The main difference between urine and filtrate is that urine is waste liquid excreted through urethra whereas filtrate is the liquid formed during the formation of urine.
Urine vs. Filtrate
Water is the major constituent of urine forming almost 95% of urine, and the remaining part is composed of other organic and inorganic constituents. Other constituents are urea 9.3 g/L, sodium 1.17 g/L, potassium 0.75 g/L, chloride 1.87 g/L, creatinine 0.67 g/L and some ions, organic and inorganic compounds in small quantities. Composition of filtrate is the same as plasma of the blood; the only difference between filtrate and blood is that blood contains blood cells. The filtrate contains glucose, protein, creatinine, uric acid, and different ions. Urinalysis is used to monitor urinary tract infections, kidney or liver diseases. It can also be used for diabetes, some diseases of blood and bladder stone. Changes in color, volume, turbidity, and odor are also indicators of different diseases. For example, dark orange color to brown urine is seen in case of jaundice, sweet smell is seen in diabetic patients, and increased volume of urine is produced in polyuria. The filtrate is also used to assess kidney health by glomerular filtration rate (GFR). The speed at which the blood is filtered in glomeruli is known as GFR. It is altered in the case of kidney diseases and hence can be used to assess the damage to kidneys because of different diseases. GFR test is done in patients of diabetes, frequent urinary tract infections, hypertension and kidney infections, etc. Normal GFR is 90 or higher in adults while less than 60 GFR indicates disease condition.
What is Urine?
Urine is formed in tubules by three steps, filtration, reabsorption, and secretion in the kidneys. Kidneys consist of nephrons which act as filters for blood and separate the waste material from it produce urine. A network of capillaries called renal glomerulus is surrounding the Bowman’s capsule at the beginning of each nephron. The glomeruli receive blood from each artery and exeunt it via another artery. This passing blood is filtered through the glomeruli’s membrane and enters a collecting cup called the renal tubule. This fluid exiting the glomerular membrane is known as glomerular filtrate. This is the first step called filtration. The rate at which filtrate is produced is about 125 mL/min, but only 1.5 to 1.8 liters of urine is excreted from our body under normal conditions. After leaving the Bowman’s capsule, the filtrate goes into the renal tubules. Almost 99% of water, glucose and amino acids and Na+ and Cl+ ions are reabsorbed back into the blood. This is the second step called reabsorption. As the fluid passes further, more substances are reabsorbed, and finally, urine is produced which is excreted from the body through the urethra. This is the last step excretion. Urine tests are used to diagnose different diseases. For example, urine color is an indicator of hydration. Urine pH tells about the type of diet. Urine smell reflects the age of the urine and also indicates the presence of glucose and ketones and urinary tract infection can be determined by urine turbidity.
What is Filtrate?
The filtrate is the second step in urine formation process but it has its significance as the glomerular filtration rate (GFR) is used to assess the health of kidneys. It is produced by the glomerulus when the hydrostatic pressure produced by the heart pushes water and solute through the filtration membrane. It is a passive process as cellular energy is not used at the filtration membrane to produce filtrate fluid. The filtration membrane lies between the blood in the glomerulus, and the filtrate in the Bowman’s capsule and this filtration membrane is highly fenestrated allowing the passage of small molecules such as sodium, glucose, and water, etc. The quantity of filtrate formed by kidneys per minute is termed as the glomerular filtration rate. Approximately 20% of cardiac output is filtered by kidneys per minute under resting conditions. The working of the kidneys produces almost 180 L/day in men and 150 L/day filtrate in women. However, 99% of this filtrate is returned to the circulation through reabsorption resulting in only 1 to 2 liters of urine per day. Insulin and creatinine are two endogenous substances that are used to determine glomerular filtration rate. These markers are carried to the kidney by blood via a renal artery and are filtered at the glomerulus. The rate at which these substances are filtered from the blood into the urine per minute reflects GFR of the kidney.
- Urine is the waste liquid excreted from the body whereas filtrate is formed during urine formation.
- Urine composition is water, urea, sodium, chloride, potassium, and creatinine whereas filtrate composition is water, glucose, urea, uric acid, creatinine, ions, organic and inorganic compounds.
- Urine is formed through steps, filtration, reabsorption, and secretion whereas the only filtration is involved in the production of the filtrate.
- Urine is used to diagnosing different diseases whereas filtrate is used to detect kidney health.
- The whole kidney is involved in the formation of urine whereas filtrate is formed only in glomerulus present in Bowman’s capsule.
- The average rate of urine is 800-1000 mL/day whereas normal GFR is 90 ml/min.