Renal physiology

Question 1

What is the function of the kidney ? (8)

Answer 1

• makes urine
• excretes waste
• electrolyte balance
• extracellular fluid vol
• BP (renin)
• gluconeogenesis
• RBC numbers (EPO)
• plasma Ca2+ (PTH target organ)

Question 2

kidneys:
- where are the located ?
- what is the blood supply ?
- what is the functional unit ?

Answer 2

• retroperitoneal organ
• blood supply from the renal artery (direct form aorta)
• nephron is the functional unit

Question 3

what % of the CO do the kidneys receive ?

Answer 3

20%

Question 4

what is auto regulation in regards to the kidney ?

Answer 4

pressure changes (auto regulation) controlled by afferent + efferent arteriolar resistance - prevents glomerular pressure increase when arterial pressure increases
- over varying MAP, GFR remains quite steady (important because large volumes)

Question 5

how much urine is produced per day

Answer 5

1-1.5 L

Question 6

what are the ureters ?
located where ?

Answer 6

parked muscle tubes
- retroperitoneal
- curve down obliquely towards bladder (makes sphincter)
- urine moves along ureter by peristalsis

Question 7

describe the vague anatomy of the bladder ? what is the capacity ?

Answer 7

muscular bag, reggae stretch out as bladder fills
- 99% time storage
- Capacity: 400-500ml (should be 0ml post-void)

Question 8

why are women more prone to incontinence ?

Answer 8

muscle at bladder neck is v weak so rely on pelvic floor = external urethral sphincter (both voluntary)

Question 9

what happens as bladder fills ? describe detrosrs and sphincter changes
- PSNS or SNS ?

Answer 9

as bladder fills => detrusor relax (sym T11-L2), external urethral sphincter close (prudential S2-S4)
- bladder stretch => inhibit para, Sam stimulated, somatic => external contraction

Question 10

what is receptive relaxation in terms of the bladder

Answer 10

detrusor relax
- allow increase in vol without increase in pressure

Question 11

what happens when bladder at max stretch and time to void ? describe detrusor and sphincters

Answer 11

increased signals from detrusor indicate time to void
- detrusor contract (para) + external sphincter relax (pudendal inhibition)

Question 12

describe the PSNS involvement in micturition ? what nerve roots

Answer 12

para (cholinergic) S3-5: depressor contraction, smooth muscle sphincter relaxation

Question 13

describe the SNS involvement in micturition ? what nerve roots

Answer 13

sympathetic (NAd) T10-12: inhibit detrusor contraction (allows receptive relaxation), smooth muscle sphincter contraction

Question 14

describe the somatic involvement in micturition ?

Answer 14

striated external sphincter contraction/relaxation

Question 15

what happens when the macular dense cells detect low NaCl ?

Answer 15

increased NaCl absorption at PCT => low NaCl detected at macula dense => dilation of afferent arteriole => increase hydrostatic pressure => restore GFR

Question 16

increased NaCl reabsorption at PCT. How is GFR restored ?

Answer 16

• dilation of afferent arteriole
• renin release (efferent arteriole vasoconstriction)

Question 17

where is renin released from ? in response to what ? what does this cause ?

Answer 17

macula dense cells detect decrease in sodium delivery to distal convoluted tubule => renin please from juxtaglomerular cells => angiotensin II => efferent vasoconstriction => increase hydrostatic pressure = restore GFR
- released in response to low Na, reduced renal perfusion, SNS

Question 18

what is creatinine ? what is the clearance ratio ?

Answer 18

creatine is a waste product of metabolism => usually all excreted (1:1 between production + excretion) so an increase suggests renal impairment

Question 19

what factors can lead to a reduction in GFR ?

Answer 19

• damage to filtration membrane (HTN, diabetes)
• increase BCP (kidney stone)

Question 20

what is the glomerulus ? function ?

Answer 20

it is a loop of capillaries in ball shape surrounded by Bowmans capsule
- site of ultrafiltration

Question 21

what 3 layers does the filtration barrier of the glomerulus have ? describe a bit ?

Answer 21

• endothelial cells:have many fenestrations (prevent filtration of RBC)
• glomerular basement membrane: limit filtration of intermediate-large sized solutes
• podocytes (Bowmans capsule epithelial cells)

Question 22

where is ACE predominantly produced ?

Answer 22

produced by vascular endothelial cells in the lungs

Question 23

what does angiotensin II act on ? to cause release of what form where ?

Answer 23

acts on the adrenal cortex => stimulates release of aldosterone (mineralocorticoid - steroid hormone released from zona glomerulosa)

Question 24

what electrolyte changes does aldosterone cause ?

Answer 24

• increase serum Na2+
• decrease serum K+

Question 25

what inhibits renin release ?

Answer 25

ANP

Question 26

describe kidney anatomy from out to in ?

Answer 26

cortex => medulla => pyramids + columns => major + minor calyx => renal pelvis => pelvicureteric junction => ureter

Question 27

causes of haematuria ? (13)

Answer 27

• renal (cancer, glomerulonephritis, trauma, HSP)
• stones
• bladder (cancer, cystitis)
• prostate (cancer, prostatitis, BPH)
• vagina (menstruation)
• drugs (rifampin, beetroot)

Question 28

what investigations for patient presenting with haematuria ?

Answer 28

all patients with haematuria need: full set of blood, US or CT, + flexible cystoscopy

Question 29

common causes of voiding LUTS ? (4)

Answer 29

• BPH
• prostate Cx
• urethral stricture
• phimosis

Question 30

common causes of storage LUTS ?

Answer 30

• overactive active bladder
• cystitis