Veterinary Pelvis and Perineum (Animal)

  Pelvis and Perineum

Pelvis  =  caudal region of trunk

                     The  pelvis consists of pelvic viscera within   pelvic                                         cavity that is bounded on five sides.

     

Pelvic Viscera:  

                                rectum & anal canal;  distal ureters, urinary  

                                bladder & urethra;

                                male or female genitalia;  blood vessels, 

                                lymphatics & nerves

 Pelvic Cavity Boundaries:

  cranial opening— pelvic inlet, bounded by sacrum, ilium &  

                                  pubis (rigid boundary)

   cavity walls— osseous pelvis + obturator & gluteal mm. &       

                            sacrotuberous ligament (dog)

     

   caudal boundary — perineum

Perineum  =    both a region & a wall

                                As topographic region:  from tail to scrotal  attachment or entire vulva; between ischiatic tuberosities.

As caudal wall of trunk: muscles,  fascia   &  skin  surrounding anal canal    and urogenital tract; includes

 1. Pelvic diaphragm = levator ani & coccygeus mm. associated

                                       deep fascia

2. Urogenital diaphragm = external urethral sphincter  associated    

                                               deep fascia                                                                                                                                                            3 External anal  sphincter m.

 4 Genital striated mm:

           

                 male    — bulbospongiosus m. & paired ischiocavernosus  

                                mm. 

                 female — constrictor vestibuli, constrictor vulvae &

                                  ischiocavernosus mm.

                                                 

 5. Smooth mm.: rectococcygeus  m.& retractor penis m.

  Micturition

Anatomy:

Urinary Bladder — apex; body; neck (trigone   = region of neck  demarcated by ureters & urethra).

Urethra — female: terminates in vestibule;

                      male: pelvic urethra  [preprostatic (cat); prostatic; &   

                       postprostatic regions] & penile urethra  

Musculature:

Detrusor m. = smooth muscle coat of apex & body; innervated by pelvic n  (S2 +S1 & S3 ) 

Internal urethral sphincter = smooth    m.; innervated hypogastric    n. (L2,  L3,  L4) 

               female   — vesical neck & cranial half of urethra 

               male      — neck (dog);  neck & preprostatic urethra (cat) 

External    urethral     sphincter   = urethralis m. (striated);       innervated  by pudendal n. (S2 & S3 + S1 ) 

               female — caudal half of urethra

               male — postprostatic urethra 

Urine Storage:

Sphincters  active via spinal  reflexes and detrusor    m. inhibited        

     - internal sphincter exerts tonic activity after bladder is half full 

     - external sphincter is activated voluntarily or reflexly during          phasic pressure increase

Micturition:

Requires prolonged detrusor contraction and sphincter inhibition 

    - free nerve endings (receptors) —>    GVA fibers in pelvic n.          —>   ascending          pathways —> pons —> descending spinal pathways —> activate detrusor & inhibit sphincters

Pain:

GVA pain   fibers travel through the hypogastric nerve to reach the spinal cord and brain.