BIO 004 · Human Anatomy
The Integumentary System
Block 1 · Module 4: Integumentary & Skin
A reference for the integumentary video and lab. The skin is the body's largest organ. This page names its layers, the strata of the epidermis, and the accessory structures that grow from it: hair, nails, and glands.
How to use this sheet Toggle the toolbar above. Notes prints the full reference for review. Study prints as a fill-in-the-blank worksheet. Print it, then write each definition while you watch the video or read your book. Quiz me is on-screen typing practice: type the term, click Reveal to check yourself. The comparison grids and the sequence respond to Study and Quiz too, with a Reveal button on each row or step.
The Foundations video gives you a complete foundational understanding of this topic, enough on its own for a foundational course. Learn it first, then move on to the Deep dive, which adds the majors-level material: the epidermal strata, the cell types, and the accessory structures of the skin.
- Name the two layers of the skin and the hypodermis beneath them.
- List the five strata of the epidermis in order and identify the cell types of the epidermis.
- Distinguish the papillary and reticular layers of the dermis and the structures each contains.
- Identify the accessory structures of the skin: hair, nails, and the glands.
Your pre-work
Work through these the evening before class. None of it is turned in. It is how you learn the material and build your spaced recall.
This is more than a checklist. Ticking these boxes is the start, not the finish. Committing this material to memory and being able to apply it takes considerable time and repeated effort. You are not done when the boxes are checked. Put in the real hours, and keep coming back for frequent recall and review until the material is genuinely yours.
Skin layers
Add a cross-section showing the epidermis, dermis, and hypodermis.
Epidermal strata
Add a labeled view of the five strata of thick skin.
Hair follicle and glands
Add a view of a hair follicle with its sebaceous and sweat glands.
The Integument, an Overview
The integumentary system is the skin plus the structures that grow from it. The skin itself has two layers, with a fatty hypodermis beneath.
- Integumentary systemthe skin together with its accessory structures: hair, nails, and glands
- Skin (integument)the body's largest organ, made of two layers, the epidermis and the dermis
- Epidermisthe superficial layer, keratinized stratified squamous epithelium, no blood vessels
- Dermisthe deep layer, mostly connective tissue, holds the vessels, nerves, and glands
- Hypodermisthe subcutaneous layer beneath the skin, mostly adipose, anchors the skin to the structures below, not part of the skin proper
The Epidermis
The strata, deep to superficial
The epidermis is built in layers. A keratinocyte is born in the deepest stratum and is pushed toward the surface as new cells form beneath it. Follow the strata in order, deep to superficial.
- Stratum basalethe deepest layer, a single row of dividing cells, sits on the basement membrane
- Stratum spinosumseveral cell layers with a spiny appearance
- Stratum granulosumcells filled with granules, where keratinization begins
- Stratum luciduma clear, thin layer, present only in thick skin
- Stratum corneumthe surface layer, many flat dead keratinized cells
- Thick vs thin skinthick skin of the palms and soles has all five strata, thin skin lacks the stratum lucidum
Cells of the epidermis
| Cell | Also called | Function |
|---|---|---|
| Keratinocytes | the main epidermal cell | produce keratin, the tough protective protein of the epidermis |
| Melanocytes | the pigment cell | produce melanin, the pigment that colors the skin and shields against UV light |
| Tactile cells | Merkel cells | paired with a nerve ending for the sense of touch |
| Dendritic cells | Langerhans cells | immune cells that patrol the epidermis |
The Dermis
The dermis has two layers. Compare them by depth, the tissue each is made of, and what each one is known for.
| Dermal layer | Depth | Tissue | Notable features |
|---|---|---|---|
| Papillary layer | the superficial dermis | areolar connective tissue | thrown into dermal papillae, finger-like projections up into the epidermis; on the palms and soles they raise friction ridges, the basis of fingerprints |
| Reticular layer | the deep dermis, the bulk of the dermis | dense irregular connective tissue | collagen and elastic fibers give strength and stretch; holds the blood vessels, nerve endings, glands, and hair follicles |
Accessory Structures
Hair, nails, and glands all develop from the epidermis and reach down into the dermis.
Hair
- Haira strand of keratinized cells produced by a hair follicle
- Hair shaftthe part of the hair above the skin surface
- Hair rootthe part of the hair within the follicle
- Hair folliclethe tube of epidermal and dermal tissue surrounding the root
- Hair bulbthe expanded base of the follicle, where the hair grows
- Arrector pilia small smooth muscle that pulls the hair upright
Nails
- Naila plate of hard keratin on the dorsal tip of a finger or toe
- Nail platethe visible body of the nail
- Nail bedthe skin underneath the nail plate
- Nail matrixthe growth region at the proximal end of the nail
- Lunulethe pale crescent at the base of the nail
- Cuticlealso called the eponychium, the fold of skin over the proximal nail
Glands
Five gland types develop from the epidermis. Compare them by what they secrete and where the secretion goes.
| Gland | Secretion | Where it opens |
|---|---|---|
| Sebaceous glands | sebum, an oily secretion | into hair follicles; softens the hair and skin |
| Eccrine sweat glands | watery sweat | directly onto the skin surface; the most numerous sweat gland |
| Apocrine sweat glands | a richer, thicker sweat | into hair follicles of the axillary and genital regions |
| Ceruminous glands | cerumen, or earwax | into the ear canal; a modified sweat gland |
| Mammary glands | milk | through ducts to the nipple; a modified sweat gland |
See also: Histology: The Four Tissue Types, where the epithelial and connective tissues that build the skin are covered.
Study questions
Work on answering these in writing, in your own words. They are the questions to bring to class, and good practice for the reasoning the exams ask for.
- Name the two layers of the skin plus the hypodermis, and the tissue each is made of.
- List the five epidermal strata in order and explain how a keratinocyte changes as it moves up.
- Compare the papillary and reticular layers of the dermis by tissue and what each contains.
- Explain how the depth of a burn maps onto the skin layers it destroys.
Step 2 . Retrieval check
Now explain it back, in your own words.
In 60 words or more, pull together what the video just taught you. Include the key concepts. This is the point where the learning actually sticks. After you submit, your spaced-recall cards for this topic unlock.