9.6 Micturition; Autonomic Bladder Innervation; Renal Pathologies Flashcards
When does the urge to urinate appear in terms of bladder capacity? What is max capacity?
- Urge appears at 200mL
- Bladder has capacity of approx. 700-800mL
At what capacity do detrusor muscle contractions force the internal urethral sphincter open?
~500mL
Under what situations will opening of the internal urethral sphincter result in micturition regardless of voluntary input?
- Underdeveloped neural pathways for external sphincter control (e.g. infants)
- Weakened external sphincter (e.g. elderly)
Describe the micturition reflex? What other process occurs?
- 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
Which vertebrae do the sympathetic nerves that innervate the bladder originate from? Which ganglia can these nerves synapse in?
- Lower thoracic and upper lumbar
- Synapse in paravertebral ganglia and inferior mesenteric ganglion
Which segments of the spinal cord do the parasympathetic nerves that innervate the bladder arise from? What plexus do the postganglionic neurons arise from?
- Originate from sacral region of spine
- Arise from the pelvic plexus or bladder wall itself
Which vertebrae do the somatic nerves that innervate the external urethral sphincter originate from? What nerves do they travel in?
- S2-S4
- Travel in pudendal nerves
What muscle makes up the bladder wall?
Detrusor muscle
Which type of autonomic innervation relaxes and contracts the bladder wall?
- Sympathetic: relaxes
- Parasympathetic: contracts
Describe the neurotransmitters, receptor types, and forms of innervation associated with the bladder
Parasymp: Ach (contract) -> M3 receptor
Symp: NA (relax) -> beta 3 receptor
Describe the neurotransmitter, receptor type, and form of innervation associated with the internal urethral sphincter
Symp: NA (contract) -> alpha 1 receptor
Describe the neurotransmitter, receptor type, and form of innervation associated with the external urethral sphincter
Somatic: ACh (contract) -> nicotinic receptor (like usual)
What are the three centres of control of micturition?
- Cortical centre
- Brainstem centre
- Spinal cord
List some brain regions responsible for bringing micturition under voluntary control
- Pontine micturition centre
- Periaqueductal grey
- locus coeruleus
- Hypothalamus
- Cingulate gyrus
- Laracentral lobule
- Frontal lobe
What are the two types of nervous system disease that can cause bladder dysfunction?
- Central: Stroke, Spinal Cord Injury (SCI), ALS
- Peripheral: Disc herniation
What is detrusor hyperflexia?
Involuntary, uninhibited contraction of the detrusor muscle
What is detrusor sphincter dyssnergia?
Bladder outlet obstruction due to detrusor muscle contraction with urethral sphincter activation
What is areflexia?
Detrusor muscle cannot contract - flaccid bladder
What effects can suprapontine lesions have on bladder function? Why?
- Detrusor hyperreflexia: involuntary, uninhibited detrusor contractions
- Tonic inhibitory control of the spinal reflex pathway is lost
What effects can spinal lesions above T12 have on bladder function?
- Hyporeflexive bladder activity
- Detrusor sphincter dyssynergia
What effects can sacral lesions have on bladder function?
- Acontractile bladder (failure to contract when full)
What types of infections are UTIs?
Bacterial
What regions are lower UTIs associated with? Are these uncomplicated or serious?
- Lower: Bladder, urethra
- Considered uncomplicated
What regions are upper UTIs associated with? Are these uncomplicated or serious?
- Upper: Ureters, kidneys
- Considered more serious
Why are UTIs more common in women?
Easier for bacteria to gain access due to shorter urethra
What are kidney stones?
Crystallisations of salts and minerals in urine
What causes kidney stones?
Excess calcium and dehydration (think: vitamin D supplementation)
Provide a basic description of renal failure
kidneys cannot filter wastes from the blood and can no longer maintain homeostasis.
What are some flow-on effects of renal failure?
- Blood pressure increases
- Anaemia develops (EPO decreases)
- CNS problems
What are the two types of renal failure?
- Acute
- Chronic
Describe the differences between chronic and acute renal failure. In which situation can kidney function be regained?
- Chronic occurs gradually, whereas acute occurs suddenly
- Kidneys may regain function in acute failure, whereas progression can only be slowed in chronic failure
What are some causes of acute renal failure?
- Renal ischaemia
- Urinary obstruction
- Trauma
- Nephrotoxic drugs
What are some causes of chronic renal failure?
- Unmanaged diabetes
- Hypertension
How can UTIs be resolved?
- Drink lots of water to flush out urinary system
- Antibiotics in more serious cases
How does kidney dialysis work
- 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
