Kidney


Image Caption : Female Body Showing Kidney : Anterior Female Nude Body, kneeling with kidneys. Visible : aorta, vena cava, rib cage, pelvis and right femur. The kidneys are bean-shaped organs, each about the size of a fist, located near the middle of the back. The kidneys play key roles in body function, not only by filtering the blood and getting rid of waste products, but also by balancing levels of electrolytes in the body, controlling blood pressure, and stimulating the production of red blood cells.

ANATOMY OF THE KIDNEY & URETER

Paired Organ: Yes.

Each kidney or ureter is considered a separate primary, unless bilateral involvement is stated to be metastatic from one side to the other (exception: bilateral Wilms tumor of the kidney).

The kidneys have two functional areas that are managed and staged independently, the kidney parenchyma and the renal pelvis.

The ureters are the tubes that carry urine from the renal pelvis to the bladder. They are staged the same way as the renal pelvis.

ANATOMY OF THE KIDNEY AND URETER

Illustration of a kidney

  1. Parenchyma
  2. Cortex
  3. Medulla
  4. Perirenal fat
  5. Capsule
  6. Ureter
  7. Pelvis of kidney
  8. Renal vessels
  9. Hilum
  10. Calyx

Key Words

ParenchymaThe solid part of the kidney, where the process of waste excretion takes place.

CortexThe outer layer of the parenchyma consisting of connective tissue.

GlomeruliConvoluted tubules where filtration is performed.

MedullaArea of the kidney where filtration and concentration of wastes takes place, Henle's loops, pyramids of converging tubules.

NephronBasic functional unit of kidney.

Calyx (plural calyces)Collecting area for urine within kidney before it is passed through to renal pelvis.

CapsuleDense fibrous covering of kidney.

PelvisCentral collecting system of kidney.

HilumArea of convergence of the renal collecting system, ureter, renal artery and vein.

Ureteropelvic junctionPoint at which the renal pelvis becomes the ureter.

Gerota's fasciaLayer of connective tissue between the kidneys and the psoas muscles and the lumbar spine.

Perinephric fatLayer of fat surrounding kidney outside of capsule.

Perihilar fatLayer of fat in the area of the renal hilum.

National Cancer Institute / NIH

Kidneys

The kidneys are the primary organs of the urinary system. The kidneys are the organs that filter the blood, remove the wastes, and excrete the wastes in the urine. They are the organs that perform the functions of the urinary system. The other components are accessory structures to eliminate the urine from the body.

The paired kidneys are located between the twelfth thoracic and third lumbar vertebrae, one on each side of the vertebral column. The right kidney usually is slightly lower than the left because the liver displaces it downward. The kidneys, protected by the lower ribs, lie in shallow depressions against the posterior abdominal wall and behind the parietal peritoneum. This means they are retroperitoneal. Each kidney is held in place by connective tissue, called renalfascia, and is surrounded by a thick layer of adipose tissue, called perirenal fat, which helps to protect it. A tough, fibrous, connective tissue renal capsule closely envelopes each kidney and provides support for the soft tissue that is inside.

In the adult, each kidney is approximately 3 cm thick, 6 cm wide, and 12 cm long. It is roughly bean-shaped with an indentation, called the hilum, on the medial side. The hilum leads to a large cavity, called the renal sinus, within the kidney. The ureter and renal vein leave the kidney, and the renal artery enters the kidney at the hilum.

Illustration of a kidney

The outer, reddish region, next to the capsule, is the renal cortex. This surrounds a darker reddish-brown region called the renal medulla. The renal medulla consists of a series of renal pyramids, which appear striated because they contain straight tubular structures and blood vessels. The wide bases of the pyramids are adjacent to the cortex and the pointed ends, called renal papillae, are directed toward the center of the kidney. Portions of the renal cortex extend into the spaces between adjacent pyramids to form renal columns. The cortex and medulla make up the parenchyma, or functional tissue, of the kidney.

The central region of the kidney contains the renal pelvis, which is located in the renal sinus, and is continuous with the ureter. The renal pelvis is a large cavity that collects the urine as it is produced. The periphery of the renal pelvis is interrupted by cuplike projections called calyces. A minor calyx surrounds the renal papillae of each pyramid and collects urine from that pyramid. Several minor calyces converge to form a major calyx. From the major calyces, the urine flows into the renal pelvis; and from there, it flows into the ureter.

Each kidney contains over a million functional units, called nephrons, in the parenchyma (cortex and medulla). A nephron has two parts: a renal corpuscle and a renal tubule.The renal corpuscle consists of a cluster of capillaries, called the glomerulus, surrounded by a double-layered epithelial cup, called the glomerular capsule. An afferent arteriole leads into the renal corpuscle and an efferent arteriole leaves the renal corpuscle. Urine passes from the nephrons into collecting ducts then into the minor calyces.

The juxtaglomerular apparatus, which monitors blood pressure and secretes renin, is formed from modified cells in the afferent arteriole and the ascending limb of the nephron loop.

National Cancer Institute / NIH

NIDDK / NIH

The kidneys are bean-shaped organs that serve several essential regulatory roles in vertebrates. Their main function is to regulate the balance of electrolytes in the blood, along with maintaining pH homeostasis. They also remove excess organic molecules from the blood, and it is by this action that their best-known function is performed: the removal of waste products of metabolism. Kidneys are essential to the urinary system and also serve homeostatic functions such as the regulation of electrolytes (including salts), maintenance of acid–base balance, maintenance of fluid balance, and regulation of blood pressure (via the salt and water balance). They serve the body as a natural filter of the blood, and remove water-soluble wastes which are diverted to the bladder. In producing urine, the kidneys excrete nitrogenous wastes such as urea and ammonium. They are also responsible for the reabsorption of water, glucose, and amino acids. The kidneys also produce hormones including calcitriol and erythropoietin. An important enzyme, renin, is also produced in the kidneys; it acts in negative feedback.

Located at the rear of the abdominal cavity in the retroperitoneal space, the kidneys receive blood from the paired renal arteries, and drain into the paired renal veins. Each kidney excretes urine into a ureter which empties into the bladder.

Renal physiology is the study of kidney function, while nephrology is the medical specialty concerned with kidney diseases. Diseases of the kidney are diverse, but individuals with kidney disease frequently display characteristic clinical features. Common clinical conditions involving the kidney include the nephritic and nephrotic syndromes, renal cysts, acute kidney injury, chronic kidney disease, urinary tract infection, nephrolithiasis, and urinary tract obstruction. Various cancers of the kidney exist. The most common adult renal cancer is renal cell carcinoma. Cancers, cysts, and some other renal conditions can be managed with removal of the kidney. This is known as nephrectomy. When renal function, measured by the glomerular filtration rate, is persistently poor, dialysis and kidney transplantation may be treatment options. Although they are not normally harmful, kidney stones can be extremely painful.



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