Processes and Cycles:

Question 1

Ornithine Cycle

Answer 1

Amino acids are Deaminated and form NH3

Ornithine + NH3 + CO2 —> Citruline + H2O

Citruline + NH3 —> Arginine + H2O

Arginine + H2O —> Urea + Ornithine

Question 2

ADH Mechanism

Answer 2

Osmoreceptors in Hypothalamus detect low water potential and baroreceptors detect low blood pressure so ∴ low blood Vol.
ADH is released from Posterior Pit. Gland and is carried in the blood
It bind to receptors on cell membrane of CD and cAMP forms
cAMP then causes vesicles to fuse with membrane
Vesicles contain aquaporins that increase membrane permeability

Question 3

Clear Piss Cycle

Answer 3

Ψ increases and Ψs decreases
Detected by osmoreceptors
Less ADH released
Less H2O reabsorbed
Dilute urine
Decreased Ψ

Question 4

Yellow piss cycle

Answer 4

Ψ decreased so Ψs increases
Detected by osmoreceptors
More ADH released
More H2O reabsorbed
Concen. urine
Increased Ψ

Question 5

Ultrafiltration in the Kidneys

Answer 5

Afferent Arteriole supplies glomerulus with blood and leaves via efferent arteriole which is narrower
Pressure Gradient formed
∴ blood forced out through cap walls into bowmans capsule
Basement membrane prevents blood cells and proteins through and podocytes are a 2nd barrier

Question 6

Reabsorption by Kidneys

Answer 6

PCT = Glu, AA, Vitamins etc are moved from filtrate back to blood via AT and H2O + Cl- via diff

LofH = ascending limb AT’s Cl-/Na+ out and so Ψ outside decreases so H2O moves out of descending limb via Os
So @ hairpin = very concen so as it moves up ascending limb more ions diff out

DCT= affected via ADH so water tuning occurs here

CD= Here the filtrate is Hypotonic to the to Tissue fluid so water leaves via Os. and Concen urine forms

Question 7

Nervous Transmission and the generation of an Action potential

Answer 7

RP = -70mV
(Na/K pump (3Na out for every 2K in)
Na/K diffuse back down EC grad but Voltage gated Na channels closed so less Na movement)

Energy from stimulus opens VG Na channels so Na ions diffuse into axon which causes an AP = +40mV

AP causes VG Na channels to close again ∴ decreasing charge inside (more -ve inside)

Hyperpolarisation occurs where inside more -ve than RP, the VG K channels close

Then Na/K pump repolarises axon

K still diffusing out of axon