Have you ever seen the kidney of a goat or cow? If you have not, try to see one when next you go to buy meat.
We have two kidneys in the lower abdomen on the back, above the hips. They are reddish brown and are bean shaped.. Each kidney contains about a million tiny coiled tubes. Blood flows through these tubes and the liquid waste products in the blood are filtered out, along with water and substances such as glucose. Salt and some other useful salts are taken back into the blood (reabsorbed) and the remaining water, waste urea and salts are removed in the form of urine.
This liquid substance passes from the kidneys through two tubes into a sac, where it is temporarily stored. This storage sac is the urinary bladder. When the bladder is full, it causes you to want to empty it, a process called urination.
Suppose you drink a lot of water, your kidneys will excrete plenty of urine. Suppose you from a small amount of water, your kidneys will eliminate less water through urine. If the weather is cold, and you do not sweat, your kidneys will excrete more urine. If it is a warm day and you sweat a lot, your kidneys will have only a small amount of urine to excrete.
So, your kidneys control the amount of water in your body. Hence it is called an osmo-regulator. The kidneys also control the amount of salt and urea in the system.
Urea is a poisonous substance produced in the river when amino acids are broken down. The kidneys have two major functions, excretion and osmo-regukation. The kidneys with the urinary tubes and bladder make up the primary system.
Urine is sent out through a tube called urethra, which in the male passes through the penis. The oenis is also used in transferring sperm to the female organ. So the urinary system and reproductive system are very closely associated. Hence they are sometimes called the urina genital system.