The excretion system in humans is a system that processes the disposal of metabolic waste substances. Substance residual metabolism consists of carbon dioxide (CO2), water (H20), ammonia (NH3), urea, and bile substances. This metabolic waste product must be removed from the body. It is toxic and can cause disease.
The Roles of Kidney in the Excretion System
In addition to filtering the blood, controlling body fluid balance, and maintaining electrolyte levels in the body, the kidneys are very closely related to the excretion system in humans. It is responsible for removing the body’s waste and toxins. The blood entering the kidneys will be filtered, as well as body fluids. The kidneys are also responsible for maintaining the body’s water intake, salt, and mineral to a normal level. The filtered blood will flow back to other organs through the kidney blood vessels. The filtered waste substances will be removed through urine submission in the pelvic kidney (renal pelvis). Then, the ureter will transfer the urine to the bladder, where urine is stored. Finally, urine runs from the bladder and out of the body through the urinary tract.
The kidneys are important organs as a part of the urinary system. Further, they have many functions, including:
- Removing (excreting) metabolic waste from the body. The kidneys filter toxins, excess salt, and urea, as well as nitrogen-based wastes that are created from cell metabolism. Urea is processed in the liver and transported through the blood to the kidneys to be removed.
- Balancing fluid and electrolyte levels. Since the kidneys are the key in the formation of urine chemistry, the kidneys will react to changes in water levels in the body throughout the day. When water intake decreases, the kidneys will adjust and hold water in the body so the body does not experience fluid deficiency.
- Regulates blood pressure. The kidneys need constant pressure to filter the blood. When blood pressure drops too low, the kidneys will increase blood pressure. This is done by producing angiotensin, which can constrict blood vessels and maintain salt and water in the body. This process will help blood pressure return to normal.
- Regulation of red blood cells. If the kidneys do not get enough oxygen, the kidneys will send an emergency sign in the form of erythropoietin. This is a hormone that stimulates the bone marrow to produce more oxygen-carrying red blood cells.
- Helps calcium absorption and maintain bone health, by producing the hormone calcitriol
- Regulates acid levels in your body.
Excretion System (kidneys) in infants
Newborns have a chemical balance range and a small safety range. Rapid infections, diarrhea, and irregular eating patterns can cause acidosis and fluid imbalances such as dehydration. Edema of kidney irregularities can limit the ability of newborns to excrete drugs. Usually, a small amount of urine is present in the baby’s bladder at birth but the newborn allows not to urinate for 12-24 hours. Urination often occurs during this period. Urinating 6-10 times with a pale urine color shows enough fluid intake. Generally, the term infant excretes 15 to 60 ml per kilogram/day.
Fetal kidneys begin to form at 12 weeks’ gestation. In the bladder, there is urine secreted into the amniotic water. In newborns, the bladder capacity is approximately 45 cc and the production of urine is an average of 0.05 – 0.10 cc per minute. The newborn kidney shows a decrease in renal blood flow and a decrease in glomerular filtration speed. This condition can cause fluid retention and water intoxication. A tubular function is immature so that it can cause large amounts of sodium loss and other electrolyte imbalances. Newborns are not able to concentrate urine properly. This is reflected in urine weight (1.004) and low urine osmolality. All these kidney limitations will be worse for the less than one month baby.
Newborns excrete a little urine in the first 48 hours of life, often only 30 to 60 ml. There should be no protein or blood in the urine of a newborn baby. Many cell debris can identify any injury or irritation in the kidney system.
The kidney cannot function optimally, because:
- The limited number of nephrons (compared with adults)
- Imbalance of the glomerular surface area and proximal tubular volume
- Relatively less blood renal (compared to adults)
Due to the incomplete of the baby’s kidneys, glomerular filtration is only about 30%. Also, immature tubular function, resorbing sodium, glucose, organic phosphate, amino acids, and bicarbonate are also at low levels. Newborns have difficulty concentrating urine but can disperse urine like an adult. Glomerular filtration maturity and tubular function are almost complete around the age of 20 weeks. While the maturity is completed after 2 years. As the low flomerular filtration, the ability to excrete drugs has also been extended. This scientifically because the inability of the kidneys to hold water and salt, evaporation of water, abnormal loss or administration of sodium-free water. Where these all quickly fall into severe dehydration and electrolyte imbalance especially hyponatremia. Giving fluids and calculating loss or the degree of dehydration require more precision than adults. Similarly, in the case of electrolyte circulation, the usual one is included in each circulation of fluids.
Glomerular Filtration Rate
After birth, the baby’s blood pressure is very low while the resistance in the blood vessels is very high. Glomerular filtration is very low. This situation also occurs because the amount of filtration area is also still minimal. This very low filtration rate causes limited ability of kidney function both in regulating water, electrolytes, hemostasis, and excretion from ingredients or metabolic waste.
Glomerular filtration rate increases rapidly because there is an increase in blood pressure, decreased resistance or resistance of renal arteries and increased filtration surface of the kidneys. Glomerular filtration rate in infants is related to gestational age. Kidney’s function in infants is still not optimal than compared to children or in adults. Kidney’s function in neonates has been able to work well to overcome physiological effects and maintain the development, maturation of the kidneys. Further, the ability to deal with stress is still very limited, such as in a state of illness or because of medical actions are taken. In light therapy, even though the baby is dehydrated. He is not able to adapt. So the baby’s urine production is not reduced even though it is dehydrated. If this happens, it will endanger the baby’s condition. The ability to concentrate and disperse the urine.
In a fetus, the metanephric start producing urine at 8 weeks’ gestation. In newborns, the ability of the kidneys to concentrate urine is still very limited. So that the baby is very easy to experience dehydration in the state of diarrhea, vomiting or during light therapy. However, it does not mean that the kidneys in the baby easily remove water. The ability of the kidneys to excrete water is also limited because the function of the glomerulus is still low.