The Human Excretory System
Kaylee Gelms
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Introduction:
The excretory system helps with homeostasis and gets rid of waste that is in the body. The main organs that contribute to the excretory system are the kidneys, ureters, urinary bladder and the urethra. The Kidneys are on either side of the spine and they are the body's filters. Blood enters from the renal artery and leaves the kidneys through the renal vein. The ureter comes after the kidneys and leads to the bladder. The bladder holds the urine until it has as much as it can handle (about 300 - 400 mL) and then the urine goes to the urethra.
Kidneys:
The Kidneys are important because they remove waste and toxins. They also make sure that blood has a balanced pH.
The kidney filters the blood which comes from the renal artery. The kidney filters and cleans the blood. The blood that has just been cleansed goes to through the renal vein which goes throughout the rest of the body.
The renal pelvis is a hollow area which connects to the bladder. The urine goes to the bladder and it leaves through the urethra so that the bladder can be empty again. The medulla is the inner part of the kidneys and the cortex is the outer layer which is on top of the medulla.
Nephron:
The nephrons are inside of the kidneys. There are around 1 000 000 nephrons in each kidney. The nephrons contain a filter called the Bowman’s Capsule and different tubules called the proximal convoluted tubule and the distal convoluted tubule. The blood is filtered through the Bowman’s Capsule and then goes to a proximal tubule. Then it goes through a descending and ascending loop of Henle and goes through the distal tubule. Finally the blood arrives at the collecting duct.
This system is important because it preserves the amount of water, nutrients, salts that are in the body. This way the body doesn't have too much or not enough. This is how the excretion system aids homeostasis.
Terms:
Nephron: a part of the kidney that takes waste out of the blood
Bowman's Capsule: a small unit at the beginning of the nephron that surrounds the glomerulus, first part of the Nephron that the blood goes through
Afferent Arteriole: where the blood enters the Bowman's Capsule
Efferent Arteriole: the tube where the filtered blood exits the Bowman's Capsule
Glomerulus: tubes that help with filtration, inside the Bowman's Capsule
More Terms:
Proximal Convoluted Tubule: a tube that is attached to the Bowman's Capsule and the loop of Henle, the second part of the Nephron that the blood goes through
Loop of Henle: there is an descending and ascending part, attached to the Proximal Tubule and the Distal Tubule
Distal Convoluted Tubule: attached to the loop of Henle and the Collecting Duct and whatever is inside of it goes to the renal pelvis
Vasa Recta: keeps the osmolarity of blood at the right level, small tubules around the loop of Henle
Interstitial Fluid: the fluid between capillary and the cells, fluid that surrounds cells
What gets Filtered:
water
glucose and amino acids
NaCl and Potassium
urea
These will go through the Bowman's Capsule.
What doesn't get filtered:
large proteins (albumin)
red blood cells
platelets
These are too big to fit through the filtration system. They will continue to stay in the blood and go out through the efferent arteriole. These can't go through the Bowman's Capsule.
Reabsorption:
Things are reabsorbed because the body needs some of the things that have been put through the filter. Anything that is not reabsorbed will be excreted. Urea and other forms of waste are left in the nephron because the body doesn't want them. Sometimes water is reabsorbed but if the body has too much than the water stays in the nephron so that it will be excreted. This is how the body helps with water balance.
Practically all of the Nacl and Potassium is reabsorbed. This happens at the proximal tubule where 65% of it is reabsorbed. The loop of Henle reabsorbs around 25% of it and the distal tubule reabsorbs 5%. The rest of the NaCl and Potassium is reabsorbed at the collecting duct.
Almost all of the glucose and amino acids are reabsorbed at the proximal tubule and put into the interstitial fluid.
Excretion:
Excretion is made up of urea, a small bit of NaCl, Potassium, water and other toxins.
The bladder holds the urine until it is full and then the urine goes out of your body through a tube called the urethra. The bladder muscles contract because of a signal from the brain.
Resources:
Fraser, LeDrew, Vavitsas, White-McMahon, Biology 12. Toronto, Cengage Learning, 2010.
Biologydictionary.net Editors. “Excretory System.” Biology Dictionary, Biologydictionary.net, 19 Mar. 2017, https://biologydictionary.net/excretory-system/.
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