B5 - Digestion and Excretion Flashcards
Why do you need to digest food?
The large molecules in the food have to be broken down (digested) into smaller molecules so that they can pass across your gut wall and into your blood or lymph. Then your circulatory system takes the digested food to your cells and tissues. Here, you use the food for energy or growth and repair.
What is physical digestion? Why is this important?
Chewing food in your mouth and squeezing food in your stomach are both forms of physical digestion. The resulting smaller pieces of food can move more easily through the rest of the digestive system.
What type of enzyme breaks down carbohydrates? Where does this enzyme work and what are the products?
Enzyme : carbohydrase
Part : mouth and small intestine
Products : starch, converted to maltose and then to glucose, a simple sugar
What type of enzyme breaks down fats ( lipids ) ? Where does this enzyme work and what are the products?
Enzyme : lipase
Part : small intestine
Products : fatty acids and glycerol
What type of enzyme breaks down proteins ? Where does this enzyme work and what are the products?
Enzyme : protease
Part : stomach and small intestine
Products : amino acids
What pHs will the enzymes work best at?
You have hydrochloric acid in your stomach, giving it a very low pH of between 1 and 2. The protease enzyme in your stomach is well adapted to this low pH and will not work at higher pH values. However, other enzymes in your mouth and small intestine work best at higher pH values of between 7 and 8.
What is bile? Where is it stored and how does it work?
To help you digest fats in the small intestine, your liver makes bile. Bile is stored in your gall bladder and released into the small intestine. Bile emulsifies the fats (breaks the fats into smaller droplets). This gives the lipase enzymes more surface area to work on.
What happens at the small intestine? How is it adapted for its job?
The products of digestion diffuse across the wall of the small intestine into the blood plasma or lymph.
Adaptions :
• It is very long.
• It has a large surface area because its lining is folded and has finger-like projections called villi.
• The cells covering each villus have microvilli, which increase the surface area even more.
• The lining is thin.
• There is a good blood supply.
What is the purpose of the large intestine?
The large intestine absorbs water and some minerals into the blood. The semi-solid waste (faeces) that is left in the large intestine is then passed out of the anus. This is called egestion.
What is the difference between egestion and excretion?
During digestion, the semi-solid waste (faeces) that is left leaves your body via your anus. This is egestion, not excretion – this waste was not made in your body.
How is skin involved in excretion?
Your skin makes sweat to cool you. The water in the sweat uses your body heat to evaporate. Sweating also gets rid of excess water and salts.
How are your lungs involved in excretion?
Your lungs excrete carbon dioxide that was made in your cells. The carbon dioxide would otherwise poison you because it would lower your blood pH. Your enzymes would not work properly and you would die.
As carbon dioxide levels in your blood increase they are detected by the brain. The brain then increases your breathing rate to remove the carbon dioxide more quickly.
What does the liver do?
It breaks down old red blood cells. The chemicals from them go into the bile and pass out with the faeces. Your liver also breaks down hormones and medicines or other drugs, such as alcohol.
How does your liver produce urea?
- If you have eaten excess protein , the liver breaks down the amino acids into ammonia.
- Ammonia has a high pH and is very soluble, so if it got into your blood it would be very harmful. Enzymes would not be able to function.
- In your liver cells the ammonia reacts with carbon dioxide (another waste product) to make urea.
- Urea is toxic, but not as toxic as ammonia. Your blood carries the urea to your kidneys, which remove it.
