Anatomy and Physiology of the Vagina and Uterus

Anatomy and Physiology of the Vagina and Uterus

 1.The Vagina

• It is a canal running from the vestibule to the cervix, passing upwards and backwards into the pelvis along a line approximately parallel to the plane of pelvic brim.

•   Relations

         - The knowledge of the relations of the vagina is essential for the accurate examination
                of the pregnant woman and her safe delivery.
         - Anterior: In front of the vagina lie the bladder and urethra, which are closely
                connected to the anterior vaginal wall.
         - Posterior: Behind the vagina lie the pouch of Douglas, the rectum and the perineal
                 body each occupying at least one third of the posterior vagina wall.
         - Lateral: On either side of the upper two thirds are the pelvic fascia and the ureter
                which pass beside the cervix on either side of the lower third are the muscles of the
                  pelvic floor.
         - Superior: Above the vagina lies the uterus.
         - Inferior: Below the vagina les the external genitalia.  

• Structure

•  The posterior wall is 10 cm long where the anterior is 7.5 cm in length because the cervix projects at right angle into its upper part
• The upper end of the vagina is known as the vault, where the cervix projects into it, the vault forms circular recess that is described as four arches or fornic
• The posterior fornix is the largest because the vagina is attached to the vagina at a higher level behind than in front.
• The anterior fornix lies in front of the cervix.
•  The lateral fornices lie on either side.
• The vagina walls are pink in appearance and thrown into small folds known as ruggae, these allow the vagina to stretch during intercourse and child birth.  

•  Layers 
• The lining is made of squamous epithelium, beneath the epithelium lies a layer of connective tissue.
• The muscle layer is divided into a weak inner coat of circular fibres and a stronger outer coat of longitudinal fibres.

• Content           
• There are no glands in the vagina. It is moistened by mucous from the cervix and transudate from the blood vessels of the vaginal wall.
•  Inspite of the alkaline mucous, the vaginal fluid is strongly acid (pH 4.5) due to the presence of lactic acid formed by the action of Doderlein’s bacilli on glycogen found in the squamous epithelium of the lining 
•  
• Function

•  It is a passage which allows the escape of menstrual flow.
•  Receives the penis and the ejected sperms during sexual intercourse
   - Provides an exit for the fetus during delivery.
   
•  Blood supply
   - This comes from branches of internal iliac artery and includes the vaginal artery and
  descending branch of uterine artery.
•  The blood drains through corresponding veins.
   
• Lymphatic drainage
  o This is via the inguinal, the internal iliac and the sacral glands.
• Nerve supply
  o This is derived from the pelvic plexus.
  o The vaginal nerves follow the vaginal arteries to supply vaginal walls and also the
  erectile tissue of the vulva.
   
• 2.The Uterus
•  Position
  o It is situated in the cavity of the true pelvis behind the bladder and in front of the
  rectum. It leans forward which is known as anteversion and bends forward on itself,
  which is known s anteflexion.
  o When the woman is standing the uterus is almost horizontal with the fundus resting on
  the bladder
• Relations
  o Anterior - In front of the uterus lie the uterovesical pouch and the bladder
  o Posterior - Behind the uterus are the recto uterine pouch of Douglas and rectum.
  o Lateral - On either side of the uterus are the broad ligaments, the fallopian tubes and
  the ovaries.
  o Superior - Above the uterus lie the intestines.
  o Inferior - Below the uterus is the vagina.
•  Supports
  o The uterus is supported by the pelvic floor and maintained in position by several
  ligaments

      - The transverse cervical ligament - These fan out from the sides of the cervix to the
             side walls of the pelvis. They are sometimes known as the cardinal ligaments or
              mackenrodt’s ligaments.
    - The uterosacral ligaments - They pass backward from the cervix to the sacrum.
    - The pubocervical ligaments - They pass forward from the cervix, under the
            bladder to the pubic bones.
    - The broad ligaments - These are formed from the folds of peritoneum which are
         draped over the fallopian tubes. They hang down like a curtain and spread from
          the sides of the uterus to the side walls of the pelvis.
     - The round ligaments - Maintain the anteverted position of the uterus,they arise
          from the cornua of the uterus in front of and below the insertion of each fallopian
           tube and pass between the folds of the broad ligaments, through the inguinal canal
      - The ovarian ligaments - These also begin at the cornua of the uterus but behind
         the fallopian tubes and pass down between the folds of broad ligaments to the
            ovaries.

•   Functions

o It is the shelter of the fetus during pregnancy
o It prepares the possibility of pregnancy each month
o Following pregnancy it expels the uterine content.

•  Structure

o The non pregnant uterus is a hollow muscular pear shaped organ situated in the true
pelvis, it is 7.5 cm long, 5 cm wide and 2.5 cm in depth, each wall being 1.25 cm
thick. The cervix forms the lower third of the uterus and measures 2.5 cm.

•  Parts of the uterus

o The body or corpus - makes up the upper two thirds of the uterus and is the greater
part.
o The fundus - is the doomed upper wall between the insertions of the uterine tubes.
o The cornua - are the upper outer angles of the uterus where the uterine tube joins.
o The cavity - is a potential space between the anterior and posterior walls. It is triangle
in shape; the base of the triangle being uppermost.
o The isthmus - is a narrow area between the cavity and the cervix, which is 7 mm long.
It enlarges during pregnancy to form the lower uterine segment.
o The cervix or neck - this protrudes into the vagina. The upper half which is above the
vagina is known as supravaginal portion while the lower half is the infravaginal
portion
 - The internal os (mouth) - the narrow opening between the isthmus and cervix.
 - The external os - is the small round opening at the lower end of the cervix. After
child birth it becomes a transverse slit.
 - The cervical canal - lies between these two openings and is a continuation of the
uterine cavity.
 - Layers

The uterus has three layers
 1. The endometrium - This layer forms a lining of ciliated epithelium (mucous
membrane) on a base of connective tissue or stroma. In the uterine cavity this
endometrium is constantly changing in thickness throughout the menstrual cycle
 2. The mayometrium or muscle coat - This layer is thick in the upper part of the uterus
and sparse in the isthmus and cervix. Its fibres run in all directions and interlace to
surround blood vessels and lymphatics that pass to and from the endometrium. The
outer layer is formed of longitudinal fibres that are continuous with those of the
uterine tube, uterine ligaments and vagina.
 3. The perimetrium - This is a double serous membrane, an extension of the peritoneum
which is draped over the uterus covering all but a narrow strip on either side of the
supravaginal cervix.

•   Blood supply

o The uterine artery which is a branch of internal iliac artery, it sends a branch to the
upper vagina and runs upwards to meet the ovarian artery and form an anastomosis
with it near the cornua. The ovarian artery is a branch of the abdominal aorta. It
supplies the ovary and fallopian tubes before joining the uterine artery
o The blood drains through corresponding veins

•  Lymphatic drainage

o Lymph is drained from the uterine body to the internal iliac glands and also from the
pelvic area to many other pelvic glands.

•  Nerve supply

o Mainly from the autonomic nervous system, sympathetic and parasympathetic via Lee
Franken and Hauser’s plexus or pelvic plexus.
Step 3: Anatomy and Physiology of the Fallopian tubes and Ovaries (45
minutes)

3.The Fallopian Tubes or Uterine Tubes

•  The Fallopian tubes extend laterally from the cornua of the uterus towards the side walls

of the pelvis. They arch over the ovaries, there fringed end hovering near the ovary in
order to receive the fertilized ovum.

•  Functions

o Propels the ovum towards the uterus
o Receives the spermatozoa
o Provide a site for fertilization
o It supplies the fertilized ovum with nutrition during its journey to the uterus.

•  Relations

o Anterior, posterior and superior - In front of, behind and above the uterine tubes are
peritoneum cavity and intestines.
o Lateral - On either side of the uterine tubes are the side walls of the pelvis.
o Inferior - The broad ligaments and ovaries lie below the uterine tubes.
o Medial - The uterus lies below the two uterine tubes.

•  Supports

o The uterine tubes are held in place by their attachment to the uterus. The peritoneum
folds over them as the broad ligaments and extend at the sides to form the
infundibulopelvic ligaments.

•  Structure

o The tube is 10 cm long. The lumen of the tube provides a pathway from outside to
the peritoneum cavity. The uterine tube has 4 portions
o The interstitial portion is 1.25 cm long and lies within the walls of the uterus. Its
lumen is 1 mm wide.
o The Isthmus it is another narrow part which extends to 2.5 cm from the uterus.
o The Ampulla is the wider portion, 5 cm long where fertilization usually occur.
o The infundibulum is the funnel-shaped fringed end which is composed of many
processes known as fimbriae. One fimbria is elongated to form the ovarian fimbria
which is attached to the ovary

•   Layers

o The lining - This is a mucous membrane of ciliated cubical epithelium that are thrown
into folds known as plicae. These folds slow the movement of the ovum on its way to
the uterus. The cells in the lining produce a secretion containing glycogen which
nourishes the ovum.
o Beneath the lining is a layer of vascular connective tissue
o The muscle coat - This consists of two layers of smooth muscles, an inner circular
layer and outer longitudinal layer. The peristaltic movement of the tube is due to these
muscles.
o The tube is covered with peritoneum.

•  Blood supply

o This is via uterine and ovarian arteries. Blood drain via corresponding veins.

•  Lymphatic drainage

o This is to the lumber glands.

•  Nerve supply

o From the ovarian plexus.

 
 figure The fallopian tube ,uterus and ovaries


 


 4.The Ovaries

•  The ovaries are the female gonads which produce ova and the hormones estrogen and progesterone

•  Position

o The ovaries are attached to the back of the broad ligaments within the peritoneal
cavity

•  Relations

o The ovary is attached to the broad ligaments; it is supported from above by the
ovarian ligament and infundibulopelvic ligament laterally.

•  Structure

o The ovary is composed of medulla and cortex covered with germinal cells
o The medulla. It is the supporting frame work which is made of fibrous tissue blood
vessels, nerves and lymphatic pass through it
o The cortex. It is the functioning part of the ovary. It consist of ovarian follicles in
different stages of development, surrounded by stroma. The outer layer is formed of
fibrous tissue known as tunica albuginea, over this lies the geminal epithelium.

•  Blood supply

o The blood is from ovarian arteries and drains by the ovarian veins. The right ovarian
vein joins the inferior vena cava, the left returns its blood to the left renal vein.


Summary

•   A knowledge of the relations of the vagina to other organs is essential for the accurate examination of the pregnant woman and her safe delivery
• The non pregnant uterus lies almost horizontal with the fundus resting on the bladder when the woman is standing.
•  The uterus is supported by the pelvic floor and maintained in position by several ligaments
•  The fallopian tubes propel the ovum towards the uterus, receive spermatozoa as they travel upwards and provides site for fertilization. It supplies fertilized ovum with nutrition during its journey to the uterus.
•  The ovaries produce ova and the hormones oestrogen and progesterone