Urine formation

Introduction

Urine formation is a very important process of the body to remove waste and toxic products after filtration. What is the definition of urine formation? 

Urine is the human body’s liquid waste that is made up of urea, uric acid, salts, water, and other waste products that are produced by the body’s metabolic activities. It is produced in the kidneys, which are the primary excretory organs. 

The nephrons are the anatomical and functional units of the kidneys. The production of urine requires the participation of millions of nephrons. 

Parts of the Kidney Involved in Urine Formation

Before we learn more about urine, let’s discuss the parts of the kidney involved in the formation of urine.

The human excretory system’s major organ is the kidney. The outer layer of the kidney is called the renal cortex. The inner layer is the renal medulla. Finally, the renal pelvis is responsible for transporting urine from the kidney to the ureter. 

The functional unit of a kidney is the nephron. Each kidney has millions of nephrons. They work together to filter blood and eliminate waste items. 

Each nephron is made up of the following components:

1.     Bowman’s capsule is the nephron’s initial segment. The blood is received by this cup-shaped structure. This is where glomerular filtration takes place. Blood cells and proteins are still present in the blood. Bowman’s capsule collects blood-derived fluids from the glomerulus.
2.     The Loop of Henle is formed when the proximal tubule forms a u-shaped loop. The descending limb, the u-shaped bend, and the ascending limb are the three components. As water is reabsorbed, urine concentrates in this location. Water permeates the descending limb but not the ascending one.
3.   The Distal Convoluted Tubule (DCT) is connected to the Loop of Henle by the collecting duct. It is here that the renal hormones exert their influence.
4.     The collecting ducts are connected to the distal convoluted tubules of each nephron. The renal pelvis is formed by the collecting ducts coming together. Urine flows into the ureter and subsequently into the bladder through the renal pelvis.

Process of Urine Formation

Let us discuss each of the steps in detail:

Step 1 

Glomerular filtration– Over a million microscopic structures called nephrons are found in each kidney. Each nephron has a glomerulus, which is where blood is filtered. The glomerulus is a part of the circulatory system surrounded by the glomerular capsule (or Bowman’s capsule). 

Blood pressure drives water and solutes from the capillaries into the capsule through a filtering membrane through the glomerulus. Approximately 10% of the water in the filtrate is lost by osmosis in the Henle loop. 

Step 2

Tubular Reabsorption– All substances, excluding blood cells and proteins, are driven through the capillaries at high pressure during glomerular filtration. Some of the chemicals in the filtrate are reabsorbed at the level of the Proximal Convoluted Tubule (PCT). Sodium chloride, potassium, glucose, amino acids are some items reabsorbed.

Step 3

Tubular Secretion– The glomerular filtrate then travels to the renal tubule, where nutrients and water are reabsorbed into capillaries. Waste ions and hydrogen ions go into the renal tubule at the same time from the capillaries. Secretion is the term for this procedure. 

Urine is formed when the released ions mix with the leftover filtrate. The urine is collected in a collecting duct by the nephron tubule. It exits the kidney via the renal pelvis, ureter, and bladder.

What Does Urine Constitute?

Urine is a water-based fluid solution that contains more than 95% water. Urea, chloride, sodium, potassium, creatinine, and other dissolved ions, as well as inorganic and organic molecules, are among the other ingredients. 

Urea is a non-toxic chemical composed of poisonous ammonia and CO2. Chemical composition of urine formation includes:

•       9.3 g/L urea
•       1.87 g/L chloride
•       1.17 g/L sodium
•       0.750 g/L potassium
•       Creatinine concentration: 0.670 g/L
•       Inorganic and organic molecules, as well as other dissolved ions (proteins, hormones, metabolites)

Urine is produced to control the amount of water in the body as well as eliminate several cellular waste products. Urine volume regulation is a form of homeostasis in that it affects blood volume directly by reducing the volume of water in the blood.

Conclusion

Urine production is a crucial procedure for the entire body. It affects not only acid-base balance, but also blood osmotic pressure, plasma constitution, and fluid volume, and thus all cells in our body. When there is no urine formation by the kidneys, anuria or enuresis develops. Oliguria, or a decreased urine flow, may occur first, followed by anuria. 

Urination is necessary for the removal of waste as well as excess fluids from the body. A quart of urine is produced by the kidneys every day. Hormones such as antidiuretic hormone, aldosterone, and parathyroid hormone regulate the urinary system through the endocrine system.