Clin Med Lecture 2: Skin Physiology

Skin

comprised of the epidermis and dermis; exists to give barrier protection, prevent water loss, block pathogen/environmental injury, synthesize Vitamin D, do wound healing, thermoregulate, and sense

Epidermis

Provides a protective barrier that prevents water loss and blocks pathogens. Contains melanocytes, keratinocytes, and no blood vessels.

melanocytes

produce melanin in the epidermis

dermis

Contains blood vessels, lymphatics, nerves, hair follicles, sebaceous glands, sweat glands, and connective tissue that provide structural support and nourish the avascular epidermis

hypodermis

Composed primarily of adipose tissue and connective tissue. Provides insulation, energy storage, cushioning, and anchors the skin to underlying structures

hair

part of skin that provides protection, thermoregulation, sensory perception

nails

part of skin that protects the distal phalanges, improves fine motor function, enhances tactile sensation

Sebaceous glands

An associated gland of the dermis that secretes oily sebum to lubricate skin and hair

Sweat Glands

An associated gland of the dermis that has two subtypes

Eccrine glands

a type of sweat gland that presents all over the body, opens straight onto the surface through pores, and aids in thermoregulation

Apocrine glands

a type of sweat gland that is present in armpits and groin, opens into hair follicles, makes a thick fluid that causes body odor, and starts working at puberty due to hormonal changes

Stratum corneum

outermost layer of the epidermis with deals with barrier function and moisture retention

stratum lucidum

thin, clear layer of dead skin cells in the epidermis that helps with skin stretching

Stratum granulosum

A layer of epidermis that releases lipids and proteins to create

Stratum spinosum

A layer of epidermis that has squamous cells that move and change from column shaped to multisided to give strength and flexibility to skin; cells here make keratin

keratin

fibrous protein that gives skin, hair, and nails their hardness and water-resistant properties

stratum basale

The deepest layer of the epidermis that is constantly dividing to make new skin cells; contains melanocytes and merkel cells

merkel cells

A cutaneous sensory receptor, specifically a mechanoreceptor in the epidermis, that detects pressure and fine touch

innate immune defense of skin

skin utilizes antimicrobial peptides to disrupt bacterial membranes as well as skin lipids + microbiome to inhibit pathogen colonization

langerhans dendritic cells

immune cells that can detect and capture pathogens

dermal macrophages

detect and engulf bacteria

hemostasis

the first step of wound healing that begins immediately after injury; blood vessels constrict, and platelets aggregate to form a fibrin clot. (minutes to hours)

inflammatory phase

the second step of wound healing where immune cells infiltrate the injury site to attack pathogens and clear out debris. Blood vessels dilate, allowing for increased blood flow. (Day 1-3)

proliferative phase

the third step of wound healing where new tissue is built; Fibroblasts (cells that contribute to connective tissue formation and are found throughout the body) produce collagen, leading to granulation tissue formation. Blood vessels grow into the area, and new epithelial cells grow. (Day 3-21)

remodeling phase

the fourth step of wound healing where the wound strengthens and matures. Collagen fibers reorganize and scar contracts, becoming (like) normal skin. (Weeks to months)

vitamin D synthesis

a function of skin where UVB converts 7-dehydrocholesterol into vitamin D3 in the skin; Vitamin D3 is activated after hydroxylation in the liver and kidney.

thermoregulation

A function of the skin due to its large surface area, allowing it to conserve and release heat through vasoconstriction and vasodilation; sweating (eccrine glands) is another major cooling mechanism.

sensation

A function of the skin through cutaneous sensory receptors to detect pain, temperature, touch, pressure, vibration, and stretch in order for us to perceive our environment and respond appropriately

free nerve endings

A cutaneous sensory receptor that detects pain and temperature

meissner corpuscles

A cutaneous sensory receptor, specifically a mechanoreceptor, that detects light touch

Pacinian corpuscles

A cutaneous sensory receptor, specifically a mechanoreceptor, that detects vibration

Ruffini endings

A cutaneous sensory receptor, specifically a mechanoreceptor, that detects stretch