The ultrastructural detail of the avian loop of Henle was examined, and comparisons were made to the loop of Henle of mammalian kidneys. Birds are the only group of vertebrates other than mammals that have the capability of elaborating a urine more concentrated than the plasma. Therefore, a comparison of the principal tubular element responsible for this phenomenon was made. Gambel's quail (Callipepla gambelii) were used as experimental animals. The animals were anesthetized with Inactin, and the kidneys were perfused-fixed in situ. The results show that the transition from the pars recta of the proximal tubule to the thin descending limb of Henle's loop (DLLH) is very abrupt. The upper part of the DLLH appears to be composed of type 2 and the lower part of type 3 epithelia, a condition somewhat similar to mammals. The junctions of the upper portion of DLLH are of the zonula adherens type and those of the lower portion of DLLH are of the macula adherens type. The epithelium of the loop always thickens before the formation of the hairpin turn with the thick descending limb being approximately 15% of the total DLLH. The structure of the avian renal medulla, in particular that of the loop of Henle, appears to parallel quite closely that postulated by the original formulation of the countercurrent multiplier system for the mammalian kidney.

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Tissues from the proximal, middle, and distal regions of the ceca of Gambel's quail and domestic fowl were examined by scanning and transmission electron microscopy. Cellular and subcellular structures, including epithelial cell height, mitochondrial volume fraction, microvillous surface area, proportion of goblet cells, and junctional complex characteristics, were quantified by a variety of stereologic procedures and other measurement techniques. The mucosal surface of quail cecum shows a much more highly developed pattern of villous ridges and flat areas than that of fowl cecum. The fowl has significantly greater cell heights than the quail in all cecal regions. The mitochondrial volume fraction does not differ significantly with species or region, but mitochondria are concentrated on the apical side of the nucleus. In both species, the proximal cecal region has the greatest microvillous surface area. All 3 components of junctional complexes, including zonula occludens, zonula adhaerens, and macula adhaerens, are quantified. When all factors are considered, the quail cecum appears to have morphological characteristics consistent with a greater potential capacity for absorption than the fowl cecum.

Tissues from the proximal, middle, and distal regions of the ceca of Gambel's quail and domestic fowl were examined by scanning and transmission electron microscopy for ultrastructural detail. Cellular aad subcellular structures, including epithelial cell height, mitochondrial volume fraction, microvillar surface area, and junctional complex characteristics, were quantified by stereologic procedures. The mucosal surface of the quail ceca shows a more highly developed pattern of ridges and flat areas than that of the fowl. The fowl has significantly greater cell heights than the quail in all cecal regions. The mitochondrial volume fraction does not differ significantly with species or region, but the mitochondria in all samples tend to be concentrated on the apical side of the nucleus. In both species, the proximal cecal region has the greatest microvillar surface area. In the fowl cecum, the zona occludens and macula adherans heights are significantly less in the proximal than in the middle or distal regions. In the quail cecum, the zona adherans height is least is the distal region. The zona occludens height in the fowl middle and distal regions is significantly greater than those for the quail. The middle region of the quail cecum has the lowest proportions of cell boundaries with zona adherans and macula adherans in the junctional complexes. When all factors are considered, the quail ceca appear to have morphological characteristics consistent with a greater potential capacity for absorption by passive diffusion than the fowl ceca.The gross anatomy, including form, function, and occurrence, of the avian cecum has been well covered by McLelland (this issue) and others in the older literature (Leopold, '53; Ziswiler and Farner, '72; Duke, '86). However, relatively little work has been done on the ultrastructure of avian ceca. Hodges ('74) described the various layers in the walls of the ceca of the domestic fowl (Gallus domesticus), including muscularis externa, submucosa, muscularis mucosae, and mucous membrane, and he discussed three distinct regions of the ceca. The proximal region had well developed villi, with lymphoid cells in the tunica propria and many goblet cells in the epithelium. In the middle region, cecal walls were thinner than in the proximal region, and well developed longitudinal folds were present in the mucous membrane. In the distal region, the folds were less developed, and the villi were short and blunt. The proportion of goblet cells decreased from the proximal to the distal region. Clarke ('78) examined the ileocecorectal junction in the domestic fowl and found a muscular ring of tissue projecting into the lumen of the intestine immediately anterior to the cecal openings. These openings were narrow and filled with villi. Clarke suggested 0 1989 ALAN R. LISS, INC.that this structure could be related to filtering of material during filling of the ceca. Hanssen ('79) qualitatively described the microanatomy of the ceca and small intestine of wild and captive willow grouse (Lagopus l...

The weaker correlation between capillary perfusion and capillary compression in DWB-reperfused hearts suggests that factors other than compression contribute to no-reflow after hypothermic preservation. Regardless of the composition of the reperfusate, recovery of left ventricular function after hypothermic ischemia is directly related to coronary capillary perfusion upon reperfusion.