Lecture 63 - Filtration and Clearance Flashcards
What happens to GFR when the afferent arteriole dilates?
GFR increases
NB as the arteriole dilates, the pressure of the blood in the glomerulus does not decrease.
What happens to renal blood flow when the afferent arteriole dilates?
Resistance decreases (Poiseuille’s equation)
Thus, blood flow increases
(Flow proportional inversely proportional to resistance)
What is the difference between plasma and blood?
Blood: plasma + RBC
Plasma: fluid component
What is Inulin used for?
Why?
GFR
Because:
- not reabsorbed
- not secreted
- none metabolised
- exogenous
Compare amount in the urine per unit time and the amount in the blood per unit time. This will give us GFR
What is renal clearance?
Rate of urinary excretion of a substance, relative to its plasma concentration
UV/P
In UV/P, what are the parameters?
U: concetration of substance in urine
V: volume of urine excreted per unit time
P: plasma concentration of substance
What happens to GFR when MAP increases?
How?
Stays the same
Kidneys regulate their blood flow to keep it roughly constant, despite MAP
Autoregulation:
- Myogenic response
- Tubuloglomerular feedback
What is the myogenic response?
Where does it happen?
In arterioles and small arteries
When there is stretch, the smooth muscle constricts
Mechanism: • stretch • ion channels open • Ca2+ influx • cross bridge cycling • smooth muscle contraction
Describe tubuloglomerular feedback
- Increased pressure
- Increased GFR
- Increased flow past macula densa, nascent urine is more concentrated
- Paracrine diffuses from macula densa to afferent arteriole
- Afferent arteriole constricts
- Decrease in GFR
Which processes affect renal excretion?
- RAAS
- Sympathetic nervous system
- Atrial natriuretic peptide
- Vasopressin
What is the fundamental change that RAAS and sympathetic nervous system bring about?
Increase in BP
What are determinants of MAP?
CO
TPR
What element of the vasculature is most important for TPR?
Arterioles
What is atrial natriuretic peptide?
Natriuretic: excretion of Na+
Peptide from the atria of the heart that leads to salt excretion
Describe what happens in the atria with increased BP
- Increase BP in atria
- Stretch on atrial cells
- Release of natriuretic peptide (ANP)
What does stand for ANP?
Atrial natriuretic peptide
What is vasopressin?
Describe its function
Also known as ADH
- Increased osmolarity of blood
- Detected by osmolarity receptors
- Release of ADH from posterior pituitary
- ADH acts on V2 receptor in collecting duct
- G-protein / cAMP system activated
- AQP2 put into apical membrane
- Increased water resorption
Where does aldosterone come from?
Adrenal glands
What is the action of Angiotensin II?
- Constriction of efferent arteriole
• Increased GFR - Increased resorption
Where is renin released from?
Juxtaglomerular cells; specifically, granular cells in the afferent arterioles
What hormones act on the proximal and distal nephron?
Proximal: angiotensin II
Distal: aldosterone
What is the action of aldosterone on the nephron?
Increased Na resorption in distal nephron
- Diffuses into DCT cell
- Binds to Aldosterone receptor
- Acts as transcription factors
- Production of channels: Na+ and K+
Increased Na/K ATPase activity - Increased sodium reabsorption
What is the action of NA on the nephron?
- Constriction of afferent arteriole
2. Increased Na resorption in PCT
Where does Angiotensin II act?
Efferent arteriole
NB efferent more sensitive to A II than afferent
Where does aldosterone act?
Distal nephron
Where does noradrenaline act?
Afferent arteriole
PCT
Where does ANP act?
Afferent arteriole
Collecting duct
Describe the mechanism of action of ANP?
- Dilation of afferent arteriole
Increased flow into glomerulus
Increased GFR - Collecting duct
Inhibition of Na reabsorption
Inhibits:
- ADH
- Aldosterone
- renin
Do ANP and Angiotensin work together?
No, they are roughly antagonistic
Describe the mechanism of RAAS
- Release of renin
- Angiotensinogen –> ANG I
- ANG I –> ANG II under ACE
- ANG II has many effects
- Increased BP
What are the stimuli for release of renin?
- Decreased NaCl transport across macula densa
- Decreased stretch on granular cells
- Baroreceptor reflex
What are the effects of ANG III?
- vasoconstriction
- ADH release
- Aldosterone release
- vasoconstriction of the afferent arteriole
- increased reabsorption in the PCT
- thirst
- increased SNS activity
Is aldosterone a short or long term response?
Long
Involves gene transcription
What are the two main stimuli for aldosterone release?
- ANG II
2. Hyperkalaemia
What are the stimuli for release of ADH / vasopressin?
- Increased osmolarity of the blood
2. ANG II
What is the primary system for regulation of water balance?
What about salt balance?
Water balance: ADH / vasopressin
Salt balance: RAAS
What affects NaCl transport across the Macula densa?
Decreased BP → Decreased GFR → Decreased NaCl transport
Increased BP → increased Transport
