The distal convoluted tubule follows the loop of Henle in the nephron structure. In addition to lowering the filtrate concentration, it is also used to reabsorb sodium ions and secrete potassium ions. Aldosterone acts on the distal tubule and further stimulates these two actions.

The nephron is composed of multiple sections, which are used to alter the solute composition and concentration of the filtrate. The first section is the proximal convoluted tubule. While the solute composition of the filtrate will change due to reabsorption and secretion of specific solutes, the overall concentration does not change. In the proximal convoluted tubule, filtrate is kept isotonic with blood.

The collecting duct of a nephron is normally impermeable to water. In the presence of antidiuretic hormone (ADH), aquaporin proteins are inserted, making the collecting duct permeable to water. Water then diffuses into the medulla due to the solute concentration of the surrounding tissues, generated from ion reabsorption in the loop of Henle. This loss of water from the urine makes it more concentrated.

The glomerulus is a capillary structure associated with the first section of the nephron where blood enters the renal corpuscle. The glomerulus is responsible for filtering fluid, plasma, and dissolved particulates out of circulation and into Bowman's capsule, resulting in a primary filtrate that will go through the rest of the nephron.

All of the answer choices are true. The macula densa cells are sensitive to changes in concentration of sodium chloride. A decrease in concentration of  is detected, which stimulates the macula densa cells to secrete paracrine factors that ultimately increase the pressure in the glomerulus, and thus the glomerular filtration rate, and stimulates the release of renin, which ultimately increases blood pressure, volume and cardiac output.

After filtration of the blood through the glomerulus, approximately 70% of the water and salts is reabsorbed in the proximal convoluted tubule.  Additionally, 100% of the glucose is reabsorbed here in a healthy, functioning nephron.  The lumenal cells of the proximal convoluted tubule are lined with microvilli and are called brush border cells.  Histology of the proximal convoluted tubule is indicative of these structures and the proximal convoluted tubule's lumen can be seen as "crowded" with epithelial surface area, which is distinct from the lumen of the distal convoluted tubule.

ADH acts upon the collecting ducts and distal convoluted tubules of nephrons to increase water reabsorption.  It causes an increase in the number of aquaporins in order to allow for this.

As filtrate passes through the Loop of Henle, the level of concentration of the fluid that will become urine is determined by the length of the loop of Henle (how far into the medulla it dips) and, the osmolality of the medulla. Depending on the levels of circulating hormones, the distal convoluted tubule and collecting duct could be the part of the nephron that determines the concentration of the urine, but to a lesser extent than the length of the loop of Henle. 

The descending limb of the loop of Henle is both water permeable and solute impermeable.  These properties of the limb allow the filtrate moving through the nephron to become either concentrated or diluted depending on the circumstance.

The afferent and efferent arterioles are located near the glomerulus and control the glomerular filtration rate by constriction and dilation.  The peritubular capillaries wind around the proximal convoluted tubule and the distal convoluted tubule to allow for reabsorption and secretion there.  The vasa recta on the other hand wind around the loop of Henle and maintain countercurrent multiplication.