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Urinary > Session 2 - Measurement of Kidney Function > Flashcards

Session 2 - Measurement of Kidney Function Flashcards

1
Q

What are some of the main functions of the kidney?

A 
Control of:
BP
Blood volume
pH
Electrolytes
Osmolality

Excretion - waste, drugs
Metabolism - Drugs, hormones, proteins
Endocrine - 1-alpha calcidiol, renin, erythropoetin

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2
Q

How is kidney function measured?

A

Glomerular filtration rate GFR

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3
Q

What is a normal GFR range?

A

90-120 mL/min/1.73 meters squared.

(women - lower end, men - higher end)

Normal total glomerular filtrate per day:
140-180 L/day

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4
Q

Which factors can affect the value of GFR?

A 
Gender
Age
Size of individual
Size of kidneys
Pregnancy
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5
Q

How does GFR change from birth to old age?

A

After birth - low (20ml/min/1.73m^2)
Normal by 18 months.

Decline after 30 years.
by 6-7 ml/min per decade.

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6
Q

What is compensatory hypertrophy?

A

Existing nephrons (thus kidney) get bigger, due to reduced number of nephrons.

Occurs much greater extent in childhood.
Also in old age nephron loss.

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7
Q

When may someone develop compensatory hypertrophy?

A

During pregnancy.

Failure/ reduced function of other kidney. (e.g. atrophy due to poor blood supply).

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8
Q

How much do kidneys increase in size in pregnancy? When do they go back to normal size?

A

1cm increase.
Due to increased fluid volume.
6 months post-partum - back to pre-pregnancy levels.

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9
Q

Why may GFR not always be the best indicator of kidney health?

A

GFR may not fall until significant kidney damage has occured, as individual nephrons can hypertrophy and compensate.

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10
Q

What is ‘clearance’?

A

The volume of plasma cleared of a substance per unit of time where the substance is denoted as ‘X’

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11
Q

What is the formula for clearance? Is it useful in reality?

A

Cx = Ax / Px

Cx = Clearance
Ax = Amount of substance eliminated from plasma
Px = Plasma concentration of substrate

Clearance is an imaginary concept

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12
Q

What is the formula for renal clearance?

A

Cx = Ux (amount of urine) x V (urine flow rate)
——————————————————-
Pa (arterial plasma conc)

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13
Q

How can GFR be worked out clinically?

A 
Inulin clearance
Inulin is produced at constant rate.
Freely filtered across glomerulus.
Not reabsorbed in nephron.
Not secreted into nephron.

51 Cr-EDTA (radioactive labelled marker)
Exclusive renal clearance.
(used in children/ transplant work up)
10% lower clearance than inulin)

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14
Q

Why is inulin not used in reality to work out GFR?

A

Requires constant IV drip to maintain steady state.

Requires catheter and times urine collections.

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15
Q

How is creatinine used to measure GFR? Why is it not as accurate?

A
  • Creatinine is endogenous.
  • End product of muscle breakdown.
    It is freely filtered across nephron, and not reabsorbed, but IS secreted.

24hr urine collection, serum creatinine measured.
(Overestimate by 10-20% due to secretion!)

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16
Q

What units are serum creatinine values measured in?

A

Mmol/L (micro moles per liter)

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17
Q

Which factors affect serum creatinine in individuals?

A

Muscle mass
Gender (< in male)
Race (< in black, > in hispanic etc)
Vegetarian

Intake of protein.
Muscle metabolism.
Extra-renal excretion.
Renal excretion.

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18
Q

Why is the patients plasma creatinine a lower level than the GFR?

A

Some creatinine is secreted into the tubule, so more creatinine is lost than in GFR alone, so the GFR is slightly higher, and creatinine lower on the graph than you would expect.

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19
Q

What is the relationship between serum creatinine and GFR?

A

Overall would assume as GFR decreases, serum creatinine increases. There is a relationship, but some people with normal serum creatinine can have a significantly reduced GFR.
eGFR - estimated from different factors.

20
Q

How is eGFR estimated? Who can it be used on?

A

4 variable questions:
1) Serum creatinine
2) Age
3) Sex
4) Caucasion or black
Standardised to body surface area of 1.73m^2.
Only really useful in people with chronic kidney disease.

21
Q

For which groups would eGFR be inaccurate?

A
  • People without CKD
  • Children
  • Pregnancy
  • Old age
  • Other ethnicities
  • Amputees
  • Patients with higher levels of kidney function
22
Q

Which factors can mean eGFR is unreliable?

A
  • Underestimates true GFR when serum creatinine is close or within normal range.
  • Risk of patients being labelled as having CKD.
  • eGFR is taken from serum creatinine, and not all changes in serum creatinine are DUE to GFR!
23
Q

Why is eGFR less accurate with mild kidney disease?

A

1) Reduction in GFR (e.g. if glomerular surface area reduced), causes increased blood flow.
2) Reduced nephron number leads to nephron hypertrophy, so no change in GFR.
3) Reduced filtration of creatinine, results in increased serum creatinine, and increased SECRETION into tubule. Maintaining a relatively steady state.

24
Q

Which part of the mesoderm will differentiate and form the parts of the urogenital system?

A

The intermediate mesoderm.

25
Q

Generally, how do the kidneys form in the embryo?

A

3 systems develop in a cascade (as on forms, the last disappears)

  • Pronephros
  • Mesonephros
  • Metanephros
26
Q

Where does the pronephros initially appear? What is it?

A

Appears briefly in cervical region.

Some kidney characteristics, but has no function in embryo, and disappears very fast.

27
Q

Why is the pronephros important to the mesonephros?

A

Pronephros creates a duct which extends from cervical region, down to the cloaca. This duct drives the development of the mesonephros. (in the pelvic region)

28
Q

What is the urogenital ridge?

A

A region of intermediate mesoderm giving rise to both the embryonic kidney and the gonad.

29
Q

How does the mesonephros develop? What are its characteristics?

A
  • Mesonephric tubules develop caudal to the pronephric region.
  • Mesonephric tubules PLUS duct = the embryonic kidney!
  • There is no water conserving function.
30
Q

How does the mesonephric duct affect development?

A

Role in male reproductive system.

Mesonephric duct sprouts the Uteric bud.

31
Q

What is the importance of the uteric bud?

A

It induces development of the definitive kidney.

32
Q

What is the uteric bud?

A

Undifferentiated intermediate mesoderm, caudal to mesonephros.

33
Q

What is a calyx?

A

Name of the parts of the lumen of the kidney.

Minor calices drain into major calices, this empties into the renal pelvis. > into ureters.

34
Q

Which two structures are the precursors to the kidney?

A
  • Uteric Bud

- Metanephric Blastema (primitive clump of cells)

35
Q

How does the definitive kidney begin to form?

A
  • Uteric bud and metanephric blastema interact.
  • Bud expands + brances
  • Formes minor and major calyces, renal pelvis, and ureter.
36
Q

Which part of the kidneys are formed from which tissues in the embryo?

A
  • Collecting system from the uteric bud itself.

- Excretory component derived from intermediate mesoderm, under influence of uteric bud.

37
Q

Where does the metanephric kidney first appear?

A

In the caudal, (pelvic) region of the embryo.

38
Q

How do the kidneys end up in their normal anatomical position during development?

A

An apparent ascent upwards of the kidneys.

Partly a shift, but also due to elongation of the trunk.

39
Q

How does the kidney’s blood supply during ascent change?

A

New branches from the aorta are formed as the kidneys migrate. As new branches are formed, the old one apoptose and disappear.
Until > kidneys in final position (renal arteries)

40
Q

What happens to the position of the gonad as the kidneys ‘ascend’?

A

As kidney’s ascend, the gonad decends.

41
Q

What is renal agenesis?

A

When kidney fails to develop (no interaction of uteric bud with intermediate mesoderm).

42
Q

What is a horseshoe kidney? What causes it?

A

Kidneys fuse, overly the aorta.

- Inferior aspects touch and fuse during development.

43
Q

What are duplication defects?

A

Defects where more than one of a structure is formed, e.g. two ureters from one kidney.

44
Q

What is an ectopic ureteral orifice?

A

When a ureter goes to the wrong place (not bladder).
- e.g. ureteral opening into vagina, into the urethra.
(incontinence)

45
Q

What is the urogenital sinus? How is it formed?

A
  • A structure which gives rise to the bladder and urethra.
    (And many other structures in males and females, e.g. prostate, vagina etc)
  • Formed from separation of the urorectal septum into two parts, divides cloaca.
    (anterior - urogenital sinus, posterior - GI tract)
46
Q

Describe the structure of the urogenital sinus?

A
  • Superior part connects to umbilicus
  • Majority differentiates to form urinary bladder
  • Inferior part develops into the urethra
47
Q

What is hypospadias?

A

Defect in fusion of urethral folds in male.
(could have penis malformation)
Urethral opening onto ventral surface rather than at the end of the glans.

Urinary (7 decks)

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