Functions of the Distal Convoluted Tubule
The distal convoluted tubule
- reabsorbs Na+ ions through coupled secretion of H+ or K+ ions into the
tubular fluid, a process which requires the presence of the adrenal hormone
aldosterone. By acidifying the urine the distal convoluted tubule plays an
important role in acid-base balance.
- normally is relatively impermeable to water. However in the presence of
antidiuretic hormone (ADH) its permeability to water increases permitting
concentration of the urine.
- secretes ammonium ions and some drugs
- forms part of the juxtaglomerular apparatus.
The Juxtaglomerular Apparatus
- is important in the control of systemic blood pressure and volume.
- is a complex found at the vascular pole of the renal corpuscle. This complex
- juxtaglomerular cells which are modified smooth muscle cells
in the walls of the afferent arteriole that sense changes in blood pressure
and secrete the enzyme renin.
- the macula densa, a region of the distal tubule that associates
with the glomerulus as it loops back into the cortex. The cells at the
side of the distal tubule closest to glomerulus become taller, more densely
packed and possess prominent nuclei. The cells of the macula densa are
thought to be able to detect Na+ concentration changes in the distal tubule
and relay this information to juxtaglomerular cells.
- extraglomerular mesangial cells (lacis cells) which support