9.6 Micturition; Autonomic Bladder Innervation; Renal Pathologies

Question 1

When does the urge to urinate appear in terms of bladder capacity? What is max capacity?

Answer 1

• Urge appears at 200mL
• Bladder has capacity of approx. 700-800mL

Question 2

At what capacity do detrusor muscle contractions force the internal urethral sphincter open?

Answer 2

~500mL

Question 3

Under what situations will opening of the internal urethral sphincter result in micturition regardless of voluntary input?

Answer 3

• Underdeveloped neural pathways for external sphincter control (e.g. infants)
• Weakened external sphincter (e.g. elderly)

Question 4

Describe the micturition reflex? What other process occurs?

Answer 4

• Stretch receptors -> spinal cord -> internal sphincter opens and bladder contracts
• Information also sent from spinal cord to brain, whereupon we can voluntarily open the external sphincter

Question 5

Which vertebrae do the sympathetic nerves that innervate the bladder originate from? Which ganglia can these nerves synapse in?

Answer 5

• Lower thoracic and upper lumbar
• Synapse in paravertebral ganglia and inferior mesenteric ganglion

Question 6

Which segments of the spinal cord do the parasympathetic nerves that innervate the bladder arise from? What plexus do the postganglionic neurons arise from?

Answer 6

• Originate from sacral region of spine
• Arise from the pelvic plexus or bladder wall itself

Question 7

Which vertebrae do the somatic nerves that innervate the external urethral sphincter originate from? What nerves do they travel in?

Answer 7

• S2-S4
• Travel in pudendal nerves

Question 8

What muscle makes up the bladder wall?

Answer 8

Detrusor muscle

Question 9

Which type of autonomic innervation relaxes and contracts the bladder wall?

Answer 9

• Sympathetic: relaxes
• Parasympathetic: contracts

Question 10

Describe the neurotransmitters, receptor types, and forms of innervation associated with the bladder

Answer 10

Parasymp: Ach (contract) -> M3 receptor
Symp: NA (relax) -> beta 3 receptor

Question 11

Describe the neurotransmitter, receptor type, and form of innervation associated with the internal urethral sphincter

Answer 11

Symp: NA (contract) -> alpha 1 receptor

Question 12

Describe the neurotransmitter, receptor type, and form of innervation associated with the external urethral sphincter

Answer 12

Somatic: ACh (contract) -> nicotinic receptor (like usual)

Question 13

What are the three centres of control of micturition?

Answer 13

• Cortical centre
• Brainstem centre
• Spinal cord

Question 14

List some brain regions responsible for bringing micturition under voluntary control

Answer 14

• Pontine micturition centre
• Periaqueductal grey
• locus coeruleus
• Hypothalamus
• Cingulate gyrus
• Laracentral lobule
• Frontal lobe

Question 15

What are the two types of nervous system disease that can cause bladder dysfunction?

Answer 15

• Central: Stroke, Spinal Cord Injury (SCI), ALS
• Peripheral: Disc herniation

Question 16

What is detrusor hyperflexia?

Answer 16

Involuntary, uninhibited contraction of the detrusor muscle

Question 17

What is detrusor sphincter dyssnergia?

Answer 17

Bladder outlet obstruction due to detrusor muscle contraction with urethral sphincter activation

Question 18

What is areflexia?

Answer 18

Detrusor muscle cannot contract - flaccid bladder

Question 19

What effects can suprapontine lesions have on bladder function? Why?

Answer 19

• Detrusor hyperreflexia: involuntary, uninhibited detrusor contractions
• Tonic inhibitory control of the spinal reflex pathway is lost

Question 20

What effects can spinal lesions above T12 have on bladder function?

Answer 20

• Hyporeflexive bladder activity
• Detrusor sphincter dyssynergia

Question 21

What effects can sacral lesions have on bladder function?

Answer 21

• Acontractile bladder (failure to contract when full)

Question 22

What types of infections are UTIs?

Answer 22

Bacterial

Question 23

What regions are lower UTIs associated with? Are these uncomplicated or serious?

Answer 23

• Lower: Bladder, urethra
• Considered uncomplicated

Question 24

What regions are upper UTIs associated with? Are these uncomplicated or serious?

Answer 24

• Upper: Ureters, kidneys
• Considered more serious

Question 25

Why are UTIs more common in women?

Answer 25

Easier for bacteria to gain access due to shorter urethra

Question 26

What are kidney stones?

Answer 26

Crystallisations of salts and minerals in urine

Question 27

What causes kidney stones?

Answer 27

Excess calcium and dehydration (think: vitamin D supplementation)

Question 28

Provide a basic description of renal failure

Answer 28

kidneys cannot filter wastes from the blood and can no longer maintain homeostasis.

Question 29

What are some flow-on effects of renal failure?

Answer 29

• Blood pressure increases
• Anaemia develops (EPO decreases)
• CNS problems

Question 30

What are the two types of renal failure?

Answer 30

• Acute
• Chronic

Question 31

Describe the differences between chronic and acute renal failure. In which situation can kidney function be regained?

Answer 31

• Chronic occurs gradually, whereas acute occurs suddenly
• Kidneys may regain function in acute failure, whereas progression can only be slowed in chronic failure

Question 32

What are some causes of acute renal failure?

Answer 32

• Renal ischaemia
• Urinary obstruction
• Trauma
• Nephrotoxic drugs

Question 33

What are some causes of chronic renal failure?

Answer 33

• Unmanaged diabetes
• Hypertension

Question 34

How can UTIs be resolved?

Answer 34

• Drink lots of water to flush out urinary system
• Antibiotics in more serious cases

Question 35

How does kidney dialysis work

Answer 35

• Artificial membrane as opposed to glomerular filtration
• Plasma proteins cannot ass through, but ions and waste can
• Lost solutes can be added back into the machine