Why is the kidney described as retroperitoneal?

The kidney lies between the peritoneum and body wall rather than in the peritoneal cavity.

Which is larger, the efferent arteriole or the afferent arteriole? How does the difference affect the function of the glomerulus?

The afferent arteriole is bigger. The relatively large inlet to the glomerulus and its small outlet results in hgh blood pressure in the glomerulus. This is the force that drives glomerular filtration.

Why are women more susceptible to bladder infections than men are?

The relatively short female urethra is less of an obstacle for bacteria travelling from the perineum to the urinary bladder.

The long-looped nephrons of animals adapted to survive with minimal water consumption, such as desert rats, have relatively much longer loops of Henle than human have. Of what benefit would these longer loops be?

The longer loops of Henle in desert rats (also known as kangaroo rats) permit a greater magnitude of countercurrent multiplication and thus a larger medullary vertical osmotic gradient. As a result, these rodents can produce urine that is concentrated up to an osmolarity of almost 6000 mOsm/litre, which is 5 times more concentrated than maximally concentrated human urine at 1200 mOsm/liter. Because of this tremendous concentrating ability, kangaroo rats never have to drink; the water produced metabolically within their cells during oxidation of food is sufficient for their needs.

What are the signs and symptoms of lupus nephritis?

Sufferers of lupus nephritis may or may not have symptoms of kidney disease, but it can manifest itself through weight gain, high blood pressure, darker foamy urine or swelling around the eyes, legs, ankles or fingers.

Furthermore, patients may suffer from other symptoms of lupus unrelated to kidney function. Such symptoms can include arthritis, fevers, gastro-intestinal disturbances, headaches, fatigue, and fluid in the joints.