Chapter 6 Pt 2

The dermis is the layer beneath the epidermis and is organized into two sublayers: a superficial capillary-focused layer (papillary dermis) and a deeper layer (reticular dermis).
Papillary dermis features:
- Finger-like projections (dermal papillae) with a loose connective tissue matrix (areolar tissue).
- Sensory receptors reside in the papillary dermis; notable tactile receptors include the Meissner's corpuscles.
- A capillary network within this layer supplies nutrients to the dermis.
Meissner's corpuscles are located in the papillary dermis and are responsive to light touch.

There are defined lines of cleavage (Langer’s lines) in the skin where collagen and elastic fibers are oriented in parallel bundles, shaped by habitual stress.
These fiber bundles resist tensile stresses during movement.
Incisions perpendicular to these lines tend to pull on the wound, causing gaping and recoil of the skin during normal movement.
For better healing, incisions are typically made parallel to cleavage lines.
If the skin is stretched beyond its capacity, collagen fibers can tear, leading to stretch marks (striae) or striding.
With UV exposure and aging, the dermis becomes less flexible and thinner, contributing to sagging or wrinkling of the skin.

The hypodermis is the subcutaneous layer positioned beneath the dermis and contains adipose tissue (subcutaneous fat).
Fat distribution in the subcutaneous layer is influenced by hormones; higher testosterone levels tend to accumulate fat in specific regions: neck, upper arms, abdomen, lower back, and gluteal area.
Note: fat distribution can depend on body positioning and overall physiology.

Primary role: protection from the external environment.
The integument acts as a physical barrier against harmful chemicals, toxins, microbes, and excessive heat and cold.
It also protects deeper tissues from solar radiation, especially UV rays.
Even if epidermal damage (e.g., sunburn) occurs, the underlying tissues are protected by the outermost layer.
The skin helps prevent water loss and water gain; hormones play a significant role in this balance.
The epidermis is water resistant but not waterproof, allowing some water loss.
Water balance and cooling: evaporation of water from the skin (sweat) provides a cooling effect for thermoregulation.

Sebum is an oily mixture of lipids produced by sebaceous glands and helps lubricate the skin.
Lipids in sebum also contribute to the skin’s barrier properties.
Substances such as hormones and drugs can be delivered through patches on the skin; these compounds can penetrate the epidermis and be absorbed into the bloodstream via dermal blood vessels.

Temperature regulation involves vasoconstriction (narrowing of blood vessels) and vasodilation (widening of blood vessels).
Vasodilation increases blood flow to the skin to dissipate heat when body temperature rises.
Vasoconstriction reduces blood flow to conserve heat when needed.

Langerhans cells reside in the stratum spinosum of the epidermis and play a key role in immune defense.
- They initiate immune responses against pathogens penetrating the skin.
- They can also mount an immune response against epidermal cancer cells.
Sensory reception in the skin includes tactile receptors such as tactile cells and Meissner's corpuscles; these contribute to the sense of touch in the skin.

Papillary dermis: superficial dermal layer with capillary loops, loose connective tissue, and Meissner's corpuscles.
Reticular dermis: deeper dermal layer (not detailed in the transcript but part of the two-layer dermis concept).
Dermal papillae: finger-like projections containing capillaries and sensory receptors.
Meissner's corpuscles: touch receptors in the papillary dermis.
Langer’s lines (lines of cleavage): preferred incision directions to minimize tension.
Striae: stretch marks resulting from tearing of collagen fibers.
Hypodermis (subcutaneous layer): fat-rich layer beneath the dermis; fat distribution influenced by hormones.
Sebum: lipid-rich oil that lubricates skin and aids barrier function.
Langerhans cells: epidermal immune cells in the stratum spinosum.
Tactile cells and sensory receptors: components of the skin's touch system.

Surgical incisions should follow cleavage lines to reduce wound tension and improve healing.
Age-related dermal thinning and UV exposure contribute to wrinkles and sagging; preventive measures may include sun protection and skin care to preserve dermal thickness.
Hormonal status can influence fat distribution, which may affect appearance and risk profiles in different body regions.
Transdermal drug delivery leverages the skin’s barrier properties to release medications into the bloodstream.
Immune surveillance by Langerhans cells helps defend against pathogens and cancerous changes in epidermal tissue.