Human Excretion and Kidney Physiology

The characteristic shared by urea, uric acid and ammonia are they are nitrogenous wastes. In comparison to Ammonia and Urea, uric acid is the least toxic and the least soluble in water. It can be stored in cells and body tissues without any toxic effects and hence needs less water for excretion when compared to Ammonia and urea.

Ammonia is more water soluble and more toxic than Urea or uric acid. Ammonia is extremely toxic and its accumulation in the body can be lethal. So the liver converts toxic ammonia into less toxic urea through the urea cycle.

While water is reabsorbed in the renal tubules of the kidney, the question asks where absorption of water in the human body can be found. The large intestine is the primary site for water absorption from undigested food residue. Renal tubules are involved in reabsorption, but the large intestine is the standard answer for water absorption in the digestive context.

Blood maintains water balance in the body by bringing constant exchange of water between circulating blood and tissue fluid. Regulating pH and transportation of excretory material are other functions performed by blood.

Urea is synthesized in the liver from ammonia and carbon dioxide. The urea synthesis is a five-step cyclic process, with five distinctive enzymes. This urea is released into the bloodstream from the liver cells. Through blood, urea is transported to kidneys where the blood is filtered and urea is passed out of the body in the urine. Hence the waste matters (urea) are transported by the blood.

In order for blood to perform its essential functions of bringing nutrients and oxygen to the cells of the body, and carrying waste materials away from those cells, the chemical composition of the blood must be carefully controlled. Blood contains particles of many different sizes and types, including cells, proteins, dissolved ions, and organic waste products. Some of these particles, such as proteins like hemoglobin, are essential for the body. Others, such as urea (a waste product from protein metabolism), must be removed from the blood or they will accumulate and interfere with normal metabolic processes. But the largest responsibility for maintaining the chemistry of the blood falls to the kidneys, a pair of organs located just behind the lining of the abdominal cavity. It is the job of the kidneys to remove the harmful particles from the blood and to regulate the blood's ionic concentrations, while keeping the essential particles in the blood. Dialysis is a process for removing waste and excess water from the blood and is used primarily as an artificial replacement for lost kidney function in people with kidney failure.

Kidney stones or renal calculi are solid masses made of crystals. Calcium stones are the most common. They can be made of calcium oxalate
So, the correct answer is 'Calcium oxalate'

Accumulation of urea in body is called uraemia. It may be due to kidney failure and other metabolic waste products may also accumulate. Uraemia develops after about 7 days of anuria (absence of urine) because of the reduced glomerular filtration rate and impaired tubular secretion of urea. Increased blood urea usually leads to confusion and mental disorientation.

Oliguria is the condition of less than 400 ml of urine per day in adults, whereas severe oliguria means less than 100 ml of urine per day in adults. Anuria means absence of urine and diuresis is the production of a large volume of urine. Diuresis may lead to acute dehydration and electrolyte imbalance.

• Dialysis is an artificial procedure of excretion of metabolites from the blood when kidneys do not work. 
• In this process, the harmful waste products are removed from the blood. The dialysis apparatus of the dialyzer is commonly known as an artificial kidney.
• The process of dialysis is generally recommended for the person who has been suffering problems related to the kidney and the kidney is not functioning properly.

Diuresis as a pathological condition occurs  under hyposecretion of ADH or Vasopressin, which affects the water rreabsorption by the tubule into the blood by the peritubular network.This results in excretion of dilute urine. A disorder known as diabetes insipidus.

Diabetes insipidus is caused by a deficiency of ADH (vasopressin), leading to the excretion of large volumes of dilute, tasteless urine.

Increase in frequency of urination is called as Polyurea. The most common cause of polyurea in children and adult is uncontrolled diabetes mellitus.it may also occur due to various reasons such as urinary tract infractions, hypopituitarism, Hyperglycemia etc.

Ketonuria is the Presence of the high number of ketone bodies in urine. It may occur due to diabetes, starvation, fasting or glycogen storage disease. Ketone bodies(acetoacetate, beta-hydroxybutyrate) are water-soluble molecules containing keto group these are not carbohydrates like Ketone sugar (fructose).