The Urinary System
Each kidney is supplied with blood through the renal artery, which branches out from the aorta. The blood entering is at high pressure. Once the blood is filtered in the kidneys, the blood passes out through the renal vein, to the vena cava. The urine passes out of the kidneys via the ureters, and is stored in the bladder. The urine passes out of the bladder via the urethra – and then you piss. 😎 😎
The walls of the urethra contain ring like muscles called sphincters, which contract to hold back urine. The lower muscle is voluntarily controlled, while the upper one is involuntary – automatically relaxing when the bladder is full.
The Kidneys 👇
The outer region is called the cortex, and contains many blood vessels branching out from the renal artery. It also contains microscopic filtering units called nephrons. The nephrons run down the middle layer called the medulla. The medulla has pyramids pointing towards the concave side of the kidney. The tubules in the medulla eventually join up and lead to the tips of the pyramids, where urine is emptied into the pelvis. The pelvis connects to the ureters, carrying urine to the bladder.
The Nephrons
A nephron is the single tubule found in the cortex. In I/GCSE Biology, we need to know ach kidney has about a million of these.
Production of urea 😂😂
Blood enters the kidneys through the renal artery, which divides into arterioles. They supply the capillaries of the glomerulus – a ball of capillaries where blood is filtered. It is surrounded by a cup of cells called the Bowman’s capsule. Since the blood pressure is high, the pressure forces fluid from the blood through the walls of the capillaries and into the middle of the Bowman’s capsule. The glomerulus and the space in the capsule are separated by two cell layers – the capsule and the capillary wall. Between those is a third layer called the basement membrane. These layers act as a filter, allowing water, ions and small molecules to pass through, but holding back blood cells and large molecules such as proteins. The fluid that enters is called the glomerular filtrate. This process, where the filter separates different sized molecules under pressure, is called ultrafiltration.
Reabsorption of water and other solutes such as glucose take place in the proximal convoluted tubule. It reabsorbs different amounts of various substances. This is called selective reabsorption in I/GCSE Biology. The function of the loop of Henle is really to concentrate the fluid in the tubule more, by causing more water to be reabsorbed. In the rest of the tubule, more water and ions are reabsorbed, and the final urine contains a much higher concentration of urea, as well as water and salts. Finally, the urine enters the pelvis, into the ureters and down to the bladder.
That's the end of the topic!
Drafted by Joey (Biology)