5.16 Kidneys 1 - Overview & ADH Flashcards
What is the role of the kidneys? (3)
- To filter the blood and remove waste we don’t want
- Regulate the levels of ions which we need to keep at right levels. We get ions like sodium and potassium from our diet. If levels of ions get too high or low, it can start to damage our cells and cause problems, so we have to keep them perfect. We lose ions naturally through sweating which is why sweat tastes a bit salty, but the main way we regulate our ions is through our kidneys.
- The kidneys play a vital role in balancing the level of water in the body - they control how much water is lost in urine by varying the volume of urine produced and how concentrated it is.
What is urea?
The main waste product that kidneys remove. They are made in the liver during the process of deamination which is where excess amino acids which we don’t need anymore are converted to fats and carbohydrates for storage.
What type of fluid are body cells surrounded by?
Tissue fluid
Where does tissue fluid come from?
Blood capillaries
Describe how water moves through tissue fluid and cells
The tissue fluid will usually have a different concentration to the fluid inside a cell. This means that water will either move into the cell from the tissue fluid, or out of the cell by osmosis.
- If there are more water molecules in the tissue fluid than in the cell (i.e. the tissue fluid is a less concentrated solution than the fluid in the cell), there will be a net movement of water into the cell by osmosis. If too much water moves into the cell, then the cell may burst - this is called lysis.
- If there are fewer water molecules in the tissue fluid in the cell (i.e. the tissue fluid is a more concentrated solution than the fluid in the cell), there will be a net movement of water out of the cell and into the tissue fluid. This causes the cell to shrink.
So it’s really important that the water content of the blood (and therefore of the tissue fluid) is controlled to keep cells functioning normally.
What are the millions of tiny structures in kidneys called?
Nephrons
Describe how urine is formed in the nephrons
Blood flows through the glomerulus at high pressure and small molecules including water, sugar, salt (sodium chloride) and urea are filtered out into bowmans’ capsule. The liquid then flows along the tubule and useful substances are selectively reabsorbed. All the sugar is reabsorbed. Sufficient salt is reabsorbed and excess salt isn’t. Sufficient water is reabsorbed, according to the level of the hormone ADH. This helps to keep the blood plasma at the correct concentration to prevent cell lysis or shrinkage. Whatever isn’t reabsorbed forms urine, which is excreted by the kidneys and stored in the bladder.
What is the process in which small molecules are reabsorbed in the tubule called?
Selective reabsorption
What hormone is the concentration of urine controlled by?
Anti-diuretic hormone (ADH)
What gland is ADH released into the bloodstream by?
Pituitary gland
Describe in detail how the concentration of urine is controlled by ADH
- The concentration of urine is controlled by a hormone called anti-diuretic hormone (ADH). This is released into the bloodstream by the pituitary gland.
- The hypothalamus contains receptors that are sensitive to the water content of the blood. The hypothalamus processes the information it receives from these receptors and instructs the pituitary gland to release ADH into the blood according to how much is needed.
- ADH makes the kidney tubules more permeable so that more water is reabsorbed back into the blood.
- The whole process of water content regulation is controlled by negative feedback. This means that if the water content gets too high or too low, a mechanism will be triggered that brings it back to normal.
- So, using negative feedback, the amount of water in your body can be closely regulated. The more water your kidneys reabsorb, the less water will pass out as urine - so you’ll produce a smaller volume of urine. Your kidneys will still excrete all the waste products they need to though, so your urine will be more concentrated.
Describe how sweating and dehydration will effect the concentration of urine
Losing more water than you take in causes dehydration. This can happen when it’s hot or when you exercise (which makes you hot) because you sweat more. Sweat contains water, so sweating contains water loss.
- Water is detected by receptors in the hypothalamus.
- The hypothalamus processes this change and instructs the pituitary gland to release more ADH.
- This makes the kidneys reabsorb more water, so the water content of the blood increases and only a small volume of concentrated urine is produced.
The brain also triggers feelings of thirst when you’re dehydrated. This makes you want to drink more, which helps to restore water balance in the body.
Describe how excess water intake effects the concentration of urine
Receptors in the hypothalamus detect an increase in blood water content and the pituitary gland secretes less ADH. The kidneys reabsorb less water, so lots of dilute urine will be produced - this lowers the blood water content.
Deamination (3)
- If the body has more amino acids than it needs, it can convert them into lipids or carbohydrates, which can be stored as an energy source for later.
- This process is known as deamination, and takes place in the liver.
- The downside of this process is that it produces the waste product urea, which has to be excreted by the kidneys.
What are the two ways that ions can be removed from the body?
- By the kidneys
- By sweating
