1. Urinary Bladder and
micturition

2. We can divide urinary bladder into:
Parts:
We can divide urinary bladder into:
Body: which is the major part in which the urine collects
Neck (posterior urethra): funnel-shaped that connects to urethra
A) Body of Bladder:
Inner cavity:
The posterior wall of the body, immediately above the bladder neck , shows a triangular zone, called trigone
The apex of trigone joins the bladder neck, and its base marks the opening of the two ureters
Wall :
3 layers
Mucosa and submucosa
Muscle layer (detrusor muscle)
Adventia

3. Physiological anatomy of urinary bladder
1) Submucosa:
The wall of UB is lined by a transitional epithelium that is continuous with that in the ureters.
When the bladder is empty, the mucosa has numerous folds called rugae.
As the bladder fills with urine these rugae flatten out and distend with little change in intravesical pressure
This results in high compliance of the bladder, so the volume of the bladder can ↑ from 10 ml to 400 ml with a pressure change of only 10 cm H2O

4. Physiological anatomy of urinary bladder
2) Submucosa:
It supports the mucous membrane.
It is composed of connective tissue with elastic fibers.
3) Muscle layer (Detrusor muscle):
It is composed of smooth muscle.
The smooth muscle fibers are interwoven in all directions and collectively these are called the detrusor muscle.
It consist of a mixture of spiral and longitudinal muscle fibers
It can increase the pressure in the bladder to 40 – 60 mmHg.

5. Physiological anatomy of urinary bladder

6. Physiological anatomy of urinary bladder
Bladder Neck :
It is a funnel shaped extension of the body toward the urogenital triangle, to join the anterior urethra (external urethra).
The lower 2-3 cm of the bladder neck is called the posterior or internal urethra.
The ms fibers in the bladder neck are arranged in 3 layers: inner longitudinal, middle circular, and outer longitudinal.
The inherent tone of the bladder neck ms, specially the middle layer, prevents emptying of the bladder until the appropriate time for micturition.
ladder Neck :
The urethra passes through the urogenital diaphragm where it is surrounded by the external urethral sphincter (under voluntary control) used to prevent or interrupt urination, specially in males, it is poorly developed in females.

7. Innervations of Urinary
Bladder

8. Autonomic Innervations of the bladder
Coursing through the pelvic
nerves are both sensory nerve fibers and motor nerve
fibers. The sensory fibers detect the degree of stretch in
the bladder wall.

9. Autonomic Innervations of the bladder Parasympathetic Supply
Nerve
Pelvic nerve
Hypogastric Nerve
Efferents:
Origin:
Supply:
Functions
-LHCs of the S 2,3, and 4.
-Body and neck of the bladder.
a) Contraction of bladder wall.
b) Relaxation of the bladder neck → stimulation of the detrusor ms of the body causes longitudinal layers to open the bladder neck.
- L1,2, and 3.
- Bladder neck
a) Contraction of bladder neck, specially the middle layer→ facilitate the storage of urine.
b) Relaxation of the bladder wall by inhibiting the parasympathetic ganglia.
Afferents:
a) Carry input from stretch receptors in the bladder neck..
b) Detect bladder fullness.
c) Carry pain and temperature sensation.
Transmit pain sensation
Detect bladder fullness
LHC= Lateral horn cell

10. (Hypogastric nerve)
(Pelvic nerve)

11. Somatic Innervations of the bladder
The Pudendal nerves (AHCs of S 2,3,and 4)
Its efferent fibers arise as the parasympathetic nerves from the 2nd, 3rd and 4th sacral segments of the spinal cord but from the AHCs.
They supply and control the activity of the external urethral sphincter

12. Autonomic and Somatic Innervations of the bladder

13. Functions of the Urinary Bladder
In healthy individuals, the bladder has two discrete phases of activity:
The storage phase, when urine is stored in the bladder; and
The voiding phase, when urine is released through the urethra.

14. Storage Phase
During storage, bladder pressure stays low, because of the bladder's highly compliant nature.
This property is helped by the presence of the transitional epithelium.
This function is studied by a curve or plot between bladder (intravesical) pressure against the volume of fluid in the bladder (called a cystometrogram)

15. Cystometrogram
Def.
It is a curve which studies the relationship between intravesical pressure (IVP) and volume.
Method:
It is done by inserting a catheter into the bladder to fill and empty the bladder by water, and through special transducer, the intravesical pressure is recorded.
First, the bladder is emptied from urine and the pressure is recorded, then the bladder is filled with 50 ml water and the pressure is recorded for every ↑ in the volume.

17. Intravesical Pressure Intravesical Volume (ml)
Cystometrogram II
Intravesical Pressure
(cm H2O2) Ib Ia
Intravesical Volume (ml)

18. Cystometrogram Ia Ib II Initial slight rise Long flat segment
Sharp rapid rise
Produced by the 1st increment of volume by about 50 ml.
Produced by further increase in volume up to 400 ml.
Produced by further increase in volume above 400 ml.

21. Cystometrogram
Segment Ib is a manifestation of the law of Laplace, which states that the pressure in a spherical viscus is equal to twice the wall tension divided by the radius.
In the case of the bladder, the tension increases as the organ fills, but so does the radius.
Therefore, the pressure increase is slight until the organ is relatively full.
P=2T/r

22. Micturition

23. Micturition
Def:
It is the periodic evacuation of urinary bladder through urethra
Mechanism:
Micturition is fundamentally a spinobulbospinal reflex facilitated and inhibited by higher brain centers and, like defecation, subject to voluntary facilitation and inhibition.

24. Micturition Reflexes Center: sacral segments 2, 3 & 4.
Receptors: stretch (receptor) in the wall of bladder.
Afferent & efferent: pelvic nerve.
Response:
Contraction of detrusor muscle (body).
Relaxation of internal sphincter of urethra.
Relaxation of external urethral sphincter via the pudendal nerve which is somatic nerve originating from AHC of sacral segment 2, 3, & 4.

25. ↑ IVP Stretch receptors Center S2,3,4, Contraction of wall Afferents
Pelvic Nerve
Relaxation of int. sphincter
Efferent
Pelvic Nerve
Relaxation of ext. sphincter

26. MICTURITION REFLEX

27. Voluntary Control of Micturition

28. Higher Centers Control Micturition
1) Cerebral cortex: Motor cortex exerts a voluntary control of micturition either stimulation or inhibition.
2) Hypothalamus: There is facilitatory area in the hypothalamus.
3) Midbrain: Inhibition.
4) Pons: facilitation

29. Higher Centers Control Micturition
Keeping the micturition reflex partially inhibited all the time except when there is a desire for micturition.
Prevent the micturition even when the reflex is initiated until appropriate time allows.

30. Voluntary Initiation of Micturition
Relaxation of perineal ms causing traction on the bladder
Contraction of anterior abdominal wall and diaphragm to increase intra-abdominal pressure  compressing bladder.
Relaxation of external urethral sphincter.
Flow of urine in urethra  intensification of the reflex.
If the condition unfavourable, the higher center will delay micturition until convenient time by:
1) Inhibition of sacral segment of micturition.
2) Stimulation of external urethral sphincter.
3) Contractions of perineal muscle  decrease intravesical pressure.

31. If the bladder fluid content exceeds 700 ml, urine starts to dribble in spite of the voluntary control

33. Uninhibited Neurogenic Bladder
Caused by Lack of Inhibitory Signals from the Brain.
This condition derives from partial damage in the spinal cord or the brain stem that interrupts most of the inhibitory signals.
Which results in frequent and relatively uncontrolled micturition.
Therefore, facilitative impulses passing continually down the cord keep the sacral centers so excitable that even a small quantity of urine elicits an uncontrollable micturition reflex, thereby promoting frequent urination.
4- Transection of spinal cord:
Complete transection of spinal cord affects micturition as such:
During the spinal shock  over flow incontinence.
After recovery  automatic bladder the U.B fill with urine, till certain volume and pressure capable of micturition reflex to be carried out in the spinal sacral centers without supraspinal influence and with conscious feeling of micturition as infants and children below 2 years

34. Automatic/Reflex Bladder
Caused by Spinal Cord Damage Above the Sacral Region. If the spinal cord is damaged above the sacral region but the sacral cord segments are still intact.
typical micturition reflexes can still occur.
However, they are no longer controlled by the brain.
During the first few days to several weeks after the damage to the cord has occurred, the micturition reflexes are suppressed because of the state of “spinal shock” caused by the sudden loss of facilitative impulses from the brain stem and cerebrum.
However, if the bladder is emptied periodically by catheterization to prevent bladder injury caused by overstretching of the bladder, the excitabilityof the micturition reflex gradually increases until typical micturition reflexes return; then, periodic (but unannounced) bladder emptying occurs.

35. Atonic Bladder Caused by Destruction of Sensory Nerve Fibers.
Micturition reflex contraction cannot occur if the sensory nerve fibers from the bladder to the spinal cordare destroyed, thereby preventing transmission of stretch signals from the bladder.
When this happens, a person loses bladder control, despite intact efferent fibers from the cord to the bladder and despite intact neurogenic connections within the brain.
Instead of emptying periodically, the bladder fills to capacity and overflows a few drops at a time through the urethra. This is called overflow incontinence.
A common cause of atonic bladder is crush injury to the sacral region of the spinal cord. Certain diseases can also cause damage to the dorsal root nerve fibers that enter the spinal cord. For example, syphilis can cause constrictive fibrosis around the dorsal root nerve fibers, destroying them. This condition is called tabes dorsalis, and the resulting bladder condition is called tabetic bladder.