Describe The Structure and Function of the Basic Filtering Unit of Kidney. (b) List Two Factors On Which Reabsorption of Water from Urine Depends?

Introduction

The kidney is a vital organ in the human body that performs the crucial function of filtering waste products from the bloodstream and removing them from the body through urine. The kidney is made up of millions of tiny units called nephrons, which are responsible for the filtration process.

Each nephron is composed of a glomerulus and a tubule, which work together to filter and reabsorb important substances from the blood.

The content below describes the structure and function of the basic filtering unit of the kidney, and discuss the factors that influence the reabsorption of water from urine.

Structure of the Basic Filtering Unit of the Kidney

The basic filtering unit of the kidney is the nephron, which is made up of a glomerulus and a tubule. The glomerulus is a network of tiny blood vessels that filters blood from the renal artery, which supplies blood to the kidney. The blood is filtered through a specialized membrane called the glomerular basement membrane, which separates the blood from the tubule. The tubule is a long, coiled structure that reabsorbs important substances from the filtrate and returns them to the bloodstream.

The tubule is composed of several sections, each with its own unique structure and function. The first section of the tubule is the proximal convoluted tubule, which is responsible for reabsorbing most of the water, electrolytes, and other important substances from the filtrate.

The proximal convoluted tubule is lined with specialized cells called epithelial cells, which have tiny hair-like projections called microvilli. These microvilli increase the surface area of the epithelial cells, allowing for more efficient reabsorption of substances.

The next section of the tubule is the loop of Henle, which is divided into three sections: the descending limb, the thin ascending limb, and the thick ascending limb. The loop of Henle is responsible for creating a concentration gradient in the interstitial fluid surrounding the tubule, which allows for the reabsorption of water and other important substances in the later sections of the tubule.

The distal convoluted tubule is the next section of the tubule, which is responsible for fine-tuning the reabsorption of substances based on the body's needs. The distal convoluted tubule is lined with specialized cells called principal cells, which are responsible for reabsorbing sodium and secreting potassium. The distal convoluted tubule also contains specialized cells called intercalated cells, which are responsible for regulating the body's acid-base balance.

The final section of the tubule is the collecting duct, which is responsible for reabsorbing the remaining water and concentrating the urine. The collecting duct is lined with specialized cells called principal cells, which are responsible for reabsorbing water and sodium. The collecting duct also contains specialized cells called intercalated cells, which are responsible for secreting acid and regulating the body's acid-base balance.

Function of the Basic Filtering Unit of the Kidney

The function of the basic filtering unit of the kidney is to filter waste products from the bloodstream and remove them from the body through urine. The glomerulus filters blood from the renal artery, which is then passed through the tubule. As the filtrate passes through the tubule, important substances such as water, electrolytes, and nutrients are reabsorbed and returned to the bloodstream.

The reabsorption of water from the filtrate is a critical function of the nephron, as it helps to maintain the body's fluid balance. The reabsorption of water from the filtrate is regulated by the hormone antidiuretic hormone (ADH), which is produced by the hypothalamus and released by the pituitary gland. ADH stimulates the reabsorption of water from the collecting duct, which helps to concentrate the urine and conserve water in the body. The reabsorption of water from the collecting duct is also influenced by two other factors: osmotic gradient and permeability.

Factors Affecting Reabsorption of Water from Urine

Osmotic Gradient

The osmotic gradient is a concentration difference between the interstitial fluid surrounding the tubule and the filtrate in the tubule. The osmotic gradient is created by the loop of Henle, which allows for the reabsorption of water and other important substances in the later sections of the tubule.

The descending limb of the loop of Henle is permeable to water but not to solutes, which allows water to flow out of the tubule and into the interstitial fluid. The thin ascending limb is permeable to solutes but not to water, which allows solutes to flow out of the tubule and into the interstitial fluid.

The thick ascending limb is permeable to sodium and other solutes, which allows sodium and other solutes to be reabsorbed from the tubule and returned to the bloodstream. The concentration gradient created by the loop of Henle allows for the reabsorption of water in the later sections of the tubule, which helps to conserve water in the body.

Permeability

The permeability of the collecting duct is another factor that influences the reabsorption of water from the filtrate. The permeability of the collecting duct is regulated by the hormone ADH, which stimulates the insertion of water channels called aquaporins into the membrane of the collecting duct.

Conclusion

The basic filtering unit of the kidney is the nephron, which is composed of a glomerulus and a tubule. The glomerulus filters blood from the renal artery, which is then passed through the tubule. As the filtrate passes through the tubule, important substances such as water, electrolytes, and nutrients are reabsorbed and returned to the bloodstream. The reabsorption of water from the filtrate is regulated by the hormone ADH, which stimulates the insertion of water channels called aquaporins into the membrane of the collecting duct.

The reabsorption of water from the filtrate is also influenced by the osmotic gradient and permeability of the collecting duct. Understanding the structure and function of the basic filtering unit of the kidney is essential for maintaining the body's fluid balance and overall health.