Lecture Notes: Structures in the Dermis

Overview

• Focus on identifying structures in dermis from biopsy slides.
• Key structures discussed: vessels, nerves, hair follicles, sebaceous glands, eccrine glands, and apocrine glands.

1. Blood Vessels

Types of Vessels

• Capillaries:
  • Round to oval, thin-walled.
  • Mostly found in the papillary dermis (upper part).
• Veins/Venules:
  • Irregularly shaped, flattened lumen.
  • Single endothelial cell layer, located in mid to deep dermis.
  • Stellate lumen (star-shaped).
• Arteries/Arterioles:
  • Round, thick-walled structures.
  • Thick muscular layer in walls.
  • Round lumen, found deeper in the dermis.

Identification in Slides

• Capillaries: Round structures with individual endothelial cells.
• Venules: Flattened, larger structures with thin walls.
• Arterioles: Thick-walled with muscle fibers visible.

2. Nerves

• Characteristics:
  • Wavy, light pink fibers.
  • Centrally elongated nucleus with pointed ends.
  • Found in mid to deep dermis and subcutis.

Importance in Diagnosis

• Essential for diagnosing conditions like Hansen's disease (leprosy).
  • Look for perineural inflammation (inflammation around nerves).

3. Hair Follicles

Structure

• Divided into two segments:
  • Upper Segment: From erector pili to ostia (opening).
  • Lower Segment: From erector pili to root shaft.

Components

• Infundibulum: From ostia to sebaceous gland opening.
• Isthmus: From sebaceous gland opening to erector pili.
• Stem: From isthmus to Adamson’s fringe (tip of dermal papilla).
• Bulb: Contains matrix cells and melanocytes.

Identification in Slides

• Granular layer present in infundibulum, absent in isthmus.

4. Sebaceous Glands

• Structure: Multi-lobular (acini) draining into a common duct.
• Function: Production of sebum via holocrine secretion.
• Process:
  • Cells migrate from basal to center, becoming larger and lipid-filled.
  • Burst to release sebum into hair follicle.

Pylosebaceous Unit

• Combination of hair follicle and sebaceous gland.

5. Eccrine Sweat Glands

Structure

• Derived from primitive epidermal ridge.
• Two portions: secretory coil and ductal portion.

Cell Types

• Clear Cells: Secretory, located at the basement membrane.
• Dark Cells: Mucoid, apical, smooth surface, regulatory function.
• Myoepithelial Cells: Contractile, aid in sweat expulsion.

Function

• Proximal part of the duct absorbs sodium, resulting in hypotonic sweat.

6. Apocrine Sweat Glands

Location

• Found in axilla, anogenital region, areola, and nipple complex.

Structure

• Opens into the infundibulum of hair follicles.

Secretion Type

• Mixed apocrine and microcrine secretion.
• Undulating appearance of cells due to apocrine secretion.

Conclusion

• Review of key histological structures in the dermis.
• Next lecture will cover dermal reaction patterns.

Recommended Readings

• Fundamentals of Pathology of Skin
• IDville textbook on Dermatopathology
• Pathology Outlines (online resource)
• McKinsey Dermatopathology
• Fitzpatrick Dermatology, 9th Edition
• Rook's 10th Edition

Additional Notes

• Importance of reviewing histopathology slides along with readings for better understanding.