Discuss the mechanism of urine formation in human.
Discuss the mechanism of urine formation in human.
Urine
The urine is a straw-colored, watery fluid, slightly acidic with a characteristic ammonium smell formed by nephrons and excreted from the body. It is mainly composed of water, organic and inorganic wastes.
Mechanism of Urine formation in humans
Urine in humans is formed by nephrons, the structural and functional unit of the kidneys. The formation of urine is a result of a three-step process:
- Ultrafiltration or Glomerular filtration
- Tubular reabsorption
- Tubular secretion
Ultrafiltration
Ultrafiltration, also known as glomerular filtration, is the first step of urine formation. It is the step in which the filtration of blood takes place. The glomerulus receives blood under high pressure from the renal artery and afferent arteriole, due to which substances are filtered through the pores of the glomerulus and are received by the bowman's capsule. The filtrate thus created is called the nephric filtrate or the glomerular filtrate.
Tubular reabsorption
The filtrate created now passes into the proximal convoluted tubule (PCT), where it is called tubular fluid. Once it reaches the PCT, all the essential nutrients like glucose, amino acids, etc., are reabsorbed but selectively up to a threshold level. Hence, this step is also known as selective reabsorption. The amount of reabsorption depends upon the amount of excess of that particular substance is. The reabsorption continues along the entire tubule based on the permeability of the nephron and the amount of ADH (vasopressin) hormone secretion. ADH hormone regulates water reabsorption.
Tubular secretion
Tubular secretion is the opposite of tubular reabsorption. Certain chemicals such as creatinine, pigments, drugs, etc., present in the blood that were not removed during ultrafiltration are now removed by this process.
The urine, thus formed, is finally expelled from the body by urination or micturition.
Urine
The urine is a straw-colored, watery fluid, slightly acidic with a characteristic ammonium smell formed by nephrons and excreted from the body. It is mainly composed of water, organic and inorganic wastes.
Mechanism of Urine formation in humans
Urine in humans is formed by nephrons, the structural and functional unit of the kidneys. The formation of urine is a result of a three-step process:
- Ultrafiltration or Glomerular filtration
- Tubular reabsorption
- Tubular secretion
Ultrafiltration
Ultrafiltration, also known as glomerular filtration, is the first step of urine formation. It is the step in which the filtration of blood takes place. The glomerulus receives blood under high pressure from the renal artery and afferent arteriole, due to which substances are filtered through the pores of the glomerulus and are received by the bowman's capsule. The filtrate thus created is called the nephric filtrate or the glomerular filtrate.
Tubular reabsorption
The filtrate created now passes into the proximal convoluted tubule (PCT), where it is called tubular fluid. Once it reaches the PCT, all the essential nutrients like glucose, amino acids, etc., are reabsorbed but selectively up to a threshold level. Hence, this step is also known as selective reabsorption. The amount of reabsorption depends upon the amount of excess of that particular substance is. The reabsorption continues along the entire tubule based on the permeability of the nephron and the amount of ADH (vasopressin) hormone secretion. ADH hormone regulates water reabsorption.
Tubular secretion
Tubular secretion is the opposite of tubular reabsorption. Certain chemicals such as creatinine, pigments, drugs, etc., present in the blood that were not removed during ultrafiltration are now removed by this process.
The urine, thus formed, is finally expelled from the body by urination or micturition.
