What is the Difference Between Amniotic Fluid and Urine

The main difference between amniotic fluid and urine is that amniotic fluid is the protective liquid which occurs in the amniotic sac, serving as a cushion for the growing fetus, whereas urine is a liquid by-product of metabolism produced by kidneys. Furthermore, amniotic fluid is responsible for facilitating the exchange of nutrients and water between the mother and the fetus while urine is responsible for the excretion of nitrogenous by-products and other water-soluble chemicals from the body. 

Amniotic fluid and urine are two types of fluids produced by the animal body to perform different functions of the body. Significantly, both contain urea and creatinine. 

Key Areas Covered 

1. What is Amniotic Fluid
     – Definition, Composition, Function
2. What is Urine
     – Definition, Composition, Function
3. What are the Similarities Between Amniotic Fluid and Urine
     – Outline of Common Features
4. What is the Difference Between Amniotic Fluid and Urine
     – Comparison of Key Differences

Key Terms 

Amniotic Fluid, Amniotic Sac, Kidney, Nitrogenous Wastes, Urine

What is Amniotic Fluid 

Amniotic fluid is the watery fluid that surrounds the fetus. Therefore, it maintains a steady temperature around the baby while offering protection through cushioning. It also helps the development of the lungs and the digestive system of the baby. Generally, the baby breaths and swallows amniotic fluid. Meanwhile, amniotic fluid prevents the compression of the umbilical cord, giving the baby the ability to move, which in turn improves the development of muscles and bones.

Figure 1: Amniotic Fluid

Furthermore, amniotic fluid occurs within the amniotic sac, which develops around 12 days after conception. Although its main component is water, amniotic fluid also contains the baby’s urine to a considerable extent. The color of the amniotic fluid can be either clear or tinted yellow. However, in the case of meconium, which is the first bowel movement of the baby, the amniotic fluid becomes green or brown in color. Generally, this condition may require treatment after birth in order to prevent breathing problems. Normally, one of the main signs of the amniotic fluid leaking is the uncontrolled flow which is continuous. 

What is Urine 

Urine is the pale yellow color liquid formed due to the function of the kidney. Generally, urine formation is a three-step process. These steps include filtration, reabsorption, and secretion. Typically, filtration forms the glomerular filtrate at the Bowman’s capsule. Then, it moves through the nephron, which is the functional unit of the kidney, producing urine through the reabsorption of water, small molecules, and salts from the filtrate and the secretion of creatinine, drugs, and hydrogen ions into the filtrate. Ultimately, the kidney flows urine to the bladder through ureters and the bladder releases urine through the urethra out from the body.

Figure 2: Urine

Moreover, urine is composed of 95% of water. In addition, it contains urea (9.3 g/L), chloride (1.87 g/L), sodium (1.17 g/L), potassium (0.750 g/L), and creatinine (0.670 g/L). Urine serves as the main excretory medium of nitrogenous wastes, excess salts, and other water-soluble chemicals from the body. Therefore, it maintains the osmotic balance of the body. 

Similarities Between Amniotic Fluid and Urine 

• Amniotic fluid and urine are two types of fluids produced by animals. 
• Both are generated from the plasma by passing through membranes by osmotic and hydrostatic pressure. 
• They are mainly composed of water and electrolytes. In addition, both contain urea and creatinine.  
• Both have a function in removing metabolic wastes. 
• Meanwhile, swallowed amniotic fluid creates urine. 
• It is difficult to distinguish between amniotic fluid which causes water break and urine during pregnancy. 

Difference Between Amniotic Fluid and Urine 

Definition 

Amniotic fluid refers to the fluid which surrounds the fetus within the amnion while urine refers to the watery and typically yellowish fluid, which is one of the chief means of eliminating excess water and salt. 

Significance 

Moreover, amniotic fluid occurs inside the amniotic fluid while kidneys produce urine. 

Appearance 

Amniotic fluid is watery and clear but sometimes yellow, green or with white specks while normal urine is either colorless or pale yellow in color. 

Odor 

While amniotic fluid is odorless, urine has a strong “fish-like” odor due to bacterial growth after urination. 

Composition 

Amniotic fluid contains nutrients including proteins, carbohydrates, and lipids, hormones, immune system cells, and the urine of baby while urine contains mainly water, inorganic salts, proteins, hormones, and a wide range of metabolites. 

Normal Levels  

The normal level of amniotic fluid is about one quart by 36 weeks after pregnancy, and it drops after that until delivery while the normal range of urine is 0.6 to 2.6 L per person per day.  

Function  

Furthermore, the amniotic fluid serves as a cushioning liquid to the fetus and facilitates the exchange of nutrients and water between mother and baby while urine is responsible for excreting nitrogenous wastes, excess salts, and other water-soluble chemicals out of the body. 

During Pregnancy 

A true amniotic fluid leak cannot be controlled while the flow of urine can be controlled by squeezing muscles. 

Conclusion 

Amniotic fluid is the cushioning liquid which surrounds the fetus. It is also clear and watery. However, it allows the exchange of nutrients and water between mother and baby. In contrast, urine is the pale yellow color liquid produced by the kidney. It allows the excretion of nitrogenous wastes, excess salts, and other water-soluble chemicals from the body. Therefore, the main difference between amniotic fluid and urine is their occurrence and function. 

References:

1. “Everything You Need to Know About Amniotic Fluid.” Babylist, Available Here.
2. “29.8: Urine Composition and Function.” Chemistry LibreTexts, Libretexts, 5 June 2019, Available Here.

Image Courtesy:

1. “Blausen 0747 Pregnancy” By BruceBlaus.  – Own work (CC BY 3.0) via Commons Wikimedia   
2. “Urine sample” By Turbotorque – Own work (Public Domain) via Commons Wikimedia