6.6 - Controlling blood water potential Flashcards
1
Q
Define osmoregulation
A
control of blood WP
2
Q
Describe ultrafiltration
A
- blood enters kidney via renal artery (pressure from heart)
- divides into afferent arteriole and capillary network (glomerulus)
- H2O and soluble plasma components forced out of glomerulus (not large proteins)
- how: pressure aided by efferent arteriole being narrower than afferent
3
Q
Describe selective reabsorption
A
- Na+ ions AT from PCT epithelial cells into blood
- creates sodium conc gradient in epithelial cells
- Na+ ions FD from lumen into epithelial cells bringing glucose with it (reabsorbed) via co-transport
- glucose FD from epithelial cells into capillaries
- increases WP in nephron filtrate (lumen)
- H2O moves by osmosis into blood capillaries
4
Q
Describe the role of the loop of Henle
A
- acts as a counter-current multiplier
- Na+ ions AT out of ascending limb using ATP
- creates low WP between 2 limbs (interstitial space)
- ascending limb impermeable to H2O
- H2O only moves out of descending limb by osmosis to area of low WP
- H2O enters blood capillaries in this region by osmosis
5
Q
Describe what happens in the distal convoluted tube and collecting duct
A
- water naturally exits DCT and collecting duct by osmosis
- moving down medulla = ion conc increases, as collecting duct runs parallel to loop of Henle
6
Q
How can the permeability of the collecting duct be increased by hormones?
A
- osmoreceptors in hypothalamus detect fall in blood WP
- receptor shrinks and MORE ADH released by posterior pituitary gland, secreted into blood
- bind to receptors on collecting duct surface and activates enzyme phosphorylase
- causes vesicles containing aquaporins to embed in cell surface membrane
- increases H2O permeability and urea permeability
- urea leaves collecting duct; more H2O leaves and is reabsorbed into blood
- urine is more concentrated and lower volume
7
Q
How can the permeability of the collecting duct be decreased by hormones?
A
- osmoreceptors in hypothalamus detect rise in blood WP
- LESS ADH released by posterior pituitary gland
- decreases H2O permeability and urea permeability
- less H2O reabsorbed into blood
- urine is more dilute and larger volume
8
Q
What would a longer nephron do?
A
- increase multiplier effect
- area around DCT has even higher solute conc
- so more H2O enters capillaries by osmosis because there is a greater WP gradient
9
Q
Where is urea produced and what from?
A
in liver from breakdown of EXCESS amino acids
10
Q
Describe the structure of the nephron
A
- outer fibrous capsule (for protection)
- cortex: Bowman’s capsule, convoluted tubes, blood vessels
- medulla: loops of Henle, collecting ducts, blood vessels
- renal pelvis (collects urine into ureter; sphincter muscle)
11
Q
Where does ultrafiltration occur?
A
Bowman’s capsule
12
Q
Where does selective reabsorption occur?
A
PCT
