Nephron structure

The kidney of most fish is primarily involved in hematopoiesis and osmoregulation. Fresh-water fish are hypertonic relative to the water. The continual osmotic uptake of water is balanced by production of as large amounts as 2-4 ml/kg/h of dilute urine. Salt-water fish, on the other hand, are hypotonic relative to their environment, resulting in body water loss. In response, marine species produce much smaller volumes of urine. Large differences exist among different fish species in regard to nephron structure to facilitate these functional responses. These features may influence the renal contribution to drug disposition apprecia-... 

The vasa recta are modified peritubular capillaries. As with the peritubular capillaries, the vasa recta arise from efferent arterioles. However, these vessels are associated only with the juxtamedullary nephrons and are found only in the medullary region of the kidney. The vasa recta pass straight through to the inner region of the medulla, form a hairpin loop, and return straight toward the cortex. This structure allows these vessels to lie parallel to the Loop of Henle and collecting ducts. 

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. 

Kidney development can be used again here to illustrate the kinds of events that occur during organ maturation, which takes place during fetal and postnatal development. While the induction of the organ and formation of its basic structure are initiated in the embryonic period, differentiation of the nephrons is not complete until term in humans, and not until the 2nd week postnatally in rodents. 

The control of water content has an effect on the blood pressure. Therefore drugs which can affect the balance of water or ions within the nephron can have a clinical use in the treatment of hypertension (high blood pressure). These pharmaceuticals are known as diuretics because their use results in an increased excretion of water. Since they all have the same general effect, diuresis, they represent a pharmacological class of compounds. Some may be related to each other on a structural level and be further associated as members of a structural class as well. 

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... 

Chorev, M. 2002. Parathyroid hormone 1 receptor insights into structure and function. Receptors Channels 8 219-242. Fukugawa, M. and K. Kurokawa. 2002. Calcium homeostasis and imbalance. Nephron 92 (Suppl. 1) 41—45. 

Figure 12.1 illustrates the main structure of a nephron [1], The measurements to be reported in this chapter were performed on rats. A rat kidney contains approximately 30000 nephrons as compared to the one million nephrons in a human kidney. The process of urine formation starts with the filtration of plasma in the glomerulus, a system of 20-40 capillary loops. The presence of a relatively high hydrostatic pressure in this system allows water, salts and small molecules to pass out through the capillary wall and into the proximal tubule. Blood cells and proteins are retained, and the filtration process saturates when the protein osmotic pressure balances the hydrostatic pressure difference between the blood and the filtrate in the tubule. For superficial nephrons, the proximal tubule is visible in the surface of the kidney and easily accessible for pressure measurements by means of a thin glass pipette. 

Fig. 12.1 Main structural components of the nephron. Note particularly how the terminal part of the loop of Henle passes within cellular distances of the afferent arteriole. This forms the anatomical basis for the tubuloglomerular feedback mechanism by which the nephron regulates the incoming blood flow in response to variations in the ionic composition of the fluid that leaves the loop of Henle.

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...

As illustrated in Fig. 12.14 the nephrons are arranged in a tree-like structure with their afferent arterioles branching off from a common interlobular artery [29]. This... 

In order to examine the synchronization phenomena that can arise in larger ensembles of nephrons, we recently developed a model of a vascular-coupled nephron tree [35], focusing on the effect of the hemodynamic coupling. As explained above, the idea is here that, as one nephron reduces its arterioler diameter to lower the incoming blood flow, more blood is distributed to the other nephrons in accordance with the flow resistances in the network. An interesting aspect of this particular coupling is that the nephrons interact both via the blood flow that controls their tendency to oscillate and via the oscillations in this blood flow that control their tendency to synchronize. We refer to such a structure as a resource distribution chain, and we have shown that phenomena similar to those that we describe here... 

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.)...

Finally, histopathologic examination of tissue can reveal structural changes that have occurred in response to nephrotoxicants, often allowing identification of affected areas of the nephron (Figure 29.8). For instance, fight microscopy can identify changes in renal morphology caused by chemicals, such as the presence of... 

Q1 The glomerulus is a ball of capillaries which is part of the renal corpuscle the other portion of this structure is Bowman s capsule, which forms the start of the nephron. The wall of Bowman s capsule is composed of a layer of specialized epithelial cells with extensions or foot processes which are in contact with the glomerulus and are called podocytes. The gaps between the foot processes are known as slit pores. These pores allow small molecules to pass through the epithelial layer into the nephron tubules. Below the epithelium is a basement membrane which prevents the passage of large proteins and whole cells into the renal tubules. 

Nephron The basic structural and functional unit of the kidney. The basic function of the nephron is to regulate water and soluble substances... 

The kidney tissue has a very intriguing structure. It is organized into several thousand structural and functional units. A single unit - a nephron (Figure 2.15b) - spans the better part of the entire distance between the organ periphery and the renal pelvis, which simply collects the final urine and feeds it into the ureters.. 

Diuretics related to the thiazides. Several compounds, although strictly not thiazides, share structural similarities with them and probably act at the same site on the nephron they therefore exhibit moderate therapeutic efficacy. Overall, these substances have a longer duration of action, are used for oedema and hypertension and their profile of adverse effects is similar to that of the thiazides. They are listed below. 

The effects of sevoflurane, isoflurane, and desflurane on macroscopic renal structure have been studied in 24 patients undergoing nephrectomy (35). All anesthetics were administered using a fresh gas flow of 11/minute and a sodium hydroxide absorber and had an average duration of 3 hours. No injury to nephrons was observed by pathologists blinded to which anesthetic agent had been used. Postoperative creatinine concentrations and urine volumes did not differ significantly between the groups. 

Gabriels G, Stockem E, Greven J. Potassium-sparing renal effects of trimethoprim and structural analogues. Nephron 2000 86(l) 70-8. 

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... 

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