What is the kidney?
The kidney is a reddish-brown organ that occurs in pairs in the body. Both organs are bean-shaped. Their longitudinal diameter is ten to twelve centimetres, the transverse diameter five to six centimetres and the thickness about four centimetres. A kidney weighs between 120 and 200 grams. The right kidney is usually somewhat smaller and lighter than the left.
Each kidney has two surfaces (anterior and posterior surface, facies anterior and posterior), two poles (upper and lower renal pole) and two edges (inner and outer edge, margo medialis and lateralis).
In the inwardly curved edge of the organ towards the center is a niche-shaped depression, the so-called renal portal (-hilus). The renal artery (arteria renalis) and vein (vena renalis) run through it: the artery carries blood loaded with waste products into the organ, the vein brings the purified blood out again. The entry and exit points of nerves and lymph vessels are also located on the hilus of the kidney.
Structure consisting of three zones
A longitudinal section of the kidney anatomy shows three zones:
Inside is the renal pelvis, the collecting chamber for the urine produced. On the outside is the finely striated renal medulla (medulla renalis). The renal cortex (cortex renalis), which appears lighter in color than the medulla, lies on the very outside.
The tips of the cone-shaped medullary pyramids are called renal papillae and each has a microscopically small opening. These open into a small cavity, the renal calyx. The finished urine is collected in the calyces and passed into the renal pelvis.
The medulla and cortex together form the renal parenchyma. It contains around 1 to 1.4 million small filter units, the so-called nephrons. It also contains specialized cells that produce the hormones renin and erythropoietin. Renin is important for the regulation of blood pressure, erythropoietin for the formation of red blood cells.
Connective tissue capsule and fat layer
Each kidney is covered by a rough capsule, a transparent connective tissue envelope. Around this is a strong layer of fatty tissue, which is surrounded by another thin connective tissue envelope.
The fat and connective tissue capsule protects the sensitive organ from impact injuries and anchors it to the posterior abdominal wall.
Nephron
Nephrons are the functional units of the kidney. Structure of these filter units You can find out more about the structure of the nephrons in the article Nephron.
What is the function of the kidney?
You can read everything you need to know about renal function in the side text Kidney function.
Where is the kidney located?
Where exactly are the kidneys located?
They are located between the posterior wall of the peritoneum and the back muscles (psoas muscle and quadratus lumborum muscle). The exact position depends on breathing and body position. The difference in height between the two organs caused by breathing is three centimeters.
The kidneys extend approximately from the twelfth thoracic vertebra to the third lumbar vertebra. However, because of the liver (in the right upper abdomen), the right kidney is on average up to two centimetres lower than the left.
The right kidney lies in the vicinity of the liver, duodenum and the right bend of the large intestine (right colonic flexure). On the left, there are neighboring relationships with the stomach and spleen, the tail of the pancreas, the descending part of the large intestine (descending colon), the splenic vein and splenic artery.
An adrenal gland (suprarenal gland) sits on top of each of the two upper organ poles. This is an important hormonal gland.
In front of and behind each kidney are connective tissue constrictions, so-called fasciae. They extend from the diaphragm to the intestinal ridge.
The architectural unit of kidney, fat capsule and fascia is often summarized under the term renal bed.
What problems can the kidney cause?
Possible symptoms of renal diseases include dull back pain and colicky back pain radiating towards the bladder. The urine may be red in color or cloudy and smell unpleasant. Foaming of the urine can also often be observed in renal diseases.
In addition, urine production may be reduced so that patients only pass very little urine or none at all (anuria). Swelling of the eyelids or ankles (edema) can also indicate renal disease.
Additional symptoms may occur as the disease progresses. These include loss of appetite, nausea, vomiting, a general feeling of weakness, pale or grayish skin color, shortness of breath and water retention (especially in the legs). Itching of the skin, bad breath or a metallic taste in the mouth as well as a strong acidic body odor can also accompany a renal disease.
The most important renal diseases are
- Kidney stones (nephrolithiasis)
- Kidney (pelvic) inflammation (glomerulonephritis, pyelonephritis)
- Organ damage due to medication such as certain painkillers
- Organ malformations
- renal arteriosclerosis
- Acute and chronic kidney failure (renal insufficiency)
- Benign and malignant tumors
One option is blood washing, where the patient’s blood is filtered either via a machine (haemodialysis) or the patient’s own peritoneum (peritoneal dialysis). The second option is to transplant a healthy kidney from an organ donor.