Biology 120 ww5
The inner lining of the uterus is called the
The function of the endometrium as a lining of the
uterus to be an implantation site for a blastocyte
upon its arrival to the uterus. By that time, the
endometrium is a thick, blood vessel rich tissue
During pregnancy, the glands and blood vessels
increase in number and size which then forms the
placenta that supplies the baby with nutrients and
It consists of a single layer of columnar epithelium,
resting on a layer of connective tissue, which varies
in thickness according to hormonal influences -
The endometrial lining undergoes cyclic regeneration
It initially proliferates under the influence of estrogen. However,
once ovulation occurs, in addition to estrogen, the ovary will also
start to produce progesterone.
If the blastocycte does not implant and provide feedback to the
body with human cortico goandotropin and continued feedback
through pregnancy with placental progesterone and estrogen, the
endometrial lining is either reabsorbed (estrous cycle) or shed
The process of shedding involves the breaking down of the
lining, the tearing of small connective blood vessels, and the loss
of the tissue and blood that had constituted it through the vagina.
The entire process occurs over a period of several days.
Menstruation may be accompanied by a series of uterine
contractions; These help expel the menstrual endometrium.
In case of implantation, it remains as decidua
which becomes part of the placenta; it
provides support and protection for the
The glands and blood vessels in the
endometrium further increase in size and
number. Vascular spaces fuse and become
interconnected, forming the placenta, which
supplies oxygen and nutrition to
the embryo and fetus.
The organ in which the developing fetus
resides in is called the uterus.
The uterus (also know as the womb) is a
hollow, pear-shaped organ with a thick
muscular wall, a mucous membrane lining,
and a rich supply of blood. It is located in a
woman's lower abdomen between the
bladder and the rectum.
The narrow, lower portion of the uterus is the
cervix; the broader, upper part is the corpus.
The corpus is made up of two layers of
The endometrial lining of the uterus that
contains a rich blood supply, reacts to
hormonal changes that prepare it to receive a
fertilized ovum that plants itself into the
endometrial wall. It provides nutrients and
protection for the baby.
The uterus during pregnancy
During pregnancy the uterus grows upwards out of the woman's pelvis.
The top of the uterus (or fundus) can be felt by your caregiver feeling
your belly after about 12 weeks of pregnancy. By 24 weeks of
pregnancy, the myometrium muscles start stretching upwards, forming
the thicker upper segment of the uterus. This leaves a thinner layer of
muscle below it, known as the lower segment. The lower segment
separates the cervix from the upper segment and has the role of 'taking
up' or absorbing the cervix as it dilates during labor.
The muscles in the lower segment encircle the lower third of the uterus
and is a relatively weaker layer of muscle with less blood supply,
compared to the upper segment. This is why the cut to perform
a Caesarean operation is done in the lower segment (across the top of
the pubic hairline), where it is less likely to cause excessive bleeding.
The uterus has a natural tendency to lean slightly towards the woman's
right side during later pregnancy, but is held in place by ligaments.
These ligaments stretch as the uterus grows, acting like supportive
anchors to stabilize it, while facilitating the baby's movements within.
The time required
development of a
fetus is called
The carrying of an embryo or fetus inside a female animal.
Pregnancy can be divided into three trimesters, each three
months long. The first trimester is from the last period to the 13th
week, the second trimester is from the 14th to 27th week, and
the third trimester is from the 28th week through the 40th week.
Birth normally occurs at a gestational age of about 40 weeks,
though a normal range is from 37 to 42 weeks which is 9 months
and 1 week. Childbirth occurring before 37 weeks of gestation is
considered preterm, (premature) whereas childbirth after 42
weeks is considered post term (late). Preterm and low birth
weight babies make up the second leading cause of infant death
at about 17%. Preterm births solely consist of 12% of infant
deaths with an 84% majority within the 32–36 week period. It is
estimated that two million babies worldwide die annually within
24 hours of birth.