Untitled

Lecture B9: The Unique Ones: Trophoblast Cells, Bladder Epithelium, Corneal Epithelium

Overview of Topics Covered

  • Trophoblast Cells

    • Function of trophoblasts

    • Origin of trophoblasts

    • Structure formed by trophoblast cells

  • Bladder Epithelium

    • Function of the epithelium

    • Structure of the epithelium

    • Cell types in the bladder epithelium

    • Changes in epithelium

    • Stem cells and repair of the epithelium

  • Corneal Epithelium

    • Function of the epithelium

    • Structure of the epithelium

    • Stem cells and repair of the epithelium

Trophoblast Cells

Main Functions

  • Role of the Placenta:

    • The placenta facilitates the exchange of:

    • Nutrients

    • Wastes

    • Oxygen (O2)

    • Carbon Dioxide (CO2)

    • Contains tissues from both the mother and the fetus.

    • Major functions of the placenta are performed by trophoblast cells.

Origin

  • Trophoblast cells originate from the trophectoderm of the early blastocyst, marking the first extraembryonic lineage formed.

Structure Formation

  • Primary Villi Formation:

    • Occurs 2 days post-implantation.

    • Comprises simple cords of proliferating cytotrophoblast cells covered by syncytiotrophoblast that extend into lacunae containing maternal blood.

  • Secondary Villi Formation:

    • Begins around the 15th day of embryonic development as primary villi are invaded by extraembryonic mesenchyme.

  • Tertiary Villi:

    • Develop within a few days post secondary villi, with mesenchyme differentiating to form capillary loops integrated into the embryonic circulatory system.

    • By the end of the first month of pregnancy, the placenta consists of thousands of tertiary chorionic villi with various capillary loops branching out.

Gas and Nutrient Exchange

  • Exchange of gases, nutrients, and wastes takes place between fetal blood in capillaries and maternal blood surrounding the villi, utilizing diffusion across the trophoblast layer and the capillary endothelium.

Invasion and Syncytium Formation

  • Trophoblast Interaction with Endometrium:

    • Trophoblast cells, derived from the blastocyst's outer layer, begin implantation by binding to glycoprotein ligands (pinopodes) on the endometrial epithelium.

    • Trophoblast differentiates into the following during implantation:

    • Cytotrophoblast (CT)

    • Syncytiotrophoblast (SCT)

Placental Barrier

  • Formed by a monolayer of syncytiotrophoblast (ST) overlying cytotrophoblast (CT) cells, acting as a barrier for maternal-fetal exchange.

Bladder Epithelium

Main Functions

  • Urine transport occurs through the ureters from the renal pelvis to the urinary bladder, where it is stored until micturition via the urethra.

  • The mucosa is lined by transitional epithelium (uroepithelium), which is organized into three layers:

    • Basal Cells: Single layer of small cells at the base.

    • Intermediate Region: A middle layer.

    • Superficial Layer: Comprises large bulbous or elliptical umbrella cells capable of expansion and contraction with bladder filling.

  • The bladder epithelium maintains urine composition similar to that produced by the kidneys.

Uroepithelium Structure

  • Cross-section of the ureter exhibits:

    • Transitional epithelium

    • Lamina Propria

    • Muscle layers (inner, middle, outer smooth muscle) and adventitia.

  • Bladder architecture allows for expansion and contraction in response to changes in bladder volume.

Changes in Epithelium

  • Uroepithelium adjusts in thickness and behavior in response to bladder filling and emptying.

  • Homeostasis and Repair:

    • Turnover rate for uroepithelial cells is approximately 3 to 6 months.

    • Stem cells are thought to be located in the basal layer of the urothelium, with B1 integrin playing a role in retention of DNA labels over extended periods.

Corneal Epithelium

Main Functions

  • The cornea shields the eye from external agents such as germs, dust, and other harmful matter.

  • It serves as the outermost lens of the eye, allowing for light transmission and vision clarity.

Structure of the Cornea

  • The cornea consists of five primary layers:

    • Corneal Epithelium: Outer surface; nonkeratinized and 5-6 cell layers thick (comprising about 10% of total corneal thickness).

    • Bowman's Layer: Anterior limiting membrane beneath the corneal epithelium.

    • Stroma: Thick middle layer supporting corneal structure.

    • Descemet's Membrane: The posterior limiting membrane providing additional structural integrity.

    • Endothelium: Simple squamous layer lining the inner surface.

Corneal Stem Cells

  • Corneal epithelial stem cells (CESC) are localized in the limbal region.

  • Stem cells are characterized as:

    • BD43 negative

    • K3 negative

    • K14 positive

  • CESC possess the ability to differentiate into normal corneal epithelial cells, conjunctival cells, and epidermal cells, showcasing the adaptability and plasticity of these stem cells under various microenvironments.

Regenerative Medicine Approaches

  • Different strategies for corneal repair and regeneration include:

    • Autologous Conjunctival Transplantation

    • Cultivated Epithelial Transplantation (CET)

    • Keratoplasty

    • Artificial Corneas:

    • Boston keratoprosthesis, Osteodental-acrylic complex, KeraKlear keratoprosthesis, MICOF KPro.

  • Cell sheets as a method for transplanting stem cells effectively by attaching them to temperature-responsive surfaces for easy detachment and application post-surgery.

Current Challenges

  • Ongoing development in scaffold-free cell growth factor delivery, hydrogels, and other materials are critical for optimizing corneal regeneration and achieving successful patient outcomes post-surgery.

These extensive notes cover the structure, function, and regenerative strategies of trophoblasts, bladder, and corneal epithelium as discussed in today's lecture.