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Answer:
Nephron Segmentation
The nephron is a blood filtration apparatus carrying out additional functions such as pH regulation and reabsorption of water and solutes. Blood is filtered at the glomerulus (Figure 8.2(C)). The filtrate travels through a long tubule composed of various segments with highly specialized functions and different shapes (lumen diameter and cellular morphology) and it arrives at the bladder as concentrated urine. Because different segments of the nephron along the proximal-to-distal axis have different physiological functions regarding reabsorption and secretion, multiple types of epithelial cells are required to make a nephron and all of the different types of regionalized epithelial cells of the nephron originate from the cap mesenchyme [2,3]. Although not all of the steps involved in forming all the epithelial cell types from this common progenitor population are fully understood, Notch signaling has important roles early in the process that affects later cell fate determination during nephrogenesis.
The nephron is connected to the collecting duct system in a process that is initiated at RV and completed at the SSB. The distal end of RV invades into the collecting duct epithelium and the luminal interconnection between a developing nephron and the collecting duct seems to form at the late SSB stage [28,32]. The connection of nephrons to the collecting duct occurs even in the mutant kidney lacking the proximal segments of nephrons [4,16], but not in the mutant kidney whose developing nephrons are proximalized [32]. Therefore, the ability to make a connection to the collecting duct seems an intrinsic property of the distal segment of RV and SSB.
The fact that SSB can form proximal tubules in the presence of γ-secretase inhibition [16] suggested that major regional identities are already established at SSB. S-shaped bodies can be divided into three segments: proximal, medial, and distal [28]. The distal segment of SSB, marked by the expression of Lgr5 [33], forms the distal tubules and connecting segment lineages as well as the thick ascending limb. Likewise, Cre recombinase under the control of cis-regulatory elements controlling expression of Osr2 (Osr2-IRES-Cre) mark the median and distal segments of SSB and the marked cells develop into proximal tubules and glomeruli [34]. Although lineage analysis of other nephron segments progenitors within the SSB has not been completed, it is likely that the proximal and medial segments of SSB form glomeruli and proximal tubules, respectively (Figure 8.2(C)). Because the medial part of SSB gives rise to at least half of the loop of Henle [33], it is possible that the nephron fates are elaborated along the P/D axis of the SSB.
Answer:
T4
Explanation:
As more energy is needed
Maximum energy