regulation of water balance Flashcards
(16 cards)
what is osmoregulation
when water levels in the body are unbalanced, eletrolytes levels are also unbalanced.
osmoregulation - regulation of body fluids
- the process of controlling the water content of the human body and it’s solute concertation
- water balance is closely associated with the concertation of ions, i.e. the concertation of mineral salts (eletrolytes) - such as Na+ (sodium) and K+ (potassium) in the blood.
- when water levels in the body are unbalanced, electrolyte levels are also unbalanced.
what to remember about maintainging water balance
- water is gained from fluids we drink, the food we ingest, metabolic processes
- water is lost from the lungs, skin, gut, kidneys
- water is not stored so a balance must be maintained between water loss and gain.
(intake 2.2L/day)+( metabolic production 0.3L/day)-(output (0.9+1.5+0.1) L/day) = 0
osmolality - an indicator of water level
- if the blood plasma osmolality is higher than normal, this means that the water level is too low
- if osmalality is below normal, this means that the water level is too high
- osmoreceptors can detect the change in osmolality from passing blood.
- it is tightly regulated, largely due to the presence of sodium ions.
sources of water gain
- fluids from drinks (60%)
- fluid content of foods (30%)
- internally produced metabolic water (10%)
general stimulus - response model, water balance; the regulation of osmolality and blood pressure and volume
- stimulus; change in water volume causing change in osmolality, blood volume, and blood pressure.
- receptor; (baroreceptors - 1), (osmoreceptors - 2)
- modulator; (cells in the kidney - 1), (the hypothalamus and pituitary gland)
- effector; (cells in the distal convoluted tubule and collecting duct - 1), (the hypothalamus -2)
- response; alteration in the reabsorption of water which changes the osmolality of blood and blood pressure and volume
sources of water loss
- from skin and lungs (28%)
- from sweat glands (as fluid) (8%)
- from the gut (as fluid in faeces) (4%)
- from the kidneys (as urine) (60%)
key organs in osmoregulation
The brain:
* Hypothalamus - location of osmoreceptors
- stimulate the release of a hormone as antidiuretic hormone (ADH) or vasopressin.
* lamina therminalis
- stimulates the thirst response
The kidney:
* when plasma osmolality falls:
- produce larger volumes of more dilute urine
* when plasma osmolality rises:
- producing smaller volumes of more concertrated urine
- this response is stimulated by the gormone ADH
key hormones in osmoregulation
Antidiuretic hormone (ADH) - a peptide hormone
* released from the posterior pituitary in response to a signal from the hypothalamus
* ADH travels through the blood stream to the kidney.
- mainly binds to receptors on the cell that line the collecting ducts in the kidney (making these cells more permeable to water.)
* ADH-stimulates the insertion of specific channel proteins called aquaporins into the plasma membrane of these cells.
- aquaporins enable the more rapid movement of water from fluid in the collecting ducts back into the bloodstream.
antidiuretic hormone (ADH), low and high
when water levels are low and solute levels are high:
* ADH is released from the hypothalamus
- water is reabsorbed in the kidneys
- smaller volumes of more concertrated urine are produced
when water levels are high and solute levesl are low;
* ADH levels are decreased
- excess water is excreted in the kidneys
- larger volumes of more dlute urine are produced.
osmoregulation - when water levels decrease
- when water levels fall too low the concertration of solutes in body fluid rises.
- homeostatic mechanisms are activated to restore the balance.
water levels in the body - can become too low due to:
- an excessive loss of water (such as sweating in hot conditions)
- an inadequate intake of fluids (drinking enough)
- an abnormal loss of body fluids
- e.g. severe diarrhoea, prolonged vomiting, significant haemorrhage or serious burn injuries.
- if water intake is less than water output - can lead to a toxic increase in excess ions and waste product in the blood.
Drop in water levels (low); the stimulus response model for a drop in body water levels
-
stimulus,
* decrease in water volume
* increase in osmolality of body fluids -
receptor,
* osmoreceptors in hypothalamus detect change -
modulators or control centre,
* hypothalamus signals ADH release
* thirst response signalled -
effectors,
* kidney collecting ducts become more permable to water.
* thirst behaviour is stimulated -
response,
* increased reabsorption of water from kidney collecting ducts
* decreased urine volume
* water intake by drinking
osmoregulation - when water levels increase
- when water levels are high the concertration of solutes in body fluid falls.
- homeostatic mechanisms are activated to restore the balance
rise in water levels (high); the stimulus repone model for an increase in body water levels
- stimulus, - increase in water volume, - decrease in osmolality of body fluids
- receptor, -osmoreceptors in hypothalamus are silent, - stretch receptors in heart detect increased blood volume
- modulators or control centre, -hypothalamus sends signal to inhibit release of ADH hormone.
-
effectors, -kidney collecting ducts become almost impermeable to water, - ADH release in inhibited, -thirst response inhibited.
5.** response**, -decreased reabsorption of water from kidney tubules, - increased urine volume to expel water
water levels in the body - can become too high due to;
- impaired kidney function - produces insufficient urine
- drinking excessive amounts of water
- medical conditions, such as SIADH (syndrome of inappropriate secretion of antidiuretic hormone).
( if water intake is in excess of water output, a person can become over-hydrated, a situation sometimes called ‘water intoxication’. This can cause cells to swell.)
