Characteristics of the children's urinary system

2021-01-30 12:00 AM

Each kidney has 9-12 calyces, divided into 3 groups: upper, middle, and lower. The shape of the renal pelvis system by age is very different due to the need to contract to push urine down.

Anatomic and structural features of the children's urinary system

Th Compliments, suggestions

Location: Young children lying lower kidney than adults and adults, the lower extremity of the kidney’s horizontal vertebrae IV -V.

Weight: the kidneys of children are relatively larger than that of adults and increases gradually with age: newborn kidney weighs 11-12g; Double 6 months (24-25g); 1 year old 3 times (36-37g); wire age - 10 times (115-120g).

Appearance: Small kidney womb-shaped.

Structure: The ratio between the shell and the pulp in a newborn is 1: 4, in a breastfed child is 1: 3, in an adult is 1: 2.

Nephron: The functional structural unit of the kidneys. Each kidney has between 1 and 1.5 million Nephrons as adults. Nephron includes: Glomerulus, proximal tubule, Henle loop, distal tubule, manifold, and glomerular scale.

The glomerular basal membrane consists of 3 main layers:

The innermost layer is the glomerular capillary endothelium (Endothelia).

The middle layer is the glomerular capillary basal membrane (Lamina d ensa) with many small holes (por) with a diameter of 50 - 200 A °. As a result, molecules larger than 70,000 Daltons will not be able to pass through the basal membrane of the glomerulus to descend with the first urine.

The outermost layer is the cells with the legs (Podocytes).

mesangial cells are located between glomerular capillaries.

Radioactive kidney

Each kidney has 9-12 calyces, divided into 3 groups: upper, middle, and lower. The shape of the renal pelvis system by age is very different due to the need to contract to push urine down.


The ureters in children are relatively large and long, making it easy to fold.

Children: The ureter comes out of the renal pelvis forming a right angle; In older children and adults is the prison corner.

As a result, young children are very susceptible to urinary stagnation in the pyrenoid radio.


Location: The bladder in children is high, so when it is filled with urine, it is easy to feel the bladder bridge.

Bladder capacity in children varies with age:

Infants: 30 - 60 ml

+ Breastfed babies: 60-100 ml

+ Children 5 years old: 100 - 200 ml

+ Children 10 years old: 150 - 350 ml

+ Children 15 years old: 200 - 400 ml

45 ± 15 ml

80 ± 20 ml

150 ± 50 ml

250 ± 100 ml

300 ± 100 ml


The size of a child's urethra not only depends on age, but also on gender.

Girls: wide but short urethra: 2 - 4 cm.

Boys: narrow but long urethra: 6 - 15 cm.

As a result, girls get more urinary tract infections than boys.

Physiological characteristics of children's urinary system

Kidney function characteristics

Filtering function of the glomeruli:

Filtration is the most important function of the glomerulus and the first stage of the formation of urine. This is a passive process, depending on the hydrostatic pressure in the glomerular capillaries, the hydrostatic pressure in the Bowman’s cavity and the colloidal pressure. In particular, the hydrostatic pressure in the glomerular capillaries depends on the circulating volume, the force of the heart muscle and the glomerular capillary state; while the colloid pressure is determined by blood protein. Through the filtration process, waste substances that are not needed by the body such as acids, ammonia, urea, creatinine, drugs or excess substances such as Na, K ... are eliminated from the body.

To evaluate the filtering function of the glomerulus, it is determined the clearance (Clearance) of endogenous substances such as creatinine, urea or exogenous such as inulin, radioactive substances. Clearance is the amount of plasma (ml) filtered by the kidneys from an endogenous or exogenous substance, when the blood passes through the kidneys within 1 minute. Thus, the unit of measurement of glomerular filtration rate is ml / min. For example: Clearance urea of ​​a child is 80ml / rich, which means that every 1 minute, 80 ml of plasma is filtered out of urea. In order to facilitate the assessment of renal filtration function in children of different ages, the clearance parameters are specified in standard units according to adult skin area (height 170 cm, weight 70 kg). 1.73 m2. Example: A child has a skin area (S) of 1.2 m2; Clearance creatinine is 80ml / min, then the filtration rate per standard unit (Cst) will be:                

Cst = C.1,73 / S = 80.1,73 / 1,2 = 115ml / min / 1.73m2

The glomerular filtration function in the newborn is still not absorbed, only reaching 25% of the average value of the adult child.

Breastfed babies, the filtration function is often low, but constantly increasing and will reach the normal values ​​as adults (120ml / min / 1.73m2) when the child reaches school age. However, according to Mc Crory WW, the child's endogenous creatinine clearance increased rapidly in the first year and achieves the same mean as adults when the child is 2-3 years old.

The renal tubular reuptake function:

After glomerular filtration, the first urine is formed and then goes through the kidney tubules pouring into the pyramid station. The composition of first urine, if not to mention Protide, is almost like plasma. That means that there are enough substances such as amino acids, glucose, Ca, Mg, Na, K, Cl ... salts. In the process of going in the kidney tube, essential substances for the body are reabsorbed. blood. For example: In the proximal tubule, 100% of amino acids, glucose, K, phosphates and 80% Na are reabsorbed into the bloodstream. In the renal tubules 99% of the water in the first urine is reabsorbed. Re-absorption is an active process that requires the participation of corresponding enzymes and energy consumption.

Children <2 years: The function of reabsorption is still poor, so the proportion of urine is low.

Children> 2 years: Function of reuptake almost as adults.

Thus, the ability to concentrate urine in children under 2 years old is poor. The maximum concentration capacity in this object is only 400-450mOsm / l, while in older children it is 800-1200mOsm / l. Therefore, when dehydrated, young children cannot concentrate urine to retain water for the body like adults and adults.

Excretion function of the renal tubules:

Substances that are not essential to the body, but have large molecules over 70,000 Daltons or have structures that link the molecules together to form networks (such as methylene blue), cannot be eliminated by filtration. glomerular okay. They are eliminated by excretion in the distal tubule and part of the manifold. The renal tubular secretion function in children under 2 years old is worse than that of children over 2 years old and adults.

Endocrine function:

Is the function of glomerular balance. Glomerular weight organization works well from the moment of birth and produces 2 substances:

Erythropoietin: A substance that stimulates the bone marrow to produce red blood cells.

Renin: Has a vasoconstrictor effect, increases blood pressure. Renin will be secreted by the glomerular weight-organizing cells when blood flow to the glomerulus decreases or when the amount of urine through the distal tubule is low.

Number of children's pee

Postpartum, according to Laugier and Gold F., 92% of babies urinate for the first time within the first 24 hours, about 7% of babies pee the first time on day 2 and only 1% of babies urinate on time. first on the 3rd.

In the first days of life, babies have very little diabetes, even anuria due to physiological dehydration and late breastfeeding. Then the number of urination times increased and reached 20-25 times / day in the first month, due to small bladder capacity and poor control capacity of the central nervous system. After 1 year of age, the number of urinary spells in a child drops much:

The first few days after giving birth: The baby has very little urination.

Newborn: 20-25 times / day (about 1 hour for pee 1 time).

Children 3 months: 15 -20 times / day (about 1.5 hours of pee 1 time).

Children 1 year: 12-16 times / day (about 2 hours pee 1 time).

Children 3 years old: 7-8 times / day (about 3 hours pee 1 time).

Children> 3 years old: 6-8 times / day (about 3 hours pee 1 time).

Mothers should be educated to train their babies to form an active urinary reflex, not to have nocturia by injecting their babies right from the first days after giving birth.

The frequency of urination depends not only on age, but also on diet, drinking, and hot and cold weather.

The amount of the child's urine

The amount of urine in a child depends on many factors such as age, diet, hot and cold weather and kidney function.

Children 1-4 days old: 20-60ml / day.

Children 5 - 7 days old: 100 - 150 ml / day.

Children 2 - 3 weeks old: 150 - 300 ml / day.

Children 1-2 months: 250 - 450 ml / day.

Children 2 months - 1 year old: 400 - 600 ml / day.

Children> 1 year to 7 years old, the amount of urine per day can be calculated by the following formula:

V = 600 + 100 (N - 1)

V: The amount of urine (ml) / day.

N: The age of the child.

600: The amount of urine of a 1-year-old child.

100: The amount of urine increases after each age.

Children over 7 years old: 1200 - 1400 ml / day.


Liquid diets such as breastfed, porridge or drinking lots of water will lead to more urination than a dry, low-water diet.

When the weather is hot, if the surgery is bad, the child will urinate less; on the contrary, in the cold season the child will urinate more often.

Poor filtration of the kidneys, less urine output; on the contrary, if the kidney tube has poor function of filtering or concentrating urine (reabsorption), the child will urinate a lot.

Urine composition and density


Protein: Not normally present in urine. Particularly, newborn babies can be in the form of traces.


Normally in the urine, leukocytes and leukocytes are absent:

1 million red blood cells / 24 hours (or 1000 missing cells / minute).

2 million WBCs / 24 hours (or 2000 WBCs / minute).

There are no pillars.


Due to the weak function of concentrating urine in children, the proportion of children's urine is lower than that of adult urine. To fully evaluate the function of the kidneys, it is necessary to conduct a Zimnisky test, which means measure the amount of urine and the proportion of urine after each urination for 24 hours, then calculate:

The amount of urine in 24 hours:

To determine whether a child is normal, having low urination, oliguria or anuria, we have to rely on the amount of urine per day (24 hours). On the other hand, daytime urine volume should be 2/3 or 3/4 of the amount in 24 hours. Conversely, if the amount of urine at night is more than 1/3 of the 24-hour urine output, it is called nocturia due to the poor ability of the tubules to concentrate urine.

Density of urine:

Normally, within 24 hours, the density of urine ranges from 1,002 - 1,030 and should have at least:

1 time the proportion of urine> 1.018.

The difference between the maximum density - minimum> 0.010.

Density difference max - min <0.010 is called co-density:

If the difference in density max - min <0.010 and there is no time of density> 1.018, it is called "Low density" and is common in urine.

If the difference in density max-min <0.010 and maximum density> 1.025, it is called "High density copper" and is common in diabetes.


Measure the density of urine at a temperature of 15 degrees C.

If measured at a higher temperature then every 3 degrees C plus 0.001 and vice versa, if lower then subtract.

For every 4g / l Protein increases the proportion of urine by 0.001.

For every 1% increase in sugar increases urine density 0.004.