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The Uterine Tubes

Function

The uterine tubes (also called Fallopian tubes or oviducts):  

  1. transport the ovum from the ovary to the site of fertilization
  2. help transport spermatozoa, the haploid male gametes, from the site of deposition to the site of fertilization
  3. provide an appropriate environment for fertilization
  4. transport the fertilized ovum (embryo) to the uterine horns where implantation and further development may occur.

Structure

The uterine tubes can be divided into three major parts:

  1. the infundibulum
  2. the ampulla
  3. the isthmus
Porcine Female Reproductive System Diagram Gross Porcine Female Reproductive System
The infundibulum (in-fun-DIB-u-lum) is the region most proximal to the ovary.  It is funnel-shaped and has finger-like projections called fimbriae (FIM-bre-e) that extend into the pelvic cavity and make close contact with the ovaries.  The tunica mucosa occupies most of the thickness of the wall of the organ. The ampulla is the middle, one-third region in which fertilization usually occurs. Histologically it is very similar to the infundibulum having a very thick tunica mucosa and relatively thick tunica muscularis. The thick-walled isthmus is the lower one-third region most proximal to the uterine horns. The smooth muscle in the wall of the isthmus helps propel (by peristalsis) the fertilized ovum toward the uterine horns and body of the uterus where implantation occurs.  The tunica muscularis is the thickest part of the wall and the tunica submucosa is very thin as in the infundibulum and ampulla.   

 

About the time of ovulation, the infundibulum, closest to the ovary, moves to cover the site of rupture of the mature (Graafian) follicle.  

The ovum moves down the infundibulum of the uterine tube toward the ampulla, assisted by peristaltic contractions of the smooth muscle in the wall of the tube as well as fluid moved by ciliated epithelial cells in the mucosa of the tube.  The ampulla is usually the site of fertilization.  

After fertilization, the embryo moves down through the isthmus which connects the uterine tube with the uterine horns or uterus.  The thick muscular wall of the isthmus of the uterine tube helps propel the embryo into the uterus where it can be nourished during further development.

Regional Variations:

The uterine tubes are paired tubular organs with the typical organization of a tubular organ, i.e., four tunics consisting of:
  1. tunica mucosa
  2. tunica submucosa
  3. tunica muscularis
  4. tunica serosa.

The thickness and specific characteristics of these tunics varies with the region of the uterine tube. 
As always, structure reflects function.
   
all images below should be clicked to view micrographs

The tunica mucosa of the infundibulum helps capture the ovum from the surface of the ovary, bathes it in a supportive fluid and helps move it toward the uterus.

The tunica mucosa of the ampulla provides the proper environment for fertilization.

Consequently, in the infundibulum and ampulla the tunica mucosa is thick and highly developed.

Click to see gross histology
It is the tunica muscularis of the isthmus that provides the strong contractions that at the right time propel the ovum or embryo into the uterine horns.

As a result, in the isthmus the tunica mucosa is reduced in thickness and the tunica muscularis is much thicker

 

Click to see gross histology

Histology: 

Light micrographs of uterine tubes.

The lamina epithelialis of the tunica mucosa of the uterine tubes is an intermittently ciliated columnar epithelium that contains two types of cells:  a ciliated cell and a non-ciliated, secretory cell.  In the cow and sow the lamina epithelialis may be pseudostratified intermittently ciliated columnar.  The secretory product of the non-ciliated, secretory cells is moved toward the uterine horns by the movement of the cilia on the ciliated cells.  This secretion probably also protects and nourishes the ovum.  

The lamina propria consists of a typical loose areolar connective tissue without glands, and it blends with the underlying, thin tunica submucosa.  There is no lamina muscularis mucosae in the entire female reproductive tract. The tunica muscularis is sparse in the infundibulum and the ampulla but thick in the isthmus consisting of an inner circular and an outer longitudinal layer of smooth muscle.   The tunica serosa is typical containing many blood vessels in a distinct vascular layer.

Click here to see the Uterine tube Histology slides.Link to histological slides of uterine tubes.

 

Scanning electron micrographs of a uterine tube from a sow.
  1. Note the extensive folding of the tunica mucosa which serves to increase the surface area providing large numbers of epithelial cells.
  2. Higher magnification view of shaded area showing the extensive sheet of epithelial cells.
  3. Higher magnification of shaded area showing a surface view of the intermittently ciliated columnar epithelium of the uterine tube.  Note the numerous ciliated cells that provide the movement of the male and female gametes to the site of fertilization.  Note the numerous non-ciliated secretory cells that provide nourishment to the ovum and zygote.  The size of non-ciliated secretory cells is under the control of progesterone.  With higher levels of progesterone, the non-ciliated cells become taller and have a greater secretory rate.

Click here to see SEM images of a uterine tube from a sow. 

Link to scanning electron micrographs of uterine tubes.

Click here to see more SEM images of a uterine tube from a sow.

 Link to more scanning electron micrographs of uterine tubes.

More scanning electron micrographs of a uterine tube from a sow.
  1. Note the highly folded tunica mucosa and the relatively thin tunica muscularis (double arrows).  
  2. Enlarged view of the shaded area in "A".  Note the appearance of the lamina epithelialis and the thin lamina propria.  
  3. Enlarged view of shaded area in "B" showing the cells of the lamina epithelialis in longitudinal section.  Note that the epithelium consists of both ciliated and non-ciliated cells. 

Cyclic Changes in the Epithelium : Under the influence of estrogen, the ciliated epithelial cells increase in height and in the number of cilia.  Under the influence of progesterone, these cells decrease in height and in the number of cilia.   These cells are at their tallest with the most numerous cilia at the time of ovulation.  Their main function is to assist in the movement of the ovum toward the site of fertilization and the embryo toward the uterus.  This action is secondary to the peristaltic movement of the isthmus region.

Clinical:  The uterine tubes are the site of tubal ectopic pregnancies.  They can also be the site of bacterial infection which can lead to Pelvic Inflammatory Disease, a major cause of infertility in women.

 

Quick Checks:
1. Fertilization usually occurs in which part of the uterine tube:
infundibulum
ampulla
isthmus

2. The lamina epithelialis of the uterine tube consists of ciliated cells and non-ciliated cells.  What is the main function of the non-ciliated cells?
protection
absorption
secretion

3. Under the influence of estrogen the height and number of cilia on the ciliated epithelial cells of the uterine tube increase.  What purpose could this serve?
Increase the secretory surface area
Increase the absorptive surface area
Increase the ability of these cells to move materials located near them

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This page was last updated 10/19/07 09:53:56 AM