Pelvis Flashcards
1
Q
Perineum & Borders
A
- Located between thighs & represents most inferior part of pelvic outlet
- Seperated from pelvic cavity superiorly by pelvic floor
- Contains structures that support urogenital & gastrointestinal systems - important in micturition, defecation, sexual intercourse & childbirth
- Diamond-shaped
- Can be subdivided into urogenital (anterior) & anal triangles by theoretical line between ischial tuberosities
Anatomical Borders
Anterior - pubic symphysis
Posterior - tip of coccyx
Lateral - inferior pubic rami & inferior ischial rami, sacrotuberous ligament
Roof - pelvic floor
Base - skin & fascia
Surface Borders - best seen when legs are abducted & elevated (lithotomy position)
Anterior - mons pubis (females), base of penis (males)
Posteior - medial surfaces of thighs
Lateral - superior end of intergluteal cleft
2
Q
Anal Triangle Contents
A
Main Contents
- anal aperture - opening of anus
- located centrally in triangle
- external anal sphincter muscle - voluntary muscle responsible for opening & closing anus
- ischioanal fossae (x2) - spaces located laterally to anus
- contain fat & CT which allow for expansion of anus during defecation
- extend from skin of anal region (inferiorly) to pelvic diaphragm (superiorly)
- pudendal nerve - supplies the whole perineum with somatic fibres
3
Q
Urogenital Triangle Layers
A
- Associated with external genitalia & urethra
- Complex with a number of fascial layers & pouches
- Has an additional layer of strong deep fascia - perineal membrane (has pouches on superior & inferior surfaces
Layers of Urogenital Triangle (deep to superficial)
-
deep perineal pouch - potential space between deep fascia of pelvic floor (superiorly) & perineal membrane (inferiorly)
- contains part of the urethra, external urethral sphincter & vagina (females)
- also contains bulbourethral glands & deep transverse perineal muscles (males)
-
perineal membrane - layer of tough fascia, perforated by urethra (& vagina in females)
- role is to provide attachment for muscles of external genitalia
-
superficial fascia - continuity of abdominal fascia that has two components:
- deep fascia - covers superficial perineal muscles & potruding structures (e.g penis & clitoris)
- superficial fascia composed of two layers:
- superficial - continuous with Camper’s fascia of anterior abdominal wall
- deep (Colles’ fascia) - continuous with Scarpa’s fascia of anterior abdominal wall
- skin - urethral & vaginal orifices open out onto skin
4
Q
Perineal Body
A
- Irregular fibromuscular mass
- Located at junction of urogenital & anal triangles - central point of perineum
- Contains skeletal & smooth muscle and collagenous & elastic fibres
- Lies just deep to skin - acts as point of attachment for muscle fibres from pelvic floor & perineum itself
- Acts as a tear-resistant body between vagina & external anal sphincter in women - supporting posterior part of vaginal wall from prolaspe
- In males, lies between bulb of penis & anus
Attachments
- levator ani (part of pelvic floor)
- bulbospongiosus muscle
- superficial & deep transverse perineal muscles
- external anal sphincter muscle
- external urethral sphincter muscle fibres
5
Q
Perineum Neurovascular Supply
A
- Innervation from pudendal nerve (S2-S4)
- Bloody supply from internal pudendal artery/vein
- Bundle travels along inner surface of ischial tuberosities, through a ‘canal’ formed by a thickening of the obturator fascia (Alcock’s canal)
- Bundle courses downwards through each ischioanal fossa & gives branches to both anal & genital triangle
6
Q
Pudendal Nerve
A
- Major somatic nerve of sacral plexus
- Nerve roots - S2-S4
Anatomical Course
- Formed from sacral plexus
- Descends & passes between pitformis & ischiococcygeneus muscles
- Leaves pelvis via lower part of greater siatic foramen
- Crosses sacrospinious ligament & re-enters pelvis through the lesser sciatic foramen
- After re-entering pelvis, accompanies internal pudendal artery & vein, coursing anterosuperiorlu through pudendal canal (formed by fascia of obturator internus muscle)
- Inside the canal, nerve branched into inferior rectal nerve, perineal nerve & dorsal nerve of penis/clitoris
7
Q
Motor & Sensory Function of Pudendal Nerve
A
Sensory Function
- Supplies sensation to external genitalia of both sexes & skin around anus, anal canal & perineum through branches:
- inferior rectal nerve - innervates the perianal skin & lower third of anal canal
- perineal nerve - innervates skin of the perineum, labia minora & majora/posterior scrotum
- dorsal nerve of penis/clitoris - innverates skin of penis/clitoris, thus responsible for afferent component of penile & clitoral erection
Motor Function
- Perineal nerve innervates muscles of perineum & pelvic floor:
- bulbospongiosus
- ischiocavernosus
- levator ani muscles (including iliococcygeus, pubococcygeus & puborectalis)
- also innervates the external urethral sphincter
- inferior rectal nerve (branch of pudendal) provides motor supply
- provides voluntary/somatic control of faceal & urinary continence
8
Q
Clinical Relevance - Pudendal Nerve Block
A
- Form of analgesia occasionally given before vaginal childbirth, episotomy & other minor vaginal procedures
- Patient is places into lithotomy position & ischial spine is palpated transvaginally
- Local anasethetic is then injected into tissues around ischial spine - procedure is then completed on opposite side
- As pudendal nerve is accompanied by internal pudendal artery, it is essential to aspirate before injecting the local anasthetic - ensures it is not administered into systemic circulation
9
Q
Pelvic Floor
A
- Funnel-shaped structure
- Attaches to wall of the lesser pelvis
- Seperates the pelvic cavity from the perineum inferiorly
To allow for urination & defacation, there are two holes within the floor that have significance:
- urogenital hiatus - anteriorly situated gap, allows passage of urethra (& vagina in females)
- rectal hiatus - centrally positioned gap, allows passage of anal canal
Between the two gaps lies a fibrous node (perineal body), joins pelvic floor to perineum
10
Q
Function of Pelvic Floor Muscles
A
- Support of abdominopelvic viscera (bladder, intestines, uterus etc) through tonic contraction
- Resistance to increases in intra-pelvic/abdominal pressure during activities such as coughing/lifting heavy objects
- Urinary & faecal continence - muscle fibres have a sphincter action on rectum & urethra (relax during urination/defecation)
11
Q
Structure of the Penis
A
Root
- proximal, fixed part
- located in the superficial perineal pouch of pelvic floor (not visible internally)
- contains three erectile tissues: two cura & bulb of penis
- contains two muscles: ischiocavernosus & bulbospongiosus
Body
- free part of penis
- located between root & glans, suspended from pubic symphysis
- composed of three cylinders of erectile tissue: two corpora cavernosa & corpus spongiosum
Glans
- most distal part of penis
- conical shape
- formed by distal expansion of corpus spongiosum
- contains opening of urethra (external urethral orifice)
12
Q
Erectile Tissues
A
# * Fill with blood during sexual arousal, producing an erection * Root & body of penis are spanned by three masses of erectile tissue
Root: left & right crura + bulb of penis
- bulb is situated in the midline of penile root, transversed by urethra
- left & right crura are located laterally, attached to ipsilateral ischial ramus & covered by the paired ischiocavernosal muscles
Body: two corpora cavernosa & corpus spongiosum
- left & right crura continue anteriorly into the dorsal part of the penis - form the two corpora cavernosa
- two corpora cavernosa are seperated by the septum of the penis, incompletely
- bulb forms the corpus spongiosum - lies ventrally
- male urethra runs through the corpus spongiosum - fills to a reduced pressure during errection to prevent it becoming occluded
- distally, corpus spongiosum expands to form glans penis
13
Q
Muscles of Penis
A
Bulbospongiosus x2
- assoicated with the bulb of penis
- contracts to empty spongy urethra of any residual semen & urine
- anteior fibres also aid in maintaing erection by increasing pressure in the bulb of penis
Ischiocavernosus x2
- surrounds left & right crura of penis
- contracts to force blood from the cavernous soaces in the crura into the corpus cavernosa - helps maintain erection
14
Q
Fascia of Penis
A
- Each mass of erectile tissue has two fascial coverings
- Most superficial layer, immediately under skin is the external fascia of Colles
- Colles fascia is continious with fascia of scarpa which covers the abdominal wall
- Deeper stratum is the deep fascia of the penis, known as Buck’s fascia
- Continuation of the deep perineal fascia, forms a strong membranous covering which holds all three erectile tissues together
- Underneath deep fascia is stronger fascia called tunica albuginea
- Tunica albuginea forms an individual caspule around each cavernous body & fuses in the midline
- Incomplete septum between the two corpora is comprised of tunica albuginea
15
Q
Ligaments of Penis
A
Penis is supported by two ligaments which attach it to surrounding structures:
-
suspensory ligament
- condensation of deep fascia
- connects erectile bodies of the penis to pubic symphysis
-
fundiform ligament
- condensation of abdominal subcutaneous tissue
- runs down from linea alba, surrounding penis like a sling & attaching to pubic symphysis
16
Q
Neurovascular Supply to Penis
A
Arterial Supply
Recieves arterial supply from threes sources:
- dorsal arteries
- deep arteries
- bulbourethral artery
- all are branches of the internal pudendal artery
- vessel arises from anterior division of the interal iliac artery
Venous Drainage
- venous blood is drained by paired veins
- cavernous spaces arre drained by the deep dorsal vein of the penis - empties into the prostatic venous plexus
- superficial structures (skin & cutaneous tissues) are drained by the superficial dorsal veins
Innvervation
- suppkied by S2-S4 spinal cord segments & spinal ganglia
- sensory & sympathetic innveration to skin and glans penis = dorsal nerve of penis = branch of pudendal nerve
- parasympathetic innervation = cavernous nerves from peri-prostatic nerve plexus - responsible for vascular changes that cause errection
17
Q
Role of Urinary Bladder
A
Plays two main roles:
-
Temporary storage of urine
- hollow organ with distendable walls
- folded internal lining (rugae), allows it to accomodate 400-600ml of urine in healthy adults
-
Assists in the expulsion of urine
- musculature of bladder contracts during micturition, with concomintant relaxation of sphincters
19
Q
Urinary Bladder - Trigone
A
- Triangular area located within the fundus
- Orifices of two ureters & urethra form the triangular shape
- Has smooth walls compared to rest of internal bladder
- Surface is explained by different embryological origin - trigone is developed by the integration of two mesonephric ducts at the base of bladder
