5.3.3 Maintaining water and nitrogen balance in the body. Flashcards
(20 cards)
Explain the function of the kidneys
Include descriptions of filtration and selective reabsorption.
Make urine by removing waste products from the blood, maintaining the water balance of the body.
Substances are filtered out of the blood as it passes through the kidneys. This process is called filtration.
Useful substances like glucose, some ions and the right amount of water are then absorbed back into the blood. This is called selective reabsorption
Give 3 substances removed from the body in urine.
- Urea
- Ions
- Water
How are excess amino acids excreted from the body?
Excess amino acids need to be excreted safely. In the liver, these amino acids are deaminated to form ammonia . Ammonia is toxic so it is immediately converted to urea for safe excretion.
Ions
- how do they enter the body?
- what happens if the ion content of the body is wrong?
- How are ions removed from the body to ensure the correct balance of them in the body?
- ions such as sodium are taken into the body in food and absorbed into the blood.
- This could upset the balance between ions and water, meaning too much or too little water is drawn into the cells by osmosis. This means the cells become damaged or don’t work as well as usual.
- Some are lost in sweat, however this amount is unregulated, so the right balance of ions in the body must be maintained by the kidneys. The right amount of ions is reabsorbed into the blood after filtration and the rest is removed from the body in urine.
Water
- the body must constantly balance the amount of water entering and leaving the body
- water is lost from the skin in sweat and the lungs when breathing out
- We can’t control the amount lost in these ways, so the amount of water is balanced by the amount we consume and the amount the kidneys remove in urine.
What is lost via the lungs in exhalation?
Water
What is lost from the skin in sweat?
Water, ions and urea
True or false, the lungs have control over water loss but the skin doesn’t have contol over water, ion and urea loss
False - There is no control over water, ion or urea loss by the lungs or skin.
How do excess amino acids end up in the body?
The digestion of proteins from the diet results in excess amino acids whch need to be excreted safely.
1 treatment and 1 cure for kidney failure
treatment - dialysis
cure - kidney transplant
Kidney transplants
- who donates the kidney?
- Risk - how is it reduced
-advantages
- disadvantages
- either someone who died suddenly (provided they are on an organ donor list or carry an organ donor card and the family agree.
OR
people who are alive (as we all have 2), but there is a small risk to the person donating the kidney - risk of patient’s immune system rejecting donor kidney. Patient is treated with drugs to reduce this risk but it can still happen.
- Cheaper than dialysis in the long run and patients don’t have to spend hours on dialysis.
- long waiting lists
Dialysis
- why must it be done regularly
-how does a dialysis machine work?
- disadvantages and advantages
- to keep the concentration of dissolved substances in the blood at normal levels and remove waste substances
- blood flows between partially permeable membranes, surrounded by dialysis fluid. Membranes, like kidneys, are permeable to things like ions and waste substances but not big molecules like proteins.
- dialysis fluid has same concentration of dissolved ions and glucose as healthy blood, so useful dissolved ions and glucose won’t be lost from the blood during dialysis
- only waste substances, (e.g. urea) and excess ions and water diffuse across the membrane.
DISADVANTAGES
- many patients need a dialysis session 3-4 times per week and each session takes 3-4 hours
- dialysis could cause blood clots or infections
- Being on a dialysis machine is an unpleasant experience and it’s expensive for the NHS to run
ADVANTAGE
- can buy a patient valuable time until an organ donor is found
What is the purpose of ADH (anti-diuretic hormone)
To control the concentration of urine
What gland releases ADH
pituitary gland
The role of the brain in controlling urine concentration
The brain monitors the water content of the blood and instructs the pituitary gland to release ADH into the blood according to how much is needed
How does ADH control urine concentration?
ADH acts on the kidney tubules. It’s released by the pituitary gland when blood is too concentrated and causes more water to be reabsorbed back into the blood from the kidney tubules by increasing the permeability of the kidney tubule.
True or false, Water content is not controlled by negative feedback
False - water content IS controlled by negative feedback.
What happens when water content is too high?
4 steps
Receptor in brain detects that the water content is too high
Coordination centre in the brain receives the information and coordinates a response
The pituitary gland releases less ADH, decreasing the permeability of the kidney tubules, so less water is reabsorbed from the kidney tubules.
Water content decreases
What happens when water content is too low?
4 steps
Receptor in brain detects that the water content is too low
Coordination centre in the brain receives the information and coordinates a response
The pituitary gland releases more ADH, increasing the permeability of the kidney tubules, so more water is reabsorbed from the kidney tubules.
Water content increases
What happens if the kidneys don’t function properly?
Waste substances build up in the blood and you lose the ability to control the levels of ions ad water in your body, which eventually results in death.
