Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Systems: Urinary AB > Physiology of Micturition > Flashcards

Physiology of Micturition Flashcards

1
Q

Why is it important to be able to assess renal function?

A

Because it plays a central role in homeostasis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

When is the ability to measure GFR particularly useful?

A
  • In patients with renal disease

- When administering certain drugs

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the total GFR equal to?

A

Sum of all filtration by functioning nephrons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What about the GFR would indicate progression of disease?

A

Reduction in GFR

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

In patients with renal disease, what does progression of the underlying disease process result in?

A

Nephron destruction and decrease in nephron function

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Why may you need to adjust the dose of certain drugs in decreased renal function?

A

Many drugs eg digitalis and many antibiotics are removed from the body by excretion by filtration. When GFR falls, excretion falls so that [drug] in plasma may rise causing toxicity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is used to measure renal function?

A

Plasma clearance tests

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What do plasma clearance tests measure?

A

The ability of the kidney to clear the plasma of various substances

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What does clearance relate to?

A

Clearance relates to a volume of plasma cleared NOT a quantity of substance removed from the plasma

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the calculation for plasma clearance?

A

Plasma clearance is equal to urine concentration of x times the urine flow rate divided by the plasma concentration of x

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the gold standard substance used to calculate plasma clearance?

A

Inulin (polyfructose)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How is inulin used to assess plasma clearance?

A
  • Loading IV dose of inulin
  • Allow time to equilibrate
  • Sample simultaneously plasma and urine (during a timed urine sample)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Why can inulin clearance be used to meaure GFR?

A

Inulin is freely filtered at the glomerulus and neither reabsorbed nor secreted. It is not metabolized by the kidney, nor does it interfere with normal renal function so inulin clearance is a measure of GFR.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What substances will have a lower clearance than inulin?

A

Substances filtered and reabsorbed will have a lower clearance than inulin, because [UX] will be less than if only filtered and [PX] higher. uese

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What substances will have a higher clearance than inulin?

A

Substances filtered and secreted will have a higher clearance than inulin because [UX] will be higher and [PX] lower.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the normal GFR in man?

A

125mls/min

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What does GFR correlated with?

A

Surface area

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

How does GFR differ between men and women?

A

Women have ~10% lower GFR than men even after corrected for surface area

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How much does GFR decline each year?

A

~1ml/min/year after 30 years of age

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Why is inulin no longer used in clinical practice?

A

It is too cumbersome

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is used in clinical practice instead of inulin now?

A

51Cr-EDTA is used instead, a suitable radioactive substance that is handled by the kidney in the same way as inulin.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is routinely used to estimate GFR?

A

Creatinine clearance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is creatinine?

A

Creatinine is endogenous (breakdown produce of muscle creatine

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What do formulae using serum creatinine to estimate GFR take into account?

A

Confounding variables

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
What factors can affect serum creatinine?
- Muscle mass: athletes vs malnutrition - Dietary intake: creatinine supplements vs vegetarians - Drugs: Some lead to spurious increases as does ketoacidosis
26
Why is GFR sometimes expressed as a percentage of normal?
Variability across range of adults, sexes for kidney function and size
27
What is the clearance of glucose?
0
28
Why is the clearance o of glucose 0?
It is normally all reabsorbed
29
Why is the clearance of urea less than that of inulin?
Some urea is reabsorbed
30
What is used to measure renal plasma flow?
The organic anion para-amino-hippuric acid (PAH)
31
How is PAH processed through the kidney?
PAH is freely filtered at the glomerulus and then the PAH remaining in the plasma is actively secreted into the tubule so that > 90% of plasma is cleared of its PAH content in one transit of the kidney.
32
What is renal plasma flow?
The plasma flowing through the kidneys in a given time
33
What is the normal renal flow rate?
~660mls/min
34
Why does penicillin have a greater clearance than inulin?
It is filtered and secreted
35
What is the renal handling of a substance which is freely filtered at the glomerulus and filtration is greater than excretion?
Net absorption of X
36
What is the renal handling of a substance which is freely filtered at the glomerulus and excretion is greater than filtration?
Net secretion of X
37
What is the renal handling of a substance which is freely filtered at the glomerulus and filtration and excretion are the same?
No net reabsorption or secretion
38
What is the renal handling of a substance which is freely filtered at the glomerulus and clearance of X is less than inulin clearance?
Net reabsorption of X
39
What is the renal handling of a substance which is freely filtered at the glomerulus and clearance of X is equal to inulin clearance?
X is neither reabsorbed nor secreted
40
What is the renal handling of a substance which is freely filtered at the glomerulus and clearance of X is greater than inulin clearance?
Net secretion of X
41
How does urine flow from the kidneys to the ureters?
Via peristaltic contraction of the smooth muscle of the ureters
42
How do the ureters enter the bladder?
At an oblique angle to prevent reflux of urine
43
What happens to the composition of urine once it leaves the kidneys?
It does not change
44
What is the bladder?
Bladder is a bag of smooth muscle, arranged in spiral, longitudinal and circular bundles = detrusor muscle
45
What is responsible or emptying the bladder during micturition?
Contraction of the detrusor muscle
46
What is the internal urethral 'sphincter'?
- It is not a true sphincter | - It is where the smooth muscle at the start of the urethra acts as a sphincter when the smooth muscle is relaxed.
47
What is the external urethral sphincter?
A true sphincter, made up of skeletal muscle under voluntary somatic control
48
What is the bladder overlain with?
Peritoneum
49
Where does the bladder lie?
- Lies in the midline posterior to the pubic bones | - Lies anterior to reproductive system and rectum
50
What is the bladder made of?
Smooth muscle (detrusor muscle)
51
What lines the bladder?
Transitional epithelium
52
What are the 3 points of the trigone of the bladder?
- 2 Vesicoureteric openings | - Urethral opening
53
What are the Vesicoureteric openings?
1-2cm oblique passage through muscular wall
54
What will a urethral obstruction result in?
Bilateral renal problems
55
What will ureter obstruction result in?
Unilateral renal problems
56
What is the characteristic shape of the pressure-volume curve of the bladder?
There is a long flat segment as the initial increments of urine enter the bladder and then a sudden sharp rise as the micturition reflex is triggered.
57
What does normal daily urine production vary between?
750ml-2500mls in temperate climates
58
What are the 3 components of motor innervation to the bladder?
- Rich parasympathetic supply (pelvic nerves) - Sparse sympathetic supply (hypogastric nerves) - Somatic motorneurones (pudendal nerves)
59
What affect does the parasympathetic system have on the bladder?
- Increase in parasympathetic activity leads to an increase in contraction of the detrusor muscle - Consequent increased of pressure within the bladder, S2-S4
60
What does cutting the hypogastric nerve result in?
Increased frequency of micturition
61
What role does the sparse sympathetic supply (hypogastric nerve) play in the control of micturition?
-Inhibit bladder contraction and closes the internal urethral “sphincter"
62
What is the main function of the hypogastric nerves?
Main function is to prevent reflux of semen into the bladder during ejaculation L1-L3.
63
What role do the somatic motorneurones (pudendal nerves) play in the control of micturition?
Innervate the skeletal muscle that forms the external urethral sphincter, keeps the sphincter closed, even against strong bladder contractions S2-S4
64
What type of reflex is micturition?
Micturition is basically a spinal reflex which may or may not be influenced by higher centres.
65
What sensory innervation is involved in the control of micturition?
-Stretch receptor afferents from the bladder wall. As the bladder fills there is increased discharge in afferent nerves to the spinal cord via interneruones
66
What occurs as a result of the increased discharge of afferent nerves to the spinal cord via internerones as the bladder fills?
- Excitation of parasympathetic outflow - Inhibition of sympathetic outflow - Inhibition of somatic motoneurones to external sphincter - Pathways to sensory cortex which leads to sensation of fullness
67
What stimulates the stretch receptors in the bladder?
As the bladder, fills it becomes distended and the stretch receptors are increasingly stimulated
68
The stretch receptors output becomes great enough to cause bladder contraction via:
- Stimulation of the parasympathetic systems | - Relax the external sphincter by inhibiting the somatic motonerones
69
What volume of urine is required in the bladder to initiate the spinal reflex in adults?
~300-350mls
70
Who is the local spinal reflex particularly visible in?
- Babies as their higher brain connections have yet to be established - Adults with spinal cord transection after the initial period of spinal shock
71
How is delay of micturition achieved?
It is accomplished by descending pathways from many brain centres, including cortex and brainstem
72
How do the descending pathways delay micturition?
Inhibiting the parasympathetic system -Stimulation of the somatic nerves to the external sphincter thus, over-ridding the input from the bladder stretch receptors
73
Voluntary initiation of micturition involves descending pathways which:
- Stimulate the parasympathetic system | - Inhibit the somatic motor neurones thus summating with the stretch receptor effects
74
What does potty training involve?
The setting up the controlling descending pathways
75
What is one of the main initial events in voluntary urination?
Relaxation of the muscles of the pelvic floor which may cause a sufficient downward tug on the detrusor muscle to initiate its contraction
76
How can urine flow down the urethra be or flow once urination has began be interrupted?
Perineal muscles and external sphincter can be contracted voluntarily
77
How does the female urethra empty after urination?
By gravity
78
How is urine remaining in the male urethra after urination expelled?
Expelled by contractions of the bulbocavernosus muscle.
79
What are the 3 major types abnormalities of micturition due to neural lesions?
- Interruption of afferent nerves - Interruption of both afferent and efferent nerves - Interruption of facilitatory and inhibitory descending pathways from the brain
80
What occurs in all 3 types of abnormalities of micturition due to neural lesions?
The bladder contracts but the contractions are generally insufficient to empty the bladder completely and urine is left in the bladder
81
How can some paraplegic patients train themselves to initiate voiding?
]By pinching or stroking their thighs initiating a mild mass reflex
82
Why does pinching or stroking their thighs sometimes initiate voiding in paraplegic patients?
- After spinal section, afferent stimuli irradiate from one reflex centre to another. - When a relatively minor noxious stimulus is applied to the skin it may irradiate to autonomic centres and evoke bladder or rectal voiding.

Systems: Urinary AB (26 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions