Identify the incorrect statement regarding GFR:
1. The GFR averages approximately 180 L per day (about 125 ml/min).
2. The GFR increases during sympathetic stimulation due to the vasodilation of afferent arterioles.
3. A decrease in GFR results in a decrease in the total urine output.
4. Renal auto-regulation maintains the GFR at a relatively constant rate normally.

The branch of renal artery that directly supplies the glomerulus is the:

Glomerular ultrafiltrate normally does not contain:

The urine concentrating ability of mammals and birds is correlated with the length of their:

The part of the nephron that is least permeable to water is the:
1. ascending limb of the loop of Henle
2. descending limb of the loop of Henle
3. collecting duct
4. proximal convoluted tubule

Urea in humans is synthesized in:

The most toxic nitrogenous metabolic waste product is:

Malpighian body or the renal corpuscle is made up of:
1. Glomerular capillaries and PTCN
2. Bowman's capsule and renal tubules
3. Afferent and efferent arterioles
4. Glomerular capillaries and Bowman's capsule

Filtration slits in the glomerular membrane are formed by:
1. The capillary endothelial cells
2. The basement membrane
3. The podocyte cells
4. Mesangial cells

All the following are secreted by the tubules of nephrons except: