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Kofi: Pure Clinical Sem 3 > Urinary: Introduction/Anatomy > Flashcards

Urinary: Introduction/Anatomy Flashcards

1
Q

Which vertebral level can the kidneys be found?

A

T11/T12

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2
Q

What is the purpose of the bladder?

A

Storage of urine that empties periodically via the urethra

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3
Q

What are body fluid compartments?

A

42L of water split into:

  • 28L of intracellular fluid
  • 14L of extracellular fluid.

14L of extracellular fluid split into:

  • 11L of interstitial fluid
  • 3L of intravascular fluid
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4
Q

What is the purpose of the kidney?

A
  • Maintenance of a stable environment to enable function in all parts of the body
  • Regulation by controlling the concentrations of key substance in extracellular fluid
  • Excretion of waste products
  • Endocrine via synthesis of renin, erythropoietin, prostaglandins
  • Metabolism though the formation of the active form of vitamin D, catabolism of insulin, PTH and calcitonin
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5
Q

How is kidney function measured?

A

Glomerular filtration rate

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6
Q

What is the GFR?

A

Amount of filtrate that is produced from blood flow per unit time

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7
Q

How does advancing age affect the glomerular filtration rate?

A
  • Declines after 30 years of age
  • Rate of decline is 6-7mls/min per decade
  • Loss of functioning nephrons
  • Some compensatory hypertrophy
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8
Q

What is compensatory hypertrophy?

A
  • If the nephron number decreases
  • Exisiting nephrons get bigger
  • Healthy kidney can also get bigger
  • Occurs to much greater extent in childhood
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9
Q

What are the risks associated with compensatory hypertrophy?

A
  • Nephrons have to work harder
  • Greater risk of wearing out
  • Cortical scarring
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10
Q

What happens to the kidneys and their function in pregnancy?

A
  • GFR increases
  • Kidney size increases due to increased fluid volume
  • Nephrons number stays the same
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11
Q

What does a decline in GFR show?

A
  • Decline in the number of nephrons
  • Decline of GFR within individual nephrons

Overall the kidney function has worsened

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12
Q

A patient arrives with significant kidney damage. Their GFR has been stable but recently has decreased. Upon examination, you notice there is kidney hypertrophy. What does this tell you about the kidney function?

A

The kidney function has declined slowly so GFR didn’t fall until there was significant kidney damage

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13
Q

Why do we need a surrogate marker?

A

The actual GFR cannot be measured

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14
Q

What is the formula for clearance?

from the body

A

C=A/P

C= clearance
A= amount of substance eliminated from plasma
P= plasma concentration of substrate
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15
Q

What is the formula for Renal clearance?

A

C=(UxV)/Pa

C= clearance
U= amount in urine
V= urine flow rate
Pa= arterial plasma concentration
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16
Q

What is clearance?

A

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

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17
Q

What are the properties of substances used to measure GFR?

A
  • Produced at a constant rate
  • Be freely filtered across the glomerulus
  • Not be reabsorbed in the nephron
  • Not be secreted into the nephron
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18
Q

Why isn’t inulin used to measure GFR?

A
  • Requires a continuous IV to maintain a steady state

- Requires catheter and timed urine collections

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19
Q

When is 51 Cr-EDTA used clinically?

A
  • In children
  • Where indication renal function is required

Approximately 10% lower clearance than inulin. Radioactively labelled and cleared by renal filtration

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20
Q

What is creatinine?

A

-Endogenous substance that is an end product of muscle breakdown

21
Q

What are the properties of creatine in regards to being an indicator of clearance?

A
  • Produced at a constant rate
  • Freely filtered across the membrane
  • Not reabsorbed along the nephron
  • However it is secreted into the nephron
22
Q

How is creatinine clearance measured?

A
  • Urine is collected over 24 hours

- The serum creatinine is measured

23
Q

What are the issues associated with using creatinine as a measurement of clearance?

A
  • Cumbersome and frequently inaccurate

- Overestimates GFR by 10-20% due to creatinine secretion

24
Q

Which population is creatinine best for in terms of indicators of clearance?

A

-Pregnant women

25
Q

What factors lead to increased creatinine measurement?

A
  • Muscle cell break down
  • Large muscle bulk
  • Black
  • Male
  • Creatinine supplements
  • Certain drugs
26
Q

What factors lead to reduced serum creatinine?

A
  • Reduced muscle mass
  • Old
  • Hispanic/Indo-asian
  • Female
  • Vegetarian
27
Q

What is the eGFR?

A

A ‘best guess’ of the GFR which uses models to try and better estimate the GFR from serum creatinine levels. It is not the same as GFR.

28
Q

What are the variable for the equation for the MDRD eGFR based on?

A
  • Serum creatinine
  • Age
  • Sex
  • Caucasian or Black
29
Q

When is MDRD eGFR inaccurate?

A
  • People without kidney disease
  • Children
  • Pregnancy
  • Old age
  • Other ethnicities
  • Amputees
  • People with significantly reduced muscle mass
  • Patient with higher levels of kidney function
30
Q

Why is there a risk of patient being labelled as CKD due to the MDRD eGFR?

A

There is an underestimation of the true GFR when the serum creatinine is close or within normal range

31
Q

Why is eGFR less accurate with mild kidney disease?

A
  • Reduction in GFR causes increase in blood flow
  • Reduced nephron number lead to nephron hypertrophy so no change in GFR
  • Reduced filtration of creatinine results in increased serum creatinine and increased secretion into the tubule
32
Q

What is the sequence of arteries from the renal artery?

A

Renal artery > Segmental artery > Interlobar artery > Arcuate artery > Interlobular Artery

33
Q

What are the 2 types of nephrons found in the kidney?

A
  • Cortical nephrons

- Juxtamedullary nephrons

34
Q

What are the features of the cortical nephrons?

A
  • Short loop of henle which just enters the medulla
  • Peritubular capillaries covering most of the nephron
  • Rich sympathetic innervation
  • High concentration of renin
  • In the outer part of the cortex
  • Small glomerulus
35
Q

What are the features of the juxtamedullary nephrons?

A
  • Glomerulus sits juxtaposed to the medullary boundary
  • Loop of henle is very long and penetrates deep into medullary tissue
  • Vasa recta runs in parallel to the loop of henle.
  • Poor sympathetic innervation
  • Almost no renin
  • Glomerulus is large
36
Q

What is renal plasma flow and blood flow?

A

Renal blood flow = About 1.1 L/min

Plasma flow = (1-haemotocrit) X renal blood flow

37
Q

What is the renal corpuscle and function of the renal corpuscle?

A

The glomerulus + bowman’s capsule

To produce ultra filtrate of plasma

38
Q

What produces the filtration barrier in the renal corpuscle?

A
  1. Capillary endothelium - permeable. Water, salts, glucose. Filtrate moves between cells
  2. Visceral layer of Bowman’s capsule - Acellllar gelatinous later of collagen/glycoproteins which is permeable to small proteins. Glyocproteins repel protein movement
  3. Podocyte layer - Pseudopodia interdigitate froms filtration slits
39
Q

Which molecules cannot cross the filtration barrier?

A

Cells and large proteins

40
Q

What is the effect as a result of the negative charge on the filtration barrier being lost?

A

-Proteins are more readily filtered and result in a condition called proteinuria

41
Q

What is the myogenic mechanism?

A
  • Arterial smooth muscle response to decrease and increase in vascular tension
  • Contribute to total auto-regulatory mechanism
  • Occurs rapidly
  • Property predominantly of the preglomerular resistance vessels
42
Q

Why do we need Autoregulation of GFR?

A

Feedback mechanism intrinsic to the kidney to keep RBF and GFR constant. Without this a slight change in the blood pressure would cause a significant change in the GFR

Two mechanism

  • Myogenic reflex
  • Tubuloglomerular feedback
43
Q

What is the myogenic response to an increase in blood pressure?

A

-Constriction of the afferent arteriole predomantly or dilation of the efferent arteriole to decrease the blood volume arriving to be filtered. This keep the GFR unchanged

44
Q

What is the myogenic response to a decrease in blood pressure?

A

-Dilation of the afferent arteriole predominantly or constriction of the efferent arteriole in order to increase the blood volume arriving to be filtered. This keep the GFR unchanged.

45
Q

How does the Tubular glomerular feedback mechanism work?

A
  • Links the sodium and chloride concentration at the macula densa with control of renal arteriole resistance (efferent and afferent)
  • Acts in response to acute deviation in the delivery of fluid and solutes to the JGA.
  • Control the distal solute delivery and hence tubular reabsorption
46
Q

What is the action of the Tubular goloemrular feedback when the arterial pressure increases?

A
  • Increase in renal plasma flow and increase in GFR leads to increase in NACl
  • Macula densa cells detects NaCl via a concentration-dependant salt uptake through the NaKCC co-transporter and responds to changes in NaCL arriving in the distal convoluted tubule
  • Juxtaglomerular apparatus is stimulated to release adenosine which constricts the afferent arteriole by stimulating the Alpha 1 receptors. The efferent arteriole is dilated by stimulation of the Alpha 2 receptors
  • This reduces the GFR
47
Q

When is the sympathetic innerveation of the renal vessels most active?

A

During haemorrhage, ischamia or the fight or flight response.

Vasoconstriction occurs in order to conserve blood volume and can cause a fall in GFR

48
Q

How does the parasympathetic nervous system act on the blood vessels?

A

Release of nitrous oxide for endothelial cells and vasodilation

49
Q

What is the glomerulotubular balance?

A

It blunts the sodium excretion in response to any GFR changes which occur do occur despite the Myogenic
and TG feedback response.

Kofi: Pure Clinical Sem 3 (44 decks)

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