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osmoregulation

Key Concepts:

Terms in this set (22)

why urine of diabetic patient usually contains glucose and requires frequent urination?
urine contains glucose
1. pancreas cannot produce enough insulin
2. liver cannot convert excess glucose in the blood into glycogen and inefficient uptake of glucose
3. high blood glucose concentration
4. high level of glucose in the glomerular filtrate
5. kidney tubules cannot reabsorb all the glucose from the glomerular filtrate

frequent urination
1. unreabsorbed glucose lowers water potential of glomerular filtrate in kidney tubules
2. less proportion/ smaller amount of water reabsorbed
3. larger volume of urine produced
why haemodialysis takes a long time and needs to be repeated at regular intervals?
takes a long time: small volume of blood enters the kidney machines per unit time--> allow time to remove most urea from body

repeated at regular intervals: remove urea which is continually produced/ excess salts taken up in diet
why kidney transplant is not preferred?
-rejection by immune system treating transplanted organ as 'foreign'
-have to wait long time for suitable donor
when does the excretion of glucose in urine happen in a healthy person?
1. after excessive intake of sugary food
2. some glucose is reabsorbed from glomerular filtrate into blood capillaries
3. kidneys cannot reabsorb all the glucose from the glomerular filtrate into blood capillaries when the glucose concentration in blood plasma is too high
how presence of caffeine in the blood increase the rate of urine production?
1. increase flow rate of blood in affluent arteriole due to dilation caused by caffeine
2. increase rate of formation of glomerular filtrate
3. rate of water reabsorption in kidney tubule remains the same
why a larger volume and more concentrated urine is produced after consuming a salty meal or drinking sea water?
1. more salts absorbed into the plasma
2. decrease water potential in glomerular filtrate
3. excess salt excreted in urine
4. less water reabsorbed
importance of osmoregulation
keep water content in cells and body fluids (ie blood and tissue fluid)
water loss
-exhalation
1. lining of air sacs covered with a water film
2. water in the water film evaporates into air of the air sac/ respiratory tract
3. water is lost
-sweating
-urination
-defaecation
water gain
-drinking
-eating
-cellular respiration
urinary system
structure of kidney
structure of nephron
ultrafiltration
1. under the effect of high hydrostatic pressure in glomerulus due to pumping action of the heart
2. water and other small molecules (glucose, amino acids, mineral salts, urea=20% plasma without plasma protein) in the blood forced through the walls (serve as a filter) of the glomerulus (that is differentially permeable and thin) and the Bowman's capsules to form glomerular filtrate
filtration barriers inside the nephron
-endothelium of the glomerular capillaries
-basement membrane
-epithelium of the Bowman's capsule (podocyte)
reabsorption
in proximal convoluted tubule,
1. all glucose and amino acids and some salts reabsorbed into the blood capillaries by diffusion and active transport
2. glomerular filtrate becomes more dilute and has higher water potential
3. 80% water reabsorbed into the blood capillaries by osmosis (net absorption)
4. glomerular filtrate becomes more concentrated with urea
5. urea reabsorbed into the blood capillaries by diffusion

in loop of Henle, distal convoluted tubule and collecting duct,
6. remaining salts, water and urea reabsorbed into blood capillaries
structural adaptation of proximal convoluted tubule
-highly coiled--> increases SA and lengthens time
-wall contains single layer of cells--> shortens diffusion distance
-epithelial cells contain numerous mitochondria--> site of respiration--> produce energy--> active transport and microvilli--> increase SA
osmoregulation
1. change in water potential of blood (drinking a large amount of water/ after heavy sweating)
2. detected by osmoreceptors in hypothalamus
3. control release of antidiuretic hormone by pituitary gland
4. permeability of wall of collecting ducts to water
5. proportion of water reabsorbed from glomerular filtrate into blood capillaries
6. volume and concentration of urine
7. change water potential of blood to normal
excretion
removal of waste products formed in metabolic reactions like carbon dioxide, urea, bile pigments
haemodialysis
1. blood with metabolic wastes is pumped into the dialysis machine
2. urea (only small molecules but not red blood cells and plasma proteins) diffuses through the pores of the dialysis tubing(which is differentially permeable) down a concentration gradient into dialysis fluid which contains glucose, amino acids and salts at similar concentrations to those in normal blood plasma--> not net flow of useful substances
3. treated blood is returned to the patient's body
counter current flow (dialysis fluid flow in the opposite direction as the blood flows in the tubing)
maintains a steep concentration gradient for removing metabolic wastes from the blood efficiently
miscellaneous definitions
excretion: removal of waste products formed in metabolic reactions
digestion: removal of undigested materials from the alimentary canals as faeces
large volume of urine was produced by the diabetic person
-blood glucose level of the diabetic person is higher than the upper limit for complete reabsorption of glucose,
-so glucose is present in the filtrate / urine in the collecting duct.
-The water potential of the filtrate / urine is lowered by the glucose present,
-Thus the reabsorption of water is reduced
and a larger volume of urine would be produced
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