Lecture 18 Flashcards
The body is around ____ water (_______ for men, ______ for women)
60%
60%
55%
What is the most important function of the kidneys?
water homeostasis
What is the response of the kidneys when there is an increase in body water?
there is an increase in the excretion of water by the kidneys
An increase in body water means what has happened to the osmolarity?
it has decreased
A decrease in the body water means what has happened to the osmolarity?
it has increased
What is the response of the kidneys when there is a decrease in body water?
there is an increase in the reabsorption of water by the kidneys
How do we know that we are thirsty?
Thirst receptors (osmoreceptors and baroreceptors) are detecting changes in the osmolarity of the water
Where are the osmoreceptors located?
in the macula densa cells
What percent of total body water is ICF and what percent is ECF?
66% ICF
33% ECF
What is the ECF made of and what percent do these make up?
interstitial fluid (75%)
plasma (20%)
transcellular (5%)
Where do we get water input from? How many mLs per day does this equate to?
fluid intake
in food
metabolically produced from food
2500mL
Where do we get water output from? How many mLs per day does this equate to?
insensible sweat faeces urine 2500mL
Water intake equals what? This means the net flow is what?
intake = output
net flow = 0
H2O excretion = H2O ______________ - H2O ______________
filtered
reabsorbed
Which segments of the nephron are permeable to water?
Proximal tubule
Thin descending limb loop of Henle
Late distal tubule
Collecting duct
Which parts of the nephron are permeable to H2O but only under the influence of vasopressin/ADH?
late distal tubule
collecting duct
Which segments of the nephron are not permeable to H2O?
both the thick and thin ascending limb of loop of Henle
early distal tubule (there is still debate about this)
Which of the following statements is TRUE?
A. 65%of a male’s body is composed of water.
B. Normally, a person has 4 litres of plasma in their blood.
C. The net water intake and water output of person per day is 0.
D. A person can live without water for 3 months.
C. The net water intake and water output of person per day is 0.
What are the two ways the H2O can move across a membrane?
paracellularly and transcellularly via aquaporin channels
What is water movement dependent on?
the osmotic gradient
Describe how water moves transcellularly across the proximal tubule
There is the transport of a solute, such as Na+ from the apical to the basolateral membrane which increases the osmolarity on the basolateral side which causes H2O to move due to the osmotic gradient. It travels through AQP1 on both the apical and basolateral membrane
Why can the proximal tubule also transport water paracellularly?
because it has leaky epithelium
What are aquaporins?
they are a family of plasma membrane proteins that form channels permitting a high rate of water flow