Diabetes mellitus is the product of decreased insulin effectiveness in the body. As a result, blood glucose levels are extremely high. When filtrate enters the nephron through Bowman's capsule, glucose is generally transported as well. In a healthy individual, this glucose is rapidly removed from the filtrate in the proximal convoluted tubule. In a diabetes patient, however, the level of glucose in the filtrate can overwhelm the reabsorption of the tubule, resulting in glucose in the urine. This increases urine osmolarity, causing the filtrate to retain water. The result is an increase in urine volume, resulting in more frequent urination.

The purpose of the proximal tubule is to reduce the amount of filtrate in the nephron. The proximal tubule does alter the solute concentrations in the filtrate, but it does not alter the osmolarity of the filtrate. This is because the proximal tubule is where reabsorption of solutes, proteins, and glucose takes place. Meanwhile, drugs and toxins are being secreted into the filtrate. Essentially, the volume of filtrate in the proximal tubule decreases, but the filtrate remains isotonic to the blood.

The descending loop of Henle is responsible for the first step in urine concentration. Due to the high concentration of salt in the space surrounding the descending limb of the loop of Henle, water flows out of the tubule, concentrating the filtrate. The descending limb is impermeable to sodium, potassium, and albumin (the principle protein component in blood).

The glomerulus is a capillary bed. Afferent arterioles carry blood to enter the glomerulus, and efferent arterioles carry blood away from the glomerulus after filtration. Both types of arteriole are able to tighten and relax to modulate pressure within the glomerulus, driving filtration. Though fenestrated capillaries form the glomerulus itself, these vessels cannot regulate flow and pressure because they have no smooth muscle.

The kidney is responsible for excreting nitrogenous waste produced by the urea cycle, maintaining water balance (and thus blood pressure), maintaining salt concentrations in the blood, and controlling blood pH by excreting or retaining protons. Blood flows into the nephrons through the glomerulus and is pushed into Bowman's capsule. The filtrate then flows through the proximal tubule, the main site for most reabsorption of glucose, proteins, and electrolytes. From the proximal tubule it enters the loop of Henle, where salt and water balance is regulated via the ion gradient in the extracellular space of the renal medulla. Finally, the filtrate enters the distal tubule and collecting duct, where salt, water, and proton balance is further regulates.

The liver is responsible for gluconeogenesis and glycogen storage.

The distal tubule of the nephron is responsible for reabsorbing sodium and calcium and secreting potassium, hydrogen, and bicarbonate. Remember that aldosterone is responsible for increasing reabsorption of sodium and increasing excretion of potassium.

The glomerulus is the capillary bed of the afferent arterioles, which filter the blood and allows the nephron to concentrate waste into urine. Glucose is a sugar is filtered into the glomerular capsule. It is, however, quickly reabsorbed back into the bloodstream in the proximal convoluted tubule, and returned to the efferent arterioles. In a healthy individual, the nephron will be able to reabsorb all the glucose that gets filtered into the glomerular capsule.

The main function of the Loop of Henle is to establish a concentration gradient so that water can be reabsorbed from the collecting duct and avoid being lost as urine. Although the ascending limb does absorb water, this water would be lost as urine if it were not for the concentration gradient established in the medulla of the kidney. Neither sodium nor potassium is absorbed in the Loop of Henle.

The correct path of filtrate through a nephron starts in the renal corpuscle, which is comprised of the glomerulus and Bowman's capsule. Filtrate then passes through the proximal convoluted tubule, where the majority of reabsorption takes place. It then travels through the descending and ascending limbs of the Loop of Henle, creating the counter current multiplier gradient that will allow urine to be concentration in the collecting duct. From the Loop of Henle, filtrate enters the distal convoluted tubule for final reabsorption before entering the collecting duct and being trasported to the bladder.

The renal artery is used to carry blood into the kidneys. Filtrate originates from the renal artery, but it is not a part of the nephrons.

The Loop of Henle creates a countercurrent multiplier system. As the filtrate descends through the Loop of Henle, water leaves the filtrate and is reabsorbed, making the filtrate very concentrated. When the Loop of Henle ascends, salt ions leave the filtrate and are reabsorbed making the filtrate less concentrated. This creates a strong concentration of ions in the interstitial fluid toward the bottom of the loop, as compared to the concentration at the top. When filtrate flows down the collecting duct, this gradient helps concentrate the urine by removing water.