Biology

• the blood is carried into the kidney by the renal artery
• The healthy kidney constantly cleaning about a half cup of blood every minute and getting rid of waste materials, toxins and excess water in the bloodstream
• An adult human produces about 1.5 dm cubic of urine every day depends on the amount of water drunk and the volume lost in the form of sweat
• The urine contains 95% water and 5% waste. the waste: urea, ammonia, creatinine, and uric acid
• in the kidney, there are millions of tiny blood filters called Nephrons
• Nephrons are so small you can see them only with a high powered microscope
• each nephron is made up of very small filter called a glomerulus which is attached to a tubule
• as blood passes through nephron, fluid and waste products are filtered out into the ureters
• Ureters are narrow tubes that carry urine from the kidneys to the bladder
• muscles in the ureter walls continually tighten and relax forcing urine downward away from the kidneys, not allowing them to back up/stand still. the urine then enter the bladder
• the bladder

  The bladder is about the size and shape of a pear
• the wall of the bladder relax and expand to store urine, allowing urination to be controlled
• the normal capacity of the bladder is 400-600 ml
• the bladder has a direct line of communication with the brain, it is full of receptors
• an invisible fill line that tells your brain how full your bladder is
• when your bladder is full, the nerves alert the person that it is time to urinate. The brain signals the bladder muscles to tighten, which squeezes urine out of the bladder. At the same time, the brain signals sphincter muscles to relax to let urine exit the bladder through their urethra
• the urethral sphincter either male/female are two muscular structure that regulate the out flow of urine and hel[ keep urine from leaking by closing tightly
• this is why elders and babies often pee in their pants, it is because their sphincters have not develop completely
• 1 liter of urine contain 40 gram of waste products and salts
• ammonia and urea are nitrogenous waste that means they contain the element nitrogen
• all animal have to excrete a nitrogenous waste products because it might be harmful if it built up in the body. If these substances build up in the blood, they would be toxic to cells.
• carbohydrates and fats contain carbon, hydrogen and oxygen and when they are too much in the body, it will be stored as glycogen and fat. While the protein also contain nitrogen so when it is too much, it cannot be stored and amino acid (final product of protein) will be broken down in the liver then convert into carbohydrate (glycogen) and main nitrogen containing waste product, urea. It passes into the blood to be filtered out by the kidneys during the formation of urine.
• The urea is made by chemical reaction in the cell body (the body’s metabolism)
• excretion means getting rid of waste of this kind
• The urine is excretion because it is made by chemical reactions in the cell body (the body’s metabolism). While feces (a solid waste of the digestive system) is not excretion because it contains only few products of metabolism, just the ‘remains’ of undigested food, along with bacteria and dead cells
• 2 functions of kidney:- a homeostatic organ, controlling the water and salt (ion) concentration in the body.

  • As an excretory, concentrating nitrogenous waste in a form that can be eliminated.
• A baby cannot control its voluntary sphincter. When the bladder is full, the baby’s involuntary sphincter relaxes, releasing the urine. A toddler learn to control this muscle and hold back the urine. 
• Each kidney is supplied with blood through a short renal artery. It carries oxygenated blood to the kidneys. This leads straight from the body’s main artery, the aorta, so the blood entering the kidney is at high pressure.
• Inside the kidney, the blood is filtered, and the ‘cleaned’ blood passes out through each renal vein to the main vein or vena cava. While the urine leaves the kidneys through two tubes, the ureters and is stored in a muscular bag called bladder
• The bladder has a tube leading to the outside called urethra
• the wall of urethra contains two ring-shaped muscles called Sphincter Muscles
• The sphincter muscles can contract to close the urethra and hold back the urine. the lower muscled is under conscious control or ‘voluntary’ while the upper one is involuntary - it automatically relaxes when the bladder is full.
• Blood is transported to the kidney through the renal artery. The blood is filtered at high pressure and the kidney selectively reabsorb any useful materials such as glucose, salt ions and water. After it has been purified, the blood returns to circulatory system through the renal vein
• the kidneys produce urine and this helps maintain water balance. the urine is taken from the kidneys to the bladder bu the ureters. The bladder stores the urine until it convenient to expel it from the body.
• note that ‘ureter’ differs from the word ‘urethra’. The ureters are tubes that carry urine from the kidneys to the bladder, whereas the urethra is the tube that carries urine out of the body.