REPRO: Uterus, Uterine Tubes and Cervix

Question 1

How does the uterus and cervix size change as we grow?

Answer 1

The maternal steroids (oestrogen) increase the size of a new-born baby’s uterus. It grows with height during infancy.

The myometrium is dependant on oestradiol. The corpus of the uterus undergoes a greater increase in size than the cervix.

Question 2

Describe the structure of the myometrium.

Answer 2

The outer, muscular myometrium grows gradually throughout childhood. It increases rapidly in size and configuration during puberty.
There are changes in size throughout the cycle. It is also capable of vast expansion during pregnancy.

Inner Layer: circular fibres
Middle Layer: figure-8/spiral fibres
Outer Layer: longitudinal fibres

Question 3

Describe the endometrium of the uterus.

Answer 3

It is very thin in childhood, and begins to thicken at puberty.

It is dependant on steroids; it responds cyclically to hormone changes (oestrogen). It can be seen an measured on an ultrasound scan.

There are changes in the glandular and epithelial cells through the cycle. At menstruation, most of the endometrium is lost.

After menstruation, there is still the stromal matrix with small columnar cells with glandular extensions that are 2-3mm thick. The glands are simple and straight.

Question 4

Describe the endometrial proliferative phase.

Answer 4

The proliferative phase is stimulated by oestradiol from the dominant follicle.

There is stromal cell division with a ciliated surface. The glands expand and become tortuous, with an increased vascularity (neoangiogenesis) and maximal cell division by days 12-14.

When the endometrium is >4mm thick, induction of progesterone receptors occurs, leading to small muscular contractions in the myometrium.

Question 5

Describe the endometrial secretory phase.

Answer 5

The secretory phase (luteal phase of the ovary) occurs 2-3 days after ovulation. The gradual rise in progesterone causes a reduction in cell division.

The glands increase in tortuosity and distend; the secretion of glycoproteins and lipids commences.

Oedema (increased vascular permeability) causes the arterioles to contract and grow tightly wound.

The myometrial cells enlarge and movement is suppressed as the blood supply increases.

Question 6

Describe the regression of the corpus luteum.

Answer 6

The corpus luteum is stimulated by LH from the pituitary during the luteal phase.

The fertilised oocyte becomes a blastocyst and produces human chorionic gonadotrophin (hCG), which acts on the LH receptor, and ‘rescues’ the CL.

In the absence of this, the falling levels of steroids from the CL (e.g. progesterone) result in menstruation.

Question 7

How does menstruation actually occur?

Answer 7

• If we are not pregnant, then corpus luteum dies as it cuts off its own supply of LH and so progesterone levels drop.
• Prostaglandin release causes the constriction of spiral arterioles, the ensuing hypoxia causes necrosis
• The vessels then dilate and bleeding ensues
• Proteolytic enzymes are released from the dying tissue to help get rid of rest of tissue
• The outer layer of the endometrium is shed, 50% is lost in 24 hours, up to 80ml is considered normal; the bleeding normally lasts 4+ days
• The basal layer remains and is then covered by an extension of the glandular epithelium
• Oestrogen from the follicle in the next follicular phase starts the cycle off again

Question 8

What are the three parts of the uterine tube?

Answer 8

• Intramural portion - not much mucosa and it is very muscular.
• Isthmus - inner circular layer with an outer longitudinal layer containing blood vessels and lymphatics in it. Enables the uterine tube to undergo peristalsis and contract in both longitudinal and circular directions.
• Ampulla - huge number of convoluted mucosa so there is a huge surface area for secretory cells. Egg and sperm will be amongst these in the first few days of fertilisation.

Question 9

What are the three kinds of mucosal cells in the uterine tube?

Answer 9

1) secretory cells - secretes growth factors, nutrients, signalling molecules are required early embryo development.

2) columnar ciliated epithelial cells - maybe waft the embryo down the
tube

3) non-ciliated peg cells - unknown function. May be an immature form of another type of cell.

Question 10

What are the muscularis and serosa of the uterine tube?

Answer 10

MUSCULARIS:

• comprised of inner circular and outer longitudinal layers
• contains blood vessels and lymphatics

SEROSA:
- the outer layer (on top of muscular layer)

Question 11

Describe the changes to the cells lining the uterine tubes (ciliated and secretory) throughout the menstrual cycle.

Answer 11

FOLLICULAR/PROLIFERATIVE PHASE:
Ciliated epithelial cells express high numbers of oestrogen receptors and undergo differentiation in response to an oestradiol: they increase in height mid-cycle.

OVULATION:
The oocyte can only pass during mid-cycle. The cilia beat and the secretory cells are active, along with muscle layer contractions, all in response to oestrogen.

LUTEAL/SECRETORY PHASE:
After a few days of exposure to progesterone, the oestrogen receptors are suppressed and the effects of oestrogen are overcome, causing a decrease in height mid-luteal phase onwards.

Question 12

Where does fertilisation occur?

Answer 12

Fertilisation occurs in the ampulla of the uterine tube.

The egg remains in the tube for approximately 5 days.

Question 13

What can damage to the lining of the uterine tube lead to?

Answer 13

Damage to the lining of the tube by infection, endometriosis, surgery or adhesions may cause blockage or damage to the ciliated epithelia, resulting in:

• pain
• infertility
• ectopic pregnancy

Question 14

Describe the structure of the cervix.

Answer 14

It is a muscular structure between the vagina and uterus, capable of great expansion.

The endocervical mucosa is about 3mm thick, lined with a single layer of columnar mucosa cells. These contain numerous tubular mucous glands which empty viscous alkaline mucus into the lumen. Acts as a protective barrier to infection; however, it has to allow the passage of motile sperm.

The ectocervix is covered with nonkeratinised, stratified, squamous epithelium, resembling the squamous epithelium lining the vagina.

Question 15

Describe the cervix during the follicular phase.

Answer 15

Oestrogen in the follicular phase causes a change in vascularity of the cervix, and oedema.

The mid-cycle oestrogen levels cause changes in mucous to make it less viscous:

• a change in mucous composition
• contains glycoproteins which become aligned and form microscopic channels
• sperm swim up channels since it is less viscous and more permeable

Question 16

Describe the cervix during the luteal phase.

Answer 16

Progesterone in the luteal phase causes:

• reduced secretion and viscous mucous (reduced water content)
• glycoproteins now form a mesh-like structure: acts as a barrier (one mechanism of action of oral contraceptives)

Question 17

Describe the vagina.

Answer 17

Thick-walled tube (around 10 cm long) lined by specialised ‘squamous epithelial’ cells. It is a warm, damp environment containing glycoproteins.

It is susceptible to infection, which is prevented by:

• layers of epithelial cells shed constantly and ‘flow’ downwards with the secretion
• secretions are from the cervix and transudation from vaginal epithelium
• secretions change with the cycle and are generally acidic, providing anti-microbial protection

Bartholins glands are located slightly posterior and to the left and right of the opening of the vagina. They secrete mucus to lubricate the vagina and are homologous to the bulbourethral glands in males.