Lecture 12 : bladder histology and micturition Flashcards
Describe the structure of calyces in the kidney?
how do they branch out?
- the renal pelvis divides into **2 or 3 major calyces **
- each of the major calyces subdivides into 2/3 minor calyces
- the minor calyces fit over renal tissue called pyramids
- each tip of the pyramid is called a papilla and they project into a minor calyx
what is the function of the calyces?
- The calyces collect the ultrafilrate from the collecting ducts of all the nephrons in the kidney
- they then empty the ultrafiltrate (ie urine) into the renal pelvis where it flows to the ureter
what are the 4 main histological layers of the bladder & ureter & what do they contain?
- the lumen which contains the epithelium - called the urothelium
2.** lamina propia** - contains loose connective tissue - muscular region - contains inner & longitudinal layer and outer circular layer (opp to GIT)
- ** adventitia** - contains blood vessels, lymphatics etc
Describe the** structure of the urothelium**
- the urothelium lines the inner surface of the renal pelvis, ureters and the bladder
- **stratified **epithelium
- contains a **basal layer **@ bottom near lamina propia - 1 layer thick - cuboidal cells
- contains an** intermediate layer** - columnar cells -several layers
- contains **umbrella cells **on the surface of the epithelium - rounded cells
why is the urothelium also called ‘transitional’ epithelium?
- As it contains an intermediate layer
what are umbrella cells or the urothelium interconnected by & what is present on their apical membrane?
- they are interconnected by tight junctions
- there are impermeable plaques called uroplakin proteins on the apical membrane
how does a peristaltic ureteral contraction occur?
- when the** renal calyxes** and** upper regions of the ureters** become **distended **(stretched) due to urine accomodation, a perstaltic contraction occurs in the ureters to propel the urine into the bladder
what is the ureterovescial junction?
- the junction between the ureter and the renal pelvis of the kidney
Describe the anatomy/structure of the utererovesical junction
- the bladder is anatomically divided into the fundus/body & the neck
1. the fundus of the bladder contains detrusor muscle (smooth muscle) that is arranged into 3 layers (outer circular, inner & outer longi)
2.** internal urethral sphincter** - evolves from the smooth muscle detrusor fibres
3.** external urethral sphincter**- ring of skeletal muscle
Describe the pressure-volume relationship for the normal human bladder
- after the initial phase of urine filling in the bladder, the volume of the bladder increases by 3/4 fold but there is little increase in intra-vesical pressure
- as more urine fills the bladder, the volume increases and the **pressure rises rapidly **- leads to sense of discomfort and need to urinate / urgency
what is** micturition**?
release of urine from bladder ie urination
what is micturition controlled by?
- ANS - sympathetic & parasympathetic system controls the smooth involuntary muscle (ie the detrusor muscle & internal urethral sphincter)
- Somatic NS - controls the skeletal voluntayr muscle ie the external urethral sphincter)
Where do the sympathetic nerves that innervate the bladder originate from?
- originate from the T11-L2 segments of the spinal chord
what** nerve** do the sympathetic fibres run through
- the hypogastric nerve (HGN)
- this nerve innervates the detrusor and internal urethral sphincter
What neurotransmitter to the postganglionic sympathetic neurons release?
NA - noradrenaline
Where do the parasympathetic fibres that innervate the bladder originate from?
- they arise from the S2-S4 segment of the spine
where do the preganglionic parasympathetic nerves reach the postganglionic nerves?
in the pelvic plexus (PP)
what is the** function** of of ACH and ATP released by the postganglionic nerves?
also, what effect does this have ie contraction or relaxation and where?
- ACH activates the M3 muscarinic receptor in the detrusor smooth muscle
- ATP activates the P2X purinergic receptor in the detrusor muscle
- this causes the detrusor muscle and hence the bladder to contract
what is the function of NO released by the postganglionic nerves?
also, what effect does this have ie contraction or relaxation and where?
- NO activates the NO-cGMP- dependent inhibitory receptors (-) on the internal urethral sphincter
- this causes relaxation of the sphincter
Describe the micturition ‘storage reflex’
ie the sympathetic system pathway
- as the urine accumulates in the bladder, the mechanoreceptors in the wall of the bladder stimulate afferent nerves fibres of **pelvic nerves **
- at low pressures, this activity** activates sympathetic fibres** of the hypogastric nerve - which inhibit detrusor muscle contraction (NA binds to B adrenergic inhib receptors) and causes contraction of the IUS (NA binding to a adrenergic excitatory receptors)
- NB also strong input from somatic neurons via pudenal nerve which cause contraction of the external urethral sphincter (Ach and nicotinic receptor)
Describe the micturition ‘voiding reflex’
ie the parasympathetic system
- As urine accumulates, afferent impulses triggered by stretching of wall travel to the spinal chord and stimulate the parasym outflow
- afferent impulses also activate the pontine micturition centre (results in conscious desire to urinate)
- parasympathetic efferent nerves stimulate the contraction of the detrusor muscle (via ACH and ATP) and they relax the internal urerthral sphincter (NO), causing it to open
- NB the** sympathetic efferent nerves are inhibited **
- the somatic efferent nerves are inhibited - which causes relaxation of the external urethral sphincter
