failures? A case for the affirmative

Threshold strain ranges help to control the ability of modeling to increase bone strength and "mass" and the ability of remodeling to conserve or decrease them. Whether expressed as strains or stresses, the probable remodeling threshold of bone (MESr) lies below its modeling threshold (MESm), which lies below its operational microdamage threshold (MESp), which lies well below its ultimate strength (Fx). Given normal modeling and remodeling potentials, that arrangement should tend to cause whole-bone strength and stiffness to keep typical peak bone strains ("E") from voluntary activities from exceeding bone's modeling threshold and therefore from reaching its microdamage threshold. Satisfying that laddered "MESr < "E" < MESm << MESp <<< Fx" arrangement should minimize fatigue failures of bones, which might be at least one purpose of normal bone design. That arrangement would have practical implications that include, in part, the following. (A) It could make healthy young adult bones about six times stronger than needed for the largest voluntary loads they usually carry. (B) It suggests a biomechanical pathogenesis for different kinds of osteoporosis. (C) It suggests design criteria that load-bearing bone implants and endoprostheses should satisfy to endure their voluntary mechanical usage. (D) It also suggests features that future models of mechanical loading effects on bone strength, architecture, and "mass" might incorporate. Received: October 20, 1999 / Accepted: February 10, 2000     

Suppression of growth plate chondrocyte proliferation by corticosteroids

Growth depression is a side effect of high-dose glucocorticoid therapy in childhood. It is partially mediated by alterations of the somatotropic hormone axis and partially by direct local effects on growth plate chondrocytes. The mechanisms of interaction of corticosteroids and somatotropic and calciotropic hormones at the cellular level were recently investigated in more detail, using experimental models of primary cultures of growth plate chondrocytes. In proliferative chondrocytes, growth hormone (GH) and the calciotropic hormones parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D [1α,25(OH)₂D₃] increase cell proliferation via stimulation of paracrine insulin-like growth factor-I (IGF-I) secretion. Corticosteroids decreased GH, and PTH or 1α,25(OH)₂D₃ stimulated cell growth in a dose-dependent manner. Corticosteroids in high doses reduced the expression of the GH receptor and type 1 IGF receptor. But the main antiproliferative molecular effect of corticosteroid was the reduction in basal and hormone-stimulated IGF-I secretion. The in vitro results are in accordance with the observation in animal experiments and in children treated with corticosteroids, demonstrating that the growth-depressing effect of corticosteroids can be compensated for by supraphysiological doses of GH or IGF-I. Received: 16 May 1999 / Revised: 31 January 2000 / Accepted: 8 February 2000     

Does growth hormone therapy harmonize distorted morphology and body composition in chronic renal failure?

Recombinant human growth hormone (rhGH) therapy of growth retardation in chronic renal failure (CRF) has become well established. While there are ample data about its effectiveness in restoring longitudinal growth delay, data on complex anthropometry are scarce. Twenty-three children with CRF (6 after renal transplantation) were investigated using 24 different parameters. The analysis revealed disproportionate growth in CRF. While parameters of the trunk and transverse dimension of the head were preserved, the extremities were affected more severely. Bone dimensions of the legs and arms as well as muscle mass were affected the most. RhGH therapy was effective in restoring impaired longitudinal dimensions of the body in CRF. The restoration of growth retardation occurred predominantly in the extremities. This was accompanied by an increase in transversal dimensions, circumferences and soft tissue of the extremities, as well as an increase in bone and muscle volume, indicating harmonization of the total body shape. The dimensions of trunk, forehead diameter and morphological face height remained within the normal range. There was no evidence of acromegaly in children with CRF and rhGH therapy. We conclude that rhGH therapy at a dose of 28 iU/m²/week is effective in restoring previously disproportional body structure and shape in children with CRF. Received: 3 December 1999 / Revised: 27 July 2000 / Accepted: 1 August 2000     

不同类型叶面肥对忍冬生长发育及金银花质量的影响

目的：研究不同类型叶面肥对忍冬生长发育及金银花质量的影响。方法：采用紫外分光度法测定绿原酸含量。结果：在新稍旺长期喷施全营养叶面肥（含N、P、K等大量元素和Zn、Mn、Fe、B、Cu、Mo等微量元素）可提高忍冬花枝比例，促进花枝伸长，增加叶面积，提高产量和金银花内绿原酸含量，其中高N型肥料效果最为显著；尿素和磷酸二氢钾的效果小于全营养叶面肥。结论：高N型叶面肥可促进忍冬生长发育，提高金银花产量和质量，较适合用于金银花生产。