4.5.3.3 Maintaining Water and Nitrogen Balance in the Body (biology only) Flashcards
1
Q
How should the body keep the levels of water in the blood?
A
important that body keeps level of water in blood as constant as possible
2
Q
What is the effect on cells of osmotic changes in body fluids?
A
- if blood becomes too dilute then water moves into cells by osmosis
- if blood becomes too concentrated water move by osmosis out of cells into blood
3
Q
What happens to body cells if they gain or lose too much water and what does the body have in place to prevent this?
A
- if body cells gain or lose too much water by osmosis then they don’t work efficiently
- so body has a system in place to maintain its water balance - part of homeostasis
4
Q
How does the body take in water?
A
body takes in water through food and drink
5
Q
How does the body lose water?
A
- water leaves body via lungs during exhalation
- water, ions (e.g. sodium ions) and urea are lost from the skin in sweat
- no control over water, ion or urea loss by the lungs or skin - as sweating is part of body’s temperature control system
- excess water, ions and urea are removed by the kidneys in the urine
6
Q
How does the body control water loss through urine?
A
- if blood is too dilute, the kidneys remove the excess water and produce greater volume of urine
- urea and excess ions also removed in urine
7
Q
How many kidneys do humans have?
A
2 kidneys
8
Q
How does blood enter and leave the kidney and what does the kidney remove?
A
- blood enters kidneys through an artery and this blood contains the waste product urea
- the kidney removes this urea as well as excess ions and excess water
- these leave the kidney as urine and is stored in the bladder
- blood leaves the kidney through a vein and the blood then contains no urea
9
Q
How do the kidneys adjust the levels of molecules in the blood?
A
- blood passes through capillaries
- small molecules are filtered out of the blood into tiny tubules - includes urea, ions and water as well as the sugar, glucose
- protein and blood cells not filtered out of blood due to larger molecule size
- these pass into a tube - all of the glucose, some of the ions and some of the water is reabsorbed back into the blood (selective reabsorption)
- glucose and ions get reabsorbed via active transport, which requires cells to have and use energy using aerobic respiration which requires oxygen
- urea, excess ions and excess glucose are released as urine
- kidneys remove all of the waste product urea out of the blood and adjust the levels of ions and water
10
Q
How do the concentration of urea, ions and glucose change in the blood after it passes through the kidney?
A
- concentration of ions has decreased after it has passed through the kidneys - kidneys filter ions out of the blood
- then reabsorb certain amount of ions back into the blood depending on the body’s needs
- concentration of urea in the blood falls to virtually 0 as it passes through the kidneys
- kidneys filter out all of the urea and do not reabsorb it
- concentration of glucose in blood remains same as kidney filters out the glucose and then the blood reabsorbs it
- all of urea has been removed from the blood and the concentrations or water and ions have been adjusted - kidneys carrying out homeostasis
- urea has higher concentration in urine as other substances have been removed (reabsorbed - glucose, most of ions and water)
- water gets reabsorbed - due to ADH
11
Q
How do the kidneys produce urine?
A
kidneys produce urine by the filtration of the blood and selective reabsorption of useful substances such as glucose, some ions and water
12
Q
What are proteins?
A
proteins are long chains of amino acids
13
Q
How does the kidney deal with excess amino acids?
A
- get a lot of protein in our diet
- digestion of protein leads to excess amino acids in the blood which need to be excreted safely
- often eat more protein than the body needs so the excess amino acids are deaminated in the liver to form the chemical ammonia
- ammonia is a toxic chemical so it is immediately converted to urea by the liver for safe excretion
- urea can then be safely excreted by the kidneys
14
Q
What hormone controls the water level in the body and how?
A
hormone ADH cause kidney tubules to become more permeable
15
Q
What happens if the blood becomes too concentrated?
A
- if blood becomes too concentrated (level of water in blood falls) then the pituitary gland releases the hormone ADH into the bloodstream
- ADH travels to the kidneys and causes the kidney tubules to become more permeable to water - so more water can pass out of the kidney tubules → more water reabsorbed back into the blood from the kidney tubules
- because of this less urine is produced and the amount of water in the blood rises back to its normal level
- controlled by negative feedback
- makes concentrated + low volume urine
- as levels of water in blood returns to normal, pituitary gland stops releasing ADH
- negative feedback cycle
16
Q
What happens if blood becomes too dilute?
A
- if blood becomes too dilute pituitary gland stops releasing ADH
- kidneys tubules stop becoming more permeable to water and so reabsorb less water into the blood
- makes dilute + high volume urine
- more urine produced and the conc of water in blood returns back to normal
17
Q
What happens if your kidneys fail?
A
- You have two kidneys, but you can manage with just one
- But if both kidneys fail, urea (waste) rises, and the body is poisoned
18
Q
What are the treatments for kidney failure?
A
- dialysis
- kidney transplant
19
Q
How does dialysis work?
A
- You are attached to a kidney machine via a tube from a vein
- when a patient has a kidney failure, their blood will contain a higher concentration of water ions and urea than it should
- in kidney dialysis the patients blood passes over a semi-permeable membrane, flows into a machine, is cleansed and then returns to your body
- excess salt moves out of the blood along a concentration gradient
- urea moves out of the blood by diffusion along a steep concentration gradient
- dialysis fluid also contain normal concentrations of water and ions so some of the water and some of the ions will diffuse from the blood into the dialysis fluid
- because of this, concentrations of water and ions in the patient’s blood will return to normal
- larger molecules like blood cells and proteins cannot pass through the dialysis membrane
- dialysis membrane - partially membrane
- dialysis fluid - low in salt and ureas; sugar and mineral concentration is the same as blood
- there is no net movement of sugar and other substances needed by the body
- fluid and blood moves in opp directions and dialysis fluid constantly refreshed to maintain high conc gradient
20
Q
What does dialysis do?
A
- Restores the concentrations of dissolved substances in the blood to normal levels
- It removes the waste product urea and excess water
21
Q
Which substances are retained in kidney dialysis?
A
- Dialysis fluid contains the same concentration of useful substances as the blood so glucose and useful mineral ions are not lost – as if it has a lower conc then the useful substances will diffuse into the dialysis fluid from the blood from area of high con to area of low conc
- But urea passes out from the blood into the dialysis fluid – dialysis fluid does not contain any urea so diffuses into dialysis fluid from area of high urea conc
22
Q
How long are you attached to a dialysis machine?
A
you are attached for about 4 hours, 3 times per week
23
Q
Haemodialysis:
A
- being ‘on dialysis’ in the traditional understanding means being linked up to a machine for several hours while the machine filters your blood
- Most people need three sessions of haemodialysis a week, with each session lasting around four hours
- The dialysis machine is made up of a series of membranes that act as filters and a special liquid called dialysing fluid
24
Q
Haemodialysis diagram:
A
25
Q
Peritoneal dialysis:
A
- where a fluid is pumped into your abdomen and drains away into a bag
- waste products are removed from the blood by diffusion as the dialysis fluid sits in the abdominal cavity
26
Q
Peritoneal dialysis diagram:
A
27
Q
What is a kidney transplant?
A
- An operation to remove your failed kidney and replace it with a working kidney from a donor
- One or both kidneys may need to be transplanted
28
Q
What is needed for a successful organ match?
A
- For a successful organ match, the donor and transplant patient ideally should have compatible:
- Blood group
- Tissue type
- And a variety of other factors involving the white blood cells that would reduce the chances of rejection
29
Q
Pros of dialysis:
A
- immediately available - no donor needed
- cleans and filters the blood like a kidney
- don’t need medication
- no change of rejection
- no surgery risks
30
Q
Cons of dialysis:
A
- dialysis isn’t cheap – about £23,000 per year, for life - more expensive long term
- time consuming and inconvenient- attached for about 4 hours, 3 times per week
- eat controlled diet so don’t produce too much urea
- limits mobility
31
Q
Pros of kidney transplant:
A
- someone with a successful transplant can lead a completely normal life + have full mobility
- diseased kidney is replaced with healthy kidney from a donor
- changes in concentrations of substances in blood and urea in blood is minimised → so less chance of causing damage to body cells
- not repeatedly puncturing skin/in contact with machine unlike in dialysis → less chance of infection / less or no chance of blood clots / don’t need to take anti-clotting drug
- can eat what you like
- less expensive in long term
32
Q
Cons of kidney transplant:
A
- taking drugs (immunosuppressants) to stop their body rejecting the new kidney
- expensive - a transplant costs about £42,000 for the operation plus £6,500 a year in drugs and check-ups
- in some cases, donated kidney might be rejected by patient’s immune system
- may be a long waiting list for donor
- surgery risk - risk of infections
33
Q
Why is urea more concentrated in urine than in blood?
A
- after filtering water is reabsorbed
- urea not reabsorbed
34
Q
What do the bubble traps, anti-coagulants and warm temps do in a dialysis machine?
A
- bubble traps - get rid of air bubbles
- anticoagulant - stops blood clotting in machines
- warm temp - stops blood clotting
35
Q
What does a carbon dioxide build up lead to?
A
low pH/acidic conditions = denatures enzymes
36
Q
What does a salt build up lead to?
A
- lowers water potential in blood
- water moves by osmosis into blood from cells
- raises blood pressure
- leads to heart problems
