Formation of urine

1. The main organs in the excretory system are:

the kidneys: they form part of the urinary tract and are most important excretory organs they are algo regulatory organs 

the lungs : these released the carbon dioxide produced by cellular respiration and water vapour 

the liver : this organs eliminates waste subtances that are found in bile that are expellled with faeces

2.Urine is the result of complicated three step process that are:

filtration: blood plasma in the capillaaries of the glomerulus is filtered due to the pressure of the blood.

reabsorption: the filtered liquid passes through the renal tubule and water and nutrients are reabsorbed through its walls.

secretion : molecules that remain in the plasma afetr filtration are selectively eliminated for the peritubular capillaries and secreted actively in the filtering process

4. 3 parts 

cerebrum: this is the largest part of the brain it consist of two parts whitch are separated by a groove and joined at the base. Each one controls the activities of the opposite side of the body and is divided into four sections called lobes 

cerebellum: this is located below the brain its controls the body's movements and posture 

medulla: this is located in the brain stem it is composed of neuronal axons and nuclei of neuronal boddies it is attaches of the spinal cord