Uterus
General
Anatomy & histology

Editorial Board Member: Jennifer Bennett, M.D.
Editor-in-Chief: Debra Zynger, M.D.
Kyle Devins, M.D.
Lauren Schwartz, M.D.

Topic Completed: 29 June 2020

Minor changes: 30 July 2020

Copyright: 2002-2020, PathologyOutlines.com, Inc.

PubMed Search: Anatomy[TI] uterus[TI]

Kyle Devins, M.D.
Lauren Schwartz, M.D.
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Cite this page: Kyle D, Schwartz L. Anatomy & histology. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/uterusnormal.html. Accessed August 13th, 2020.
Definition / general
  • Pear shaped organ which serves as physiologic site of implantation for fertilized egg and undergoes changes to support subsequent placental attachment and embryonic / fetal development
Essential features
  • Mucosal component (endometrium) is hormonally responsive and undergoes physiologic and morphologic changes throughout the menstrual cycle
Terminology
  • Anatomic divisions
    • Uterine corpus: upper two - thirds of uterus, which houses the endometrial lined cavity
      • Fundus: domed superior portion of uterus located superior to points of fallopian tube insertion
      • Cornua: lateral portions of uterine corpus; sites of fallopian tube insertion
      • Body
      • Isthmus (lower uterine segment): inferior portion of corpus, which connects to the cervix
    • Uterine cervix: lower one - third of uterus, which attaches to vaginal canal; see Histology
  • Histologic divisions
    • Endometrium: mucosal layer lining the cavity composed of endometrial glands and specialized stroma; blood supplied by spiral arteries
      • Stratum basalis: deep layer of endometrium, which is minimally hormone responsive and serves to replenish the stratum functionalis following menses
      • Stratum functionalis: hormone responsive superficial layer of endometrium; undergoes functional and morphologic changes throughout menstrual cycle; shed during menses
    • Myometrium: structural wall of uterus composed primarily of smooth muscle
    • Serosa: thin, outermost layer of uterus consisting of loose connective tissue and mesothelium
Physiology
  • In infants and children, the endometrium is functionally inactive
  • Menarche:
  • In gestational aged women, the endometrium undergoes hormonally driven changes throughout the menstrual cycle (Endotext: The Normal Menstrual Cycle and the Control of Ovulation [Accessed 11 June 2020])
    • Menstrual phase (days 0 - 5):
      • Estrogen and progestin levels fall in the absence of implantation of a fertilized egg, resulting in breakdown of endometrial stroma
      • Stratum functionalis is shed; spiral arteries constrict to minimize blood loss
    • Proliferative phase (days 6 - 14):
      • Stratum functionalis is regenerated by cells from stratum basalis
      • Primarily driven by increasing estrogen levels
      • Corresponds to follicular phase of cycle in ovary
      • Ends at approximately day 14 when ovulation occurs
    • Secretory phase (days 15 - 28):
      • Stratum functionalis undergoes changes to support implantation in the event of fertilization
      • Glands become convoluted and endometrial cells increase glycogen stores
      • Primarily driven by progestin
      • Corresponds to luteal phase of cycle in ovary
  • Following menopause, the endometrium becomes inactive and may eventually undergo atrophy
  • Pregnancy changes
    • Endometrium retains secretory phenotype and stroma becomes decidualized in response to progestins (detailed in Microscopic description section)
    • Myometrium undergoes mechanoadaptation to allow distension and accommodation of developing fetus (J Cell Mol Med 2008;12:1360)
Diagrams / tables

Contributed by Kyle Devins, M.D.
Average 28 day cycle

Average 28 day cycle

Gross description
  • Pear shaped, smooth external surface
  • Anatomic position within the pelvic cavity between the urinary bladder (anterior) and rectum (posterior)
  • Anterior portion can be identified by a higher peritoneal reflection, due to location of the bladder in vivo (J Clin Pathol 1993;46:388)
  • Hysterectomy specimens are often opened in the coronal plane by inserting a probe into the external cervical os and cutting along the probe to reveal the endometrial cavity
  • Endometrial cavity is shaped like an inverted triangle when viewed in the coronal plane
Gross images

Contributed by Kyle Devins, M.D.
Missing Image

Uterus

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Bivalved uterus

Microscopic (histologic) description
  • Endometrium (Mod Pathol 2000;13:285)
    • Proliferative phase
      • Cellular blue appearance at low power
      • Round to tubular glands
      • Even, regular spacing between glands
      • Pseudostratified columnar cells in glands
      • Numerous mitotic figures in glands and stroma
    • Secretory phase
      • Relatively pink appearance at low power
      • Convoluted, irregularly shaped glands
      • Single layer of columnar or cuboidal cells in glands
      • Early secretory phase
        • Subnuclear vacuoles in glandular cells, progressing to both subnuclear and supranuclear vacuoles
        • Endometrial stromal edema
      • Late secretory phase
        • Epithelial cell vacuoles diminish and cells are left with abundant pink cytoplasm which steadily decreases in abundance throughout late secretory phase
        • Secretions in gland lumina
        • Predecidual change in stroma begins around spiral arteries and glands in late secretory phase, then progresses to involve most of stroma by end of secretory phase
          • Predecidual change: stromal cells become plump by gaining more eosinophilic cytoplasm, cellular borders become distinct
    • Menstrual phase
      • Endometrial stromal breakdown: dense round aggregates of stromal cells in a background of blood
      • Papillary syncytial metaplasia is common, thought to be a reparative response
    • Gestational changes
      • Decidual change: stroma gains abundant eosinophilic cytoplasm, appears polygonal with distinct cell borders
      • Arias-Stella reaction in glandular cells (Am J Case Rep 2012;13:271)
        • Nuclear enlargement and hyperchromasia
        • Abundant eosinophilic vacuolated cytoplasm
        • Hobnail appearance with cells protruding into glandular lumen
    • Atrophy
      • Common in postmenopausal women due to estrogen withdrawal
      • Glands composed of inactive low columnar to cuboidal cells
      • Glands often detached from stroma, forming hairpin structures
      • May have cystic change
    • Myometrium
      • Short fascicles of smooth muscle
      • Large, thick walled blood vessels
    Microscopic (histologic) images

    Contributed by Kyle Devins, M.D.
    Missing Image

    Endometrium

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    Proliferative phase

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    Secretory phase

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    Early secretory phase

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    Late secretory phase


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    Endometrial stromal breakdown

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    Arias-Stella reaction

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    Atrophy

    Cytology description
    Cytology images
    Positive stains
    Videos

    Histology of benign cycling endometrium

    Board review style question #1

      What phase endometrium is pictured in the image?

    1. Atrophy
    2. Menstrual phase
    3. Proliferative phase
    4. Secretory phase
    Board review answer #1
    D. Secretory phase. The endometrial glands are lined by a single layer of low columnar cells with pink cytoplasm and prominent glandular secretions. There is predecidual change in the stroma.

    Comment Here

    Reference: Anatomy & histology
    Board review style question #2

      The pictured endometrial sample was most likely obtained from which of the following patients?

    1. Gestational age woman during menses
    2. Postmenopausal woman
    3. Pregnant woman
    4. Prepubertal female
    Board review answer #2
    C. Pregnant woman. The image shows an example of gestational endometrium. There is decidual change in the stroma with abundant eosinophilic cytoplasm and polygonal cells with prominent cell borders. The glandular cells show Arias-Stella reaction.

    Comment Here

    Reference: Anatomy & histology
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