Excretion in Humans

What does the urinary system consist of?

The excretion system consists of the kidneys, ureters, bladder and urethra

What does the nephron constist of?

The nephron consists of the Bowman’s capsule, the Glomerulus, the Loop of Henle and the collecting duct

What is the role of the Bowman’s capsule and glomerulus?

Blood is flown into the glomerulus where ultrafiltration occurs. This is where small molecules such as salts, glucose, water, ions, salts and amino acids are forced out of the blood and into the Bowman’s capsule, whereas big molecules like proteins are too large to pass through.

What happens next at the proximal convoluted tube?

The filtrate is passed through the proximal convoluted tube where selective reabsorption takes place. This is where by active transport, glucose and amino acids are reabsorbed back into the blood

What happens next at Loop of Henle?

At the descending loop, water is reabsorbed into the blood from the filtrate by osmosis as the descending loop is permeable to water. Then at the ascending loop, it is no longer permeable to water but ions such as chlorine and sodium are pumped out of the filtrate by active transport

What happens next at distal convoluted tubule?

The distal convoluted tubule is permeable to both water and salts. Therefore, even more water and salts are reabsorbed back into the blood, and the distal convoluted tubule responds to the hormone of ADH to either increase or decrease the permeability of itself

What happens next at collecting duct

At the collecting duct, if there is a lot of water in the blood, no ADH is produced and the collecting duct will not absorb any more water and urine will be dilute. However, if there is not a lot of water in the blood, the collecting duct will respond to ADH and increase its permeability to absorb more water and make the urine more concentrated

What does the body do if one is dehydrated?

The loss of water means that the concentration of the blood increases, and the body detects this with osmoreceptors in the hypothalamus. The hypothalamus signals the pituitary gland to produce and release more ADH. ADH travels in blood to the kidney and at the kidney tubules it causes the collecting duct to be more permeable to water. Therefore, more water is reabsorbed back into the blood and urine becomes more concentrated and blood becomes more dilute

What does the body do if one has too much water

If there is too much water in the blood, the osmoreceptors detect this in the hypothalamus. The hypothalamus send a signal to the pituitary gland to produce and release less ADH. Less ADH travels to the kidney via the blood, and at the kidney tubules the collecting duct becomes less permeable to water. Therefore, less water is reabsorbed into the blood, and urine becomes more dilute and the blood becomes more concentrated

What is urine composed of?

Urea, water and ions