Types of Cells in the Uterus
The uterus contains three main tissue layers with distinct cell types: the endometrium (inner layer), myometrium (middle layer), and perimetrium (outer layer), each containing specialized cells that serve different functions in reproductive health.
Endometrial Layer (Inner Layer)
The endometrium is the innermost lining of the uterus that undergoes cyclical regeneration during the menstrual cycle and significant remodeling during pregnancy. It contains:
Epithelial cells: Form the luminal surface and glandular structures 1
- Luminal epithelial cells (line the uterine cavity)
- Glandular epithelial cells (form endometrial glands)
- Ciliated epithelial cells (specialized epithelial cells with motile cilia) 1
Stromal cells/fibroblasts: Form the supporting tissue framework 1, 2
- Endometrial stromal fibroblasts
- Predecidual cells (during secretory phase and pregnancy)
Immune cells: 1
- Macrophages
- Lymphocytes (including T cell subtypes, particularly T regulatory cells)
- Natural killer (NK) cells
Vascular cells: 1
- Endothelial cells (line blood vessels)
- Perivascular cells
Myometrial Layer (Middle Layer)
The myometrium is the muscular middle layer of the uterus and consists of:
- Smooth muscle cells: Organized in three sublayers 1, 3
- Inner layer of smooth muscle cells
- Intermediate layer (richly vascularized)
- Outer layer of smooth muscle cells
These smooth muscle cells are responsible for uterine contractions during labor and menstruation. They contain cyclooxygenase (COX) enzymes (COX-1 and COX-2) that are essential for prostaglandin production, particularly important during parturition 1.
Perimetrial Layer (Outer Layer)
The perimetrium is the outermost serosal layer of the uterus:
- Mesothelial cells (simple squamous epithelium)
- Connective tissue cells
Pathological Cell Types
In certain uterine pathologies, additional cell types may be present:
Uterine sarcomas: 1
- Low-grade endometrial stromal sarcoma (LGESS) cells: Small cells with low-grade cytology resembling stromal cells in proliferative endometrium
- High-grade endometrial stromal sarcoma (HGESS) cells: Small cells with high-grade cytology, frequent necrosis, and brisk mitotic activity
- Undifferentiated uterine sarcoma (UUS) cells: Cells with high-grade cytologic features lacking resemblance to normal stromal cells
- Uterine leiomyosarcoma (uLMS) cells: Malignant smooth muscle cells
Adenomyosis: Characterized by endometrial epithelial cells and stromal fibroblasts abnormally found in the myometrium 4
Developmental Aspects
During fetal development, the uterine wall undergoes significant changes:
- Mesenchymal cells without myofilaments are present until 16 weeks gestation
- Immature smooth muscle cells appear around 18 weeks gestation in the outer layer
- By 31 weeks gestation, mature smooth muscle cells form the myometrium 5
Clinical Implications
Understanding the cellular composition of the uterus is crucial for:
- Diagnosing uterine pathologies
- Understanding mechanisms of menstruation and pregnancy
- Developing targeted therapies for uterine disorders
The different cell types interact through complex signaling pathways, particularly during the menstrual cycle and pregnancy, when significant tissue remodeling occurs. Recent single-cell RNA sequencing studies have revealed even greater cellular heterogeneity and identified previously unrecognized cell subtypes within the uterus 1.
Human Perspective
AI: I've provided a comprehensive overview of the different cell types in the uterus, organized by the three main tissue layers. I've prioritized information from the most recent guidelines while incorporating relevant details from research studies. The answer is structured to clearly identify the main cell types and their functions, which is important for understanding uterine physiology and pathology.