water regulation Flashcards
is water in the body pure?
Not pure; contains dissolved substances
why should the vol and conc be controlled for water?
Vital that the volume of the water and concentration of dissolved substances is controlled to remain within the tolerance levels for the body
what role does the water in the body play?
- Transporting substances from one area of the body to another
- Facilitating movement across membranes
- Site of chemical reaction
intracellular fluid
fluid inside the cells, 2/3 of total body water
extracellular fluid
fluid outside the cells, 1/3 of total body water
intravascular fluid
blood plasma located within the blood cells, 1/4 of extracellular fluid
interstitial fluid
fluid between the cells, 3/4 of extracellular fluid
transcellular fluid
fluid in specific body regions
are the diff. types of body fluids isolated from eachother?
No, different body fluids are not isolated from each other – continuous exchange of materials between them
Plasma is separated from the interstitial fluid by…
thin walls of the capillaries; free exchange of materials between the two
what type of materials remain within the blood vessels?
Dissolved materials that are large molecules (Eg. Proteins of the plasma) will remain within the blood vessels – too large to move through capillary walls
how long does any difference in osmotic concentration between the intracellular and extracellular fluid last?
doesn’t last long as water moves easily through plasma membranes
Osmotic concentration
concentration of solutes; also known as osmolarity
osmotic pressure
the tendency of a solution to take in water
The greater the difference in osmotic concentrations between two solutions…
the greater the osmotic pressure
osmotic pressure results from…
Higher conc level on one side of membrane
Higher the conc. of solute…
the higher the osmotic pressure
how do you keep the composition of body fluids to stay constant?
Fluid gain = fluid lost
Most body fluid is obtained from…
water (taken in as liquid or contained in food)
metabolic water
Small amount obtained as a by-product of chemical processes within cells
how much fluid is lost from the body each day?
around 2.5L
how is fluid lost?
- Via kidneys
- Through the skin
- From the surface of the lungs
- From alimentary canal
Excretion
removal of waste products of metabolism from the body
why does excretion occur?
Many wastes are toxic and would be harmful to health if allowed to accumulate in the body fluids, hence they are excreted
excretion: lungs
Carbon dioxide:
Carbon dioxide and water are produced by all body cells during cellular respiration. Body
can’t use carbon dioxide; carried in the body until it reaches the lungs → excreted
excretion: alimentary canal
Bile pigments that entered the small intestine with the bile.
Pigments are breakdown products of haemoglobin from RBC
Leave the body with faeces (in addition to undigested food materials)
excretion: sweat glands
Water containing by products of metabolism (salts, urea and lactic acid)
excretion: kidneys
Urea
Produced in the liver during the breakdown of proteins
Nephron
functional unit of the kidney; carries out the kidney’s role in excretion and water regulation
kidney’s process in controlling water levels
- Water lost in sweat, urine, faeces and exhaled breath is usually balanced by water intake
- At time of strenuous activity or extreme heat, water loss can be quite high
1. As water is lost, plasma becomes more concentrated → higher osmotic pressure
2. Water moves from the interstitial fluid into the plasma by osmosis
3. Interstitial fluid becomes more concentrated → water diffuses out of the cells
(cells shrink due to dehydration)
4. Osmoreceptors in the hypothalamus detect the increase in osmotic pressure → responses triggered to lower osmotic pressure
Drinking lots of water causes
production of a large volume of diluted urine
not drinking enough water (become dehydrated) causes
production of smaller volume of concentrated urine
kidneys: 99% of water filtered through…
the glomeruli of the kidneys = reabsorbed
Occurs through the walls of the kidney tubules
Reabsorption occurring at PCT and LoH is by osmosis
Reabsorption at DCT and CD is active reabsorption
what does antidiuretic hormone controls?
Level of active reabsorption
Permeability of the walls of the DCT and CD
what happens when the conc. of ADH in the blood plasma is high?
tubules are very permeable to water = water able to leave the tubule and enter the surrounding capillary network
Outward flow of water from the fluid within the tubules reduces it’s volume →increases the concentration of the materials remaining
what happens when conc. of ADH in the blood plasma is low?
- tubules are not permeable to water = very little water is reabsorbed into the plasma of the bloodFluid within tubules remains dilute → volume is not reduced to any significant extent
kidney: increase stimulus
The osmotic pressure of the blood is raised due to the decrease in water in the blood.
kidney: receptors
Osmoreceptors in the hypothalamus detect the increased osmotic pressure of the blood.
kidney: modulator
The hypothalamus stimulates the posterior lobe of the pituitary gland to release ADH into the bloodstream.
kidney: effector
ADH is carried all over the body by the blood but it affects its target organs, which are the nephron tubules in the kidney. The permeability to water of the distal convoluted tubules and the collecting ducts is increased.
kidney: response
More water is then reabsorbed into the blood plasma from the distal convoluting tubule and collecting duct.
kidney: feedback
The reabsorption of water increases the amount of water in the plasma and so the osmotic pressure of the blood is decreased. This adjustment has eliminated or reduced the original stimulus; a negative feedback has occurred.
Aldosterone role
plays a part in the regulation of water output
acts on the kidney to reduce the amount of sodium in the urine and increase the amount of potassium
aldosterone by adrenal cortex is secreted in response to:
- Decrease in the concentration of sodium ions in the blood
- Decrease in blood volume
- Decreased in blood pressure
aldosterone acts in the DCT and CDs to increase…
- the amount of sodium ions reabsorbed into the bloodstream and the amount of potassium secreted into the urine
- Achieves this through active transported using a sodium-potassium pump
For every three sodium ions reabsorbed, two potassium ions are secreted
Net movement of ions into the blood → transport of water into the blood via osmosis
Water level of the body can be increased by…
taking in more fluid
Osmoreceptors are able to stimulate the thirst centre in the hypothalamus to
prompting the person to drink water
thirst response
- Water level of the body can be increased by taking in more fluid
- Osmoreceptors are able to stimulate the thirst centre in the hypothalamus, prompting the person to drink water
- Caused by increased osmotic pressure → nerve impulses to the cerebrum
- Fluid is absorbed across the wall of the alimentary canal → blood (decreases osmotic pressure)
thirst response: stimulus
Water concentration of blood
plasma decreases; osmotic pressure of the blood is increased; mouth becomes dry.
thirst response: receptors
Osmoreceptors in the thirst centre of the hypothalamus are stimulated.
thirst response: modulator
thirst centre prompting the person to drink water
thirst response: effectors
The person feels thirsty.
thirst response: responses
The person responds to the feeling of thirst by drinking.
thirst response: feedback
Water drunk is absorbed into the blood from the alimentary canal
Water leaves the blood, and the extracellular and intercellular fluids return to their normal concentrations.
Dehydration
excessive loss of water and salts from body; loses more fluid than takes in
dehydration: causes
sweating, vomiting or diarrhoea
dehydration symptoms
severe thirst, blow BP, dizziness and headache
Water intoxication
- drinking too much water
Body fluids become diluted and cells take in extra water by osmosis
water intoxication causes
Can occur if a person loses a lot of water and salts through sweat and replaces the loss with plain water; electrolytes should always be consumed in addition to replace the lost salts
