pelvis and perineum Flashcards
Where is the pelvis located in relation to the abdomen?
The pelvis is inferoposterior to the abdomen.
What is the function of the pelvis?
It serves as the transition area between the trunk and the lower limbs.
What is the greater pelvis?
The greater pelvis contains some inferior abdominal viscera.
Where is the lesser pelvis located?
It is located between the pelvic inlet and outlet.
What does the lesser pelvis contain?
It houses the pelvic cavity and the perineum.
What structure separates the pelvic cavity from the perineum?
The pelvic diaphragm.
What does the perineum include?
The anus and external genitalia.
What is the pelvic girdle?
A basin-shaped ring of bones that connects the vertebral column to the two femurs.
What are the 4 primary functions of the pelvic girdle?
To bear weight
transfer weight
provide muscle attachment
protect pelvic viscera
How does the pelvic girdle help with weight?
It bears the weight of the upper body when sitting and standing.
How does the pelvic girdle transfer weight?
It transfers weight from the axial skeleton to the lower appendicular skeleton for standing and walking.
What muscles attach to the pelvic girdle?
Powerful muscles of locomotion and posture, as well as muscles of the abdominal wall.
What does the pelvic girdle protect?
The pelvic viscera, including inferior urinary tract and internal reproductive organs.
What is notable about the tilt of the pelvic girdle?
It is tilted anteriorly, so the pubic symphysis and anterior superior iliac spines lie in the same vertical plane.
What is another name for the pelvic girdle?
The bony pelvis.
What bones form the pelvic girdle?
Right and left hip bones (formed from ilium, ischium, and pubis).
Sacrum (fusion of five sacral vertebrae) + fused coccyx.
How are the hip bones joined anteriorly?
At the pubic symphysis (secondary cartilaginous joint).
How are the hip bones joined posteriorly?
At the sacroiliac joints:
Anterior part: Synovial joint
Posterior part: Syndesmosis
What are the three bones that fuse to form each hip bone?
The ilium, ischium, and pubis.
How many bones make up each hip bone in infants and children?
Three separate bones – ilium, ischium, and pubis.
What structure unites the three hip bones in children?
The triradiate cartilage at the acetabulum
What is the acetabulum?
A cup-like depression on the lateral hip bone that articulates with the head of the femur.
What happens to the hip bones after puberty?
The ilium, ischium, and pubis fuse to form a single hip bone.
What is another name for the pelvic inlet?
The superior pelvic aperture.
What does the pelvic inlet separate?
The greater (false) pelvis from the lesser (true) pelvis
What are the main structures forming the pelvic inlet?
Promontory and ala of the sacrum
Right and left linea terminalis (terminal line)
What 3 structures make up the linea terminalis?
Arcuate line (on the inner surface of the ilium)
Pecten pubis (pectineal line)
Pubic crest
What is the arcuate line?
A ridge on the inner surface of the ilium forming part of the pelvic inlet.
What is another name for the pelvic outlet?
The inferior pelvic aperture.
What does the pelvic outlet separate?
The pelvic cavity from the perineum.
What 5 structures form the pelvic outlet?
Pubic arch (anteriorly)
Ischiopubic rami (anterolaterally)
Ischial tuberosities (laterally)
Sacro tuberous ligament (posterolaterally)
Tip of coccyx (posteriorly)
What is the function of the interosseous sacroiliac ligaments?
They lie deep between the tuberosities of the sacrum and ilium and facilitate weight transfer from the trunk to the two ilia.
What is the function of the posterior sacroiliac ligament?
It runs obliquely upward and outward from the sacrum and helps compress the sacrum between the ilia, stabilizing the sacroiliac joints.
What effect does axial weight have on the sacrum?
It pushes the sacrum downward, causing the ilia to be pulled inward and compressing the sacrum, further locking the sacroiliac joint.
Why are there sexual differences in the pelvic girdle?
Differences are mainly due to the adaptation of the female pelvis for childbearing.
When does the pubic arch start to show differences between male and female pelvises?
Early during gestation.
How does the false pelvis differ between males and females?
Female: Shallow
Male: Deep
How does the true pelvis differ between males and females?
Female: Wide and shallow; cylindrical
Male: Narrow and deep; tapering
How does the pelvic inlet differ between males and females?
Female: Oval and rounded; wide
Male: Heart-shaped; narrow
How does the pubic arch and subpubic angle differ between males and females?
Female: Wide (90-100°)
Male: Narrow (<70°)
How does the sacral promontory differ between males and females?
Female: Less pronounced projection
Male: Greater projection
What is the pelvic cavity?
The space between the pelvic inlet and the pelvic diaphragm (outlet).
What structures form the pelvic walls and floor?
Muscles
What is the pelvic floor (diaphragm)?
The inferior boundary of the pelvic cavity, suspended superior to the pelvic outlet.
What lies inferior to the pelvic floor?
The perineum.
What 2 things is the pelvic floor composed of?
Levator ani
Coccygeus
What 3 muscles make up the levator ani?
Puborectalis
Pubococcygeus
Iliococcygeus
What is the function of the pelvic wall muscles?
They support the pelvic cavity and contribute to locomotion.
What fascia covers the obturator internus muscle?
The obturator fascia.
What muscle is found in the posterior pelvic wall?
The piriformis muscle.
What is the function of the pelvic floor?
It supports the abdominopelvic viscera and maintains urinary and fecal continence.
Which muscle forms the pelvic floor?
The levator ani.
How does the pelvic floor help with continence?
It remains tonically contracted most of the time to support the organs and control urinary and fecal continence.
During what 3 activities is the pelvic floor actively contracted?
Forced expiration
Coughing and sneezing
Lifting heavy objects
What is the main function of the pelvic floor during periods of increased intra-abdominal pressure?
It increases support for the pelvic organs.
What are the 2 key openings in the pelvic floor?
Urethral hiatus
Anorectal hiatus
How does the puborectalis muscle aid defecation?
It helps maintain the 80° anorectal angle, which relaxes during defecation.
What is the perineum?
A shallow compartment of the body bounded by the pelvic outlet and separated from the pelvic cavity by the pelvic floor.
Where is the surface of the perineum in the anatomical position?
It is the narrow region between the proximal parts of the thighs.
What happens to the perineum when the lower limbs are abducted in the lithotomy position?
It becomes a diamond-shaped area.
What are the boundaries of the perineum? anteriorly, laterally, posterioly
Anteriorly: Mons pubis (in females)
Laterally: Medial surfaces of the thighs
Posteriorly: Gluteal folds
What is a simple way to describe the perineum?
It is the area that underpants cover.
What are the boundaries of the perineum?
The same as the pelvic outlet.
What divides the perineum into two triangles?
A transverse line joining the ischial tuberosities.
What lies posterior to this transverse line?
The anal triangle.
What 3 major structures are found in the anal triangle?
The anal canal and anus, surrounded by ischio-anal fat.
What lies anterior to the transverse line?
The urogenital triangle.
What lines the urogenital triangle?
A thin sheet of deep fascia called the perineal membrane.
What perforates the perineal membrane?
Urethra (both sexes)
Vaginal canal (females)
Where is the perineal body located?
It is the midpoint of the line joining the ischial tuberosities.
What is another way to describe the perineal body’s position?
It is the central point of the perineum.
What is the function of the perineal body?
It is a site of convergence for fibers of multiple muscles.
Which 3 muscles attach to the perineal body?
Levator ani
External anal sphincter
External urethral sphincter
When is the perineal body most at risk of injury?
During childbirth.
Which muscles may be injured during childbirth?
Levator ani (particularly the Puborectalis and Pubococcygeus)
Why are these muscles important?
They support the urethra, vagina, and anal canal.
What are the 3 consequences of weakening these muscles?
Urinary stress incontinence
Uterine prolapse
Fecal incontinence (when intra-abdominal pressure increases)
Why does damage to the perineal body have serious consequences?
It is the site of convergence of multiple muscles, so its weakening affects pelvic floor stability.
