KIDNEYS
KIDNEYS(disambiguation)
-principal excretory organ of the body
- functions such as the regulation of electrolytes, maintenance of acid–base balance, and regulation
of blood pressure
LOCATION OF KIDNEYS
• The kidneys lie on either side of the vertebral column in a depression high on the posterior wall
of the abdominal cavity.
• The upper and lower borders of the kidneys are generally at the levels of the twelfth thoracic
and third lumbar vertebrae, respectively.
STRUCTURE OF KIDNEYS
The superior end of the ureter is expanded to
form a funnel-shaped sac called the renal pelvis, which
is located inside the renal sinus. The pelvis is subdivided
into two or three tubes, called major
calyces (sing., calyx), and they, in turn, are subdivided
into several minor calyces.
A series of small elevations project into the
renal sinus from its wall. These projections are
called renal papillae, and each is pierced by tiny
openings that lead into a minor calyx.
The substance of the kidney includes two
distinct regions - an inner medulla and an outer cortex.
The renal medulla is composed of conical masses of
tissue called renal pyramids.
The renal cortex, which appears somewhat
granular in a sectioned kidney, forms a shell around the
medulla. Its tissue dips into the medulla between
adjacent renal pyramids, forming renal columns. The
granular appearance of the cortex is due to the random
arrangement of tiny tubules associated with
the nephrons, the functional units of the kidney.
FUNCTIONS OF KIDNEYS
• The kidney remove metabolic wastes from the blood and excrete them to the outside. They also
carry on a variety of equally important regulatory activities, including helping control the rate of
red blood cell formation by secreting the hormone erythropoietin and helping regulate the
blood pressure by secreting the enzyme renin.
• The kidneys also help regulate the volume, composition, and pH of the body fluids. These
function involve complex mechanisms that lead to the formation of urine.
Renal Blood Vessels
• A renal artery enters a kidney through the hilum and gives off several branches, called
the interlobar arteries, which pass between the renal pyramids. At the junction between the
medulla and cortex, the interlobar arteries branch to form a series of incomplete arches, the
arcuate arteries which, in turn, give rise to interlobular arteries. The lateral branches of the
interlobular arteries, called afferent arterioles, lead to the nephrons, which are functional units
of the kidneys.
• Venous blood is returned through a series of vessels that correspond generally to the arterial
pathways. The renal vein then joins the inferior vena cava as it courses through the abdominal
cavity.
Nephrons
-basic structural and functional unit of the kidney.
- chief function is to regulate the concentration of water and soluble
substances like sodium salts by filtering the blood, reabsorbing what is
needed and excreting the rest as urine
Blood Supply of a Nephron