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The Uterus: Changes in the Uterus during the Estrous Cycle LowRes

Domestic animals are either monestrous or polyestrous.   Monestrous animals such as bitches have one estrous cycle per year; each cycle is followed by a long anestrous period.  Polyestrous animals are either continuously cycling without an anestrous period such as cows and sows or seasonally cycling with an anestrous period such as mares, ewes, goats and queens.  The uterine wall, especially the endometrium, undergoes greater changes in the monestrous animal than in the polyestrous animal but changes can be clearly seen in polyestrous animals.

During the estrous cycle the uterus undergoes changes controlled by hormones secreted by the ovary.  The changes are most pronounced in the glands in the tunica submucosa of the endometrium and in the smooth muscle and stratum vasculare located in the tunica muscularis. 

The Chart and Diagrams below allow you to see the differences in the uterine wall between Proestrus, early in the estrous cycle, and Diestrus, later in the estrous cycle.  First read through the text and view the associated images, then review the material by comparing the appearance of the uterus in proestrus versus diestrus by using the colored bars below the text.

Pie Chart indicating the portion of the Bovine Estrous Cycle in Estrus (1 day), Metestrus (2 days), Diestrus (15 days), and Proestrus (3 days). Proestrus
  1. endometrial glands at lowest  level of size & secretion
  2. estrogen rises from granulosa cells in the developing follicles of the ovary
  3. uterine epithelial cells hypertrophy
  4. uterine glands proliferate
  5. vascular supply increases
Estrus
  1. after ovulation progesterone rises from 
    · granulosa & theca lutein cells in the corpus hemorrhagicum
    · granulosa & theca lutein cells in the corpus luteum
  2. uterine epithelial cells continue to hypertrophy
  3. uterine glands continue to proliferate 
  4. vascular supply continues to increase
Metestrus
  1. progesterone levels remain high
  2. uterine glands undergo hyperplasia & coiling
  3. uterine glandular secretory activity high
Diestrus After Diestrus
  1. endometrial glands at maximum size, coiling & secretion
  2. normal state (no fertilization)
    · secretory activity is arrested
    · lining cells and glands begin to involute
    · vascularity of the entire wall decreases
     fertilized state
    · secretory activity is maintained 
      (in order to nourish embryo/fetus during pregnancy)
  3. The wall of the uterus returns to a state that resembles that of the Proestrus uterus.  

Monestrous (not shown on diagram) 
animals enter Anestrus

  1. the endometrium becomes very thin and lined with simple low columnar to cuboidal epithelium 
  2. the uterine glands become very sparse & simple or branched tubular 
  3. the wall of the uterus remains in this low activity state until stimulated to enter Proestrus.

Polyestrous (corresponds to diagram)
animals enter Proestrus and begin the cycle again under the influence of rising estrogen secretion from the ovary.  The histologic appearance of the uterus is very similar in the Anestrus and Proestrus phases of the Estrous Cycle.

 

Uterus images change from appearance at proestrus to appearance at diestrus with different parts of the uterus highlighted to make the changes more apparent.
Point to (don't click) the name in the chart below to change the uterus images.LowRes

Proestrus

Labeled

Diagram Overlay

Perimetrium

Myometrium

Stratum vasculare

Endometrial Glands

Diagram
Diestrus Labeled Diagram Overlay Perimetrium Myometrium Stratum vasculare Endometrial Glands Diagram

     

Quick Checks:

  1. Changes in the uterus associated with the estrous cycle are induced by the following hormones:
    estrogen only
    progesterone only
    both estrogen and progesterone
    neither estrogen nor progesterone

  1. During diestrus of the estrous cycle, which of the following occurs in the uterus under the influence of progesterone from an active corpus luteum?
    the lumen of the uterus gets larger
    the endometrial glands proliferate and the blood vessels of the stratum vasculare enlarge
    all layers of the wall of the uterus become thicker

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