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SGUL - Physiology 1 > Micturition > Flashcards

Micturition Flashcards

1
Q

What is micturition?

A

Urination

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2
Q

What three stages are involved in micturition?

A
  • urine made in the kidneys
  • urine stored in the bladder
  • urine released from the bladder
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3
Q

Describe the basic process of micturition. PART 1

A
  • Urine passes from the collecting ducts of the renal tubules into the renal pelvis.
  • Contraction of the smooth muscle of the pelvis aids in the movement of the urine into the ureter.
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4
Q

Describe the basic process of micturition. PART 2

A
  • As the ureter gets distended, the smooth muscle which is arranged circularly contracts.
  • Contraction closes the junction between the pelvis and the ureter, and pushes urine further into the ureter, causing distension and further contraction.
  • Peristaltic wave is initiated and propagated along the length of the ureter until it propels urine into the bladder.
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5
Q

Describe the basic process of micturition. PART 3

A
  • Ureters open at an oblique angle to the wall of the bladder.
  • When the pressure within the bladder rises, the ureters are compressed, preventing the reflux of urine back up into the ureters.
  • Ureteric peristalsis is myogenic in origin, i.e. originating in the smooth muscle.
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6
Q

Describe the renal pelvis.

A

Funnel-like dilated proximal part of the ureter

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7
Q

What is not required for micturition? Explain how you know.

A

Neural control by the CNS is not needed.
- Ureters seem to function normally when their extrinsic nerves are cut

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8
Q

What is required for control of micturition?

A
  • Coordination of peristaltic waves
  • Response to changes in volume of urine produced by the kidney.
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9
Q

Describe kidney stones (renal calculi) and how they develop.

A
  • Common disorder of the urinary tract
  • Develop from crystals that separate from the urine within the urinary tract.
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10
Q

What does urine contain to prevent kidney stone formation?

A

Citrate inhibitors

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11
Q

Outline the composition of kidney stones.

A
  • Calcium usually as calcium oxalate as calcium phosphate.
  • Uric acid
  • Struvite and cystine.
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12
Q

Why are kidney stones more common in men than women?

A

Difference in levels of testosterone

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13
Q

What can kidney stones be caused by?

A
  • Poor urine output/ obstruction
  • Low concentration of inhibitors
  • Infection
  • Excess dietary intake of stone-forming substances.
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14
Q

What are the symptoms of kidney stones?

A
  • dysuria (painful urination)
  • haematuria
  • urinary tract obstruction
  • if the stone approaches the tip of the urethra, pain can inhibit micturition (strangury)
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15
Q

Describe the mucosal lining of the bladder.

A
  • Transitional epithelium - capable of stretching without damage.
  • Consists of ridges that flatten out the bladder as it fills.
  • Impermeable to salts and water - no exchange between the urine and the capillaries of the bladder wall.
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16
Q

Describe the muscle coat lining the epithelium of the bladder.

A
  • Made up of bundles of smooth muscle interlacing and running in various directions.
  • Considered as a single structure known as the detrusor muscle.
  • Mucosal layer is generally loosely attached to the underlying muscle except at the base of the bladder
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17
Q

Describe the trigone.

A
  • Where entrance of the 2 ureters and the exit of the urethra form a triangle.
  • Where the mucosa is firmly attached, making it the thickest and least distensible part of the bladder.
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18
Q

What is the outlet of the bladder into the urethra guided by?

A

Internal and external sphincter

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19
Q

Describe the internal sphincter.

A
  • Formed by a loop of muscle that is an extension of the detrusor
  • Not under voluntary control.
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20
Q

How does the internal sphincter open?

A
  • When detrusor contracts, fibres forming loop shorten and open sphincter.
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21
Q

Describe the external sphincter.

A
  • Composed of skeletal muscle and is continuous with the levator ani.
  • 2 striated muscles, the compressor urethrae and the bulbocavernosus.
  • Muscles surround the urethra - responsible for continence, so under conscious, voluntary control.
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22
Q

What is the levator ani?

A

Muscle situated on either side of the pelvis

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23
Q

What is the difference between female and male sphincters? Explain why there is a difference.

A
  • Females require both sphincters for effective continence
  • Males can manage with either sphincter intact
  • REASON: different anatomical arrangement of urethra.
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24
Q

Describe the differences between a male and female urethra.

A
  • Female urethra only carries urine
  • Male urethra needed for the ejaculation of semen during reproduction.
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25
Q

Describe the anatomical differences between a male and female bladder. PART 1

A

IN WOMEN:
- Structures around the neck of the bladder are the end of the system and point of exit of urine from the body.
- External sphincter is poorly developed
- More prone to incontinence, particularly after childbirth

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26
Q

Describe the anatomical differences between a male and female bladder. PART 2

A

IN MEN:
Urethra continues through the penis - urine remaining in the urethra can be expelled by contractions of the bulbocavernosus muscles.

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27
Q

What is the effect of men and women having anatomical differences?

A

Develop different pathologies and diseases

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28
Q

Describe bladder innervation.

A
  • Neural circuits of the brain and spinal cord coordinate smooth muscle activity in the bladder and urethra.
  • Circuits act as switches to alternate the urinary tract between the two modes of operation: storage and elimination.
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29
Q

What is the effect of neurological damage on micturition?

A
  • Disrupt the voluntary control of micturition
  • Re-emergence of reflex micturition
  • Bladder hyperactivity and urge incontinence
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30
Q

What three types of peripheral nerves is the lower urinary tract innervated by?

A
  • Somatic nerves
  • Sympathetic nerves
  • Parasympathetic nerves
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31
Q

What are the two types of bladder innervation?

A

SENSORY
MOTOR

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32
Q

What is the effect of sensory innervation?

A

Causes sensation (awareness) of fullness, and also pain from disease

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33
Q

What is the effect of motor innervation?

A
  • Contraction and relaxation of the detrusor muscle and the external sphincter
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34
Q

Describe the nature of parasympathetic fibres on the bladder.

A
  • Arises in the ventral horn at the sacral region (S2-S4) of the spinal cord
  • Preganglionic fibres synapse onto postganglionic fibres on the wall of the bladder and internal sphincter.
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35
Q

Describe the nature of sympathetic fibres on the bladder.

A
  • Arises in the lateral horn at the lumbar region (T11-L2) of the spinal cord.
  • Preganglionic fibres synapse onto the postganglionic neurones in the hypogastric ganglia.
  • Few neurons end in the detrusor muscle; more are found in the trigone area.
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36
Q

What effects do some of the postganglionic sympathetic fibres have on the bladder?

A
  • Some supply the internal sphincter
  • Others innervate with the parasympathetic ganglia in the bladder wall (inhibiting parasympathetic transmission).
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37
Q

Describe the nature of somatic fibres on the bladder.

A
  • Arises from the sacral region of the spinal cord
  • Supply the striated muscle of the external sphincter.
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38
Q

Describe the parasympathetic innervation of the detrusor muscle.

A
  • Main transmitter is acetylcholine, but also releases ATP.
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39
Q

What is atropine and what effect does it have?

A
  • Muscarinic agonist
  • Inhibits detrusor contraction.
40
Q

Describe sympathetic innervation of the detrusor muscle.

A
  • Transmitter is noradrenaline - acts on α-receptors to inhibit transmission at the parasympathetic ganglion.
  • Relaxation of the bladder body is caused by direct release of noradrenaline acting on β-receptors (usually in the trigone).
41
Q

Describe the parasympathetic innervation of the sphincters.

A
  • Release nitric oxide to act on muscarinic receptors
  • Relaxes the internal sphincter.
42
Q

Describe the sympathetic innervation of the sphincters.

A
  • Release noradrenaline to act on the α1-receptors
  • Contracts the internal sphincter.
43
Q

Describe somatic innervation of the sphincters.

A
  • Release acetylcholine, which acts on nicotinic receptors
  • Holds the external sphincter closed with tonic (continual) activity,
44
Q

Describe the sensory innervation of the bladder.

A
  • Pelvic, hypogastric and pudendal nerves contain afferent axons that transmit information from the lower urinary tract to the lumbosacral spinal cord.
45
Q

Describe the afferent pathway through the pelvic nerve.

A
  • Small myelinated Aδ–fibres, which cause a micturition reflex
  • Stretch receptors to signal wall tension
  • Volume receptors to signal bladder filling
  • Pathway is parasympathetic
46
Q

What are the effect of the unmyelinated C fibres?

A

Have nociceptors for pain (eg. during infection of the bladder lining, such as cystitis, excessive distension) at epithelium

47
Q

Compare and contrast the hypogastric and pudendal nerves.

A
  • Hypogastric is sympathetic but pudendal is somatic pathways.
  • Both involve nociceptors and flow receptors (on the external sphincter).
48
Q

With afferent (sensory) nerves, what is the difference between A and C fibres?

A

A FIBRES: sense tension in the detrusor:
- filling of the bladder
- detrusor contraction
- bladder fullness, discomfort
C FIBRES: respond to damage and inflammatory mediators.
- PAIN as an urgent desire to micturate

49
Q

Describe the changes in the bladder nerve stimulation when it’s being filled. PART 1

A
  • Initially, the bladder is empty. Bladder pressure is low.
  • Sphincters are closed (due to the tonic activity from the sympathetic and somatic nerves).
50
Q

Describe the changes in the bladder nerve stimulation when its being filled. PART 2

A
  • Detrusor muscle begins to relax progressively (as the sympathetic activity is inhibiting the parasympathetic transmission).
  • Little increase in pressure
  • Sphincters are still closed.
51
Q

What is receptive relaxation?

A

Phenomenon of a hollow organ relaxing as it fills

52
Q

How do we feel the bladder filling and its pressure?

A
  • Initially become conscious of the bladder filling when there’s 100-150 ml of urine in the bladder.
  • Above this volume, the sensation becomes more distinct till discomfort begins between 300-400 ml.
  • Further distension beyond this causes mounting distress.
53
Q

Describe the changes in the bladder nerve activity during the micturition (emptying) reflex. PART 1

A
  • Receptors detect tension in the bladder wall
  • Afferent activity is excited
  • Triggers activity in the parasympathetic efferents which supply the detrusor and internal sphincter by the spinal reflex arc.
  • Detrusor muscle contracts due to acetylcholine, and it is reinforced by ATP.
54
Q

Describe the changes in the bladder nerve activity during the micturition (emptying) reflex. PART 2

A
  • Other parasympathetic fibres relax the internal sphincter (with acetylcholine and nitric oxide) and urine flows out.
  • Urine entry in first part of the urethra triggers the afferent nerves.
  • Reinforce micturition by inhibiting the somatic nerves which tonically contract the external sphincter.
55
Q

Describe the changes in the bladder nerve activity during the micturition (emptying) reflex. PART 3

A
  • Detrusor muscle is contracting, both the internal and external sphincters are relaxed and urine flow is established.
  • Positive feedback from the tension receptors in the bladder walls and urine in the urethra reinforce micturition until the bladder is empty.
56
Q

How can the micturition reflex be modified by higher centres?

A
  • Widespread involvement of the cortical and subcortical areas by viewing activation pattern linked to micturition using MRI
  • Neuron populations are involved, including the specific pontine micturition centre (PMC).
57
Q

Describe the different ways of voluntary modification of the micturition reflex. PART 1

A
  • Contract the external sphincter and levator muscle consciously
  • Increase the sympathetic firing to the bladder and the internal sphincter (due to the contraction of the levator and external sphincter muscles, causes the urethra to compress)
58
Q

Describe the different ways of voluntary modification of the micturition reflex. PART 2

A
  • Interferes with the positive feedback to the bladder emptying by the inhibition of parasympathetic transmission and tightens the internal sphincter.
  • Urine stream can be halted by ‘strangury’ (urethral pain) due to urethritis
  • Pinching the glans penis can inhibit micturition
59
Q

Describe the different ways of voluntary modification of the micturition reflex. PART 3

A
  • At night, if the bladder fills to capacity, recognised by the PMC and the arousal centre wakes you up
60
Q

What is the purpose of increasing sympathetic activity in control of micturition?

A
  • Stop the micturition message from reaching the micturition inhibitory centre in the frontal lobe and the micturition centre in the pons.
61
Q

What is the result of increasing sympathetic activity during control of micturition?

A
  • Blocks parasympathetic activity
  • Keeps the bladder relaxed and the internal sphincter closed
62
Q

What can be done during control of micturition to allow voluntary release of urine?

A
  • Pons and cerebrum quieten the sympathetic input into the bladder and allow the parasympathetic system to take over
63
Q

How is urine released voluntarily during control of micturition?

A
  • Brought about by contracting abdominal muscles which increases bladder pressure.
  • Urine enters the bladder neck and urethra under pressure
  • This stimulates stretch receptors in the wall, which excite the micturition reflex.
64
Q

What is the importance of the bladder emptying?

A
  • Release the urine within in the bladder.
  • Complete emptying restores sterility since urine can contain bacteria.
  • Ordinarily, all the urine is emptied, with rarely more than 5-10 ml left in the bladder.
65
Q

What is the effect of retained urine?

A
  • UTIs
  • If repeated, renal function can be impaired
66
Q

Describe UTIs (urinary tract infections).

A
  • Infection that can happen anywhere along the urinary tract.
67
Q

Why are UTIs more common in women?

A

Shorter urethra

68
Q

Why are UTIs more common in men over 40?

A
  • Prostatic disease - causes bladder outflow obstruction
69
Q

What are the risk factors for UTIs?

A
  • diabetes mellitus
  • long-term catheterisation
  • pregnancy
  • kidney stones
  • bowel incontinence
  • advanced age
70
Q

UTIs have different names depending on what part of the urinary tract is infected.

Elaborate.

A

BLADDER: an infection in the bladder is also called CYSTITIS or a bladder infection
KIDNEYS: an infection of one/both kidneys is called PYELONEPHRITIS
URETERS: rarely a site of infection
URETHRA: an infection of the urethra is called URETHRITIS

71
Q

What are some problems associated with an aging bladder? PART 1

A
  • Slow urine stream - commonly due to prostate enlargement (BPH - benign prostatic hyperplasia)
  • Incomplete emptying of the bladder, which could lead to an infection.
72
Q

What are some problems associated with an aging bladder? PART 2

A
  • Sphincters will also weaken with age.
  • Normal bodily functions such as coughing or laughing raises bladder pressure sufficiently enough to squeeze urine past them.
  • Socially very embarrassing and distressing.
73
Q

What are some problems associated with an aging bladder? PART 3

A

Overactive bladder (OAB)
- Detrusor muscle contracts spastically, sometimes without a known cause, which results in sustained, high bladder pressure and the urgent need to urinate.

74
Q

What are some problems associated with an aging bladder? PART 4

A
  • Experience urgency at inconvenient and unpredictable times and sometimes lose control before reaching the toilet (urge incontinence).
  • Interferes with work, daily routine and diminishes self-esteem and quality of life.
75
Q

What normally maintains continence?

A
  • Increased intra-abdominal pressure forces the urethra against the intact pubocervical fascia
  • This closes the urethra
76
Q

Where is the ureterovesical junction (UV junction) located?

A

Located where the ureter (the tube that drains urine from the kidney) meets the bladder.

77
Q

What occurs during stress urinary incontinence?

A
  • Defective fascial support allows posterior rotation of the UV junction due to the increased pressure
  • Urethra opens and urine loss occurs.
78
Q

How would we treat incontinence with medications? PART 1

A
  • Antimuscarinics, which affect the central nervous system and muscarinic receptors in smooth muscle.
  • Relax the smooth muscle of the bladder, reducing detrusor contraction and subsequent wetting accidents within two weeks.
79
Q

How would we treat incontinence with medications? PART 2

A
  • Side effects such as headache, blurred vision, hypertension, drowsiness and urinary retention.
  • Used with caution in patients with narrow-angle glaucoma / certain kidney, liver and urinary problems.
80
Q

How can exercise be used to treat incontinence?

A
  • Kegel exercises can also be used for bladder retraining (used for stress and urge incontinence).
  • Squeeze pelvic flow muscles (as if trying to stop urine flow) for 10 seconds, then rest for 10 seconds. Done 10 to 20 times a day for several weeks can make a huge difference.
81
Q

How can surgery be used to treat incontinence?

A
  • Examples - bladder neck suspension or sling, collagen injections around the urethra, implantation of an artificial urinary sphincter, tension-free vaginal tape (TVT).
  • Botox is injected into the sides of the bladder to treat urge continence and OAB
82
Q

How can Botox treat incontinence?

A
  • Relaxes the bladder and lasts for several months before repeat injections are needed.
83
Q

How can sacral nerve stimulation be used to treat incontinence?

A
  • Electrical current is applied to the sacral nerve, supplying the lower urinary tract via an implanted pulse generator.
  • Provides complete continence in 50% of patients and improvements in 80% of patients - Works better in women than in men.
84
Q

How can stem cell therapy be used to treat incontinence?

A
  • Cultured stem cells are inserted into the bladder wall.
  • Limited by the supply of stem cells (bone marrow).
85
Q

How can synthetic organs be used to treat incontinence?

A
  • Synthetic and natural scaffolds are used to form a 3D structure using human tissues.
  • Currently in Phase II trials.
86
Q

What is the innervation of the detrusor muscle like?

A

→ Parasympathetic pre-ganglion synapse onto post-ganglion neurons in the bladder wall
→ release ACh (and ATP)
→ acts on nicotinic receptors - cause contraction

87
Q

What receptor does ATP act on?

A

Purinergic

88
Q

What kind of a reflex is micturition?

A

Autonomic

89
Q

How is the micturition reflex modified?

A

→ By voluntary control
→ Inhibited by higher centres in the brain

90
Q

What disrupts voluntary control of micturition?

A

→ Disease/injury/aging
→ Bladder hyperactivity + urge incontinence
→ Stress incontinence

91
Q

Using what you know, outline the steps for micturition. PART 1

A
  • As receptors detect tension, transmit information via afferents ( A delta system) to the spinal cord
  • Synapse to parasympathetic efferents to override storage
  • Detrusor contracts and internal sphincter relaxes
  • Bladder constricts
92
Q

Using what you know, outline the steps for micturition. PART 2

A
  • Urine forced out and activates flow receptors in the urethra
  • Pudendal afferents are excited and switch off the tonic system
  • Tonic contraction removed by inhibition of somatic input
93
Q

Using what you know, outline the path of innervation to the bladder.

A

Cerebral cortex (frontal lobe)
Brain stem
Spinal efferents
Ganglion
Bladder

94
Q

What sends signals from the bladder to the spinal efferents?

A

Unmyelinated afferents

95
Q

Where is the bladder?

A

→ Floor of abdominal cavity

SGUL - Physiology 1 (68 decks)

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