Overview
The kidneys are two bean-shaped organs responsible for filtering minerals from the blood, maintaining overall fluid balance, excreting waste products, and regulating blood volume to name a few.
The kidneys are very important organs in the body. About one-third of all blood leaving the heart passes into the kidneys for filtration before being pumped to the cells and tissues of the body. When the kidneys malfunction, or if they stop working (kidney failure), it may lead to various complications such as fluid retention that can lead to edema or swelling of the extremities, pulmonary edema or fluid in the lungs, hyperkalemia or increased potassium levels in the blood, anemia, heart disease, and pericarditis, among others.
Anatomy of the Kidney
Location
The kidneys are located on either side of the spine, in the retroperitoneal space. The left kidney is situated a little higher than the right one, because of the liver on the right side of the abdominal cavity, above the right kidney.
Structure
Each of the two bean-shaped organs weighs about 125 to 175 grams and 115 to 155 grams in males and females respectively. The kidney typically measures approximately 11 to 14 centimeters in length, 6 centimeters in width and is about 4 centimeters thick.
The kidneys are protected by fat, muscles, and ribs of the back. Perirenal fat, also called the renal fat pad, protects the kidneys from external force or damage. The kidneys have a medial dimple called the renal hilum, which is the entry and exit point for structures that supply or drain the kidneys such as the nerves, ureters, vessels, and lymphatics.
Vascular Supply
The kidneys are supplied with blood by the renal arteries, direct major branches of the abdominal aorta. These enter and divide into multiple levels to form a highly specialized and uniform network of afferent arterioles that then form the specialized capillary beds called the glomeruli. Each glomerulus forms one component of a nephron. The capillaries then merge again to form the efferent arterioles. In the outer cortex, these efferent arterioles twine around the tubules to form a peritubular network. In the inner third of the cortex and medulla, the peritubular network is replaced by long straight branches called the vasa recta.
The filtered blood travels through the left and right renal veins which empty into the inferior vena cava to reach the heart.
Parts of the Kidney
Nephrons
The nephrons are the functional units of the kidneys, and number about 1.3 million per kidney. A nephron has two main parts – tubules and corpuscles. The cup-shaped corpuscles contain the glomeruli. The tubules are small tubes traveling through the inner part of the kidney that regulate the passage of various chemicals to and from the blood. They have three parts, two highly coiled parts separated by a U-shaped curve (like a hairpin), called the proximal convoluted tubule, the loop of Henle and the distal convoluted tubule.
Other Parts of the Kidney
The cortex is the outer renal tissue located under the renal capsule. It appears lighter in color compared to the other parts of the kidney. The renal corpuscles, as well as the proximal and distal convoluted tubules are found here. It reaches into the inner renal tissue or medulla, splitting it into triangular parts called renal pyramids.
The renal pyramids contain the loops of Henle of each renal tubule, as well as the collecting ducts. Each of the renal pyramids opens at the apex, or renal papilla. Here the urine formed inside the pyramids is collected through a structure called the minor calyx. Several of the minor calices join to form a major calyx. Urine moves through the major calices to reach the renal pelvis.
The pelvis is a funnel-shaped collecting structure formed by the junction of all the major calices. It carries urine from the whole kidney to the ureter, which begins where the pelvis ends, at the pelvi-ureteral junction.
The pelvis is a funnel-shaped collecting structure formed by the junction of all the major calices. It carries urine from the whole kidney to the ureter, which begins where the pelvis ends, at the pelvi-ureteral junction.
The Gerota’s fascia is a thin fibrous tissue located outside the kidney and also enclosing the adrenal glands sitting atop the kidneys. It anchors the organ to the posterior abdominal wall. The renal capsule is a layer of tough fibrous tissue surrounding the kidney, found just inside the renal fat pad.
Kidney Terminology
Medical terminology can add to the confusion of a situation when a patient is dealing with health issues related to acute or chronic kidney disease. Below are some common words and definitions that can help aid patients in their understanding of kidney terminology as it relates to their health diagnosis
nb The term “renal”, from the Latin word renes meaning kidney, is often used interchangeably with the word “kidney”.
ACR (Albumin:Creatinine Ratio) is a urine test (into a small sample pot)
best done in the morning. It helps check if the nephrons (kidney filters) are damaged and leaking albumin, which is a type of protein normally in the blood. (See also Albuminuria and Proteinuria) This test contributes to the Kidney Health Check
Acute Kidney Injury (previously known as Acute Renal Failure) is a sudden loss of kidney function which is often reversible. However, sometimes it can lead to Chronic Kidney Disease. Causes of acute kidney injury can be from dehydration (most common), a toxin or illness that damages the kidney, or a blockage such as a kidney stone. Dialysis is sometimes used but is stopped once the kidney recovers.
Albuminuria occurs when a protein called albumin, which is normally in your blood, is found in your urine. When the nephrons (kidney filters) are damaged and the kidneys aren’t working as they should, they let this protein leak into the urine. (see also Proteinuria)
Microalbuminuria is when only a small amount of this protein has leaked into the urine. (Micro = small)
Macroalbuminuria is when a larger amount of this protein has leaked into the urine. (Macro = large)
Chronic Kidney Disease (commonly called CKD) is defined by altered kidney structure (shape) or reduced kidney function lasting more than 3 months. There are many different causes of CKD including diabetes, inflammation in the kidney and high blood pressure. There are 5 stages of CKD based on the level of function of the kidneys. If CKD progresses, then it can lead to End Stage Kidney Disease. (Also called Stage 5 CKD or Kidney Failure)
Creatinine is a waste product from the breakdown of muscles and is measured using a blood test. When the kidneys are working well, creatinine is filtered out of the blood and into the urine. When the kidneys aren’t working as well as they should then the amount of creatinine builds up in the blood. It is used to calculate the eGFR (Estimated Glomerular Filtration Rate) which is like a percentage of kidney function.
Dialysis may be used if your kidneys stop working properly. During dialysis, a different filter or machine does the kidneys’ job by filtering out the waste and excess fluid. Dialysis may be done in a hospital or at home.
Haemodialysis is where the blood is filtered through a dialysis machine and returned to the patient. Sometimes this occurs at home or at a dialysis unit at a hospital.
Peritoneal dialysis (PD) is a filtering process using the peritoneum in the abdomen. The peritoneum is a thin sac that surrounds the abdominal organs.
eGFR (Estimated Glomerular Filtration Rate) is a blood test result based on creatinine and your age and indicates the how well the kidneys function. The result is like a percentage of your kidney function compared to normal. It helps work out the stage of CKD.
End Stage Kidney Disease (also called ESKD, End Stage Renal Disease, Kidney Failure and Stage 5 Chronic Kidney Disease) occurs when the kidney function has deteriorated to less than 15%. When the kidney function is less that about 10%, Renal Replacement Therapy treatment such as dialysis or kidney transplant is needed to maintain life.
Haematuria is when blood is found in the urine. This occurs when the kidneys aren’t filtering well and red blood cells leak into the urine. Sometimes it can be obvious and the urine changes colour to red or brown (called Macroscopic Haematuria), or it may only be a small amount found when the urine is tested (called Microscopic Haematuria).
Kidney Health Check combines three tests your GP can do to check (screen) for kidney disease. These include having your blood pressure checked, having a blood test measuring your eGFR(Estimated Glomerular Filtration Rate), and a urine test for your ACR (Albumin:Creatinine Ratio). Together, these three tests indicate how well your kidneys are working.
Kidney Biopsy (also called Renal Biopsy) is a test sometimes used to find the cause of Acute Kidney Injury or Chronic Kidney Disease. The test involves using a needle under guidance to collect small samples of a kidney. It is performed under local anaesthetic using an ultrasound machine or CT scanner.
Kidney transplant (also called Renal Transplant) is a treatment option for End Stage Kidney Disease. A transplant can come from a live donor, such as a partner, friend or relative, or a deceased donor who decided to donate their organs after death.
Kidney Ultrasound (also called Renal Ultrasound) is a test using an ultrasound machine which uses soundwaves to form images of the kidneys and is used to help check for the cause of kidney disease.
Nephrologist (Also called a Renal Physician, Kidney Specialist or a Kidney Doctor) is a doctor who specialises in kidney health. Like the word ‘Nephron’, the term is derived from the Greek word Nephros meaning kidney.
Nephron is the basic structure in the kidney that filters the blood. The term is derived from the Greek word Nephros meaning kidney.
Proteinuria is where protein is found in the urine usually because filters (Nephrons) are damaged and leaking. The most common protein found is called albumin. (See Albuminuria)
Renal Replacement Therapy summarised the four ways of managing ESKD. These include Kidney Transplant, Peritoneal Dialysis, Haemodialysis, and Supportive Care.
Supportive Care is a treatment option for End Stage Kidney Disease. It involves using medications and treatments other than dialysis to treat symptoms that may occur. It is used when dialysis is thought to be too burdensome.
Glossary of kidney disease terms
Acute kidney injury (AKI): an abrupt reduction in kidney function with elevation of blood urea nitrogen (BUN) and plasma creatinine
Acute renal failure (ARF): see AKI
Acute tubular necrosis (ATN): most common cause of ARF. It can be caused by ischaemia (blood vessel obstruction) post surgery, sepsis, obstetric complications or severe burns.
Afferent arteriole: transports blood into a structure (e.g. glomerulus)
Anaemia: medical condition in which the percentage of red blood cells circulating in the blood is reduced
Analgesic: a compound that relieves pain
Analgesic nephropathy: kidney disease caused from high consumption of analgesic (pain-relieving) medications
Artery: blood vessel taking blood from the heart to other parts of the body
Azotemia: increased serum urea levels and frequently increased creatinine levels as well
Bacteriuria: the presence of bacteria in the urine
Bladder: a membranous sac
Blood typing: procedure to determine the compatibility between donor and recipient red blood cells
Cadaver: dead person
Calculi: see renal stones
Catheter: hollow tube used to transport fluids to or from the body
Cellulitis: an acute, diffuse, spreading, oedematous, pus-producing inflammation of the deep subcutaneous tissues
cfu: colony forming units
Chronic glomerulonephritis: encompasses several glomerular diseases with a progressive course leading to chronic renal failure
Chronic kidney disease (CKD): at least 3 months of either
- structural or functional abnormalities of the kidney that can lead to kidney failure; or
- GFR < 60 mL/min/1.73 m2
Chronic renal failure (CRF): slow and progressive deterioration of kidney function -¬now replaced by the phrase chronic kidney disease (see above)
Colic: acute, abdominal pain
Complete proteins: foods, such as meat, fish and eggs, which contain all of the protein-building materials that a body needs
Continuous ambulatory peritoneal dialysis (CAPD): form of continuous peritoneal dialysis in which dialysis fluid is exchanged at regular intervals throughout the day
Continuous cycling peritoneal dialysis (CCPD): form of continuous dialysis in which the peritoneal cavity is continuously filled with dialysis fluid by a machine
Creatinine: a waste product of muscle activity that is removed from the body by the kidneys, and excreted in the urine; high levels of creatinine represent reduced kidney function
Cystitis: inflammation of the bladder
Detrusor muscle: a basket weave of smooth muscle fibres that form the urinary bladder
Diabetes mellitus: disease of the pancreas in which production of insulin is decreased (commonly called diabetes) or insufficient for the body's needs, resulting in disturbed levels of glucose in the blood
Diagnosis: identification of problem from patient's symptoms
Dialyser: the part of a kidney machine which acts like a filter to remove wastes from the body
Dialysis fluid: special fluid used in dialysis into which wastes are passed
Dialysis: a treatment for kidney failure which removes wastes and water from the blood; a process by which small molecules pass from one fluid where they are in high concentration to another fluid where the concentration is lower, through a porous membrane
Diuretic: any agent that enhances the flow of urine
Donor: person who donates something
Dyselectrolytemia:·an imbalance of certain ionized salts (i.e., bicarbonate, calcium, chloride, magnesium, phosphate, potassium, and sodium) in the blood
Efferent arteriole: transports blood out of a structure (e.g. glomerulus)
End-stage kidney disease (ESKD): stage in kidney disease when treatment, such as dialysis or transplantation, becomes necessary. " End-stage" refers to the end of kidney function
End-stage kidney failure (ESKF): irreversible total kidney failure
End-stage renal disease (ESRD): see ESKD
End-stage renal failure (ESRF): See ESKF
Endothelium: tissue that covers body surfaces, lines body cavities and forms glands
Energy foods: foods, particularly sugar and fats, which provide the body with energy Usually measured in calories or kilojoules
Erythropoietin (EPO): a hormone made by the kidneys that stimulates the bone marrow to produce red blood cells
Euglycaemia: a normal level of sugar in the blood
Exchange: one complete cycle of peritoneal dialysis, consisting of inflow, equilibration, and outflow of dialysis fluid
Exoriate: to scratch and remove the skin
External urethral sphincter: striated muscle under voluntary control
Extracorporeal shockwave lithotripsy (ESWL): Ultrasound waves are used to break up stones in the kidney, ureter and bladder into smaller pieces which can eliminated from the body in the urine
Fistula: a passage or duct, commonly used method for providing access to the bloodstream in which a vein and an artery in the arm are joined together
Glomerular capillaries: fist-like structure of 4-8 capillaries subdivided from the afferent arteriole
Glomerular endothelium: composed of cells in continuous contact with the basement membrane
Glomerular filtration membrane: the wall of the glomerular capillary serves as a filtering membrane
Glomerular filtration rate (GFR): the filtration of the plasma per unit time and is directly related to the perfusion pressure in the glomerular capillaries. GFR provides the best estimate of functioning renal tissue. Loss or damage to nephrons lead to a corresponding decrease in GFR.
Glomerulonephritis (GN): condition in which the glomeruli, the tiny filters in the kidneys are damaged; often referred to as nephritis
Glomerulus: a tuft of capillaries that loop into a circular capsule, called the Bowman Capsule
Graft: commonly used method of providing access to the bloodstream in which a vein and an artery in the arm are joined together with a piece of special plastic-like tubing
Haematuria: a large number of red blood cells in the urine
Haemodialysis: treatment for kidney failure in which the blood passes through an artificial dialyser to remove wastes and water
Haemoglobin: colouring matter of the red corpuscles of the blood, that transports oxygen in the blood
Haemorheology: study of the deformation and flow properties of the cellular and plasma components of the blood and the blood vessels
Health: complete physical, mental, emotional and spiritual wellbeing, not merely an absence of disease; a resource for life
Heparin: substance added to blood during haemodialysis to prevent it from clotting in the dialyser during haemodialysis
Hydronephrosis: accumulation of urine in the renal collecting system
Hydroureter: accumulation of urine in the ureter
Hypertension: high blood pressure. May be either the cause of, or the result of, kidney disease
Hypoproteinaemia: abnormal decrease in the amount of protein in the blood
Idiopathic: of unknown origin
Incomplete proteins: foods, such as fruits, vegetables and cereals, which do not contain all of the protein-building materials that a body needs
Insulin: hormone produced by the pancreas that regulates the level of glucose (sugar) in the blood
Intermittent peritoneal dialysis (IPD): form of peritoneal dialysis in which exchanges are done hourly for two or three days each week
Interstitial cystitis: a persistent and chronic form of 'non-bacterial' cystitis occurring primarily in women
Internal urethral sphincter: a ring of smooth muscle at the junction of the urethra and the bladder
Ischaemia: localised anaemia caused by interruption/obstruction of arterial blood flow
Jugular vein: blood vessel located in the side of the neck sometimes used to provide access for haemodialysis
Juxtaglomerular apparatus: composed of 2 types of cells which control renal blood flow, glomerular filtration and renin secretion
Kidney: the primary function of the kidney is to maintain a stable internal environment for optimal cell and tissue metabolism. These tasks are achieved by balancing solute and water transport, excretion of metabolic wastes, conserving nutrients and regulating acids and bases. The kidney also has an endocrine function by secreting the hormones renin, erythropoietin and 1,25-dihydroxyvitamin D3 for the regulation of blood pressure, red blood cell production and calcium metabolism respectively.
Kilojoules: a metric measure of energy value of food (previously called calories)
Kt/V: an expression of the efficiency, or the fractional urea clearance of one haemodialysis session: K is the rate of clearance, t is the amount of time of the session, and V is the urea distribution volume after haemodialysis.
Loop of Henle: a hollow, hairline loop of the nephron, composed of thick and thin portions. Solutes are actively transported across the thick section of the loop resulting in urine concentration.
Membrane: porous material which is used to filter wastes from the blood
Metabolic disturbance: disruption of the chemical processes of the body
Micturition: urination
Neoplasm: any new and abnormal growth, in particular new growth of tissue in which the growth is uncontrolled and progressive
Nephritis: see glomerulonephritis
Nephrolithiasis: see renal stones
Nephrology: the branch of medical science that deals with the kidneys
Nephron: the structural and functional units of the kidney, numbering over a million in each kidney, which are capable of forming urine
Nephropathy: any disease of the kidney
Nephrosis: degeneration of the renal tubular epithelium
Nephrotic syndrome: the excretion of large amounts of protein in the urine per day. This is characteristic of glomerular injury.
Neurogenic bladder: a functional urinary tract obstruction caused by an interruption of the nerve supply to the bladder
Oliguria: diminished excretion of urine (< 400 mL/d or 30 mL/h)
Organ: structurally distinct part of the body which usually performs a particular function. Usually made up of several types of tissue in a very organised structure, e.g. kidney, heart, lungs, liver.
Osteomalacia: inadequate or delayed mineralisation of the bone matrix in mature compact and spongy bone
Peritoneal cavity: abdominal cavity that contains the intestines and other internal organs; lined by the peritoneum or peritoneal membrane
Peritoneal dialysis (PD): treatment for kidney failure in which dialysis fluid is introduced into the peritoneal cavity to remove wastes and water from the blood
Peritoneum: thin membrane that encloses the peritoneal cavity and surrounds the abdominal organs
Peritonitis: inflammation of the peritoneum
Phosphate binder: medication that binds with phosphate in the intestine causing some of the phosphate to be passed in the faeces
Phosphate: mineral in the body fluids regulated by the kidneys. At normal levels, keeps bones and other parts strong and healthy. At high levels, causes itching and painful joints
Plasma creatinine (PCr) concentration: a blood test which is directly related to GFR. When the GFR decreases, PCr increases
Podocytes: specialised cells located in the glomerular epithelium. These foot-like cells interlock and form a network of intracellular clefts called filtration slits which filter the glomerular filtrate, forming the primary urine
Polycystic kidney disease: inherited kidney disease that produces fluid-filled cysts in the kidneys that produce chronic renal failure over many years
Potassium: mineral in the body fluids regulated by the kidneys. At normal levels, helps nerves, muscles and other cells work well. At high levels, may result in cardiac arrest or arrhythmias
Protein: substance obtained from food which builds, repairs and maintains body tissues
Pruritus: itching
Purpura: a disease characterised by purple or livid spots on the skin or mucous membranes caused by blood being forced out of the blood vessels and into the surrounding tissue
Pyuria: white blood cells in the urine
Pyelonephritis: an infection of the renal pelvis and interstitium
Recipient: person who receives (a new organ)
Reflux nephropathy: kidney disease caused by the backflow of urine from the bladder up the ureters into the kidney tissue
Renal arteries: arise as the fifth branches of the abdominal aorta and supply blood to the kidneys
Renal cortex: area of the kidney that contains all the glomeruli and portions of the tubules
Renal failure: loss of kidney function
Renal insufficiency: decline in renal function to about 25% of normal or a GFR of 25-30 ml/min
Renal pelvis: a hollow structure which is an extension of the upper end of the ureter
Renal stones (also known as calculi, nephrolithiasis): masses of crystals and protein and are common causes of urinary tract obstruction in adults
Renin: an enzyme which is produced, secreted, and stored by the kidneys, that plays a role in regulating blood pressure
Renin-angiotensin system: a major hormonal regulator of renal blood flow, which can increase systemic arterial pressure and thus change renal blood flow.
Septicaemia: the presence and persistence of pathogenic microorganisms or their toxins in the blood which affects the body as a whole (i.e. a systemic disease)
Sodium: mineral in the body fluids regulated by the kidneys. Affects the level of water retained in the body tissues
Staghorn calculi: large stones which grow in the pelvis and extend into the calyces to form branching stones
Steroid: medication which reduces inflammation and is used to fight rejection
Subclavian vein: blood vessel located underneath the collarbone sometimes used to provide access for haemodialysis
Tissue typing: procedure to determine the degree of compatibility between lymphocytes (type of white blood cell) of a donor organ and a recipient
Tissue: cells of a particular type massed together, e.g. blood, nerves
Transplant: to transfer, as an organ or a portion of tissue, from one person to another
Ultrafiltration: the process of producing a filtrate of protein-free plasma
Uraemia: a syndrome of renal failure and includes elevated blood urea and creatinine levels accompanied by fatigue, anorexia, nausea and vomiting
Urea: waste product from the breakdown of protein and the major constituent of urine along with water
Ureterorenoscopy (URS): visual inspection of the interior of the ureter and kidney by means of a fiberoptic endoscope
Ureter: tubular structure that transports urine form the kidney to the bladder
Urethra: tubular structure which transports the urine from the bladder to the outside of the body
Urethral syndrome: symptoms of cystitis, such as frequency, urgency and dysuria, but with negative urine cultures
Urinalysis: test to measure the presence of protein, blood and other substances in the urine
Urology: the branch of medicine dealing with the urinary system in females and the genitourinary system in males
Vein: blood vessel returning blood to the heart
Vitamin D: a fat-soluble chemical that is activated naturally in the body on exposure to sunlight
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