The American journal of physiology
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Mathematical modeling and simulation techniques were used to analyze the role of medullary collecting duct NaCl transport in the urinary concentrating process. The mathematical model incorporated experimentally determined epithelial transport parameters and anatomical parameters obtained chiefly from experiments in rabbit kidneys. ⋯ However, despite optimal choice of collecting duct transport parameters and the use of experimentally determined permeability coefficients, only modest total solute gradients could be generated axially in the inner medullary interstitium, and passive luminal dilution did not occur in the thin ascending limb. We conclude: 1) Axial heterogeneity of transport properties along the inner medullary collecting duct must be assumed to explain in vivo findings from micropuncture and microcatheterization studies. 2) Active NaCl transport from the inner medullary collecting ducts is important chiefly for efficient conservation of NaCl rather than for concentration of solutes in the renal inner medulla. 3) Important inconsistencies exist between several previously reported experimental observations and the theoretical requirements for passive luminal dilution in the thin ascending limb of Henle's loop.
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A hypothesis for the operation and control of nasal heat exchange in reindeer is presented that originated from studies of the nasal vascular anatomy and has been supported by physiological measurements as well as test experiments on a physical prototype model of the reindeer nose. A central theme of our hypothesis is that the nasal mucosa possesses arterial and venous retia that communicate by way of capillaries and arteriovenous anastomoses. ⋯ During heat dissipation, however, the retia are perfused unidirectionally in the anterior direction, whereby the temperature gradient along the nasal mucosa is reduced and heat loss facilitated. In this situation cooled venous blood, routed by way of the dorsal nasal vein, may be distributed either to the caval veins directly, for general body cooling, or, by way of the cavernous sinus that encases the carotid rete, for selective cooling of the brain.
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The metabolic effects of NaHCO3 therapy in hypoxic lactic acidosis were evaluated in the anesthetized dog. Hypoxic lactic acidosis was induced by ventilating the dogs with a hypoxic gas mixture of 8% O2/92%N2, resulting in arterial PO2 of less than 30 mmHg, pH below 7.20, bicarbonate less than 12 mM, and lactate more than 7 mM. In this situation lactate accumulates because of overproduction of lactate by gut and carcass in the presence of a diminished capacity of the liver to extract lactate. ⋯ Concomitantly NaHCO3-treated animals showed a decrement in liver and gut blood flow that did not occur with NaCl treatment. Only NaHCO3 therapy was associated with a further decrease of liver intracellular pH, which could be attributed to both an increase in the CO2 load to the liver and increased tissue lactate levels, which were not observed with NaCl or no therapy. Additionally, liver lactate extraction was not improved by administration of NaHCO3 or NaCl.(ABSTRACT TRUNCATED AT 250 WORDS)