What are the functions
of the kidney?
The kidney regulates
fluid and electrolyte balance by filtration, secretion and reabsorption
The kidney is an
endocrine organ – it activates both erythropoeitin (for production of
red blood cells) and vitamin-D (which regulates calcium metabolism). It
also produces renin (in the afferent arteriole) which affects various
aspects of water and electrolyte homeostasis.
functional anatomy of the kidney
There are three major
anatomical demarcations in the kidney: the cortex, the medulla, and the
renal pelvis. The cortex receives most of the blood flow, and is mostly
concerned with reabsorbing filtered material. The medulla is a highly
metabolically active area, which serves to concentrate the urine. The
pelvis collects urine for excretion.
The functional unit of
the kidney is the nephron. There are five parts of the nephron: 1. The
glomerulus, which is the blood kidney interface, plasma is filtered from
capillaries into the Bowman’s capsule. 2. The proximal convoluted tubule,
which reabsorbs most of the filtered load, including nutrients and
electrolytes. 3. The loop of Henle, which, depending on it’s length,
concentrates urine by increasing the osmolality of surrounding tissue and
filtrate. 4. The distal convoluted tubule, which reabsorbs water and
sodium depending on needs, 5. The collecting system, which collects urine
for excretion. There are two types of nephrons, those localized to the
cortex, and those extending into the medulla. The latter are characterized
by long loops of Henle, and are more metabolically active.