Urea is produced in the liver and excreted by the kidneys.

Ultrafiltration involves the net movement of metabolic waste products such as urea down a concentration gradient from the bloodstream into the Bowman's capsule. 

Excretion is the removal of undigested matter and is harmful to the body when the undigested matter is accumulated to a toxic level. 

The basement membrane of the glomerulus is partially permeable and allows small molecules like glucose to pass through.

In a healthy person, some glucose is reabsorbed into the bloodstream while majority is lost in the urine. 

When water potential of the blood plasma rises above norm, less ADH is released by the pituitary gland. Less water is reabsorbed by the collecting duct. Urine becomes diluted. 

The dialysis fluid contains a higher concentration of glucose so that the patient is able to gain glucose from the fluid. 

The dialysis fluid contains a lower concentration of urea so that urea from the patient's blood can diffuse into the dialysis fluid. 

Homeostasis is the maintenance of a constant internal environment.

When blood glucose level rises above norm, islets of Langerhans secrete insulin into the bloodstream.

Insulin converts excess glucose to glycogen for storage in liver and muscle cells. 

When body temperature rises above norm, vasodilation of arterioles occurs to bring more blood to the surface of skin so that more heat is lost through radiation, conduction and convection.

When rate of sweating increases, more sweat evaporates, more latent heat of vapourisation is lost, bringing body temperature back to norm.

Shivering is the sporadic contractions of muscles so that heat is released to keep the body warm.