L2 RBF and GFR

Question 1

Characteristics of RBF

Answer 1

Kidneys receive 1/4th of CO
High flow not needed for metabolism
Needed to support filtration (20% of plasma is filtered)

180L of filtrate formed per day

Entire plasma volume filtered 65 times per day
If everything filtered lost, would lose entire plasma volume in <30min
Must reabsorb a lot

Question 2

Vasoconstrictors

Answer 2

Sympathetic nerves:
Vasoconstriction via alpha1 receptors
decrease RBF & GFR

Angiotensin II, ADH, ATP, endothelin- decrease RBF & GFR

AT II- constricts both afferent and efferent arterioles but efferent is more sensitive at lower concentrations of AT II- increase GFR and decrease RBF

Question 3

Vasodilators

Answer 3

Atrial natriuretic peptide (ANP), glucocorticoids, NO, prostaglandins (PGE2, PGI2)

Increase RBF & GFR

Question 4

Autoregulation of RBF and GFR

Answer 4

Constant blood flow and GFR through a range of arterial pressures

Pressure range 80-180mmHg

During severe blood loss, decreased RBF and GFR will occur due to hypotension

If arterial pressure > 180 both RBF and GFR will increase proportionally

Question 5

Two mechanisms of autoregulation

Answer 5

Myogenic mechanism

Tubuloglomerular feedback (flow-dependent)

Question 6

Myogenic mechanism

Answer 6

Intrinsic to VSMC

Contract in response to stretch

Question 7

Tubuloglomerular feedback

Answer 7

Flow dependent

Increasing GFR increases NaCl delivery to LOH

sensed by the macula densa which causes resistance of the afferent arteriole (RA) to increase thereby decreasing RBF & GFR

defends RBF & GFR by changing resistance of afferent arteriole

Maintains constancy of salt load delivered to distal tubule

Signal unidentified, may be thromboxane, ATP, or adenosine

Question 8

Nature of filtrate

Answer 8

Protein does not normally pass the filter in significant quantities

All small MW solutes that are not protein bound appear in the filtrate in the same concentrations as in blood plasma

Fluid in bowmans capsule is essentially a protein free filtrate of blood plasma

Question 9

Route of filtrate

Answer 9

Fenestrae, basal lamina, filtration slits between pedicels of podocytes

Filtration slits bridged by diaphragms

Substances separated by size (7000 easy, 70000no) and electrical charge (basal lamina and slits coated with - charges) proteins usually have a - charge and are repelled

Basal lamina and filtration slits are main barriers to proteins

Question 10

Permeability based on charge

Answer 10

Polycation will filter more readily than neutral (control) and polyanion

Filter ability decreases with size

Question 11

Capillary filtration coefficient

Kf

Answer 11

Filtration rate (ml/min/mmHg) produced by each mmHg of net filtration pressure

Glomerular capillary Kf May be 7-15

Kf for glomerular capillaries is 50-100 greater than capillaries in muscle or skin

Can be altered by mesangial cell (all reduces Kf)

Use to calc GFR

Question 12

Net filtration pressure

NFP

Answer 12

PGC- blood pressure in glomerular capillary- driving force for GFR

PBC- back pressure in Bowmans capsule, reduces GFR

OncoticGC- oncotic pressure of glomerular capillary blood, due to proteins unable to cross barrier, retards GFR, increases as plasma diverted into BC

Question 13

P GC

Answer 13

Blood pressure in glomerular capillary

Driving force for GFR

Remains constant at afferent and efferent arteriole ends because outlet is an arteriole and arterioles are resistance vessels

Question 14

P BC

Answer 14

Back pressure in bowmans capsule

Reduces GFR

Question 15

Oncotic GC

Answer 15

Oncotic pressure of glomerular capillary blood

Due to protein unable to cross barrier

Retards GFR

Increases as plasma diverted into BC

Increases from afferent to efferent arteriole end because moving fluid but proteins don’t move, they’re confined to inter vascular space

Question 16

Increase P GC

Answer 16

Increase GFR

Question 17

Decrease P GC

Answer 17

Decrease GFR

Question 18

NSAIDs block effects of prostaglandins

Answer 18

PGE2 and PGI2 produces locally in kidney in response to SNS stimulation of vascular smooth muscle in afferent arteriole and high levels of circulating AT II

both vasodilate the afferent arteriole reducing vasoconstriction production by SNS stimulation to maintain blood flow

NSAIDs inhibit synthesis of prostaglandins
Which inhibit activity of COX 1 and 2 and interfere with the protective effects of prostaglandins on RBF