Final answer:
The glomerular oncotic pressure increases from the afferent to the efferent arteriole ends across the glomerular capillaries, caused by the protein retention while fluid is filtered out increasing protein concentration and, in turn, oncotic pressure.
Step-by-step explanation:
The force that tends to increase from the afferent to the efferent arteriole ends across the glomerular capillaries is the glomerular oncotic pressure. As blood flows from the afferent arteriole through the glomerulus, water and small solutes are filtered into Bowman's capsule, leaving behind cells and large proteins that cannot pass through the filtration membrane. This increases the concentration of proteins, particularly albumin, in the blood of the glomerular capillaries, thus raising the oncotic pressure along the length of the capillary from the afferent to the efferent end. Because proteins are retained while the fluid is filtered out, the osmotic pressure attributable to these retained solutes, or the oncotic pressure, will tend to rise as the blood moves towards the efferent arteriole.
The hydrostatic pressure in Bowman's capsule and the glomerular filtration rate (GFR) are also relevant to the process of filtration. The hydrostatic pressure is the pressure exerted by the fluid in the Bowman's capsule, which opposes the movement of fluid into the capsule, while GFR represents the volume of filtrate the kidneys produce each minute.