13. The Excretory System Flashcards
What is a difference between plants and humans in terms of the removal of waste products?
Unlike plants, humans have organs which are specialised for the removal of certain excretory products
What are 3 examples of organs which are vital for excretion?
- lungs
- kidney
- liver
What do the lungs mainly excrete?
carbon dioxide
Why are lungs a part of the excretory system?
The lungs excrete CO2 (a waste product of aerobic respiration) during exhalation
What do the kidneys mainly excrete?
excess water, salts and urea
Why are kidneys a part of the excretory system?
The kidneys excrete excess water, excess salts and urea (formed in the liver from excess amino acids) by producing urine
Excretion definition
Excretion is the removal of the waste substances of metabolic reactions (the chemical reactions that take place inside cells), toxic materials and substances in excess of requirements
Why must carbon dioxide be excreted?
Carbon dioxide must be excreted as it dissolves in water easily to form an acidic solution which can lower the pH of cells
This can reduce the activity of enzymes in the body which are essential for controlling the rate of metabolic reactions
What substances are toxic to the body?
For this reason, too much carbon dioxide in the body is toxic
Urea is also toxic to the body in higher concentrations and so must be excreted
What happens to many digested food molecules once absorbed?
Many digested food molecules absorbed into the blood in the small intestine are carried to the liver for assimilation (when food molecules are converted to other molecules that the body needs)
What is an example for the use of amino acids?
Amino acids, which are used to build proteins such as fibrinogen, a protein found in blood plasma that is important in blood clotting
- What happens to excess amino acids and why?
Excess amino acids absorbed in the blood that are not needed to make proteins cannot be stored, so they are broken down in a process called deamination
- What plays a key role in deamination?
ENZYMES in the liver split up the amino acid molecules
- During deamination, what happens to the carbon present in the amino acids?
The part of the molecule which contains carbon is turned into glycogen and stored
- During deamination, what happens to the nitrogen present in the amino acids?
The other part, which contains nitrogen, is turned into ammonia, which is highly toxic, and so is immediately converted into urea, which is less toxic
- What happens to the urea after deamination?
The urea dissolves in the blood and is taken to the kidney to be excreted
A small amount is also excreted in sweat
- What is a brief summary of deamination?
In deamination, the nitrogen-containing amino group is removed and converted into ammonia and then urea to be excreted
What is the difference between excretion and egestion? Give definitions
Excretion is the removal from the body of waste products of metabolic reactions, toxic substances and substances in excess of requirements.
Egestion is the expulsion of undigested food waste from the anus.
What are the 4 main structures involved in the urinary system?
Kidney
Ureter
Bladder
Urethra
Kidney definition
two bean-shaped organs that filter the blood
ureter defintion
Tube connecting the kidney to the bladder
Bladder definition
Organ that stores urine (excess water, salts and urea) as it is produced by the kidney
urethra definition
Tube that connects the bladder to the exterior,; where urine is released
What are two different factors to examine when looking at changes in urine?
The colour and quantity of urine produced in the body can change quickly
What are large quantities of urine associated with?
Large quantities of urine are usually pale yellow in colour because it contains a lot of water and so the urea is less concentrated
What are small quantities of urine associated with?
Small quantities of urine are usually darker yellow / orange in colour because it contains little water and so the urea is more concentrated
What are three factors which affect the concentration of urine?
- water intake
- temperature
- exercise
How does water intake affect urine?
the more fluids drunk, the more water will be removed from the body and so a large quantity of pale yellow, dilute urine will be produced
How does temperature affect urine?
the higher the temperature the more water is lost in sweat and so less will appear in urine, meaning a smaller quantity of dark yellow, concentrated urine will be produced
How does exercise affect urine?
the more exercise done, the more water is lost in sweat and so less will appear in urine, meaning a smaller quantity of dark yellow, concentrated urine will be produced