The kidneys are bean-shaped organs that serve several important functions in vertebrate animals.
They remove excess organic molecules ( such as glucose) and it is by this
action that their best-known function is carried out: the removal of waste
products of the metabolism (e.g. urea, though 90% of this is reabsorbed
along the nephron.)
They are core in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and regulation of blood pressure.
They serve the body as a natural filter of the blood, and remove water soluble wastes, which are diverted to the urinary bladder.
In producing urine, the kidneys excrete wastes such as urea and ammonium, and they are also responsible for the reabsorption of water, glucose, and amino acids.
The kidneys also produce hormones including calcitriol, erythropoietin, and the enzyme renin, the latter of which indirectly acts on the kidney in negative feedback.
Located at the rear of the abdominal cavity in the retroperitoneum, the kidneys receive blood from the paired renal arteries, and drain into the paired renal veins. Each kidney excretes urine into a ureter, itself a paired structure that empties into the urinary 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, or nephrectomy.
When renal function, measured by glomerular filtration rate, is persistently poor, dialysis and kidney transplantation may be treatment options. Although they are not normally harmful, kidney stones can be painful, and repeated, chronic formation of stones can scar the kidneys.
The removal of kidney stones involves ultrasound treatment to break up the stones into smaller pieces, which are then passed through the urinary tract.
One common symptom of kidney stones is a sharp to disabling pain in the medial/lateral segments of the lower back or groin.
The kidney accomplishes these homeostatic functions both independently and in concert with other organs, particularly those of the endocrine system.
Various endocrine hormones coordinate these endocrine functions; these include renin, angiotensin II, aldosterone, antidiuretic hormone, and atrial natriuretic peptide, among others.
Many of the kidney's functions are accomplished by relatively simple mechanisms of filtration, reabsorption, and secretion, which take place in the nephron.
Filtration, which takes place at the renal corpuscle, is the process by which cells and large proteins are filtered from the blood to make an ultrafiltrate that eventually becomes urine.
The kidney generates 180 liters of filtrate a day, while reabsorbing a large percentage, allowing for the generation of only approximately 2 liters of urine.
Reabsorption is the transport of molecules from this ultrafiltrate and into the blood. Secretion is the reverse process, in which molecules are transported in the opposite direction, from the blood into the urine.
The concentration of nitrogenous wastes, in the urine of mammals and some birds, is dependent on an elaborate countercurrent multiplication system.
This requires several independent nephron characteristics to operate: a tight hair pin configuration of the tubules, water and ion permeability in the descending limb of the loop, water impermeability in the ascending loop and active ion transport out of most of the ascending loop.
In addition, countercurrent exchange by the vessels carrying the blood supply to the nephron is essential for enabling this function.
A plasma glucose level of approximately 160 is sufficient to allow glucosuria, which is an important clinical clue to diabetes mellitus.
Amino acids are reabsorbed by sodium dependent transporters in the proximal tubule. Hartnup's disease is a deficiency of the tryptophan amino acid transporter, which results in pellagra.
They are core in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and regulation of blood pressure.
They serve the body as a natural filter of the blood, and remove water soluble wastes, which are diverted to the urinary bladder.
In producing urine, the kidneys excrete wastes such as urea and ammonium, and they are also responsible for the reabsorption of water, glucose, and amino acids.
The kidneys also produce hormones including calcitriol, erythropoietin, and the enzyme renin, the latter of which indirectly acts on the kidney in negative feedback.
Located at the rear of the abdominal cavity in the retroperitoneum, the kidneys receive blood from the paired renal arteries, and drain into the paired renal veins. Each kidney excretes urine into a ureter, itself a paired structure that empties into the urinary 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, or nephrectomy.
When renal function, measured by glomerular filtration rate, is persistently poor, dialysis and kidney transplantation may be treatment options. Although they are not normally harmful, kidney stones can be painful, and repeated, chronic formation of stones can scar the kidneys.
The removal of kidney stones involves ultrasound treatment to break up the stones into smaller pieces, which are then passed through the urinary tract.
One common symptom of kidney stones is a sharp to disabling pain in the medial/lateral segments of the lower back or groin.
Functions
The kidney participates in whole-body homeostasis, regulating acid-base balance, electrolyte concentrations, extracellular fluid volume, and blood pressure.The kidney accomplishes these homeostatic functions both independently and in concert with other organs, particularly those of the endocrine system.
Various endocrine hormones coordinate these endocrine functions; these include renin, angiotensin II, aldosterone, antidiuretic hormone, and atrial natriuretic peptide, among others.
Many of the kidney's functions are accomplished by relatively simple mechanisms of filtration, reabsorption, and secretion, which take place in the nephron.
Filtration, which takes place at the renal corpuscle, is the process by which cells and large proteins are filtered from the blood to make an ultrafiltrate that eventually becomes urine.
The kidney generates 180 liters of filtrate a day, while reabsorbing a large percentage, allowing for the generation of only approximately 2 liters of urine.
Reabsorption is the transport of molecules from this ultrafiltrate and into the blood. Secretion is the reverse process, in which molecules are transported in the opposite direction, from the blood into the urine.
Excretion of wastes
The kidneys excrete a variety of waste products produced by metabolism. These include the nitrogenous wastes called "urea", from protein catabolism, as well as uric acid, from nucleic acid metabolism. Formation of urine is also the function of the kidney.The concentration of nitrogenous wastes, in the urine of mammals and some birds, is dependent on an elaborate countercurrent multiplication system.
This requires several independent nephron characteristics to operate: a tight hair pin configuration of the tubules, water and ion permeability in the descending limb of the loop, water impermeability in the ascending loop and active ion transport out of most of the ascending loop.
In addition, countercurrent exchange by the vessels carrying the blood supply to the nephron is essential for enabling this function.
Reabsorption of vital nutrients
Glucose at normal plasma levels is completely reabsorbed in the proximal tubule. The mechanism for this is the Na+/glucose cotransporter. A plasma level of 350 mg/dL will fully saturate the transporters and glucose will be lost in the urine.A plasma glucose level of approximately 160 is sufficient to allow glucosuria, which is an important clinical clue to diabetes mellitus.
Amino acids are reabsorbed by sodium dependent transporters in the proximal tubule. Hartnup's disease is a deficiency of the tryptophan amino acid transporter, which results in pellagra.
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