5-3 They Hypodermis

Definition: The dermis is the tissue layer that supports the epidermis.
Learning Outcome: Describe the structures and functions of the dermis.
Positioning: The dermis lies between the epidermis and the subcutaneous layer.

Accessory Structures: Accessory structures of epidermal origin, such as hair follicles and sweat glands, extend into the dermis.
Other Components: The dermis contains networks of blood vessels and nerve fibers.

Two Major Layers: The dermis is composed of two main layers:
1. Superficial Papillary Layer
- Composition: Made up of areolar tissue.
- Function: Contains capillaries, lymphatic vessels, and sensory nerve fibers that supply the surface of the skin.
- Features: Named for the dermal papillae that project between the epidermal ridges, aiding in increasing surface area.
- Pain Sensitivity: Due to the abundance of sensory nerve endings, any regional infection or inflammation can be very painful.
- Dermatitis: Inflammation of the skin that primarily involves the papillary layer, often starting in a specific skin area.
1. Deeper Reticular Layer
- Specific details regarding composition and function not provided explicitly in the transcript.

Definition: The subcutaneous layer, also referred to as the hypodermis, lies deep to the dermis.
Indistinct Boundary: The boundary between the dermis and the subcutaneous layer is generally indistinct due to extensive interwoven connective tissue fibers.
Function:
- Stabilizes the position of the skin relative to underlying structures like skeletal muscles and organs.
- Allows for independent movement of the skin.
Composition: Primarily made up of adipose tissue, which is an areolar tissue dominated by adipocytes.
Subcutaneous Fat:
- Also known as subcutaneous fat, it constitutes about 80% of total body fat.
- The remaining fat is visceral fat associated with internal organs.
Vascular Supply: Only the superficial region contains large arteries and veins, which can shift into general circulation upon constriction.
- Thus, skin is often described as a blood reservoir.
Injection Methodology: The limited presence of vital organs in this layer makes it suitable for drug administration via hypodermic needles.

Infants and Small Children: Have extensive baby fat that helps with insulation and energy reserves for physical activities.
Adult Distribution: Changes in subcutaneous fat occur due to hormonal influences:
- Males: Tend to accumulate fat in areas such as the neck, arms, lower back, and buttocks.
- Females: Typically accumulate fat in breasts, buttocks, hips, and thighs.
Elderly Changes: In adults, fat may decrease in certain areas like the backs of hands and upper surfaces of feet but can increase in the abdominal area.
Health Risks: An excessive amount of abdominal fat, known as central adiposity, is linked to cardiovascular disease.

Prevalence: Millions of cosmetic procedures are performed annually in the United States.
Common Procedures:
- Rhinoplasty: Nose reshaping; can relieve breathing problems.
- Breast Augmentation: Involves implants (silicone or saline) for aesthetic enhancement and is linked to difficulties in mammography screening.
- Nips and Tucks: Remove excess skin and fat from areas like the face, chin, arms, belly, buttocks, and thighs.
- Abdominoplasty (Tummy Tuck): For reducing loose skin after weight loss or childbirth; leaves visible scars.
- Liposuction: Involves suctioning subcutaneous fat through a tube; carries risks such as anesthesia reactions and fluid loss.
- Botulinum Toxin (Botox) Shots: Reduce wrinkles by weakening muscles; effects are temporary.
- Dermal Fillers: Injected substances (calcium hydroxylapatite, hyaluronic acid, collagen) that plump sagging skin, also temporary due to macrophage clearance.