Anatomy and Physiology - Exam 2 - Integumentary System

Layers of the Skin - Epidermis

The thin, visible outer layer of the skin made of epithelial tissue that acts as the body’s primary protective barrier. The epidermis contains 5 layers.

Epidermis - Stratum Corneum

Outermost layer with up to 30 layers of dead, scaly keratinized cells (keratin makes skin strong/tough). These surface cells flake off (exfoliate).

Epidermis - Stratum Lucidum

This layer is found only in thick skin (palms/soles). It is a thin translucent zone, where light passes through, seen only in that thick skin. The rest of the body doesn’t have this layer. The function of this layer is to act as a barrier against mechanical stress, friction, and damage in high wear areas like hands and feet.

Epidermis - Stratum Granulosum

This is a thin middle layer of cells that produces lipid-filled vesicles that release a glycolipid by exocytosis which acts as a waterproof barrier, preventing water loss.

• “Helps make you waterproof”

Epidermis - Stratum Spinosum

This has several layers of keratinocytes spines (thick) that holds skin cells tightly together so the skin resists tearing and friction as well as housing langerhans cells (dendritic cells) that act as macrophages (white blood cells), consuming invading pathogens to trigger a immune response.

Epidermis - Stratum Basale

Bottom germinal layer that generates new skin cells and anchors the epidermis to the dermis.

• Contains keratinocytes - makes skin more durable.

• Contains melanocytes - synthesizes melanin which gives skin its pigment and helps protect cells from UV radiation.

• Contains Merkel cells - cells with neurons just beneath, act as mechanoreceptors to detect light touch and shape of objects that come into contact with the skin.

Layers of the Skin - Dermis

The thick middle layer under the epidermis and above the hypodermis that consists of two primary tissue regions:

• Papillary Layer - the top layer of the dermis (thin) made of loose, areolar connective tissue featuring finger like projections called papillae that lock into the epidermis above. These help deliver nutrients to the outer layer supplying nutrients, house touch receptors, help regulate temperature, and create fingerprints.

• Reticular Layer - The thicker, deeper layer made of dense irregular connective tissue (bundles of collagen fibers) that provides strength and flexibility.

Layers of the Skin - Hypodermis

• NOT APART OF THE SKIN*

• The deepest layer and is known as subcutaneous tissue, it is made primary of loose areolar connective tissue and fat-storing adipose tissue. It functions as an energy reservoir, thermal insulation, and cushioning/shock absorption.

• Highly vascular - the layer in which a shot goes into

Thick vs Thin Skin

Thick Skin:

• Has all 5 layers of the epidermis, including the stratum lucidum

• Contains no hair follicles, subaceous (oil glands), or arrestor pili muscle

• Has sweat glands

• Found only on high-friction areas like the palms of the hands, fingertips, and soles of the feet.

Thin Skin:

• Only has 4 layers, lacks the stratum lucid

• Contains hair follicles, subaceous (oil glands), and sweat glands

• Covers the rest of the body, such as the eyelids, back, and forearms.

Why is Thick Skin not the thickest skin?

This is because overall thickness is determined by both the epidermis and dermis. Areas of the body covered by thin skin - such as the back or forearms - possess a massive, thick dermis that makes the actual total skin measurement much thicker than the specialized “thick skin” of the palms and soles.

Sweat Glands - Eccrine and Apocrine

• Eccrine - most common sweat glands found across almost the entire body. They open directly onto the skin surface and produce sweat that cools the body down through evaporation (thermoregulation).

• Apocrine - restricted to areas with many hair follicles, they open into hair follicles rather than directly onto skin. They produce “sexy sweat” to the armpit and groin, causing body odor.

  • Become active during puberty

  • Respond to stress, sex, emotions, hormones

Sebaceous Glands

An oil-producing gland that secretes sebum, a way lipid-rich substance, that keeps skin and hair moisturized.

Ceruminous Glands

The specialized sweat glands in the ear canal that secrete earwax. The earwax is waterproof which keeps the eardrum flexible and it is also bitter which repels mites and other pests.

Mammary Gland

Specialized exocrine gland found in mammals that produce milk to nourish newborn offspring.

• Mammary glandular tissue found only during lactation and pregnancy.

Hair - Shaft, Root, and Follicle

• Shaft - the visible part of the hair that extends above the skin, made of dead, hardened (Keratinized) cells.

• Root - the part of the hair that is anchored inside the skin, beneath the surface. The bottom of the root expands into the hair bulb that provides nutrients.

• Follicle - a tunnel-oblique like structure in the skin that surrounds and protects the hair root, responsible for growing hair.

Arrector Pili - Smooth Muscle

A tiny smooth muscle attached to a hair follicle that contract to make hair stand up, creating goosebumps.

Hair Receptor

Wraps around the base of the hair follicle and detects movement of the hair/light touch.

Free Nerve Endings

Unencapsulated/Bare branches of sensory nerve fibers that detect pain.

Meissner’s (Tactile) Corpuscle

Found in the dermal papillae of the skin that are receptors that senses light touch.

Pacinian (Lamellar) Corpuscle

Receptor that detects deep pressure and high-frequency vibrations.

Characteristics of Human Hair - 3 Different Types

1. Lanugo - fine, unpigmented fetal hair

2. Vellus - fine, unpigmented hair of children and women

3. Terminal - course, long, pigmented hair of scalp

Functions of Hair

• Body Hair - temp regulation and alert us when parasites crawling on skin

• Scalp Hair - Provides heat retention (traps heat) and sunburn cover

• Beard/Pubic/Axillary Hair - indicate sexual maturity and help distribute sexual scents

• Guard Hairs/Eyelashes - prevent foreign objects from getting into nostrils, ear canals, or eyes.

Nails

• Made of hard keratinized cells ( derivative of stratum Corneum)

• Flat nails —> sensory of fingertips

• Growth rate is 1mm per week