Document

FEMALE GENITALIA
Vulva
The vulva, or pudendum, is a collective term for the external genital organs that
are visible in the perineal area. The vulva consists of the following: the mons
pubis, labia majora, labia minora, hymen, clitoris, vestibule, urethra, Skene's
glands, Bartholin's glands, and vestibular bulbs.
The boundaries of the vulva extend from the mons pubis anteriorly to the
rectum posteriorly and from one lateral genitocrural fold to the other. The
entire vulvar area is covered by keratinized, stratified squamous epithelium. The
skin becomes thicker, more pigmented, and more keratinized as the distance
from the vagina increases
•
Mons Pubis: is a rounded eminence that becomes hairy after puberty. It
is directly anterior and superior to the
symphysis pubis. The hair pattern, or
escutcheon, of most women is
triangular.
•
Labia
Majora:
are two
large,
longitudinal, cutaneous folds of
adipose and fibrous tissue. Each
labium majus is approximately 7 to 8
cm in length and 2 to 3 cm in width.
The labia extend from the mons pubis
anteriorly to become lost in the skin
between the vagina and the anus in the area of the posterior fourchette.
The skin of the outer convex surface of the labia majora is pigmented
and covered with hair follicles. The thin skin of the inner surface does
not have hair follicles but has many sebaceous glands.
•
Labia Minora: are two small, red cutaneous folds that are situated
between the labia majora and the vaginal orifice. They are more
delicate, shorter, and thinner than the labia majora. The skin of the labia
minora is less cornified and has many sebaceous glands but no hair
follicles or sweat glands. The labia minora and the breasts are the only
areas of the body rich in sebaceous glands without hair follicles. Among
women of reproductive age, there is considerable variation in the size of
the labia minora. They are relatively more prominent in children and
postmenopausal women.
•
Hymen: is a thin, usually perforated membrane at the entrance of the
vagina. There are many variations in the structure and shape of the
hymen. Small tags, or nodules, of firm fibrous material, termed
carunculae myrtiformes, are the remnants of the hymen identified in
adult females.
•
Clitoris: is a short, cylindrical, erectile organ at the superior portion of
the vestibule. The normal adult glans clitoris has a width less than 1 cm,
with an average length of 1.5 to 2 cm.
•
Vestibule: extends from the clitoris to the posterior fourchette. The
orifices of the urethra and vagina and the ducts from Bartholin's glands
open into the vestibule. Within the area of the vestibule are the
remnants of the hymen and numerous small mucinous glands.
•
Urethra: is a membranous conduit for urine from the urinary bladder to
the vestibule. The female urethra measures 3.5 to 5 cm in length.
•
Skene's Glands: or paraurethral glands, are branched, tubular glands
that are adjacent to the distal urethra.
•
Bartholin's Glands: are vulvovaginal glands that are located beneath the
fascia at about 4 and 8 o'clock, respectively, on the posterolateral aspect
of the vaginal orifice. Each lobulated, racemose gland is about the size of
a pea
•
Vestibular Bulbs: are two elongated masses of erectile tissue situated on
either side of the vaginal orifice. Each bulb is immediately below the
bulbocavernosus muscle.
The vagina is a thin-walled, distensible, fibromuscular tube that extends from
the vestibule of the vulva to the uterus. The potential space of the vagina is
larger in the middle and upper thirds. The walls of the vagina are normally in
apposition and flattened in the anteroposterior diameter. Thus the vagina has
the appearance of the letter H in cross section.
Cervix
The lower, narrow portion of the uterus is the cervix. The word cervix originates
from the Latin word for neck. The Greek word for neck is trachelos, and when
the cervix is removed, the surgical procedure is termed trachelectomy. The
cervix may vary in shape from cylindrical to conical. It consists of predominantly
fibrous tissue in contrast to the primarily muscular corpus of the uterus.
The vagina is attached obliquely around the middle of the cervix; this
attachment divides the cervix into an upper, supravaginal portion and a lower
segment in the vagina called the portio vaginalis The supravaginal segment is
covered by peritoneum posteriorly and is surrounded by loose, fatty connective
tissue, the parametrium, anteriorly and laterally.
The canal of the cervix is fusiform, with the widest diameter in the middle. The
length and width of the endocervical canal varies; it is usually 2.5 to 3 cm in
length and 7 to 8 mm at its widest point. The width of the canal varies with the
parity of the woman and changing hormonal levels. The cervical canal opens
into the vagina at the external os of the cervix. In the majority of women the
external os is in contact with the posterior vaginal wall. The external os is small
and round in nulliparous women. The os is wider and gaping following vaginal
delivery.
Uterus
The uterus is a thick-walled, hollow, muscular organ located centrally in the
female pelvis. Adjacent to the uterus are the urinary bladder anteriorly, the
rectum posteriorly, and the broad ligaments laterally The uterus is globular and
slightly flattened anteriorly; it has the general configuration of an inverted pear.
The short area of constriction in the lower uterine segment is termed the
isthmus The dome-shaped top of the uterus is termed the fundus. The size and
weight of the normal uterus depend on previous pregnancies and the hormonal
status of the individual. The uterus of a mulliparous woman is approximately 8
cm long, 5 cm wide, and 2.5 cm thick and weighs 40 to 50 g. In contrast, in a
multiparous woman, each measurement is approximately 1.2 cm larger, and
normal uterine weight is 20 to 30 g heavier. The upper limit for weight of a
normal uterus is 110 g. The capacity of the uterus to enlarge during pregnancy
results in a 10- to 20-fold increase in weight at term. After menopause the
uterus atrophies in both size and weight.
Oviducts
The paired uterine tubes, more commonly referred to as the fallopian tubes or
oviducts, extend outward from the superolateral portion of the uterus and end
by curling around the ovary . The uterine tubes connect the cornua of the
uterine cavity and the peritoneal cavity. The ostia into the endometrial cavity
are 1.5 mm in diameter, whereas the ostia into the abdominal cavity are
approximately 3 mm in diameter.
The oviducts are between 10 and 14 cm in length and slightly less than 1 cm in
external diameter. Each tube is divided into four anatomic sections. The uterine
intramural, or interstitial, segment is 1 to 2 cm in length and is surrounded by
myometrium. The isthmic segment begins as the tube exits the uterus and is
approximately 4 cm in length. This segment is narrow, 1 to 2 mm in inside
diameter, and straight. The isthmic segment has the most highly developed
musculature. The ampullary segment is 4 to 6 cm in length and approximately 6
mm in inside diameter. It is wider and more tortuous in its course than other
segments. Fertilization normally occurs in the ampullary portion of the tube.
The infundibulum is the distal trumpet-shaped portion of the oviduct. From 20
to 25 irregular fingerlike projections, termed fimbriae, surround the abdominal
ostia of the tube. One of the largest fimbriae is attached to the ovary, the
fimbria ovarica.
Ovarios
The paired ovaries are light gray, and each one is approximately the size and
configuration of a large almond. The surface of the ovary of adult women is
pitted and indented from previous ovulations. The ovaries contain
approximately 1 to 2 million oocytes at birth. During a woman's reproductive
lifetime, about 8000 follicles begin development. The growth of many follicles is
blunted in various stages of development, however approximately 300 ova
eventually are released. The size and position of the ovary depend on the
woman's age and parity. During the reproductive years, ovaries weigh 3 to 6 g
and measure approximately 1.5 cm × 2.5 cm × 4 cm. As the woman ages, the
ovaries become smaller and firmer in consistency.
El CICLO MENSTRUAL
El ciclo normal de una mujer puede durar de 28 +-7días. Se separa en 2 fases
que se siguen una de otra y depende de las hormonas que sean secretadas en
cada mes, la recomendación es: tengan el ciclo, la imagen del retrocontrol y
procedan a leer lo siguiente:
I. Ciclo Ovárico
Desarrollo Folicular:
En la mujer, en el feto en formación, a partir de células germinales aparecen los
oocitos, (ovogonia recubierta de epitelio superficial o célula pregranulosa)
alrededor de la semana 20 existen unos 7000000 de oocitos, que han iniciado
la meiosis y se detienen en profase I, para entrar en un periodo de latencia
(diploteno), el cual culminará en la pubertad. Al momento del nacimiento, han
sobrevivdo aproximadamente 2000000 de oocitos, y en la pubertad sólo
quedan 400000.
Los oocitos se mantienen en fase de diploteno, aparentemente por un Inhibidor
de la Maduración del Oocito (OMI). En la pubertad, al darse una descarga
rápida de LH (por el mecanismo de retroalimentación positiva al encontrarse
bajo efectos estrogénicos) se reanuda la Meiosis I como se explicará a
continuación. Para efectos de estudio se divide el ciclo en una fase folicular y
una fase lútea.
Fase folicular: los cambios en la variación del ciclo se deben a la duración de
éste.
•El Folículo Primordial:
Al inicio de cada ciclo, unos 12 oocitos son reclutados e iniciados, ésta selección
e inicio es independiente de FSH, sin embargo una vez iniciado, la maduración
del folículo será dependiente de FSH. El reclutamiento está completo en el 2-5
día de ciclo menstrual. Se da un cecimiento del oocito, así como un desarrollo
de las células foliculares, éstas últimas pasaran a formar un epitelio cúbico
pseudoestratificado alrededor del oocito (cèlulas de la granulosa) y existe
todavía una capa de células que lo recubren. La FSH es liberada principalmente
porque al final de la fase lútea anterior ha disminuido la cantidad de
progesterona e inhibina con lo que se estimula la secreción de FSH.
•Folículo preantral (primario):
Con el aumento de la FSH se da un desarrollo de las células de la granulosa, y
éstas se apoyan en otras células foliculares que se han diferenciado en teca
folicular. Éstas células de la teca van a producir un aumento en la
concentración de estrógenos. Las células de la granulosa y el ovocito bajo la
influencia de la FSH van a producir una glicoproteína que formará la zona
pelúcida. La zona folicular se diferenciará en una teca interna y una externa.
Solamente un folículo pasará a ser secundario y el resto experimentará atresia;
se desconoce el mecanismo se selección.
Existe una teoría de 2 células y 2 gonadotropas que dice lo siguiente: La LH
estimula a las células de la teca para que éstas produzcan andrógenos, las
células de la granulosa por medio de aromatización va a transformar los
andrógenos en estrógenos, ésta aromatización es estimulada por la misma FSH.
Los estrógenos en junto con la FSH provoca un aumento en la síntesis y
expresión de receptores de FSH y proliferación de células de la granulosa. Los
andrógenos a concentraciones bajas estimula la actividad aromatasa, mientras
que a concentraciones altas, los andrógenos se transforman en andrógenos con
diferente configuración que no se pueden aromatizar, éstos a su vez inhiben la
expresión de receptores de FSH. Al mismo tiempo, aumentan las cantidades
periféricas de estrógenos, que inhiben la liberación de GnRH y se ha liberado
inhibina por parte del ovario.
Entonces se tiene un microambiente adverso en el cual han disminuido la
concentración de FSH así como receptores sus celulares, la FSH es necesaria
para el desarrollo completo del folículo, por tanto sobrevivirá aquel folículo que
tenga una mayor concentración estrogénica circundante así como la mayor
cantidad de receptores para FSH.
•Folículo de Graaf (secundario o preovulatorio):
A medida q aumenta el desarrollo aparecen espacios ocupados por líquido
(plasma y secreciones de las células granulosas) que al unirse forman el antro,
es cuando se denomina folículo de Graaf. En éste punto, los estrógenos
(producidos en la teca interna) han aumentado su concentración, lo cual
disminuye la FSH y a la vez, pasadas unas 12 horas de descarga constante, van
a tener un efecto de retroalimentación positiva sobre la LH con lo que
sobreviene un pico de LH que va a tener efectos importantes:
a. ovulación: al aumentar las prostaglandinas y enzimas proteolíticas
permiten que el oocito salga a través de la membrana debilitada.
b. se completa la meiosis I y se inicia la meiosis II. Aparece entonces el
primer cuerpo polar; la fase de Meiosis II se completará si se da la
fecundación.
c. estimula la producción de progesterona por las células del estroma
folicular lo que se denomina luteinización.
•Fase Lútea: Es siempre constante, de 14 días.
La corteza folicular restante se transforma en el cuerpo lúteo, productor de
progesterona. Además se produce inhibina y estrógenos en cantidades
importantes. Los cambios por retroalimetación negativa (disminución de FSH y
LH) van a provocar la regresión del cuerpo lúteo (luteólisis) si no se da la
fecundación, caen así los niveles de progesterona y estrógeno. Además existe
una disminución de la inhibina. Se elimina la inhibición central de GnRH, FSH y
de LH, iniciando así nuevamente el ciclo.
Si se diera la fecundación será la gonadotropina coriónica humana placentaria
limitará la acción de la LH y estimulará la secreción de progesterona por el
cuerpo lúteo.
II. Ciclo uterino y menstruación
Cambios Cíclicos en el endometrio:
El endometrio, a lo largo del ciclo bajo la influencia hormonal desarrollará
cambios que teleológicamente le preparan para la implantación. Se habla de
una fase proliferativa y una fase secretora, que coinciden con la fase folicular y
la fase lútea respectivamente. Están determinados en gran parte por la
concentración de estrógenos de origen folicular y la progesterona.
•Fase proliferativa:
Inicia con el día 1 del ciclo menstrual (primer día de la menstruación). Se da un
crecimiento mitótico de la desidia funcional, así como la proliferación de
glándulas endometriales que son cortas y rectas no tienen secreción alguna. La
infiltración por neutrófilos comienza unos 2 días antes de la menstruación. Es
entonces una restitución epitelial.
•Fase secretoria:
En el ciclo típico de 28 días la ovulación se produce en el día 14, en 48-72
horas, la secreción de estrógenos y principalmente de progesterona va a
determinar los cambios. Se vuelve mucho más vascularizado y ligeramente
edematoso, las glándulas más grandes empiezan a secretar un líquido claro. Es
entonces una preparación para la implantación
El endometrio que es irrigado por dos tipos de arterias los dos tercios
superficiales que se desprenden durante la menstruación están irrigadas por
arterias espirales largas y enrolladas. La capa profunda está irrigada por
arterias basilares rectas y cortas. Al experimentar regresión el cuerpo lúteo se
interrumpe del apoyo hormonal del endometrio Aparecen focos de necrosis de
la mucosa y de los vasos que producen focos hemorragicos que confluyen y
producen el flujo menstrual.
Patterns of histologic changes throughout menstrual cycle. (Modified from Noyes RW, Hertig
AT, and Rock J: Fertil Steril 1:3, 1950. Reproduced with permission of the publisher, The
American Fertility Society.)
Menstruation
There has been relatively
little research regarding
the
mechanism
of
menstruation since the
classic studies of Markee
and those of Bartelmez
in the 1930s and 1940s.
In
Markee's
study,
endometria from rhesus
monkeys
were
transplanted into the
anterior chamber of the
eye of the same animal
from which the tissue
was
obtained.
He
observed that during the
cycle the transplants
underwent four periods
of change: (1) the period
of rest (just after menses), (2) the first period of growth, (3) the second period
of growth (after ovulation, when the transplants doubled in size again), and (4)
the period of regression (when menstruation occurred) (Figure 4-47) . Markee
noted that as steroid levels fell several days before menstruation, there was
regression in the size of the transplants, resulting in coiling of the spiral arteries
and slowing of the blood flow within them. Subsequently, vasoconstriction of
the coiled arteries occurred. About 4 to 24 hours after vasoconstriction began,
the coiled arteries relaxed, blood escaped from them, and menstruation began.
Only the spiral arteries that supply the upper two thirds of the endometrium
became coiled and constricted. The straight arteries supplying the stratum
basale did not constrict.
After this sequence of events, the cells are reorganized in structure and
participate in the new proliferative process as described earlier, and the same
cells that previously formed the secretory endometrium also form the new
proliferative endometrium. Thus menstruation in humans is probably a
combination of superficial tissue shedding brought about by ischemia, increases
in IL-8, lysis from hydrolytic enzymes from macrophages, and loss of cell-cell
binding proteins followed by reorganization and regeneration of endometrial
cells.
Diagram of changes in normal human ovarian and endometrial cycles. (From
Shaw ST Jr and Roche PC: Menstruation. In Finn CA, editor: Oxford reviews of
reproduction and endocrinology, vol 2, London, 1980, Oxford University Press.)
Stenchever, A; et al. Comprehensive Gynecology. 4ª Edición. 2001
Berek, Jonathan. Novak's Gynecology. 2003
http://www.msnbc.com/news/wld/graphics/menstrual_cycle_dw2.swf