AFFERENT = carry to
EFFERENT = carry away from
(a) Structure. Each renal capsule is drained by a renal tubule. The
first part of this tubular system runs quite a distance in a coiled formation and is called
the proximal convoluted tubule. A long loop, the called the descending loop or the
descending limb of Henle leads down to the medulla with two straight parts and a sharp
bend at the bottom. The sharp bend at the bottom is called the loop of Henle and is U-
shaped. As the tube returns to the cortex layer, it once again becomes coiled and here
is known as the distal convoluted tubule. The distal tubule is the end of the nephron
(b) Function -- tubular reabsorption. The fluid (also called filtrate)
passes through the tubular system of the nephron. Here, the majority of the water,
glucose, and other valuable substances are removed from the fluid and returned to the
cardiovascular system. Essential electrolytes such as sodium, chloride, and
bicarbonate are reabsorbed in the tubules. Reabsorption of sodium salts is controlled
by the hormone aldosterone. Water and electrolytes such as glucose, amino acids, and
nutrients are also absorbed from the renal tubes. Other fluids reabsorbed include
water and nonelectrolyte such as glucose and amino acids.
(c) Function -- tubular secretion. Tubular reabsorption removes
substances from the filtrate into the blood, but tubular secretion adds materials to the
fluid from the blood. These secreted substances are included: potassium ions,
hydrogen ions, ammonia, creatinine, and the drugs penicillin and aminohippuric acid.
There are two main effects from tubular secretions. The substances in the secretions
help rid the body of certain materials and also help control the blood pH.
GENERAL CHARACTERISTICS OF DIURETICS
The kidneys have an important role in maintaining the volume and composition of
fluids in the body. It is sometimes necessary to reduce the amount of fluid in the body.
Diuretics can perform this function. A number of diuretic drugs have been developed
over the years. Most diuretics operate in one of two ways: they inhibit renal tubular
sodium reabsorption or they increase the filtration of sodium. Drugs used as diuretics
can be classified according to their specific effect on the renal system. In such a
system, diuretics can be grouped into five classes: Water, osmotic diuretics, loop
diuretics, thiazide diuretics, potassium sparing diuretics, and combination diuretics.
Drugs used as diuretics effect the body is many ways, but remember that the chief
effect on the urinary system is to increase the rate of urine formation and, subsequently,
urine flow out of the body.