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The bony plevis is formed by four
bones united at four joints.The
bones are two hip bones in front
and on the sides,and the sacrum
and coccyx behind.The joints are
the two sacroiliac joints,the
ligaments between hip bone and
spinal column,the pubic symphysis
, the sacrococcgeal joint.
Sacroiliac joint
It is formed by the auricular surfaces
of the sacrum and the ilium.The
irregular articular surfaces of
each bone contact closely with
each other.The articular capsule
is very tight and is strengthened
by the anterior sacroiliac
ligament,the posterior sacroiliac
ligament and the interosseous
sacroilac ligament.The movements
of this joint are very limited
because the joint is adapted to
support the weight of the body.
The joints are somewhat more
movable during the pregnancy as
the ligaments become more lax from hormonal action.
Ligaments between hip bones and spinal column
The sacrotuerous ligament is
situated at the lower and back part
of the pelvis.It passes from the
lateral margin of both the cacrum
and coccyx to the medial margin
of the ischial tuberosity.
The sacrospinous ligament is a thin
and triangular ligament,situated in
front of the sacrotuberous ligament.
It bridges between the lateral margin
of both the sacrum and coccyx to
the ischial spine.
These two ligaments
convert the greater and lesser
sciatic notches into the greater sciatic
foramen and the
lesser sciatic foramen.
The foramina allow muscles,blood
vessels and nerves to pass through
between the pelvic
cavity and the gluteal region.
Sacrococcygeal joint
(see the joints of vertebral column)
Pubic symphysis
It is a fibrocartilaginous joint
formed by the interpubic disc
between the two articular
surfaces of the pubic bones.
The disc may contain a small
cavity and reinforced by some
ligaments.The superior pubic
ligament connects the two pubic
bones together superiorly.
The arcuate pubic ligament connects
the two pubic bones inferiorly,
and forms the upper boundary
of the pubic arch.No perceptible
movements take place at the
pubic symphysis.However,during
the later stage of gestation and
parturition,the interpubic disc
tends to become more pliable
and allows some separation of
the pubic symphysis.
The pelvis is divided by the
plane of the pelvic inlet or
superior aperture of the pelvis
into two parts:The upper part
is known as the greater or false
pelvis.the lower part is known
as the lesser or true pelvis.The
plane of the pelvic inlet passes
from the sacral promontory to
the upper margin of the pubic
symphysis.The greater pelvis
includes the two iliac fossae,and
forms a part of the posterior
abdominal wall.The lesser pelvis
contains the pelvic viscera.
The lesser pelvis
The lesser pelvis includes the
plevic inlet,the plevic outlet,
the plevic cavity,the plevic axes,
the plevic walls and
the pelvic diaphragm.
The pelvic inlet is an oblique
plane,making an angle of 50
to 60 degrees with the horizontal.
It is bounded posteriorly by the
sacral promontary,anteriorly by
the upper margin of the pubic
symphysis,and on each side by
the linea terminalis.
The linea terminalis includes
the anterior
margin of the ala of the sacrum,
the arcuate line,pecten pubis,
and the pubic crest.The pelvic
inlet is heart-shaped in the male
,and is widest in its posterior part.
In the female,it is oval,and is
widest more anteriorly than in
the male.Posterorly,the inlet is
indented by the sacral promontory,
more so in the
male than in the female.
The pelvic outlet is bounded
anteriorly by the arcuate pubic
ligament;posteriorly by the
coccyx;and on each side by the
ischiopubic rami or side of
the pubic arch,the ischial
tuberosities and the sacrotuberous
ligaments. The pubic arch is
formed by the ischiopubic rami
of the two sides and by the lower
margin of the pubic symphysis
which is rounded off by the arcuate
pubic ligament. These arches meet
below the pubic symphysis to
form the subpubic angle.
The cavity between the pelvic
inlet and the pelvic outlet is
called plelvic cavity.The pelvic
cavity is continuous above with
the abdominal cavity at the
plevic inlet,and is limited
below by the plevic diaphragm.
The cavity is curved in such a
way that is is first directed
downwards and backwards,
and then downwards and forwards.
It has unequal walls, measuring
only about 5 cm anteriorly and
15 cm posteriorly.The cavity is
more larger in female
than in the male.
The axis of the pelvic inlet
transverses its enter at
right angles to its plane,
directed down and backwards
.When prolonged (projected)
it passes through the umbilicus
and midcoccyx.An axis is similarly
established for the pelvic outlet:
projected upwards it impinges on
the sacral promontory.Axes can
likewise be constructed for any
plane,and one for the whole cavity
is a concatenation of an infinite
series of such line.
It follows the
curvature of the cavity ,indicated
by the profile of the sacrum and
coccyx in lateral views.The form
of this pelvic axis and the disparity
in depth between the anterior and
posterior contours of the cavity
are prime factors in the mechanism
of fetal transit in the pelvic canal.
Wall of the pelvis
Internal iliac artery
The internal iliac artery is a
terminal branch of the common
iliac artery.In the fetus,internal
iliac artery is double the size of
the external iliac artery because
it transmits glood to the placenta
through the umbilical artery,
which is a branch of internal iliac
After birth the proximal
part of umbilical artery
persists to
form the proximal part
of superior
vesical artery,the rest of it
degenerates into a fibrous cord,
the medial umbilical ligament.
The internal iliac artery begins
in front the sacroiliac joint.It is
divided into anterior and
posterior divisions
Branches of anterior division
In the male,it gives off six
branches:superior vesical artery;
obturator artery,middle rectal
artery,inferior vesical artery,
inferior gluteal artery;and
internal pudendal artery.
In the female,it gives off seven
branches.The inferior vesical
artery is replaced by the vaginal
artery.The uterine artery
is the seventh branch
Superior vesical artery
The proximal part of the
superior vesical artery
represents the persistent
part of the umbilical artery.
It supplies to the upper part
of the urinary bladder.One
of these branches gives off
the artery to
the ductus deferens.
Obturator artery
It runs forward and downwards,
and passes through the obturator
foramen to leave the plevis and
enters the thigh.It gives off
branches to iliac fossa and the
urinary bladder,and a pubic
branch ,which anastomoses
with the pubic branch of the
inferior epigastric artery.
Middle rectal artery
It usually arises with the inferior
vesical artery and supplies the
rectum and the prostate
and seminal vesicles.
Inferor vesical artery
It usually arises with the
middle rectal artery and
supplies the trigone of the
bladder,the prostate,the
seminal vesicles,and the lower
part of the ureter.Sometimes
the artery to the ductus
deferens arises from the
inferior vesical artery.
Inferior gluteal artery
It is the largest branch
of the anterior division
of internal iliac artery.
It runs downwards and
enters the gluteal region
through the lower part of
the greater sciatic foramen
below the piriformis.It
supplies chiefly the buttock
and the back of the thigh.
Internal pudendal artery
It is the smaller terminal
branch of the anterior
division of the internal iliac
artery.It suppplies the
perineum and external genitalia.
It leaves the pelvis and passes
through the greater sciatic
foramen below the piriformis,
thus entering the gluteal region.
In the gluteal region,it passes
through the lesser sciatic foramen
and enters the pudendal canal.
In the pudendal canal,the artery gives off the inferior rectal artery,
the perineal artery.The internal pudendal artery continues
into the deep perineal space as the artery of the penis or
of the clitoris.The artery of the penis or clitoris is divided
into the deep and dorsal arteries of the penis or of clitoris.
Vaginal artery
It corresponds to the inferior
vesical artery of the male,and
supplies the vagina,the bulb
of the vestibule,the base of the
urinary bladder,and the
adjacent part of the rectum.
Uterine artery (see Chapter)
Branches of posterior division
It gives off:Iliolumbar artery;
two lateral sacral arteries;
and superior gluteal arteries.
Iliaolumbar artery
It runs upwards in front of
the sacroiliac joint and divides
into the lumbar and iliac
branches.The lumbar branch
supplies the psoas,the quadratus
lumborum and the erector
spinae.Its spinal branch supplies
the cauda equina.The iliac branch
supplies the iliac fossa and iliacus.
Lateral sacral arteries
These are usually tow in number,
upper and lower.They run downward
and medially over the sacral nerves.
Their branches enter the four anterior
sacral foramina to supply the contents
of the sacral canal and the muscles,
skin on the back of the sacrum.
Superior gluteal artery
It runs backwards and leaves
the pelvis through the greater
sciatic foramen above the
piriformis.For further course
see gluteal region.
Internal iliac vein
It ascends with the internal
iliac artery,and joins the
external iliac vein to form the
common iliac vein at the pelvic
brim.Its tributaries correspond
with the branches of the artery.
The tributaries are as follows.
Superior gluteal vein is the
largest tributary;inferior g
luteal vein;internal pudendal
vein;obturator vein and
lateral sacral veins.
Veins arising from the plexuses
of the plevic viscera:
The rectal venous plexus is
drained by the superior,middle
and inferior rectal veins;the
prostatic venous plexus is drained
into the vesical and internal iliac
veins;the vesical venous plexus
is drained by the vesical veins;
the uterine venous plexuses are
drained by the uterine veins;
and the vaginal venous plexuses
are drained by the vaginal veins.
Nerves of the pelvis:
1.Sacral plexus
The sacral plexus is formed by
the lumbosacral trunk and the
ventral rami of the first to third
sacral nerves,and part of the
fourth sacral nerve.The
lumbosacral trunk is formed
by the descending branch of
the ventral ramus of nerve L4
and the whole of L5.The trunk
descends over the ala of the
sacrum and joins with nerve S1
The main plexus lies in front
of the piriformis.Before uniting
to form the plexus,the ventral
rami give off:Twigs to the
piriformis;the levator ani,the
coccygeus,the sphincter ani
externus;and the plevic
nerves.The plexus tends to divide
into ventral and dorsal divisions.
Branches derived
from both dorsal
and ventral divisions
are the sciatic
nerve and posterior cutaneous
nerve of thigh.
Branches from dorsal
division are the superior
gluteal nerve,the inferior
gluteal nerve,nerve to
piriformis and perforating
cutaneous nerve.Branches
from ventral division are
muscular branches to the
quadratus femoris,the obturator
internus,the levator ani,the
coccygeus,the sphincter ani
externus. Pudendal nerve
and pelvic splanchnic nerves.
Coccygeal plexus
It is formed by the ventral rami
of spinal nerves S4 (descending
branch),S5 and the coccygeal
nerve.The three nerves join on
the plevic surface of the
coccygeus to form a small plexus
known as the coccygeal plexus.
It gives off the anococcygeal
nerves,which supply the skin
in the region of the coccyx.
Pelvic autonmic nerves
Pelvic sympathetic system
The pelvic part of the
sympathetic chain runs
downwards and slightly
medially over the body
of sacrum,and then along the
medial margins of the anterior
sacral foramina.The two chains
unite in front of the coccyx
to form a small ganglion impar.
The chain bears four sacral
ganglia on each sede and the
single ganglion impar
in the central part
The branches of the chain are:
Grey rami commicans to all
sacral and coccygeal ventral
rami;branches to the inferior
hypogastric plexus from the
upper ganglia;branches to the
median sacral artery from
lower ganglia;branches to the
rectum from the lower ganglia;
and branches to the glomus
coccygeum.The inferior
hypogastric plexus one
on each side of the
rectum and other pelvic viscera
is formed by:the hypogastric nerve
from the superior hypogastric
plexus and the plevic splanchnic nerves.
Pelvic splanchnic nerves
represent the sacral outflow
of the parasympathetic nervous
system.The nerves arise as fine
filaments from the ventral rami
of S2,S3 and S4.They join the
inferior hypogastric plexus and
are distributed to the plevic
organs.Some parasympathetic
fibres ascend with the hypogastric
nerve to the superior hypogastric
plexus and thence to the inferior
mesenteric plexus which is
distributed to the descending
colon,the sigmoid colon and the rectum
Pelvic muscles and pelvic diaphragm
The pelvic muscles include
two goups:The pirifomis
and obturator internus,
which are describbed with
the muscles of the lower limbs;
and the levator ani and coccygeus,
which with the corresponding
muscles of the opposite side,
form the pelvic diaphragm.
The diaphragm separates
the pelvis from the perineum.
The levator ani and coccygeus
may regarded as one morphological
entity,divisible from before
backwards into the pubococcygeus,
the iliococcygeus and the
ischiococcygeus or coccygeus.
They have a continuous linear
origin from the body of the pubis
,the tendinous arch or the obturator
fascia and the ischial spine.
The muscle fibres slope downwards
and backwards to the midline,
making a gutter-shaped pelvic floor.
The levator ani
The levator ani is divisible into
a pubococcygeus part and an
iliococcygeus part.The levator ani
is supplied by a branch from the
fourth sacral nerve;and a branch
either from the inferior rectal
nerve,or from the pudendal nerve.
Pubococcygeus part
The anterior fibres of this part
arise from the meidal part of the
body of the pubis.In the male
these these fibres surround the
prostate called the levator prostatae.
In the female these fibres surround
the vagina called sphincter vaginae.
The middle fibres arise from the
lateral part of the body of the pubis.
They form the puborectalis.
The posterior fibres of the
pubococcygeus arise from
anterior part of the tendinous arch.
They get attached to anococcygeal
ligament and tip of coccyx.
Ilococcygeus part
The fibres of this part arise from
the posterior part of the tendinous
arch and the ischial spine.They are
inserted into the anococcygeal
ligament and the side of coccyx.
The coccygeus
This muscle is also called
ischiococcygeus.It is triangular
in shape.Its fibres arise from
the ischial spine and the
sacrospinous ligament.It is
inserted into the side of the coccyx,
and into the fifth sacral vertebra.
The muscle is supplied by a branch
derived from the fourth
and fifth sacral nerves.
The pelvic diaphragm
The pelvic diaphragm is
a sheet consisting of two muscles,
the levator ani and coccygeus,
two fasciae,the superior and
inferior fasciae of plevic diaphragm.
This diaphragm supports the pelvic
organs,seals the inferior opening
of the bony pelvis,and lifts
superiorly to help release feces
during defecation.The plevic
diaphragm is pierced by the
rectum,the urethra and the vagina.