Kidneys - Anatomy, Functions, Disorders, Interesting Facts Kidney
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The Kidneys

Authored by DesiMD Doctor on 20 Mar 2013 - 18:30

Anatomy:

The kidneys are two bean shaped structures located in the abdomen, with either one on each side of the spinal cord. The right kidney lies lower than the left kidney, due to the location of the liver above it. On top of each kidney lies an adrenal gland, with the average weight of an adult kidney ranging between 115 g to 170 g (depending on gender). The left kidney is also a bit larger than the right side.

Image:Kidneys
The Kidneys
Credit: Dr. Ram Prasad

The kidneys receive blood supply from the renal arteries, which although their small size, consume 20 % of cardiac blood output. The kidneys are also innervated and controlled to a large extent by the sympathetic nervous system.

Functions of the Kidneys
The kidney plays various regulatory roles including acid balance, control of blood pressure, blood electrolyte levels and overall body homeostasis (balance). It may achieve its mandate of functions either alone or in conjunction with other body organs especially endocrine glands. Most of the functions of the kidney are attained by simple methods namely secretion, filtration and reabsorption which take place in the nephron.  The kidneys produce about 45 gallons of waste daily, but most is reabsorbed (the water, sodium) eventually leading to about only 2 litres being excreted as urine.

The functions can then be classified as:

  1. Excretion of Waste: The kidneys are responsible for eliminating a variety of waste materials produced by a range of metabolic .
  2. Acid-Base Balance: The kidney accomplishes these functions by virtue of collaboration with the lungs. The mechanisms for this are achieved via excretion of carbon dioxide via the lungs, and two roles by the kidneys; excretion of excess hydrogen ions, and reabsorption of bicarbonate ions which help to buffer blood acid levels.
  3. Secretion of Hormones: The kidneys secrete a variety of hormones including calcitriol, an activated form of vitamin D which promotes absorption of calcium in the intestines and excretion of phosphate in the urine, erythropoietin which signals the body to increase production of red blood cells in response to low oxygen levels in cells, and rennin a hormone responsible for regulating aldosterone levels which determine blood pressure control.
  4. Electrolyte RegulationElectrolyte concentration (sodium, potassium, many more) must be maintained in order for physiological functions to continue in the body. Changes in the concentration of bodily fluids is identified by the hypothalamus, which then signals the posterior pituitary gland to secrete ADH- antidiuretic hormone, which causes the kidney to increase water reuptake and increase urine concentration. These mechanisms help to return blood electrolyte levels to normal.
  5. Blood Pressure MaintenanceControl of blood pressure is regulated mainly by the kidneys. In large part this is maintained by maintenance of an extracellular fluid compartment. In response to renin levels aldosterone and angiotensin 2 levels either increase or decrease, contracting or expanding the fluid compartment and either decreasing or increasing blood pressure.

Disorders of the Kidneys
Disorders affecting the kidney(s) can be acquired upon birth, or developed over years. Briefly, the most common manifestations of these disorders are:

  1. Congenital
    • Congenital hydronephrosis- accumulation of fluid with the glomerulous of the kidney
    • Obstructed urinary tract
    • Duplex kidneys- very rare condition, in which each kidney has its own ureter instead of joining into one
    • Horseshoe kidney- fusion of both kidneys into one, horseshoe shaped structure
    • Polycystic kidney disease- formation of cysts in either or both kidneys leading to severe swelling
    • Renal agenesis- failure of one or both kidneys to develop completely
    • Renal dysplasia- familial trait leading to undifferentiation of different cells within the kidneys
    • Multicystic dysplastic kidney- formation of various cysts within the kidney at birth, leading to inability to function. Commonly seen as a mass in an infant
  2. Acquired
    • Diabetic nephropathy- disease resulting in angiopathy ( vessel disease) of capillaries in the kidney. Leads to impaired blood flow  and progressive damage
    • Glomerulonephritis- inflammation of the glomeruli within the kidney with or without blood or protein in urine
    • Hydronephrosis
    • Interstitial Nephritis- nephritis affecting the interstitium of the kidneys
    • Kidney stones
    • Tumors of the kidneys
    • Nephrotic syndrome- damage to the glomerulous resulting in excessive protein excretion, including albumin secretion and edema
    • Pyelonephritis- commonly caused by an infection or complicated by a urinary tract infection
    • Renal failure
    • Minimal change disease-  disease resulting in nephrotic syndrome in children

Interesting Facts about the Kidneys:

  • The largest ever kidney stone found weighed over 2 pounds
  • Each kidney contains over one million individual filters
  • The kidneys have the highest blood flow of any organ in the body, even more than the brain
  • Approximately 0.1 % of filtered blood becomes urine
  • Excessive sugars along with milk or antacids can cause kidney stones
  • 50% working capacity of one kidney can do the total work of both kidneys
  • Babies born with a deficient kidney sometimes have the remaining one grow to double its normal size