‘Excretion is the process by which waste
products of metabolism are removed
from the body’
Excretion happens in both animals and plants. Plants also oxygen (a waste product of the photosynthesis reaction) and carbon dioxide (from the respiration reaction). However, most of the detail here is about excretion in animals.
Nitrogenous waste has to be excreted by all animals.This is because it cannot be stored in the body in the same way that carbohydrates and fats can. Excess proteins are the main source of nitrogenous waste, and are converted either into carbohydrates or into urine.
Humans have a special excretory system. Most of the body's waste products are removed in sweat and urine.
Nitrogenous waste has to be excreted by all animals.This is because it cannot be stored in the body in the same way that carbohydrates and fats can. Excess proteins are the main source of nitrogenous waste, and are converted either into carbohydrates or into urine.
Humans have a special excretory system. Most of the body's waste products are removed in sweat and urine.
Urine contains:
- · Urea
- · Ammonia
- · Other nitrogenous waste
- · Potassium (not nitrogenous)
- · Phosphate (not nitrogenous)
Filtration happens in 3 stages:
1.
Blood from the aorta (the largest artery in the body) enters the renal artery (renal meaning to do with the kidneys). This blood is carried to the kidneys.
2.
The kidney filters out the waste products
3.
The ‘clean’ blood leaves via the renal vein and enters the vena cava (a larger vein).
The urine travels down the ureters (connecting tubes) into the bladder. At the top of the urethra, the two sets
of sphincter muscles control whether
the urine can flow out of the body.
The voluntary sphincter muscles can be relaxed consciously, but the upper sphincter muscles relax when the bladder is full.
The voluntary sphincter muscles can be relaxed consciously, but the upper sphincter muscles relax when the bladder is full.
The kidney has 3 important types
of structure:
Ø
Cortex. The blood flows into the cortex from the renal artery. The cortex contains
blood vessels that branch from there, as well as nephrons (also known as kidney tubules)
Ø
Nephrons/kidney tubules run from the cortex to
the medulla. The urine is emptied
from there into the pyramids.
Ø
Pyramids join to the medulla, and they take the
urine from there that has been filtered by the nephrons. The urine collects in
the pelvis, which leads to the
ureter.
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