Question

Describe the three major renal processes: glomerular filtration, tubular reabsorption, and tubular secretion. Include where they occur in the nephron and constituents involved.

Answer 1

1. Glomerular filtration :

Glomerular filtration is the first step in urine formation and constitutes the basic physiologic function of the kidneys. It describes the process of blood filtration in the kidney, in which fluid, ions, glucose, and waste products are removed from the glomerular capillaries.

Filtration is the mass movement of water and solutes from plasma to the renal tubule that occurs in the renal corpuscle. About 20% of the plasma volume passing through the glomerulus at any given time is filtered.

2. Tubular reabsorbtion :

Tubular reabsorption mechanisms in the nephrons of your kidneys return the water and solutes that you need back into your extracellular fluid and circulatory system. In addition to reabsorbing the substances that you need, your nephrons are able to secrete unwanted substances from your bloodstream into the filtrate. Together these processes complete the transformation of the glomerular filtrate into urine.Tubular reabsorption is the process that moves solutes and water out of the filtrate and back into your bloodstream. This process is known as reabsorption, because this is the second time they have been absorbed; the first time being when they were absorbed into the bloodstream from the digestive tract after a meal.

Reabsorption takes place mainly in the proximal convoluted tubule of the nephron . Nearly all of the water, glucose, potassium, and amino acids lost during glomerular filtration reenter the blood from the renal tubules.

3. Tubular secretion:

During secretion some substances±such as hydrogen ions, creatinine, and drugs—will be removed from the blood through the peritubular capillary network into the collecting duct. The end product of all these processes is urine, which is essentially a collection of substances that has not been reabsorbed during glomerular filtration or tubular reabsorbtion.

Urine is mainly composed of water that has not been reabsorbed, which is the way in which the body lowers blood volume, by increasing the amount of water that becomes urine instead of becoming reabsorbed. The other main component of urine is urea, a highly soluble molecule composed of ammonia and carbon dioxide, and provides a way for nitrogen (found in ammonia) to be removed from the body. Urine also contains many salts and other waste components. Red blood cells and sugar are not normally found in urine but may indicate glomerulus injury and diabetes mellitus respectively.

Tubular secretion occurs throughout the different parts of the nephron, from the proximal convoluted tubule to the collecting duct at the end of the nephron.