The Integumentary System

The skin is an important barrier for protection against foreign bodies. It is crucial for body temperature regulation. It produces vitamin D in response to sunlight, a vitamin crucial for calcium absorption from food. Touch is dependent on receptors located in the skin. This system is composed of the skin, nails, glands, and hair. Ladies and gentlemen... your integumentary system.

22) INTEGUMENTARY STRUCTURES AND FUNCTIONS

The epidermis- Most superficial layer of the skin

- Composed of stratified squamous epithelia that are keratinized at the outermost surface

- Also contains melanocytes, immune cells, and sensory receptors

The dermis - Lies beneath the epidermis

- Composed of two layers of connective tissue: a loose layer (papillary), and a dense, irregular layer (reticular)

- Both layers include connective tissue components (collagen, elastin, fibroblasts) along with blood vessels, sensory receptors, and lymphatics

The hypodermis- Composed of loose adipose and areolar connective tissue

- Technically not part of the integumentary system, but still important to recognize

23) INTEGUMENTARY LEVELS OF ORGANIZATION

Molecular Level (keratin & melanin)

Keratin- A group of fibrous proteins that give hair, nails, and skin their tough, water-resistant properties

- Formed from the polymerization of intermediate filament proteins

Melanin- A class of photopigment with a molecular structure that allows it to absorb UV radiation from the sun

- Prevents DNA damage from the sun that is responsible for many skin cancers

- Gives skin, hair, and eyes their color

Microscopic Level ~ Cells of the epidermis (epithelial layer)

• Top layers made up of keratin-containing keratinocytes

• Basal cells- An example of tissue-specific stem cells that typically replace lost keratinocytes

• Desmodomes in the epidermis interlock with papillae in the dermis

• Merkel cells- Sensory receptors that detect light touch by forming synaptic connections with sensory nerves that carry touch information to the brain; abundant on hands and feet

• Melanocytes- Cells in the bottom layer of epidermis that produce melanin

• Dendritic/Langerhans cells- Tissue macrophages that contribute to the immune function of the skin by engulfing foreign organisms and signaling the immune system

Skin Cancer

Three types:

1. Basal cell carcinoma

- Caused by mutations that lead to lack of control over the growth of stem cells in the basal layer

- Most common form of ALL cancers in the US

- Head, neck, arms, and back are most susceptible

- Can be caused by UV radiation, electromagnetic radiation, or skin exposure to carcinogenic chemicals

- Surgical excision is a common and effective form of treatment

2. Squamous cell carcinoma

- Second most common skin cancer

- Affects keratinocytes

- Most common on scalp, ears, and hands

- May metastasize if not removed

3. Melanoma

- Affects melanocytes

- Most fatal type of skin cancer

- Highly metastatic

Epidermic Layers (deep to superficial)

Stratum basale

Stratum spinosum

Stratum granulosum

Stratum lucidum (only present in thick skin on hands, feet, and lips)

Stratum corneum

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