Functional morphology of the kidney

The kidneys have multiple functions. They do not only excrete water, electrolytes and metabolic waste products like urea, creatine, uric acid and end products of hemoglobin breakdown(e.g. bilirubin) but they also serve many homeostatic functions.

Kidney Functions

 * Excretion of metabolic waste products and foreign chemicals
 * Regulation of water and electrolyte balance -The intake of these substances must match their excretion
 * Regulation of acid-base balance - Kidneys work together with lings and body fluid buffers to control acid-base balance. Kidneys are the only means oof the body which can eliminate acids like sulfuric acid and phosphoric acid.
 * Regulation of concentrations of electrolytes and body fluid osmolality
 * Regulation of arterial pressure
 * Secretion, metabolism, and excretion of hormones(e.g. erythropoietin-regulation of production of red blood cells-erythrocytes)
 * Gluconeogenesis - Kidneys are able to synthesize glucose during prolonged periods of fasting from amino acids and other precursors.

Functional anatomy of the kidney
The two kidneys lie on the posterior wall of the abdomen - retroperitoneum space. Each kidney is composed of 8 to 10 lobes and weighs about 150 grams. The medial side of each kidney contains a region called the hilum through which pass the renal artery and vein, lymphatics, nerve supply, and ureter, which carries the final urine from the kidney to the bladder, where it is stored until emptied. The kidney is surrounded by a tough, fibrous capsule that protects its delicate inner structures. The kidney divided into two regions – medulla and cortex. The medulla is divided into multiple cone-shaped masses of tissue called renal pyramids. The base of each pyramid originates at the border between the cortex and medulla and terminates in the papilla, which projects into the space of the renal pelvis, a funnel-shaped continuation of the upper end of the ureter. The outer border of the pelvis is divided into open-ended pouches called major calyces that extend downward and divide into minor calyces, which collect urine from the tubules of each papilla. The walls of the calyces, pelvis, and ureter contain contractile elements that propel the urine toward the bladder, where urine is stored until it is emptied by micturition.

Physiologic Anatomy of the Kidneys
Kidneys lie outside the peritoneal cavity on the posterior wall of the abdomen. Each kidney weighs about 150 grams. There is an indented region at the medial side of each kidney known as hilum. The renal artery and vein, lymphatics, and nerve supply and ureter pass through the hilum. The hilum carries the final urine from the kidney to the bladder. Moreover, there is a capsule surrounding the kidneys. This is a tough, fibrous capsule which protects them and also prevents their expansion.

The kidneys have an outer cortex and an inner medulla region. The medulla has 8-10 renal pyramids (lobes). The loose connective tissue in the medulla allows accumulation of osmotically active substances. The base of each pyramid is at the border between the cortex and the medulla whereas the apex of the pyramid is called a papilla and it projects into the space of the renal pelvis.