El aprendizaje basado en problemas. De herejía artificial a res popularis / Problem based learning. From artificial heresy to res popularis

La extensa implementación del aprendizaje basado en problemas (ABP) en el proceso enseñanza-aprendizaje ha resultado en su transformación de herejía artificial ares popularis con la consecuente proliferación de publicaciones, libros y congresos sobre el tema. A menudo, esta avalancha de información, ha creado una confusión en la comprensión de qué es el ABP como estrategia de aprendizaje. Este artículo presenta al lector una definición de lo que se consideró que era el ABP y su extensión, además de incluir la resolución de problemas. Se indica la importancia de los objetivos de aprendizaje (resultados del aprendizaje) y se presentan algunos pasos que se deben seguir en la preparación de situaciones/escenarios/problemas/casos. De forma general, se describen la evaluación de los estudiantes fundamentalmente formativa, basada en las observaciones hechas en las sesiones de tutoría, y la evaluación de carácter sumativo. La descripción de las etapas más comunes en el ABP tiene el propósito de indicar lo que los estudiantes pueden hacer y no que deben hacer. Si se consideran las limitaciones de recursos que tienen la mayoría de las instituciones que desean implementar el ABP, se describe la aplicación de esta estrategia en grupos grandes. Se discute el rol del tutor facilitador y se indican las características de sus intervenciones en un continuo que va desde jerárquica a facilitadora de la autonomía del estudiante en su aprendizaje. Este artículo finaliza con una reflexión sobre el aprendizaje autodirigido y su relación con el aprendizaje autorregulado (AU)

From artificial heresy to res popularis The vast use of problem based learning (PBL) in the teaching learning process has resulted in its transformation from an artificial heresy to a res popular is with the subsequent proliferation of publications, books and congresses on the subject. This deluge of information, very often, has created confusion on the comprehension of what PBL is as learning strategy. This article presents a definition of what PBL was considered in its conception, and its extension to problem resolution. The importance of learning objectives (learning outcomes) is indicated and some steps in the preparation of situations/scenarios/problems/cases are described. Also, student evaluation is described, both the formative evaluation based on tutorial observations as well as the summative. The description of the stages in the PBL process has solely the purpose to indicate what the students could do, not what they should do. Taking into account the resource limitations of most institutions which wish to implement PBL, the application of this strategy in large groups is also described. The role of the tutor facilitator and the characteristics of his intervention from hierarchical to one of facilitating student autonomy are discussed. This article ends with a reflexion on self-directed learning and its relationship to self-regulated learning (AU)

[Nursing education innovations]. / Innovaciones educativas en Enfermería.

Problem-Based Learning is a pedagogical method which has already been adopted by a large number of educational programs for health professionals, including nurses. Problem-Based Learning tends to combine learning based on problems, in small groups and is student-centered. The disadvantages of a traditional pedagogical program for students have been established for many years now. Even though the implementation of Problem-Based Learning has corrected many of those problems which occur through use of traditional methods, this new method does present some risky situations which require mechanisms to prevent and correct them.

The role of phospholipids in the binding of oxytocin to its receptors in lactating rabbit mammary gland.

Phospholipase C (Clostridium welchii and Bacillus cereus) treatment of lactating rabbit mammary gland membranes (140,000 g pellet and sucrose density gradient purified plasma membranes) resulted in a large decrease in the binding of [3H]oxytocin to these subcellular fractions. This decrease was not due to a solubilization of oxytocin receptors but was the result of the removal of phospholipids which may participate in the hormone-receptor interaction. Phospholipase C treatment of the membrane fractions resulted in a dose-dependent removal of different classes of phospholipids. Sphingomyelin, phosphatidylcholine and phosphatidylethanolamine were removed by phospholipase C (C. welchii and B. cereus) treatment. No significant change was observed in the content of phosphatidylinositol. Phospholipase C from B. cereus reduced the content of phosphatidylserine, while the enzyme from C. welchii did not.

Identification and characterization of receptors for oxytocin in the myometrium of the pregnant ewe.

Receptors for oxytocin were identified in a particulate fraction from the myometrium of the pregnant ewe. Specific binding of [3H]-oxytocin was rapid, reversible, and saturable. It showed an absolute requirement for Mg2+ and the selectivity among oxytocin analogues expected for the receptor. On fractionation of the myometrium by differential and discontinuous gradient centrifugation, [3H]-oxytocin binding showed a fractionation pattern which was similar to that for plasma membrane markers, but different from those for endoplasmic reticulum or mitochondrial markers. It is concluded that oxytocin receptors are located in the plasma membrane of the ewe myometrium. This subcellular fraction is a useful preparation for the study of receptor mechanisms and the regulation of myometrial contractility.

Oxytocin binding sites in lactating rabbit mammary gland.

Material which specifically binds oxytocin was prepared from a crude preparation of lactating rabbit mammary gland by purification on a sucrose density gradient. On examination of activities of enzyme markers and the molar ratio of cholesterol to phospholipid, this material was considered to be a highly purified plasma membrane fraction. For the determination of specificity and time course of oxytocin binding, a Scatchard plot analysis was carried out for the crude and purified fractions. Dissociation constant (Kd) and binding capacity values were found to be as follows: crude, Kd equals 1.83 X 10(-9) M, capacity equals 670 fmol/mg protein; purified, Kd equals 2.8 X 10(-9) M, capacity equals 1700 fmol/mg protein. Treatment of the purified material with different detergents resulted in loss of all [3H]oxytocin binding capacity. However, preincubation of this material with [3H]oxytocin prior to detergent treatment resulted in solubilization of a receptor-hormone complex. This complex remained in the supernatant even after centrifugation at 210 000 X g for 30 min. Using oxytocin analogs, we have shown this solubilized complex to be oxytocin specific.

Localization of the oxytocin receptor in the plasma membrane of rat myometrium.

The distribution of [3H]oxytocin binding sites among various subcellular fractions of rat myometrium paralleled the distribution of 5'-nucleotidase, a plasma membrane marker enzyme, but not of NADPH-cytochrome c reductase or succinate-cytochrome c reductase, which are endoplasmic reticulum and mitochondrial marker enzymes respectively. [3H]Oxytocin binding to the most enriched plasma membrane fraction showed the degree of selectivity with respect to hormone analogues that is expected for the oxytocin receptor. The binding of oxytocin to this fraction showed an apparent Kd of 1.98 X 10(-9) M and a capacity of 1.28 pmol mg-1. It is concluded that the oxytocin receptor is located on the plasma membrane of the smooth muscle cells of the rat uterus.

The synthesis and some pharmacological properties of (2-L-DOPA)-oxytocin.

The first reported synthetic analogue of a naturally occurring peptide with a residue of L-3,4-dihydroxyphenylalanine (L-DOPA) was prepared by coupling N-carbobenzoxy-S-benzylcysteinyl-L-DOPA azide with isoleucylglutaminylasparaginyl-S-benzylcysteinylprolylleuclglycinamide. The protecting groups were removed from the resultant nonapeptide derivative by sodium in liquid ammonia and the peptide analogue was formed by short term oxidation of the dithiol-containing compound. It was isolated by sequential partition chromatography and exclusion chromatography on Sephadex G-25. It was unstable at neutral or alkaline pH. [2-L-DOPA]-oxytocin was found to possess a minimum milk-ejection-like activity of 54 +/- 9 U/mg and uterotonic activity of 26 +/- 4 U/mg. These potencies are approximately 12% and 5% of the corresponding potencies of oxytocin.

Synthesis and some pharmacological properties of (2-tryptophan)-oxytocin.

Previous studies have suggested that an aromatic amino acid residue at position 2 in oxytocin facilitates the expression of the hormone's biolgocial activities. [2-Tryptophan]-oxytocin, in which a residue of tryptophan has replaced that of tyrosine in oxytocin, has been synthesized by the method of azide coupling of the N-terminal dipeptide and C-terminal heptapeptide amide. It was found to have approximately 0.1% of the potency of oxytocin in milk ejection and uterotonic biological activities.

Synthesis and some biological properties of 1-deamino-4-glu-oxytocin (1-beta-mercaptopropionic acid-4-glutamic acid-oxytocin) and its use in preparing a hormone-agarose complex.

1-Deamino-4-glu-oxytocin (1-beta-mercaptopropionic acid-4-glutamic acid - oxytocin) was synthesized by sequential reduction by sodium in liquid ammonia and oxidation by hydrogen peroxide of the octapeptide derivative, S-benzyl-beta-mercaptopropionyl-tyrosyl-isoleucyl-gamma-O-benzyl-glutamyl-asparaginyl-S-benzyl-cysteinyl-prolyl-leucyl-glycinamide. The oxidation analogue was isolated and purified by partition chromatography in two different solvent systems followed by exclusion chromatography on Sephadex G-25. It was found to possess approximately 13 I.U. of uterotonic activity, 34 I.U. of milk ejection activity, and 83 I.U. of milk ejection-like activity per milligram, measured on an isolated strip of lactating mouse mammary gland. 1-Deamino-4-Glu-oxytocin was coupled to AH-Sepharose 4B by the way of the free gamma-carboxyl group of its residue of glutamic acid. The water soluble 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride caused the coupling with approximately 70% effectiveness. The resultant peptide-agarose complex had low biological potency in the assay of milk ejection-like activity.