There are two kidneys in human body located on both sides of spine under rib cage. Right kidney is placed lower because of liver. Kidneys have various functions and crucial one is excretion of waste material in urine.
Kidney anatomy
Kidneys are covered in capsule (1) and on top of it is fat.
On the cross section is visible cortex (2) and medulla (3).
Medulla is made of pyramids (4) which continue with calyces (5). Kidney calyces gather primary urine and merge into renal pelvis (6) which continues to ureter (7).
Blood is brought to kidney by afferent artery (8) and diverts by efferent vein (9).
Kidneys are innervated by sympathetic nervous system.
Nephrone
Morphological and functional unit of kidney is nephron.
Nephron is made of glomerulus, juxtaglomerular apparatus, proximal tubule, Henle’s loop, distal tubule and collecting duct.
Glomerulus, juxtaglomerular apparatus, proximal tubule and distal tubule are placed in cortex. Whole Henle’s loop is in the medulla.
Each kidney consists of 1 million nephrons.
Kidney function
Main function of kidney is excretion of metabolites, organic products and ions, as well as body regulation.
- Keeping consistent osmolality and steady volume of body fluids is guaranteed by excretion of water and sodium chloride (NaCl). It is important for keeping homeostasis (stability of biological system) and correct functioning of other organs, especially cardiovascular system.
- pH of extracellular fluid (fluid that is outside of cells, e.g. vasculature) should be steady around 7,36-7,44. It is very important for activation of enzymes as well as proper functioning of nervous system. Another role is in binding and release of oxygen on red blood cells, keeping steady volume of potassium. Incorrect volume of potassium can cause hypokalemia (too little potassium) or hyperkalemia (too much potassium). Wrong pH level can cause acidification of organism because of metabolism of proteins. Secondarily kidneys regulate pH by reabsorption of bicarbonate. Acidosis is a condition when kidneys don’t work properly.
- Kidneys produce a lot of hormones like renin, erythropoietin, prostaglandins and kinins.
- Blood pressure is regulated by amount of sodium and water. These parameters are recognized by receptors in proximal tubule. If there is impairment in their balance, renin is released. Renin is hormone which is made in kidneys and with angiotensin II influences blood pressure.
- Kidneys participate in creation of blood cells, erythropoiesis. This process is regulated by production of hormone erythropoietin. Kidneys can register oxygen in blood which activates production of this hormone. If there is damage in kidney, erythropoiesis is impaired and causes disease as anemia.
- Kidneys excrete final products of metabolism as urea (product of metabolism of amino acids), uric acid (product of metabolism of nucleic acids), creatinine as well as final products of metabolism of hemoglobin, hormones and others.
Urine made in kidneys goes into upper urinary tract which by help of smooth muscles transport urine into urinary duct. Bladder stores urine. Increasing pressure in the bladder pushes smooth muscles of the ladder which causes urge to urinate. Then the bladder releases urine in the process of urination by flow of urine through urethra out of the body.
Basic kidney tests
There are three processes which made urine, glomerular filtration (blood circulating through arteriols in nephrone where substances are being filtrated), tubular reabsorption and tubular secretion (post on this topic is being made).
One of the main tests that examine kidney functions is CLEARANCE. It reflects “cleaning ability” of kidneys, therefor amount of blood plasm that is cleaned from certain substance in certain time frame. Measurement lasts 24 hours.
We test amount of urine (diuresis) over 3, 6, 12 or 24 hours. Based on the amount of the urine we can state whether diuresis is alright (normouresis) or there are some pathologies like oliguria (less than 500 ml urine over 24 hours) or even anuria (less than 100 ml urine over 24 hours). On the contrary there is polyuria (more than 3,5 l urine over 24 hours).
Another tested parameter is amount of urea in blood. Urea is made in the liver during metabolism of proteins. Amount of urea in blood is higher if the glomerular filtration is low. Amount of urea in blood can be increased during dehydration as well. Low amount of urea is during pregnancy, malnutrition or too little amount of proteins in diet.
Creatinine is tested parameter as well which is produced during muscle metabolism. 90% is excreted by kidney and impaired glomerular filtration causes increase of creatinine.
Red blood cells, white blood cells, kidney tissue and microorganisms are being tested too.