4.5.3.3 Maintaining Water and Nitrogen Balance in the Body (biology only) Flashcards
How should the body keep the levels of water in the blood?
important that body keeps level of water in blood as constant as possible
What is the effect on cells of osmotic changes in body fluids?
- 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
What happens to body cells if they gain or lose too much water and what does the body have in place to prevent this?
- 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
How does the body take in water?
body takes in water through food and drink
How does the body lose water?
- 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
How does the body control water loss through urine?
- 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
How many kidneys do humans have?
2 kidneys
How does blood enter and leave the kidney and what does the kidney remove?
- 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
How do the kidneys adjust the levels of molecules in the blood?
- 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
How do the concentration of urea, ions and glucose change in the blood after it passes through the kidney?
- 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
How do the kidneys produce urine?
kidneys produce urine by the filtration of the blood and selective reabsorption of useful substances such as glucose, some ions and water
What are proteins?
proteins are long chains of amino acids
How does the kidney deal with excess amino acids?
- 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
What hormone controls the water level in the body and how?
hormone ADH cause kidney tubules to become more permeable
What happens if the blood becomes too concentrated?
- 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
- as levels of water in blood returns to normal, pituitary gland stops releasing ADH
- negative feedback cycle
How does dialysis work?
- 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
Haemodialysis diagram:
Peritoneal dialysis diagram:
