S4: Uterus, Uterine Tubes and Cervix

Question 1

What fruit is the uterus the same size as?

Answer 1

The uterus is the same shape and size of an upside down pear.

Question 2

Path of sperm and embryo

Answer 2

• The sperm will enter through the cervix into the uterus.
• Sperm swims up the uterine tube, around the region of the ampulla the sperm will usually meet the oocyte. The oocyte would have been released from the ovary and picked up by the fimbriae.
• Once fertilisation occurs the embryo continues moving down the uterine tube, this takes about 5 days until it reaches the uterus where it implants into the endometrium.
• The uterus is very well supplied with blood.

Question 3

Describe changes in uterus and cervix with age

Answer 3

• The uterus of a newborn is larger than that of a four year old. The reason for this is that the uterus (endometrium and myometrium) responds to oestrogen. During pregnancy maternal steroids (oestrogen) increases the size of the newborn uterus. While pregnant the women will see very high levels of oestrogen.
• After birth, these high levels of oestrogen are no longer present so the uterus shrinks, which is why the four year old uterus is smaller than the newborns.
• The uterus does grow with height during infancy.
• At puberty it is about medium size.
• A nulliparous uterus is one of a woman that hasn’t given birth, this is quite large. This is because there is a lot of growth once the menstrual cycle has kicked in properly.
• A multiparous uterus is much larger, due to the high levels of oestrogen during pregnancy. It never goes back to the smaller size it was before pregnancy.
• In the post-menopausal woman, oestrogen is very low and the uterus shrinks back to around its pubertal size.
• The myometrium is dependent on oestradiol.
• It is the corpus of the uterus that undergoes a greater increase in size than the cervix.

Question 4

What are the three layers of the uterus?

Answer 4

• Endometrium is the mucosal lining of the uterus. It is shed every month.
• Myometrium is the muscular layer that makes up the body of the uterus.
• Perimetrium surrounds the uterus.

Question 5

Describe the myometrium

Answer 5

There are three types of muscle fibres which mean the myometrium is a very dynamic and well-developed organ:
- An inner layer, which is made of circular fibres.
- A middle layer which is made up of figure-of-8 or spiral fibres,
- An outer layer that is made up of longitudinal fibres.
It is the myometrium where uterine fibroids (benign smooth muscle tumours of the uterus) develop, they are responsive to oestrogen. The myometrium grows gradually throughout childhood and then increases rapidly in size and configuration during puberty. Throughout the menstrual cycle it changes its size and is capable of vast expansion during pregnancy.

Question 6

Describe the endometrium and its changes throughout the menstrual cycle

Answer 6

• In a fully developed endometrium, the arteries supplying the endometrium become spiralled increasing surface area. There is dense capillary network and it is heavily vascularised.
• When the endometrium is reaching full receptivity (about a week after ovulation) it develops uterine glands which secrete substances onto the luminal surface of the uterus such as growth factors, adhesion molecules.
• The endometrium is dependent on steroids and responds cyclically to hormone changes.
• There are changes in the glandular and epithelial cells through the cycle.
• The first half of the menstrual cycle is dominated by oestrogen which causes proliferation of the stromal layer (layer of connective tissue on which endothelial cells lay on). After ovulation the corpus luteum is secreting mainly progesterone which causes differentiation/maturation/become receptive of the endometrium, the coiling of the arteries and development of glands.
• When the corpus luteum dies, most of the endometrium is shed back down to its stromal matrix.
• The stromal matrix left over after menstruation consists of small columnar cells with glandular extensions 2-3mm thick. The glands are simple and straight.
• The second half of the cycle is progesterone dependent which causes little proliferation, mainly differentiation.

Question 7

Why is an ultrasound a good ‘bioassay’ of oestrodiol levels?

Answer 7

Endometrium responds to hormone changes which can be seen on an ultrasound.

Question 8

What are the two phases of the menstrual cycle in respect to the ovary?

Answer 8

The first half of the cycle is the follicular phase, the second half is the luteal phase.

Question 9

What are the two phases of the menstrual cycle in respect to the endometrium?

Answer 9

The first half is the proliferative phase under oestrogen and the second part is the secretory phase under progesterone.

Question 10

Describe the endometrial proliferative phase

Answer 10

• The proliferative phase is stimulated by oestrodiol released from the dominant follicle. Lots of oestrogen around causes proliferation of the endometrium. This involves stromal cell division, development of the ciliated surface. The glands expand and become tortuous and there is increased vascularity as neoangiogenesis occurs.
  By days 12-14 there is maximum cell division. The gonadotrophins are low due to negative feedback.
  When the endometrium is above 4mm, there is induction of progesterone receptors on the endometrium.
• After there has been sustained high oestrogen for about 2 days, this causes a switch to positive feedback. Causing the LH surge and ovulation.

Question 11

Describe the endometrial secretory phase

Answer 11

• The secretory phase (luteal phase of ovary) involves the gradual rise in progesterone from the corpus luteum. Progesterone causes a reduction in cell division (proliferation). The progesterone causes the endometrium to start differentiating/maturing.
• The glands increase in tortuosity and distend. They also start to secrete glycoproteins and lipids. Oedema is also seen as there is increased vascular permeability, the arterioles also become coiled. Myometrial cells enlarge and movement is suppressed and blood supply increases.
• This creates a good enviroment for implantation.

Question 12

Describe regression of the corpus luteum and effect on endometrium

Answer 12

• The corpus luteum while it secretes progesterone is stimulated by LH from the pituitary during the luteal phase. The corpus luteum has a lifespan of only 14 days because the -ve feedback of progesterone causes LH to fall, leading to the corpus luteum dying. As the corpus luteum dies, progesterone falls, this causes menstruation as progesterone is required to maintain the endometrium.
• If the oocyte is fertilised it becomes a blastocyst and starts to produce hCG which maintains the corpus luteum, it actually binds to the LH receptor and has a similar structure to it. This is despite LH falling. This ‘rescues’ to CL.

Question 13

Describe mechanism of menstruation

Answer 13

• When progesterone drops it causes the cells of the endometrium to release prostaglandins. This prostoglandins release results in constriction of the spiral arterioles, causing hypoxia and necrosis. The vessels then dilate and bleeding ensues.
• Proteolytic enzymes are released from the dying tissue, which help the process.
• Initially it is the outer layer of the endometrium that is shed, 50% is lost in 24hrs and up to 80ml is considered normal. - Bleeding normally lasts 4,5,6 days and most of the endometrium is lost except for a few mm of the stomal matrix.
• The basal layer remains and is then covered by extension of glandular epithelium
• Oestrogen from maturing antral follicles starts to be released causing endothelium to start growing and the cycle starts again.

Question 14

What is the function of the uterine tube?

Answer 14

The uterine tube is not just a passive tube connecting ovary to uterus. The uterine tube is where fertilisation occurs, the secretions of the uterine tube are critical here. This is where the early embryo survives for its first 5 days.

Question 15

Describe structure of uterine tube wall

Answer 15

• The intramural section is where the uterine tube meets the uterus.
• The outermost layer is the serosa.
• It then has an (outer) layer of smooth longitudinal fibres and then an inner layer of circular muscle fibres. This persists all the way down the tube. The inner circular muscles can be peristaltic.
• On the inside is the mucosa.

Question 16

What are the 3 main cell types in the mucosa of the uterine tubes?

Answer 16

1. Secretory -> secretes nutrients for the early embryo.
2. Columnar ciliated epithelium -> waft oocyte and embryo down the uterine tube.
3. Non ciliated Peg -> Peg cells are thought to be immature ciliated cells.

Question 17

What are the sections of the uterine tube?

Answer 17

There are fourpartsof the ovary to theuterus: The fimbria, infundibulum, ampulla and isthmus.

• In the isthmus there is much more of the secretory mucosa.
• In the ampulla, the secretory mucosa becomes very convoluted to give a massive surfacse area, this is where the sperm meets the egg.

Question 18

Describe the changes in cells lining the uterine tubes affected by the menstrual cycle

Answer 18

Start of cycle, the secretory and ciliated cells aren’t doing much. As oestrogen levels rise and cycle progresses, the cells in the uterine tubes differentiate (oestrogen has different effect to uterus where oestrogen causes proliferation). The secretory and ciliated cells then cause secretion (maximum during ovulation). Progesterone production then occurs from CL which overcomes oestrogen which causes de differentiation of the cells in the uterine tube.

Question 19

How are eggs transported along the uterine tube?

Answer 19

• Beating of the cilia stimulated by oestrogen.
• Rapid contractions of muscular layer caused by oestrogen.
  There are high number of oestrogen receptors present in follicular phase which allow this. However, Oestrogen receptors suppressed by progesterone. Therefore, all of above stops by mid- luteal phase, even if an egg was released it would be unable to pass.

Question 20

Where in the uterine tube does fertilisation occur?

Answer 20

Ampulla

Question 21

What symptoms does damage to lining of the uterine tube cause? list some causes

Answer 21

Causes: Damage by infection, endometriosis, surgery or adhesions may cause blockage or damage to ciliated epithelia.
Symptoms: Pain, infertility or ectopic pregnancy

Question 22

What are the two main ways to check the uterine tubes are blocked (tube patency)?

Answer 22

They both involve passing a dye through the vagina, through the cervix and into the uterus. The only way the dye can get out of the uterus is through the uterine tube.

1. Laproscopy and Dye.
2. Hystero Salpingo-contrast Sonography (HyCoSy).

Question 23

Describe Laproscopy and Dye

Answer 23

1. A uterine cannula goes through the cervix and introduces a dye into the uterus.
2. A laproscope goes through the abdominal wall and you can look down it and see inside the pelvic cavity.
3. Can see the dye emerge out the end of the uterine tube (out the fimbrial end) this means there is no blockage. But if it doesn’t emerge it means there is something blocking it.

Question 24

Describe Hystero Salpingo-contrast Sonography (HyCoSy)

Answer 24

1. Fill uterus with dye via vagina, only way is out through uterine tube.
2. The dye is opaque to ultrasound, so put an ultrasound scanner on patient abdomen and we can see the progress of the dye through the tube.
3. Thus a non-invasive method and cheaper

Question 25

Why is Laprascopy and Dye sometimes done rather than HyCoSy?

Answer 25

A laproscopy allows us to visually inspect the pelvis, we can visually see endometriosis or adhesions. This therefore might be done even though it is more invasive than HyCoSy.

Question 26

Describe the structure of the cervix

Answer 26

• The cervix is a muscular structure that is capable of great expansion
• The endocervical mucosa lined with a single layer of columnar mucosal cells containing numerous tubular mucous gland which secrete viscous alkaline mucus into the lumen. It also has a secretory mucosa that secretes cervical mucus. There are many secretory glands here producing mucous.
• The mucus even changes throughout the menstrual cycle. The mucus is important and acts as a protective barrier to the cervical os, which is the gateway from the outside world to the uterus. It acts as a barrier to infection and other agents.

Question 27

How does the cervix allow passage of sperm?

Answer 27

• When a woman is ovulating the mucus becomes thin and runny enabling sperm to swim through with ease.
• During other times of the cycle the mucus becomes thick and sticky so sperm can’t swim through it. Forms a mucal plug.

Question 28

Describe cervix and cervical mucous in follicular phase of the menstrual cycle

Answer 28

• Oestrogen in the follicular phase causes change in vascularity of cervix and oedema.
• Mid-cycle oestrogen levels cause change in mucous to become less viscous. There is a change in mucous composition and it contains glycoproteins. Glycoproteins become aligned and form microscopic channels and sperm swim up channels!

Question 29

Describe cervical mucous in luteal phase of the menstrual cycle

Answer 29

Progesterone in luteal phase affects cervical mucus causes reduced secretion and viscous mucous (reduced water content) and glycoproteins now form mesh like structure: acts as barrier. This is one mechanism of action of oral contraceptives.

Question 30

What is the vagina?

Answer 30

The vagina is a thick-walled tube approx. 10cm long. It is lined by specialised squamous epithelial cells and is a warm, damp environment that contain glycoprotein.

Question 31

As the vagina is open to the outside world. It is susceptible to infection. How is this prevented?

Answer 31

• The layers of epithelial cells lining the vagina are constantly shed and flow downwards with secretions.
• There are secretions from the cervix and also transudation from the vaginal epithelium. The latter meaning that plasma leaks out from capillaries in the vagina wall and into the vagina.
• Secretions also change with cycle and are generally acidic, this provides anti-microbial protection.

Question 32

What are Bartholinian glands?

Answer 32

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