ISSN:1420-4096    

DOI:10.1159/000173052

出版商:S. Karger AG    

年代:1985

数据来源: Karger

ISSN:1420-4096    

DOI:10.1159/000173053

出版商:S. Karger AG    

年代:1985

数据来源: Karger

ISSN:1420-4096    

DOI:10.1159/000173054

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

Glomerular ultrafiltration of the plasma is a fundamental component of vertebrate renal function. The importance of the glomerulus is reflected by its near-universal presence and great elaboration among the vertebrates. Although the general structural features and functional properties of the glomerulus appear to be largely similar among diverse groups, there exists considerable variation in the magnitude of the rate of filtration. The kidney is the primary vertebrate organ responsible for water and metabolic waste excretion, and glomerular filtration plays an important role in these functions. Therefore, the magnitude of the GFR appears to be influenced primarily by the rates of water influx and metabolism. Major phylogenetic differences in morphological, physiological and metabolic design have a decisive impact on the magnitude of the GFR. The endothermic classes, with more numerous glomeruli, high metabolic rates, and high ultrafiltration pressures, have proportionately higher rates of glomerular filtration than the ectothermic groups. As a group, the reptiles, with presumably the lowest rates of water influx, exhibit the lowest GFRs. Within each class, there are trends toward species with greater access to free water having higher GFRs (e.g. fresh water vs. marine; mesic vs. xeric. The clearest examples exist for the teleosts, with marine forms having lower GFRs than their fresh water relatives. The coupling of the GFR to environmental influences is also demonstrated by the response of the animal to environmentally imposed perturbations, such as dehydration. In terrestrial animals during dehydration, reductions in the rate of glomerular filtration occur reducing the rate of urinary water loss. And increases in GFR appears to be important in the rapid elimination of water loads in nonmammalian vertebrates. This short-term modulation of the GFR occurs by either changing glomerular plasma flow or glomerular capillary hydrostatic pressure, or both. In addition, shifts in the filtering populations of glomeruli can take place, as has been demonstrated in birds. Although the mediators of these effects have not been unequivocally identified, several hormones, including antidiuretic hormone, angio-tensin, and catecholamines, have been implicated.

ISSN:1420-4096    

DOI:10.1159/000173055

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

The comparative physiology of the renal proximal tubule (PT) is reviewed in the context of vertebrate evolution and vertebrate strategies of salt and water balance. Though extrarenal machanisms of salt and water balance contribute importantly to extracellular fluid (ECF) homeostasis in the lower vertebrates, the kidney acquires these functions with evolutionary progress and becomes the dominant organ of ECF homeostasis in mammals. In acquiring the major responsability over the ECF compartment the kidney favored filtration-reabsorption as the preferred mechanism for the rapid turnover of ECF with the advantage of providing quick renal regulatory responses. In spite of this specialization the structure and function of the PT do not appear to have undergone major evolutionary changes. In present-day vertebrates the PT remains as an immensely diverse transport epithelium with impressive capacities for both reabsorptive and secretory work, as exemplified by the mammalian PT with mostly reabsorptive functions and the PT of aglomerular kidneys with mostly secretory functions. The recent evidence for NaCl and fluid secretion in the PT of, unexpectedly, glomerular kidneys is consistant with the functional diversity and the conservative nature of evolution in the case of the PT.

ISSN:1420-4096    

DOI:10.1159/000173056

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

The similarity (or lack of) of mechanisms for ion and water transport across segments of the distal nephron of the various vertebrate classes is considered. Except for the reptilian distal nephron, the early distal nephrons from vertebrates of different classes appear to share certain morphological and functional characteristics. Among these are a relative impermeability of the tubule to water and the ability to preferentially reabsorb solute. This osmodilution of the luminal contents seems to be attributed to the presence of a sodium-chloride cotransport system located in the lumen membrane. The characteristics of solute and water transport of the late distal tubule are also considered. The available data suggest that there are striking similarities for the solute transport characteristics of the various vertebrate classes which have been studied. On the other hand, not all vertebrates appear to have developed the hydroosmotic response to antidiuretic hormone that has been observed in the mammals.

ISSN:1420-4096    

DOI:10.1159/000173057

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

Only birds and mammals can produce urines that have higher osmolalities than their plasma. In both of these vertebrate groups this is accomplished through the operation of a countercurrent multiplier system although the details of the system may differ somewhat between the two groups. In most mammals the loop of Henle has a thin ascending limb of variable length. In birds, the loop of Henle does not have a thin ascending portion as the tubule epithelium always thickens before the hairpin turn. In mammals, both urea and sodium chloride contribute to the medullary interstitial osmotic gradient although the exact contribution of each osmolyte can vary in time and from species to species. In birds the interstitial osmotic gradient is made up almost entirely of sodium chloride. The development of the avian renal medulla (medullary cone) is very similar to the outer medulla of mammals.

ISSN:1420-4096    

DOI:10.1159/000173058

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

The renal excretion of nitrogenous compounds plays an important role not only in the elimination of nitrogen end-products but also in regulating the acid-base and osmotic balance of body fluids. The major nitrogenous compounds excreted by the vertebrate kidney are ammonia, urea and uric acid. The present review addresses the renal excretion of these compounds and, in addition, the amino acid taurine. The functions of excretion; the mechanisms of excretion including renal metabolism, renal handling (secretion, reabsorption, and filtration), and transepithelial transport processes; and the factors regulating these mechanisms are discussed. Renal nitrogen excretion among the vertebrate classes from fish to mammals is compared.

ISSN:1420-4096    

DOI:10.1159/000173059

出版商:S. Karger AG    

年代:1985

数据来源: Karger

摘要:

Hormones influence renal function by both extrarenal and intrarenal mechanisms. Extrarenal mechanisms include the effects through systemic hemodynamic and neural pathways, whereas intrarenal mechanisms can be largely divided into the effects on intrarenal hemodynamics and those on tubular transport epithelia. Neurohypophysial hormones and the renin-angiotensin system appear to act primarily on systemic and preglomerularvasculature in primitive vertebrates, while direct tubular action appears to have evolved at a later stage of phylogeny. Although aldosterone is an essential hormone for fluid mineral balance in mammals, the action of mineralocorticoids on tubular Na transport has not been established in nonmammalian tetrapods. In bony fishes in hyperosmotic environments, cortisol accelerates active Na extrusion from the gill. In contrast, prolactin is important for maintaining low osmotic water permeability of the transport epithelia in fishes in hypoosmotic media. Thus, both function and site of hormone action appear to have changed during the evolution of vertebrates interacting with changing environments, and in response to the demands from other bodily functions. Furthermore, evolution of interactions, at the cellular level, between systemic and locally formed hormones such as prostaglandins, kinins, and perhaps angiotensin may have developed more elaborate controlling systems of renal handling of solutes and water.

ISSN:1420-4096    

DOI:10.1159/000173060

出版商:S. Karger AG    

年代:1985

数据来源: Karger