(Renal Physiology 4) Micturition

1. (Renal Physiology 4) Micturition Ahmad Ahmeda aahmeda@ksu.edu.sa Cell phone: 0536313454

2. Learning Objectives: • Identify and describe the Functional Anatomy of Urinary Bladder • Describe the mechanism of filling and emptying of the urinary bladder • Cystometrogram • Appreciate neurogenic control of the mechanism of micturition and its disorders.

3. Introduction • Urinary bladder functions as a temporary storage organthat can empty at appropriate time. • Problems related to bladder are often obvious like enuresis, incontinence or may not be apparent like recurrent UTIs, day time urgency frequency syndrome. • Early intervention may prevent any further renal damage from retrograde effects of high bladder pressures.

4. Urinary Bladder Anatomy • The bladder is situated in the pelvic cavity when empty, but expands superiorly into the abdominal cavity when it becomes full. • The urinary bladder is an abdominal organ at birth, positioned at the extraperitoneal area of the lower abdominal wall. Around the 5th or 6th year of age the bladder gradually descends into the area of the true (minor) pelvis.

5. Urinary Bladder Anatomy It has 4 parts • Apex • Base • Superior surface • Inferolateral surfaces

6. Urinary Bladder Anatomy • The mucosal lining on the base of the bladder is smooth and firmly attached to the underlying smooth muscle coat of the wall-unlike elsewhere in the bladder where the mucosa is foldedand loosely attached to the wall. The smooth triangularareabetween the openings of the ureters and urethra on the inside of the bladder is known as the trigone.

7. Urinary Bladder Anatomy Ureterovesical Junction As the ureter approaches the bladder, 2 to 3 cm from the bladder, a fibro-muscular sheath (of Waldeyer) extends longitudinally over the ureter and follows it to the trigone. • The ureter pierces the bladder wall obliquely and terminates at the ureteral orifice. As it passes through a hiatus in the detrusor (intramural ureter), it is compressed and narrows considerably. • The intravesical portion of the ureter lies beneath the urothelium, it is backed by a strong plate of detrusor muscle. With bladder filling, this arrangement is thought to result in passive occlusion of the ureter, like a flap valve which prevent reflux.

8. Urinary Bladder Anatomy Mucosa • 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 intravesicalpressure • 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

9. Urinary Bladder Anatomy Submucosa • It supports the mucous membrane. • It is composed of connective tissue with elastic fibers. 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.

10. Urinary Bladder Anatomy 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 muscle fibers in the bladder neck are arranged in 3 layers: inner longitudinal, middle circular, and outer longitudinal. • Thetone of the bladder neck muscles, specially the middle layer, prevents emptying of the bladder until the appropriate time for micturition.

12. Urinary Bladder Anatomy Bladder Neck cont: • 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.

13. Nerve Supply to the Bladder Afferent supply: • Sympathetic nerve • It transmit impulses from the pain receptors to the upper lumbar segment (via the lumbar dorsal n. roots)  resulting in the perception of pain sensation from the urethra & bladder e.g. severe bladder distention & in inflammation.

14. Nerve Supply to the Bladder B. Pelvic nerve • It transmit impulses from the tension (stretch) & pain receptors present in the wall of U.B. to the sacral region of spinal cord (via the sacral dorsal n. roots)  resulting in both reflex micturition & sensation of bladder fullness (i.e. desire for micturition) [The tension receptors are stimulated when I.V.P. ]

15. Nerve Supply to the Bladder C. Pudendal nerve • It transmit impulses for the sensation of: • Distention of the urethra. • Passage of urine through the urethra.

16. Nerve Supply to the Bladder Efferent Supply A. Sympathetic supply • Pregang. fibres  arise from the upper 4 L. The fibres of both sides unite to form presacral nerve when then divides into  The post. gang. fibres arise from hypogastric ganglia. • Functions of sympathetic nerves: • Inhibitory to the bladder wall (detrusor muscle). • Motor to the internal urethral sphincter. • Motor to the seminal vesicle, ejaculatory duct & prostatic musculature. It prevents the reflux of semen into the bladder.

17. Nerve Supply to the Bladder B. Parasympathetic supply • The pregang. fibres arise from the 2nd, 3rd, 4th sacral segments. • They form the pelvic nerve which relays in the terminal ganglia embedded in the wall of the U.B. Functions of parasympathetic: • Motor to the bladder wall (detrusor muscle). • Inhibitory to the internal urethral sphincter.

18. Nerve Supply to the Bladder C. The somatic supply (pudendal N.) • It arise from the 2nd, 3rd, 4th sacral segments. • It supplies the external urethral sphincter. Function of somatic supply: • Motor to the external uretheral sphincter.

19. The Reservoir functionof U.B • Urine enters the urinary bladder without producing much increase in I.V.P. till the bladder becomes well-filled. • A plot of I.V.P. against the volume is called “cystometrogram”. • It is composed of three components: • Stage Ia: • Represent initial slight rise in I.V.P. by about 10 cm H2O when the first increment in volume is produced by about 50 ml.

20. Cystometrogram • Stage Ib: • It is a long, nearly flat segment produced by further  in filling up to nearly 150 ml. • Stage II: • This segment is produced by further increment of volume (150 – 400 ml) & represent rise of pressure.

21. Cystometrogram • In the urinary bladder  the tension on the wall increases as the volume increases & also the radius increases, so there is little change in pressure until the organ is filled & any increase in volume beyond this will not be accommodated & is reflected by rapid rise of pressure. • Superimposed on this curve, periodic acute increase in pressure which lasts very few seconds, & called “micturition waves” & are caused by micturition reflex.

22. Sensations from the U.B at different urine volumes: • At a urine volume of 150 –300 ml  the first urge to void urine. • From 300 –400 ml  sense of fullness of the bladder. • From 400 –600 ml  sense of discomfort. • From 600 –700 ml  sense of pain. • Micturition reflexes start to appear at the first stage. They are progressively intensified in the subsequent stages up to stage 4. Micturition reflexes can be voluntarily suppressed. • At about 700 ml  break point  micturition can not be suppressed.

23. Micturition • Unconditioned (automatic) micturition: • In infants urination occurs through a series of spinal reflexes called “the micturition reflexes” which are automatic (not under voluntary control) because the nerve tracts are not yet myelinated in infants. • The stimulus that initiates these reflexes is rise of the IVP (which stimulates stretch receptors in the bladder wall) & they are integrated by a spinal micturition centre in the 2nd, 3rd & 4th sacral segments of the spinal cord.

24. Micturition reflexes The micturition reflexes can be summarized as follows: • Distention of the U.B. (as a result of  I.V.P. & not by an  in the bladder volume) produces reflex contraction of its wall & relaxation of the internal urethral sphincter & external urethral sphincter. • The flow of urine in urethra will produce contraction of the U.B. wall & relaxation of both internal & external urethral sphincters.

25. Micturition reflexes • B) Voluntary or conditioned micturition: • In adults  the act of micturition occurs also through the micturition reflexes, but however, it can be voluntarily controlled by certain higher (or supra-spinal) centers in the brain, which include the following:

26. Mechanism of voluntary control of micturition: • Filling of the bladder beyond 300 –400 ml causes stretching of sensory stretch receptors. • These sensory signals stimulate sacral segment, which is consciously appreciated by higher centers.

27. If the condition is favourable • The cortical centers facilitate micturition by discharging signals that leads to: • Stimulation of sacral micturition center. • Inhibition of pudendal nerves  relaxation of external urethral sphincter. • Contraction of anterior abdominal muscle & diaphragm to increase intra-abdominal pressure  the intra-vesical pressure is increased. This intensifies the micturition reflex.

28. If the conditions are unfavorable • The higher centers will inhibit the micturition reflex by: • Inhibition of sacral micturition center. • Stimulation of pudendal nerves  contraction of external urethral sphincter.

29. Disturbances of micturition • Denervation of the afferent supply e.g.in tabes dorsalis (tabetic bladder): • Characterized by: • Loss of the U.B. sensations & reflex micturition. • Some intrinsic responses of the smooth muscle are retained. • The bladder becomes distended, thin walled & hypotonic (a tonic bladder). • There is retention with overflow i.e. dribbling of urine when the bladder becomes over filled.

30. Disturbances of micturition • Denervation of the afferent & efferent supply e.g. tumour, injury to cauda equina. • Characterized by: • Reflexes are abolished. • Intrinsic responses of the smooth muscles are increased. • The bladder is hypertonic. • This is due to denervation hypersensitivity because: •  degradation of acetyl choline by process of reuptake. •  cholinesterase in the tissue •  number of cholinergic receptors. • This condition is associated with uncontrolled periodic micturition about 25 – 100 ml at a time

31. Disturbances of micturition • Spinal cord transection (above the sacral region). • Stage of spinal shock • This occurs due to the sudden separation of the spinal centers from the higher centers that control them. • The spinal centers become functionless for 2 – 6 weeks. So, the micturition reflex is abolished “retention with overflow” i.e. the bladder distends until the I.V.P. exceeds the urethral sphincter resistance & so, urine starts to dribble.

32. Disturbances of micturition • Stage of recovery of the spinal centres • “Automatic micturition” occurs as soon as the I.V.P. rises to 15 – 20 cm water  reflex micturition occurs. • Stage of failure recovery • Damage of the spinal centers by toxins of bacterial infections  abolishes the micturition reflex “Retention with overflow”.

34. Thanks

35. Composition of Urine

36. Physical Characteristics of Urine • Color and transparency • Clear, pale to deep yellow (due to urochrome) • Concentrated urine has a deeper yellow color • Drugs, vitamin supplements, and diet can change the color of urine • Cloudy urine may indicate infection of the urinary tract

37. Physical Characteristics of Urine • Odor • Fresh urine is slightly aromatic • Standing urine develops an ammonia odor • Some drugs and vegetables (asparagus) alter the usual odor

38. Physical Characteristics of Urine • pH • Slightly acidic (pH 6) with a range of 4.5 to 8.0 • Diet can alter pH • Specific gravity • Ranges from 1.001 to 1.035 • Is dependent on solute concentration

39. Chemical Composition of Urine • Urine is 95% water and 5% solutes • Nitrogenous wastes include urea, uric acid, and creatinine • Other normal solutes include: • Sodium, potassium, phosphate, and sulfate ions • Calcium, magnesium, and bicarbonate ions • Abnormally high concentrations of any urinary constituents may indicate pathology