Nephron, physiology

Yalcin AU, Kudaiberdieva G, Sahin G, et al. Effect of sertraline hydrochloride on cardiac autonomic dysfunction in patients with hemodialysis-induced hypotension. Nephron Physiology 2003 93 21-28. 

Tumlin, J. A. (1997). Expression and function of calcineurin in the mammalian nephron Physiological roles, receptor signaling, and ion transport. Am. J. Kidney Dis. 30, 884-895. 

Since the distal nephron reabsorbs under physiological conditions less than 10% of the filtered load of... 

Northern blot analysis revealed that expression of NHE-1 is tissue-specific with highest transcript abundance in stomach and minimal levels in liver and skeletal muscle. Moreover, there is physiological evidence that certain segments of the nephron lack a basolateral Na /H" exchanger [76]. Using RT-PCR, Krapf and Solioz [77] observed that NHE-1 transcripts are not detectable in SI and S2 segments of superficial nephrons. 

The physiological role of the ICOR is not clear and may be heterogeneous in the various tissues. In the thick ascending limb of the loop of Henle this channel appears to serve as the exit for CP at the basal cell pole [16,65,66], This conductive mechanism, therefore, is required for the reabsorption of Na and CP by this segment of the nephron [16]. In the rectal gland of Squalus acanthias a very similar channel is utilized for Na" and CP secretion. In these latter cells the CP-channel is present in the luminal membrane and is controlled by cytosolic cAMP [15,56,71]. It has been claimed that this kind of channel is also responsible for the secretion of CP in the colonic crypt cell, in colonic carcinoma cells and in respiratory epithelial cells [17,19,20,22]. Recent data have cast some doubt on this concept ... 

Calcium is freely filtered along with other components of the plasma through the nephrons of the kidney. Most of this calcium is reabsorbed into the blood from the proximal tubule of the nephron. However, because the kidneys produce about 1801 of filtrate per day, the amount of calcium filtered is substantial. Therefore, the physiological regulation of even a small percentage of calcium reabsorption may have a significant effect on the amount of calcium in the blood. Parathyroid hormone acts on the Loop of Henle to increase the reabsorption of calcium from this segment of the tubule and... 

Assuming the capsular pressures opposing the movement of water out of the blood and into the top of the nephron are constant, the net filtration pressure is due largely to the blood pressure. Any fall in blood pressure can have a dramatic effect on the efficiency of filtration and therefore clearance of waste materials. So important is the pressure within the renal vasculature that the kidney is critical in regulating systemic blood pressure via the renin-angiotensin-aldosterone (RAA) axis, a physiological process which relies on transport mechanisms within the renal tubules. 

This chapter is divided into three sections. The first section covers renal tubule transport mechanisms. The nephron is divided structurally and functionally into several segments (Figure 15-1, Table 15-1). Many diuretics exert their effects on specific membrane transport proteins in renal tubular epithelial cells. Other diuretics exert osmotic effects that prevent water reabsorption (mannitol), inhibit enzymes (acetazolamide), or interfere with hormone receptors in renal epithelial cells (aldosterone receptor blockers). The physiology of each segment is closely linked to the basic pharmacology of the drugs acting there, which is discussed in the second section. Finally, the clinical applications of diuretics are discussed in the third section. 

The main functions of the human kidney are the formation and excretion of urine, and control of the composition of body fluids. Details of the structure and functions ofthe human kidney may be found in textbooks of physiology [1] or biomedical engineering [13]. Each ofthe two human kidneys contains approximately one million units of tubules (nephrons), each 20-30 pm in diameter, and with a total... 

Most diuretics act upon a single anatomic segment of the nephron (Figure 15-1). Because these segments have distinctive transport functions, the first section of this chapter is devoted to a review of those features of renal tubule physiology that are relevant to diuretic action. The second section is devoted to the basic pharmacology of diuretics, and the third section discusses the clinical applications of these drugs. 

Kamel, K. S., Oh, M. S. and Halperin, M. L. (2002). Bartter s, Gitelman s, and Gordon s syndromes. From physiology to molecular biology and back, yet still some unanswered questions. Nephron. 92(Suppl. 1), 18-27. 

The purpose of this section is to illustrate how one can integrate different physiological processes into a consistent description of the feedback mechanisms that generate the complicated bimodal dynamics observed in the tubular pressure variations of individual nephrons. Let us start with the variation of the proximal tubular... 

The above discussion completes our description of the single-nephron model. In total we have six coupled ordinary differential equations, each representing an essential physiological relation. Because of the need to numerically evaluate Ce in each integration step, the model cannot be brought onto an explicit form. The applied parameters in the single-nephron model are specified in Table 12.1. They have all been adopted from the experimental literature, and their specific origin is discussed in Jensen et al. [13]. 

Figure 12.6a shows the temporal variation of the proximal tubular pressure Pt as obtained from the single-nephron model for a = 12 and T = 16 s. All other parameters attain their standard values as listed in Table 12.1. Under these conditions the system operates slightly beyond the Hopf bifurcation point, and the depicted pressure variations represent the steady-state limit cycle oscillations reached after the initial transient has died out For physiologically realistic parameter values the model reproduces the observed self-sustained oscillations with characteristic periods of 30-40 s. The amplitudes in the pressure variation also correspond to experimentally observed values. Figure 12.6b shows the phase plot Here, we have displayed the normalized arteriolar radius r against the proximal intratubular pressure. Again, the amplitude in the variations of r appears reasonable. The motion... 

Fig. 12.9 Two-dimensional bifurcation diagram for the single-nephron model. The diagram illustrates the complicated bifurcation structure in the region of 1 1, 1 2, and 1 3 resonances between the arteriolar dynamics and the TGF-mediated oscillations. In the physiologically interesting regime around T = 16 s, another set of complicated period-doubling and saddle-node bifurcations occur. Here, we are operating close to the 1 4...

The focus of this chapter is threefold (1) to review components of renal physiology contributing to susceptibility to chemically induced nephrotoxicity, (2) to examine current methodologies for assessment of nephrotoxicity, and (3) to provide examples of a few specific nephrotoxicants, emphasizing mechanisms thought to contribute to the unique or selective susceptibility of specific nephron segments to these toxicants. 

Figure 29.2. Schematic representation of nephron and vasculature. The glomerulus is positioned between afferent and efferent arterioles, and the juxtaglomerular apparatus is the point of contact between the vascular pole and distal tubule of the nephron. A capillary network surrounds tubular structures. (From Guyton, A. C., and Hall, J. E., Textbook of Medical Physiology, 11th ed. Elsevier Saunders Company, Philadelphia, 2006. Reproduced with permission.)...

Renal function is an indication of the physiological state of the kidney glomerular filtration rate (GFR) describes the flow rate of Altered fluid through the kidney, while creatinine clearance rate (Ccr) is the volume of blood plasma that is cleared of creatinine per unit time, and is a useful measure for approximating the GFR. Most clinical tests use the plasma concentrations of the waste substances of creatinine and urea, as well as electrolytes, to determine renal function. The nephron is the functional unit of the kidney (Figure 10.1) it consists of two parts ... 

The nephron and its related cells perform diverse physiological functions. It is the major organ of excretion and homeostasis for water-soluble molecules because it is a metabolically active organ, it can concentrate certain substances actively. In addition, its cells have the potential to bioconvert chemicals and metabolically activate a variety of compounds. There are a number of other processes described in the following that establish the potential for cellular injury. Specific physiological characteristics are localized to specific cell types. This makes them susceptible to, and the target for, chemicals. 

Appel GB. Aminoglycoside nephrotoxicity physiologic studies of the sites of nephron damage. In Whelton A, Neu HC, editors. The Aminoglycosides. New York, Basel Marcel Dekker, 1982 269. 

Although most nephrotoxicity occurs in the proximal part of the nephron, some chemicals damage distal structures. The function of these structures facilitates their vulnerability to toxicants. For instance, the loop of Henle is critical to the process of urinary concentration and therefore utilizes relatively high rates of Na, K -ATPase activity and oxygen demand. This, and the fact that oxygen supply to the medulla is minimally sufficient to meet physiological needs, contributes to... 

---