By: Maria Camila Ambuila To: T. AngelWatler Grade: 5A Science Human Excretion
HUMAN EXCRECTION The main organs concerned with excretion in the body are thekidneys. They are situated just above the hips at the back of the abdomen and are then connected via the ureter to the bladder which is then connected to the urethra. The kidneys are supplied with blood from the renal artery. The most important structure in the kidneys are the microscopic nephrons, which are the units that filter the blood to produce urine . The nephron consists of Bowman's capsule which filters everything, except for the blood cells and plasma protein, out of the blood into the proximal (close) tubule. This is accomplished by a difference in size and therefore pressure of the blood vessels entering and leaving the glomerulus
Proximal and distal convoluted tubule Now that all the potentially dangerous substances from the blood have been removed, the useful substances are ready to be reabsorbed back into the blood stream. The main substances that are re-absorbed in the proximal convoluted tubule are glucose, water and salt. Dangerous substances in the blood are also secreted into the distal tubule. After the loop of Henle the filtrate passes through the distal (far) tubule. It then continues on to the collecting duct where water is reabsorbed. The water is reabsorbed by diffusion because of the higher salt concentration on the outside in the medulla of the kidney. The filtrate which now consist mainly of urea and other harmful substances, as well as a varying amount of water depending on the need for it in the body, is excreted via the urethra.