BIO 004 · Human Anatomy
The Integumentary System
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
Notes prints the full reference for review.
Study prints as a fill-in-the-blank worksheet to complete while you watch the video or read.
Quiz me is on-screen practice: type the term, or click Reveal to check yourself.
The tables and sequences respond to Study and Quiz too, with a Reveal button on each row.
- 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.
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 keratohyalin granules, where keratinization begins; keratinocytes here release lamellar granules of lipid that waterproof the epidermis
- 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; tactile (Meissner) corpuscles for light touch sit within the papillae |
| 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; lamellated (Pacinian) corpuscles for deep pressure lie in the deep reticular layer |
Cells of the dermis
- Fibroblaststhe main dermal cell, builds the collagen and elastic fibers of the matrix
- Macrophageswandering phagocytes that engulf debris and pathogens
- Mast cellsscattered through the dermis, release chemicals during injury and allergy
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
- Cortex and medullathe keratinized layers that make up the hair itself; melanocytes deposit pigment here, which sets hair color
- Epithelial root sheaththe epidermal tube that wraps the root inside the follicle
- Dermal root sheaththe connective tissue layer surrounding the follicle
- Hair root plexussensory nerve endings around the follicle that detect hair movement
- 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 |
How exocrine glands release their product
Glands are also classified by the mechanism they use to release secretion. Three modes appear in the skin.
| Mode | How the secretion is released | Example |
|---|---|---|
| Merocrine (eccrine) | the cell stays intact and releases product by exocytosis | eccrine sweat glands |
| Apocrine | the apical part of the cell pinches off with the secretion | apocrine sweat glands, mammary glands |
| Holocrine | the whole cell fills with product and ruptures, becoming the secretion | sebaceous glands |
See also: Histology: The Four Tissue Types, where the epithelial and connective tissues that build the skin are covered.
Build the word
Term breakdown
Skin terms come from Greek and Latin roots for skin, horn, layers, and the glands and cells within it. Learn the roots and the layered names line up in order.
- integ- (integumentum)a coveringintegument
- epi- + derm-upon + skinepidermis
- derm- / dermat-skindermis, dermatology
- hypo- + derm-below + skinhypodermis (subcutaneous)
- kerat-hornkeratin, keratinocyte
- corne-hornystratum corneum
- bas-basestratum basale
- granul-grainstratum granulosum
- lucid-clearstratum lucidum
- spin-thornstratum spinosum
- melan-blackmelanin, melanocyte
- seb-grease, tallowsebaceous gland, sebum
- sudor-sweatsudoriferous (sweat) gland
- pil- / pilo-hairarrector pili, pilosebaceous
- papill-nippledermal papillae
- -cytecellkeratinocyte, melanocyte
Draw it from memory Sketch and label before you check
Work on blank paper, from memory, before you look back at the figures. Drawing the skin in section forces you to put the layers in order, not just recognize them.
- Draw a cross-section of thick skin. Label the five epidermal strata in order from deep to superficial: basale, spinosum, granulosum, lucidum, corneum.
- Draw the full skin in section: epidermis, dermis (papillary and reticular layers), and hypodermis. Add and label a hair follicle, a sebaceous gland, a sweat gland, and an arrector pili muscle.
- From memory, draw and label the cells that live in the epidermis (keratinocytes, melanocytes, tactile/Merkel cells, dendritic/Langerhans cells) and note in one phrase what each contributes.
Then check yourself. Compare your section against the figures and tables above. Whatever you missed or put out of order is tonight's study list. Redraw it until the layers come out right without looking.
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.