Urine formation

How will you define Urine?

1. kidneys filter large amounts of plasma and reabsorb most of it, which is filtered and leaves behind the unwanted metabolic waste to be eliminated is called urine
2. The kidneys form urine, passes through the ureters, and is stored in the urinary bladder.
3. Normal urine specific gravity is around 1.024, and the color is clear.

How does urine formation take place?

1. Urine formation takes place in three steps:
   1. Ultrafiltrate formation from the glomeruli from the plasma.
   2. Reabsorption of the water and solutes from the ultrafiltrate.
   3. Secretion of the extra solutes into the tubular fluid, like urine.

What is the function of kidneys in urine formation?

1. Urine formation.
2. Protein conservation.
3. Regulation of acid-base balance.
4. Regulation of fluid and electrolyte balance.
5. Hormonal function.
6. Removal of potentially toxic material is one of the main functions of the kidneys.

What is the role of nephrons in urine formation?

1. Ultrafiltration is a protein-free plasma filtrate.
2. Maintain the body fluid volume.
3. Maintain the balance of the composition of the electrolytes.
4. Maintain the pH.

What is the role of tubular reabsorption process in urine formation?

1. This is the movement of fluids and substances from the tubular lumen to the peritubular capillary plasma.
   Tubular Reabsorption:

   Mode of transport	Substances	Site of reabsorption
   Active transport	Sodium (Na)	Proximal and distal  convoluted tubule
   	Chloride (Cl–)	The ascending loop of Henle
   	Glucose, salts, and amino acids	Proximal convoluted tubule
   Passive transport	Urea	Proximal convoluted tubule The ascending loop of Henle
   	Sodium (Na+)	The ascending loop of Henle
   	Water  (H2O)	Proximal convoluted tubule Descending loop of Henle Collecting tubules.

What is the tubular secretion process in urine formation?

• This is the transfer of substances and fluids from the plasma of the peritubular capillaries to the tubular lumen.

Tubular secretion process in urine formation:

Chemical substances and their excretion and absorption in the renal system:

1. Each day, an average of 115 to 180 L for females and 130 to 200 L of fluids for men were filtered through the glomeruli.
   1. Water 180 L is filtered, 178.2 L is reabsorbed, and only 1.5 L is excreted daily.

2. Sodium 25,200 meq/day is filtered, 25050 is reabsorbed, and only 150 meq is excreted daily.
3. Potassium 720 meq/day is filtered, 620 is reabsorbed, and only 100 meq is filtered per day.

What are the types of Urine samples?

1. Random Sample:
   1. This is collected without any precaution and may be collected at any time of the day.
   2. This may be collected for the drug abuse analysis.
2. Morning sample:
   1. This is the first sample when the patient gets up in the morning.
   2. This is concentrated urine.
   3. This is the choice of sample for microscopic examination.
   4. This is also the sample choice for the urine constituents to detect protein, HCG, and other substances.
3. 8 hours sample:
   1. This may be an alternative to the first-morning sample because this will also be concentrated in the urine.
4. 24-hour sample:
   1. This sample is used to quantify any urine solutes like proteins to avoid that substance’s diurnal variation.
   2. Instruct the patient to void the first sample and note the time. After that, all the samples will be collected until 24 hours have passed.
   3. Now, void the last sample in the container.
   4. 24 hours of samples are used for the substances with diurnal variations like catecholamines, 17-hydroxysteroids, and electrolytes.
5. Timed Specimen:
   1. These samples are collected at a predetermined time, like 1,4, or 24 hours.
   2. A sample patient is given special diet or drug-use instructions for a collection of times.
6. Clean catch sample:
   1.  In this case, the patient is instructed to clean the genitalia with water and soap.
   2. Then, the midstream sample is collected.
   3. These are used for the bacteriological culture.
   4. Caution should be taken that the container should not touch the genitalia.
7. Catheter samples:
   1. These are usually collected from seriously ill patients who are already catheterized.
   2. Or insert the catheter into the urinary bladder to collect the sample.
   3. These are used for the microbiological examination of critically ill patients.
8. Suprapubic sample:
   1. The sample is directly collected from the urinary bladder using a suprapubic needle that has been completely sterilized.
   2. This sample is ideal for the culture, and there is a bypass of the urethra.
   3. This will be a good sample for the culture of the urinary bladder.
   4. This is usually done from the distended urinary bladder.
9. Urine from children:
   1. Collecting the samples from infants is difficult.
   2. There are adhesive bags available to put on the urethra to collect urine.

What are the types of urine and their indications?

What is the role of urine preservatives?

1. These preservatives are added for the following purposes:
   1. Reduce bacterial growth.
   2. Decrease the decomposition of the chemicals.
   3. Keep the substance in solute form.
   4. Decreases the atmospheric oxidation of unstable compounds.
2. Refrigeration is the most useful tool for collection, and its utility increases with adding preservatives.
3. The tablets commercially available are:
   1. Potassium acid phosphate.
   2. Sodium benzoate.
   3. Benzoic acid.
   4. Methenamine.
   5. Sodium bicarbonate.
   6. Red mercuric acid.

What are the advantages of preservatives?

1. These tablets act mainly by lowering the pH of urine and releasing formaldehyde.
2. Formalin is used as a preservative, but in large amounts, it precipitates urea and inhibits some chemical reactions.
3. Acidification of the urine below pH 3 is widely recommended. This is widely used to preserve urine for 24 hours and is particularly useful for calcium, steroids, and vanillylmandelic acid determination.  HCL 10 mL, 6 mol/L per 24 hours of urine is used.
4. Sulfamic acid is used at 10 g/L to reduce the pH.
5. Boric acid is used at 5 mg/30 mL, but it causes precipitation of the urates.
6. Toluene is only an organic preservative and is still used; this will not prevent anaerobic microorganisms’ growth.
7. Sodium carbonate is used at 5 g/for 24 hours urine sample to preserve the porphyrins and urobilinogen.

What are the various urine preservatives?

Refrigeration:

1. When there is a delay in examining urine, refrigerate at 2 C to 8 C.
2. Urine can be freezed at -24 C to -16 C.
3. If urine collection for the examination is delayed by more than 2 hours, it needs preservatives.
4. When urine is refrigerated:
   1. This will not interfere with the urine chemical tests.
   2. It prevents bacterial growth.
   3. Refrigerate for albumin, aldosterone, amylase, chloride, cortisol, estradiol, FSH, lipase, oxalate, protein, and uric acid.
5. The disadvantage is there is an increase in the specific gravity.
   1. Precipitate amorphous phosphates and urates.

HCl (Hydrochloric acid):

1. Add 6 mL of hydrochloric acid (HCL) for Aldosterone, calcium, creatinine, cystine, homovanillic acid, 17-ketosteroids, oxalate, and VMA.

Boric acid:

2. It will preserve protein.
3. Preserves formed elements.
4. It will not interfere with the routine examination except for the pH.
5. This is bacteriostatic.
6. Add boric acid for albumin, cortisol, estrogen, aldosterone, amino acid, chloride, HCG, citrate, cortisol, creatine, DHEA, FSH, glucose,  phosphate,  17- Ketosteroids,  protein, uric acid, and zinc.
7. The disadvantage is that it may precipitate crystals when used in large amounts.
   1. It interferes with drugs and hormones.

Formalin (formaldehyde):

1. It is the best for urine sediments.
   1. It acts as a reducing agent.
   2. Rinse the container with formalin to preserve the cells and casts.
2. The disadvantage:
   1. It interferes with chemical tests like glucose, esterase, blood, and white blood cells.

Sodium fluoride:

1. It prevents glycolysis.
2. This is a good preservative for the drug’s analysis.
3. The disadvantage:
   1. It will interfere with test strips for glucose, white blood cells, and red blood cells.

Phenol:

1. It does not interfere with routine tests.
2. It changes the odor.
3. Use one drop of phenol per ounce of urine.

Toluene:

2. It does not interfere with routine tests.
3. The disadvantages are that it floats over the surface of the urine and may block the pipette.

Thymol:

1. It is an excellent preservative for glucose and sediments.
2. The disadvantage:
   1. It interferes with acid precipitation for the protein.

Commercial preservative tablets:

1. It is easy to use when refrigeration is not available.
2. Check the tablets’ composition to find any effect on the test.
3. These tablets contain the above preservatives and sodium fluoride.

Summarize various urine preservatives?

Questions and answers: